Abstract This study details the development and validation of a finite element methodology to robustly simulate the inertia friction welding (IFW) process. There are many difficulties involved in modelling IFW. These include the short and violent process to complete a weld, as well as the challenges in obtaining experimental data throughout the process to complement, validate and inform the modelling effort. The objectives here are to model the macroscale multiphysical process leading to an accurate prediction of key process output variables, ultimately leading to a reliable method for predicting the post weld microstructure.
The Inertia Friction Welding (IFW) process is a high-temperature and high pressure process, with heavy plastic deformation, high power density, fast heating and fast cooling of the weld material. The microstructure produced in the weld line （WL）zones is therefore very different from parent material. A detailed microstructural investigation of the WL zones has been conducted using transmission electron microscopy and scanning electron microscopy. It has been shown that the morphology, energy status and microchemistry of grain boundaries in the WL zones are quite different from those in the parent material. It is also observed that, compared to a bi-modal distribution of intragranular ¢ particles in the parent material, a unimodal distribution of very fine spherical ¢ particles is produced in high density in the WL zones. This work provides a detailed understanding of the physical and chemical changes occurring across the weld line.
The widespread use and development of inertia friction welding is currently restricted by an incomplete understanding of the deformation mechanisms and microstructure evolution during the process. Understanding phase transformations and lattice strains during inertia friction welding is essential for the development of robust numerical models capable of determining optimized process parameters and reducing the requirement for costly experimental trials. A unique compact rig has been designed and used in-situ with a high-speed synchrotron X-ray diffraction instrument to investigate the microstructure evolution during inertia friction welding of a high-carbon steel (BS1407). At the contact interface, the transformation from ferrite to austenite was captured in great detail, allowing for analysis of the phase fractions during the process. Measurement of the thermal response of the weld reveals that the transformation to austenite occurs 230 °C below the equilibrium start temperature of 725 °C. It is concluded that the localization of large strains around the contact interface produced as the specimens deform assists this non-equilibrium phase transformation.
Abstract This work presents an alternative processing route to the conventional powder HIP—forge route for Nickel-based superalloys. Demonstrating how the field-assisted sintering technology (FAST) process can be exploited to successfully diffusion bond or functionally grade two or more Nickel-based superalloys from powder feedstock. The robustness of the process has been further demonstrated by the successful bonding of one alloy in powder form to another in the solid form. Chemical and microstructural analysis of the diffusion bond between the alloys is characterised, in both cases, with a short diffusion zone—in agreement with thermodynamic model predictions. A gradual transition in microhardness across the bond region was measured in all samples. A machinability assessment was also carried out through a simple face turning operation. Analysis of the cutting forces and machined surface shows signs of a directionality when machining across the bond region between two alloys, indicating that care must be taken when machining multi-alloy FAST-DB components.
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