Generated In Situ Powder Metallurgy Of Titanium Matrix Composites

The high cost and the difficulty in processing restrict the mass application of titanium matrix composites alloys. Looking for simple and convenient manufacture techniques, lowering the cost has been the hotspot of the research of titanium alloys. PM process is believed to be the most promising one for high performance and low cost titanium alloys owing to near shape formation. In this work, the densification process, mechanical properties and microstructure of PM Ti matrix composite were investigated by means of expansion/contraction behavior testing, thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Effects of Fe, Mo, Al, Nd elements on the sintering behavior and mechanical properties of titanium alloys were investigated. PM titanium alloys with good mechanical properties have been produced. The microstructure and properties of TiC particulate reinforced Ti matrix composites were investigated. PM titanium intake and exhaust valve seating for automobile use were produced. The following results are obtained:1) Addition of Al may lower the sintering density owing to the partial diffusion of Al during sintering. Addition of Fe can bring about higher sinterability and accelerate the densification of PM titanium alloy.2) Addition of Mo refines the microstructures of Ti-Mo alloy due to the low diffusion rate of Mo, and raising sintering temperature can effectively increase the density without grain coarsening.3) Addition of Fe can influence the mechanical strength greatly. With the increase of Fe content the sizes of prior β phase and the a phase colonies increase slightly, the thickness of a lamellar decreases rapidly and the mechanical properties improve greatly. The addition of Mo refines the microstructure, and improves the mechanical strength by Hall-Petch relationship.4) Addition of Nd can accelerate the densification of PM titanium alloy and refine the grain. Owing to the liquid phase occured during sintering, the density of Ti alloy can achieve 99%.5) According to the effect of alloy elements and rare earth element, a newtype alloy, Ti-15Fe-2.25Mo-l.2Nd-0.4Al was designed. The mechanical properties can achieve the same degree of as-cast Ti-6A1-4V.6) It is feasible to synthesize TiB particles reinforced Ti matrix composite through the reaction between Ti and TiB2,and Ti matrix composite with TiB +TiC reinforcements through the reaction between Ti and B4C. We also can synthesize TiC reinforced Ti matrix composite from the reaction between Ti and Cr3C2.7) The mechanical properties of TN+5C composite (one of the TiC particles reinforced Ti matrix composite ) are the best of all three type of composites. Owing to the existence of TiC particles, the wear resistance of the newly designed PM titanium alloy is better than that of other materials.