Inertia Friction Welding Research Articles

Creep Behavior and Fracture Mechanisms of the Dissimilar Inertia Friction Welded Joints of Deformed and Powder Metallurgy Ni‐Based Superalloys

ABSTRACTIn this research, the microstructure and precipitate characteristics of the dissimilar inertia friction welded (IFW) joints of deformed and powder metallurgy (PM) nickel‐based superalloys were studied using optical, scanning electron, and transmission electron microscopy. In addition, several creep tests were conducted. The high‐temperature mechanical properties of the IFW joints were systematically analyzed. Under the creep testing condition of 680°C, the specimens exhibited creep fracture at the thermomechanically affected zone (TMAZ) of the PM superalloys. Further, the failure lifetime is enhanced with a reduction in the applied creep loading. Owing to the IFW process, various γ′ precipitates and carbide distributions were observed in the various zones of a dissimilar IFW joint. Undissolved powder particle boundary (PPB) defects in the TMAZ of the PM superalloy initiated creep cracks under creep loading. Based on the experimental results and theoretical analysis, the creep fracture mechanisms of the dissimilar IFW joints were revealed. Thus, the findings of this study provide guidance for controlling the microstructures and properties of dissimilar deformed/PM nickel‐based superalloy IFW joints.

Enhanced inertia friction welding of aluminum alloy and high-strength steel using CrCoNi interlayer: Microstructural and mechanical characterization

Enhanced inertia friction welding of aluminum alloy and high-strength steel using CrCoNi interlayer: Microstructural and mechanical characterization

A novel method to establish friction coefficient model for numerical simulation of inertia friction welding

The precise friction coefficient at interface determines the friction behavior in inertia friction welding (IFW), its model is the basis to precisely describe the friction behavior in the numerical simulation of IFW. To measure the friction coefficient related to the temperature, pressure, and sliding velocity, the IFW trials between 2219-O Al alloy and 304 stainless steel were conducted with the simultaneous measurement of temperature and angular velocity evolutions. Two types of friction coefficient models were established by considering whether the effects of temperature and friction pressure were independent. The S-(T&P) L model, which considered the couple effect of temperature and friction pressure, was recommended as the best suitable model with its very high accuracy and best simplicity. The proposed model was successfully used in simulating the temperature evolution of IFW between Al alloy and steel tubes. The effect of the influencing variables on the friction coefficient was also discussed.

Omnidirectional simulation analysis of thermo-mechanical coupling mechanism in inertia friction welding of Ni-based superalloy

The coupling between heat and pressure is the kernel of inertia friction welding (IFW) and is still not fully understood. A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface. The numerical model successfully simulated the deceleration, deformation processes, and peak torsional moments in IFW and captured the evolution of temperature, contact pressure, and stress. The simulated results were validated through measured thermal history, optical macrography, and axial shortening. The results indicated that interfacial friction heat was the primary heat source, and plastic deformation energy only accounted for 4% of the total. The increase in initial rotational speed and friction pressure elevated the peak temperature, reaching a maximum of 1525.5 K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa. The interface heat generation could form an axial temperature gradient exceeding 320 K/mm. The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius. The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure, which could reach 1.7 times the set pressure at the center. The circumferential inhomogeneity of thermo-mechanical distribution during rotary friction welding was revealed for the first time, benefiting from the 3D model. The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding. The critical Mises stress was 0.5 times the friction pressure in this study. The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.

A promising strategy of multicomponent alloy intermedium for enhancing the mechanical performance of inertia friction welding joints of Inconel 718 alloys

A strategy of using multicomponent alloy (MCA) intermedium for inertia friction welding of IN718 alloys was proposed in this work. Exceptional metallurgic bonding was attained between the IN718 and non-equiatomic CoCrNi–AlTa MCA layer, and the as-received weld joint was absent of any defects like micro-cracks or voids. Compared with the counterpart without an intermedium layer (∼530 MPa), the yield strength of the IN718-MCA weld joint was increased to ∼610 MPa. Moreover, by conducting a two-step ageing treatment, the yield strength of the weld joint was further improved to over 1360 MPa with prominent strain hardening behavior. Noteworthily, the fracture along the interface boundary between the two materials initially observed in the unaged weld joint was fully eliminated, indicating that the ageing treatment efficiently improved the bonding of the interfacial region and further enhanced the reliability of the weld zone. Moreover, the significant strengthening effect of the aged dissimilar weld joint was found to originate from the enhanced atomic diffusion and extra back-stress hardening from geometric necessary dislocations (GNDs) produced within the interfacial regions, as well as the high density of nano-sized dispersive precipitates (for IN718) and ordered structures (for MCA) generated in the alloy matrix at elevated temperatures. The result verifies that the present strategy of adding an MCA intermedium layer can efficiently improve the mechanical performance of the weld joint for IN718 alloys, which is promising for real applications in aerospace engineering.

