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Direct comparisons are made between the crystallographic texture and residual stress distribution within two otherwise identical Inconel cubes produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) additive manufacturing processes. In both respects, significant differences were observed; the SLM process produced a sample with high residual stress and cubic texture, while the EBM process generated negligible residual stress and a fibre texture. In the case of the SLM sample, the paper continues on to examine two different approaches to modelling the residual stress field; 1. a simplistic version based on an assumed radially symmetric isotropic eigenstrain, and 2. a layer-by-layer combined thermo-mechanical approach based on finite element modelling. Both models were able to capture the important overall features of the residual stress distribution, however the layer-by-layer approach showed more fidelity in the finer details. • Residual stress and crystallographic texture from two 3D printing processes for inconel-718 samples are compared (SLM vs EBM). • Significant residual stresses up to yield are observed from SLM while EBM produced no detectable residual stress. • SLM and EBM produced very different texture; 'Goss' texture in the SLM sample, fibre texture in the EBM sample. • Two residual stress modelling approaches were compared; 1. An empirical model, and 2. A mechanistic layer-by-layer approach. • Both models captured the overall distribution of stress; the layer-by-layer showed more fidelity to small details. [ABSTRACT FROM AUTHOR]

Protective coatings based on an Al-Al2O3 metal matrix composite (MMC) were sprayed using dynamic metallization (DM), a low-pressure cold spray variant. A series of samples approximately 1 mm in thickness were sprayed using different spray process parameters (temperature, velocity) and different feedstock powder compositions (Al, Zn, Al2O3). This resulted in MMCs of different phase compositions and slightly different physical conditions of coating formation. The through-thickness residual stresses that accumulate in coatings during the spray process were studied using neutron diffraction in all phases comprising the MMCs. The overall residual stress in the coating (macrostress) was compressive, which is in good agreement with the data on residual stress observed in other cold spray coatings, accumulating as a result of the peening process. However, due to the slightly elevated spray temperature characteristic of DM in comparison with other cold spray variants, thermal stresses are also present and play an equally important role in the accumulation of residual stress in each phase. Because of the multi-phase composition and thermal mismatch between the metal and ceramic components of the MMC, inter-phase microstresses also accumulate. A micro-mechanical explanation of the observed tensile microstress in Al/Zn versus compressive stress in Al2O3 is proposed. [ABSTRACT FROM AUTHOR]

Abstract: In this work a heat treatment procedure was performed on laser clad Ti–6Al–4V, which resulted in a reduction of tensile residual stresses in the clad samples as well and a decrease in the hardness of the clad layer with an increasing heat treatment time. The reduction in the residual stress was attributed to inter-phase stress relaxation brought about by the growth of the β phase. The reduction in hardness was attributed to an increase in the volume fraction of the soft β phase. Both the reduction in residual stress and hardness due to this heat treatment makes it an attractive method to heat treat both laser clad and additively manufactured Ti–6Al–4V components for improved mechanical properties. [Copyright &y& Elsevier]

Abstract: Al and Al alloy cold spray coatings were deposited on Mg substrates using two different cold spray systems – a Kinetic Metallization system (convergent barrel, sonic nozzle) and a CGT system (convergent-divergent barrel, supersonic nozzle). The residual stress profiles in the coatings were measured using neutron diffraction with high spatial resolution. In the first part of the study, the residual stress profile in pure Al coatings was compared when sprayed using the Kinetic Metallization system (using both helium and nitrogen as the driving gas), and with the CGT system using nitrogen gas. In this way the effect of impact velocity and process temperature was studied. In the second part of the study, the residual stress profile was compared in coatings of pure Al, 7075 Al and 6061 Al sprayed using the same process conditions in the CGT system. The residual stress profiles depend more on the alloy content, i.e. intrinsic resistance to plastic deformation, than on the processing conditions, and this is interpreted using a simple model that incorporates the effect of peening stresses in the cold spray process. [Copyright &y& Elsevier]

When neutron diffraction is used to measure residual stresses, estimates of the unstressed lattice spacing (d0) are often required. These are generally measured on a sample that is considered representative of the component. In the case of welded samples, the possibility of variation in weld shape between the d0 sample and the area where stresses are determined must be taken into account. To assess this, d0 values are measured on an area considered representative of the sample, and then are re-measured on a sample cut from the actual strain measurement plane. The residual stresses are re-calculated with these new d0 values and the results compared to those based on the initial d0 measurement. Methods of estimating these errors are discussed. The errors in residual stress that arise from the spatial variation of d0 values are greater than the commonly reported peak fitting errors. These errors can be estimated and should be included in the reported residual stress measurements. Cutting a d0 sample from the measurement plane makes this a destructive technique. [ABSTRACT FROM PUBLISHER]

