文献类型：期刊文献

中文题名：TA19钛合金电子束焊接头微观组织与性能研究

英文题名：Microstructures and Mechanical Properties Research of Electron Beam Welding Joint of TA19 Titanium Alloy

作者：韩秀峰[1,2];王伦[2];朱明亮[3];廖仲祥[2];张露[2]

机构：[1]上海交通大学材料科学与工程学院,上海200030;[2]中国航发商用航空发动机有限责任公司,上海201108;[3]华东理工大学机械与动力工程学院,上海200237

年份：2021

卷号：45

期号：7

起止页码：778

中文期刊名：稀有金属

外文期刊名：Chinese Journal of Rare Metals

收录：CSTPCD;;EI(收录号：20213310789881);Scopus;北大核心:【北大核心2020】；CSCD:【CSCD2021_2022】；

基金：工信部民用飞机专项科研项目(MJ-G-2013-16)资助。

语种：中文

中文关键词：TA19;电子束焊;显微组织;力学性能

外文关键词：TA19;electron beam welding;microstructure;mechanical properties

摘要：采用电子束焊接方法对TA19钛合金进行焊接,分析了电子束焊接头各区域的显微组织类型及形貌,测试了接头的显微硬度、室温拉伸、疲劳裂纹扩展速率及断裂韧性等力学性能,并与TA19钛合金母材进行对比。研究表明,焊缝区为粗大的柱状晶组织并存在大量相互交错分布的针状马氏体相,热影响区内随着离熔合线距离的增加马氏体数量逐渐减少;焊缝区显微硬度最高,比母材区显微硬度高出约HV80,随着向母材区过渡显微硬度逐渐降低;焊接接头室温抗拉强度、屈服强度性能及断面收缩率均与母材基本相当,但延伸率略有下降;焊缝区粗大的柱状晶组织硬度高,脆性大,导致焊缝区对疲劳裂纹扩展的抗裂性要低于母材;母材及焊缝KIC值分别为54.49和52.88 MPa·m^(1/2),母材抵抗裂纹扩展断裂的能力略好于焊缝。
TA19(nominal composition Ti-6Al-2Sn-4Zr-2Mo)titanium alloy was a near-αalloy,offering good tensile strength and creep strength,as well as fatigue strength up to 540℃,which had been widely used for compressor case and blade of aero engine.Electron beam welding(EBW)was still the main joining process for aero engine components manufacturing,it could provide highquality joint with narrow fusion zone(FZ)and heat affected zone(HAZ)due to high energy density,low heat input,and vacuum atmosphere.However,there was very little data available on tensile strength,fatigue crack propagation rate and fracture toughness of TA19 titanium alloy electron beam welding joint.The aim of the present work was to investigate the microstructure types and morphology,tension and fatigue behavior of the welded joint and to compare with the base material(BM).TA19 titanium alloy was welded by electron beam welding process,the welding parameters for full penetration on 17-mm-thick butt welds were:beam voltage of 150 kV;beam current of 100 mA at a welding speed of 20 mm·s^(-1).Post-weld heat treatments were employed at 595℃for 8 h and air cooling.The different regions microstructure types and morphology of electron beam welding joint were studied by optical microscope(OM)and scanning electron microscope(SEM).Microhardness profiles across the joint were obtained using Vickers hardness testing machine with 1.96 N load.Tensile testing at ambient temperature was performed with round specimens of 5 mm gauge diameter and 30 mm gauge length,the weld joint was located at middle of specimens,the tensile axis was perpendicular to the weld line.Tensile specimens with the same geometry were prepared from the TA19 forging and tested under the same conditions as the weld joint to compare the tensile properties.Fracture surface of tensile specimens was studied by SEM.Fatigue crack propagation rate testing was measured on high frequency fatigue testing machine(PLG-100 C)at the stress ratio of 0.1 with compact tension(CT)specimens,the initial crack was located at the center of weld,BM specimens with same geometry were prepared and tested.Fracture toughness testing was measured on universal tensile testing machine(Instron 8088)at loading speed of 0.5 mm·min^(-1) with CT specimens.A good quality weld joint without under fill,unmelting or voids was observed by OM from the cross section of weld samples.Three distinct zones were identified from themicrostructure,which were FZ,HAZ and BM.The width of HAZ was 1 mm.For the BM,a duplex structure combination of equiaxed and lamellar morphology was observed by SEM,the equiaxed microstructure was primary a phase,the lamellar microstructure was secondaryαphase generated inβgrain.For the FZ,it was thick columnar crystal within a large number of cross distribution acicular marten site phase,several equiaxed grains were observed in the fusion center.For the HAZ,different microstructure morphologies were observed,βphase was generated in near fusion line,and the marten site phase number in HAZ gradually decreased with the increase of the distance from the fusion line.The microhardness raised from the BM toward the HAZ and the FZ,a symmetric microhardness profile was observed for the two sides of the weld centerline.The average microhardness in BM was HV 340,the microhardness in the weld zone was the highest which was HV 80 higher than that of BM.The average tensile strength,yield strength and reduction of area of welded joint at room temperature were 948 MPa,845 MPa and 42%respectively,basically similar to that of the BM,but the elongation decreased slightly.Curve of da/dN-△K for BM and welding joint was plotted,a linear fitting was constructed,and Paris equation coefficients were obtained,the fatigue crack growth resistance in the weld joint was lower than in the BM.The K_(IC) of BM and weld zone were 54.49 and 52.88 MPa·m^(1/2),respectively,and the resistance crack propagation of BM was slightly better than weld zone.During electron beam welding process,the TA19 BM was heated to liquid,the temperature was far aboveβ-transus temperature and cooled down at a very high cooling rate,the duplex structure consisting of primaryαphase and secondaryαphase generated inβgrain had been melted and fully transformed intoβphase during electron beam welding process,βgrains were grown as columnar structure with the direction of temperature gradient,acicular martensite phase was precipitated inβgrain due to rapid cooling rate.The microstructure morphologies of HAZ were influenced by the temperature endured and the cooling rate during electron beam welding process,and the martensite phase number in HAZ was gradually decreased with the increase of the distance from the fusion line.For HAZ near the fusion line,the temperature was higher thanβ-transus temperature during electron beam welding process,but it did not exceed the melting temperature,singleβphase was generated andα’marten site phase was precipitated inβgrain due to rapid cooling rate.For the HAZ near the BM,the temperature was lower thanβ-transus temperature,the primaryαphase was slightly decreased during rapid cooling.The FZ had the highest microhardness which was resulted by acicular martensite phase precipitated,and the microhardness gradually decreased with the transition to the BM zone due to the martensite phase decreased.The tensile tests of TA19 titanium EBW joints and BM showed that EBW joints exhibited similar tensile strength with the BM,but the elongation decreased slightly.The fracture location of tensile test specimen for TA19 titanium EBW joints was within the BM due to its lower microhardness and strength than that of HAZ and FZ as indicated by themicrohardness measurements,the elongation for EBW joints was lower than that of the BM due to less deformation occurred in HAZ and FZ.The fatigue crack growth resistance in the weld joint was lower than in the BM,the KIC of the weld joint was slightly lower than that of BM.The thick columnar crystal microstructure had high hardness and brittleness,which resulted in worse anti-crack property than BM.