Microstructural and Mechanical Characterization of W-3Re Coatings on TZM Produced by Vacuum Plasma Spraying

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Tungsten–rhenium (W–Re) alloys supported by titanium–zirconium–molybdenum (TZM) substrates are relevant to high-heat-flux components, including the focal tracks of rotating-anode medical X-ray tubes. In this study, a nominal W–3 wt.% Re coating was deposited on a TZM substrate by vacuum plasma spraying (VPS), and its microstructure, density, through-thickness hardness, and surface residual stress were evaluated relative to a vacuum-sintered W–3Re reference. Field-emission scanning electron microscopy revealed the characteristic lamellar morphology of a plasma-sprayed deposit, while energy-dispersive X-ray spectroscopy detected W and Re throughout the analyzed coating region. The VPS and sintered specimens exhibited measured densities of 17.08 and 15.62 g cm−3, corresponding to relative densities of 88.04% and 80.52%, respectively, when referenced to a theoretical density of 19.4 g cm−3. The mean Vickers hardness of the VPS deposit was 419.7 ± 14.75 HV1, 90.6% higher than 220.2 ± 15.61 HV1 measured for the sintered reference. Surface tensile residual stresses were approximately 97 ± 35 MPa for the VPS specimen and 219 ± 21 MPa for the sintered specimen. The higher hardness of the VPS deposit was associated with its higher measured density and lower tensile residual stress, although these data do not establish a single causal mechanism; porosity, inter-splat bonding, local microstructure, and other processing-dependent factors may also contribute. Under the processing conditions investigated, VPS produced a denser and harder W–3Re material than the vacuum-sintered reference, supporting further evaluation of VPS for refractory-metal coating applications.