ADVANCED MATERIALS & PROCESSES | APRIL 2025 36 iTSSe TSS iTSSe TSS 5 least surface roughness (Sa) of 0.73 ± 0.01 μm (n=10) was obtained compared to 1.32 ± 0.04 μm of unoptimized parameters. • Hardness: While overall hardness values were similar across trials around 1000 HV, however, the hardness is measured higher than the regular sized powder coatings. Post-indentation SEM analysis further highlighted the resilience of optimized coatings. While unoptimized coatings showed extensive cracking under microhardness testing, optimized coatings remained crack-free, emphasizing their ductility (Fig. 4). • Theoretical optimization of spray parameters can e ectively mitigate these issues, producing dense, crack-free, and ductile coatings. • Fine powders can achieve properties akin to regular-sized powders, with added benefits for thermally sensitive substrates. The findings pave the way for the broader adoption of fine-cut WC-NiCr powders in industries demanding high-performance, cost-efficient coatings. By harnessing the power of parameter optimization, manufacturers can unlock new possibilities for lightweight, durable components in aerospace, marine, and beyond. ~iTSSe Acknowledgments The authors acknowledge support from the Australian Research Council (ARC) Industrial Transformation Training Centre on Surface Engineering for Advanced Materials (SEAM) via award IC180100005. Also, the authors are thankful to LaserBond Ltd. for organizing the HVOF spray trial at their own facility, providing feedstock powder and flame temperature calculator. For more information: Andrew Siao Ming Ang, associate professor, SEAM ARC Training Centre, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122, Australia, +61.3.9214.5851, aang@swin.edu.au, swinburne.edu.au. References 1. S. Singh, et al., Applications and Developments of Thermal Spray Coatings for the Iron and Steel Industry, Materials, 16(2), 2023, doi.org/10.3390/ma16020516. 2. A.S.M. Ang, et al., Manufacturing of Nickel Based Cermet Coatings by the HVOF Process, Surf. Eng., Taylor & Francis, 32(10), p 713–724, 2016, doi.org/10.1179/17432944 15Y.0000000031. 3. A. Ghabchi, et al., Behavior of HVOF WC-10Co4Cr Coatings with Different Carbide Size in Fine and Coarse TABLE 1 — XRD PHASE FRACTION AND EDS ELEMENTAL ANALYSIS OF HVOF SPRAYED FINE-CUT POWDER COATINGS DEPOSITED USING UNOPTIMIZED AND OPTIMIZED SPRAY PARAMETERS XRD EDS Ratio Conditions/ Trial no. W2C WC W CrNi C W2C/WC Powder 0.7 82.2 0.8 16.3 6.8 0.01 OP 32.4 57.8 0.8 9.0 6.8 0.56 UOP 58.2 29.2 3.8 12.6 ND 1.99 Notes: OP = optimized parameters, UOP = unoptimized parameters, ND = not detected, XRD = x-ray di raction, and EDS = electron dispersive spectrometry. Fig. 4 — Post microhardness indentation SEM analysis of HVOF sprayed fine-cut powder coatings (a) unoptimized parameter (UOP) (b) optimized parameter (OP). Corrosion Resistance. Electrochemical testing demonstrated that fine-cut coatings deposited with optimized parameters matched the corrosion resistance of benchmarked regular-sized powder coatings. This parity underscores the potential of fine powders to replace traditional feedstocks, even in demanding marine environments. CONCLUSIONS The optimization of HVOF spray parameters for fine WC-NiCr powders marks a significant advancement in thermal spray technology. The study demonstrated that: • Excess oxygen and prolonged high temperatures contribute to decarburization, brittleness, and porosity in coatings. FEATURE
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