Linear Friction Welding Joint Research Articles

Investigating microstructure, mechanical properties, and pitting corrosion resistance of UNS S32760 super duplex stainless steel after linear friction welding

High-performance alloys such as super duplex stainless steels (SDSS) are of interest to the oil and gas industry, especially in deep and ultra-deep reservoirs where high pressures and highly corrosive environments are prevalent. SDSS have high nitrogen contents and pitting resistant equivalent number (PREN) values greater than 40, however, fusion welds of these alloys can exhibit unsuitable microstructures and defects that may result in failure during usage. Solid-state linear friction welding (LFW) offers an alternative for the effective joining of SDSS with a less detrimental effect on microstructure and properties. In this work, four LFW joints in UNS S32760 SDSS were produced and investigated by evaluating the process parameters required to achieve a high-quality joint with the desirable metallurgical, mechanical, and localized corrosion properties. These properties were assessed through metallography (optical microscopy and scanning electron microscopy), tensile and microhardness tests, and corrosion analysis according to the ASTM G48A standard. Results indicated that one specific combination of LFW parameters led to a defect-free joint, and that the mechanical properties of the weld in this case were comparable to those of the base material. Additionally, an adequate balance between ferrite and austenite phases was achieved throughout the microstructural gradients seen in the weld region. Microhardness values were below 350 HV, thus complying with the DNV–OS–F101 standard. Furthermore, no pitting corrosion was observed in this joint under the testing conditions suggested by ASTM G48A.

Anomalous enhancing effects of electric pulse treatment on strength and ductility of TC17 linear friction welding joints

Mechanical properties of TC17 titanium alloy undergo a significant reduction after linear friction welding (LFW), of which the strength and ductility are hard to be improved simultaneously by traditional aging heat treatment (AHT), seriously limiting the application of LFW in the manufacturing of TC17 titanium alloy blisks. To this end, the present work proposes to use electric pulse treatment (EPT) to enhance the strength and ductility of TC17 LFW joints simultaneously by improving its microstructure. The results show that, in comparison to the uneven distribution of α phases in the welding zone (WZ), heat-affected zone (HAZ), and base metal (BM) zone after AHT, EPT can selectively homogenize the α phase distribution of WZ and HAZ without impacting the BM. The selective effect of EPT is reflected as the synergistic influence of the local Joule heating effect and the electron wind effect, which promotes the diffusion of β phase stabilizing element Mo and leads to a competitive precipitation of β phase and α phase in the α phase transition temperature range. The ratio of α phase to β phase in the WZ and HAZ finally approaches an equilibrium point which is similar to that of BM, leading to a uniform distribution of α phase and realizing the synergy of strength-ductility of LFW joint: the maximum strength increase observed is 12.9 %, accompanied by a corresponding elongation increase of 122 % (by AHT & EPT), and the maximum plasticity improvement is 185 %, accompanied by a corresponding strength increase of 4.3 % (by EPT for 1 h). This study provides essential insights for improving the strength and ductility of LFW TC17 titanium alloy blisks and enhancing the applications of LFW in aeroengine components.

Sound dissimilar linear friction welding of A7075-T6 Al and mild steel by simultaneous interfacial deformation using higher forging speed

Sound dissimilar welding of heat-treatable A7075-T6 aluminum and mild steel is extremely difficult due to the formation of interfacial cracks. The present study aims to attempt linear friction welding (LFW) of high-strength A7075-T6 Al alloy and mild steel to obtain sound joints with the highest strength ever by controlling the quality deteriorating phenomena that previous studies have faced. In this study, LFW joints were fabricated under two different applied pressures of 100 MPa and 300 MPa at a forging speed of 5 mm/s, along with various forging speeds ranging from 5 mm/s, 10 mm/s, to 20 mm/s under an applied pressure of 300 MPa, and the joint microstructure, mechanical properties and interface macrostructure were investigated. Furthermore, thermal dependence behaviors of both alloys were systematically investigated to optimize the processing parameters, especially applied pressure during LFW. At lower forging speeds of 5 mm/s and 10 mm/s, the weld defects and un-bonded regions were observed near the center of the weld accompanied by unevenness of butt surface due to the relatively thick intermetallic compound (IMC) formed in the interface which greatly influenced the joint strength. In contrast, at the higher forging speed of 20 mm/s, weld defects at the joint interface were effectively suppressed by promoting the simultaneous and uniform interfacial deformation of both alloys thanks to the extremely thin IMC during LFW. Consequently, a highly efficient joint with 100 % efficiency was successfully obtained at higher forging speed of 20 mm/s and despite the occurrence of softening towards A7075, the fabricated joint displayed a base metal fracture towards the steel side.

