A reevaluation of the mechanical properties of molybdenum- and tungsten-based alloys containing hafnium and carbon

Abstract

It is the purpose of this paper to reexamine data on the behavior of molybdenum- and tungsten-based alloys which are strengthened by hafnium carbide. This reanalysis suggests that claims of apparently unusual high-temperature behavior in the above systems, specifically (1) the “solute-weakening” effect of hafnium and (2) the fact that increasing the amounts of HfC can have a weakening effect, may not be valid. In the present description, it is postulated that there are significant changes in the amounts of carbide available for precipitation in alloys where the additions of carbide former to carbon are varied about the ratio needed for complete or stoichiometric combination. By recalculating the amounts of hafnium carbide available for precipitation in the molybdenum- and tungsten-based alloys it is possible to demonstrate that excess hafnium does not have a “solute-weakening” effect as had been claimed. Instead, a trend of improved creep strength and high temperature tensile strength with an increase in the amount of HfC available for precipitation is observed.