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.

Friction welding influence on microstructure,microhardness and hardness behavior of CrNiMo steel(AISI 316)

For joining high Cr,Ni and Mo austenitic stainless steel(AISI 316)by direct drive friction welding(DDFW),with friction weld-ing conditions:rotation speed of 3000 r/min,friction time of 10 s,friction pressure of 130 MPa,forge time of 5 s and forge pressure of 260 MPa.The results of microstructure showed that the temperature at the interface reached 819℃while forge applied between 357-237℃,which subdivided welded joint into four distinct regions of highly plastically deformed zone(HPDZ),thermo-mechanically affected zone(TMAZ),heat affected zone(HAZ)and the base metal,with grain size about 10µm,100µm,90µm and 30µm respectively.These re-gions were created due to dynamic recrystallization(DRX)at the interface and thermo-mechanical deformation with heat diffusion in the neighboring regions.Whereas,high level of microhardness about 300 HV0.1 and hardness roughly 240 Hv10 at the interface due to HPDZ creation while low level of 240 HV0.1 for microhardness and moderately of 205 HV10 for hardness in neighboring regions.

Evolution of microstructural and mechanical properties of AISI 316 during continuous drive friction welding process

The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase's time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_(0.1), tensile tests and scanning electronic microscopy(SEM).The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.

THE COUPLED FEM ANALYSIS OF THE TRANSIENT TEMPERATURE FIELD DURING INERTIA FRICTION WELDING OF GH4169 ALLOY

The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.

Analysis of the Microstructure and Mechanical Properties during Inertia Friction Welding of the Near-α TA19 Titanium Alloy

The current research of titanium alloy on friction welding process in the field of aero-engines mainly focuses on the linear friction welding.Compared to the linear friction welding,inertial friction welding of titanium alloy still has important application position in the welding of aero-engine rotating assembly.However,up to now,few reports on inertial friction welding of titanium alloy are found.In this paper,the near-alpha TA19 titanium alloy welded joint was successfully obtained by inertial friction welding(IFW)process.The microstructures and mechanical properties were investigated systematically.Results showed that the refined grains within 15‒20μm and weak texture were found in the weld zone due to dynamic recrystallization caused by high temperature and plastic deformation.The weld zone consisted of acicularα′martensite phase,αp phase and metastableβphase.Most lath-shapedαs andβphase in base metal were transformed into acicular martensiteα′phase and metastableβphase in thermo-mechanically affected zone and heat affected zone.As a result,the microhardness of welded joint gradually decreased from the weld zone to the base metal.Tensile specimens in room temperature and high temperature of 480℃ were all fractured in base metal illustrating that the inertia friction welded TA19 titanium alloy joint owned higher tensile strength compared to the base metal.

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.

Study on Mt control method of friction welding

A new type control method in friction welding is suggested in this pa- per,that is compositive control method of friction torque and friction time,it called Mt control method for short.The principle of Mt control method and its feature are concisely explained.

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.

Friction welding of TiAl intermetallics and structural steel by applying Inconel 718 as interlayer

Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents single fin showing less welding deformation on TiAl side. The correlations between tensile strength and the interlayer thickness were analyzed and fitted to a model. It indicates an optimum interlayer thickness ranged from 0.9 - 1.1 mm where the tensile strength reaches as high as 360 MPa. Otherwise, while the interlayer thickness decreases to 0. 1 mm, brittle compounds of TiC, Al2Ti4C2 and MTC3 are formed in the welded zone so that the tensile strength decays. Thicker interlayer should be also avoided as double joints may occur at TiAl -lnconel 718 and lnconel 718 -AISI 4140, respectively, which lowers the tensile strength to some extent.

Study on deformation and microstructure characterizations of mild steel joints by continuous drive friction welding

Macro-deformation characteristics of continuous drive friction welded mild steel joints were examined by using one deformable workpiece （objective） and the other undeformable one （rigid）. The microstructure evolution and hardness change across the joint were studied. The results show that the axial shortening and radial increment of joints increase with increasing the frictiou time at l 200 rpm. The cementite particles of pearlites in the weld center are uniformly distributed on the ferrite matrix, while the cementites of the pearlite in the thermal-mechanically affected zone are broken and discontinuously dispersed in the pearlite. The hardness decreases rapidly from the weld center to the parent metal under the coupled effects of heat and deformation during the rapid heating and cooling processes.

Numerical analysis of thermal process in continuous drive radial friction welding

A heat source model for radial friction welding was proposed, which was determined by friction pressure, friction coefficient, material properties and extrusion speed of material. A 3D model was established to analyze the continuous drive radial friction welding temperature field of 45 steel pipe. The influences of friction pressure, friction time and rotation speed on the temperature of the friction interface were analyzed. The results showed that the temperature on the friction interface rapidly rose to a peak temperature in initial friction stage and kept constant in the stable friction stage. Welding parameters of friction pressure, friction time and rotation speed had few influences on the peak temperature, while the increase of frlctlon pressure and rotation speed could shorten the time to reach the peak temperature.

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.

Reduction of ultrasonic echo noise based on improved wavelet threshold de-noising algorithm for friction welding

In the ultrasonic detection of defects in friction welded joints, it is difficult to exactly detect some weak bonding defects because of the noise pollution. This paper proposed an improved threshold function based on the multi-resolution analysis wavelet threshold de-noising method which was put forward by Donoho and Johnstone, and applied this method in the de-noising of the defective signals. This threshold function overcomes the discontinuous shortcoming of the hard-threshold function and the disadvantage of soft threshold function which causes an invariable deviation between the estimated wavelet coeffwients and the decomposed wavelet coefficients. The improved threshold function is of simple expression and convenient for calculation. The actual test results of defect noise signal show that this improved method can get less mean square error （ MSE ） and higher signal-to-noise ratio of reconstructed signals than those calculated from hard threshold and soft threshold methods. The improved threshold function has excellent de-noising effect.

