Effect Of Melt Hydrogenation On Microstructure And Mechanical Properties Of (TiB+TiC)/Ti-6Al-4V Composites

Particle-reinforced in-situ titanium matrix composites because of its excellent mechanical properties such as high specific modulus and high specific strength is widely used in aerospace and automotive industries and other important fields.However,the density of as-cast composites is not high,and the defects of as-cast shrinkage holes inevitably exist,which leads to poor mechanical properties of materials in practical application.At the same time,because of the high thermal deformation resistance of titanium matrix composites,many difficulties and problems are brought to the hot working process.Melt hydrogenation technology is based on the principle of hydrogen phase composition and micro-structure improvement.Hydrogen is added into titanium-based alloys as a temporary alloying element to improve the hot working performance of titanium alloys by changing the phase composition and micro-structure of titanium alloys.After forging,the mechanical properties of the composites have been improved obviously,and the strength and shape of the composites have been greatly improved.The effect of liquid hydrogenation on the microstructure and mechanical properties of forged composites was studied.In this paper,the melt hydrogenation method is used to electrically remelt the in-situ autogenous reaction of 5vol.%（TiB+TiC）/Ti matrix composite ingot after 5times of remelting.The matrix of the melt titanium hydride matrix composite is refined,and the reinforcing phase segregates towards the primaryβgrain boundary.The atomic diffusion coefficient increases due to the superheat of the melt surface caused by the addition of hydrogen atoms,thus the length-diameter ratio of the reinforcing phase TiB whisker and TiC particles increases.Melt hydrogenation can reduce the agglomeration of reinforcing phases in as-cast composites and improve the bonding strength between reinforcing phases and matrix.The yield strength and ultimate strength of as-cast materials increased from 862.91MPa and 901.42MPa to974.6MPa and 1038.42MPa respectively when the hydrogen content was 7.87×10^-2wt.%.The elongation increased from 0.47%to 0.78%.Hot working forging of 5vol.%（TiB+TiC）/Ti matrix composite ingot was carried out.The experimental results show that the TiB whiskers are aligned perpendicular to the forging direction,and the structure of the matrix alloy is refined.The room temperature tensile properties and fracture toughness of the composites after forging were studied.The data showed that the room temperature strength and elongation of the 0 wt.%composites were increased by about 114 MPa compared with that of the as-cast composites.When the hydrogen content was 7.87×10^-2 wt.%,the room temperature strength of the forged composites was increased by 65MPa compared with that of the as-cast composites,and the room temperature elongation of the as-forged composites was increased by 1.05%.The fracture mechanism of forged titanium matrix composites at room temperature is quasi-cleavage fracture,which is the same as that of as-cast titanium matrix composites.Compared with as-cast titanium matrix composites,the dimple size,number and depth of fracture matrix of as-cast titanium matrix composites at room temperature increase.No obvious debonding and drawing phenomena of TiB whiskers and TiC particles were found,which indicated that the interface between reinforcement phase and matrix alloy was well bonded.Compared with the SEM structure near as-cast fracture surface,the fracture of TiB whisker after forging is more obvious,the degree of fracture is greater,the number of fracture is more and the proportion is higher.Because of forging strengthening composite matrix,there are fewer cracks in the matrix,and the fracture direction of TiB whisker is parallel to the tensile direction.