The Essentials of Material Science and Technology for Engineers

By A. K. Rakhit Ph.D.

For optimum design of an engineering product, it is
important that engineers are quite familiar with material
properties besides their knowledge in mechanics of materials.
Finally, availability, cost of materials, and environmental regulations
all play an important role in selecting the right material for the
product.

• Language: English
• Publisher: Xlibris US
• Release date: Oct 16, 2013
• ISBN: 9781483684932

Book preview

THE ESSENTIALS OF

MATERIAL SCIENCE

AND TECHNOLOGY

FOR ENGINEERS

A. K. Rakhit Ph.D.

Consulting Engineer

Copyright © 2013 by A. K. Rakhit, Ph.D.

All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the copyright owner.

Rev. date: 06/10/2015

Xlibris

1-888-795-4274

www.Xlibris.com

600278

Contents

Preface

Acknowledgments

Introduction

Chapter 1 Creation of Materials

Structure of an Atom

Interatomic Bonding Forces

- Ionic Bonding

- Covalent Bonding

- Metallic Bonding

- Secondary Bonding

REVIEW QUESTIONS: CHAPTER 1

Chapter 2 Atomic Arrangement in Elements

Crystal Structure

- Unit Cell

- Noncrystalline Materials

Grain Structure

- Types of Grains

- Grain Size Determination

REVIEW QUESTIONS: CHAPTER 2

Chapter 3 Defects in the Atomic Arrangement of Crystal Structures

Crystalline Defects

- Point Defects

• Vacancies

• Substitutional defects

• Interstitial defect

• Impurities in solids

- Holes and Electron Imperfections

- Line Defects

- Surface Defects

- Grain Boundary Defects

- Volume Defects

Diffusion Mechanisms

- Vacancy (Substitutional) Diffusion

- Interstitial Diffusion

REVIEW QUESTIONS: CHAPTER 3

Chapter 4 Metal-Strengthening Mechanisms

Strengthening by Controlling Grain Size

- Control of Grain Size and Number of Grains

- Grain Size and Mechanical Properties of Steel

- Grain Size and Its Effects on Heat Treatment of Steel

Solid Solution Strengthening

Strain Hardening of Metals

- Cold-Working/Drawing/Rolling

- Effect of Cold-Work on the Mechanical Properties of a Copper-Zinc Alloy: An Example

- Recovery, Recrystallization, and Grain Growth

- Grain Growth after Recrystallization

- Strengthening of Nonmetals

REVIEW QUESTIONS: CHAPTER 4

Chapter 5 Metallography

Sample Preparation

- Mounting of a Sample

- Grinding and Polishing

• Rough grinding

• Fine grinding

• Rough polishing

• Fine polishing

- Cleaning and Drying

- Etching

Microstructures

- Failure Analysis

REVIEW QUESTIONS: CHAPTER 5

Chapter 6 Properties and Testing of Materials

Physical Properties

Mechanical Properties

Concept of Stress

- Types of Stresses

Concept of Strain

Relationship between Stress and Strain

Elastic and Plastic Behavior of Materials

Purpose of Mechanical Testing

Test Sites

Nature of Tests

Application of Load during Testings

Test Conditions

Testing Machines

Test Specimens for Tensile Testing

Recording Instrument

- Determination of Yield Strength

- Proof Strength and Proportional Limit

- Young’s Modulus of Elasticity (E)

- Percent Elongation and Area Reduction Calculation

- Upper and Lower Yield Points

- Ultimate Stress Point

- Rupture Stress

Stress-Strain Diagram for Brittle Materials

- True Stress-Strain Diagram

Elastic vs. Plastic Behavior of Materials

Additional Properties from a Stress-Strain Diagram other than Strength and Modulus of Elasticity

Ductility

Ductile Fractures

- Correlation of Tensile Properties with a 0.505 in. Diameter Specimen

Compression Test

Shear Test

Shear Strength

Hardness Test

- Modern Hardness Tests

Brinell Hardness Test

- Limitations of Brinell Test

- Brinell Hardness and Tensile Strength Relationship

- Rockwell Hardness Measurement

Rockwell Hardness Test

- Equipment Used

- Designation of a Rockwell Hardness Number

- Precautions and Limitations of Rockwell Test for Accurate Readings

- Rockwell Hardness Scales

- Anvils

- Rockwell Superficial Hardness Test

Microhardness Testing

- Relationship between Brinell and Rockwell Hardnesses

Vickers Hardness Test

- Relationship between Various Hardness Scales

Durometer Hardness Test

Impact Test

- Toughness

• Principle of impact resistance testing

• Impact test machine

• Temperature effects of impact test

• Use of impact test properties

• Fracture toughness

Creep

- Stress Rupture

Fatigue

- Fatigue Test

- Types of Loading in Fatigue Tests

Fatigue Characteristics of Ferrous and Nonferrous Materials

- Influence of Loading Rate and Heat Treatment on Fatigue Life

- Fatigue Fractures

- Keyways and Splines

- Nondestructive Testing (NDT)

REVIEW QUESTIONS: CHAPTER 6

Chapter 7 Alloys and Phase Diagrams

Concept of Phase

- Phase/Equilibrium Diagrams

- Phase Diagrams of Completely Soluble Alloys

- Determination of Phase Amounts

- Alloys Completely Soluble in a Liquid State and Insoluble in a Solid State

- Alloys Completely Soluble in a Liquid State, Partially Soluble in a Solid State

Use of Phase Diagram for Material Selection

Iron-Carbon Alloys

- Morphology of Iron

Alloys of Iron

Iron-Iron Carbide Phase Diagram

REVIEW QUESTIONS: CHAPTER 7

Chapter 8 Heat Treatment of Metals

Heat Treatment of Iron

Heat Treatment of Steel

Transformation (Decomposition) of Austenite

- Austenite to Pearlite

- Effect of Cooling Rates from Austenitizing Temperature to Room Temperature

- Austenite to Bainite

- Austenite to Martensite

Influence of Alloying Elements on Steel Properties and Microstructure after Heat Treatment

