Sintering mechanisms for Metals

Sintering mechanisms for Metals (right for metallic glasses):

• Evaporation -> vapor diffusion --> Condensation
• Surface diffusion from surface to neck
• Bulk diffusion from surface to neck
• Grain boundary diffusion from grain boundary to neck
• Bulk diffusion from grain boundary to neck
• Plastic flow by dislocation motion

Alumina densification rates (0.8 and 1.3 mm mean, log-normal) illustrate sintering stages:

Stage I: Initial sintering

• Surface smoothing
• Grain boundary formation, neck growth
• Rounding of interconnected open pores
• Small, slow reduction of porosity, increase in density

Stage II: Intermediate sintering

• Shrinkage of open pores intersecting grain boundaries
• Lots of fast porosity reduction
• Small amount of grain growth

Stage III: Final sintering

• Pores close at 92% dense
• Closed pores shrink to a limited size, or vanish
• More grain growth, leading to internal pores within grains
• Metals often dissolve all gases, leading to 100% density

Ref: Click here!