Influences of sintering parameters on shape-retention ability of porous Ni3Al intermetallic fabricated by powder metallurgy

Abstract

Porous Ni3Al intermetallic is successfully fabricated through elemental powder metallurgy of Ni-25 at% Al samples. The influences of sintering parameters, such as heating rate, isothermal treatment on the sintering behaviors of the samples are investigated. When the samples are heated continuously from room temperature to 1000 °C at a relatively high rate (>5 °C/min), the reaction between Ni and Al happens in an intense way. The heat suddenly released by the reaction produces liquid phase in the material, which facilitates the reaction significantly. Therefore, a sudden expansion (∼6%) occurs, resulting in severe deformation of the samples. The shape retention ability of the sample can be improved by isothermally treating the sample at a proper temperature (470–490 °C) for prolonged time or heating it up at a low heating rate. Under these sintering conditions, the reaction between Ni and Al happens in a much more controllable solid-state way. Therefore, the abrupt expansion can be decreased to ∼0.5%. During the solid-state reaction, imbalanced diffusion between Al and Ni results in more Al diffusing into Ni than the other way around, therefore creating pores on the Al side. As a result, homogeneous porous Ni3Al intermetallic samples can be fabricated and the regular shape of the sample can be well preserved.