ADVANCED MATERIALS & PROCESSES | APRIL 2025 34 iTSSe TSS iTSSe TSS Hexavalent chromium plating is a widely used industrial process for applying a hard and corrosionresistant chrome coating to various metal surfaces[1]. While it has excellent properties, hexavalent chromium has certain drawbacks, including environmental concerns due to the use of toxic compounds and the potential for worker exposure to hazardous materials. THE APPEAL OF FINE-CUT WC-NiCr POWDERS The thermal spray industry is in transition to replace conventional hexavalent hard chrome plating with highvelocity oxy-fuel (HVOF) spray due to its superior corrosion resistance, mechanical properties, and eco-friendliness[1,2]. However, the deposition of conventional tungsten carbidenickel-chromium (WC-NiCr) powders (–45 + 15 μm or –53 + 20 μm) often requires an extensive diamond abrasive grinding and finishing efforts to convert the as-sprayed products to make the product suitable for many applications, increasing processing costs. Fine-cut powders (–30 + 5 μm) offer a compelling alternative by producing a smoother as-sprayed finish, reducing the need for labor-intensive grinding[3,4]. However, the high surface area-to-volume ratio of fine agglomerated carbide-matrix powder particles renders them vulnerable to decarburization during spraying. This process, driven by prolonged exposure to oxygen-rich flames, depletes carbon content, forming brittle phases like W2C and W, which compromise coating performance[4]. Therefore, deploying fine powders presents challenges, such as decarburization-induced brittleness, necessitating precise optimization of spray parameters. This feature delves into the innovative strategies to overcome these hurdles, unlocking the potential of HVOF spraying to produce fine carbide powder coatings. VALIDATION OF COMPUTATIONAL MODELING OF SPRAY PARAMETERS AS A TOOL TO OPTIMIZE FINE PARTICLE SIZE WC-NiCr HVOF COATINGS Optimized high-velocity oxy-fuel spraying of fine-cut WC-NiCr powder results in dense, crack-free, and ductile coatings, with a smoother as-sprayed surface that is expected to reduce grinding efforts and enhance coating performance. Surinder Singh,* Alexender Osi, Vinit V Joshi, Scott Wade, Christopher C. Berndt, FASM, TSS-HoF,* and Andrew Siao Ming Ang,* Australian Research Council Industrial Transformation Training Centre in Surface Engineering for Advanced Materials, Swinburne University of Technology, Hawthorn, Australia Thomas Schläfer, LaserBond Ltd., Cavan, SA, Australia Hugo Howse, LaserBond Ltd., Altona, VIC, Australia OPTIMIZING SPRAY PARAMETERS Effective parameter optimization is critical to mitigate decarburization and achieve dense, defect-free coatings. Instead of traditional trial-and-error methods, the study adopted a theoretical framework from Tawfik and Li to identify ideal spray parameters, saving time and resources[5,6]. An HVOF spray process with a kerosene fueled system (GTV HVOF K2, GTV Verschleißschutz GmbH, Germany) available at LaserBond Ltd. Australia (see Fig. 1) was used to deposit WC-NiCr coatings. The details about the theoretical and experimental framework can be found in the extended version of the work published elsewhere[7,8]. 3 *Member of ASM International FEATURE Fig. 1 — Swinburne postdoc preparing the thermal spray booth for HVOF-K2 spray trials at LaserBond Ltd., Altona, Australia, highlighting ARC-SEAM and LaserBond collaboration.
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