Abstract
This paper presents a new indicator that enables accurate prediction of the γ′ phase fraction in hafnium-containing superalloys. This indicator is based on the concentration of alloying elements typical of MC carbides, i.e. tantalum, titanium and hafnium. Assuming that hafnium will be present only in the form of HfC carbide, it was believed that the concentration ratio of tantalum and titanium to the hafnium in MC-type carbides would provide an index to quantify the contribution of the γ′ phase. The main feature of the proposed indicator is the ability to determine the fraction of the γ′ phase at any stage of heat treatment, since it depends not on the nominal chemical composition of the alloy, but on the concentration of selected alloying components, a variable value because of heat-activated diffusion processes. The effectiveness of this component was verified on the example of René 108DS alloy subjected to complete heat treatment together with the process of aluminization (1st degree ageing), and additional treatment “repairing” the microstructure of René 108DS alloy after this process. Experimental results of measuring the γ′ phase content in correlation with the proposed index indicated a linear relationship between these quantities.