Study On Hot Extrusion And Heat Treatment Process Of 2.5vol.%TiBw/TA15 Composites Bar

The titanium matrix composites with lightweight,high strength and durability have received widespread applications in aerospace.However,the room temperature brittleness easily coming into presence limits the enhancement effects of reinforcement.The ideal method to improve the room temperature brittleness and increase the enhancement effects is to enable the reinforcement to distribute inhomogeneously.Therefore,in this paper,the columnar network structure TiBw/TA15 titanium matrix composites with the raw materials of spherical TA15 and TiB₂ were successfully fabricated by the process of low energy milling,pre-sintering and hot canned extrusion based on the in situ synthesis reaction of TiB₂+Ti?2TiB and the relatively reasonable TiBw reinforcements content and the matrix particle size were determined.The effect of hot extrusion temperature?950°C,?+? phase region;1050°C,near phase transition;1150°C,? phase region?on the microstructure and mechanical properties of TiBw/TA15 composites and the sample extruded at 950°C and its rotary forgrd condition were adopted as research objects to systemically analyze the solution and aging effect on the structure and properties of the composites.The TiB volume fraction and the TA15 particles size influence the alignment degree of the columnar network structure reinforcement commonly.The results indicated that a proper matching of 2.5vol%TiBw and TA15 particle s with particle size arranging from 75?m to 150?m are expected for TiBw/TA15 composites to obtain outstanding mechanical properties.The extrusion temperature manifestly affected the structure and properties of extruded TiBw/TA15.Specifically speaking,the deformation temperature is in ?+? phase region when extruded at 950 °C,the structure consisted of tiny ? colony and elongated primary ?,and the primary ? formed a strong <10-10>?//ED deformation texture.When extruded at 1050°C and 1150°C,the composites matrix exhibited a bio-modal microstructure consist of equal ? and Widmannstatten structure,the texture of which was mainly made up of <0001>?//ED component from <110>?//ED transition and <10-11>?//ED component from dynamic recrystallization.The <11-22>?//ED texture from <112>?//ED transition also emerged when extruded at 1150°C.The texture intensity of the composite were influenced by the degree of recrystallization and the influence significantly descend as the extrusion temperature rising.The exist ence of TiBw was prone to enable the surrounding ? nearly equiaxed so as to destory the Burger orientation of ??? and weaken the extrusion texture intensity.Affected by the distinguished structure,the joint effort of deformed ? and tiny TiBw reinforcement presented at 950°C empowered the composites a property of high strength and low plasticity,the tensile strength of which was 1383.6MPa and the elongation was merely 2.5%.With the temperature rising,? phase recrystallized to a complete extent and the ambient strength gradually declined to 1235.5MPa at 1050°C and the fracture elongation impressively leveled up to 10.0%.The high temperature tensile test at 550°C implied the matrix softness greatly lowered the high temperature strength and the plasticity remarkably increased.The high proportion of grain boundary slide extruded at 950°C resulting in 28.7% elongation.The strength of the extruded composites at 1150°C was 808.2MPa at most and the elongation was only 11.1%,which demonstrate a considerable controlling effect of extrusion temperature on the microstructure and properties of TiBw/TA15 composite.Comparing the microstructure and property of the extruded and extrusion-rotary forged processed?with water quenching and air cooling?work piece,it can be observed that there are abundant kinked ? and transformed ? came into existence after extrusion-rotary forged processing,resulting in the decrease of strength and the increase of plasticity.After subsequent solution quenching to the extruded at 950°C and its rotary forged?with air cooling?materials,there emerged quenched martensite and equiaxed ? phase,the strength and elongation of which decreased moderately.The increase of equiaxed ? and the disassembled of quenched martensite resulted in the improve of plasticity and the decrese of strength after aging treatment,and the strength are 1285 MPa and 1334 MPa respectively with both of the elongation are greater than 3%.Material extrusion-rotary forged processed?with water quenching?completely transformed into quenched martensite after solution with increase of strength and decrease in elongation.Quenched martensite decomposed and coarse grain boundary ? phase appeared after aging treatment and lowered the strength and the plasticity to 1203 MPa and 5.7% respectively.