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

-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 degrees C consists of two supersaturated solid solutions based on fcc nickel (gamma-solid solution) and bcc chromium (alpha-solid solution) and a small amount of the Ni3Al phase; subsequent aging at 560 degrees C leads to a decrease in the supersaturation of the gamma solid solution and the formation of a higher content of bcc chromium and Ni3Al phases. Nitriding at 540 degrees C leads to the formation of a continuous 3-4-mu m-thick layer of the CrN phase, the decomposition of the Ni3Al phase, and the formation of phase AlN in a lower layer 100-140 mu m 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 HV0.1) for the CrN phase and insignificantly decreases from 740 to 650 HV0.1 in the subsurface layers due to the transformation of Ni3Al into AlN.