Fabrication Of Low Cost Ti-6Al-4V Alloy By Metal Injection Molding And Its Thermohydrogen Processing

The performance of titanium and titanium alloys are excellent, but its preparation and processing cost are high. The process of Metal injection molding processes (MIM) is short, and can make finished products or close to the sizes of finished product components directly, so MIM processes can greatly reduce the production cost of titanium alloy parts. The hydrogen-treating processing technology can improve the microstructure of titanium alloy, and enhances the operational performance of titanium workpiece. This article discussed how to use low cost TiH2powder as raw materials to fabricate Ti-6Al-4V alloy by MIM processes, the hydrogen-treating processing technology with MIM Ti-6Al-4V alloy has also been researched.The process of preparation MIM Ti-6Al-4V alloy with TiH2powder as raw material was studied. Experimental results indicate that:using the new high-efficiency clean bonding agent system which our laboratory had developed for TiH2powder injection molding, the powder loading can reach to66%. Blended powder and binder was mixed in a vacuum kneading machine for1hour at the temperature of160℃, we could get a suitable feeding for injection after the mixture was granulated. When the mould at normal temperature condition, the optimal molding parameters for the feedstock were as following:temperature for molding was130℃, molding pressure was7.5Mpa. Two steps of debinding were used in this reseach. Firstly, geen parts were dipped into the solvent CH3(CH2)5CH3for7hours with debind rate up to about32%. And then themal debinding in high pure argon atmosphere (99.999%), the rest of the binder could be removed completely. The debinding process and parameters were determined by both thermal decomposition properties of the binder constituent and the dehydrogenation properties of TiH2powder. And the optimized follow-up thermal debinding process was determined as follows:The effects of Sintering parameters such as temperature, sintering time on the densification,microstructure and mechanics performance of as-sintered titanium alloy products were investigated sysmatically when the sintering process in a10-3Pa vacuum atmosphere. The results showed that full dengsity sintered titanium alloy products could be manufacture with TiH2powders as raw materials by MIM. With sintering temperature and time increase, their porosity was reduced, the density and mechanics performance increased markably. The optimized sintering process in a10-3Pa vacuum atmosphere could be fixed as follows:Obtained under optimal sintering process conditions, the sintered products has a relative density of99.1%, a tensile strength of587MPa, yield strength439MPa, elongation4.93%.The H content in the samples was0.0049wt%, andC, O, N were0.12wt%,0.21wt%and0.0024wt%, respectively.The hydrogen-processing technology can improve the titanium alloy microstructure and performance, when the MIM Ti-6A1-4V after hydrogen treatment, the original bulky sheets microstructure was gradually broken into tiny α+β needle microstructure, and the higher the hydrogen content the more obvious of the refinement effect. The alloy specimens with hydrogen content of0.51wt%after hydrogen treatment, the final tensile strength was661MPa and the elongation rate was6.11%. Compared with the original alloy sample, the tensile strength and the elongation rate increased by11%and19%respectively.