热处理对TC21钛合金线性摩擦焊接头组织与性能的影响

基于先进飞机构件研制需求,针对TC21钛合金线性摩擦焊接头,设计了3种热处理制度,开展了焊态及不同热处理状态下接头显微组织及力学性能研究. 结果表明,焊态试样的焊缝区由细化的β晶粒组成,晶内析出含有大量位错的针状马氏体,起到了位错强化作用,显微硬度相比母材明显提高,热力影响区由于次生α相发生了溶解,显微硬度相比母材有所降低. 热处理后焊接接头内的α相发生了显著变化,在高温区退火时,长时间保温导致初生条状α相长大,在低温区退火则促进了次生针状α相的析出;所有热处理后的接头进行拉伸试验后均断裂于母材区,经过双重退火的接头其焊缝区及热力影响区组织均为β转变组织+初生长条状α相 + 次生针状α相,并且各区域显微硬度基本与母材一致,组织更加均匀.     

热处理对TC17(α+β)/TC17(β)线性摩擦焊接头组织及力学性能的影响

针对热处理前后TC17(α+β)/TC17(β)钛合金线性摩擦焊接头组织和性能进行了对比分析. 结果表明,焊态时焊缝区组织发生动态回复和再结晶,两侧的热力影响区组织均被不同程度地拉长,热处理后焊缝中的亚稳相分解析出弥散的α和β相,TC17(α+β)侧热力影响区的初生α相有所长大. 焊态接头焊缝区显微硬度比母材低,接头的抗拉强度和屈服强度略低于母材,分别达到母材的91.9%,96.2%,接头拉伸性能试件断裂位置均在焊缝区;经过热处理,母材显微硬度未发生明显变化,焊缝区显微硬度显著提高,接头抗拉强度和屈服强度达到与母材相当,与焊态相比分别提高11.9%,8.2%,接头拉伸性能试件断于母材区.     

TC17钛合金线性摩擦焊接头组织及力学性能分析

针对固溶时效态TC17钛合金焊态及焊后热处理态线性摩擦焊接头,进行显微组织及力学性能对比分析. 结果表明,焊态时焊缝组织发生了回复与再结晶,由于焊后冷却速度较快,生成了亚稳定β相,焊缝区发生了软化;热力影响区组织沿受力变形方向拉长、细化、交替呈带状分布,加工硬化程度较高,显微硬度明显高于其它区域;热影响区由于二次次生α相基本溶解于亚稳定β相,导致显微硬度显著降低. 经过焊后热处理,亚稳定β相发生时效分解,析出了弥散程度更高的针状次生α相使得焊接区硬度大幅度提高. 由于亚稳定相的生成,焊态接头发生软化,拉伸均断裂在焊缝区,抗拉强度达到母材强度91.8%,断口呈脆性断裂形态;焊后热处理态接头由于二次次生α相的析出,起到弥散强化的作用,拉伸试验均断在母材,断口呈典型韧性断裂形态.     

TC4钛合金线性摩擦焊接头组织和力学性能

文中阐述了线性摩擦焊的原理、特点,并针对TC4钛合金线性摩擦焊接头组织和力学性能进行了研究.对比分析TC4钛合金线性摩擦焊接头焊态和焊后热处理态的接头组织和力学性能.结果表明,焊接接头共分为母材、热力影响区和焊缝区三部分;TC4钛合金的接头(包括焊态和焊后热处理态)抗拉强度和屈服强度均达到母材的90%以上;焊缝中心的硬度值最高,焊后热处理能使接头的硬度分布更加均匀.     

Ti6242合金线性摩擦焊及焊后热处理接头显微组织与力学性能的多尺度表征（英文）

通过线性摩擦焊技术对一种近α钛合金(Ti6242)进行连接,并进行焊后热处理。为了研究显微组织演变并建立显微组织与接头力学性能的关系,对焊态与焊后热处理的两种接头进行多尺度表征。结果表明,两种接头的断裂位置均位于母材,而经焊后热处理的接头在焊缝与热力影响区的硬度进一步提升。经过热处理后焊缝处的等轴晶粒中产生薄片状的α相集束,而热力影响区处的马氏体相分解为(α+β)相,从而提高焊接接头处的硬度。     

