(寶雞文理學(xué)院 機(jī)電工程學(xué)院，寶雞 721004)
摘 要: 采用TC4焊絲對(duì)TB8板材實(shí)施TIG，焊后分別在500、550、600和650 ℃對(duì)接頭退火1 h后爐冷。測試不同焊后熱處理接頭的室溫拉伸強(qiáng)度和硬度；利用OM觀察未熱處理接頭(NTWJ)的宏觀組織；利用SEM研究焊縫的微觀組織及拉伸斷口形貌；利用EDS分析NTWJ焊縫的成分分布；利用TEM研究NTWJ焊縫中的亞穩(wěn)相。結(jié)果表明：NTWJ焊縫為成分分布不均勻的鑄態(tài)組織，其[Mo]eq為6.5~11，基體由粗大的亞穩(wěn)β相構(gòu)成。拉伸實(shí)驗(yàn)時(shí)位于NTWJ焊縫中部的α″相發(fā)生解理，使接頭從焊縫中部脆性斷裂。500 ℃退火后，α″相消失，但沒有α相片層組織形成。550 ℃退火后，β相中析出了極細(xì)小的α相片層，接頭的拉伸強(qiáng)度達(dá)到最大值1223 MPa。經(jīng)600 ℃和650 ℃退火后，β相中析出的α相片層粗化，因此，接頭拉伸強(qiáng)度下降，斷口呈現(xiàn)完全脆性斷裂。
關(guān)鍵字: TB8鈦合金；TIG；焊接接頭；拉伸強(qiáng)度；焊縫；亞穩(wěn)相
（School of Mechanical and Electrical Engineering, Baoji University of Arts and Sciences, Baoji 721004, China）
Abstract: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 metastable β phases. Cleavage of α″ phase in middle part of welded seam in NTWJ during tensile test occurs, the joint brittle fracture from the center of welded seam. The α″ phase disappear from welded joint annealed at 500 ℃, but no laminar α phases are precipitated. When welded joint is annealed at 550 ℃, fine laminar α phases precipitating from matrix β phases made the strength of welded joint reach the maximum value of 1223 MPa. When welded joints are annealed at 600 ℃ and 650 ℃, the laminar α phases are coarsened, as a result, the ultimate tensile strengths decrease and the fractographs show completely brittleness.
Key words: TB8 alloy; TIG; welded joint; tensile strength; welded seam; metastable phase
