The Dilatometric Analysis of the High Carbon Alloys from Ni-Ta-Al-M System

Abstract

Abstract In the following work presents results of high carbon alloys from the Ni-Ta-Al-M system are presented. The alloys have been designed to have a good tribological properties at elevated temperatures. Despite availability of numerous hot work tool materials there is still a growing need for new alloys showing unique properties, which could be used under heavy duty conditions, i.e. at high temperatures, in a chemically aggressive environment and under heavy wear conditions. A characteristic, coarse-grained dendritic microstructure occurs in the investigated alloys in the as-cast condition. Primary dendrites with secondary branches can be observed. Tantalum carbides of MC type and graphite precipitations are distributed in interdendritic spaces in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, while Tantalum carbides of MC type and Chromium carbides of M7C3 type appeared in the Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys. In all alloys g’ phase is present, however, its volume fraction in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys is small.During heating from as-cast state in Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, the beginning of the tantalum carbides precipitation process (MC type) followed (or simultaneous) by the intermetallic phase precipitation (g’ – Ni3(AlTa)) was stated, while in Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys, besides Tantalum carbides also the Chromium carbides precipitation occurred. It means that the investigated alloys were partially supersaturated in as-cast state. Above 1050°C in all investigated alloys the g’ phase is dissolving. In addition, the precipitation of secondary carbides during slow cooling was occured.