Liquid Phase Sintering of Nickel Base Superalloys

Sintering in the presence of a liquid phase has been applied to several nickel base superalloy powders. The optimal sintering conditions have been inferred from a systematic study of densification parameters (temperature, sintering time, particle size distribution, etc.). Under these conditions, closed porosity sintered materials whose shape conforms closely to that of the container (ceramic mould) can be obtained. The mechanical properties of the sintered preforms are rather low because of residual porosity. A subsequent densification by hot isostatic pressing or forging is therefore necessary to attain high performances. However, this complete densification stage can be carried out without a sealed container, as long as the porosity is closed. Liquid phase sintered structures do not exhibit deleterious effects from the partial melting; these are revealed only by the titanium, molybdenum, and aluminium microsegregations. The grain size of the sintered materials is nearly identical to the prior particle size. Consequently, sintering in the presence of a liquid phase can be advantageously used to obtain coarse grained preforms. PM/02l3