Browsing by Author "Wong, YC"

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    The effect of laser cladding deposition rate on residual stress formation in Ti-6Al-4V clad layers
    (Trans Tech Publications, 2012-08) Cottam, R; Thorogood, KJ; Lui, Q; Wong, YC; Brandt, M
    The effect of deposition rate on the residual stresses formed during the laser cladding of Ti-6Al-4V powder onto a Ti-6Al-4V substrate was investigated. To isolate the deposition rate from the heat input an analytical laser cladding model was employed to control the melt pool depth to 0.1mm. The clad height was also held constant by the model at 1mm. The laser traversing speed was varied between 300 and 1500 mm/min. The residual stresses were measured using the contour method and it was found that the distribution of residual stress was similar for the different deposition rates and that there was a small variation in the tensile stress level reached in the clad and heat affected zone (HAZ) layer. The microstructures for all three clad layers were a’ martensite and the size of the HAZ was consistent from sample to sample. It was concluded that residual stress development is independent of deposition speed for the laser cladding of Ti-6Al-4V. © 2025 Trans Tech Publications Ltd.
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    Evaluation of residual stress in SPR joint by neutron diffraction
    (Trans Tech Publication Inc., 2012-01-01) Haque, R; Beynon, JH; Kirstein, O; Wong, YC; Durandet, Y
    The feasibility of measuring residual stresses in Self-Pierce Riveted (SPR) joints by neutron diffraction was evaluated in this study. Despite the small dimensions involved, meaningful results were obtained. It was observed that residual stress in the rivet head was higher in the centre and lower at the edge. For the SPR joints examined, the maximum value of residual stress evaluated was 550MPa, compressive and occurred in the rivet leg. Stresses in material adjacent to the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. The results are discussed with respect to the physical events involved during SPR. © 2011, Trans Tech Publications
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    Investigation into heat treatment and residual stress in laser clad AA7075 powder on AA7075 substrate
    (Springer US, 2013-06-04) Cottam, R; Luzin, V; Liu, Q; Wong, YC; Wang, J; Brandt, M
    The laser cladding of AA7075 powder onto a AA7075 substrate was conducted to evaluate the effect of heat treatment and to measure residual stress between the clad layer and substrate to better understand the effect of laser cladding. The microstructure formed in the clad region was characteristic of a high cooling rate, which is typical for laser cladding. The heat-affected zone (HAZ) showed coarser precipitates when compared with the substrate and was attributed to the heating from the laser. A solution heat treatment followed by aging was employed to restore the strength in the HAZ. Nanohardness traverses of the clad and substrate was performed and it was shown the hardness in the 7075 clad layer was lower than the substrate both pre- and post-heat treatment and was attributed to the vaporization of zinc and magnesium. Neutron diffraction was employed to measure the residual stress both before and after heat treatment. The residual stresses formed in the clad layer were tensile and about 50 MPa in magnitude; heat treatment increased the stress level to approximately 100 MPa. © 2013, Springer.
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    Neutron diffraction studies of advanced tool steels
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Doyle, ED; Wong, YC; Ripley, MI
    Martensitic stainless steels, based around AISI 420 grade, are being increasingly specified for the production of small to medium sized moulds, which are used to manufacture high value-added plastics components for use in the automotive and food packaging industries. However, the increasing complexity of modern die design is leading to an increased incidence of mould failure due to (a) fracture as a consequence of the build-up of high residual stresses during heat treatment and (b) stress corrosion cracking in water channels. The response of the international steel industry has been to introduce modified grades of AISI 420 to overcome these problems. However, there have been no reports to date of the effect of such modification on the generation of residual stress as a function of key heat treatment parameters. ln the present study, neutron diffraction was used to identify the bulk residual stress distribution as a function of the quench rates in high pressure vacuum heat treatment for two different grades of AISI 420. Details of the results plus their analysis in terms of hardenability of the steels will be presented and discussed in the paper. © 2005 The Authors
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    Optimising parameters for meaningful measurement of residual strain by neutron diffraction in self-pierce riveted joints
    (Maney Publishing, 2013-11-18) Haque, R; Durandet, Y; Wong, YC; Paradowska, AM; Beynon, JH; Blacket, S
    The aim of this work is to examine the uncertainties involved in measuring residual strain and their dependence on both the gauge volume of the neutron beam and the acquisition time in self pierce riveted (SPR) joints while using the neutron diffraction technique. The main challenge involved dealing with the very small dimensions of SPR joints and developing optimum instrument configuration that allowed faster and/or more accurate stress measurement in SPR while maintaining the same time resolution required for the millimetre scale of the problem. Two different gauge volumes were used (0.125 and 1.0 mm(3)), and two different measuring directions were chosen in order to examine the rotational accuracy of the sample table. All measurements were conducted in steel–steel joints. Even though small sizes were involved, meaningful results were obtained and measurement errors were reduced by optimising the instrument parameters. © 2013, Maney Publishing
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    Residual stress profiles in riveted joints of steel sheets
    (Taylor and Francis, 2014-12-28) Haque, R; Wong, YC; Paradowska, AM; Durandet, Y
    The residual stress profiles in two different self-piercing riveted (SPR) joints were characterised using the neutron diffraction technique. The joints were produced using semi-tubular steel rivets and carbon steel sheets of different thicknesses and hardnesses. The residual stress in the sheet material inside the bore of the rivet was compressive at the centre and the stress became tensile away from the centre. The stresses found in the semi-tubular rivet were compressive, with a lower magnitude in the rivet head compared with those in the rivet leg. For the SPR joints examined, the compressive residual stress in the rivet leg was greater for the thin joint than the thick joint, and this was due to the higher force gradient encountered during the rivet flaring stage. The originality of this work was to relate the residual stress profile to the physical event that occurred during the SPR process. © 2021 Informa UK Limited
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    The role of metallurgical solid state phase transformations on the formation of residual stress in laser cladding and heating
    (Trans Tech Publications, 2014-02) Cottam, R; Luzin, V; Thorogood, KJ; Wong, YC; Brandt, M
    There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress. © 2014 Trans Tech Publications.
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    The role of microstructural characteristics in the cavitation erosion behaviour of laser melted and laser processed nickel–aluminium bronze
    (Elsevier, 2014-09-01) Cottam, R; Luzin, V; Moody, H; Edwards, DP; Majumdar, A; Wong, YC; Wang, J; Brandt, M
    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. © 2014, Elsevier B.V.
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    The role of microstructure in the stress relaxation and tempering of laser clad Ti–6Al–4V
    (Elsevier, 2014-04-17) Cottam, R; Luzin, V; Liu, Q; Mayes, E; Wong, YC; Wang, J; Brandt, M
    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.© 2014, Elsevier B.V.
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    SPR characteristics curve and distribution of residual stress in self-piercing riveted joints of steel sheets
    (Hindawi, 2017-02-15) Haque, R; Wong, YC; Paradowska, AM; Blacket, S; Durandet, Y
    Neutron diffraction was used to describe the residual stress distributions in self-piercing riveted (SPR) joints. The sheet material displayed a compressive residual stress near the joint, and the stress gradually became tensile in the sheet material far away from the joint. The stress in the rivet leg was lower in the thick joint of the softer steel sheet than in the thin joint of the harder steel sheet. This lower magnitude was attributed to the lower force gradient during the rivet flaring stage of the SPR process curve. This study shows how the residual stress results may be related to the physical occurrences that happened during joining, using the characteristics curve. The study also shows that neutron diffraction technique enabled a crack in the rivet tip to be detected which was not apparent from a cross-section. © 2017 Rezwanul Haque et al. This is an open access article distributed under the Creative Commons Attribution License