Effects of the Modification of Processing Parameters on Mechanical Properties of HVOF Cr 2 C 3 -25NiCr Coatings
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JTTEE5 24:938–946 DOI: 10.1007/s11666-015-0255-x 1059-9630/$19.00 Ó ASM International
Effects of the Modification of Processing Parameters on Mechanical Properties of HVOF Cr2C3-25NiCr Coatings Israel Lo´pez Ba´ez, Carlos Agustı´n Poblano Salas, Juan Mun˜oz Saldan˜a, and Luı´s Gerardo Tra´paga Martı´nez (Submitted March 25, 2014; in revised form April 21, 2015) The present work shows that some mechanical properties of Cr2C3-25NiCr coatings processed by HVOF thermal spraying such as elastic modulus, hardness, fracture toughness, and wear resistance are closely linked to selected processing parameters as well as to chemistry, structure, and morphology of the feedstock material. Optimization of processing parameters was based on oxygen concentration measurements inside the flame, studied by a contour plot, and curvature data recorded during spraying. The increase in velocity of in-flight particles strongly affected the interfacial fracture toughness of the coatings, as a maximum KIC of 3.71 MPa m1/2 was reached when particle velocity increased to ~765 m/s. The micro-hardness of Cr2C3-25NiCr coatings was widely varied by changing the HVOF spray conditions, i.e., the amount of reinforcing phases and inter-splat adhesion were quite sensitive to any modification of the processing parameters. It was also found that coatings having a high inter-splat adhesion and/or low degradation of reinforcing hard phases showed reduced weight loss during erosive wear tests. Finally, from the experimental evidence reported in this work, a correlation between the elastic bending modulus of coatings and indentation crack length was also found.
Keywords
feedstock, HVOF flame, interfacial fracture toughness, particle velocity, structural integrity
1. Introduction The high velocity oxy-fuel (HVOF) process has been employed successfully in many industrial applications requiring surface modifications which result in increased wear, oxidation, and/or corrosion resistance. HVOF involves the introduction of powdered raw materials into the flame, in which they are melted and propelled towards the substrate. Upon impact, the particles flatten, cool down, and solidify, forming a solid layer. Coatings show quite different properties from bulk materials having the same composition; such differences arise from the formation of new phases, porosity, anisotropy, and residual stress. Furthermore, the processing conditions also significantly affect the microstructure and properties of the Israel Lo´pez Ba´ez, Departamento de Minas, Metalurgia y Geologı´a, Universidad de Guanajuato, Ex Hacienda de San Matı´as s/n., Fraccionamiento San Javier, 36025 Guanajuato, GTO, Mexico; Carlos Agustı´n Poblano Salas, CIATEQ A.C. – Materiales avanzados, Av. Manantiales No. 23-A, Parque Industrial Bernardo Quintana, El Marque´s, 76246 Quere´taro, QRO, Mexico; and Juan Mun˜oz Saldan˜a and Luı´s Gerardo Tra´paga Martı´nez, Centro de Investigacio´n y de Estudios Avanzados del Instituto Politecnico Nacional - Materials Science, Libramiento Norponiente 2000 Fracc. Real de Ju
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