The microstructural evolutions and variations in mechanical performance of electron beam welded (EBW) Ti-6Al-4V (Ti64) alloy have been investigated. The effects of heat treatment on the microstructure of welded samples have been studied after post-welding solution treatment and ageing. The martensitic phase α' has been confirmed using transmission electron microscopy (TEM). Electron backscatter diffraction (EBSD) has been used to investigate the phase and grain morphology. Results showed that the martensitic α′ phase coarsened, the size of heat-affected zone (HAZ) changed and grains in the base materials (BMs) had grown after the post-weld heat treatments (PWHT). The tensile behaviour of electron beam welded Ti64 has been investigated using in situ tensile testing monitored by optical microscopy. The deformation and failure were directly revealed during the in situ tensile process. Results showed that the EBW Ti64 samples have different failure locations after receiving different post-weld heat treatments. The relationship between the post-weld heat treatments, microstructural evolution and mechanical properties of EBW Ti64 were investigated. Thermodynamic databases were used to predict mechanical properties—including the yield strengths—of the titanium alloy for different grain sizes, representing different post-weld heat treatment operations, and these were embedded into a finite element modelling framework to simulate the tensile testing specimens to understand the mechanical fields experienced such as stresses and strains, just prior to failure.

A detailed microstructural characterisation of the emerging weld-line grain structure, for bead-upon-plate welds in Ti-6Al-4V (Ti64) of differing plate thickness, was performed. The microstructure studied was formed during both steady state and non-steady state sections within the weld path, with the non-steady state portion being taken from the end of the plate as the weld bead and heat source overhang the edge of the plate. This allows for the effects of welding process conditions on the microstructural evolution to be determined. The weld pool geometry and 3D tomography of the weld-induced defects have been investigated. Detailed characterisation of microstructure and texture for different welding parameters and for steady and non-steady states have been used to identify physical parameters for the microstructure predictions that are difficult to obtain otherwise. The different states significantly affect the weld crown shape and formation, weld toe, weld bead depth and width. However, the heat affected zone (HAZ) remains unchanged. Regarding the microstructural evolution, both the steady and non-steady states have similar microstructure and texture. No defects were observed in the steady state section of welds, but sub-surface spherical pores have been observed in the non-steady state section of a weld. Finite element modelling to simulate the thermal-metallurgical-mechanical fields within the steady and non-steady state sections of the welds was considered, and the cooling rates predicted within steady state and non-steady sections were interrogated to improve the theoretical understanding of the microstructure and defect formation differences in these Ti64 EB weld regions.

A microstructural characterisation and computational modelling framework for simulating the coupled thermal mechanical cycles with two different initial parent microstructures, and their impact upon the emerging microstructure features including beta grain size and phase volume fractions during electron beam welding (EBW) of Ti-6Al-4 V (Ti64) alloy is presented. Ti64 plates (measuring 5.5 mm in thickness) with different thermal processing have been electron beam welded using differing process parameter sets. These experimental welds have been fully characterised to provide information on the effect that a prior heat treatment has upon the micro structural evolution caused by the EB welding. Microstructure characterisation was investigated using both light microscopy and scanning electron microscopy. The results from this microstructure characterisation have been used to identity physically-based parameters required for microstructure predictions.

The precipitation kinetics of gamma prime in the nickel based superalloy RR1000 has been characterised after solid-solution heat treatments and isothermal aging conditions relevant to service conditions. Multimodal precipitate dispersions are formed within the alloy. Numerical methods are presented for determining the three dimensional size of the particle populations combining information obtained from Scanning Electron microscopy and Transmission Electron microscopy. This information has been used to develop a multicomponent mean-field model descriptive of precipitation kinetics. The smallest particle population increases in mean size during isothermal aging at 700 BC where classical mean-field models of coarsening kinetics suggest that these particles should dissolve. A phenomenological model has been proposed to capture this behaviour within a statistical formulation that is applicable to both processing and service conditions. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Selective-laser melting (SLM) is one of the most rapidly developing and promising of all the so-called "Additive Manufacture" routes due to its capability to produce component geometries that would prove impossible using traditional manufacture. A selective-laser melting fabricated cuboid component was built using powder CM247LC, using standard methods, and this was subsequently analysed using neutron tomography methodology to allow for three-dimensional visualisation of the exterior and the interior of the component. The resulting neutron radiographs were processed and analysed for evidence of both porosity and grain boundary segregation within the component. (C) 2018 Elsevier B.V. All rights reserved.

Inertia friction welding has been used across the aerospace, automotive, and power-generation industries for the fabrication of complex axisymmetric components for over forty years. The process involves one axisymmetric piece being held stationary and another piece being brought into contact set to rotate about its axis of symmetry by a flywheel with the system under an applied load across the joint. Plasticization at the joint interface through the frictional heating sees the two pieces bond together. The titanium alloy Ti-6Al-4V has been widely studied for inertia welding applications. A successful selection of processing parameters (flywheel energy and mass, applied load) allows an inertia welding process which produces a very high-integrity weld, with a minimal heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ), formed as a narrow band at the interface and extending further into the material. The width of this narrow band of heated material is dependent upon the process parameters used. A series of experimental inertia friction welds were performed using Ti-6Al-4V, and a finite element (FE) modeling framework was developed using the FE code Deform in order to predict the widths of the HAZ and TMAZ at the weld interface. The experimentally observed HAZ boundaries were correlated with the thermal fields from the FE model, while TMAZ boundaries were correlated with the Von Mises plastic strain fields.

Mg-Zn alloys are promising candidate materials for medical applications. The bio-corrosion performance of Mg-3 wt% Zn has been studied at 37 °C in simulated body fluid (SBF) using immersion tests and electrochemical measurements. Heat treatments (solution treatment and ageing) were used to alter the microstructure and adjust the volume fraction of precipitates. It has been found that, in the solution treated sample, the dissolution of ( -Mg +MgZn) eutectic phases led to a low corrosion rate (3.05 ± 0.20 ⁄ / ). The volume fraction of precipitates increases with ageing time at 160 °C and causes the corrosion performance to deteriorate because of micro-cathodic effects. Thus the aged sample with the largest volume fraction of precipitates exhibits the worst corrosion resistance (4.65 ± 0.01 ⁄ / ).