Metals Expert

Before Starting

1. Which metal system? (steel, aluminum, titanium, nickel superalloy)
2. Structural performance or processing focus?
3. Design selection or failure analysis?

Core Expertise Areas

Crystal Structure and Defects

BCC: body centered cubic, iron at room temperature, less close-packed. FCC: face centered cubic, aluminum, copper, austenitic steel, more ductile. HCP: hexagonal close packed, titanium, magnesium, limited slip systems. Dislocations: line defects that allow plastic deformation at low stress. Grain boundaries: planar defects, strengthen by impeding dislocation motion.

Phase Diagrams

Iron-carbon: fundamental for steel design, austenite, ferrite, cementite regions. Eutectic: composition with lowest melting point, simultaneous solidification. Eutectoid: solid state transformation at 0.77 wt% C in iron-carbon system. Lever rule: phase fraction from composition and tie line intersection.

Strengthening Mechanisms

Solid solution: solute atoms distort lattice, impede dislocations. Precipitation hardening: fine precipitates block dislocation motion. Work hardening: plastic deformation increases dislocation density. Grain refinement: smaller grains increase yield strength via Hall-Petch. Hall-Petch: sigma_y = sigma_0 + k over sqrt d, d is grain diameter.

Steel Metallurgy

Heat treatment: anneal, normalize, quench and temper, case hardening. Martensite: hard metastable phase from rapid quench of austenite. TTT diagram: time-temperature-transformation, guides heat treatment design. Hardenability: ability to form martensite throughout section, Jominy test. Stainless steel: austenitic, ferritic, martensitic, duplex types.

Best Practices

• Specify heat treatment precisely, vague terms cause inconsistent properties
• Consider corrosion environment when selecting alloy
• Use fracture mechanics for fatigue and fracture critical applications
• Verify mechanical properties with testing not just datasheet values

Common Pitfalls

Pitfall	Fix
Hydrogen embrittlement in high strength steel	Avoid acid cleaning, bake after plating
Sensitization in austenitic stainless	Use low carbon grade or stabilized grade near welds
Wrong alloy for corrosive environment	Select alloy based on actual service conditions
Overheating during welding	Control heat input and use proper filler metal

Related Skills

• composites-expert
• ceramics-expert
• mechanics-of-materials-expert