The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
P.j Byrd - One of the best experts on this subject based on the ideXlab platform.
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An investigation into delamination mechanisms in inclined laser drilling of thermal barrier coated aerospace superalloys
Journal of Laser Applications, 2005Co-Authors: H. K. Sezer, Andrew J. Pinkerton, Lin Li, P.j ByrdAbstract:Thermal barrier coatings are widely used in aircraft engine hot-end components to protect the component materials from direct exposure to the damaging high temperatures. Effusion cooling techniques are widely used in these situations and laser drilling is normally employed to produce holes of less than 1.5 mm diameter in tough aerospace alloys coated with heat-resistant ceramics. In order to provide the essential cooling effects, a large proportion of these holes must be drilled at acute angles to the surface. During this low-angle laser drilling, microstructural damage of the thermal barrier coating may occur; this is highly undesirable as propagation of the delamination may occur in service, leading to premature failure of the coating. In this article, the role of melt ejection and the coaxial Assist Gas Jet in low angle laser drilling of a thermal barrier coated substrate is studied using a finite volume method. The work identifies the significant role of melt ejection in the formation of cracks and delamination at the coating/substrate interface on the leading edge of a laser-drilled cooling hole. The numerical model shows that the melt particles are accelerated towards the leading edge by the coaxial Assist Gas Jet, and as a result of molten metal flowing across the edge the damage through mechanical stresses and subsequent erosion is found to be more serious here than at the trailing edge. The higher shear stress found at the leading edge also implies higher viscous forces acting parallel to the free stream direction to overcome the bonding strength of the coating interface.Thermal barrier coatings are widely used in aircraft engine hot-end components to protect the component materials from direct exposure to the damaging high temperatures. Effusion cooling techniques are widely used in these situations and laser drilling is normally employed to produce holes of less than 1.5 mm diameter in tough aerospace alloys coated with heat-resistant ceramics. In order to provide the essential cooling effects, a large proportion of these holes must be drilled at acute angles to the surface. During this low-angle laser drilling, microstructural damage of the thermal barrier coating may occur; this is highly undesirable as propagation of the delamination may occur in service, leading to premature failure of the coating. In this article, the role of melt ejection and the coaxial Assist Gas Jet in low angle laser drilling of a thermal barrier coated substrate is studied using a finite volume method. The work identifies the significant role of melt ejection in the formation of cracks and de...
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The effect of Gas Jet and melt flow on laser drilling of thermal barrier coated nickel alloys
International Congress on Applications of Lasers & Electro-Optics, 2004Co-Authors: H. K. Sezer, P.j ByrdAbstract:Thermal Barrier Coating (TBC) is widely used in aircraft engine hot-ended components to protect the engine components from direct exposure to corrosive high temperatures. Cooling holes of less than 1.5mm diameter in tough heat resistant aerospace alloys, coated with high heat resistant ceramics is normally laser drilled for effusion cooling. A large proportion of these holes are drilled at acute angles from the surface in order to provide essential cooling effects. When low-angle laser drilling these TBC components, laser drilling-induced micro structural damage of the thermal barrier coating occurs. This is undesirable as the propagation of the delamination may occur in service, leading to failure of the coating. In this paper the role of melt ejection and coaxial Assist Gas Jet on laser drilling of TBC substrate is studied by using a numerical analysis based on finite volume simulation. The work has identified a significant role of meltejection on the formation of cracks and delamination at the coating/substrate interface on the leading edge. Findings with the model showed that the melt particles were accelerated towards the leading edge by the coaxial Assist Gas Jet. As a result of molten metal flowing across the leading edge, the damage through mechanical stresses and subsequent erosion was found more serious on the leading edge than the trailing edge. Higher shear stress implies higher viscous forces acting parallel to the free stream direction and may overcome the bonding strength of the coating interface.Thermal Barrier Coating (TBC) is widely used in aircraft engine hot-ended components to protect the engine components from direct exposure to corrosive high temperatures. Cooling holes of less than 1.5mm diameter in tough heat resistant aerospace alloys, coated with high heat resistant ceramics is normally laser drilled for effusion cooling. A large proportion of these holes are drilled at acute angles from the surface in order to provide essential cooling effects. When low-angle laser drilling these TBC components, laser drilling-induced micro structural damage of the thermal barrier coating occurs. This is undesirable as the propagation of the delamination may occur in service, leading to failure of the coating. In this paper the role of melt ejection and coaxial Assist Gas Jet on laser drilling of TBC substrate is studied by using a numerical analysis based on finite volume simulation. The work has identified a significant role of meltejection on the formation of cracks and delamination at the coating/...
