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Dr Vasileios Katranidis


Postgraduate Research Student
+44 (0)1483 686568
33 BC 02

Academic and research departments

Department of Chemical and Process Engineering.

My publications

Publications

When a complex geometry is rotated in front of the thermal spray gun, the following kinematic parameters vary in a coupled fashion dictated by the geometry: Stand-off distance, spray angle and gun traverse speed. These fluctuations affect the conditions of particle impact with major implications on the coating?s properties. This work aims to probe into the interplay and isolated effect of these parameters on vital coating characteristics in applications requiring variable stand-off distance and spray angles. WC-17Co powders are sprayed via HVOF on steel substrates in a set of experiments that simulates the spray process of a non-circular cross section, while it allows for individual control of the kinematic parameters. Comprehensive investigation of their influence is made on deposition rate, residual stresses, porosity and microhardness of the final coating. It was determined that oblique spray angles and long stand-off distances compromise the coating properties but in some cases, the interplay of the kinematic parameters produced non-linear behaviours. Microhardness is related negatively with oblique spray angles at short distances while a positive correlation emerges as the stand-off distance is increased. Porosity and residual stresses are sensitive to the spray angle only in relatively short stand-off distances.
Katranidis Vasileios, Gu Sai, Ramirez Reina Tomas, Alpay Esat, Allcock Bryan, Kamnis Spyros (2017) Experimental study of high velocity oxy-fuel sprayed WC-17Co
coatings applied on complex geometries. Part B: Influence of
kinematic spray parameters on microstructure, phase composition
and decarburization of the coatings,
Surface & Coatings Technology 328 pp. 499-512 Elsevier
The aim of this study is to evaluate comprehensively the effect of spray angle, spray distance and gun traverse speed on the microstructure and phase composition of HVOF sprayed WC-17 coatings. An experimental setup that enables the isolation of each one of the kinematic parameters and the systemic study of their interplay is employed. A mechanism of particle partition and WC-cluster rebounding at short distances and oblique spray angles is proposed. It is revealed that small angle inclinations benefit notably the WC distribution in the coatings sprayed at long stand-off distances. Gun traverse speed, affects the oxygen content in the coating via cumulative superficial oxide scales formed on the as-sprayed coating surface during deposition. Metallic W continuous rims are seen to engulf small splats, suggesting crystallization that occurred in-flight.
The aim of this study is to evaluate comprehensively the effect of spray angle, spray distance and gun traverse
speed on the microstructure and phase composition of HVOF sprayed WC-17 coatings. An experimental setup
that enables the isolation of each one of the kinematic parameters and the systemic study of their interplay is
employed. A mechanism of particle partition and WC-cluster rebounding at short distances and oblique spray
angles is proposed. It is revealed that small angle inclinations benefit notably the WC distribution in the coatings
sprayed at long stand-off distances. Gun traverse speed, affects the oxygen content in the coating via cumulative
superficial oxide scales formed on the as-sprayed coating surface during deposition. Metallic W continuous rims
are seen to engulf small splats, suggesting crystallization that occurred in-flight.
Katranidis Vasileios, Gu Sai, Cox David, Whiting Mark J, Kamnis Spyros (2018) FIB-SEM Sectioning Study of Decarburization Products in the Microstructure of HVOF-Sprayed WC-Co Coatings, Journal of Thermal Spray Technology 27 (5) pp. 898-908 Springer
The thermal dissolution and decarburization of WC-based powders that occur in various spray processes are a widely studied phenomenon, and mechanisms that describe its development have been proposed. However, the exact formation mechanism of decarburization products such as metallic W is not yet established. A WC-17Co coating is sprayed intentionally at an exceedingly long spray distance to exaggerate the decarburization effects. Progressive xenon plasma ion milling of the examined surface has revealed microstructural features that would have been smeared away by conventional polishing. Serial sectioning provided insights on the three-dimensional structure of the decarburization products. Metallic W has been found to form a shell around small splats that did not deform significantly upon impact, suggesting that its crystallization occurs during the in-flight stage of the particles. W2C crystals are more prominent on WC faces that are in close proximity with splat boundaries indicating an accelerated decarburization in such sites. Porosity can be clearly categorized in imperfect intersplat contact and oxidation-generated gases via its shape.