Multistage sintering process for Ni3Al powder metallurgical products

Abstract

A multistage sintering process for powder metallurgical products of nickel aluminide intermetallic compound has been investigated. It comprises at least two stages of sintering and interstage cold deformation to collapse and eliminate the sintering pores. Most of all, a thermally absorbing material has to keep in contact with the powder compacts during the preliminary heating stage (650 °C, the first stage of reactive sintering). It depresses the maximum temperature of specimens to develop the useful transient phase Ni2Al3. This transient phase is a brittle and especially crispy material with a relatively low melting point (1135 °C). It plays an important role in preventing the development of any significantly large cracks during the pore-eliminating process. The purpose of the second stage of sintering material at an elevated temperature (1200 °C) is to develop a transient liquid phase from the Ni2Al3 to heal or eliminate any microcracks, crazes, and collapsed pores from previous steps, as well as to transfer the material to the final Ni3Al structure. It is beneficial to produce a sound product having a large dimension and excellent mechanical properties. Consequently, the specimens will be further densified by a repeated cycle of thermal mechanical treatment (TMT).