- Effect of Chromium on Hardening of Steel

- Effect of Alloy Elements on Transformation Temperature

- Effect of Alloy Elements on the Critical Cooling Rate

Heat Treatment of Steels under Nonequilibrium Conditions

- Quench Media, Quench Rate, and Quench Temperature

- Quenching in Synthetic Fluids

Hardening and Tempering of Steel

- Tempering Temperature and Mechanical Properties of Steels

- Heat Treatment Cycle for Steel

Retained Austenite

Residual Stresses and Cracking

Age Hardening

A Case History: Tempering Omission of Carburized and Quenched Steel

Hardness and Hardenability

- Jominy Test

- Influence of Alloying Elements on Hardenability of Steels

- Grain Size

Selection of Steel for Hardenability

- A Case History

Heat Treatment under Near-Equilibrium Conditions

- Annealing

• Stress relief anneal

• Spheroidize annealing

- Normalizing

- Normalizing and Tempering

Major Heat Treatment Processes

- Through Hardening Processes

• Equipment used

- Flame and Induction Hardening

- Surface Hardening Processes

- Carburizing

• Gas carburizing

• Hardening

- Direct Quenching

- Tempering of Carburized and Quenched Components

- Cold Treatment

- Grain Size and Case Depth

- Grain Size and Core Hardness

- Effect of Carburizing Processes on Surface Carbon

- Retained Austenite and Its Effect on Carburized and Hardened Parts

- Steels for Carburizing

- Nitriding

• Gas nitriding process

• Case depth in nitriding

• Nitriding cycle time

• White layer in nitrided gears

- European Nitriding Steels

- Modern Nitriding Processes

• Ion/plasma nitriding

• Ion nitriding time and case depth

- Carbonitriding

• Materials for carbonitriding

Induction Hardening

- Tempering after Induction Hardening

- Surface Hardness and Case Depth

- Materials for Induction Hardening

Laser Hardening

Electron-Beam Hardening

Heat Treatment of Nonferrous Metals

REVIEW QUESTIONS: CHAPTER 8

Chapter 9 Ferrous Materials

Iron

Manufacturing Process of Iron Today

Wrought Iron

Iron-Carbon Alloys

Cast Irons

- White Cast Iron

- Malleable Cast Iron

- Ferritic and Pearlitic Malleable Cast Iron

- Gray Cast Iron

• Mechanical Properties of Gray Cast Iron

º Modulus of elasticity

º Yield strength

º Compressive strength

º Shear strength

º Shock resistance

º Toughness

º Other mechanical properties

• Vibration-damping characteristics of gray cast iron

Ductile Iron

Heat Treatment of Cast Irons

- White iron

- Malleable cast iron

- Gray cast iron

• Annealing

• Stress relieving

• Normalizing

• Quenching and hardening

• Tempering

• Effect of cooling rate on tensile properties of gray cast iron

• Growth in gray cast iron

Heat Treatment of Ductile Iron

Microstructures of Cast Iron

Casting Processes

- Ingot Grain Structure

- Directional Solidification and Single-Crystal Technology

- Major Casting Defects

- Casting Defect Prevention

- Dimensional Tolerance Requirement in Castings

• Surface finish of castings

• Castability of metals

- Economics of Casting Processes

Welding of Gray Cast Irons

- Joint Preparation

Welding of Ductile Iron

Corrosion Resistance of Cast Iron

Some Design Advantages with Casting

Steels

- Steelmaking Processes

• Processes based on chemical energy

• Processes based on electrical energy

- Production of Large Ingots

- Vacuum Degassing for Clean Steels

- Processing of Steel

- Kinds of Steel

- Hot-Rolling

• Effect of hot-rolling on nonmetallic inclusions in steel

• Effect of rolling on porosity

• Hot-Rolling Defects

- Forging

- Cold-Rolling/Drawing (Cold-Working)

• Frequently used cold-working processes

• Defects in Cold-Worked Steels

• Manufacturing Tolerances of Hot- and Cold-Rolled Parts

- Standard Steel Shapes

- Identification and Classification of Steels

- Types of Steels and Their Chemical Compositions

• Plain carbon steels

Application of Plain Carbon Steels

- Low-carbon steels

- Medium-carbon steels

- High-carbon steels

- Application Limits of Plain Carbon Steels

- Some Hints on the Selection of Plain Carbon Steels

Most Frequently Used Plain Carbon Steels

Structural Steels

- Identification of Structural Steels for Engineering Applications

- Mill-Heat-Treated Structural Steels

- Cold-Heading Steels

- Cold-Finished Bars and Shafting Steels

Alloy Steels

- Influence of Alloying Elements on Steel Properties

- Major Alloying Elements in High-Strength Low-Alloy Steels

- Identification of Special Groups of Steels

- Vacuum-Melted vs. Air-Melted Alloy Steels

- Cleanliness of Steel

• A Case History

- Alloy and H-Steel Compositions

Weldability of Steel

Specialty Steels

- Tool Steels

• Nomenclature of Tool Steels

• Carbon Tool Steel (W1, W2, W4)

• Characteristics of Carbon-Vanadium Tool Steel (Type W2)

• Manganese Oil-Hardening Tool Steel (Type 01)

• Medium-Carbon Low-Alloy Tool Steel (Type S)

• Medium Alloy, Air-Hardening Tool Steel (Type A)

• High-Carbon High-Chromium Tool Steel (Type D)

• Hot-Work Tool Steel (Type H)

• Mold Steels

• High-Speed Steels (HSS)

