Energy and force analysis of Ti-6Al-4V linear friction welds for computational modeling input and validation data

The linear friction welding (LFW) process is finding increasing use as a manufacturing technology for the production of titanium alloy Ti-6Al-4V aerospace components. Computational models give an insight into the process, however, there is limited experimental data that can be used for either modeling inputs or validation. To address this problem, a design of experiments approach was used to investigate the influence of the LFW process inputs on various outputs for experimental Ti-6Al-4V welds. The finite element analysis software DEFORM was also used in conjunction with the experimental findings to investigate the heating of the workpieces. Key findings showed that the average interface force and coefficient of friction during each phase of the process were insensitive to the rubbing velocity; the coefficient of friction was not coulombic and varied between 0.3 and 1.3 depending on the process conditions; and the interface of the workpieces reached a temperature of approximately approximately 1273 K (1000 °C) at the end of phase 1. This work has enabled a greater insight into the underlying process physics and will aid future modeling investigations.EPSRC, Boeing Company, Welding Institut

Maximizing the integrity of linear friction welded Waspaloy

The Ni-base superalloy, Waspaloy, was linear friction welded (LFWed) under various processing parameters and then subjected to a post weld heat treatment (PWHT). Tensile testing integrated with the optical image correlation Aramis\uae system indicated that there is a critical axial shortening value (2 mm) below which LFWed and post weld heat treated (PWHTed) Waspaloy exhibited weak integrity. At and above this critical shortening, the yield strength and ultimate tensile stress (UTS) values were more or less the same as for the parent material. However, total elongation continued to increase with axial shortening even above the critical value due to decrease in width of thermo-mechanically affected zone (TMAZ). The sample with the highest axial shortening (4.9 mm) exhibited an elongation 91% of the parent material elongation. According to Aramis\uae data, the mixture rule can be used reliably to determine the contribution of TMAZ to the tensile elongation of PWHTed Waspaloy. Microstructure characterization across the weld in the as-LFWed and PWHTed conditions was carried out to correlate the process parameters and microstructural changes that affect the tensile properties. Weak integrity at axial shortening below 2 mm was mainly due to lack of bonding and/or presence of oxides at the weld interface. In the as-welded condition, a loss in hardness was observed, and related to the extensive dissolution of strengthening phase (\u3b3\u2032) in the weld area. The applied PWHT restored the hardness in the weld region.Peer reviewed: YesNRC publication: Ye

Modeling grain size and strain rate in linear friction welded Waspaloy

The high-temperature deformation behavior of the Ni-base superalloy, Waspaloy, using uniaxial isothermal compression testing was investigated at temperatures above the \u3b3\u2032 solvus, 1333 K, 1373 K, 1413 K (1060 C, 1100 C, 1140 C) for constant true strain rates of 0.001, 0.01, 0.1, 1 s -1 and up to a true strain of 0.83. Flow softening and microstructural investigation indicated that dynamic recrystallization took place during deformation. For the investigated conditions, the strain rate sensitivity factor and the activation energy of hot deformation were 0.199 and 462 kJ/mol, respectively. Constitutive equations relating the dynamic recrystallized grain size to the deformation temperature and strain rate were developed and used to predict the grain size and strain rate in linear friction-welded (LFWed) Waspaloy. The predictions were validated against experimental findings and data reported in the literature. It was found that the equations can reliably predict the grain size of LFWed Waspaloy. Furthermore, the estimated strain rate was in agreement with finite element modeling data reported in the literature. \ua9 2013 The Minerals, Metals & Materials Society and ASM International.Peer reviewed: YesNRC publication: Ye