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spatter prevention during the laser drilling of selected aerospace materials
Journal of Materials Processing Technology, 2003Co-Authors: Lin Li, P.j ByrdAbstract:Abstract The aerospace industry has been employing laser drilling to produce high quality closely spaced holes in turbine engine components for effusion cooling. However, laser drilled holes are inherently associated with the deposition of spatter as the ejected material resolidifies and adheres around the periphery of the holes. Work has been conducted to investigate the effectiveness of an anti-spatter composite coating (ASCC) for the drilling of closely spaced array (2 mm hole pitch) holes in three aerospace materials (IN 100, Nimonic PK 33 and 263 alloys) with an optically delivered 400 W Nd:YAG laser. The ASCC comprised of a mixture of ceramic filler particles embedded in a silicone elastomer matrix was applied on the surfaces of the alloy sheets before the process of laser percussion drilling. The work shows that the ASCC effectively prevents the deposition of spatter such that laser drilled through-holes are produced whilst maintaining the as-received surface characteristic for the various Assist Gases (O 2 , air, N 2 and Ar) tested. It was observed that wetting contact angles for the ASCC and one of alloys (Nimonic 263) were 118° and 46°, respectively. Such a difference was identified to be primarily due to the low surface tension of the silicone elastomer matrix and as a result, the ejected molten material would not wet the surface of the ASCC. The spatter prevention mechanism is based on the provision of a physical constriction (i.e. ASCC hole) at the drilling site (i.e. around the to-be drilled alloy substrate hole). Due to this constriction and the sufficient thermal resistance of the ASCC, the free space on the surfaces of the alloy substrates is eliminated such that the spatter is continually ejected out of the drilling site by the high-pressure forces from the Assist Gas Jet and the recoil pressure.
J. Duan - One of the best experts on this subject based on the ideXlab platform.
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Modelling the laser fusion cutting process : II. Distribution of supersonic Gas flow field inside the cut kerf
Journal of Physics D: Applied Physics, 2001Co-Authors: J. Duan, Hau Chung Man, Tai Man YueAbstract:A mathematical model is developed to calculate the distribution of the Gas flow field at the entrance, inside and exit of a laser cut kerf for inlet stagnation pressures ≥5 bar for an inert Assist Gas Jet exiting from a supersonic nozzle. A two-dimensional analytical method is adopted to locate approximately the position and shape of the detached shock above the cutting front surface according to the geometrical shape of the cutting front. A method of two-dimensional characteristics is applied to calculate the Gas flow field distribution along the cutting front. The calculated results of the flow field distribution are simulated by the computer and can be used to estimate and analyse the cut-edge quality under different cutting conditions.
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Analysis of the dynamic characteristics of Gas flow inside a laser cut kerf under high cut-Assist Gas pressure
Journal of Physics D, 1999Co-Authors: J. DuanAbstract:The behaviour of the cut-Assist Gas Jet inside a simulating laser cut kerf for a supersonic and a conical nozzle tip were studied by a shadowgraphic technique under conditions of inlet stagnation pressure from 3 to 7 bar. The effects of the stand-off distance, kerf width, material thickness and the inlet stagnation pressure upon the dynamic characteristics and momentum thrust of the Gas flow inside the cut kerf were investigated. It was found that under a Gas pressure of 7 bar, the Gas Jet from a conical nozzle tip expands radially and the Jet momentum deteriorates rapidly inside the kerf. The behaviour of the Jet is strongly influenced by the stand-off distance and thickness of the workpiece. On the other hand, the Gas Jet from a supersonic nozzle inside the cut kerf has tidy boundary and uniform distribution of pressure and thrust. The sensitivity to the stand-off distance and the workpiece thickness of the supersonic nozzle are much less as compared with the conical nozzle. With the supersonic nozzle, a dross free clean cut on 5 mm stainless steel can be achieved at an inert cut-Assist Gas pressure as low as 5 bar instead of the normal operating range of 10 bar or above for the conical nozzle.
