TB8钛合金板材TIG焊缝组织与拉伸性能

Microstructure and property of TB8 sheets TIG welded seam

采用TC4焊丝对TB8板材实施TIG,焊后分别在500、550、600和650℃对接头退火1 h后炉冷。测试不同焊后热处理接头的室温拉伸强度和硬度;利用OM观察未热处理接头(NTWJ)的宏观组织;利用SEM研究焊缝的微观组织及拉伸断口形貌;利用EDS分析NTWJ焊缝的成分分布;利用TEM研究NTWJ焊缝中的亚稳相。结果表明:NTWJ焊缝为成分分布不均匀的铸态组织,其[Mo]eq为6.5~11,基体由粗大的亚稳β相构成。拉伸实验时位于NTWJ焊缝中部的α″相发生解理,使接头从焊缝中部脆性断裂。500℃退火后,α″相消失,但没有α相片层组织形成。550℃退火后,β相中析出了极细小的α相片层,接头的拉伸强度达到最大值1223 MPa。经600℃和650℃退火后,β相中析出的α相片层粗化,因此,接头拉伸强度下降,断口呈现完全脆性断裂。

TB8 titanium alloy sheets were welded by tungsten inert gas welding(TIG)with TC4 wire as filler metal,and the joints were annealed respectively at 500,550,600,650℃for 1 h following furnace cooling for postwelded heat treatment.The ultimate tensile strength and HV hardness of welded joints with different postwelded heat treatment were tested at ambient temperature.The macrostructures of non-heat-treated welded joint(NTWJ)were observed by OM,and the microstructure and fractograph of welded seams were studied by SEM.The composition distribution of welded seam in NTWJ was analyzed by EDS,and the metastable phases were studied by TEM.The results indicate that the welded seam in NTWJ shows as-cast structure with heterogeneity in composition,with[Mo]eq of 6.5-11,and matrix is composed of coarse metastableβphases.Cleavage ofα″phase in middle part of welded seam in NTWJ during tensile test occurs,the joint brittle fracture from the center of welded seam.Theα″phase disappear from welded joint annealed at 500℃,but no laminarαphases are precipitated.When welded joint is annealed at 550℃,fine laminarαphases precipitating from matrixβphases made the strength of welded joint reach the maximum value of 1223 MPa.When welded joints are annealed at 600℃and 650℃,the laminarαphases are coarsened,as a result,the ultimate tensile strengths decrease and the fractographs show completely brittleness.