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M. E. Fitzpatrick - One of the best experts on this subject based on the ideXlab platform.

  • Residual Strain and Fracture Response of Al_2O_3 Coatings Deposited via APS and HVOF Techniques
    Journal of Thermal Spray Technology, 2012
    Co-Authors: R. Ahmed, N. H. Faisal, A. M. Paradowska, M. E. Fitzpatrick
    Abstract:

    The aim of this investigation was to nondestructively evaluate the residual stress profile in two commercially available alumina/substrate coating systems and relate residual stress changes with the fracture response. Neutron diffraction, due to its high penetration depth, was used to measure residual strain in conventional air plasma-sprayed (APS) and Finer Powder high velocity oxy-fuel (HVOF (θ-gun))-sprayed Al_2O_3 coating/substrate systems. The purpose of this comparison was to ascertain if Finer Powder Al_2O_3 coatings deposited via θ-gun can provide improved residual stress and fracture response in comparison to conventional APS coatings. To obtain a through thickness residual strain profile with high resolution, a partially submerged beam was used for measurements near the coating surface, and a beam submerged in the coating and substrate materials near the coating-substrate interface. By using the fast vertical scanning method, with careful leveling of the specimen using theodolites, the coating surface and the coating/substrate interface were located with an accuracy of about 50 μm. The results show that the through thickness residual strain in the APS coating was mainly tensile, whereas the HVOF coating had both compressive and tensile residual strains. Further analysis interlinking Vickers indentation fracture behavior using acoustic emission (AE) was conducted. The microstructural differences along with the nature and magnitude of the residual strain fields had a direct effect on the fracture response of the two coatings during the indentation process.

  • Residual Strain and Fracture Response of Al_2O_3 Coatings Deposited via APS and HVOF Techniques
    Journal of Thermal Spray Technology, 2012
    Co-Authors: R. Ahmed, N. H. Faisal, A. M. Paradowska, M. E. Fitzpatrick
    Abstract:

    The aim of this investigation was to nondestructively evaluate the residual stress profile in two commercially available alumina/substrate coating systems and relate residual stress changes with the fracture response. Neutron diffraction, due to its high penetration depth, was used to measure residual strain in conventional air plasma-sprayed (APS) and Finer Powder high velocity oxy-fuel (HVOF (θ-gun))-sprayed Al_2O_3 coating/substrate systems. The purpose of this comparison was to ascertain if Finer Powder Al_2O_3 coatings deposited via θ-gun can provide improved residual stress and fracture response in comparison to conventional APS coatings. To obtain a through thickness residual strain profile with high resolution, a partially submerged beam was used for measurements near the coating surface, and a beam submerged in the coating and substrate materials near the coating-substrate interface. By using the fast vertical scanning method, with careful leveling of the specimen using theodolites, the coating surface and the coating/substrate interface were located with an accuracy of about 50 μm. The results show that the through thickness residual strain in the APS coating was mainly tensile, whereas the HVOF coating had both compressive and tensile residual strains. Further analysis interlinking Vickers indentation fracture behavior using acoustic emission (AE) was conducted. The microstructural differences along with the nature and magnitude of the residual strain fields had a direct effect on the fracture response of the two coatings during the indentation process.

Rahmi Unal - One of the best experts on this subject based on the ideXlab platform.

  • the influence of the pressure formation at the tip of the melt delivery tube on tin Powder size and gas melt ratio in gas atomization method
    Journal of Materials Processing Technology, 2006
    Co-Authors: Rahmi Unal
    Abstract:

    Abstract The production of metal Powder using gas atomization technique is a wide spread process for manufacturing a wide range of spherical metal Powder alloys. Metal Powder properties generally improve with smaller Powder particle size. Close-coupled atomizers are of great interest and controlling their performance parameters is critical for metal Powder producing industries. In this study a new designed close-coupled nozzle system was used to produce tin Powder to investigate the effect of the protrusion length of the melt delivery tube on the pressure formation at the melt tip. Observed improvement in particle refinement cannot be directly attributed to an increase in atomizing pressures and gas kinetics. Results from this study indicated that the observed metal flow rate was not behaving as what was earlier assumed, namely that, deeper aspiration enhanced metal flow rate. The melt flow rate was reduced with increasing the atomizing gas pressure. So that gas to melt mass flow ratio was increased for the same protrusion length and this ratio increase caused the Finer Powder particle size.

