Fabrication of Powder Metallurgy Pure Ti Material by Using Thermal Decomposition of TiH₂

Abstract

  Titanium (Ti) and titanium alloys have been interested as an engineering material because they are widely used across various industrial applications, for example, motorcycle, automotive and aerospace industries, due to their light weight, high specific strength and superior corrosion resistance. Ti materials are particularly significant for the aircraft using carbon/carbon (C/C) composites, for example, carbon fiber reinforced plastics (CFRP), because Ti materials are free from the problem of contact corrosion between C/C composites. However, the applications of Ti materials are limited because of their high cost. From a viewpoint of cost reduction, cost effective process to fabricate Ti materials is strongly required. In the present study, the direct consolidation of titanium hydride (TiH₂) raw powders in solid-state was employed to fabricate pure Ti bulk materials by using thermal decomposition of TiH₂. In general, the production cost of Ti components is expensive due to using commercially pure (CP) Ti powders after dehydrogenation. On the other hand, the novel process using TiH₂ powders as starting materials is a promising low cost approach for powder metallurgy (P/M) Ti products. Furthermore, this new process is also attractive from a viewpoint of energy saving because the dehydrogenation is integrated into the sintering process. In this study, TiH₂ raw powders were directly consolidated by conventional press technique at 600 MPa to prepare TiH₂ powder compacted billets. To thermally decompose TiH₂ and obtain sintered pure Ti billets, the TiH₂ powder billets were heated in the integrated sintering process including dehydrogenation. The hot-extruded pure Ti material, which was heat treated at 1273 K for 180 min in argon gas atmosphere, showed tensile strength of 701.8 MPa and elongation of 27.1%. These tensile properties satisfied the requirements for JIS Ti Grade 4. The relationship between microstructures, mechanical properties response and heat treatment temperature is discussed in detail.