Analysis of integrity and microstructure of linear friction welded Waspaloy

Nickel-base superalloy, Waspaloy, was linear friction welded (LFWed) under different axial shortening conditions of 2.0, 3.4, and 4.6 mm. The tensile properties and microhardness of the weldments were investigated in the as-LFWed condition and compared with those in the post-weld heat treated (PWHTed) condition. Mechanical properties were related to microstructures following examination by optical microscopy, high resolution scanning electron microscopy, and electron backscatter diffraction (EBSD). Analyses of the EBSD results in terms of the misorientation angle distribution, which represents the stored energy, were performed. In the as-LFWed condition, the yield strength (YS) and ultimate tensile strength (UTS) increased with axial shortening due to greater expulsion of the softened interfacial material toward the periphery as flash. In contrast, with increasing axial shortening the total elongation initially remained constant and then decreased. This was also related to the expulsion of the softened interfacial material into the bifurcated flash. Extensive dissolution of the strengthening phase (\u3b3\u2032) in the weld area during linear friction welding (LFW) contributed to the lower YS and UTS in the as-welded condition compared to the PWHTed condition where the \u3b3\u2032 particles were recovered. After performing post-weld heat treatment (PWHT), the total elongation improved due to the relaxation of stored energy and grain growth in the thermomechanically affected zone (TMAZ).Peer reviewed: YesNRC publication: Ye

Linear friction welding behavior of Waspaloy

Over conventional joining methods, linear friction welding (LFW) exhibits a high weld quality and economical benefits for the aerospace industry. In particular, LFW enables the removal of the fir-tree in conventional blade to disk assembly, which results in weight reduction and improvement in engine efficiency. Considering these advantages, the LFW behavior of Waspaloy, used in jet engines as blade and disc material, has been investigated at different processing conditions. This study specifically highlights the influence of frequency, amplitude, and pressure during oscillation on the microstructure and mechanical properties of the welded samples. Microstructure and mechanical characteristics of the thermo-mechanically affected zones (TMAZ) were investigated by optical microscopy, EBSD, SEM, and microhardness. The LFW operating window resulting in welds free from defects was determined from these data. Microstructure examination revealed that dynamic recrystallization (DRX) occurred in the 0.9 mm narrow band of the TMAZ resulting in up to 50% reduction in the grain size. Furthermore, at the weld interface a considerable volume fraction of the ?' precipitates dissolved, contributing to a drop in hardness.Peer reviewed: YesNRC publication: Ye

Mechanical property and microstructure of linear friction welded WASPALOY

The mechanical properties and microstructural evolution of WASPALOY joined by linear friction welding (LFW) were investigated in this study. In-situ temperature measurements using thermocouple probes indicated exposure of the weld area to a temperature of at least 1400 K (1126 \ub0C). Based on electron backscatter diffraction (EBSD) mapping of the weldments, up to 50 pct reduction in \u3b3 grain size occurred within 0.9 mm of the weld interface as a result of dynamic recrystallization (DRX). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that progressive dissolution of \u3b3\u2032 precipitates took place from the base metal to the weld interface, where almost no \u3b3\u2032 precipitates were observed. Within 3.3 mm of the weld interface, the \u3b3\u2032 dissolution significantly influenced the hardness profile measured across the extended thermomechanically affected zones (TMAZs). Investigation of strain distributions during tensile testing using the optical Aramis system revealed weak bonding at the edge of the weld due to oxidation. To extrude out oxide layers into the flash, increasing the axial shortening to higher than 1.2 mm is recommended.Peer reviewed: YesNRC publication: Ye

Post-Weld Heat Treatment of Additively Manufactured Inconel 718 Welded to Forged Ni-Based Superalloy AD730 by Linear Friction Welding

International audienceA new post-weld heat treatment (PWHT) cycle was designed for novel dissimilar linear friction welding (LFW) of selective laser melted (SLM) Inconel 718 (IN718) to AD730 forged nickel-based superalloy. The microstructure and hardness of the joints after the PWHT are investigated and compared with those of as-linear friction welded samples. The precipitation of γ′ + γ″ is determined as the main mechanism to increase the mechanical properties of SLM IN718 alloy. These particles coarsened during heat treatment at 1253 K and double aging. The results show that the thermomechanical history of linear friction welded joints can affect the microstructure of IN718 alloy such as the morphology of δ phase after solution treatment (ST) from the platelike in the weld zone (WZ) to the needlelike in the base material (BM). It was found that in AD730, nanometric size γ′ particles reprecipitated close to the weld line during rapid cooling after welding. The presence of ultrafine γ′ particles and coarsening of the remaining particles in the microstructure of the alloy, during PWHT, can enhance the strength and hardness. The developed PWHT resulted in uniform hardness across the new dissimilar joint