Effects of microstrcture composition and orientation on micro mechanical properties of linear friction welding joint weld zone for heteromorphic TC17 titanium alloy

Effects of microstrcture composition and orientation on micro mechanical properties of linear friction welding joint weld zone for heteromorphic TC17 titanium alloy

Fatigue strength improvement of linear friction welded butt joints of low carbon steel by pressurizing after oscillation

Although linear friction welding (LFW) has received significant attention as an effective solid-state welding method, the fatigue properties of LFW joints have not been fully investigated. In this study, the fatigue strength of the steel joints fabricated using LFW was investigated and improved by increasing the pressure after oscillation. Low-carbon steel SM490A was successfully joined using LFW without unbonded areas or apparent softening in the heat-affected zone (HAZ). The microhardness, microstructure, weld toe shape, and fatigue life were assessed to investigate their relationships with the pressure conditions after oscillation. The results indicated that increasing the pressure after oscillation improved the area fraction of martensite (M) and the hardness of the weld interface center. The weld toe radius (ρ) and weld toe angle (α) also increased regardless of the upset control condition. The increasing of the pressure after oscillation from 50 MPa to 300 MPa increased ρ from 0.4 mm to 2.1 mm and the α increased from 92.7° to 103.4° at the weld center, accompanied by a reduced stress concentration factor (Kt) from 3.0 to 1.7. Under the fatigue test conditions of the stress range of 380 MPa, the fatigue life of the LFW as-welded joints was increased by approximately 31 % when the pressure after oscillation was 250 MPa compared to that of 50 MPa and by 87 % when it was 300 MPa compared to that of 250 MPa. Despite the possibility of fracture initiation at the weld toe at the edge of the LFW joints, the fatigue strength demonstrated a substantially longer fatigue life than the S-N design curve FAT90 recommended by the International Institute of Welding.

Effect of friction pressure on microstructure and tensile properties of linear friction welded Ti–6Al–4V alloy joints

This investigation aims to study the influence of friction pressure (FRNP) on the evolution of microstructure and tensile properties of Ti6Al4V alloy joints developed using linear friction welding (LFW) for aeroengine applications. The Ti6Al4V alloy plates of 6 mm thickness were joined using different levels of FRNP from 10 MPa to 30 MPa. The weld joint quality was analyzed employing stereo-zoom microscope. The microstructure of LFW joints was studied using optical (OM), scanning electron (SEM) and transmission electron microscope (TEM). The hardness and tensile properties were evaluated and correlated to the microstructure of joints. The fractographs were studied using SEM and correlated to the hardness. The LF welded Ti6Al4V joints made using the optimum level of FRNP of 20 MPa exhibited greater tensile strength (UTS) of 993 MPa, and elongation (EL) of 8%. It showed notch tensile strength (NTS) of 1073 MPa and notch strength ratio (NSR) of 1.041 revealing ductile fracture. The LF welded Ti6Al4V joints revealed 96.41%, 104.10% and 66.67% of UTS, NTS and EL of base metal. The greater smooth and notch tensile properties of joints are principally imputed to maximum refinement of alpha + beta grains at interface of joint.

Texture characteristics and fracture mechanism of linear friction welded joints of dissimilar titanium alloys after annealing

In the paper, we discussed the effect of annealing on the microstructure, crystal texture, and toughness of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) and Ti–4Mo–4Cr–5Al–2Sn–2Zr (TC17) linear friction welding (LFW) joint. The results reveal that the microstructure difference on both welded zone (WZ) decreases. The TC11 WZ consists of supersaturated solid solution α′ phase and β phase, the coarse α grains disappear and the orthorhombic martensite α″ phases transform into lamellar α+α′ phases on the TC17 WZ after the double furnace annealing. Two β textures (shear and annealing textures) and two α textures (D and E textures) exist at the original joint, and both of them transform into new β textures (brass and copper textures) and α textures (F and G textures) after the double furnace annealing. The dislocation density of the TC17 WZ is significantly higher than that of the TC11 WZ at the original joint. After the double furnace annealing, dislocation density, grain type, and Schmid factor (SF) distribute uniformly throughout the entire WZ. The average dislocation density decreases slightly and the low SF (μ<0.25) almost disappears. The microhardness value of the entire joint is more uniform and stable, and the fracture toughness is 137% higher than that of the original joint, approximately reaching 91% of the TC11 fracture toughness. The research provides a theoretical basis for preparing high-toughness joints of dissimilar titanium alloys.

