Production of Low-Cost Titanium Alloys with Exceptional Mechanical Properties by Hydrogen Sintering and Phase Transformation (HSPT)

Hydrogen sintering and phase transformation (HSPT) is a new, low-cost, press and sinter process to produce titanium alloys with mechanical properties that exceed ASTM standards for wrought titanium.  These exceptional properties are the product of grain refinement due to controlled phase transformations during sintering.  During HSPT, TiH_x powder is sintered under dynamically controlled partial pressures of H₂ and subsequently dehydrogenated.  The thermodynamics and kinetics of the phase transformations vary as a function of both temperature and partial pressure of H₂.  Therefore, by controlling these parameters during the thermal cycle, HSPT is capable of producing engineered microstructures in the as-sintered state.  Additionally, the reduced reactivity of TiH_­x versus metallic powder makes it much less prone to contamination, producing a cleaner product without the need for exotic handling procedures.  And finally, the presence of solvated hydrogen during sintering significantly improves densification of titanium.  Because of these phenomena, HSPT is capable of producing near-net-shape articles of fully dense titanium alloys with application-tailored mechanical properties in the as-sintered state.  As such, HSPT is capable of circumventing the multiple steps of energy intensive thermomechanical work necessary in a typical wrought process.  Therefore, this process shows promise as a low-cost alternative to traditional wrought processing for the production of titanium alloys for demanding applications.  Densification and microstructural evolution of titanium during HSPT and the resulting mechanical properties of material produced to date will be discussed.