Phase Transformations in a Precision 40KhNYu-VI Nickel Alloy during Heat Treatment and Nitriding

Abstract

Abstract—The effect of heat and thermochemical treatment (nitriding) on the structure of the surface regions and the core of 40KhNYu-VI alloy samples have been studied by X-ray diffraction, optical microscopy, and microhardness measurements. The data on the phase transformations have been obtained as follows: the alloy quenched from 1150°C consists of two supersaturated solid solutions based on fcc nickel (γ-solid solution) and bcc chromium (α-solid solution) and a small amount of the Ni₃Al phase; subsequent aging at 560°C leads to a decrease in the supersaturation of the γ solid solution and the formation of a higher content of bcc chromium and Ni₃Al phases. Nitriding at 540°C leads to the formation of a continuous 3–4-μm-thick layer of the CrN phase, the decomposition of the Ni₃Al phase, and the formation of phase AlN in a lower layer 100–140 μm in thickness. The content of the bcc chromium phase in the surface layer decreases. The microhardness measurements after nitriding show that the microhardness is high (up to 1060 HV_0.1) for the CrN phase and insignificantly decreases from 740 to 650 HV_0.1 in the subsurface layers due to the transformation of Ni₃Al into AlN.