Elucidating the in-process interfacial friction regime and thermal responses during inertia friction welding of dissimilar superalloys

Inertia friction welding (IFW) is a robust joining technique, particularly for hybrid structures composed of similar or dissimilar alloys. The highly transient thermal responses during friction heating produce variations in heat generation and temperature distribution, which are crucial for designing and controlling the IFW process. This study establishes a finite element (FE) model of the IFW process for dissimilar superalloys and investigates the transition of the interfacial friction regime and its impact on the transient thermal responses. The in-process state variables, including the frictional stress and heat flux, along with their spatial distributions at the welding interface, are obtained through FE simulations. The predicted results indicate that the transient transition of the friction regime produces two Coulomb friction zones accompanied by a shear friction zone. To capture the transient evolution of the friction regime, a novel phenomenological formula is developed. This model accurately predicts the shrinkage and disappearance of the two Coulomb friction zones and the enhancement of the shear friction zone from the initial 0.42 R0–0.87 R0 (where R0 is the workpiece radius) to the entire interface during the IFW process. The variations in interfacial heat flux, frictional stress, and temperature caused by the transition of the friction regime are comprehensively analyzed. Our results reveal that the transition from the Coulomb friction regime to shear friction regime at the interface is beneficial for temperature homogenization at the welding interface. The FE simulation results are validated against published experimental measurements, which confirms the accuracy and reliability of the FE model.

Microstructure and Mechanical Properties of Powder Metallurgy Superalloy Joints Welded by Inertia Friction Welding.

In recent years, for the structural characteristics and design requirements of the integral rotor and disc shaft of the integrated engine, the welding quality and mechanical properties of superalloy weldments have received increasing attention. In this paper, inertia friction welding (IFW) of FGH96 alloy was carried out using different welding parameters, and the homogeneous connection of FGH96 alloy hollow bars was successfully realized. The microstructure evolution, mechanical properties and fracture failure of the welded joints at room and high temperatures were investigated. The FGH96 alloy IFW joints were divided into the weld nugget zone (WNZ), the thermo-mechanically affected zone (TMAZ), the heat-affected zone (HAZ) and the base metal (BM), and there were significant differences in grain structure and distribution of the γ' phase in each of the characteristic zones. The microhardness and tensile properties of the IFW joints were investigated, and the results showed an "M"-shaped curve in the microhardness distribution, with the lowest point of hardness observed in the HAZ. The tensile test results indicated that the fracture position moved from the BM to the WNZ with the increase in temperature, the microstructure at the fracture changed significantly and the tensile strength decreased from 1512.0 MPa at room temperature to 1201.3 MPa at 750 °C. The difference in the mechanical properties of the joints was mainly attributed to the changes in the dissolution and precipitation of the γ' phase.

The microstructural morphology of transformed α induced by β fiber texture in a dissimilar inertia friction weld between near-α and α+β titanium alloys

The microstructure and texture features of the dissimilar inertia friction welded (IFW) joint of Ti65 titanium alloy to TC25G titanium alloy were characterized. The β textures in dynamic recrystallization zone (DRZ) produced by severe hot shear deformation were dominated by the bcc D2 (11-2)[111] shear texture for both the Ti65 and the TC25G alloys. The variant selection occurred during the β α phase transformation at the final cooling stage, in which higher fraction of α variants with misorientation of [−10 5 5 3]/63.26° formed. The triangular configuration structures were frequently observed in the interior of the β grains in DRZ, which was resulted from the variant selection occurring in microregion. The formation of triangular configurations was also favored naturally by the <111>bcc β fiber texture.

Microstructure and Mechanical Properties of IN690 Ni-Based Alloy/316LN Stainless-Steel Dissimilar Ring Joint Welded by Inertia Friction Welding.

Inertia friction welding (IFW) was used to join large-diameter hollow bars made of Inconel 690 and 316LN successfully. The interfacial characteristics, microstructure, mechanical properties and fracture mechanism of welded joints under different process parameters were investigated. The results indicated that a joining mechanism with mechanical interlocking and metallurgical bonding was found in IFW joints. There was a significant mechanical mixing zone at the welding interface. The elemental diffusion layer was found in the "wrinkles" of the mechanical mixing zone. A tiny quantity of C elements accumulated on the friction and secondary friction surfaces. The tensile strength and impact toughness of the joints increased with the total welding energy input. Increasing the friction pressure could make the grain in all parts of the joint uniformly refined, thus enhancing the mechanical properties of welded joints. The maximum tensile strength and impact toughness of the welded joint were 639 MPa and 146 J/cm2, reaching 94% and 68% of that for Inconel 690, respectively, when the flywheel was initially set at 760 rpm, 200 MPa for friction pressure, and 388 kg/m2 for rotary inertia. Due to the Kirkendall effect in the welded joint, superior metallurgical bonding was at the welding interface close to the Inconel 690 side compared to the 316LN side.

