Influence of solution heat treatment on the microstructure and hardness of a high carbon alloy from the Ni-Co-Cr-Ta-Al system

Abstract

Purpose: The main purpose of this paper was to determine the influence of the temperature of solution heat treatment on the microstructure and hardness of the newly designed model alloy, intended for working at high temperatures. Design/methodology/approach: A mass weighing approx. 1 kg was test melted in a vacuum furnace and cast into a ceramic mould. Samples for investigations were solution heat treated at the temperature range of 1020-1170°C. After heating to the desired temperature, the samples were held at this temperature for 2 hours and then water-cooled. Findings: The main constituents of the microstructure of the Ni-Co-Cr-Ta-Al-C alloy in as-cast state are: the γ phase, which constitutes the matrix, the γ’ phase (γ’ phase occurs as fine globular precipitates) as well as primary TaC and Cr7C3 carbides. Irregularly shaped primary carbides are uniformly distributed and do not form agglomerates. Solution heat treatment of the investigated alloy at exceedingly higher temperatures causes a slow decrease of chromium primary carbides. Research limitations/implications: Taking into account the chemical composition of the investigated alloy, it is reasonable to expect the heat treatment should improve its properties. At 1020°C, γ’ phase precipitations dissolve and it is possible to achieve a super saturated solid solution matrix. Next, correct aging treatment should by applied. Practical implications: A new model alloy which allows to design a new material for high temperature applications. Originality/value: New chemical compositions and microstructure of Ni-based materials for high temperature application with high carbon contents. Additionally, the new alloy is strengthened not only by a high carbon volume fraction but also by intermetallic phases.