Modeling the Influence of Process Parameters and Additional Heat Sources on Residual Stresses in Laser Cladding
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F. Bru¨ckner, D. Lepski, and E. Beyer (Submitted May 9, 2006; in revised form August 2, 2006) In laser cladding thermal contraction of the initially liquid coating during cooling causes residual stresses and possibly cracks. Preweld or postweld heating using inductors can reduce the thermal strain difference between coating and substrate and thus reduce the resulting stress. The aim of this work is to better understand the influence of various thermometallurgical and mechanical phenomena on stress evolution and to optimize the induction-assisted laser cladding process to get crack-free coatings of hard materials at high feed rates. First, an analytical one-dimensional model is used to visualize the most important features of stress evolution for a Stellite coating on a steel substrate. For more accurate studies, laser cladding is simulated including the powder-beam interaction, the powder catchment by the melt pool, and the self-consistent calculation of temperature field and bead shape. A three-dimensional finite element model and the required equivalent heat sources are derived from the results and used for the transient thermomechanical analysis, taking into account phase transformations and the elastic-plastic material behavior with strain hardening. Results are presented for the influence of process parameters such as feed rate, heat input, and inductor size on the residual stresses at a single bead of Stellite coatings on steel.
Keywords
finite element method, inductive preheating and postweld heating, laser cladding, phase transformation, process simulation, residual stress, stellite coating
1. Introduction Laser cladding is increasingly used for the generation of corrosion- and wear-protective coatings and for the repair of tools and components. It is able to yield a strong interfacial bond between the substrate and the coating without significant dilution of one material into the other. In the laser cladding process, the pulverized coating material is transported by a carrier gas through a nozzle onto the workpiece surface (Fig. 1). There it penetrates into the melt pool that is generated by the laser beam on the moving substrate. Care must be taken to adjust the temperature field so that a strong metallurgical bond between the deposit and the substrate is achieved with very low dilution of the coating with substrate material. Since the coating material is in the liquid state while being deposited on the cold substrate, thermal contraction of the deposit unavoidably leads to the evolution of F. Bru¨ckner and E. Beyer, Institute for Surface Technology and Production Metrology IOF, Dresden University of Technology, Dresden, Germany; D. Lepski and E. Beyer, Fraunhofer Institute for Material and Beam Technology IWS, Dresden, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
residual stresses and workpiece distortion. Residual stresses in wear- or corrosion-protective coatings may strongly influence mechanical properties such as wear and fatigue resistance and fr
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