BASCA热处理对TB18钛合金显微组织和力学性能的影响

Effect of BASCA Heat Treatment on Microstructure and Mechanical Properties of TB18 Titanium Alloy

研究了TB18钛合金棒材经β固溶缓慢冷却时效(BASCA)热处理后的显微组织和力学性能。结果表明,TB18钛合金棒材在β相区固溶后缓慢冷却条件下,α相在β晶界和晶内均有析出,晶内α相呈点状或短针状,晶界α相基本呈薄膜状镶嵌在β晶界上。冷却速度对晶界α相影响较大,当冷却速度为1℃/min时,晶界α相以透镜状在晶界上不连续析出,形成“项链”组织。随着冷却速度的降低,析出的晶界α相越来越多且相互连接为一体,并逐渐粗化呈连续的波浪状。缓慢冷却后形成的晶界α相对合金塑性和韧性不利,随着冷却速度的减小,合金塑性和韧性均降低。TB18钛合金棒材经过β相区固溶空冷+时效处理后,可获得在抗拉强度接近1300 MPa的水平下,延伸率达到8%,断裂韧性超过80 MPa·m^(1/2)的优异综合性能。

The microstructure and mechanical properties of TB18 titanium alloy bar underβannealing,slow cooling and aging(BASCA)heat treatment were studied.The results show that theαphase precipitates under the condition of slow cooling after solid solution.The intragranularαphase is spot-like or short needle,and theαphase in the grain boundary is basically embedded in theβgrain boundary as a thin film.The cooling rate has a great influence on the grain boundaryαphase.When the cooling rate is 1℃/min,the grain boundaryαphase precipitates discontinuously on the grain boundary in the shape of a lens,forming a“necklace”structure.With the decrease of the cooling rate,more and more grain boundaryαphases are precipitated,which are connected to each other and coarsened gradually in a continuous wavy shape.The grain boundaryαphase formed after slow cooling has adverse effects on the plasticity and toughness of the alloy.With the slowing down of the cooling rate,the plasticity and toughness of the alloy are reduced.The tensile strength of TB18 titanium alloy bar exhibits excellent comprehensive properties with a tensile strength close to 1300 MPa,an elongation of 8%,and a fracture toughness exceeding 80 MPa·m^(1/2) underβphase zone solid solution air cooling and aging heat treatment process.