Heat-Resistant Superalloy Steels

Ultrahigh-Strength Steels

- Heat Treatment of Maraging Steels by Precipitation Hardening

Nitriding

- Maraging Steels of Other Countries

- Applications of Maraging Steels

Stainless Steels

- Austenitic Stainless Steels

• New design specification

- Ferritic Stainless Steels

- Martensitic Stainless Steels

- Precipitation Hardening (PH) Stainless Steels

- High-Temperature Mechanical Properties of Stainless Steels

- Low-Temperature Application of Stainless Steels and Other Metals

- Corrosion Resistance

- Fabrication

- Hot Forming

- Available Forms and Uses

- Welding

• Martensitic stainless steels

• Ferritic stainless steels

• Austenitic stainless steels

• Precipitation hardening stainless steels

• Free-machining stainless steels

- Guidelines for Selection of a Proper Stainless Steel

REVIEW QUESTIONS: CHAPTER 9

Chapter 10 Nonferrous Metals

Aluminum (Al) and Its Alloys

- Manufacturing of Aluminum

- General Properties of Aluminum

- Alloying Elements of Aluminum

• Designation of aluminum alloys

- Aluminum Products

- Strengthening of Aluminum Alloys

• Alloy additions

• Advanced Al alloy

• Aluminum matrix composites

- Heat Treatment of Aluminum Alloys

- Heat Treatment of Wrought Aluminum Alloys

• Solution heat treatment

• Time at temperature

• Heating rate

• Quenching

• Lag between soaking and quenching

• Straightening after solution heat treatment

• Precipitation hardening and aging

- Temper Designation of Wrought Aluminum Alloys

- Heat Treatment of Cast Aluminum Products

• Solution Heat Treatment

- Artificial Aging

• Stabilization by Artificial Aging

• Temper Designation of Cast Aluminum Alloys

- Strain Hardening by Cold-Work

- Extrusion of Aluminum Alloys

- Welding of Aluminum

- Corrosion Resistance of Aluminum Alloys

- Fatigue Life of Aluminum Alloys

- Considerations for Aluminum Alloy Selection

- Advanced Aluminum Alloys

- Use of Aluminum as Composite Material

Copper (Cu) and Its Alloys

- Extraction of Copper from Ore

- Alloys of Copper

- Copper-Zinc Alloys

- Copper-Tin Alloys (Bronze)

- Copper-Aluminum Alloys

- Copper-Silicon Alloys

- Copper-Nickel Alloys

- Copper-Nickel-Zinc Alloys

- Copper-Beryllium Alloys

- Metal-to-Metal Wear Resistance of Copper Alloys

- Welding of Copper

- Soldering and Brazing

- Corrosion Resistance of Copper and Its Alloys

- Superconductivity of Copper

- Machinability of Copper Alloys

Nickel (Ni) and Its Alloys

- Some Physical Properties

- Alloys of Nickel

- Heat Treatment

- Super Nickel Alloys

- Welding of Nickel Alloys

- Corrosion Resistance

Tin (Sn)

Zinc (Zn)

- Corrosion Resistance

Lead (Pb)

- Other Uses of Lead

- Coatings

Magnesium (Mg) and Its Alloys

- Some Properties of Magnesium

- Alloying Elements in Mg

- Alloy Designation

- Classification of Magnesium Alloys

• Casting alloys

• Wrought alloys

- Heat Treatment of Magnesium

• Casting alloys

• Wrought alloys

- Evaluation of Magnesium as a Structural Material

Titanium (Ti) and Its Alloys

- Important Physical Properties

- Crystal Structure

- Manufacture of Titanium

- Titanium and Its Alloys

• Characteristics of unalloyed titanium

• Alloys of titanium

º Alpha (α) titanium alloys

º Alpha-beta (α-β) titanium alloys

º Beta (β) titanium alloys

- Beta Transus Temperature

- Titanium Product Forms

- Engineering Specifications of Titanium and Titanium Alloys

- Casting of Titanium Alloys

- Forging of Titanium Alloys

- Welding of Titanium Alloys

• Fusion welding

- Weld Defects of Titanium Alloys

- Mechanical Forming of Titanium and Its Alloys

- Superplastic Forming

- Machining of Titanium

- Solid Solutions of Titanium

- Heat Treatment of Titanium and its Alloys

• Annealing

• Solution heat treatment

• Solution Heat Treatment of Titanium Alloys

- Age Hardening/Precipitation Hardening of Titanium Alloys

- Hardenability of Titanium Alloys

- High-Temperature Tensile Property of Titanium Alloys

- Fatigue Life of Titanium

- Corrosion Resistance of Titanium

- Why Use Titanium and Its Alloys?

REVIEW QUESTIONS: CHAPTER 10

Chapter 11 Ceramics

Structure of Ceramics

Processing of Engineering Ceramics

- Preparation of Powder

Manufacturing of Ceramic Parts

- Isopressing

- Sintering

Ceramic Density Computations

- Manufactured Ceramic vs. Wrought Metal

Properties of Ceramics

Imperfections in Ceramic Crystal Structures

Impurities in Ceramics

Porosity in Ceramic Components

- Influence of Porosity on Ceramic Properties

Hardness and Modulus of Elasticity of Ceramics

Fracture Toughness of Ceramics

Usage of Ceramics in Engineering Products

Other Properties of Ceramics

- Electrical and Magnetic Properties

Ceramics for Structural Applications

Advanced Ceramics

Corrosion Resistance of Ceramics

Highlights of Ceramics

Powder Metallurgy

- Manufacturing of P/M Parts

- Heat Treatment of P/M Parts

- Alloy Content and Its Influence

- Applications of P/M Products

REVIEW QUESTIONS: CHAPTER 11

Chapter 12 Polymeric Materials

Formation of Polymer Structures

Molecular Weight of Polymers

Degree of Polymerization (DP)

Degree of Polymerization, Molecular Weight, and Strength of a Polymer

Molecular Shape

Molecular Structure

- Linear

- Branched

- Cross-Linked

- Network

Polymer Crystallinity

Additives

Types of Polymers

- Thermoplastic Polymers

- Thermoset Polymers

Fabrication Processes for Thermoplastic and Thermoset Polymers

- Thermoplastics

• Injection Molding

• Reaction Injection Molding

• Blow Molding

• Calendaring

• Rotational Molding

• Extrusion

- Thermoset Plastics

• Compression Molding

• Foam Molding

• Transfer Molding

• Casting

Elastomers

- Styrene butadiene rubber (SBR)

