Effect of Fluid Convection on Dendrite Arm Spacing in Laser Deposition
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METHODS for increasing the overall efficiency of aircraft engines and gas turbines can reduce operating cost and environmental impact (e.g., emission of CO2) and has long been an issue among manufactures of these systems. Higher operating temperature is effective to increase the efficiency of turbines but components are exposed to higher temperatures and their properties may be significantly degraded. For example, in high-efficiency gas turbine engines,[1] the gas stream passing through combustor has a temperature as high as 1773 K (1500 °C). Turbine blades are exposed to high temperatures, a corrosive gas atmosphere, and high operating stresses. Wear is particularly severe at the tips of the blades since high operating efficiency requires small clearance between rotating turbine blade tips and the outer stator casing. This small clearance contributes to tip wear by mechanisms of erosion, corrosion, oxidation, deformation, and adhesive transfer, singly or in combination.[2] Since tip wear limits the life of blade life, repairing worn turbine blade tips is of great economic interest.[3] Laser cladding technology has been popularly utilized to apply worn protection layer on metallic surfaces or to YOUSUB LEE, Ph.D. Candidate, and DAVE F. FARSON, Professor, are with the Department of Materials Science and Engineering, Welding Engineering Program, The Ohio State University, Columbus, OH 43221. Contact e-mail: [email protected] MARK NORDIN, Senior Welding Engineer, is with Rolls Royce Corp, Indianapolis, IN 46206. SUDARSANAM SURESH BABU, Professor, is with the Department of Mechanical, Aerospace, and Biomedical Engineering, The University of Tennessee, Knoxville, TN 37996. Manuscript submitted October 17, 2013. Article published online April 3, 2014. 1520—VOLUME 45B, AUGUST 2014
repair damaged surfaces of structural parts.[4] In laser cladding with blown powder, the powdered metal clad materials are delivered through multiple powder feed nozzles placed annularly around the laser beam, into a laser-generated melt pool as a form of powder particles that are carried by an inert gas.[5] The schematic description is shown in Figure 1.[6] Some powder particles are heated by the laser beam during flight and others are melted once they alight on the liquid melt pool surface. Only powder particles landing in melt pool contribute to formation of the clad deposit layer after solidification. The other particles alighting outside of melt pool will ricochet off and be lost. The development of laser cladding process is required for generally applicable accurate model. However, the complexity associated with interaction between powder particles, laser beam, and substrate makes simulation difficult. Total absorbed laser power density is modified by interaction between laser beam and powder cloud. Moreover, powder input accompanies with corresponding amount of mass and momentum into the melt pool. Thus, temperature distribution and fluid flow patterns in the weld pool will be changed and subsequently resultant shape of the clad deposit. Ni superalloy is th
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