Synthesis of powder alloys in Ni-Al-Nb-C system by mechanical alloying

Structure and phase composition of the mechanically alloyed nanocrystalline Ni-AI-Nb-C alloys with a constant content of Nb and C (5 at. % of each element) and various contents of Ni and Al were investigated. It was shown that in the alloys with C-Ni/C-Al = 1 divided by1.6, the interaction between Ni and Al, and Nb and C occurs independently because of the high negative formation enthalpies of NiAl and NbC. As a result, stable phases NiAl1-x (B2 structure) and non-stoichiometric carbide NbC, were formed during milling. When the ratio C-Ni/C-Al greater than or equal to2.5, a supersaturated solid solution Ni(AI, Nh, C) with the fcc- structure was formed during the MA. Further heating up to 700 degreesC leads to the dissociation of the solid solution; Ni3AlCx phase (L1(2)) and non-stoichiometric carbide NbC, appear after the heating. The DSC curve of this alloy exhibits an exothermic effect, which corresponds to the dissociation process. Hardness was measured in pressed and sintered (700 MPa, 1200 degreesC, 2 hours) samples; the dependence between the hardness and structure of the intermetallic matrix was found.