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Study On A PM Ti-Fe-Mo-Al Alloy For Automobile Use

Posted on:2005-11-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:H P TangFull Text:PDF
GTID:1101360182969050Subject:Materials science
Abstract/Summary:PDF Full Text Request
The high cost and the difficulty in processing restrict the mass application of titanium 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. However, it is difficult to fully density titanium powder, and the mechanical properties of PM Ti are poor. The purpose of this study is to develop a cost-effective titanium alloy for automobile use. Ti-Fe-Mo-Al samples were prepared by Blended Elemental PM process and forging. In this work, the densification process, mechanical properties and microstructure of PM Ti alloys 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 accelerate the densification of PM titanium alloy, but the tensile properties were reduced owing to the coarsening of microstructures. Addition of Mo refines the microstructures of alloys so that it can improve the tensile properties of titanium alloys.2) Addition of Nd can accelerate the densification of PM titanium alloy and refine the grain. After sintering, Nd-rich particles disperse in titanium matrix. The size of particle range from 100 nm to 20um. The rare earth element can scavenge the oxygen in the titanium matrix, decreasing the solution strengthening of oxygen, while improving the plasticity. The coactions of these two factors maintain the strength andimprove the elongation. With the addition of rare earth element Nd, the elongation of PM titanium alloy can be improved from 4-6% to 14-21%.3) The tensile strength and elongation of PM forged Ti-Fe-Mo-Al alloy are almost the same as that of sintered PM Ti-Fe-Mo-Al alloy. The contractions of cross sectional area and fatigue strength are higher than that of sintered alloy.4) According to the effects of alloy elements on the densification and alloy properties, a new PM Ti-l.5Fe-2.25Mo-l.2Nd-0.3Al alloy has been developed. The tensile properties at room temperature of this sintered alloy can be equivalent to that of forging TC4 alloy.5) The in-situ TiC reinforced titanium matrix composites are prepared by a P/M technique. Through addition of Cr3C2, TiC particle forms, and then, Cr diffuses in the titanium matrix. With the addition of Cr3C2 increasing, the grain size can be refined owing to TiC particles distributing in the grain boundary. The TiC strip and Ti-Nd-O complex dispersing in the Ti matrix can improve the strength of alloy, while decrease the elongation.6) Through forging and particle-reinforcement, the wear resistance of PM titanium alloy can be enhanced. The wear resistance of newly-designed PM titanium alloy for valve seating are better than that of other materials, and the wear resistance at elevated temperature is superior. The engine test of the new PM titanium alloy proves that alloy have wide application.
Keywords/Search Tags:titanium alloy, sintering densification, rare earth element, forging, titanium matrix composite
PDF Full Text Request
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