Chapter 1 Notes: Introduction to Materials Science & Engineering

What is Materials Science & Engineering?

• Materials science – Investigate relationships between structures and properties of materials; design/develop new materials.
• Materials engineering – Create products from existing materials; develop materials processing techniques.

Why Are Materials Important?

• Materials drive advancements in our society: Stone Age → Bronze Age → Iron Age.
• What is today’s material age? Possible candidates include:
  • Silicon (Electronic Materials) Age
  • Nanomaterials Age
  • Polymer Age

Why is it Important for Engineers to Understand Materials?

• All products/devices/components that engineers design are made of materials.
• To select appropriate materials and processing techniques for specific applications engineers must:
  • have knowledge of material properties, and
  • understand the structure–property relationships.

Processing–Structure–Properties Relationships

• Processing (e.g., cooling rate of steel from high temperature) affects the structure (microstructure).
• Data context (from figures in Callister & Rethwisch): 4 wt% C composition; Fig. 10.32(a), Fig. 10.33; Fig. 11.18.
• Micrographs cited: (a) Fig. 10.19; (b) Fig. 9.30; (c) Fig. 10.34; (d) Fig. 10.22.
• Core relationship:
  • Structure is determined by Processing:
    \text{Structure} = g(\text{Processing})
  • Properties depend on Structure (and often Composition):
    \text{Properties} = F(\text{Structure}, \text{Composition})
• The structure in turn affects hardness (e.g., harder steel from certain cooling rates).
• Conceptual takeaway: Processing → Structure → Properties.

Types of Materials

• Metals:
  • Strong, ductile
  • High thermal & electrical conductivities
  • Opaque, reflective
• Polymers/plastics:
  • Compounds of non-metallic elements
  • Soft, ductile, low strengths, low densities
  • Low thermal & electrical conductivities
  • Opaque, translucent, or transparent
• Ceramics:
  • Compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides)
  • Hard, brittle
  • Low thermal & electrical conductivities
  • Opaque, translucent, or transparent

For a Specific Application: Materials Selection Process

1) Determine Required Properties for the application:

• Provide required property set

• Produce component with desired shape/size

• Example techniques: casting, mechanical forming, welding, heat treating

• Property categories: mechanical, electrical, thermal, magnetic, optical, deteriorative
  2) From List of Properties, Identify Candidate Material(s).
  3) Best Candidate Material: Specify Processing techniques.

  • Note: Materials Selection Engineers solve materials selection problems using a structured procedure.

Material Property Types

• Mechanical
• Electrical
• Thermal
• Magnetic
• Optical
• Deteriorative

Mechanical Properties

• Figure reference: 10.31 (Brinell hardness vs. carbon content for steel;
  data from Metals Handbook, 1981, ASM International).
• Main point: Increasing carbon content increases hardness of steel.
• Quantitative sense (from the figure): hardness increases as wt% C increases from about 0% toward ~1% C, illustrating the positive dependency of hardness on carbon content.
• Implication: For steels, carbon content is a key lever to tune hardness via processing.
• Conceptual relation:
  • Hardness H is a function of Carbon content C: H = f(C) with \frac{dH}{dC} > 0\,.

Electrical Properties

• Factors that affect electrical resistivity ρ for copper:
  • Increasing impurity content (e.g., Ni) increases ρ.
  • Deformation increases ρ.
  • Increasing temperature increases ρ.
• Example data (Cu + Ni):
  • Cu + 3.32 at% Ni
  • Cu + 2.16 at% Ni
  • Deformed Cu + 1.12 at% Ni
  • “Pure” Cu
• Qualitative relation: impurities and deformation raise resistivity; temperature raise resistivity.
• Conceptual relation:
  • ρ depends on impurity content p and temperature T: \rho = \rho(p, T) with \frac{\partial \rho}{\partial p} > 0, \quad \frac{\partial \rho}{\partial T} > 0.

