Surface Technology Part 1 Introduction Professor Kenneth W Miller Office A108 Phone 0841 9348 0324 Surface Technology

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 Surface Technology

Automotive Parts of Interest Body in White Suspension Components Brake Components Steering Components Space Frames Accessories Mirrors Antenna Surface Technology

Enemies List Metal to metal contact Sun Water Salt Rocks Grocery carts Time Surface Technology

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

Automotive Materials of Interest Steel Carbon Steel HSLA Stainless Steel New Alloys Aluminum Magnesium Polymers Composites Surface Technology

What is Not Covered Engine and engine components Tires Polymers will get limited coverage underbody impact protection body parts Surface Technology

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? Surface Technology

Material Structure Atomic Level Patterns of Atoms Unit Cells Body-Centered Cubic (BCC) Face-Centered Cubic (FCC) Hexagonal Close Pack (HCP) Surface Technology

Material Structure - FCC Surface Technology

Material Structure -BCC Surface Technology

Material Structure - HCP Surface Technology

Energy and Packing • Non dense, random packing • Dense, regular packing Surface Technology 2

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 Surface Technology

Material Structure Coordination Number Nearest neighbors and touching atoms Coordination Number = 12 for FCC Coordination Number = 8 for BCC Coordination Number = 12 for HCP Surface Technology

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 Surface Technology

Material Structure - BCC Metal Atomic Radius (nm) Chromium 0.1249 Iron (α) 0.1750 Molybdenum 0.1363 Tantalum 0.1430 Tungsten 0.1371 Surface Technology

Material Structure - HCP Metal Atomic Radius (nm) Cadmium 0.1490 Cobalt 0.1253 Titanium (α) 0.1445 Zinc 0.1332 Surface Technology

Strength of Materials Determined by bond strength Limited by slip planes Slip planes and dislocations Split planes and inclusions Atomic separation (distances) Surface Technology

Crystalline Defects Surface Technology

Bond Strength Surface Technology

Energy and Packing • Non dense, random packing • Dense, regular packing Surface Technology 2

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 Surface Technology

Granular Structure Polycrystalline lead ingot Magnified 7x Surface Technology

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 Surface Technology

Strain Engineering Strain True Strain Surface Technology

Stress Engineering Stress True Stress Surface Technology

Stress and Strain These are point functions >0 for tension, <0 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 Surface Technology

Stress and Strain Surface Technology

Material Properties Tensile strength Yield strength Toughness Hardness Fracture toughness Modulus of Elasticity Poisson’s Ratio Toughness – resistance to fracture, area under stress strain curve Surface Technology

Stress and Strain Elastic Range – linear Plastic Range – non-linear E is the modulus of elasticity or Young’s Modulus Full recovery, no permanent change Plastic Range – non-linear Varies with material Work hardening Necking Permanent change to size and strength Surface Technology

Modulus of Elasticity Surface Technology True or engineering stress and strain Surface Technology

Modulus of Elasticity Surface Technology

Yield Point Surface Technology

Necking Surface Technology

Stress Strain Power law relationship Typical for steel and aluminum Assumes slow strain Assumes uniform temperature Surface Technology

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 Surface Technology

Poisson’s 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 Surface Technology

Material Properties Material Elasticity Yield Poisson’s GPa MPa Ratio Tungsten 407 0.28 Steel 207 180 0.30 Nickel 138 0.31 Titanium 107 450 0.34 Copper 110 69 Brass 97 75 Aluminum 35 0.33 Magnesium 45 0.35 Surface Technology

Discussion - Surfaces Appearance Cover minor flaws Hide difference materials Protection from Corrosion Protection from scratches or impacts Increase / decrease friction Improve scratch resistance (hardness) Surface Technology

Manufacturing Considerations Cost Speed – timing for production Downstream effects Value to the consumer Weight Appearance Safety Surface Technology

Manufacturing Cost Materials Time Equipment Flexibility (changeover time and cost) Labor Waste disposal (toxic?) Surface Technology