Browsing by Author "Sacks, N"

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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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    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.