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.

Effect of temperature field on flashes formation of continuous drive friction welding

On basis of the finite element software DEFORM, the 2D coupled thermo-mechanical model of continuous drive friction welding of ring parts is established. The temperature and the flashes during the welding process are investigated. The results of numerical simulation show that the temperature of friction surface is higher than that of other region and the peak temperature increases with the increase of welding time. During the process of friction stage, no flash appears because of the low temperature and the small axial friction pressure. At the forging stage, the flashes appear, whose dimensions and bending degree increase with the increase of welding temperature. Moreover, with the increase of rotational velocity and axial forging pressure, the dimensions and the bending degree of flashes of continuous drive friction welding increase.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Achieving a high-strength dissimilar joint of T91 heat-resistant steel to 316L stainless steel via friction stir welding

The reliable welding of T91 heat-resistant steel to 316L stainless steel is a considerable issue for ensuring the safety in service of ultrasupercritical power generation unit and nuclear fusion reactor,but the high-quality dissimilar joint of these two steels was difficult to be obtained by traditional fusion welding methods.Here we improved the structure-property synergy in a dissimilar joint of T91 steel to 316L steel via friction stir welding.A defect-free joint with a large bonding interface was produced using a small-sized tool under a relatively high welding speed.The bonding interface was involved in a mixing zone with both mechanical mixing and metallurgical bonding.No obvious material softening was detected in the joint except a negligible hardness decline of only HV~10 in the heat-affected zone of the T91 steel side due to the formation of ferrite phase.The welded joint exhibited an excellent ultimate tensile strength as high as that of the 316L parent metal and a greatly enhanced yield strength on account of the dependable bonding and material renovation in the weld zone.This work recommends a promising technique for producing high-strength weldments of dissimilar nuclear steels.

Research on friction stir welding of 5754 aluminum alloy with unequal thickness

A new structure of 1+2 was designed in friction stir welding(FSW)of Al alloy sheet with unequal thickness:a specific sheet with similar composition of base metals(BMs)was placed under the thinner sheet as the supporting sheet so that the BM surfaces could be on a plane.The BMs can also be fully penetrated weld with a stirring pin longer than the thickness of the thin sheet.2 mm and 1.5 mm thick Al alloy sheets were welded by FSW,and parameters were optimized.The highest welding strength reached 96.07%of the thin base metal.Although a slight thinning phenomenon occurred at the edge of the nugget on the retreating side,the specimen still fractured in the heat-af-fected zone.

Microstructure and toughness of thick-gauge pipeline steel joint via double-sided friction stir welding combined with preheating

Fusion welding easily causes microstructural coarsening in the heat-affected zone(HAZ) of a thick-gauge pipeline steel joint. This is most significant in the inter-critically coarse-grained HAZ(ICCGHAZ), which considerably deteriorates the toughness of the joint. In the present work, 11-mm thick pipeline steel was joined by preheating and double-sided friction stir welding(FSW). A comparative study on the microstructure and toughness in the ICCGHAZs for FSW and gas metal arc welding(GMAW) was performed. The toughness in the ICCGHAZ for FSW was improved significantly than that in the ICCGHAZ for GMAW. Generally, the nugget zone(NZ) has a coarse microstructure in the FSW steel joint formed at the highest peak temperature. However, in the current study, the microstructure in the one-pass NZ was remarkably refined owing to the static recrystallization of ferrite. An excellent toughness was achieved in the NZ of the pipeline steel joint that employed FSW.

Review on friction stir welding of dissimilar magnesium and aluminum alloys: Scientometric analysis and strategies for achieving high-quality joints

Magnesium and aluminum alloys continually attract interest as lightweight structural materials for transport applications. However, joining these dissimilar alloys is very challenging. The main obstacle that hinders progress in dissimilar Mg-Al joining is the formation of brittle intermetallic compounds(IMCs). As a solid-state joining technique, FSW is an excellent candidate to attenuate the deleterious IMC effects in dissimilar Al-Mg joining due to the inherent low heat inputs involved in the process. However, the IMCs, namely Al_(3)Mg_(2) and Al_(12)Mg_(17) phases, have also been reported to form during Al-Mg dissimilar FSW;their amount and thickness depend on the heat input involved;thus,the weld parameters used. Since the heat dissipated in the material during the welding process significantly affects the amount of IMCs,the heat input during FSW should be kept as low as possible to control and reduce the amount of IMCs. This review aims to critically discuss and evaluate the studies conducted in the dissimilar Al/Mg FSW through a scientometric analysis and also with a focus on the strategies recently applied to enhance joint quality. The scientometric analysis showed that the main research directions in Mg/Al FSW are the technological weldability of aluminum and magnesium during FSW, structural morphology, and mechanical properties of dissimilar welded joints. Considering the scope of application of the aforementioned joints, the low share of articles dealing with environmental degradation and operational cracking is surprising. This might be attributed to the need for well-developed strategies for obtaining high-quality and sustainable joints for applications. Thus, the second part of this review is conventional, focusing mainly on the new strategies for obtaining high-quality Mg/Al joints. It can be concluded that in addition to the necessity to optimum welding parameters to suppress the excessive heat to limit the amount and thickness of IMC formed and improve the overall joint quality, strategies such as using Zn interlayer, electric current assisted FSW(EAFSW), ultrasonic vibration FSW(UVa FSW), are considered effective in the elimination, reduction, and fragmentation of the brittle IMCs.