- Chloroprene rubber

- Polybutadiene rubber

- Nitrile rubber

- Butyl rubber

- Ethylene propylene rubber (EPM)

- Polysulfide rubber

Silicones

Polyurethane

Thermoplastic Elastomers (TPE)

- Morphology of TPE

- Advantages and Limitations of TPEs

- Types of TPEs

• Urethanes

• Styrenic block copolymers (SBC)

• Thermoplastic olefins (TPOs)

• Copolyesters

• Newest TPEs

Joining of Plastic Parts

- Strength of the Joint

- Polymer Reinforcements

Plastics for Bearing Applications

Plastics for Gear Materials

Polymeric Seal Materials

- Neoprene

- Nitrile (buna-N)

- Butyl

- Ethylene propylene

- Fluorocarbon

- Polyacrylate

- Buna-S rubber

- Polyurethane

- Polyester

Mechanical Properties of Plastics

- Fatigue Strength

- Fracture Strength

Glassy Polymers

Long-Term Properties of Plastics Creep, Stress Relaxation, and Service Life

- Physical Properties

• Density

• Thermal expansion

Moisture Absorption

- Dimensional changes

Deformation and Failure of Plastics

- Thermoplastic Polymers

- Thermosetting Polymers

- Elastomers

Strengthening of Polymeric Materials

- Thermoplastics

• Degree of crystallinity

• Introduction of oxygen and nitrogen atoms in the main carbon chain

• Addition of glass fibers

• Average molecular mass

- Thermosetting Plastics

Special Polymeric Materials

- Smart Polymeric Materials

- Electrorheological (ER) and Magneto-Rheological (MR) Fluids

Trade Names of Polymeric Products

Corrosion Resistance of Plastics

Summary

REVIEW QUESTIONS: CHAPTER 12

Chapter 13 Composites

Particulate Composites

Fiber-Reinforced Composites

- Fibers

- Type of Fibers

- Fiber Strength

Assessment of the Strength of Fibers Compared to Metals

Laminar Composites

Sandwich Panels

Matrix

Metal Matrix Composites

Strength (Stiffness) of Composites

- Transverse Loading

Composite Design

Hybrid Composites

Processing of Composites

- Hand layup process

- Filament winding

- Spray-up

- Compression molding

REVIEW QUESTIONS: CHAPTER 13

Chapter 14 Corrosion of Materials

- Localized Corrosion

- Galvanic Corrosion

- Dealloying

- Intergranular Corrosion

- Stress Corrosion

Corrosion Susceptibility of Various Metals and Their Alloys

- Cast Iron

- Stainless Steels

- Aluminum Alloys

- Surface Treatments

- Copper and Its Alloys

- Nickel and Its Alloys

- Zinc and Its Alloys

- Titanium and Its Alloys

- Ceramics

- Plastics

Protection against Corrosion

Coatings and Paints

- Dipping and Spray Coatings

Design Considerations for Protection against Corrosion

REVIEW QUESTIONS: CHAPTER 14

Chapter 15 Selection of Material for an Engineering Application

A Typical Selection Process

Appendixes

A   Physical Properties of Some Selected Metals

B   Glossary

C   Selected References

D   Engineering Specification and Standards

This book is dedicated to the memory of my parents, Upendra and Charulata Rakhit, for their blessing from a beautiful place in this universe; to my wife, Ratna, for her love and devotion; and to my son, Amit, and my daughter, Roma, for their inspiration and support.

PREFACE

Since my retirement from the engineering profession, I had been contemplating for some time to put together the knowledge I gathered on engineering materials during my career in the form of a book. I am quite sure the contents will be of great value to engineers engaged in various aspects of engineering activities such as product design, manufacturing, testing of materials, and failure analysis. At present, a great deal of books are available on the subject, but none of them provide any comprehensive knowledge and information to meet the needs of practicing engineers. Engineers, even for their routine design work, require consulting from a number of different books, journals, and standards on materials because information they are looking for is not easily available. This is particularly true for engineers employed with small organizations which do not have the luxury of maintaining an engineering library. Also, it is my observation that engineering graduates coming out of engineering schools do not get enough training on materials either. These engineers, once they are employed, face a great deal of difficulty in designing products that are expected to perform satisfactorily under a wide range of service conditions. Very often, they are asked to take special courses on material science and technology and attend seminars to improve their design skills. In this regard, I would like to share my personal experience during a job interview after I graduated from university.

The job was for a development engineer with a medium-size machine-tool manufacturing company in Toronto, Canada. The engineering manager I was interviewing with seemed to be quite impressed with my educational background on machine design and understanding of the vibration phenomenon in machine tools. While discussing various design principles, he suddenly changed the topic to materials used in various machine parts. I had only a limited knowledge of specific materials used in these machines, their properties, and available standards. He found out about my deficiency on the knowledge of materials after going through a number of questions. The manager then abruptly finished the interview. He told me he was impressed with my credentials on machine design but was unable to offer me the job because of my limited knowledge of materials, which was also very important for the job. I was very much disheartened, no doubt, but I did not give up. Subsequently, I took various courses on material science and technology, attended several seminars on material science, and visited various metalworking industries and test laboratories.

Later on, my experiences while working in the aerospace industry in the United States became quite beneficial to further broaden my knowledge of material science.

There is no doubt materials play a significant role in developing reliable, cost-effective, and safe products, whether they are used in the energy generation industry, transportation industry, or aerospace industry. The work may also encompass design and developing products for higher efficiency and lower cost. New high-strength low-density materials are continuously in the process of development. Advanced manufacturing techniques are being introduced for improved quality. So it is a major challenge for engineers to keep abreast of these developments for successful careers in their profession.

In this book, I put some special effort to include all the important materials that are frequently used in engineering products with their latest developments. These include cast iron, steel, aluminum, copper, nickel, magnesium, and titanium. Since iron and steel are extensively used in engineering products, a great deal of information is included on these two materials, followed by aluminum and titanium. Finally, the book contains some useful information on polymeric materials, ceramics, composites, and hybrid materials. The usage of composites and hybrid materials are continuously increasing because of their superior weight-to-strength ratio.