Microstructural Features, Tensile Properties, and Impact Toughness of Linear Friction Welded High-Temperature Alloy Joints for Blisk Assembly Applications

The main objective of this investigation is to analyze the microstructure, tensile properties, and impact toughness of Ti6Al4V alloy joints developed using optimized parameters of linear friction welding (LFW) for gas turbine blisk assembly applications. The 6 mm thick plates of Ti6Al4V alloy were joined using a friction time of 40 sec, a friction pressure of 20 MPa, a forging pressure of 10 MPa, a forging time of 3 sec, and an oscillating frequency of 14 Hz. The different regions of joints were analyzed using a stereo zoom microscope. Optical and scanning electron microscope (SEM) was used for analysing the microstructural features of joints. The room temperature tensile properties, hardness, and impact toughness of LFW-Ti6Al4V alloy joints were evaluated and correlated to the microstructural features of weld region. The fractured sections of tensile and impact toughness specimens of joints were analyzed using SEM and the failure of joints was correlated with the hardness survey. Results showed that the LFW-Ti6Al4V alloy joints developed using the optimized parameters exhibited a tensile strength (TS) of 1015 MPa, a yield strength (YS) of 940 MPa, and an elongation (EL) of 8%. The joints revealed 98.54%, 95.91%, and 66.67% of tensile strength, yield strength, and ductility of the parent metal. The LFW joints disclosed impact toughness (IT) of 17.2 J which is 89.77% impact toughness of the parent metal. The superior tensile properties and impact toughness of LFW-Ti6Al4V alloy joints are mainly attributed to a greater degree of refinement of α + β grains in the weld interface, which offers greater resistance to tensile deformation and crack propagation.

Fatigue strength and fracture characteristics of linear friction welded joints of weathering mild steel

AbstractWeathering steel with high phosphorus content usually cannot be joined by fusion welding due to the possible solidification crack. The present study successfully joined the unweldable weathering steel SPA‐H by linear friction welding (LFW) above the A3 temperature. The microstructure, microhardness, and residual stress were measured and analyzed. The stress concentration factor (SCF) of LFW joints was assessed by the finite element method (FEM). The influence of flash on the fatigue strength and fracture characteristics was investigated. The results suggest that the weld center zone (WCZ) consisting of ferrite and bainite shows a necking shape. The ductile fracture of LFW joints occurred at the base metal, resulting in a joint efficiency close to 100%. The possible unbonded flash at the edge of the LFW joints greatly reduced the fatigue life. The proposed S‐N curve illustrates a much higher fatigue strength than the FAT90 design curve.

Microstructure, mechanical properties and fatigue behaviors of linear friction welded weathering steels

The weathering steels SMA490AW and SPA-H with a high phosphorus content were successfully joined by linear friction welding (LFW) without welding defects and heat affected zone (HAZ) softening. The residual stress of the welded joints was measured by X-ray diffraction (XRD) after the welding. The microstructure characteristics were observed using a scanning electron microscope (SEM) and analyzed corresponding to the microhardness distribution in different regions. The mechanical properties and fatigue behaviors were assessed using the digital image correlation (DIC). The results suggest that the bainites were crystallized in the weld center zone (WCZ), and the area fraction of bainites was obviously decreased at a small distance from the WCZ, which illustrated a large welding temperature gradient. The ductile fracture of LFW joints occurred at the base metal part of the specimens, resulting in a joint efficiency close to 100%. The fatigue strength of LFW joints was close to that of base metals and the proposed S-N curves showed a much higher fatigue strength compared to the design curve FAT112.

High Temperature Mechanical Properties and Microstructure Evolution of Ti-6Al-4V Alloy Linear Friction Welding Joints

The combination of linear friction welding (LFW) and hot forming processes is limited due to a lack of research on the high-temperature flow behavior and microstructure evolution of welded joints. In this paper, an electric-assisted high-temperature uniaxial tensile test platform based on digital image correlation (DIC) is built, and uniaxial tensile tests of Ti-6Al-4V alloy with LFW joints are performed at different temperatures (923–1023 K) and different strain rates (0.001 s−1–0.01 s−1). Then the microstructure of the LFW joints under different hot deformation conditions have been analyzed by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate that the high-temperature flow behavior of LFW joints shows an obvious correlation between temperature and strain rate: the yield stress decreases from 203 MPa at 923 K to 105 MPa at 1023 K, and increases from 85 MPa to 130 MPa when the strain rate increases from 0.001 s−1 to 0.01 s−1 at 973 K. The hot deformation mechanisms with deformation conditions have been characterized, which changes from the mechanism of dislocation creep to the mechanism of self-diffusion as the deformation temperature increases from 923 to 1023 K. Especially, the fraction of high angle boundaries (HABs) rapidly rise from 49.2% to 64.1% with the increasing temperatures, the discontinuous dynamic recrystallization (DDRX) become the primary mechanism of nucleation during high-temperature deformation of LFW joints.

