Mechanical Property of HVOF Inconel 718 Coating for Aeronautic Repair
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JTTEE5 23:380–388 DOI: 10.1007/s11666-013-0007-8 1059-9630/$19.00 Ó ASM International
Mechanical Property of HVOF Inconel 718 Coating for Aeronautic Repair Christophe Lyphout, Angelica Fasth, and Per Nylen (Submitted April 30, 2013; in revised form July 1, 2013) The module of elasticity is one of the most important mechanical properties defining the strength of a material which is a prerequisite to design a component from its early stage of conception to its field of application. When a material is to be thermally sprayed, mechanical properties of the deposited layers differ from the bulk material, mainly due to the anisotropy of the highly textured coating microstructure. The mechanical response of the deposited layers significantly influences the overall performance of the coated component. It is, therefore, of importance to evaluate the effective module of elasticity of the coating. Conventional experimental methods such as microindentation, nanoindentation and four-point bending tests have been investigated and their results vary significantly, mainly due to inhomogeneous characteristics of the coating microstructure. Synchrotron radiation coupled with a tensile test rig has been proposed as an alternative method to determine the coating anisotropic elastic behavior dependence on crystallographic orientations. The investigation was performed on Inconel 718 (IN718) HVOF coatings sprayed on IN718 substrates. Combining these experimental techniques yield a deeper understanding of the nature of the HVOF coating Youngs modulus and thus a tool for Design Practice for repair applications.
Keywords
aircraft overhaul, four-point bending, microindentation, nanoindentation, nickel alloys, synchrotron radiation, Youngs modulus
1. Introduction As described by Dowling (Ref 1), the Youngs modulus of a dense, isotropic, single phase solid is regarded as largely microstructure independent and related to the forces and distances between the constituent atoms. Widening the perspective to a single crystal, the modulus will vary dramatically with the direction of the crystal planes depending on the equilibrium distance between the atoms in the loading direction. In a polycrystalline material, a blend of these moduli will occur but will also be affected by the volume fraction of irregularities such as porosity, cracks, texture, concentration of impurities and alloying elements, and intergranular phases, typically as encountered in thermally sprayed coatings. Thermal Spray technology propels a heat powder feedstock material towards a colder target surface to build up a coating. When the particles impact onto the target surface, they have experienced a varying degree of melting and oxidation. When they collide with the substrate and cools down, a various degree, size, and distribution of porosity, microcracks, and delamination networks is formed. Depending of their respective thermo-mechanical history and intrinsic Christophe Lyphout, Angelica Fasth, and Per Nylen, Production & Engineering Science, University West, Trollha¨ttan
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