Writing a book, particularly a book that could be used as a textbook by engineering students on material science and technology, takes a great deal of support and cooperation from many colleagues. In this regard, I would like to acknowledge all those who helped me in completing this book. But it is difficult to mention all their names except for a few, of whom Professor Parthasarathy Iyengar of the County College of Morris needs to be specially recognized for his valuable suggestions in preparing this book. Finally, special thanks are due to Mrs. Adrienne Black, also of the County College of Morris, who worked tirelessly in typing and proofreading the manuscript.

A. K. Rakhit

ACKNOWLEDGMENTS

The author wishes to thank Professor V. Fuentes, chairperson, Department of Engineering Technologies/Engineering Science, County College of Morris, and Professor P. Iyengar for their valuable advice and support in completing this book. The author also expresses his gratitude to Mrs. Adrienne Black, administrative assistant, for typing and preparing the manuscript of this book, and to the County College of Morris, New Jersey.

INTRODUCTION

For optimum design of an engineering product, it is important that engineers are quite familiar with material properties besides their knowledge in mechanics of materials. Finally, availability, cost of materials, and environmental regulations all play an important role in selecting the right material for the product.

Chapters 1 through 4 discuss the basics of material science, such as formation of different elements, bonding forces between atoms, crystal structure of atoms, and defects in crystal structure that impart different physical and mechanical properties to an element or a compound. Besides bonding forces between atoms and crystal structure, the properties of materials could be enhanced by processes like solid solution strengthening, modifying grain structure. These are discussed in chapter 4.

Chapter 5 discusses the method to prepare a specimen for viewing its crystallographic structure under a microscope. Such views of the crystal structure help to find the defects that might have been introduced during manufacturing.

In chapter 6, mechanical properties that are important for a successful engineering product are defined. The testing method for each of these properties is given. The strength of some materials is found to increase by heating and cooling at a certain controlled rate. In this process of heat treatment, a material may go through phase changes with the temperature. This is discussed in chapter 7. Chapter 8 elaborates on the various heat treatment methods for different materials, steel in particular.

Of all the materials in engineering applications, iron serves as the base for some of the most important ferrous alloys. A relatively small amount of iron is used in the pure state in comparison to the amount used as alloys. Steel is an alloy of iron and carbon. The usage of steel is more than 10 times that of all other metals used in engineering applications. This is due to its high specific strength and the abundant supply of iron ores from which iron and, subsequently, steel are produced. Chapter 9 describes elaborately iron and steel and their alloys.

After iron and steel, aluminum is most widely used among nonferrous materials. New alloys of aluminum are being continually developed to be competitive with other metals and also nonmetals. Chapter 10 provides some useful information on various nonferrous metals that are of interest to engineers.

Chapter 11 discusses manufacturing and properties of ceramics. Chapters 12 and 13 are respectively dedicated to plastics and composite materials. These materials have excellent properties and are competing with steel alloys and nonferrous metals in many applications, particularly where weight and strength are of primary importance.

Designing a product with all this knowledge and information may not ultimately be successful due to some unforeseen corrosion problems the products are subjected to during service. Corrosion behaviors of both metals and nonmetals are discussed in chapter 14 and also, to some extent, in their respective chapters.

Chapter 15 is dedicated to the method of material selection for an engineering product.

CHAPTER 1

Creation of Materials

It is an age-old question of all human beings, engineers or not: where do all the materials of the universe come from? The question appears to be simple, but the answer is not so. To date, two separate approaches exist for a logical answer. One is philosophic, and the other is based on scientific analysis. From the philosopher’s and religion point of view, all elements and, subsequently, materials were created by God for the benefit of mankind and were there all along when the universe was created. The scientific theory, on the other hand, emphasizes the ancestry of everything in the universe to the cosmic explosion popularly known as the big bang. Renowned British astronomer Fred Hoyle, in jest, coined the word big bang to describe this unique explosion. It occurred when all matter compressed to a single point of infinite density, a state of singularity, due to the effects of enormous gravity. It is estimated the size of this point, also known as the cosmic egg, was approximately 10−32 cm in diameter with an infinitely high internal pressure that finally exploded. The explosion instantly raised the temperature in the surroundings of this point to trillions of degrees, and all matter was converted to energy. The theory holds that in less than a trillionth of a second after the big bang, the temperature started to cool off. When the system temperature eventually fell below a critical value, an invisible force field, the Higgs field, named after the inventor, was formed and was linked with particles called Higgs boson. This field then went on to permeate, giving mass to any particle that interacted with it. The more the interaction a particle had with the Higgs field, the heavier it became, whereas particles that never interacted with it were not able to gain any mass at all.

As the universe cooled further, a new state of matter known as plasma emerged. Plasma is neither solid, liquid, nor gas. It is the state of ionized gas which behaves more like a liquid than a pure gas. The scorching plasma soup consisted of two fundamental particles, quark and gluon. The universe, from this stage, started expanding. After expanding to about the size of our solar system, it underwent another change of state in which the free-roaming quarks in the plasma combined with the help of gluons. The gluons became the bonding superglue to form protons and neutrons in about one billionth of a second. The protons and neutrons then coalesced and captured electrons to form atoms of matter. At this point of creation of the universe, the lightest atomic element, hydrogen, was formed. This was followed by the formation of galaxies, nebulae, and stars. Stars were also being formed inside the galaxies and nebulae. In all such stars, hydrogen fuses to form helium, the next lightest element. This fusion of hydrogen into helium and vice versa provides the energy inside a star. The conversion of energy by the fusion process decays gradually until hydrogen in the core is completely exhausted, and no more energy is produced. As the energy in the core lessens, the gravitational pull of a star’s outer mass increases toward the center of the star until it reaches an extremely high density, and finally, the star explodes as either supernova or hypernova depending on the mass of the star. A mass about two to three times the size of our sun results in a supernova explosion, while the explosion of larger stars ends up in a hypernova. A supernova explosion produces the lighter elements, while the heavier elements are produced by hypernova explosions. Elements thus formed become part of new stars and planets in the universe. Our solar system is one such star system with all the elements in them. It is estimated it was formed about five billion years ago.