Influence of Joint Configuration on Linear Friction Welded Ti-6Al-4V Alloy Joints

Ti-6Al-4V alloy is a unique material for structural applications of aerospace industry for the excellent strength and lightweight. The fusion welding of this Titanium alloy resulted severe residual stress formation and coarser grains in the fusion zone. To overcome these problems, a solid state linear friction welding (LFW) is a emerge technique to joining of blade and disk assembly in the next generation aero engines. The plastic deformation followed by forging action resulted finer grain structures in welded regions. This investigation elaborated mechanical behavior and microstructural characteristics of linear friction welded joints. The welding parameters established by statistical response surface methodology. The fabricated joints yielded maximum tensile strength and joint efficiency of 1011 MPa and 98%. The lower microhardness recorded in the thermo mechanical affected zone (TMAZ) among the weld cross section. The weld nugget microstructure composed of equiaxed grain structure. The fracture surface revealed that joints failed under ductile mode. The result concluded that the weld failure mainly due to grain coarsening subsequent deformation leads to weld failure in the LFW joint.

Microstructure and Mechanical Properties of Linear Friction Welding Joint of GH4169 Alloy/S31042 Steel

Microstructure and Mechanical Properties of Linear Friction Welding Joint of GH4169 Alloy/S31042 Steel

Development and experimental study on linear friction welding titanium alloy blisk

Taking the advanced aeroengine compressor blisk as the application object, the development and experimental study on the TC11/TC17 different materials linear friction welding integral blisk was carried out. The microstructure of welded joint was analyzed, the tensile and stress rupture properties of base metal and welded joint were compared, the vibration fatigue test on welded blade test pieces, and the overrunning test and low-cycle fatigue test on welding blisk were developed. The results show that the TC11/TC17 linear friction welding joint consists of five typical zones, they are TC11 base metal zone, TC11 thermal influence zone, weld zone, TC17 thermal influence zone and TC17 base metal zone. The tensile strength of the welded joint is basically equivalent to that of the TC11 base metal, elongation is equivalent to TC17 base metal; endurance strength lower than TC17 base metal, but less higher than TC11 base metal. The median fatigue life of welded blade test pieces with three weld positions is respectively 1.501 × 106, 0.344 × 106, and 0.132 × 106 cycles, the fatigue crack isn’t at welding seam and thermal influence zone. The welding blisk pass the 115% overrunning test and 1000 cycles low-cycle fatigue test, the experiment results meet the requirement.

Computational investigation of welding heat transfer characteristics and parameters effectiveness in mild steel linear friction welding

Numerical simulation of heat transfer represented an efficient tool for the prediction of the effectiveness of the selected welding parameters in industrial application of the linear friction welding (LFW). A fully coupled model was established to study the effect of welding parameters on the welding heat transfer characteristics in LFW of mild steel. The interfacial temperature increased quickly owing to friction heat generation, and stress distribution showed dynamic variations owing to the periodic motion. The energy ratio of friction work and plastic deformation work increased with increasing friction pressure, oscillation frequency, and amplitude, thus indicating the significance of heat generation by plastic deformation. The heat transfer characteristics were found to be highly dependent on the welding parameters. A practical mathematical equation correlating the average friction power with welding parameters was proposed and used to select the suitable welding parameters for a sound LFW joint. The simulated results indicated excellent agreement with the experimental measurements. Finally, microstructures of the experimental welded joint were investigated by consideration of the thermal process. It was hoped that the greater understanding of heat transfer behavior could improve the efficient of process optimization when joining steel as well as other metal materials.

Study of the Microstructure and Fracture Toughness of TC17 Titanium Alloy Linear Friction Welding Joint

In this paper, the fracture toughness of the thermo-mechanically affected zone (TMAZ) and the weld zone (WZ) of the TC17 titanium alloy linear friction welding joint was studied. The relationship between microstructure and fracture toughness of the joint, as well as the morphologies of the joint microstructure and fracture were investigated. The results indicate that after heat treatment, there was no significant difference in hardness between the WZ and the TMAZ of the joint, which was about 420 HV. However, the microstructures of the different zones of the joint were significantly different. The TMAZ was composed of coarse grains having an internal basket-shaped α phase with an uneven grain size, while the WZ was composed of relatively uniform fine grains and contained a sheet-like α phase. The fracture toughness of the TMAZ was found to be higher than that of the WZ, indicating that the microstructure of the joint had a significant impact on the fracture toughness. In addition, the fracture resistance of the TMAZ with coarser grains and uneven microstructure was better than that of the WZ with fine grains and uniform microstructure.

