Surface Technology Part 1 Introduction

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Surface TechnologyPart 1Introduction

• Professor Kenneth W Miller
• Office A108
• Phone [phone]

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Topics for Today

• Course Syllabus
• Introductions
• My background
• What is your background
• What are your areas of interest
• Automobile Parts of Interest
• Materials of Interest
• What is Not Covered
• Fundamentals of Materials Science

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Automotive Parts of Interest

• Body in White
• Suspension Components
• Brake Components
• Steering Components
• Space Frames
• Accessories
• Mirrors
• Antenna

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Enemies List

• Metal to metal contact
• Sun
• Water
• Salt
• Rocks
• Grocery carts
• Time

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Body and Frame Functions

• Strength
• Frame
• A, B, and C Pillars
• Suspension and Steering Components
• Braking Components
• Cosmetic
• Body panels
• hood

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Automotive Materials of Interest

• Steel
• Carbon Steel
• HSLA
• Stainless Steel
• New Alloys
• Aluminum
• Magnesium
• Polymers

• Composites

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What is Not Covered

• Engine and engine components
• Tires
• Polymers will get limited coverage
• underbody impact protection
• body parts

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Summary

• Body in White is the Primary Topic
• Steel is the Primary Material
• Aluminum is Becoming Significant
• Magnesium is of Limited Interest
• What are the factors in material selection?

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Material StructureAtomic Level

• Patterns of Atoms
• Unit Cells
• Body-Centered Cubic (BCC)
• Face-Centered Cubic (FCC)
• Hexagonal Close Pack (HCP)

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Material Structure - FCC
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Material Structure -BCC
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Material Structure - HCP
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Energy and Packing
Non dense, random packing
Dense, regular packing
2
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Material Structure - APF

• Atomic Packing Factor
• APF Volume of atoms / Volume of cell
• APF 0.74 for FCC
• APF 0.68 for BCC
• APF 0.74 for HCP

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Material StructureCoordination Number

• Nearest neighbors and touching atoms
• Coordination Number 12 for FCC
• Coordination Number 8 for BCC
• Coordination Number 12 for HCP

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Material Structure - FCC
Metal Atomic Radius (nm)
Aluminum 0.1431
Copper 0.1278
Gold 0.1442
Nickel 0.1246
Platinum 0.1387
Silver 0.1445
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Material Structure - BCC
Metal Atomic Radius (nm)
Chromium 0.1249
Iron (a) 0.1750
Molybdenum 0.1363
Tantalum 0.1430
Tungsten 0.1371
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Material Structure - HCP
Metal Atomic Radius (nm)
Cadmium 0.1490
Cobalt 0.1253
Titanium (a) 0.1445
Zinc 0.1332
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Strength of Materials

• Determined by bond strength
• Limited by slip planes
• Slip planes and dislocations
• Split planes and inclusions
• Atomic separation (distances)

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Crystalline Defects
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Bond Strength
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Energy and Packing
Non dense, random packing
Dense, regular packing
2
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Granular Structure

• Pure metals are rarely used
• Practical limits to crystalline structure
• Can create anisotropy
• Reflects heterogeneous composition
• Caused and changed through
• Forming operations such as casting
• Working operations e.g. rolling, drawing
• Heat treatment

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Granular Structure
Polycrystalline lead ingot Magnified 7x
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Granular Structure

• Size effects strength
• Size effects toughness
• Orientation affects directional strength
• Orientation at surface corrosion opportunities
• Can be seen through a small microscope
• Crystalline structure requires special equipment

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Strain

• Engineering Strain
• True Strain

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Stress

• Engineering Stress
• True Stress

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Stress and Strain

• These are point functions
• gt0 for tension, lt0 for compression
• Both are directional
• Both depend on plane considered
• Normal stress and strain
• Shear stress and strain
• Full stress or strain state is represented as a
  3x3 matrix

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Stress and Strain
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Material Properties

• Tensile strength
• Yield strength
• Toughness
• Hardness
• Fracture toughness
• Modulus of Elasticity
• Poissons Ratio

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Stress and Strain

• Elastic Range linear
• s E e
• E is the modulus of elasticity or Youngs Modulus
• Full recovery, no permanent change
• Plastic Range non-linear
• Varies with material
• Work hardening
• Necking
• Permanent change to size and strength

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Modulus of Elasticity
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Modulus of Elasticity
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Yield Point
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Necking
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Stress Strain

• Power law relationship
• Typical for steel and aluminum
• Assumes slow strain
• Assumes uniform temperature

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Stress Strain
Material n K (MPa)
Low Carbon Steel 0.21 600
4340 Steel Alloy 0.12 2650
304 Stainless Steel 0.40 1400
Aluminum A2024-T3 0.17 780
Magnesium AZ-31B 0.16 450
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Poissons Ratio

• Pull it and it gets thinner
• Squish and it gets thicker
• Consider a tensile specimen pulled in z
• Upper limit is 0.5 for no material volume change

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Material Properties
Material Elasticity Yield Poissons
GPa MPa Ratio
Tungsten 407 0.28
Steel 207 180 0.30
Nickel 207 138 0.31
Titanium 107 450 0.34
Copper 110 69 0.34
Brass 97 75 0.34
Aluminum 69 35 0.33
Magnesium 45 0.35
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Discussion - Surfaces

• Appearance
• Cover minor flaws
• Hide difference materials
• Protection from Corrosion
• Protection from scratches or impacts
• Increase / decrease friction
• Improve scratch resistance (hardness)

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Manufacturing Considerations

• Cost
• Speed timing for production
• Downstream effects
• Value to the consumer
• Weight
• Appearance
• Safety

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Manufacturing Cost

• Materials
• Time
• Equipment
• Flexibility (changeover time and cost)
• Labor
• Waste disposal (toxic?)