There are other theories to explain the beginning of the universe and are beyond the scope of this book to discuss. Irrespective of all the theories, it is a fact that elements, the building blocks of materials, were formed as the universe was created.

Of all the elements identified to date, only 92 of them occur in nature. The element with the most protons that occurs in nature is uranium, with 92 protons. Elements that have more than 92 protons are artificial and are made in high-energy laboratories by nuclear reactions. Elements with atomic numbers as high as 120 have been identified. The man-made elements are relatively unstable. Sixty-eight of the naturally occurring elements had been discovered by the year 1870. A brilliant Russian chemist, Dmitri Ivanovich Mendeleev, observed that many of these elements displayed similar chemical characteristics. Sodium and potassium are very active metals that oxidize extremely rapidly. Oxygen and sulfur both react chemically with hydrogen and other elements in the same manner. Chlorine, bromine, and iodine all attack metals violently. By arranging these elements in order of increasing atomic weights, he observed that for the first two dozen or so elements, every eighth element showed some repetitive patterns of characteristics, indicating periodicity. Then he put the elements in tabular form known as the periodic table (table 1-1). The periodic nature of elements is determined in part by the nuclear particles and in part by the behavior and configuration of electrons. Going right along the table, each element has one more nuclear charge than the preceding one. This charge is neutralized by an additional electron. The period ends with a noble gas with eight electrons in its valence or outer shell. It is this periodic variation in electron configuration that leads to periodic property variations. Elements in the vertical column have the same number of electrons in their valence shell and have similar chemical behavior. By combining the atoms of different elements in the periodic table in various ratios, it is possible to build different molecules and explain every material in the universe. Materials so formed from the elements tabulated in the periodic table can be categorized as either organic or inorganic.

Organic materials contain carbon and usually hydrogen, as in all living things. Inorganic materials, on the other hand, are metals, sand, and rock. A large number of engineering materials utilize elements that constitute inorganic matters in a combined form known as alloys (a metal combined with one or more other elements), compounds (chemically combined elements with definite proportions of the component elements), and to a smaller degree, mixtures (a physical blend of two or more materials). The discussion in this book will be mostly on metallic alloys of engineering materials. A great deal of information will also be given on nonmetals such as polymeric materials, ceramics, and composites.

Table 1-1: Periodic Table of Elements

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Although proper interpretation of the periodic table lies in the domain of chemists and physicists, an engineer needs to understand how the elements and their alloys behave under service conditions for which some knowledge of atoms, their structures, and bonding of atoms is considered useful in evaluating a material for selection in a product.

Structure of an Atom

An atom is the smallest part of an element that still possesses the properties of the element. An atom of every element has a distinct atomic structure indicating the composition, such as number of protons, neutrons, and electrons. Atomic structure influences the bonding of atoms, which, in turn, helps one to identify materials as metals, polymers, ceramics, or semiconductors and permits one to make conclusions regarding mechanical and physical behavior of different materials.

Interatomic Bonding Forces

An understanding of many of the physical properties of materials is predicated on the knowledge of the interatomic forces that bind atoms together. The principles of atomic bonding are best described by considering the interaction between two isolated atoms as they are brought into close proximity from an infinite separation. At large distances (10 times the atomic diameter and more), the interactions are negligible, but as the atoms approach each other, each exerts a force on the other, both attractive and repulsive. The magnitude of each of these forces is a function of the separation or interatomic distance.

As the interatomic distance decreases, the attractive force increases until the outer electron shells of the two atoms begin to overlap, and then a strong repulsive force comes into play. Thus, the net force between the two atoms becomes the sum of both attractive and repulsive components, creating a bonding force between the atoms.

In general, the bonding of atoms influences the following properties of materials:

- Material density

- Mechanical properties such as modulus of elasticity, strength, hardness

- High bonding energies in solids cause solids to maintain their shape better; change of shape is possible only with a force greater than the bonding energy holding the atoms together. Higher bonding energy also indicates higher melting point of a metal.

If the applied force is not so great as to completely break the bond, removal of the force allows the atoms to return to their equilibrium spacing. The result is that the material returns to its original dimensions. This behavior is known as elastic deformation and is quite useful to engineers in designing machinery and their structures.

In solids, primarily, three different types of atomic bond are found. These are ionic, covalent, and metallic. In each type, the bonding results due to the tendency of the atoms to assume stable electron structures by completely filling the outermost electron shell known as the valence shell. Besides the primary energies in these three types of bonding, secondary energies are also found in some materials, which form van der Waals bonding. This type of bonding is generally weaker than the primary ones but nonetheless influences the physical properties of these materials. To understand how different types of bonding gives rise to different physical properties and behavior of materials, each of these bonding mechanisms is reviewed briefly as outlined below.

Ionic Bonding

This type of bonding exists between dissimilar atoms and is always found in compounds that are composed of both metallic and nonmetallic elements. During the bonding process, atoms of metallic elements give up their valence electrons to the atoms of the nonmetallic elements. In doing so, all the atoms acquire an electrical charge and become ions. Sodium chloride (NaCl) is a classical example of an ionically bonded material. A sodium atom gives up one of its valence electrons to a chlorine atom and becomes a Na+ ion. Chlorine, with its seven outer shell electrons, absorbs this electron and becomes a Cl− ion. Sodium and chlorine share one electron. The attraction of the ions for the electron holds the two elements together. This results in an atomic bond that is very strong. Figure 1-1(a) shows the principle of ionic bonding, and figure 1-1(b) illustrates ionic bonding between sodium and chlorine atoms. Ionically bonded materials tend to be very hard, and their melting points are quite high, as in ceramics and refractory materials.

Also, ionically bonded materials behave as electrical insulators at low temperatures. At high temperatures, they conduct electricity electrolytically, but not electronically. It means the ions move to carry the current, not the electrons. In general, ionically bonded materials are brittle and optically transparent.

