Browsing by Author "Spencer, K"

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    Analysis of the residual stress and bonding mechanism in the cold spray technique using experimental and numerical methods
    (Elsevier, 2014-08-15) Saleh, M; Luzin, V; Spencer, K
    In the current study, numerical solutions were used to simulate multi-particle deposition in the cold spray (CS) process, and to investigate some of the physical attributes of the deposition process of AA-6061-T6 particles deposited on an AA-6061-T6 substrate. Earlier experimental results are presented, with varying substrate and cladding combination; a subset of these results is analysed using single particle impact simulation, a more traditional approach in simulations of cold spray, and the smooth particle hydrodynamic (SPH) formulation to simulate multi-particle deposition. In a single particle impact simulation, a strong correlation between temperature and plastic deformation of the CS particles during the deposition process was found. The authors were able to correlate the onset of adiabatic shear instability with pronounced reduction in the flow stress with an inversely proportional relation exhibited for both temperature rise and plastic deformation. In the simulation of multiple particle impact, 400 particles, several bulk characteristics were extracted as through-thickness functions: density, equivalent plastic strain and stress profile. Stress profile from the simulation was contrasted against neutron diffraction measurements of residual stress, along with the analytical model of Tsui and Clyne, and is shown to achieve good correlation and providing validation of the results of simulations. Furthermore it was found that these stresses originate from a delicate balance between (a) the strain rate hardening and thermal softening and (b) the shot peening effects induced by the impact of CS particles. Analysis of particle morphologies in the simulation suggests a strong influence of temperature rise at the periphery of CS particles during deposition and dynamic recrystallization with the strong jetting of molten metal allowing for inter particle mixing and substrate adhesion. © 2014, Elsevier B.V.
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    Evaluation of the residual stress in the cold spray technique using smooth particle hydrodynamics modelling and neutron diffraction
    (Trans Tech Publications Ltd, 2014-02) Saleh, M; Luzin, V; Spencer, K
    Cold spray is a material deposition technique in which powdered metals are deposited onto metallic and glass substrates as a means of improving functionality, repair or protection of the underlying substrate. The residual stress that builds up in the material during spraying is closely linked to the coating’s integrity and the bonding mechanism. Neutron diffraction residual stresses measurements were carried out at the OPAL research reactor, ANSTO, using the KOWARI strain scanner to investigate an Al-6061 sample with a fine through-thickness resolution of 0.5 mm. The experimentally determined through thickness stress profiles of the macroscopically thick coatings were used to validate FE calculations made for 100 μm thick coatings using the Smooth Particle Hydrodynamics, SPH, techniques. A pronounced plastic strain gradient was apparent in the tested and modelled samples indicative of the significant residual macro-stresses which develop in the cladding/substrate during the deposition. Around the deposited particle’s periphery (in the jetting region) the temperatures are significant, this lends itself to the presence of grain refinement at the periphery of sprayed particles and the propagation of dynamic recrystallization which is closely coupled with the thermal softening of the particle. © 2014 Trans Tech Publications.
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    Residual stress and thermo-mechanical properties of cold spray metal coatings
    (Elsevier, 2011-02-01) Luzin, V; Spencer, K; Zhang, MX
    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.(C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.
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    Residual stress in coatings produced by cold spray
    (Trans Tech Publications, 2013-11-21) Luzin, V; Spencer, K; Zhang, M; Matthews, N
    Cold spray technology is used to produce metal coatings with a variety of functions, including surface corrosion protection, improvement of wear resistance, etc. Cold sprayed materials exhibit a wide range of behaviours resulting in large variation of spraying efficiency, coating properties, quality and performance in service. Residual stress, being a result and attribute of the deposition process, can be studied to test whether the coating is in tension/compression stress state and also to provide information about the thermo-mechanical history of the material during the deposition process. Residual stress distributions in a variety of coating materials have been studied by neutron diffraction. Through-thickness residual stress profiles show that the stress magnitude varies significantly and depends mainly on the mechanical properties of the coating material.
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    Residual stresses in cold spray Al coatings: the effect of alloying and of process parameters
    (Elsevier Science, 2012-05-25) Spencer, K; Luzin, V; Matthews, N; Zhang, MX
    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. © 2012, Elsevier Ltd.