Microwave processing of titanium and titanium alloys for structural, biomedical and shape memory applications: Current status and challenges

Microwave (MW) radiation has attracted increasing attention in the fabrication and/or synthesis of titanium (Ti) and Ti alloys from powder since 1999 when the first study was reported by Gedevanishvili et al. This article provides a comprehensive review of MW processing of Ti and Ti alloys. It begins by discussing the critical technical issues associated with MW processing of Ti powder, including the heating response of Ti powder to MW radiation, temperature measurement by infrared pyrometry and calibration, and interstitial absorption and control. This is followed by a detailed review of the sintering of a range of powder metallurgy (PM) Ti and Ti alloys for structural, biomedical, and shape memory applications. As a new development in the field, MW heating and sintering of titanium hydride (TiH2)powder for the fabrication of PM Ti are discussed in terms of the heating response, interstitial contamination, microstructure, and tensile properties of the as-sintered Ti. The challenges that face MW sintering of PM Ti from either Ti powder or TiH2 powder are reviewed, and solutions are proposed. Based on the heating and isothermal sintering characteristics by MW radiation, recommendations are made for the applications of MW processing of Ti and Ti alloys.