Neutron tomography methods applied to a nickel-based superalloy additive manufacture build

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

On the role of melt flow into the surface structure and porosity development during selective laser melting

In this study, the development of surface structure and porosity of Ti–6Al–4V samples fabricated by selective laser melting under different laser scanning speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The interaction between laser beam and powder particles was studied by both high speed imaging observation and computational fluid dynamics (CFD) calculation. It was found that at a high laser power and a fixed powder layer thickness (20 μm), the samples contain particularly low porosity when the laser scanning speeds are below 2700 mm/s. Further increase of scanning speed led to increase of porosity but not significantly. The porosity is even more sensitive to powder layer thickness with the use of thick powder layers (above 40 μm) leading to significant porosity. The increase of porosity with laser scanning speed and powder layer thickness is not inconsistent with the observed increase in surface roughness complicated by increasingly irregular-shaped laser scanned tracks and an increased number of discontinuity and cave-like pores on the top surfaces. The formation of pores and development of rough surfaces were found by both high speed imaging and modelling, to be strongly associated with unstable melt flow and splashing of molten material

Calculating the energy required to undergo the conditioning phase of a titanium alloy inertia friction weld

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

An Integrated Modeling Approach for Predicting Process Maps of Residual Stress and Distortion in a Laser Weld: A Combined CFD–FE Methodology

Laser welding has become an important joining methodology within a number of industries for the structural joining of metallic parts. It offers a high power density welding capability which is desirable for deep weld sections, but is equally suited to performing thinner welded joints with sensible amendments to key process variables. However, as with any welding process, the introduction of severe thermal gradients at the weld line will inevitably lead to process-induced residual stress formation and distortions. Finite element (FE) predictions for weld simulation have been made within academia and industrial research for a number of years, although given the fluid nature of the molten weld pool, FE methodologies have limited capabilities. An improvement upon this established method would be to incorporate a computational fluid dynamics (CFD) model formulation prior to the FE model, to predict the weld pool shape and fluid flow, such that details can be fed into FE from CFD as a starting condition. The key outputs of residual stress and distortions predicted by the FE model can then be monitored against the process variables input to the model. Further, a link between the thermal results and the microstructural properties is of interest. Therefore, an empirical relationship between lamellar spacing and the cooling rate was developed and used to make predictions about the lamellar spacing for welds of different process parameters. Processing parameter combinations that lead to regions of high residual stress formation and high distortion have been determined, and the impact of processing parameters upon the predicted lamellar spacing has been presented

The application of microstructure and property modelling to the prediction of forged component performance

A presentation on the application of microstructure and property modelling to the prediction of forged component performanc

Life prediction of thermal barrier coatings

A presentation on life prediction of thermal barrier coating

Modelling the Effect of Initial Heat-Treatment on the Creep of Multi- Modal Nickel Superalloys

Polycrystalline nickel superallyos used in aero-engine disc applications can often possess a bimodal gamma prime microstructure, for example in NI115 and Rene 80. During heat treatment and service the gamma prime distribution can evolve, with consequent effects on the creep behaviour. Here a modified LSW coarsening model is presented to model the effect of heat treatment and service conditions on the precipitate distribution. The distribution is then used in a physically-based, phenomenological creep model, based on the work of Dyson and McLean, to predict the effect of heat treatment on the creep behaviour. The results are compared to experiment for creep tests and heat treatments performed on NI115