I am a PhD Researcher that focuses on characterising the microstructural behaviour of superalloys.
Discover why inertia friction welding is on the increase especially within the aerospace industry
In 10 Seconds? Inertia friction welding (IFW) is a solid-state welding process, meaning that there is no melting of the materials at the weld interface. There are numerous benefits to IFW over conventional welding methods, such as, in some cases the weld joint can be exhibit higher mechanical strength than the parent material and also produces relatively small heat affected zones. However, one of the most advantageous properties of IFW is that it can weld dissimilar metals together – which is the focus of a lot of research within the IFW field.
Don’t believe it? Review three of the pinned articles that are concerned with characterising welding dissimilar alloys. One paper in particular had great success in improving the mechanical properties of the weld joint by joining a magnesium and aluminium alloy together under high frictional force.
Applications of IFW process – Inertia friction welding applications are mostly used for high cost materials for high temperature components, such as in a turbine engine.
The science behind the IFW solid-state welding
The basis of the IFW process is to obtain sufficient frictional heat at the weld interface to allow the material to plastically deform. The frictional heat is obtained by rotating one of the work pieces at a very high RPM (this piece is connected to a flywheel), and the other work piece is static with an axial force applied to bring it into contact with the rotating work piece. Therefore, allowing the kinetic energy to be transformed into frictional heat at the weld interface.
Abstract: This article describes a quantitative study of the microstructure of nickel-based superalloy RR1000 tube structures joined by inertia welding. One as-welded and three post weld heat-treated (PWHT) conditions have been investigated. The samples were characterized mechanically by measuring the hardness profiles and microstructurally in terms of γ grain size, γ′ precipitate size and volume fraction, stored energy, and microtexture. Electron backscatter diffraction (EBSD) was used to characterize high-angle grain boundaries (HAGB) and the variation of microtexture across the weld line. The coherent γ′ precipitates were investigated over a range of scales on etched samples in a field emission gun scanning electron microscope (FEGSEM), using carbon replicas in a transmission electron microscope (TEM) and from thin slices by means of high-energy synchrotron X-rays. Dramatic changes in the microstructure were observed within 2 mm of the weld line. In this region, the hardness profile is influenced by changes in grain size, γ′ volume fraction, γ′ particle size, and the work stored in the material. Further away, the observed hardness variation is still significant although only minor microstructural changes could be observed. In this region, the correlation of microstructure and hardness is less straightforward. Here, a combination of small microstructural changes appears to give rise to a significant change in strength. No significant texture or grain distortion was observed in the extensively plastically deformed region due to recrystallization.
Pub.: 01 Oct '02, Pinned: 25 Apr '17
Abstract: Inertia and linear friction welding are being increasingly used for near-net-shape manufacturing of high-value materials in aerospace and power generation gas turbines because of providing a better quality joint and offering many advantages over conventional fusion welding and mechanical joining techniques. In this paper, the published works up-to-date on inertia and linear friction welding of Ni-based superalloys are reviewed with the objective to make clarifications on discrepancies and uncertainties reported in literature regarding issues related to these two friction welding processes as well as microstructure, texture, and mechanical properties of the Ni-based superalloy weldments. Initially, the chemical composition and microstructure of Ni-based superalloys that contribute to the quality of the joint are reviewed briefly. Then, problems related to fusion welding of these alloys are addressed with due consideration of inertia and linear friction welding as alternative techniques. The fundamentals of inertia and linear friction welding processes are analyzed next with emphasis on the bonding mechanisms and evolution of temperature and strain rate across the weld interface. Microstructural features, texture development, residual stresses, and mechanical properties of similar and dissimilar polycrystalline and single crystal Ni-based superalloy weldments are discussed next. Then, application of inertia and linear friction welding for joining Ni-based superalloys and related advantages over fusion welding, mechanical joining, and machining are explained briefly. Finally, present scientific and technological challenges facing inertia and linear friction welding of Ni-based superalloys including those related to modeling of these processes are addressed.
