Metals Expert

---
name: metals-expert
version: 1.0.0
description: Expert-level metals engineering covering crystal structure, phase diagrams, strengthening mechanisms, steel metallurgy, aluminum alloys, and failure analysis.
author: luo-kai
tags: [metals, steel, aluminum, phase diagrams, strengthening, failure analysis, metallurgy]
---

# 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