Influence of heat treatment on structure, phase composition, hardness and electrical conductivity of VZhL14N-VI nickel superalloy

The phase composition of VZhL14N-VI nickel superalloy was analyzed in a wide temperature range – from room temperature to 1600 °C by means of CALPHAD (CALculation of PHAse Diagrams) calculations. In light of the findings, the authors devised potential heat treatment modes for VZhL14N-VI superalloy. The impact of different heat treatment modes on the grain size, hardness, and electrical conductivity of VZhL14N-VI superalloy samples produced by ceramic mold casting was investigated, as well as the effect on the alloy of high-temperature annealing at 1070 – 1170 ℃ for 1 – 4 h. The alloy heat treatment resulted in a notable increase in grain size and a decrease in hardness. The influence of artificial aging temperature after high-temperature annealing and quenching on the hardness and electrical conductivity of the alloy in the range of 610 – 810 ℃ was studied. At 810 °C, the alloy exhibits the most pronounced aging effect, accompanied by a rapid increase in hardness, reaching approximately 370 HV. In contrast to the observed changes in hardness, the electrical conductivity of the alloy exhibited minimal variation during the aging process. The proposed heat treatment conditions diverge from those recommended by the OST 1 90126–85 Russian standard for this alloy. The developed heat treatment mode includes the alloy heat treatment at a temperature of 1170 ± 10 ℃ for 4 h, followed by air cooling and aging at a temperature of 810 ± 10 ℃ for 10 – 14 h, followed by air cooling. The proposed heat treatment mode is expected to result in an increase in hardness of VZhL14N-VI superalloy castings by 10 – 20 HV in comparison to the samples subjected to the standard heat treatment mode.