Thermal Conductivity

• Thermal conductivity k measures a material’s ability to conduct heat.
• Impurity effects: Increasing impurity content (e.g., Zn in Cu) decreases k: \frac{\partial k}{\partial p} < 0\,.
• Highly porous materials are poor conductors of heat.
• Examples:
  • Ceramic fibers used in space shuttle applications demonstrate low thermal conductivity due to significant void space.
• Conceptual relation: impurity and porosity reduce heat transfer efficiency.

Magnetic Properties

• Magnetic permeability vs. composition: Adding ~3 atomic percent Si to Fe makes Fe a better recording medium.
• Magnetic storage: recording medium is magnetized by the recording write head.
• Materials used in magnetic storage are selected for permeability and stability of magnetization.

Optical Properties

• Light transmittance depends on structural characteristics (e.g., crystallinity, porosity).
• Aluminum oxide (Al2O3) single crystal: optically transparent.
• Aluminum oxide polycrystalline (many small grains): optically translucent.
• Aluminum oxide polycrystalline with porosity: optically opaque.

Deteriorative Properties

• Stress-corrosion cracking example: small cracks form in a steel bar stressed and immersed in sea water.
  • Source: Fig. 17.21 (Callister & Rethwisch 10e) adapted from Marine Corrosion sources.
• For stress-corrosion cracking, crack-growth rate can be diminished by heat treating (e.g., aluminum alloy 7178):
  • Example: heat treatment at 160°C for 1 h prior to testing reduces crack growth rate vs as-received condition.
• Implication: processing can mitigate deterioration mechanisms and extend component life.

Example of Materials Selection: Artificial Hip Replacement

• Anatomy and skeletal context:
  • Hip joint consists of femur (thigh bone) and pelvis; cartilage loss leads to pain and disability; joints can fracture.
  • X-ray images show a normal hip vs. fractured hip.
• Why replacements are needed:
  • Damaged/diseased joints can be replaced with artificial joints to restore function and relieve pain.
• Materials requirements for artificial joints:
  • Biocompatible (low rejection by body tissues)
  • Chemically inert to body fluids
  • Mechanical strength to support loads
  • Good lubricity and high wear resistance between articulating surfaces
• Components of an artificial hip:
  • Femoral stem – inserted into the femur
  • Head (ball) – attaches to the stem
  • Shell – fixed to the pelvis
  • Liner – fits inside the shell and articulates with the head
• Materials used in hip components:
  • Femoral stem: titanium alloy or CoCrMo alloy
  • Head (ball): CoCrMo alloy or Al2O3 (ceramic)
  • Shell: titanium alloy
  • Liner: polyethylene (polymer) or Al2O3 (ceramic)
• Visual representations:
  • Schematic diagram of an artificial hip
  • X-ray of an implanted artificial hip

Summary

• Engineers must understand materials and their properties to make appropriate processing and selection decisions.
• Materials’ properties arise from their structures, which in turn are determined by processing.
• In chemistry, materials are classified into metals, ceramics, and polymers.
• Most properties fall into six categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative.
• A central role of engineers is materials selection, guided by the processing–structure–properties relationships and real-world constraints (biocompatibility, wear, durability, cost).

Key Concepts and Connections

• Processing controls structure, and structure controls properties, which in turn govern performance in applications.
• Trade-offs are common: e.g., increasing hardness via higher carbon content improves wear resistance but may affect brittleness.
• Real-world relevance: selecting materials for implants (hip replacements) balances biocompatibility, mechanical integrity, and wear performance.
• Ethical and practical implications: durability, safety, and long-term compatibility with human tissue are critical in biomedical materials.

Equations and Notation (glossary)

• Structure from Processing:
  \text{Structure} = g(\text{Processing})
• Properties from Structure and Composition:
  \text{Properties} = F(\text{Structure}, \text{Composition})
• Hardness vs Carbon Content (typical steels):
  H = f(C),\quad \frac{dH}{dC} > 0\,.
• Electrical resistivity sensitivity:
  \rho = \rho(p, T),\quad \frac{\partial \rho}{\partial p} > 0,\; \frac{\partial \rho}{\partial T} > 0\,.
• Thermal conductivity sensitivity to impurities:
  \frac{\partial k}{\partial p} < 0\,.