Lin Li - One of the best experts on this subject based on the ideXlab platform.
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An investigation into delamination mechanisms in inclined laser drilling of thermal barrier coated aerospace superalloys
Journal of Laser Applications, 2005Co-Authors: H. K. Sezer, Andrew J. Pinkerton, Lin Li, P.j ByrdAbstract:Thermal barrier coatings are widely used in aircraft engine hot-end components to protect the component materials from direct exposure to the damaging high temperatures. Effusion cooling techniques are widely used in these situations and laser drilling is normally employed to produce holes of less than 1.5 mm diameter in tough aerospace alloys coated with heat-resistant ceramics. In order to provide the essential cooling effects, a large proportion of these holes must be drilled at acute angles to the surface. During this low-angle laser drilling, microstructural damage of the thermal barrier coating may occur; this is highly undesirable as propagation of the delamination may occur in service, leading to premature failure of the coating. In this article, the role of melt ejection and the coaxial Assist Gas Jet in low angle laser drilling of a thermal barrier coated substrate is studied using a finite volume method. The work identifies the significant role of melt ejection in the formation of cracks and delamination at the coating/substrate interface on the leading edge of a laser-drilled cooling hole. The numerical model shows that the melt particles are accelerated towards the leading edge by the coaxial Assist Gas Jet, and as a result of molten metal flowing across the edge the damage through mechanical stresses and subsequent erosion is found to be more serious here than at the trailing edge. The higher shear stress found at the leading edge also implies higher viscous forces acting parallel to the free stream direction to overcome the bonding strength of the coating interface.Thermal barrier coatings are widely used in aircraft engine hot-end components to protect the component materials from direct exposure to the damaging high temperatures. Effusion cooling techniques are widely used in these situations and laser drilling is normally employed to produce holes of less than 1.5 mm diameter in tough aerospace alloys coated with heat-resistant ceramics. In order to provide the essential cooling effects, a large proportion of these holes must be drilled at acute angles to the surface. During this low-angle laser drilling, microstructural damage of the thermal barrier coating may occur; this is highly undesirable as propagation of the delamination may occur in service, leading to premature failure of the coating. In this article, the role of melt ejection and the coaxial Assist Gas Jet in low angle laser drilling of a thermal barrier coated substrate is studied using a finite volume method. The work identifies the significant role of melt ejection in the formation of cracks and de...
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spatter prevention during the laser drilling of selected aerospace materials
Journal of Materials Processing Technology, 2003Co-Authors: Lin Li, P.j ByrdAbstract:Abstract The aerospace industry has been employing laser drilling to produce high quality closely spaced holes in turbine engine components for effusion cooling. However, laser drilled holes are inherently associated with the deposition of spatter as the ejected material resolidifies and adheres around the periphery of the holes. Work has been conducted to investigate the effectiveness of an anti-spatter composite coating (ASCC) for the drilling of closely spaced array (2 mm hole pitch) holes in three aerospace materials (IN 100, Nimonic PK 33 and 263 alloys) with an optically delivered 400 W Nd:YAG laser. The ASCC comprised of a mixture of ceramic filler particles embedded in a silicone elastomer matrix was applied on the surfaces of the alloy sheets before the process of laser percussion drilling. The work shows that the ASCC effectively prevents the deposition of spatter such that laser drilled through-holes are produced whilst maintaining the as-received surface characteristic for the various Assist Gases (O 2 , air, N 2 and Ar) tested. It was observed that wetting contact angles for the ASCC and one of alloys (Nimonic 263) were 118° and 46°, respectively. Such a difference was identified to be primarily due to the low surface tension of the silicone elastomer matrix and as a result, the ejected molten material would not wet the surface of the ASCC. The spatter prevention mechanism is based on the provision of a physical constriction (i.e. ASCC hole) at the drilling site (i.e. around the to-be drilled alloy substrate hole). Due to this constriction and the sufficient thermal resistance of the ASCC, the free space on the surfaces of the alloy substrates is eliminated such that the spatter is continually ejected out of the drilling site by the high-pressure forces from the Assist Gas Jet and the recoil pressure.
