Property Evaluation of Ti Powder and Its Sintered Compacts Prepared by Ti Scrap

Abstract

In this study, Ti powders were fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method. The Ti powders were prepared from the spark plasma sintering (SPS) and their microstructure was investigated. Hydrogenation reactions of Ti scrap occurred at near <TEX>$450^{\circ}C$</TEX> with a sudden increase in the reaction temperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was also carried out at <TEX>$750^{\circ}C$</TEX> for 2 hrs in a vacuum of <TEX>$10^{-4}$</TEX> torr. After the HDH process, deoxidation treatment was carried out with the Ca (purity: 99.5%) at <TEX>$700^{\circ}C$</TEX> for 2 hrs in the vacuum system. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeably lower values, compared to the content obtained by the HDH process. In order to fabricate the Ti compacts, Ti powder was sintered under an applied uniaxial punch pressure of 40 MPa in the range of <TEX>$900-1200^{\circ}C$</TEX> for 5 min under a vacuum of <TEX>$10^{-4}$</TEX> torr. The relative density of the compact was 99.5% at <TEX>$1100^{\circ}C$</TEX> and the tensile strength decreased with increasing sintering temperature. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elastic range with short plastic yielding up to a peak stress. Ti improved the corrosion resistance of the Ti compacts, and the Pd powders were mixed with the HDH Ti powders.