Necsa Ltd

Pretoria, South Africa

Necsa Ltd

Pretoria, South Africa
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News Article | May 16, 2017

The South African Nuclear Energy Corporation (Necsa) and French electric utility company Electricité de France (EDF) have signed a memorandum of understanding (MoU) to advance training of and development of technical skills and, for the continuous education and training of technicians, in the nuclear energy sector. The MoU will steer the development of South Africa’s resources, through the design of training courses, the coaching of instructors and the development of the training infrastructure required to efficiently educate the technicians for nuclear energy projects. Necsa and EDF will also collaborate on the development of the required network of institutes at technical and vocational education and training colleges in South Africa, with relevant connections to international institutes. Further, some technicians will receive on the job training in certain EDF facilities for selected technical positions.

Oladijo O.P.,University of Witwatersrand | Sacks N.,University of Witwatersrand | Cornish L.A.,University of Witwatersrand | Venter A.M.,NECSA Ltd
International Journal of Refractory Metals and Hard Materials | Year: 2012

WC-17 wt.% Co coatings were deposited using high velocity oxy-fuel (HVOF) spraying onto four different substrate materials, namely aluminium, brass, 304 stainless steel and super-invar. These substrates have different coefficients of thermal expansion which have been shown to influence the final coating microstructural properties. The abrasive wear properties of the coatings were characterised using an ASTM-G65 three body abrasive wear machine with silica sand as the abrasive. The highest mass loss was recorded for the coating on the aluminium substrate whilst the coated 304 stainless steel showed the lowest mass loss. The coatings on brass and super invar experienced similar mass losses. SEM studies of the worn surfaces showed preferential removal of the Co binder phase as well as cracking and rounding of the carbide grains. The differences in wear behaviour may be attributed to the presence of residual stresses where the highest compressive residual stress led to the highest wear rate. The coatings deposited onto brass showed compressive stresses whilst those deposited onto super-invar had tensile stresses, yet these two coatings had similar wear rates. Thus further study is required to provide conclusive evidence of the role of residual stresses on the abrasion resistance of these coatings. © 2012 Elsevier Ltd. All rights reserved.

Oladijo O.P.,University of Witwatersrand | Venter A.M.,NECSA Ltd | Cornish L.A.,University of Witwatersrand
International Journal of Refractory Metals and Hard Materials | Year: 2014

This investigation had been conducted to determine the influence of residual stresses on the abrasive wear resistance of HVOF thermal spray WC-17 wt.% Co coatings, as well as to derive stress relaxation after cutting by wire electric discharge machining (EDM). The abrasive wear properties of the coatings were characterised using an ASTM-G65 three body abrasive wear machine with silica sand as the abrasive. The residual stress was measured by means of X-ray diffraction techniques, on the coated samples before and after the abrasive wear tests. Compressive residual stresses were observed in the surface layer of the large coated samples. However, stress relaxation results after cutting into small sizes were distinctly different. There was strong correlation between residual stresses in the surface layer and abrasive wear resistance, as well as yield strength of a material. © 2014 Elsevier Ltd.

Venter A.M.,Necsa Ltd | Venter A.M.,University of Witwatersrand | Oladijo O.P.,University of Witwatersrand | Luzin V.,Australian Nuclear Science and Technology Organisation | And 2 more authors.
Thin Solid Films | Year: 2013

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.

Oladijo O.P.,University of Witwatersrand | Oladijo O.P.,NECSA Ltd | Venter A.M.,University of Witwatersrand | Venter A.M.,NECSA Ltd | And 2 more authors.
Surface and Coatings Technology | Year: 2012

Investigation of the residual stresses and microstructural properties associated with HVOF thermal spray coating of WC-17wt% Co of same thickness on three substrates with coefficients of thermal expansion different to that of WC. The residual stresses were measured by X-ray diffraction sin 2ψ techniques using CoKα radiation. The results indicated residual stresses that have different natures for the as-sprayed coatings despite using the same powder as feedstock. The magnitudes of the stresses in the as-sprayed condition are low. © 2012 Elsevier B.V.

Venter A.M.,Necsa Ltd | Luzin V.,Australian Nuclear Science and Technology Organisation | Hattingh D.G.,Nelson Mandela Metropolitan University
Materials Science Forum | Year: 2014

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 nondestructively 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, Switzerland.

