Browsing by Author "Venter, AM"

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    Benchmarking studies of the MPISI material science diffractometer at SAFARI-1
    (Materials Research Forum LLC, 2016-07-03) Venter, AM; Marais, D; Luzin, V
    The measurement performance of the new material science instrument MPISI at the SAFARI-1 research reactor in South Africa has been comprehensively benchmarked for strain scanning applications. In addition to the traditional VAMAS Ring and Plug specimen, the benchmarking was extended to a project that required sub-millimeter spatial resolution. For the latter the MPISI performance has been compared with experimental investigations on the same sample set at the KOWARI instrument at ANSTO. Overall, good data quality and agreement have been observed between the two instruments.© The Authors
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    Performance characterization of metallic substrates coated by HVOF WC-Co
    (Elsevier, 2013-12-31) Venter, AM; Oladijo, OP; Luzin, V; Cornish, LA; Sacks, N
    Integral to the performance of high-velocity oxygen-fuel (HVOF) coatings is the thermo-mechanical interaction associated with the thermal misfit, or differences in thermal expansion coefficients (CTEs), between coating and substrate. This investigation reports results on the microstructures, chemical phase content, coating–substrate misfit residual stress, and wear resistance. For this purpose a systematic characterization of WC–Co sprayed coatings on a number of substrates covering a range of CTE values were pursued for both the as-coated and heat-treated conditions. The neutron diffraction technique in conjunction with sub-millimeter sized gauge volumes enabled depth-resolved studies of the stress in the coatings and substrates by paying special attention to the determination of the stress contribution attributed by the final spray process. In the as-coated condition the stress values in the coatings were compressive for CTEs larger than that of WC–Co and tensile for CTE lower than WC–Co. Wear resistance increased for increased compressive stress and macrohardness. In the heat-treated condition, this trend became enhanced due to increased compressive stress in the coatings. © 2013, Elsevier B.V.
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    Quantum critical behaviour in the (Cr97.8Si2.2)(100-y)Moy alloy system
    (American Institute of Physics, 2013-05-07) Sheppard, CJ; Prinsloo, ARE; Fernando, PR; Venter, AM; Strydom, AM; Peterson, VK
    The Cr-Si system offers an ideal reference alloy as a case study to follow the evolution of the well-known first-order magnetic transition in dilute Cr-Si by doping with Mo, which is iso-electronic with Cr. This alloy system, in addition, then also offers the opportunity to search for effects of quantum criticality (QC) associated with the process of driving the Neel transition temperature (T-N) to zero. Previous investigations on the ternary (Cr97.8Si2.2)(100-y)Mo-y alloy system (0 <= y <= 9) indicated possible quantum critical behaviour at a critical concentration y(c) approximate to 3.8. The present paper extends these studies to additional concentrations in the alloy series, as well as to explore key indicators of QC, such as Hall coefficient (R-H) and magnetic susceptibility (chi) measurements. Recent results indicate the possible existence of two critical points in the (Cr97.8Si2.2)(100-y)Mo-y alloy system. The first critical point at y(c1) is postulated to be related to the concentration where the first-order transition gives way to a second-order-like continuous magnetic phase transition. Behaviour normally associated with QC is observed at the second critical concentration y(c2), accompanying a transition to paramagnetism. © 2013 American Institute of Physics.
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    Residual stresses associated with the production of coiled automotive springs
    (Trans Tech Publications, 2014-07-02) Venter, AM; Luzin, V; Hattingh
    Cold coiling of high tensile steel rod into helical coil springs for the automotive industry is a new technique being implemented amongst spring manufacturers worldwide. To characterise this coil production process, the neutron strain scanning technique has been employed to non-destructively elucidate the influence production stages have on the tri-axial residual stress state. Samples investigated represented key production steps in the cold-coil forming process: Cold coiling; Tempering; Hot setting; Hot peening; Shot peening. Investigations revealed that the stress field was axi-symmetrical, that the dominant variation in all samples occurred along the hoop direction (helical circumference), whilst the radial and axial stresses are substantially lower. Accurate two-dimensional stress maps of the rod cross section have been compiled revealing key features associated with the cold coiling step. Comparison of the stress fields after each production step revealed altered stress values. The final shot peening process stage not only reduced stress concentrations at the internal bore, but contributed to the establishment of favourable surface residual stress conditions that enhance the fatigue life of the final product. © 2014, Trans Tech Publications.
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    Study of interactive stresses in thin WC-Co coating of thick mild steel substrate using high-precision neutron diffraction
    (Trans Tech Publications Ltd, 2012-11-21) Venter, AM; Luzin, V; Oladijo, OP; Cornish, LA; Sacks, N
    Investigations of interaction residual stresses between thin WC-Co surface coated layers on thick mild steel substrates have successfully been performed with neutron diffraction. This systematic approach was conducted on the reference grit-blasted substrates and their HVOF coated WC-Co products. Using a sub-millimeter gauge volume, precisely positioned, the stress gradient through the coated and non-coated substrates were determined and used to derive the coating stress condition prevailing in the thin coating by applying the stress balance (Stoney) approach. In addition, the average stress in each 200 μm thick coating was measured directly with very good agreement obtained between the calculated and measured stress values. Investigations were extended to determine the thermal nature of the residual stresses by studying the annealed counterpart samples as well to follow the evolution of the residual stress upon annealing. © 2014, Trans Tech Publications.