Pub.: 07 Feb '15, Pinned: 25 Apr '17
Abstract: This article describes a comprehensive microstructural characterization of an inertia friction welded joint between nickel-based superalloys 720Li and IN718. The investigation has been carried out on both as-welded and postweld heat-treated conditions. The detailed metallographic analysis has enabled the relation of hardness profiles across inertia-welded alloy 720Li to IN718 and morphological changes of the precipitates present. The work demonstrates that inertia friction welding (IFW) 720Li to IN718 results in a weld free of micropores and microcracks and no significant chemical migration across the weld line. However, substantial differences in terms of grain structure and precipitation phase distribution variations are observed on each side of the dissimilar weld. The high γ′ volume fraction alloy 720Li exhibits a wider heat-affected zone than the mainly γ′′ strengthened IN718. Alloy 720Li displays only a small hardness trough near the weld line in the as-welded condition due to the depletion of γ′, while γ″-strengthened IN718 shows a soft precipitation-free weld region. Postweld heat treatment (PWHT) of the dissimilar weld at 760 °C, a typical annealing temperature for alloy 720Li, results in an overmatch of the heat-affected zone in both sides of the weld. The comparison of the as-welded and postweld heat-treated condition also reveals that IN718 is in an overaged condition after the stress relief treatment.
Pub.: 26 Jun '07, Pinned: 25 Apr '17
Abstract: The two aims of this study are first, determining the optimal welding process parameters by using the finite element simulation and second, determining the optimal tempering temperature by evaluating the mechanical properties of friction welded part for manufacturing large rotor shaft. Inertia welding was conducted in order to make the large rotor shaft of turbo charger for low speed marine diesel engine. The rotor shaft is composed of the 310mm diameter disk and the 140mm diameter shaft. Since diameters of disk and shaft are very different, the integration using friction welding reduces manufacturing cost compared with the forming process of which a disk and shaft are forged into one body. Finite element simulation was performed, because inertial welding friction process depended on many process parameters, including axial force, initial revolution speed and energy, amount of upset, and working time. It is expected that this modeling will significantly reduce the number of experimental trials needed when determining the optimal welding parameters. Inertia welding was carried out with optimal process parameter conditions obtained from the simulation results. Welded joint part, made by friction welding, had very poor mechanical properties, and so it required heat treatment. The base material used in the investigation was SFCMV1 (SANYO special steel, high strength low alloy Cr-Mo steel) of 140mm diameter. In the study, heat treatment test carried out quenching (950 °C, 4hr, oil cooling) and tempering (690–720 °C, 6hr, air cooling) for friction welding specimens. The various tests, including microstructure observation, tensile, hardness, and fatigue tests, were conducted to evaluate the mechanical properties under various heat treatment conditions after inertia welding.
Pub.: 17 Apr '10, Pinned: 25 Apr '17
Abstract: This research investigated the strengthening mechanisms associated with the as-welded microstructure developed during inertia friction welding of dissimilar superalloys LHSR and Mar-M247. The weld interface and heat affected regions of the sample were analyzed using hardness indentation techniques and subsequently characterized using SEM, TEM and advanced atom probe tomography. The yield strength of the welded joint was modeled to determine the impact of the gradients in the as-welded microstructure on strengthening mechanisms within the LSHR material. Characterization centered on formation of γ’, γ grain size and chemical segregation within the heat affected regions. Results indicate an increased hardness in the vicinity of the weld interface, resulting from the refined dispersion of γ’ and γ grains.
Pub.: 11 Mar '16, Pinned: 25 Apr '17
Abstract: The effect of inertia friction welding process parameters on microstructure evolution, weld plane quality, and the tensile behavior of welds between dissimilar nickel-base superalloys was established. For this purpose, the fine-grain, powder metallurgy alloy LSHR was joined to coarse-grain cast Mar-M247 using a fixed level of initial kinetic energy, but different combinations of the flywheel moment of inertia and initial rotation speed. It was found that welds made with the largest moment of inertia resulted in a sound bond with the best microstructure and room-temperature tensile strength equal to or greater than that of the parent materials. A relationship between the moment of inertia and weld process efficiency was established. The post-weld tensile behavior was interpreted in the context of observed microstructure gradients and weld-line defects.