Effect of Heat Treatment on the Microstructure and Properties of a Ti₃Al Linear Friction Welding Joint.

Heat treatment at different temperatures was carried out on a Ti3Al linear friction welding joint. The characteristics and evolution of the microstructure in the weld zone (WZ) and the thermo-mechanically affected zone (TMAZ) of the Ti3Al LFW joint were analyzed. Combined with the heat treatment after welding, the effect of the heat treatment temperature on the joint was discussed. The test results indicated that the linear friction welding (LFW) process can accomplish a reliable connection between Ti3Al alloys and the joint can avoid defects such as microcracks and voids. The weld zone of the as-welded Ti3Al alloy joint was mainly composed of metastable β phase, while the TMAZ was mainly composed of deformed α2 phase and metastable β phase. After being heat treated at different temperatures, the WZ of the Ti3Al LFW joint exhibited a significantly different microstructure. After heat treatment at 700 °C, dot-like structures precipitated and the joint microhardness increased significantly. Subsequently, the joint microhardness decreases with the increase in temperature. Under heat treatment at temperatures above 850 °C, the formed structure was acicular α2 phase and the joint microhardness after heat treatment was lower than that of the as-welded joint.

Multi-scale and multi-technic microstructure analysis of a linear friction weld of the metastable-β titanium alloy Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) towards a new Post-Weld Heat Treatment

Linear Friction Welding (LFW) is a solid-state joining process producing narrow joints mainly developed for the aircraft industry. The Thermo-Mechanical Processing (TMP) loads imposed on the material cause complex microstructure transformations. This study aimed at characterizing the local microstructures and crystallographic configurations to identify the mechanisms impacting the stability and the mechanical properties of a Ti17 LFW joint with the objective of establishing an innovative homogenizing Post-Weld Heat Treatment (PWHT). The process caused a narrow zone of ±2 mm from the friction interface to reach the isothermal α → β transformation temperature under a heating rate of 500 K/s followed by quenching (−100 K/s). The TMP resulted in the formation a ±3 mm wide soft Process Affected Zone (PAZ) delimited by three characteristic zones: the Welding Line (WL width ≈ 400 μm), The Thermo-Mechanically Affected Zone (TMAZ width ≈ 1 mm) and the Heat Affected Zone (HAZ). β TMP resulted in the total dissolution of the α phase in the joint core (WL + TMAZ) and formed strongly textured {110}⟨111⟩ β recrystallized grains in the WL by continuous dynamic recrystallization of squeezed prior-β grains in the TMAZ. α + β TMP led to a gradual loss of hardness in the HAZ whose microstructure is similar to the one of the base material (BM) but is subject to gradual α laths dissolution due to the local temperatures experienced during LFW. A PWHT consisting in a β annealing followed by an α + β ageing resulted in a uniformly hardened weld with a homogenized Widmanstätten microstructure in the whole assembly.

Physical simulation of microstructural evolution in linear friction welded joints of Ti–6Al–4V alloy

The novel shear compression specimen was used to simulate the microstructural evolution in linear friction welding joints of Ti–6Al–4V alloy. Similar formation mechanisms of microstructures and microtextures were found in the linear friction welding joints and shear compression specimen. Accordingly, the shear compression test was proved to simulate the microstructural evolution and the thermomechanical conditions that occurred in linear friction welding joint. Furthermore, the strain rate in linear friction welding was estimated to exceed the value of 70 s− 1.

Internal residual stress measurement on linear friction welding of titanium alloy plates with contour method

The internal residual stress within a TC17 titanium alloy joint welded by linear friction welding (LFW) was measured by the contour method, which is a relatively new and destructive technique to obtain a full map of internal residual stress. The specimen was first cut into two parts; the out-of-plane displacement contour formed by the release of the residual stress was then measured; finally, taking the measured contour of the cut plane as the boundary conditions, a linear elastic finite element analysis was carried out to calculate the corresponding distribution of residual stress normal to the cut plane. The internal stress distribution of the TC17 titanium alloy LFW joint was also analyzed. The results show that the tensile residual stress in the TC17 LFW weld is mainly present within a region about 12 mm from the weld centerline; the peak tensile residual stress occurs at the weld centerline and reaches 360 MPa (about one third of the yield strength of TC17 alloy); within the weld zone of the TC17 LFW weld, the through-thickness stress is not uniform, and the internal stress is larger than that near the top or bottom surface.