Preliminary study on effect of inertia and continuous friction welding on mechanical properties of SS 316-Zn alloys friction welded joint

The effect of inertial friction welding and continuous drive friction welding in joining SS 316 with Zn alloy is discussed in this article. Scanning electron microscopy was utilized to investigate the microstructure of the welding interaction. Energy-dispersive spectroscopy was utilized to identify the chemical composition of the element distribution at the interface. The findings reveal that a continuous drive friction welding process may produce SS 316 welded joints with Zn alloy. With a friction time of 35 s, the joint's tensile strength may reach 60 MPa. During the tensile test, all friction-welded samples failed at the interface. The fracture surface shows an almost flat surface and is not fibrous or brittle. Meanwhile, a new reaction layer from the intermetallic compound layer is not formed at the joint interface. The decrease in hardness in Zn alloys is due to the thermal softening effect caused by continuous heat from friction.

Inertia radial friction welding of Ti60(near-α)/TC18(near-β) bimetallic components: Interfacial bonding mechanism, heterogenous microstructure and mechanical properties

Inertia friction welding has emerged as a promising technique for fabricating lightweight and high-strength components in aerospace industry. To achieve high-quality weldments between dissimilar titanium alloys, this present work systematically investigates Ti60 (near-α)/TC18 (near-β) bimetal components manufactured by inertia radial friction welding. The focus is on understanding the joint interface behavior, heterogenous grain structure, microstructural evolution and resulting mechanical properties, with a particular emphasis on dynamic recrystallization, phase transformation and atomic diffusion of elements in the welded zone and thermos-mechanical affected zone. The results revealed that the significant influence of thermo-physical property mismatch between the dissimilar workpieces (Ti60-Ring and TC18-Core) on the microstructure and tensile strength of the joints. This mismatch could be effectively controlled by setting different flywheel kinetic energy (Ek) before welding. The tensile strength of the Ti60/TC18 joints manufactured with levels of Ek ranging from 174.74 kJ to 207.95 kJ, were observed to be governed by the combined effect of mechanical interlocking, grain boundary strengthening, precipitation strengthening and hetero-deformation induced strengthening. The formation of heterogeneous grain structure and intergrowth grains on the Ti60 alloy side, and the dislocation tangles in the “forked” α phase of the TC18 alloy side are identified as key factors in achieving optimized bonding strength for dissimilar Ti60/TC18 bimetallic inertia radial friction welding.

Jointing Achievement and Performance Evaluation of Bogie Crossmember Ring Joint Welded via Inertia Friction Welding.

As a major load-bearing component of trains, the weld quality of the bogie beam is critical to the safety of railway operations. This study specifically investigates the inertia friction welding process of S355 bogie crosshead tubes, with the aim of improving the weld quality and achieving one-time formation of the crosshead tube and tube seat. The microstructural features and mechanical properties of S355 inertia-welded joints were also compared with the base metal. Research indicates that inertia friction welds have no visible defects, and that the microstructure of the welding seam (WS) consists of granular bainite, acicular ferrite and little pearlite. The thermo-mechanically affected zone (TMAZ) consists of granular bainite bands and ferrite + pearlite bands. The hot work strengthening mechanism of inertia friction welding results in a higher level of hardness for both WS and TMAZ. The tensile property of the welded joints can be compared to the base metal. The yield strength, tensile strength and elongation of the welded joints, respectively, reach 87.5%, 100% and 79.5% of S355. However, the impact toughness of the welds at room temperature is lower than that of the base material, particularly in the TMAZ zone. Conversely, in an environment with a temperature of -40 °C, WS's impact toughness surpasses that of the parent material.