Tai Man Yue - One of the best experts on this subject based on the ideXlab platform.
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Modelling the laser fusion cutting process : II. Distribution of supersonic Gas flow field inside the cut kerf
Journal of Physics D: Applied Physics, 2001Co-Authors: J. Duan, Hau Chung Man, Tai Man YueAbstract:A mathematical model is developed to calculate the distribution of the Gas flow field at the entrance, inside and exit of a laser cut kerf for inlet stagnation pressures ≥5 bar for an inert Assist Gas Jet exiting from a supersonic nozzle. A two-dimensional analytical method is adopted to locate approximately the position and shape of the detached shock above the cutting front surface according to the geometrical shape of the cutting front. A method of two-dimensional characteristics is applied to calculate the Gas flow field distribution along the cutting front. The calculated results of the flow field distribution are simulated by the computer and can be used to estimate and analyse the cut-edge quality under different cutting conditions.
Tm Yue - One of the best experts on this subject based on the ideXlab platform.
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Modelling the laser fusion cutting process : II. Distribution of supersonic Gas flow field inside the cut kerf
Institute of Physics Publishing, 2001Co-Authors: Duan J, Hc Man, Tm YueAbstract:A mathematical model is developed to calculate the distribution of the Gas flow field at the entrance, inside and exit of a laser cut kerf for inlet stagnation pressures ≥5 bar for an inert Assist Gas Jet exiting from a supersonic nozzle. A two-dimensional analytical method is adopted to locate approximately the position and shape of the detached shock above the cutting front surface according to the geometrical shape of the cutting front. A method of two-dimensional characteristics is applied to calculate the Gas flow field distribution along the cutting front. The calculated results of the flow field distribution are simulated by the computer and can be used to estimate and analyse the cut-edge quality under different cutting conditions.Department of Industrial and Systems Engineerin
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Analysis of the dynamic characteristics of Gas flow inside a laser cut kerf under high cut-Assist Gas pressure
Institute of Physics Publishing, 1999Co-Authors: Hc Man, Duan J, Tm YueAbstract:The behaviour of the cut-Assist Gas Jet inside a simulating laser cut kerf for a supersonic and a conical nozzle tip were studied by a shadowgraphic technique under conditions of inlet stagnation pressure from 3 to 7 bar. The effects of the stand-off distance, kerf width, material thickness and the inlet stagnation pressure upon the dynamic characteristics and momentum thrust of the Gas flow inside the cut kerf were investigated. It was found that under a Gas pressure of 7 bar, the Gas Jet from a conical nozzle tip expands radially and the Jet momentum deteriorates rapidly inside the kerf. The behaviour of the Jet is strongly influenced by the stand-off distance and thickness of the workpiece. On the other hand, the Gas Jet from a supersonic nozzle inside the cut kerf has tidy boundary and uniform distribution of pressure and thrust. The sensitivity to the stand-off distance and the workpiece thickness of the supersonic nozzle are much less as compared with the conical nozzle. With the supersonic nozzle, a dross free clean cut on 5 mm stainless steel can be achieved at an inert cut-Assist Gas pressure as low as 5 bar instead of the normal operating range of 10 bar or above for the conical nozzle.Department of Industrial and Systems Engineerin
