A review of linear friction welding of Ni -based superalloys

Ni-based superalloys are one of the most important materials employed in high-temperature applications within the aerospace and nuclear energy industries and in gas turbines due to their excellent corrosion,radiation,fatigue resistance,and high-temperature strength.Linear friction welding(LFW)is a new joining technology with near-net-forming characteristics that can be used for the manu-facture and repair of a wide range of aerospace components.This paper reviews published works on LFW of Ni-based superalloys with the aim of understanding the characteristics of frictional heat generation and extrusion deformation,microstructures,mechanical proper-ties,flash morphology,residual stresses,creep,and fatigue of Ni-based superalloy weldments produced with LFW to enable future optim-um utilization of the LFW process.

Finite element analysis of the effect of micro-pore defect on linear friction welding of medium carbon steel

Micro-pore is a very common material defect. In the present paper, the temperature fields of medium carbon steel joints with and without micro-pore defect during linear friction welding （LFW） were investigated by using finite element method. The effect of micro-pore defect on the axial shortening of joints during LFW was examined. The x- and y-direction displacements of micro-pore during the LFW process were also studied. In addition, the shape of micro-pore after LFW was observed. The heat conducted from the weld inteace to the specimen interior. The fluctuation range of the temperature curves for the joint with micro-pore is larger than that without micro-pore. Position of micro-pore changes with the change of the friction time. The circular shape of micro-pore becomes oval after welding.

Detection and analysis of basic variables during linear friction welding of GH4169 superalloy

By monitoring the line voltage and current of the driving motor during linear friction welding （ LFW） of GH4169 superalloy, the frictional power of the rubbing interface between two components to be joined was detected. The data was recorded by a data acquisition card and processed by the LabVIEW software. By analyzing the evolution of frictional power, the joint formation mechanism was discussed. The curves of the measured basic variables （frictional power, axial shortening, interfacial temperature and axial pressure） reflected the characteristics of the LFW process and offered an effective way for welding parameter optimization.

Joining Force of Heterogeneous Titanium Alloy in Linear Friction Welding Process

A dynamometer was designed and manufactured to measure the joining force in the linear friction welding process.The error percentages of the dynamometer in the upset(x)and vibration(y)directions were 0.9% and 0.75%,respectively.The cross-sensitivity range of the dynamometer was 1.2%—3.3% in the two directions.The precision level satisfies the requirements of the dynamometer test.The joining force of the TC17 and TC11 heterogeneous titanium alloys in the linear friction welding process was used to test the manufactured dynamometer.The test results showed that the upset force was large,but the vibration force showed a smaller change in TC11 during the linear friction welding process.In addition,the upset and vibration forces of the linear friction welding were greater with a short welding time than those with a long welding time.

Stress-strain characteristics of linear friction welding of TC11 and TC17 alloys

Abstract Transient stress and strain fields of dissimilar titanium alloys （TCll and TC17 ） joint during linear friction welding （ LFW） were investigated by a two-dimensional model with ABAQUS/Explicit. The results showed that in the X-axis, the maximum compressive stress of 850 MPa occurred in the center zone of friction interface , and the maximum tensile stress of 190 MPa distributed at the flash; in the Y-axis, the maximum compressive stress of 1 261 MPa located at the junction region between the welding fixture and edge of the specimen, and the maximum tensile stress of 320 MPa distributed in the connecting portion between the flash and edge of the specimen. In addition, areas of plastic strain increased gradually during welding process. In the X-axis, tensile strain mainly existed at the heads of the specimens; in the Y-axis, compressive strain mainly occurred at the heads of the specimens.

Structure and mechanical property of TC17 linear friction welding joint

TC17 titanium alloy which usually used on the fan and compressor disk were selected.Microstructure and mechanical property of joint were investigated.Microstructure character of different part of joint was analyzed also.Results showed that the joints included three zones,base metal(BM),thermal mechanical affected zone(TMAZ)and weld zone(WZ).The microstructure of joint middle part was equiaxial grains,but the bottom part was the elongated grains.Dynamic recrystallation happened at the weld zone.Tensile test result showed that joint tensile strength equal to that of the TC17 base metal.The average hardness value of the HAZ was 486 HV which was higher than that in the BM and WZ.

Flashes formation and evaluation during linear friction welding of TC4 alloy

By the 3D coupled thermo-mechanical finite element model of linear friction welding of TC4 titanium alloy, the relation between the temperature and the flashes is researched. The numerical simulation results show that the flashes with the wrinkles appear only when the temperature of material in the friction surface is high enough. The flashes, which are made up of material with high temperature, are squeezed out of the component. The appearance of flashes makes the temperature of material in the friction susface slowly increase or even decrease. Compared with the oscillation frequency and the oscillation amplitude, the friction pressure＇ s increase can mare easily attain the flashes with the bigger dimensionz.

