Relationships Between Process Parameters, Microstructure, and Adhesion Strength of HVOF Sprayed IN718 Coatings
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JTTEE5 20:76–82 DOI: 10.1007/s11666-010-9543-7 1059-9630/$19.00 Ó ASM International
Relationships Between Process Parameters, Microstructure, and Adhesion Strength of HVOF Sprayed IN718 Coatings Christophe Lyphout, Per Nyle´n, and Lars O¨stergren (Submitted May 7, 2010; in revised form July 30, 2010) Fundamental understanding of relationships between process parameters, particle in-flight characteristics, and adhesion strength of HVOF sprayed coatings is important to achieve the high coating adhesion that is needed in aeronautic repair applications. In this study, statistical Design of Experiments (DoE) was used to identify the most important process parameters that influence adhesion strength of IN718 coatings sprayed on IN718 substrates. Special attention was given to the parameters combustion ratio, total gas mass flow, stand-off distance and external cooling, since these parameters were assumed to have a significant influence on particle temperature and velocity. Relationships between these parameters and coating microstructure were evaluated to fundamentally understand the relationships between process parameters and adhesion strength.
Keywords
adhesion strength, Design of Experiments, HVOF, Inconel 718 coating, microstructure
1. Introduction Coating adhesion is one of the most important properties of thermally sprayed coating systems since it controls the coatingÕs lifetime and its applicability (Ref 1). The adhesion is dependent on several factors such as pretreatment, process conditions during spraying and posttreatment (Ref 2, 3). In order to fundamentally understand the relationships between process parameters and the coating adhesion strength, establishment of relationships between controllable process parameters, in-flight properties of the injected powder (particles velocity and temperature), and microstructure properties is important. To be able to quantify the relationships, a measurement method for high adhesion strength is necessary. Such a method was developed in previous work since the standard tensile test ASTM C633-79 (Ref 4) which is conventionally used to
This article is an invited paper selected from presentations at the 2010 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Thermal Spray: Global Solutions for Future Applications, Proceedings of the 2010 International Thermal Spray Conference, Singapore, May 3-5, 2010, Basil R. Marple, Arvind Agarwal, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2011. Christophe Lyphout and Per Nyle´n, University West, Trollha¨t¨ stergren, Volvo Aero Corporation, tan, Sweden; and Lars O Trollha¨ttan, Sweden. Contact e-mail: [email protected].
76—Volume 20(1-2) January 2011
measure coating adhesion strength, is limited by the strength of the polymer-based adhesive. The microstructure properties, porosity and oxides content are also difficult to determine in HVOF coatings by industrial
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