Microstructure evolution and tensile strength of Al/Cu inertia friction welded joint

To save production costs and reduce the weight of structures, it is one of the common ways to replace copper (Cu) with aluminum (Al) in some industries such as the refrigeration industry. The high-quality welding of Al to Cu determines the application of the Al/Cu hybrid structure. The inertia friction welding process was used to weld Al pipe to Cu pipe and the Taguchi experiment method was used to study the effects of inertia friction welding parameters on the mechanical properties of the welded joints, and the results show that the initial speed has the greatest influence on the tensile strength of welded joints. Meanwhile, the analyses of the microstructures of the joint show that Al–Cu IMCs formed at the friction interface to realize the metallurgical bonding of the welded joints. The formation sequence of Al–Cu IMCs in the friction welding process is Al2Cu, Al4Cu9, and AlCu. Whereas the type and thickness of IMCs are closely related to the tensile strength of the joints. When the welded joint forms Al2Cu and Al4Cu9, the interfacial misfit between the IMCs layer and base materials is minimized and the tensile strength of the joint is optimized.

Effect of different friction coefficient models on numerical simulation of inertia friction welding of 2219 Al alloy to 304 stainless steel

In inertia friction welding (IFW) of Al alloy to steel, the friction coefficient of interface influences the friction heat production and determines the accuracy of the numerical simulation of welding process. A fully coupled three-dimensional model was established to simulate the IFW process of 2219 Al alloy to 304 stainless steel. By taking different simplifications in the influencing factors (i.e., temperature, sliding velocity, and pressure) of friction coefficient, three types of friction coefficient models were established and utilized in the simulation of IFW process. The strain compensated Arrhenius and Johnson-Cook models were employed to describe the deformation behavior of Al alloy and steel, respectively. Both Al alloy and steel were assumed to be the elastic-plastic body, and the friction stress was calculated by the Coulomb friction model. The friction interface temperature, angular velocity attenuation, axial shortening distance, and joint appearance were measured to verify and compare the accuracy of the established models. The temperature and stress evolutions during the IFW process were also analyzed. With the smallest error in validation, the friction coefficient model, which was a function of temperature, sliding rate, and pressure, showed the best accuracy in describing the friction behavior. By considering the effect of pressure, a more accurate shear stress at the center region of the interface was calculated with a lower value. It means that the friction resistance at the region was lower, promoting the flow of internal Al alloy and the formation of curly-shape flash.

Investigations into the Microstructure and Texture Evolution of Inertia-Friction-Welded Dissimilar Titanium Alloys

The welded joint of a dissimilar titanium alloy was obtained via inertial friction welding technology. The characteristics of the bonding interface and the microstructure of the welded joint were investigated via optical microscopy, scanning electron microscopy and electron backscattered diffraction. The results show that fine, equiaxed grains and interdiffusion bands of the elements Mo and Sn were formed in the weld zone under the high temperature and plastic deformation of the inertial friction welding. The weld zone and thermo-mechanically affected zone formed ⟨1¯21¯0⟩ α texture and ⟨111⟩ β texture, respectively.

Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints

In this work, dissimilar rotary inertia friction welds between 422 martensitic stainless steel and 4140 martensitic low-alloy steel were made to fabricate prototype heavy-duty diesel engine pistons. The influence of the inertia friction welding process and post weld heat treatment (PWHT) temperature on the interfacial microstructure evolutions and corresponding effects on mechanical properties of the 422/4140 welds were evaluated in detail. Carbon diffused from the 4140 side to the 422 side during PWHT at 650 °C for 1.5 h, causing the formation of a hard carbide-rich layer on the 422 side, and a softer but discontinuous C-depleted layer the 4140 side. PWHT at 700 °C for 1.5 h greatly accelerated C diffusion across the interface relative to 650 °C, resulting in a thicker hard carbide-rich layer and a relatively thick and continuous layer of coarse C-depleted grains (ferrite) on the 4140 side. In addition, the PWHT temperature greatly influenced the tensile properties and fracture behavior of the welds, with the 650 °C PWHT-ed samples failing predominately in a ductile manner in the 4140 heat affected zone during tensile testing. Conversely, the 700 °C PWHT specimens exhibited a strength reduction compared with the 650 °C PWHT specimens because of additional coarsening of the interfacial ferrite layer and softening of the base materials during PWHT, with brittle fracture between the hard and soft layers the predominate failure mechanism. Based on the findings, a reduced PWHT temperature and/or time, minimizing the hardness differential of the base metals, and pre-heating the 422 steel prior to welding are the potential pathways to achieve a more optimal balance between desirable tempering and stress relief of the weld microstructure and undesirable C migration across the weld interface, and to reduce the strength mismatch across the weld.

