Influence of solution heat treatment on the microstructure and hardness of the new Ni-based alloy with a high carbon content

Purpose: The main purpose of the hereby paper was the determination of the temperature and time of solution heat treatment influence on a microstructure and hardness of the newly designed model alloy, being the model Ni-based tool material - intended for operations at high temperatures - strengthened by compositions of intermetallic phases, of a high carbon and cobalt content. Design/methodology/approach: A test melt of a mass of approximately 1 kg was done in a vacuum furnace, and cast into a ceramic mould. The microstructure of the investigated material was examined by means of the light microscope Axiovert 200 MAT and the scanning electron microscope FIB Zeiss NEON 40EsB CrossBeam. Samples for investigations were solution heat treated from the temperature range: 1020-1170°C. After heating to the desired temperature they were hold at this temperature for 0.5 or for 2 hours and then water-cooled. The volume fraction of primary tantalum carbides and graphite was estimated by the point-count method. Approximately 30 measurements were performed for each variant of the heat treatment. Findings: The main constituents of the microstructure of the nickel-base investigated alloy in as-cast state are: the g phase, which constitutes the matrix, the g’ phase (g’ phase occurs as fine globular precipitates) as well as primary Ta carbides of MC type. Primary carbides of irregular shapes are uniformly distributed not forming agglomerates. Solution heat treatment of the investigated alloy from higher and higher temperatures causes a slow increase of a graphite fraction, nevertheless an application of a temperature of 1170°C significantly increases its fraction. Research limitations/implications: The investigated alloy is the model alloy. Taking into account its chemical composition the possibility of improving its properties by means of the heat treatment should not be expected. In the first place the fraction of carbide forming elements should be increased to eliminate graphite, and secondly the fraction of elements forming g’ phase should be increased to obtain the possibility of the modification of properties by means of solution heat treatment and aging. Nonetheless the achieved results will be utilised at the chemical composition modification of Ni-based alloys of a high carbon content. Practical implications: Broadening the knowledge on the carbides stability in Ni-based alloys, which will help in designing new Ni-based alloys of a high carbon content. Originality/value: Determination of the stability of primary carbides at high temperatures in Ni-based alloys of