R. Ahmed - One of the best experts on this subject based on the ideXlab platform.

  • Residual Strain and Fracture Response of Al_2O_3 Coatings Deposited via APS and HVOF Techniques
    Journal of Thermal Spray Technology, 2012
    Co-Authors: R. Ahmed, N. H. Faisal, A. M. Paradowska, M. E. Fitzpatrick
    Abstract:

    The aim of this investigation was to nondestructively evaluate the residual stress profile in two commercially available alumina/substrate coating systems and relate residual stress changes with the fracture response. Neutron diffraction, due to its high penetration depth, was used to measure residual strain in conventional air plasma-sprayed (APS) and Finer Powder high velocity oxy-fuel (HVOF (θ-gun))-sprayed Al_2O_3 coating/substrate systems. The purpose of this comparison was to ascertain if Finer Powder Al_2O_3 coatings deposited via θ-gun can provide improved residual stress and fracture response in comparison to conventional APS coatings. To obtain a through thickness residual strain profile with high resolution, a partially submerged beam was used for measurements near the coating surface, and a beam submerged in the coating and substrate materials near the coating-substrate interface. By using the fast vertical scanning method, with careful leveling of the specimen using theodolites, the coating surface and the coating/substrate interface were located with an accuracy of about 50 μm. The results show that the through thickness residual strain in the APS coating was mainly tensile, whereas the HVOF coating had both compressive and tensile residual strains. Further analysis interlinking Vickers indentation fracture behavior using acoustic emission (AE) was conducted. The microstructural differences along with the nature and magnitude of the residual strain fields had a direct effect on the fracture response of the two coatings during the indentation process.

  • Residual Strain and Fracture Response of Al_2O_3 Coatings Deposited via APS and HVOF Techniques
    Journal of Thermal Spray Technology, 2012
    Co-Authors: R. Ahmed, N. H. Faisal, A. M. Paradowska, M. E. Fitzpatrick
    Abstract:

    The aim of this investigation was to nondestructively evaluate the residual stress profile in two commercially available alumina/substrate coating systems and relate residual stress changes with the fracture response. Neutron diffraction, due to its high penetration depth, was used to measure residual strain in conventional air plasma-sprayed (APS) and Finer Powder high velocity oxy-fuel (HVOF (θ-gun))-sprayed Al_2O_3 coating/substrate systems. The purpose of this comparison was to ascertain if Finer Powder Al_2O_3 coatings deposited via θ-gun can provide improved residual stress and fracture response in comparison to conventional APS coatings. To obtain a through thickness residual strain profile with high resolution, a partially submerged beam was used for measurements near the coating surface, and a beam submerged in the coating and substrate materials near the coating-substrate interface. By using the fast vertical scanning method, with careful leveling of the specimen using theodolites, the coating surface and the coating/substrate interface were located with an accuracy of about 50 μm. The results show that the through thickness residual strain in the APS coating was mainly tensile, whereas the HVOF coating had both compressive and tensile residual strains. Further analysis interlinking Vickers indentation fracture behavior using acoustic emission (AE) was conducted. The microstructural differences along with the nature and magnitude of the residual strain fields had a direct effect on the fracture response of the two coatings during the indentation process.

Yvonne Durandet - One of the best experts on this subject based on the ideXlab platform.

  • the influence of stellite 6 particle size on the inter track porosity in multi track cladding
    Surface & Coatings Technology, 2006
    Co-Authors: Shoujin Sun, Milan Brandt, James G Harris, Yvonne Durandet
    Abstract:

    The formation of multi-track laser cladding of stellite 6 with different particle size on mild steel was carried out with different geometry profiles and levels of dilution in the single-track clad in order to examine the influence of particle size on clad geometry and inter-track porosity. The clad area and total area including clad area, the remelted area of previous track and substrate melted area in each track were measured. Both clad area and total area increase with track number and finally reach steady values, but the increase in total area is much greater than that in clad area. The remelted area of previous track increases with the level of dilution of the single-track clad and reaches the maximum value when the dilution of single-track clad is over 20%. The percentage of the maximum remelted area of the previous track equals the percentage of the track overlap. The steady values of these areas are given by empirical analysis. The inter-track porosity will appear when the difference between the total area and the remelted area of the previous track is closer to or smaller than the clad area because there is insufficient laser energy to melt the Powder captured by the melt pool. The tendency for inter-track porosity formation is higher in laser cladding with Finer Powder due to its smaller total area. A new criteria based on the single-track clad geometry for specific stellite Powder is proposed to determine the appearance of inter-track porosity.

Olivier Guillon - One of the best experts on this subject based on the ideXlab platform.

  • direct comparison between hot pressing and electric field assisted sintering of submicron alumina
    Acta Materialia, 2009
    Co-Authors: Jochen Langer, Michael J Hoffmann, Olivier Guillon
    Abstract:

    Abstract This study compares hot pressing (HP) and the electric field-assisted sintering technique (FAST) of two different electrically insulating Al2O3 submicron Powders with median particle sizes of 150 and 500 nm. Sample geometry, heating schedule, applied pressure and atmosphere were identical for both sintering methods. The densification behavior and characterization of the microstructure revealed that FAST sintered samples reached a higher density compared with HP, in particular for the Finer Powder. It was found that an increase in dwell time was required to reach the same final density by HP. However, analysis of the sintering curves showed that the densification mechanism for both sintering methods was grain boundary diffusion. Increasing the heating rate up to 150 K min−1 did not modify the densification mechanism. The sintering trajectory showed that the grain size was only dependent on density and was insensitive to the sintering method, in addition to showing a lack of preferential grain orientation.