TC4钛合金焊接接头中压电子束局部热处理技术

电子束局部热处理技术是对整体热处理的一种有益补充,针对TC4钛合金进行中压电子束局部热处理研究。电子束局部热处理后TC4钛合金接头的组织形态与电子束焊态基本相同,但焊缝区的晶粒组织略有细化,焊缝区显微硬度也得到了改善,电子束局部热处理后焊接接头的拉伸力学性能均高于焊态。优化的电子束局部热处理工艺完全可以使TC4钛合金接头的组织力学性能超过焊态。     

热处理对TC11摩擦焊接头微观组织和力学性能的影响

在C200型摩擦焊机上进行TC11同种金属的摩擦焊接,分析了热处理对TC11摩擦焊接头微观组织和力学性能的影响。结果表明:焊后接头连接完整,焊缝区为完全再结晶组织;焊件进行热处理后,焊缝组织为均匀细小的针状a+β相;工艺参数对焊缝成型和接头抗弯强度有显著影响,热处理后接头抗弯强度性能更好。     

Ti60/TC17异种钛合金惯性摩擦焊接头组织性能研究

采用惯性摩擦焊技术焊接Ti60/TC17钛合金，并对焊态/热处理态接头进行组织和性能分析；焊接过程中，有粘流态金属滴落，两侧金属材料熔合较好，且接头焊缝处飞边形貌呈现不规则曲线状，缩短量达4.2 mm，轴向错边小于0.3 mm；焊缝界面两侧区域均发生了动态再结晶，焊缝区显微硬度值较高，越远离焊缝位置显微硬度值越低；焊态下，焊缝处组织为针状α板条和等轴晶粒组成，两侧热机影响区有明显的流线形貌；热处理后，焊缝处针状α板条细化，次生α相增多，再结晶晶界明显，两侧热机影响区流线形貌消失；通过接头拉伸性能测试，焊态/热处理态试样室温拉伸断裂位置均发生在TC17侧，断口形貌呈典型解理断裂，焊态下，平均抗拉强度为978.5 MPa，达母材的92.06%，热处理后，平均抗拉强度为1 076.5 MPa，提升98 MPa，超过母材抗拉强度，这说明热处理有利于将组织内的残余应力释放，同时易于析出针状α相，进而提高接头力学性能。     

高氧TC4/TC17线性摩擦焊接头组织与显微硬度研究

对高氧TC4和TC17钛合金进行了线性摩擦焊试验,利用光学显微镜与扫描电镜对焊接接头的微观组织进行了分析,并研究了热处理对接头组织及显微硬度的影响。结果表明,焊态下高氧TC4侧焊缝比TC17侧窄,焊缝界面处生成共生晶粒,界面两侧发生动态再结晶。高氧TC4侧,靠近焊缝边缘的部分热力影响区形成大量的亚晶粒,部分区域发生动态再结晶形成细小的等轴β晶粒,冷却后晶粒内析出马氏体α'相。TC17侧,β晶粒以及α晶界被拉长形成变形带,在靠近焊缝处、形成许多细小的等轴β晶粒。经过焊后热处理,高氧TC4的TMAZ亚稳态马氏体α'相分解,高度变形的β相中析出片层状α相;TC17侧TMAZ组织为细小的针状α相。焊缝中心的共生晶粒组织不均匀,由相互交错的大小α片层组成。焊态下焊缝中心硬度最高;热处理后,TC17侧焊缝及热力影响区硬度大幅度增加。     

TC4/TA15异种钛合金激光焊焊缝的显微组织和高温力学性能（英文）

研究不同焊接工艺参数条件下TC4/TA15异种钛合金激光焊接接头的显微组织和高温力学性能。结果表明:TC4/TA15异种激光焊焊缝熔合区由含针状α’马氏体的粗化β柱状晶组成,热影响区主要由初始α相和β转变相组成,TA15侧热影响区的宽度窄于TC4侧热影响区的宽度。TC4/TA15异种接头的屈服强度和抗拉强度随温度的升高而降低,高温拉伸强度从高到低的顺序为TA15母材>异种接头>TC4母材,800°C时塑性变形程度最高。TC4/TA15异种接头横截面的最高显微硬度位于焊缝中心,热处理后接头的显微硬度整体降低,但硬度分布特征未发生改变。异种接头的高温拉伸断裂均发生在TC4母材侧,并在拉伸过程中发生明显颈缩,微观断口呈现韧性断裂特征。     

Mechanism of biaxial pre-stress method on welding residual stress and hot cracks controlling

Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion as-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks     

Liquation and post-weld heat treatment cracking in Rene 80 laser repair welds

An extensive experimental study on a nickel-based superalloy, Rene 80 using autogenous laser welding has been undertaken to determine the effect of the process parameters and weld bead geometry on cracking in the as-welded and post-weld heat treated conditions. Little cracking was observed in the as-welded condition with low powers and beam diameters around 2.5 mm. Welding speed had little effect on the incidence of cracking in the as-welded condition. Investigation of the aspect ratio (penetration divided by width) indicated that little cracking occurred in the as-welded condition when the aspect ratio was approximately 0.5. The same effect was observed with the post-weld heat treated samples. An analysis of the microstructures indicated that the cracking was caused primarily by liquation in the as-welded condition and was exacerbated by post-weld heat treatment cracking during the subsequent heat treatment. Finally the study resolved some of the contradictory findings in the literature on the effect of process parameters on the incidence of cracking in the as-welded and post-weld heat treated conditions.     

Modeling and characterization of as-welded microstructure of solid solution strengthened Ni-Cr-Fe alloys resistant to ductility-dip cracking Part II: Microstructure characterization

In part II of this work is evaluated the as-welded microstructure of Ni-Cr-Fe alloys, which were selected and modeled in part I. Detailed characterization of primary and secondary precipitates, subgrain and grain structures, partitioning, and grain boundary morphology were developed. Microstructural characterization was carried out using optical microscopy, SEM, TEM, EBSD, and XEDS techniques. These results were analyzed and compared to modeling results displaying a good agreement. The Hf additions produced the highest waviness of grain boundaries, which were related to distribution of Hf-rich carbonitrides. Experimental evidences about Mo distribution into crystal lattice have provided information about its possible role in ductility-dip cracking (DDC). Characterization results of studied alloys were analyzed and linked to their DDC resistance data aiming to establish relationships between as-welded microstructure and hot deformation performance. Wavy grain boundaries, primary carbides distribution, and strengthened crystal lattice are metallurgical characteristics related to high DDC resistance.     

变形温度对摩擦焊件显微组织与拉伸性能的影响

异种合金焊接件在航空工业中显示出巨大的应用潜力。针对线性摩擦焊接的Ti2AlNb/TC11焊件接头抗拉强度低和塑性差的特点,对其进行热变形,研究变形温度对焊件接头显微组织与拉伸性能的影响。结果表明,在温度950℃变形后,焊件室温拉伸时在Ti2AlNb合金侧出现脆性断裂;在温度1010℃变形后,母材TC11合金显微组织严重粗化,焊件在室温下表现出一定的强度,但是塑性较差;当在温度980℃变形时,焊件不仅具有较高的强度,也表现出极好的韧性,这与所观察到的显微组织特点相一致。     

Modeling and characterization of as-welded microstructure of solid solution strengthened Ni-Cr-Fe alloys resistant to ductility-dip cracking part I: Numerical modeling

This work aims the numerical modeling and characterization of as-welded microstructure of Ni-Cr-Fe alloys with additions of Nb, Mo and Hf as a key to understand their proven resistance to ductility-dip cracking. Part I deals with as-welded structure modeling, using experimental alloying ranges and Calphad methodology. Model calculates kinetic phase transformations and partitioning of elements during weld solidification using a cooling rate of 100 K.s^?1, considering their consequences on solidification mode for each alloy. Calculated structures were compared with experimental observations on as-welded structures, exhibiting good agreement. Numerical calculations estimate an increase by three times of mass fraction of primary carbides precipitation, a substantial reduction of mass fraction of M₂₃C₆ precipitates and topologically closed packed phases (TCP), a homogeneously intradendritic distribution, and a slight increase of interdendritic Molybdenum distribution in these alloys. Incidences of metallurgical characteristics of modeled as-welded structures on desirable characteristics of Ni-based alloys resistant to DDC are discussed here.     

