Waste ash-induced degradation of additively manufactured CuCr1Zr alloy for plasma torch electrode applications

Faced with the challenges of transitioning towards a circular economy, efficient methods are needed for the disposal of difficult-to-manage waste, such as municipal sewage sludge and automotive shredder residue. Plasma gasification offers advantages over traditional combustion by enabling very high temperatures that promote hydrocarbon decomposition into syngas and the vitrification of ash into inert slag. However, the thermal and chemical conditions accelerate the degradation of plasma torch electrodes, reducing their lifetime. Therefore, durable advanced electrode materials are essential, especially as electrodes are increasingly produced by additive manufacturing to improve performance and integrate complex internal cooling channels. Significant research interest is focused on CuCr1Zr alloy, which combine high thermal conductivity and mechanical strength in a plasma environment and can be used for 3D printing via Laser Powder Bed Fusion (LPBF). However, the degradation of LPBF-manufactured CuCr1Zr alloy in the plasma torch operating environment, dominated by aggressive gases, water vapour, and deposited ash, has not yet been examined. Therefore, the objective of the research presented was to comprehensively assess the mechanisms of degradation of the CuCr1Zr alloy produced by LPBF under conditions simulating high-temperature processes. Preliminary studies included proximate and ultimate analyses of the wastes, followed by thermogravimetric analysis (TGA) of waste samples and copper alloy to investigate their thermal behaviour under a CO2 atmosphere. Next, corrosion tests on CuCr1Zr alloy in the presence of deposited waste ash were conducted. The alloy was exposed at 900 °C for 168 hours under a CO2 atmosphere. After the corrosion tests, significant changes in the surface morphology of the LPBFed CuCr1Zr alloy were observed. SEM analysis revealed the formation of a heterogeneous oxide/corrosion layer, local surface roughening, microcracks, and ash-derived deposits adhered to the alloy surface. These results indicate that deposited waste ashes, combined with high temperature and a CO2 atmosphere, may accelerate oxidation and local corrosion of CuCr1Zr alloy. Nevertheless, the alloy shows potential for plasma torch electrode applications, although further studies are required to improve its long-term durability under plasma gasification conditions.