Solid phase sintering
Solid phase sintering according to its components can be
divided into single-component solid phase sintering and multicomponent system
solid phase sintering. Single-component solid phase sintering is a pure metal
compound of fixed composition or loose-fitted powder of uniform solid solution
or compact sintered below the temperature
of melting point (generally 2/3 to 4/5 of the absolute melting
temperature). Single-component solid phase sintering process in addition to the
bonding between powder particles, densification and microstructure of pure
metal, there is no dissulotion between organization, nor the emergence of a new
component or new phase.
Sintering process
Single-component solid phase sintering process roughly
divided into three stages:
(1) Low temperature phase.
Mainly
occur metal bounce, gas adsorption and evaporation of moisture, decomposition
and ruled out of compact formagen. Due to elastic stress is eliminated when rebonding, the
contact area between powder particles decrease relatively, plus volatiles,
makes sintered body contraction is not obvious, even have slight expansion. The
density of sintered body in this stage remain unchanged.
(2)Medium temperature phase.
Began recrystallization, powder
particle surface oxide was completely restore, grain contact interface formed
sintering neck, sinter strength improved obviously, and the density increases
slowly.
(3) High temperature
phase. This is the main stage for single-component solid
sintering. Diffusion and
flow process thoroughly and close to completion, plenty of blind holes of
sintered body gradually shrinked, number of pore decreases, density of sintered
body obviously increase. All performance keep stable after a certain period of
heat preservation. The major factors affect single-component solid phase
sintering is the nature of sintered components, powder characteristics(such as
particle size, shape, surface state, etc.) and sintering process conditions
(such as sintering temperature, time, atmosphere, etc.). Increasing the contact
area between the powder particles or improve the contact state, change material
activation energy of the migration process, Increases the number of atoms of
the migration process and change the ways or methods of material migration, all
can improve single-component solid phase sintering process.
Multicomponent
Multicomponent system solid phase sintering is two or
more components powder system sintered below the melting temperature of the low
melted component. Multicomponent system solid phase sintering in addition to
the phenomena that occurred to the single-component solid phase sintering, also
occur some other phenomena due to the interaction between components. For the
multicomponent system that component is not mutual dissolve, the sintering
behavior is mainly determined by the powder which takes more ratio. Such as
mixed powder of copper and graphite, the sintering is mainly between copper
powder, graphite powder block the contact between copper powder and affect the
shrinkage, has a certain influence to the strength and toughness of sintered
body. To multiple solid phase sintering that can form solid solution or
combination, except sintering between same components, mutual dissolution or
chemical reaction happen between different components. Sintered body due to the
different of component system, some will shrink and some expand.
Strange diffusion has decisive effect in the formation of
metal and alloy homogenization, all factors conducive to strange diffusion, can
promote the multicomponent system solid phase sintering process. Such as use a
finer powder, improve powder mixing uniformity, use the partial alloying
powder, and improve the sintering temperature, eliminate gas adsorption and
oxidation film on the surface of the powder particles, etc. In deciding on
sinter performance, multicomponent system of solid phase sintering alloy
homogenization is more important than the densification of sintered body. Multicomponent
solid phase system after sintering can turn into single-phase organization of
alloy, or polyphase structure of alloy, it can be judged by sintering system
alloy state diagram.
Like other metal processing as well as metal photo etching.
