SYNTHESIS OF NICKEL ALUMINIDES BY VACUUM PLASMA SPRAYING AND EXOTHERMIC IN-SITU REACTIONS

This paper describes our efforts at combining vacuum plasma spraying a nd exothermic in-situ reaction processing techniques to obtain a cost- effective method of producing dense intermetallic materials for high t emperature structural applications. It has been demonstrated that it i s possible to produce, using this technique, a layered interpenetratin g Ni3Al/NiAl composite with less than 5 vol.% residual Ni and less tha n 3% residual porosity. Exothermic reaction control through powder mix ture composition and deposit thermal management proved to be critical steps in synthesizing this composite. Mechanical testing of the Ni3Al/ NiAl composite produced in this study revealed that the presence of Ni 3Al improved appreciably the room temperature properties of the compos ite (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 yie ld a marked anisotropy in its fracture toughness. The mechanical prope rties of the Ni3Al/NiAl composite produced in this study were observed to be in good agreement with properties reported in literature for si milar materials produced by other techniques, indicating that with fur ther process optimization the technique explored here can become a via ble alternative to currently employed techniques. (C) 1997 Elsevier Sc ience S.A.