Microstructure And Property Of Electron Beam Welded TiBw/TC4 Composite Joint

Titanium Matrix Composites combine favorable mechanical properties,good corrosion resistance and high temperature durability that make them attractive in aerospace,submarine and automobile domains.In this thesis,the electron beam welding(EBW)is performed on 3.5vol.% TiBw/TC4 composites.In order to meet the mechanics performance and forming,the influences of welding processes on the microstructure evolutions and mechanical properties of the welded joints were investigated.The microstructure and properties of typical joints,the matrix grain size and the morphology of the reinforcing phase were analyzed.Finally,the influence of EBW on abrasion resistance and corrosion resistance were explored.Firstly,the microstructure and properties of the base metal(BM)were analyzed.In TiBw/TC4 composites,needle-like Ti Bw whiskers were in-situ synthesized on the Ti6Al4 V surface and formed a quasi-continuous network distribution,and the tensile strength was 1170 MPa.The welding proceduce has obvious effect on the forming and properties of welded joints.The optimum process parameters were listed as follows: the accelerating voltage of 70 k V,the beam current of 10 m A,the welding speed of 400mm/min,the focusing current of 593 m A and the electron beam scanning of X=Y=200,the frequency of 500 Hz.The results showed that the ultimate tensile strength is 1125 MPa.Based on the analysis of the stomata near the fusion zone(FZ)of the welding joint,the formation mechanism is mainly due to the combined action of hydrogen porosity and the gas inside the TiBw/TC4 composites.Due to the welding speed was too apace,the bubbles had no time to overflow,and remain in the molten pool to form pores.The effect of stomata on tensile strength,fatigue property,abrasion resistance and corrosion resistance were also discussed.The TiBw/TC4 composites EBW joints seemed to be inverted bell shaped,the equiaxed crystal zone and dendrite were observed in the weld zone(WZ).In the WZ,the average microhardness was 436 HV higher than the heat-affected zone(HAZ)and higher than the BM.Inversely,the average diameter of TC4 grain ranged from 3.05?m to 3.50?m to 12.80?m.The area close to the HAZ and BM is the weakest area of the joint.The distribution of the reinforcing phase in the WZ was still formed a quasi-continuous network distribution,the size of the network was evidently reduced compared with the base metal,and the shape of the reinforcing phase was fine whisker.Ti B2,which did not react,also reacted with Ti to form Ti B,in the process of EBW.Finally,the effect of EBW on the wear resistance and corrosion resistance of TiBw/TC4 composites was investigated.The results showed that the corrosion resistance and wear resistance were reduced after the of electron beam welding thermal cycle,and the influences of different welding processes on corrosion resistance and wear resistance were different.