Study On Preparation And Microstructural And Mechanical Characteristics Of In Situ (TiB+TiC) Hybrid Reinforced High Temperature Titanium Matrix Composites

In situ titanium matrix composites(TMCs) are a kind of light-weight andhigh-temperature materials that will be widely used in the aerospace and automotivemanufacturing and other fields. It is essential to make a systematic study on thepreparation and microstructure and mechanical properties of TMCs. In this paper,3vol.%(TiB+TiC) hybrid reinforced high temperature titanium matrix composites werefabricated by consumable electrode vacuum arc remelting technique; theirmicrostructure and mechanical properties, high temperature hot deformation behavior,hot forging and heat treatment process were investigated systematically.3vol.%(TiB+TiC) hybrid reinforced high temperature titanium matrix compositeswere in situ synthesized utilizing the reaction among B4C, C and Ti in a consumableelectrode vacuum arc remelting furnace. Reinforcements are distributed relativelyuniform in the matrix. TiB appears mainly to be acicular and short fibers, while TiC issmall lump and near equiaxed. The matrix has (+β) laminar staggered basket structure.From the edge to the center part, the grain size follows a increasing trend and thereinforcement morphology is also changed. At room temperature, center part hasrelatively better performance than other areas, the tensile strength reach to1047.5MPa,while the elongation is0.3%. Tensile strength of700℃still be maintained at538.9MPa,the elongation reaches to13.5%. Room temperature fracture mechanism is cleavagefrature, it turns to quasi-cleavage crack at600℃and700℃, while ductile fracture at800℃. The strengthening mechanism of as-cast TMCs include fine grain strengtnening,solution strengtnening and reinforcement load-bearing strengthening.By means of thermal physics simulation experiment, high-temperature deformationbehavior of TMCs were studied. In (+β) double phase region, the average hotdeformation activation energy is676.515KJ/mol and the stress index is3.316. At thesame time, the constitutive equation and the relationship about peak stress σ wereestablished, which will provide support for the equipment selection and processformulation of subsequent hot processing. Then the microstructure evolution laws ofTMCs during high-temperature deformation were revealed, under the conditions of hightemperature and low strain rate, the matrix microstructure appears to be equiaxed.Meanwhile, the optimized processing parameters for the thermal deformation wereobtained(1050℃,0.01s-1).Forged TMCs with complete crack-free surface were fabricated by hot forging. In1/2r of forging cross, it appears to be fine equiaxed organization, while lamellar organization in center part. TiB that has larger aspect ratio were broken and array alongthe direction perpendicular to the forging orientation. Tensile strength and elongation of1/2r at room temperature is relatively high, the center part follows. Compared with thecast, the tensile strength increased by11.1%, elongation increased by139.5%. At700℃,tensile strength reach to600.3MPa, elongation reach to28.4%. Room temperaturefracture mechanism is quasi-cleavage crack, it turns to ductile fracture at elevatedtemperature. The strengthening mechanism of forged TMCs include fine grainstrengtnening, dislocation strengtnening and TiB aligned strengthening.After β phase and+β phase heat treatment, equiaxed and basketweaveorganization were obtained. The high-temperature tensile results show that β heattreatment obtain better comprehensive mechanical properties. At600℃，the tensilestrength increased by about40MPa compared with forged TMCs, but elongationdecreased.