Search

The spray forming of thick, dissimilar steel clad tubes with the objective of achieving a high integrity metallurgical bond across the cladding-substrate interface able to withstand residual stresses and subsequent thermo-mechanical processing was investigated by large scale experiments, modelling and extensive microstructural characterization including microscopy, X-ray tomography, neutron scattering and mechanical testing. The simulated residual stress distributions across the cladding-substrate interface, accounting for any as-sprayed porosity and the distribution of martensitic and retained austenite phases, were compared with neutron diffraction measurements and differences used to infer the load transfer behaviour and thus the mechanical integrity of the interface. The mechanical properties of the interfaces were then also measured directly by shear testing. The link between substrate pre-heating, the spray forming temperature, and the resulting preform temperature, porosity, phase fractions, residual stress, strength and integrity of the interface were established and quantified explicitly. [ABSTRACT FROM AUTHOR]

• Bulk CoCrFeMnNi high entropy alloy was fabricated by laser melting deposition. • The residual stress distribution was characterized using ND and FEM. • Residual stress decreases along the building direction. The dynamic thermal history during the laser melting deposition (LMD) process can induce significant residual stress that can lead to distortion and deteriorate functionality. The residual stress distribution in a bulk CoCrFeMnNi high entropy alloy with a single FCC phase and the dendritic structure fabricated by LMD process was studied using neutron diffraction and finite element modelling to reveal the effects of the thermal constraints, thermal cycles and temperature gradient along the deposition direction. Residual stress was found to decrease as the thermal gradient decreases along the building direction in the LMD process. [ABSTRACT FROM AUTHOR]

Highlights • A validated analytical-numerical model of the DED process is presented. • Finite element model uses realistic track geometry to predict residual stress and distortion. • A modified catchment efficiency was utilised in the analytical model to allow a more realistic approach to be implemented. • The maximum error for the peak temperature and residual stress was 3.1% and 18% respectively. Abstract Direct Energy Deposition (DED) is being increasingly used to repair high value components that have been damaged in-service. The uptake of DED and laser cladding operations for repair is inhibited by accurate modelling techniques. Often the repair process required is unique, therefore modelling techniques are necessary to determine the process inputs for the specific application. The DED process subjects the component to high thermal gradients resulting in high magnitude residual stresses and component distortion. Prediction of these parameters would reduce the need for costly experimental trials to quantify the repair strategy. Here, a single-track deposition of IN718, utilising a Nd:YAG laser source and coaxial nozzle, was modelled using a semi analytical-numerical approach. The track profile, temperature fields, melt pool geometry and stress evolutions were simulated for a constant set of process parameters. A corresponding experimental trial was conducted to validate the proposed model, through the use of focus variation microscopy, in-situ temperature measurements, optical micrographs and neutron diffraction measurements. A good correlation between the experimental and numerical data sets were apparent. The track profile was predicted with a maximum error of 1.98% and 0.43% for the width and height respectively. The maximum error for the peak temperature and residual stress was 3.1% and 18% respectively. Overall, the modelling strategy presented encompasses the key process variables, allowing accurate predictions of the thermal and mechanical effects of the process. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Direct Energy Deposition (DED) is being widely used to repair damaged components to increase service life and economical operation. Process parameters including laser power, traverse speed and the mass flowrate of the feedstock material may be adapted in-situ. This allows bespoke repair strategies to be devised to match the variability in the condition of the parts supplied that require repair; however, there are limited modelling techniques that allow the adaptive control within the DED process to be represented. In this study, a novel modelling strategy is presented which allows the DED process to be modelled in a transient state. This allows varying process parameters to be included in the model, to predict the transient track geometry and the associated thermomechanical effects of the process. Here, a single-track deposition of IN718 with a varying cross section has been modelled utilising the proposed approach. The modelling methodology was validated with a corresponding experimental study on a deposition made using a Nd:YAG laser source with a coaxial nozzle. An in-situ modification was generated by variation of the laser power. The track profile was compared against focus variation microscopy images and the thermomechanical portion of the model was validated through in-situ temperature measurements, micrographs and residual stress, obtained from neutron diffraction measurements. A good agreement between the predicted and experimental findings were observed. The track height and width were predicted with a maximum error of 6.5% and 7.6% respectively. The peak temperature and residual stress were predicted within 6.2% and 11.4% respectively. Overall, the modelling method presented will allow complex and bespoke multi parameter repair strategies to be rapidly developed. Image 1 • A validated analytical-numerical model of the adaptive DED process is presented. • Model predicts track geometry during transient regions of the process. • The maximum error for the track width and height was 5.1% and 12.5% respectively. • The maximum error for the peak temperature and residual stress was 6.2% and 11.4% respectively. [ABSTRACT FROM AUTHOR]

Additively manufactured intersections have the theoretical risk to contain hydrostatic tensile residual stresses, which eventually cannot be thermally stress relieved. The stresses in Ti-6Al-4V wire + arc additively manufactured (WAAM) intersections are lower compared to single pass walls and stresses in continuous walls are larger compared to discontinuous walls with otherwise identical geometry. Thermal stress relief was found to virtually eliminate them. Inter-pass rolling can yield the desired grain refinement, without having any noteworthy influence on the development of residual stresses. The strain measurement itself by neutron diffraction is facilitated by the refined microstructure, because the otherwise textured microstructure produces anisotropic peak intensity, not allowing Pawley refinement. Without rolling, the 10 1 ¯ 1 and 10 1 ¯ 3 family of hcp planes are the only ones that diffract consistently in the three principal directions. [ABSTRACT FROM AUTHOR]