Another important property of ionically bonded materials is that their strength is nondirectional, which means the magnitude of the bonding strength is equal in all directions around an ion. For stability of ionically bonded materials, all positive ions must have negatively charged ions as their nearest neighbors in a three-dimensional scheme and vice versa. Ionic bonding does not exist in organic materials and materials that contain carbon.

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Figure 1-1: Ionic bonding (a) bonding between two atoms (b) bonding of sodium and chlorin atoms to form sodium chloride molecules

Covalent Bonding

In this type of bonding, adjacent atoms share electrons. Two atoms that are covalently bonded contribute at least one electron to the bond, and the shared electrons may be considered to belong to both atoms as illustrated in figure 1-2 for a methane (CH4) molecule. The covalent bond is directional; that is, it is between specific atoms and only exists in the direction between the one and another that participates in the electron sharing.

This type of bonding is found in molecules containing dissimilar atoms, such as water (H2O) and hydrofluoric acid (HF). Covalent bonding of atoms is also found in elemental solids such as diamond (carbon), silicon, germanium, and other solid compounds composed of elements that are located on the right side of the periodic table, such as gallium arsenide (GaAs) and silicon carbide (SiC).

Single covalent bonds between atoms that do not require any additional atoms to be added are said to be saturated. Saturated molecules have strong intramolecular bonds but weak intermolecular bonding. When carbon and hydrogen form unsaturated molecules, as in ethylene and acetylene, the molecules form double or triple covalent bonds. An unsaturated molecule does not have the necessary hydrogen atoms to satisfy the outer shell of the carbon atoms. Many such molecules form double bonds and are referred to as polyunsaturated compounds.

Covalent bonds may be very strong, as in diamond, which is very hard and also has a high melting point, or they may be very weak, as in bismuth (Bi), which melts at 518°F. It is also possible to have interatomic bonds that are partially ionic and partially covalent. In fact, very few compounds exhibit pure ionic or pure covalent bonding. For compounds with this type of mixed bonding, the degree of either bond type depends on the relative positions of the constituent elements in the periodic table. The wider the separation (both horizontally, relative to group IVA, and vertically) from the lower left-hand to the upper right-hand corner, the more there is ionic bonding. The closer the elements are in this table, the greater the degree of covalency. The characteristics of covalent bonding are directly responsible for many properties of organic polymers and are the bases of methods for altering their properties. All organic materials and many gases are covalently bonded. A majority of ceramics, semiconductors, and polymers (the thermoset type) are fully or partly covalently bonded.

In general, covalently bonded materials are optically transparent, opaque to X-rays, and good electrical insulators.

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Figure 1-2: Covalent bonding in a methane molecule

Metallic Bonding

It is found mostly in metallic elements and their alloys. This type of bonding is of primary importance to engineers who are involved in selecting materials for a wide variety of applications. Metallic elements have one, two, or at most three valence electrons. The valence electrons in metallic bonding are not bound to any particular atom in a solid. They are more or less free to drift throughout the entire solid metal. For this reason, they may be thought of as belonging to the metal as a whole, forming a sea of electrons or an electron cloud. The remaining nonvalence electrons and atomic nuclei form what are called ion cores, which possess a net positive charge equal in magnitude to the total valence electron charge per atom. The free electrons shield the positively charged ion cores from mutually repulsive electrostatic forces which they would otherwise exert upon one another. Consequently, a metallic bond is nondirectional in character. The free electrons also act as glue to hold the ion cores together. Metallic bonding may be weak or strong.

This type of bonding is found in group IA and IIA elements in the periodic table and, in fact, in all elemental metals where all of the atoms have similar valences and cannot directly exchange electrons. As a consequence of free valence electrons, the metals become good conductors of heat and electricity.

As with covalently bonded elements, metallic bonding between atoms is, in general, a mixture of two or more types of bonding. Iron, for example, is bonded by a combination of metallic and covalent bonding, which prevents packing of atoms as efficiently as might be expected without the mixed bonding.

The most widely used elements with metallic bonding are iron, aluminum, copper, lead, zinc, tin, nickel, chromium, molybdenum, vanadium, tungsten, and titanium. Some of these elements are used in the pure state, but by far the largest amount is consumed in the form of alloys, a combination of at least two elements.

Of the 92 elements (original periodic table), 73 are classified as metals. The rest are nonmetal and metalloids. Nonmetals are oxygen, hydrogen, nitrogen, chlorine, and all inert gases. The metalloids are intermediate between metals and nonmetals, such as carbon, sulfur, silicon, and phosphorus. These elements portray, under certain circumstances, the characteristics of metals and, under some other circumstances, the characteristics of nonmetals. A schematic illustration of a metallic bond is shown in figure 1-3.

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Figure 1-3: Metallic bond

Secondary Bonding

The most common type of secondary bonding is van der Waals bonding. In this type, molecules or groups of atoms are bonded by weak electrostatic attraction. The atoms within the molecules are joined by either a strong covalent bond or an ionic bond. An example of a van der Waals bonded molecule is that of water. It is shown in figure 1-4. In this case, electrons in the oxygen atom tend to concentrate away from the hydrogen atom. The resulting charge difference permits the water molecule to be weakly bonded.

Heating water to the boiling point breaks the van der Waals bond and changes water to steam, but much higher temperatures are needed to break the covalent bonds joining oxygen atoms and hydrogen atoms. Van der Waals bonds can also dramatically change the properties of materials. Some polymers and ceramics have this kind of bonding.

The basic knowledge of atoms, atomic structure, and atomic bonding so presented in this chapter will be useful to understanding the crystal structure of elements that is so important in developing various mechanical properties of metals and nonmetals as discussed in chapter 2.

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Figure 1-4: Van der Waals bond (a) between two atoms

(b) between two molecules

REVIEW QUESTIONS: CHAPTER 1

What is an atom? Draw the structure of an atom that is now acceptable in the present scientific community.

Define ion.

What is a valence electron? How many valence electrons does a carbon atom have? Show the valence electron configuration for water.

Calculate the number of atoms in 100 g of copper.