Pub.: 08 Jun '16, Pinned: 25 Apr '17
Abstract: Differences in the elevated temperature mechanical properties of cast Mar-M247 and forged LSHR make it difficult to produce sound joints of these alloys by inertia friction welding (IFW). While extensive plastic upset occurs on the LSHR side, only a small upset is typically developed on the Mar-M247 side. The limited plastic flow of Mar-M247 thus restricts the extent of “self-cleaning” and mechanical mixing of the mating surfaces, so that defects remain at the bond line after welding. In the present work, the effect of local preheating of Mar-M247 immediately prior to IFW on the welding behavior of Mar-M247/LSHR couples was determined. An increase in the preheat temperature enhanced the plastic flow of Mar-M247 during IFW, which resulted in extensive mechanical mixing with LSHR at the weld interface, the formation of extensive flash on both the Mar-M247 and LSHR sides, and a sound bond. Performed in parallel with the experimental work, finite-element-method (FEM) simulations showed that higher temperatures are achieved within the preheated sample during IFW relative to its non-preheated counterpart, and plastic flow is thus facilitated within it. Microstructure and post-weld mechanical properties of the welded samples were also established.
Pub.: 23 Sep '16, Pinned: 25 Apr '17
Abstract: Publication date: October 2016 Source:Journal of Manufacturing Processes, Volume 24, Part 1 Author(s): R.P. Turner, D. Howe, B. Thota, R.M. Ward, H.C. Basoalto, J.W. Brooks Inertia friction welding (IFW), a type of rotary friction welding process, is widely used across aerospace, automotive and power-generation industries. The process considers a specialist rotary friction welding machine, which asks for the critical process parameters of inertial mass, initial rotational speed and applied pressure, to complete the relevant weld. The total kinetic energy available to the system can be calculated from basic physical relationships for the kinetic energy stored in a flywheel. This kinetic energy must be converted partly to heating the specimen at the interface, and partly to mechanical work via deformations. A finite element (FE) numerical model has been developed to predict the steady-state thermal profiles formed at the onset of mechanical deformation. Therefore, the amount of this total available energy for the process which is applied to the heating of the component at the interface through frictional contact has been estimated. Thus, the available energy left to produce the mechanical deformation via the flash formation can be calculated by subtracting the thermal energy from the total energy. This is of importance to the manufacturing engineer. A method of validating the FE modelling predictions was proposed using high-speed photography methods during the process to understand the rotational speed of the moving part at the instant that the steady-state deformation commences. Results from FE modelling and experiment suggest that the width of the steady-state thermal profile formed through the IFW, and the time taken to reach steady-state is strongly dependent upon the applied pressure parameter. Graphical abstract
Pub.: 02 Oct '16, Pinned: 25 Apr '17
Abstract: The dissimilar joints between 7A04 aluminum alloy rod and AZ31 magnesium alloy rod were produced by inertia friction welding. The effects of friction pressure on microstructure and mechanical properties of the joints were investigated. Results showed that intermetallic compounds (IMCs), mainly Al12Mg17 and Al3Mg2, were formed at the interfaces. A large amount of microcracks were generated in IMCs interlayer. The thickness of IMCs layer decreased significantly with increasing friction pressure. The mechanical properties were assessed by tensile test and microhardness. The mechanical properties of joints largely lies on the characteristic of IMCs interlayers at the interface. The tensile strength of the joints increases remarkably with increasing friction pressure. The maximum tensile strength of 96 MPa was achieved under the friction pressure of 124 MPa. All the tensile specimens failed in quasi-cleavage fracture mode along the boundary between IMCs interlayer and Al base metal.
Pub.: 17 Nov '16, Pinned: 25 Apr '17