Powder Metallurgy
Content
POWDER METALLURGY
Introduction Powder metallurgy alloys are used for:
Components subjected to high temperature e.g. in aircraft Marine and land based power system Hot working tools and dies Cutting tools High density projectile Automobile components ± Friction & Anti friction components
Self lubricating bearing and bushes Consumer Goods Industry Electrical goods industry The process of compaction of metal powder by application of force at high temperature is called sintering There is no possibility of perfect contact; contact; degree of contact most important factor partial contacts between particles results in µporosity¶ or µvoids¶ or µinter-particle space µinter-
Factors for occurrence of porosity
Particle size & shape Applied pressure and method of application Temperature of Particle Metal powders manufactured by carbonyl process consist of spherical particles Minimum porosity possible by packing spheres having equal size is $ 26 % Porosity can be decreased further by addition of large or smaller particles Powders to be sintered are deliberately kept a mixture of different sizes
Shape:
Shape of the particles also plays important role in deciding the extent of porosity
Applied pressure:
Pressure applied on loosely kept powder Reduce porosity by movement of particles into the voids Reduce porosity by deformation of particles Results in considerable increase in the total contact area and cold sintered strength of the compact mass
Temperature:
Oxide film may form on surface during heating by exposure to gases which can be removed or dislodged by abrasion, melting or chemical reduction by suitable gases The adhesion strength of compact increases with temperature
Main obstructive effects to proper fusion:
Incomplete contact between surfaces Reduced contact due to surface films Insufficient plasticity of the particles
Introduction Powder metallurgy alloys are used for:
Components subjected to high temperature e.g. in aircraft Marine and land based power system Hot working tools and dies Cutting tools High density projectile Automobile components ± Friction & Anti friction components
Self lubricating bearing and bushes Consumer Goods Industry Electrical goods industry The process of compaction of metal powder by application of force at high temperature is called sintering There is no possibility of perfect contact; contact; degree of contact most important factor partial contacts between particles results in µporosity¶ or µvoids¶ or µinter-particle space µinter-
Factors for occurrence of porosity
Particle size & shape Applied pressure and method of application Temperature of Particle Metal powders manufactured by carbonyl process consist of spherical particles Minimum porosity possible by packing spheres having equal size is $ 26 % Porosity can be decreased further by addition of large or smaller particles Powders to be sintered are deliberately kept a mixture of different sizes
Shape:
Shape of the particles also plays important role in deciding the extent of porosity
Applied pressure:
Pressure applied on loosely kept powder Reduce porosity by movement of particles into the voids Reduce porosity by deformation of particles Results in considerable increase in the total contact area and cold sintered strength of the compact mass
Temperature:
Oxide film may form on surface during heating by exposure to gases which can be removed or dislodged by abrasion, melting or chemical reduction by suitable gases The adhesion strength of compact increases with temperature
Main obstructive effects to proper fusion:
Incomplete contact between surfaces Reduced contact due to surface films Insufficient plasticity of the particles