What is a periodic table? How is it prepared? Name a few advantages in having such a table.

Differentiate between metals and nonmetals. List seven elements that are metals and seven elements that are nonmetals with their chemical symbols.

Explain organic and inorganic materials.

Name a few refractory elements from the periodic table. List some of their properties.

Beryllium and magnesium, both in the IIA column of the periodic table, are light metals. Which of these elements do you expect to have a higher modulus of elasticity? Explain.

List five naturally occurring commonly used engineering materials.

Name the major atomic bonding mechanisms of materials. Cite the differences among them, and give an example for each type of bonding. Which of these mechanisms offer the highest bonding strength and why?

What type of bonding exists in carbon dioxide (CO2), aluminum bromide (AlBr), and calcium carbonate (CaCO3) molecules?

CHAPTER 2

Atomic Arrangement in Elements

Atomic arrangement is the distribution of atoms in an element. It differs from atomic bonding, which is basically bonding between the electrons of atoms. The distribution of atoms follows a definite pattern in each element and is different from one element to the other. Such a distribution of atoms results in crystal structures in the solid state of elements, which plays an important role in forming the microstructure and properties of elements. For example, the atomic arrangements in aluminum, copper, and nickel provide good ductility. In iron, on the other hand, this arrangement provides good strength.

Crystal Structure

It is an arrangement of atoms in a metallic element in the solid state, where the atoms occupy their positions in a repetitive or periodic array over large atomic distances during solidification of metals from the molten state. During solidification, each atom bonds to its nearest neighbor atoms in repetitive three-dimensional patterns, forming some kind of crystal structure. Occasionally, the term lattice is used in the context of crystal structures. A lattice is a three-dimensional array of points coinciding with the atom positions in a crystal structure.

As already stated, crystal structures of metals play an important role in determining their mechanical properties. Often, physical properties such as density and ductility depend also on their crystal structures.

All known metals seem to solidify in seven basic crystal structures. These are the following:

Cubic: simple cubic, body-centered cubic, and face-centered cubic

Tetragonal: simple tetragonal and body-centered tetragonal

Orthorhombic: simple orthorhombic, body-centered orthorhombic, base-centered orthorhombic, and face-centered orthorhombic

Rhombohedral

Hexagonal: hexagonal close-packed, face-centered cubic close-packed, and complex cubic (diamond structure)

Monoclinic: simple and body-centered

Triclinic

In general, pure metals that are ductile and malleable have face-centered cubic crystal structures, such as aluminum and copper. Body-centered cubic structure metals are a little less ductile, such as iron, while materials with a simple cubic structure are quite brittle, such as manganese.

Unit Cell

The smallest assembly of atoms which possesses complete symmetry of a crystal structure is called a unit cell; a repetition of this unit cell in space forms a crystal of recognizable size. Thus, a unit cell is regarded as the basic structural unit or building block of the crystal structure. It defines the crystal structure by virtue of its geometry and the atoms’ position within. Unit cells for most crystal structures are of a cubicle shape. A typical unit cell in the lattice is depicted in figure 2-1. Due to the nondirectional nature of the atomic bonding that is predominant in metals, there are basically no restrictions as to the number and position of nearest neighbor atoms. This leads to a relatively large number of nearest neighbors and consequently results in a dense atomic packing for most metallic structures.

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Figure 2-1; A unit cell in the atomic lattice

In nature, 14 different types of crystal lattices have been identified by the X-ray diffraction technique. Unit cells for each type of lattice are illustrated in figure 2-2. Fortunately, only three simple types of unit cells are found in metals commonly used in engineering: body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP). Crystal structures of some selected

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Figure 2-2: The fourteen types of unit cells grouped in seven crystal systems

metals with some of their physical properties are given in table 2-1. Besides metals, a few nonmetals such as ceramics and polymers, which are also used in various engineering applications, exhibit some complex crystal structures. These are discussed in the respective chapters for these materials.

Table 2·1: Crystal structures of some selected elements

with their physical properties

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Of the various metals shown in table 2-1, iron, cobalt, titanium, and chromium may exist in more than one lattice form at different temperatures as indicated below.

For this reason, these are known as allotropic materials. The allotropic property plays an important role in enhancing their mechanical properties. Furthermore, the number of atoms that can be packed in a crystal structure after heat treatment plays an important role for improvement of mechanical properties. For example, 68% of the volume in a BCC structure is occupied by atoms, and the remaining 32% is empty space. In FCC and HCP structures, 74% of the volume is occupied by atoms, and the remaining 26% is empty space. When a metal with such a crystal structure is heated, the empty space is gradually filled up by new atoms due to atomic mobility in the metal, but subsequent slow cooling removes these atoms from the structures. On the other hand, fast cooling of the metal helps to trap a good percentage of such atoms, thereby enhancing some mechanical properties. This phenomenon is further explained in the chapter for heat treatment of metals.

Crystal structures of some frequently used unalloyed annealed engineering materials with some of their mechanical properties and tensile and yield strengths are given in table 2-2. Figure 2-3 shows the locations of atoms in three such crystal structures—BCC, FCC, and HCP. The primary characteristics of these structures are given below.

Table 2-2: Crystal structures of some frequently used unalloyed materials with their tensile and yield strengths

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- Body-centered cubic (BCC) structure: In this type, an atom is placed at each corner of the cubic structure. Also, in the center of the structure, there is an atom as illustrated in figure 2-3(a). Many elements such as pure iron and chromium are found with this arrangement.

- Face-centered cubic (FCC) structure: In this type of structure, an extra atom is in the middle of each side or face of the cube as shown in figure 2-3(b). Aluminum, copper, silver, and gold are among the many elements found with this type of arrangement.

- Hexagonal close-packed (HCP) structure: The top and bottom faces of this unit cell consist of six atoms that form regular hexagons and surround a single atom in the center. Another plane that provides three additional atoms to the unit cell is situated between the top and bottom planes. The atoms in this mid plane have the nearest neighbors’ atoms in both of the two adjacent planes. Figure 2-3(c) depicts