Influence of heat treatment on the structure and properties of ZhS6U high-temperature nickel-based alloy

This study considers the structure and properties of a high-temperature nickel-based alloy (ZhS6U) after different regimes of heat treatment. Cast samples were subjected to quenching and annealing at the temperatures of 900, 1000, 1100 and 1200°C during 1 hour. The structure was investigated by optical microscopy (OM) and scanning electron microscopy (SEM). Additionally, microhardness and compression strength were measured in this study. It was shown that a cast material consisted of crystallites with a length of 100 mm and had a dendritic cellular structure. The main phases observed in samples were: free-form carbides (MC-type), elongated carbides of M23C6 and M6C probable stoichiometry, γ′-phase and non-equilibrium eutectic with composition of (γ′ + γ). It was found that heat treatment had no influence on the microstructure of samples and the morphology of carbide particles. The minimum size of the γ′ reinforcing phase (below 0.3 µm) and its minimum volume fraction were obtained after quenching from 1200°C and holding for 1 hour. The maximum microhardness value reached 598 HV after quenching from 900°C. The minimum value (449 HV) corresponded to the samples quenched from 1200°C. Compression tests revealed that ultimate tensile strength (UTS) of all samples was almost at the same level (1900–2100 MPa). Plastic strain of materials heated up to 1200°C proceeded with formation of cracks.