Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements
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Ramachandran Chidambaram Seshadri, Gopal Dwivedi, Vaishak Viswanathan, and Sanjay Sampath (Submitted July 14, 2016; in revised form September 17, 2016) Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the submicrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.
Keywords
curvature measurements, elastic properties, stress evolution, suspension plasma spray, thermal cycling
1. Introduction Conventional plasma spray processes for thermal barrier coating (TBCs) deposition use powders with particle sizes ranging from 10 to 100 lm. They result in coatings that mainly present micrometer-sized building blocks (splats), as the lamellae formed by the impact of the particles onto the substrate are a few micrometer thick with diameter from a few tens to a few hundreds of micrometers. Development and understanding thermalsprayed coatings that exhibit nanometer-size assembly of materials or notably starting with finer feedstock particles have been areas of interests for the past 30 years with increasing activity in the last 10 years (Ref 1, 2). The major drawbacks in processing nanometer-sized particles by standard thermal spraying are both the ability to handle and deliver ultrafine powders and the difficulty in injecting them into the core of the high-enthalpy and high-density plasma. For effective radial injection of particles into a Ramachandran Chidambaram Seshadri, Gopal Dwivedi, Vaishak Viswanathan, and Sanjay Sampath, Center for Thermal Spray Research, Stony Brook University, Stony Brook, NY 11790, USA. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
direct current (DC) plasma, the particle injection force ha
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