Abstract: The residual stress profiles in Cu and Al coatings cold sprayed using kinetic metallization have been studied using neutron diffraction. To interpret results and to describe them quantitatively, the measured profiles were fit to Tsui and Clyne’s progressive coating deposition model, which demonstrated that the residual stresses are largely due to kinetic and not thermal effects. The residual stress state of the coatings was found to depend mainly on the deformation behaviour and properties of the coating material, and the kinetic parameters of the cold spray process. Young’s modulus and impact strain were measured and used along with published material data for Cu and Al to approximate the residual stresses, using a model developed for shot peening. The properties of the Cu coatings such as Young’s modulus and porosity were found to be closer to their bulk values than in the case of the Al coatings, and this was related to the amount of particle deformation on impact. [Copyright &y& Elsevier]

In making residual stress measurements in welds, a common problem is that the samples are often cut before measurement, which may alter the stresses. To estimate the effects of cutting, a simplified method of modelling residual stresses in welds was developed, known as chill modelling, which requires limited material data and no welding process data. The method can be performed with elastic finite element analysis. The method does not predict the value of the stresses, just the relative reduction that occurs after cutting. The method was validated against published synchrotron measurements of welded plates, which were cut and remeasured a number of times. For welded plates only, an empirical equation was developed that predicts the change in stress after cutting. [ABSTRACT FROM AUTHOR]

In this study two types of laser surface treatment, laser surface melting and laser processing, were used to treat the surface of as cast Nickel-Aluminium Bronze. The two treatments were then subjected to cavitation erosion testing and were compared against as-cast Nickel-Aluminium Bronze. While the cavitation performance of the two types of laser surface treatment was equivalent, the morphology of the eroded surfaces was different. Several materials characterisation techniques including neutron diffraction for residual stress measurements and SEM were used to explain why the two eroded surfaces were different. It was found that the tensile residual stresses in the laser melted sample weakened the sample, which negated its superior strength when compared with the laser processed sample. It was also observed that the erosion and pitting in the laser melted sample were deeper and they were attributed to the tensile residual stresses accelerating the attack at grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: A new connection to an existing gas pipeline was made by hot-tapping, welding directly onto a pressurised pipeline. The welds were not post-weld heat treated, causing significant residual stresses. The critical weld had residual stresses determined by neutron diffraction using ANSTO''s residual stress diffractometer, Kowari. The maximum measured residual stress (290 MPa) was 60% of the yield strength. The magnitudes of errors from a number of sources were estimated. An integrity assessment of the welded branch connection was performed with the measured residual stress values and with residual stress distributions from the BS 7910 and API 579 analysis codes. Analysis using estimates of residual stress from API 579 overestimated the critical crack size. [Copyright &y& Elsevier]

Abstract: Residual stresses in gas pipelines come from forming operations in producing the coil and pipe, seam welding the pipe, and girth welding pipes together to form a gas pipeline. Welding is used extensively in gas pipelines, the welds are made without post weld heat treatment. The three normal stresses were measured by neutron diffraction for three types of sample: coil, unwelded rings cut from the pipe made from this coil, and girth welded rings cut from linepipe. All three specimens came from three thicknesses of manufacture (5.4, 6.4, and 7.1mm). The welds are manual metal arc cellulosic electrode welds made in X70 linepipe, these were measured at 5 through-thickness positions at 19 locations (from the center of the weld up to 35mm away from the weld) with a spatial resolution of 1mm3. The coil and unwelded rings were measured at the same five through-thickness positions. [Copyright &y& Elsevier]

Abstract: The current paper presents a finite element simulation of the residual stress field associated with a three pass slot weld in an AISI 316LN austenitic stainless steel plate. The simulation is split into uncoupled thermal and mechanical analyses which enable a computationally less expensive solution. A dedicated welding heat source modelling tool is employed to calibrate the ellipsoidal Gaussian volumetric heat source by making use of extensive thermocouple measurements and metallographic analyses made during and after welding. The mechanical analysis employs the Lemaitre–Chaboche mixed hardening model. This captures the cyclic mechanical response which a material undergoes during the thermo-mechanical cycles imposed by the welding process. A close examination of the material behaviour at various locations in the sample during the welding process, clearly demonstrates the importance of defining the correct hardening and high temperature softening behaviour. The simulation is validated by two independent diffraction techniques. The well-established neutron diffraction technique and a very novel spiral slit X-ray synchrotron technique were used to measure the residual stress–strain field associated with the three-pass weld. The comparison between the model and the experiment reveals close agreement with no adjustable parameters and clearly validates the used modelling procedure. [Copyright &y& Elsevier]