Materials T3 - Metals and Alloys

Diffusion

Mass transport by atomic motion

Gas and Liquid Diffusion

Brownian (random) motion

Solid Diffusion

Movement of vacancies and interstitials

What rate of vavancy jumping depends on

Vacancy concentration and frequency of jumping (increases w/ temp)

Inter-diffusion

Diffusion with 2 different elements

Self Diffusion

Diffusion with same elements

Interstitial Diffusion

Faster than vacancy diffusion, rate increases with temperature

Diffusion Rate at Grain Boundaries

Faster due to spacing between atoms

Phases

Physically and chemically distinct regions

Solution

Single phase solid, liquid and gas

Mixture

System with more than one phase

Phase Equilibrium

When phases reach their lowest energy state (don’t change with time)

Solubility Limit

Maximum concentration for which only a single phase solution exists

Eutetic

Point where liquid transitions to two solid phases without a solid + liquid phase

Eutectoid

Point where solid transitions to two solid phases without a solid + liquid phase

Strategies for Alloy Strengthening

Reducing grain size, solid solution strengthening, precipitation strengthening, dislocation strengthening

Slip

Edge dislocation slides over adjacent half-planes of atoms

Reducing Grain Size

Creates more barriers to prevent slipping, use Hall-Petch equation

Solid Solution Strengthening

Interstitial amd substitutional elements provide solute strengthening

Precipitation Strengthening

Includes dislocation bowing and shearing, precipitates in lattice structure require extra force to shear thus strengthens

Dislocation Density

Increasing density of dislocations increases strain, making slip difficult

Thickness of Material

∆x in Flux (J) Equation

Difference in Concentration

∆C in Flux (J) Equation

Shearing

A type of precipitate hardening that creates resistance against slip due to sheared precipitates

Dislocation Bowing

A type of precipitate hardening that occurs when dislocation line is pinned against precipitates and bows

R Length

% of given solution - % LHS solution

S Length

% RHS solution - % of given solution