Fabrication of alloyed aluminum nickelides by metallothermy of metals oxides

Abstract

Fabrication conditions of NiAl, NiAl–Cr, and NiAl–Cr–Mo–W alloys by joint aluminothermic reduction of initial metal oxides are investigated. Thermodynamic characteristics of accompanying reactions are determined. The temperature dependence of the change in the isobaric potential (ΔG°, kJ/mol) of reduction reactions of oxides points to the high formation probability of alloys. It is revealed by differential thermal analysis that the reduction of metal oxides enters the active phase after aluminum is melted at ~650°C and progresses according to the heterogeneous mechanism in a temperature range of 800–1100°C. The optimal composition of the initial charge, which provides the maximal yield of metals into alloys, is established. It is found experimentally that the yield of metals into alloys constitutes 85–92 wt %. Synthesis products are identified by the elemental and X-ray phase analyses as intermetallics of the Ni–Al system, which contain inclusions of chromium, molybdenum, and tungsten. It is shown that the concentration of inclusions varies in a range of 1.5–6.5 wt %. The microhardness of alloys is determined to vary from 3546 to 7436 MPa, depending on the content of alloying elements.