Swelling during sintering of titanium alloys based on titanium hydride powder

Compacts were prepared by pressing titanium and titanium hydride powders mixed with nickel powder and sintering under vacuum. Severe swelling was observed only for compacts based on TiH2 powder. Pressure changes in the vacuum furnace, dilatometry results and mass loss data all indicate that dehydrogenation of TiH2 powder compacts occurs at lower temperature than any significant sintering. Swelling appears to have been caused by a contaminant in the TiH2 powder rather than hydrogen. The onset of severe swelling during heating was associated with the formation of liquid phase as the solidus was crossed. However, some swelling appears to take place under solid state sintering conditions. Various results indicate that the mechanism of swelling is high gas pressure within closed pores. Large pores appear to form by breakage of ligaments between small pores followed by opening of the pore. It appears that the use of (uncontaminated) TiH2 powder in place of Ti powder would allow the benefit of lower green porosity to be retained during sintering to achieve low sintered porosity.