Observation of Residual Stress and Fatigue Behavior of Structurally Integrated Thermally Sprayed Nickel Coatings

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Observation of Residual Stress and Fatigue Behavior of Structurally Integrated Thermally Sprayed Nickel Coatings Gregory M. Smith1,2 • John Saputo1 • Vladimir Luzin3,4 • Sanjay Sampath1

Submitted: 6 December 2019 / in revised form: 4 April 2020 Ó ASM International 2020

Abstract Fatigue behavior is strongly correlated with the residual stress state within thermal spray coatings, with neutral or compressive residual stresses being favorable for fatigue-sensitive applications. However, determination of the coating’s residual stress state is predominately made prior to subjection of the coating to cyclic loading and does not give insight into possible changes to the residual stress state once in service. In this work, high-velocity, oxy-fuel nickel coatings were subjected to a partial fatigue loading regime, via both rotating bend fatigue and cantilever fatigue, targeting 99% of the total system fatigue life. Neutron diffraction was used to measure changes between the initial compressive residual stresses and after partial fatigue loading and was compared with the residual stress measurements made via beam curvature techniques during deposition. Results indicate that the fatigue credit typically This article is part of a special topical focus in the Journal of Thermal Spray Technology on Advanced Residual Stress Analysis in Thermal Spray and Cold Spray Processes. This issue was organized by Dr. Vladimir Luzin, Australian Centre for Neutron Scattering; Dr. Seiji Kuroda, National Institute of Materials Science; Dr. Shuo Yin, Trinity College Dublin; and Dr. Andrew Ang, Swinburne University of Technology. & Gregory M. Smith [email protected] 1

Center for Thermal Spray Research, 130 Heavy Engineering Bldg., Stony Brook University, Stony Brook, NY 11794-2275, USA

2

Currently Located at Naval Research Laboratory, 4555 Overlook Ave SW, Washington, DC 20375, USA

3

Australian Nuclear Science and Technology Organization, Lucas Heights, NSW 2234, Australia

4

School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia

associated with compressive residual stress coatings was partially dependent on the mode of loading and that there was a change in the residual stress magnitude due to changes during fatigue cycling. Additionally, metallographic assessment of the fracture surface was used to determine final fatigue failure within the substrate and crack propagation within the coating crossing through the substrate interface into the substrate. Keywords fatigue  fracture  residual stress  structural integration

Introduction Residual stress measurement has been widely discussed in the context of production and fabrication of thermal spray coatings and has recognition as a crucial design element in coating application parameterization (Ref 1-4). Residual stress, or internal stress, refers to a stress distribution present within a structure in the absence of an applied external load (Ref 5). In thermal spray coatings, the confluence of impacting particles with differi

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