Taran Y.,Joint Institute for Nuclear Research | Balagurov A.M.,Joint Institute for Nuclear Research | Sabirov B.,Joint Institute for Nuclear Research | Davydov V.,Paul Scherrer Institute | Venter A.M.,NECSA Ltd
Materials Science Forum | Year: 2014

Recently, reliable and hermetic joining of stainless steel to niobium pipes has been achieved with the explosive bonding technique. Joining of these two materials are essential to ensure production of a bimetallic transition element of pipe-type for its further use as a part of charged beam acceleration systems of the new generation. A non-destructive neutron diffraction investigation of the tri-axial strains along a radial cross-sectional line through the joint section has been performed. Residual stress results indicate inherently different natures in the residual stress values within the respective pipe sections. In the external stainless steel pipe the residual stresses are tensile, showing a sudden increase to 600 MPa as the interface is approached, whilst being compressive in the internal niobium pipe, not exceeding 650 MPa. A characteristic abrupt stress discontinuity exits at the interface region. © (2014) Trans Tech Publications, Switzerland.

Sumin V.V.,Joint Institute for Nuclear Research | Papushkin I.V.,Joint Institute for Nuclear Research | Vasin R.N.,Joint Institute for Nuclear Research | Venter A.M.,NECSA Ltd | Balagurov A.M.,Joint Institute for Nuclear Research
Journal of Nuclear Materials | Year: 2012

Results of neutron diffraction studies of crystallographic texture and residual stress tensor components in cold-worked and annealed cylindrical components made from E-110 zirconium alloy are presented. Those components are used as plugs in the fuel elements of the VVER-type reactors; the resident residual stresses influence the durability and safety of the fuel elements. The experiments were carried out on the neutron diffractometers at Dubna (the IBR-2 pulsed reactor) and Berlin Helmholtz-Zentrum (the BER II research reactor). It is shown that the samples have fiber texture that is changed considerably with annealing. The type I residual stress tensors for both samples were calculated by the BulkPathGEO model. The cold worked component has 136-166 MPa tensile residual stress in the radial direction and zero stress along the axial direction. Residual stress values in the annealed component are close to zero. © 2011 Elsevier B.V. All rights reserved.

Jun T.-S.,University of Oxford | Venter A.M.,Necsa Ltd | Korsunsky A.M.,University of Oxford
Experimental Mechanics | Year: 2011

This paper deals with the analysis of elastic strain and eigenstrain in non-uniformly shaped shot-peened 17-4PH stainless steel samples. Based on residual strain measurements by synchrotron X-ray diffraction, the finite element (FE) models are established for the inverse problem of eigenstrain analysis in slice conical sample. The eigenstrains obtained in the slice are then implemented into the FE model of the solid conical sample. It is found that the dependence of elastic strain distributions on the peening intensity and sample shape/thickness could be elucidated via the understanding of underlying permanent strain, or eigenstrain. The effect of the peening process is therefore best described in terms of the induced eigenstrain. The proposed framework is useful for the predictive modelling of residual stresses in non-uniformly shaped shot-peened materials, in that it allows efficient reconstruction of complete residual stress states. In addition, it provides an excellent basis for developing predictive tools for in service performance and design optimisation. © 2010 Society for Experimental Mechanics.

Ntsoane T.P.,NECSA Ltd | Topic M.,IThemba Laboratory | Bucher R.,IThemba Laboratory
Powder Diffraction | Year: 2011

Coatings of plasma sprayed hydroxyapatite (HAp), incubated in simulated body fluid for periods varying from 1 to 56 days, were characterized using conventional laboratory X rays. Quantitative phase analysis, employing TOPAS software, showed an opposite trend in the two main phases of the coating, viz., HAp and tetracalcium phosphate (TTCP). The former increased within the first 7 days of incubation whilst the latter decreased during the same period; both phases stabilized with further incubation. The crystallinity of the coatings exhibited a trend similar to that of HAp i.e., an increase in the early stages of incubation stabilization with further incubation. Results of residual stress determined with Bruker's D8 Discover and analyzed with LEPTOS software, showed both the normal stress tensor components, σ11 and σ22, to be tensile, relaxing significantly in the early stages of incubation before stabilizing with further incubation. © 2011 International Centre for Diffraction Data.

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