Research On Microstructure And Properties Of Titanium Matrix Composite Prepared By In-situ Reaction Of B₄Cp With Ti-555 Titanium Alloy

In recent years,based on the excellent comprehensive performance of titanium matrix composites,it has become an important strategic structural material in high-tech fields such as aerospace and automotive industries,showing great application potential.In this paper,argon gas protection sintering?APS?and spark plasma sintering?SPS?were used to prepare TiB+TiC particle reinforced titanium matrix composites by in-situ reaction between boron carbide particles?B₄C_p?and Ti-555 titanium alloy.And the effect of B₄C_p content?0³wt.%?,preparation process and solid solution aging process on microstructure and properties were studied.The research work carried out and the results achieved were as follows:?1?The microstructure and properties of sintered composites prepared by APS were studied.The results show:the phase composition of sintered composites was all mainly Ti,TiB and TiC.The addition of B₄C_p can refine the grains,and the higher the content,the more obvious the refinement.The hardness of the composite added with 3wt.%B₄C_p was increased from 434.02HV to 801.76HV,and the strengthening effect was remarkable.The porosity of the composites was 3.32%,4.69%,5.25%,6.89%,respectively.The porosity showed an upward trend and the density decreased with the increase of B₄C_p content.?2?The heat treatment process of sintered composites prepared by APS was studied.The results show:the diffraction peak intensity of TiB and TiC was enhanced compared with the sintered state,and the hardness increased first and then decreased with the increase of solid solution temperature.When the temperature near phase transition,the hardness was the highest,reaching 895.63HV.The optimum heat treatment process is 900°C×3h/AC+600°C×6h/AC,and the composite added with 3wt.%B₄C_p has a hardness of 999.28HV after heat treatment.The room temperature compressibility was 10.8%,7.9%,8.4%,and the composite with 2wt.%B₄C_p had the highest room temperature compressive strength of878.85MPa.?3?The oxidation resistance of composites prepared by APS at 750°C and 850°C was studied.The results show:the oxidation products at both two temperatures were all mainly TiO₂ and Al₂O₃.The composite with 3wt.%B₄C_p at 750°C has the best oxidation resistance,and the average oxidation rate K⁺is 0.933g·m^-2·h^-1,which is 61.45%lower than that of the base alloy(2.420g·m^-2·h^-1).At 850°C,the degree of oxidation is intensified,the matrix alloy is cracked,and the composite material is spalled.However,the strengthening effect of B₄C_p against high temperature oxidation performance is still remarkable.The best performance is obtained after adding 3wt.%B₄C_p,K⁺decreased from 7.994g·m^-2·h^-1 to 3.110g·m^-2·h^-1.After oxidation at 750°C for 100h,the composite with 3wt.%B₄C_p had the smallest oxide layer thickness of 40?m,which is 33.3%lower than that of the base alloy?60?m?.?4?The corrosion resistance of the composites prepared by APS at 750°C and 850°C was studied and 25wt.%NaCl+75wt.%Na₂SO₄ was selected as corrosive medium.The results show:the corrosion products at both two temperatures were all mainly TiO₂,Al₂O₃and a small amount of TiS₂,NaTiO₂.The composite with 2wt.%B₄C_p at 750°C has the best thermal corrosion resistance,and the weight gain per unit area is 16.744mg·cm^-2,which is13.4%lower than that of the base alloy(19.344mg·cm^-2).The composite with 1wt.%B₄C_p gained the most weight,up to 21.116mg·cm^-2.When the temperature rised to 850°C,the corrosion condition is intensified and the weight gain of the composite with 2wt.%B₄C_P is reduced from 63.47mg·cm^-2 to 51.27mg·cm^-2.At a corrosion temperature of 750°C,the corrosion thicknesses of the four samples were 60?m,40?m,24?m,and 32?m,respectively.?5?The microstructure and properties of composites?0wt.%,2wt.%?prepared by SPS were studied.The results show:the phase composition of the SPS sample was similar to that of the APS sample,which were Ti,TiB,TiC,and the SPS sample had a higher density.After adding B₄C_p,the hardness was increased from 438.38HV to 690.28HV,the compressive strength was increased from 929.86MPa to 1441.52MPa,and the APS sample with2wt.%B₄C_p was only 872.85MPa.The oxidation products at 750°C were mainly TiO₂ and Al₂O₃.After adding 2wt.%B₄C_p,K⁺decreased from 1.347g·m^-2·h^-1 to 0.579g·m^-2·h^-1,and the oxidation process was alleviated.The thickness of the oxide layer was 30?m and 20?m,respectively.Compared to the APS sample with the same composition,the SPS sample gained less weight and the oxide layer was thinner.In this paper,the APS and SPS preparation processes were innovatively used to prepare the particle-reinforced titanium-based composite materials by in-situ reaction of B₄C_p and Ti-555 titanium alloys,which will provide a reference for the performance improvement of titanium alloys.