Synthesis of nickel aluminides by vacuum plasma spraying and exothermic in-situ reactions

This paper describes our efforts at combining vacuum plasma spraying and exothermic in-situ reaction processing techniques to obtain a cost-effective method of producing dense intermetallic materials for high temperature structural applications. It has been demonstrated that it is possible to produce, using this technique, a layered interpenetrating Ni3Al/NiAl composite with less than 5 vol.% residual Ni and less than 3% residual porosity. Exothermic reaction control through powder mixture composition and deposit thermal management proved to be critical steps in synthesizing this composite. Mehanical testing of the Ni3Al/NiAl composite produced in this study revealed that the presence of Ni3Al improved appreciably the room temperature properties of the composite (compared to NiAl) and imparted an anomalous yield behavior, where the yield strength initially increased with temperature. Furthermore, the layered structure of the Ni3Al/NiAl composite was observed to yield a marked anisotropy in its fracture toughness. The mechanical properties of the Ni3Al/NiAl composite produced in this study were observed to be in good agreement with properties reported in literature for similar materials produced by other techniques, indicating that with further process optimization the technique explored here can become a viable alternative to currently employed techniques.