随焊冲击碾压整形对低匹配等承载接头硬度与残余应力的影响

随焊冲击碾压整形(weld shaping with trailing impact rolling,WSTIR)是一种能够降低应力变形、提高承载能力的随焊整形新方法.分别对原始焊态的低匹配等承载接头与随焊冲击碾压整形的低匹配等承载接头进行了硬度试验和残余应力试验.结果表明,随焊整形等承载接头焊缝表面、焊趾处表面的硬度显著高于原始焊态等承载接头的硬度,说明随焊冲击碾压整形对接头承载的关键区域有加工硬化的效果;随焊整形低匹配等承载接头各点的纵向和横向残余应力明显低于原始焊态等承载接头相应位置的纵向和横向残余应力,甚至在随焊整形接头的焊缝中心以及焊趾附近纵向均出现了残余压应力,残余压应力的引入必然能显著地提高低匹配接头承载能力.     

Strength and microstructure of 2091 Al-Li alloy TIG welded joint

　The microstructure and tensile properties of TIG welding joints of 2091 Al-Li alloy were investigated both in as-welded and different postweld heat treatment condition. The results show that solution strengthening played an important role in the as-welded condition, though the precipitation strengthening δ′ phase formed already in the as-welded weld metal, but its effect was not apparent due to the lower volume fraction of δ′ phase. So the strength coefficient (φ) of the welded joint/base metal was 64%. After artificially aging heat treatment, the precipitation strengthening effect increased much due to the formation of more δ′ phase and s′ phase. Its φ value was increased up to 89%. The highest strength of the welded joints was obtained after solid solution and then artificially aged heat treatment. Due to the proper size of precipitation strengthening phases and their well distribution, the φ value was increased up to 98%.     

Study of the Performance of Stainless Steel A-TIG Welds

The purpose of the present work was to investigate the effect of oxide fluxes on weld morphology, arc voltage, mechanical properties, angular distortion and hot cracking susceptibility obtained with TIG welding, which applied to the welding of 5 mm thick austenitic stainless steel plates. A novel variant of the autogenous TIG welding process, oxide powders (Al₂O₃, Cr₂O₃, TiO₂, SiO₂ and CaO) was applied on a type 304 stainless steel through a thin layer of the flux to produce a bead on plate welds. The experimental results indicated that the increase in the penetration is significant with the use of Cr₂O₃, TiO₂, and SiO₂. A-TIG welding can increase the weld depth to bead-width ratio, and tends to reduce the angular distortion of the weldment. It was also found that A-TIG welding can increase the retained delta-ferrite content of stainless steel 304 welds and, in consequence, the hot-cracking susceptibility of as-welded is reduced. Physically constricting the plasma column and reducing the anode spot are the possible mechanism for the effect of certain flux on A-TIG penetration.     

Microstructure and mechanical properties of friction welds between TiAl alloy and 40Cr steel rods

Direct friction welding of TiAl alloy to 40Cr steel rods was conducted, and the microstructure and mechanical properties of the resultant joints in as-welded and post-weld heat treatment (PWHT) states were investigated. The martensitic transformation occurred and brittle TiC phase formed near the interface due to C agglomeration, which degraded the joint strength and increased the microhardness at the interface in as-welded state. Feathery and Widmanstatten structure generated near the interface on TiAl alloy side. After PWHT at 580 °C and 630 °C for 2 h, the sorbite formed and C dispersed at the interface, leading to the increase of the joint strength from 86 MPa in as-welded state to 395 MPa and 330 MPa, respectively. The heat-treated specimen fractured with quasi-cleavage features through the zone 1 mm away from the interface on TiAl alloy side, but the as-welded specimen failed through the interface.     

Effect of Post-Weld Annealing Treatment on Plastic Deformation of 2024 Friction-Stir-Welded Joints

Post-weld annealing treatment (PWAT) process was developed to improve the plasticity of friction-stir-welded 2024 aluminum alloy. The effect of the PWAT on plastic deformation behavior and microstructure of the joints were studied using tensile test, the ASAME^? automatic strain measuring system, and the electron backscattered diffraction (EBSD). It is found that the elongation of the as-welded joint can be improved by PWAT and increases with the decreasing PWAT temperature. The maximum elongation of the PWAT joints can reach up to 160% of that of the as-welded joint, and the joints exhibit no decrease in the tensile strength. The deformation inhomogeneity of the as-welded joint is significantly improved by large plastic strain occurring in the thermo-mechanically affected zone (TMAZ) when the PWAT temperature is lower than 250°. As the PWAT temperature increases, the deformation in the weld nugget is found to be more beneficial than that in the TMAZ for improving the plasticity of the joint. The high plasticity of the joint is attributed to the presence of the fine-equiaxed grains in the weld nugget during PWAT.