Effect of inertia friction welding speed on microstructure and mechanical properties of 2205/316L stainless steel joints

In this paper, inertia friction welding (IFW) is used to enable a high-quality and efficient joint between 2205 duplex stainless steel and 316 L stainless steel. Specifically, stainless steel bars (2205/316 L) with a diameter of 35 mm and length of 120 mm are used. In addition, the effect of IFW speed on the microstructure and properties of welded joints is assessed using scanning electron microscopy, electron backscattered diffraction, energy dispersive X-ray spectroscopy, microhardness test, and tensile tests. The results indicate that dynamic recrystallization of the microstructure of joints occurs during IFW welding, which causes grain refinement. The diffusion of Ni from the 316 L base metal to the 2205 base metal, as well as the diffusion of Cr from the 2205 base metal to the 316 L base metal, results in a strong metallurgical bond between the two materials. In addition, the microhardness of the welding area exceeds that of the base metal (the closer to the weld zone, the greater the microhardness value). The tensile strength of the joints initially increases with increasing IFW speed, but then it starts decreasing beyond a certain point. The optimal welding parameters for achieving high-quality joints between 2205 duplex stainless steel and 316 L stainless steel are as follows: axial pressure = 5 MPa, rotational inertia = 4.17 kg·m2, and IFW speed = 2700 r/min.

Effect of Post-Welding Aging Treatment on the Microstructure and High-Temperature Properties of Inertia Friction Welded GH4065A Joint.

In this study, post-welding aging treatments were applied to a novel Ni-based superalloy GH4065A inertia friction welding (IFW) joint to improve its high-temperature properties. The effect of aging treatment on the microstructure and creep resistance of the IFW joint was systematically investigated. The results indicated that the original γ' precipitates in the weld zone almost completely dissolved during the welding process, and fine tertiary γ' precipitated during the subsequent cooling process. Aging treatment did not significantly change the characteristics of grain structures and primary γ' in the IFW joint. After aging, the size of tertiary γ' in the weld zone and secondary γ' in the base material increased, but their morphology and volume fraction did not change evidently. After 760 °C, 5 h aging treatment, the tertiary γ' in the weld zone of the joint grew from 12.4 nm to 17.6 nm. Correspondingly, the creep rupture time of the joint at 650 °C and 950 MPa increased from 7.51 h to 147.28 h, which is about 19.61 times higher than that of the as-welded joint. The creep rupture was more likely to occur in the base material instead of the weld zone for the IFW joint. This revealed that the creep resistance of the weld zone was significantly improved after aging due to the growth of tertiary γ'. However, increasing the aging temperature or extending the aging time promoted the growth of secondary γ' in the base material, and meanwhile, M23C6 carbides tended to continuously precipitate at the grain boundaries of the base material. It might decrease the creep resistance of the base material.

Effect of Semi-Aging Heat Treatment on Microstructure and Mechanical Properties of an Inertia Friction Welded Joint of FGH96 Powder Metallurgy Superalloy

Inertia friction welded joints often present different microstructures than the base metal, and subsequent heat treatment processes are always needed to maintain superior performance. This study investigates the effect of semi-aging heat treatment after welding on the microstructure, residual stress, micro-hardness, and tensile properties of inertia friction welded FGH96 powder metallurgy superalloy using optical microscopy, scanning electron microscopy, X-ray diffraction, and hardness and tensile tests. The results show that the semi-aging heat treatment after welding does not affect the grain size or grain morphology of the base metal. However, the recrystallization process can be further promoted in the weld nugget zone and transition zone. Meanwhile, the grain size is refined and the residual stress is significantly reduced in the welded joint after the same heat treatment. Under the synergetic strengthening effect of the γ′ phase, semi-aging heat treatment increased the micro-hardness of the weld nugget zone from 470 HV to 530 HV and improved the average tensile strength at room temperature by 118 MPa. These findings provide a reference for the selection of the heat treatment process after inertia friction welding of nickel-based powder metallurgy superalloys.

Bonding mechanism and fracture behavior of inertia friction welded joint of 2219 aluminum alloy to 304 stainless steel

The 2219 aluminum (Al) alloy bars were welded to 304 stainless steel bars by inertia friction welding. The intermetallic compounds (IMCs) at the friction interface were characterized and analyzed and the bonding mechanism of the welded joint was studied in detail. Characterization of the microstructure at the friction interface revealed that there were two types of IMCs layers, the nanoscale Fe4Al13 layer and the microscale Cu-rich layer. In particular, the Cu-rich layer is bonded to the base material by Al2Cu and two Fe–Al–Cu ternary IMCs. Meanwhile, it was verified both theoretically and experimentally that the Fe4Al13 layer had less misfit with the base material with higher bonding strength at the interface. The formation of the Cu-rich layer increases the lattice mismatch, particularly at the interface of the ternary IMCs layer which becomes a weak area where the crack initiates and propagates easily.