Numerical modeling of linear friction welding： a literature review

Linear friction welding （LFW） is a solid state process for joining metals together. While this process was developed originaUy for titanium alloys （e. g. blisks ） , over the past decade a number of materials were found to be weldable with LFW. In this review, the current status of understanding and development of LFW are presented. Particular emphasis has been given to the modeling of the LFW process. Finally, opportunities for further research and development of LFW are identified.

Computational analysis of linear friction welding process and micromechanical modeling of deformation behavior for medium carbon steel

Finite element simulation of linear friction welding(LFW) medium carbon steel was carried out using the ABAQUS software. A two-dimensional(2D) coupled thermo-mechanical model was established. First, the temperature fields of medium carbon steel during LFW process were investigated. And then, the Mises stress and the 1st, 2nd and 3rd principal stresses fields' evolution of the steel during LFW process were studied. The deformation behavior of LFW carbon steel was analyzed by using micromechanics model based on ABAQUS with Python code. The Lode parameter was expressed using the Mohr stress circle and it was investigated in detail.

Effects of process parameters on microstructure and mechanical properties of friction stir lap linear welded 6061 aluminum alloy to NZ30K magnesium alloy

The microstructures and lap-shear behaviors of friction stir lap linear welded as-extruded 6061 Al alloy to as-cast Mg–3.0Nd–0.2Zn–0.7Zr(wt.%)(NZ30K)alloy joints were examined.Various tool rotation and travel speeds were adopted to prepare the joints.The analysis of temperature field indicates that the peak temperature for each sample can reach 450℃,which exceeds the eutectic reaction temperatures of 437℃ and 450℃ according to the binary phase diagram of Al–Mg system.The fierce intermixing can be found at the interface between Al and Mg alloys,forming the intermetallic of Al_(3)Mg_(2).Welds with the rotation speed of 900 rpm and travel speed of 120 mm/min display the highest tensile shear failure load of about 2.24 kN.The value was increased by 13%after the sample was heat treated at 400℃ for 0.5 h.

Study on the distribution of residual stresses in linear friction welds of Ti6AI4V

The linear friction welding process of Ti6Al4 V was modeled and computed ,for obtaining the residual stresses. Temperature, stress and strain fields were simulated, based on which, the residual stresses were also cah＇ulated. Simulated resttlts showed that the longitudinal residual stresses were tensile stresses at the bonding interface, and decreased rapidly with the increase of the distance from the bonding interface until turned into compressive stresses. The compressive stresses decreased slowly as the distance increased, and approached to zero finally. The distribution of the transverse residual stresses was similar to that of the longitudinal residual stresses, but showed much smaller values. The residual stresses in one linear friction weld were measured by an X-ray diffrnctometer. The average valwe of errors between computed and measured results was 14. 5 %.

Strengthening mechanism and forming control of linear friction welded GH4169 alloy joints

Numerical simulation and experimental research on Linear Friction Welding(LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties,a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-Mechanically Affected Zone(TMAZ) with high tensile strength and low elongation.When the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.

Multi-scale analyses of phase transformation mechanisms and hardness in linear friction welded Ti17(a+β)/Ti17(β)dissimilar titanium alloy joint

The Ti17(a+β)-Ti17(β)dual alloy-dual property blisk produced using Linear Friction Welding(LFW)is considered as high-performance component in advanced aeroengine.However,up to now,microstructure evolution and relationship between microstructure and micro mechanical properties of LFWed Ti17(a+β)/Ti17(β)dissimilar joint have not been thoroughly revealed.In this work,complex analyses of the phase transformation mechanisms of the joint are conducted,and phase transformations in individual zones are correlated to their microhardness and nanohardness.Results reveal that a dissolution occurs under high temperatures encountered during LFW,which reduces microhardness of the joint to that of Ti17(a+β)and Ti17(β).In ThermoMechanically Affected Zone of Ti17(a+β)(TMAZ-(a+β))side joint,a large number of nanocrystalline a phases form with different orientations.This microstructure strengthens significantly by fine grains which balances partial softening effect of a dissolution,and increases nanohardness of a phase and microhardness of TMAZ-(a+β).Superlattice metastableβphase precipitates from metastableβin Weld Zone(WZ)during quick cooling following welding,because of short-range diffusion migration of solute atoms,especiallyβstabilizing elements Mo and Cr.The precipitation of the superlattice metastableβphase results in precipitation strengthening,which in turn increases nanohardness of metastableβand microhardness in WZ.

考虑相含量的TC17钛合金线性摩擦焊中的残余应力

为了获得准确的TC17钛合金线性摩擦焊中的残余应力,建立TC17钛合金弹性常数与相分数之间的数值关系。结合焊接区域的相分数,获得呈梯度分布的弹性常数,并将其引入轮廓法进行计算。结果表明,TC17钛合金的弹性常数与α相分数呈正相关,在宽度约4 mm的焊接区域呈现明显的梯度分布特征;若忽略相分数的梯度分布,计算残余应力时相对误差可达36.06%;修正后的残余应力呈双峰分布,在热影响区边缘处达到峰值,约为442 MPa。这说明考虑相分数的梯度分布是必要的。

热处理对同质异态TC17钛合金线性摩擦焊接头的影响

对TC17(α+β)和TC17(β)钛合金进行线性摩擦焊及焊后热处理试验,运用光学显微镜(OM)、扫描电镜(SEM)观察接头各区域的微观组织变化,采用轮廓法测试接头残余应力分布情况,分析了热处理对接头的微观组织、残余应力及力学性能的影响。结果表明:焊接过程中焊缝区发生了相变及动态再晶界过程,形成亚稳定β相;两侧热力影响区初生α相严重变形,针状α相完全溶解。经过热处理,亚稳定β相分解为稳定的α+β相,板条状α相在晶界析出,针状α相在晶粒内部析出,变形α相发生不同程度的分解。轮廓法测试结果表明,接头沿振动方向的应力呈双峰分布,接头热力影响区处拉应力峰值达到最大约360 MPa,焊缝中心拉应力值约140 MPa,经过热处理,接头沿振动方向拉应力值降低至50 MPa以下。经过热处理后接头微观组织更加均匀,并且接头残余应力得到消除,接头拉伸及疲劳性能得到明显改善。

Dissimilar linear friction welding of selective laser melted Inconel 718 to forged Ni-based superalloy AD730TM:Evolution of strengthening phases

The continuous growth in the manufacture of aerospace components such as blisks has led to an increase in the application of different hybrid materials fabricating methods,and thus the requirements for joining and strengthening of dissimilar welds.According to this goal,selective laser melted(SLM)Inconel718 was joined with forged AD730^(TM)Nickel-based superalloy through linear friction welding(LFW)in this study.Microstructure variation,specifically with respect to secondary phases precipitation was investigated.The microhardness and strengthening mechanisms of the weldment were also studied.The precipitation(volume fraction and size of particles)at different regions of both sides of the weld line was characterized.Close to the weld line,the dissolution ofγ’/γ"and Laves phases and grain refinement occurred which reveals the effects of both compression strain and high temperature on recrystallization and high degree of elemental diffusion in the weld zone(WZ).It is shown that the size,volume fraction,and shape of secondary phases increased and changed(from spherical to long-striped for Laves particles)as we went from the WZ toward the base metal.However,the measured microhardness indicated that the strength of AD730^(TM)alloy depends significantly on the grain size,while strength in SLM Inconel 718 was dominated by shape(or size)and the presence of secondary phases(γ’/γ"and Laves).

LFW系统顶锻方向位置与压力转换无扰控制原理的分析及试验

为改进线性摩擦焊接系统中所设计的顶锻方向液压控制位置和压力转换控制过程,提高顶锻方向位置精度,对其液压控制位置和压力转换控制方式的原理进行研究,明确顶锻方向位置控制和压力控制的特点及其各自应采用的控制器的形式。进一步研究顶锻方向位置控制和压力转换控制策略,提出顶锻位置控制和压力协同控制方法,对控制特性进行试验验证。研究结果对提高主机的生产效率和性能具有理论和实际意义。

The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints

Linear friction welding （LFW）, as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was inves- tigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions （x-, y-, and z-directions）. Larger variance, a, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.

TC17线性摩擦焊界面温度分析与测量

焊接过程中的界面温度是研究接头组织形成变化机理的关键参量。根据线性摩擦焊接过程准稳定摩擦阶段焊件中(不包括飞边)准稳定温度场基本保持不变,所产生的热量主要被飞边带走的特点,通过理论分析,求解出了线性摩擦焊接过程准稳定摩擦阶段焊接界面的平均温度,利用半自然热电偶实际测量了TC17钛合金线性摩擦焊接时的焊接界面不同位置的温度变化。结果表明,典型参数下TC17准稳定摩擦阶段焊接界面的实测温度大约为1228℃,焊后冷却至500℃的速度约52℃/s,准稳定摩擦阶段焊接界面中心点和边缘点的温度相差不超过10℃,界面中心点的升温速率以及降温速率均高于边缘点,测量值与理论计算值相差不超过10%。

近β型钛合金线性摩擦焊接头变形行为及组织演变的热物理模拟

为了更好地理解近β型钛合金线性摩擦焊(LFW)接头的界面连接行为,采用热压缩物理模拟的方法,以TB2近β型钛合金为研究材料,设计符合LFW工艺特点的帽形热压缩试样,在不同下压量、变形温度及应变速率条件下进行热压缩试验,研究热压缩接头的变形行为及组织演变。结果表明,热压缩过程中热压缩接头连接区(BZ)的峰值剪切应力随变形温度的降低及应变速率的增加而增大,接头BZ的宽度随变形温度和应变速率的增加而减小。接头BZ边缘由沿剪切方向变形的晶粒组成,接头BZ中心由细小的等轴再结晶晶粒组成。接头的动态再结晶机制为连续动态再结晶(CDRX),且CDRX的程度随下压量、变形温度及应变速率的增加而增大。此外,在界面剪切力的作用下接头BZ边缘形成{112}[111]织构,接头BZ中心形成{110}[001]织构。