Evaluation and improvement of the greenness of plasma spraying through life cycle assessment and grey relational analysis

Plasma spraying is a mature, efficient, and widely applied surface treatment technology. However, the high-energy consumption and harmful gas emissions are still obstacles to achieving clean production by plasma spraying. Considering that the various process parameters of plasma spraying have great impacts on both on coating performance and environmental impact, this study attempts to improve the greenness of plasma spraying including environmental and mechanical properties, through optimizing the process parameters. The greenness of plasma spraying means to achieve the balance of reducing environmental impact and improving the mechanical performance of coating. In this work, a Fe-based coating is prepared by plasma spraying on the basis of an L9 (34) orthogonal experiment with various process parameters, i.e., power, powder feeding speed, gun speed, and track pitch. A complete life cycle assessment (LCA) study is conducted to quantify and evaluate the environmental impact of plasma spraying. In addition, the microhardness and porosity of the Fe-based coating are investigated to evaluate the mechanical performance. Finally, grey relational analysis (GRA) is used to realize multiobjective decision-making and improve the greenness of plasma spraying. LCA results show that electricity contributes most to the environmental impact of plasma spraying. When hydropower is supplied, the environmental impacts can be significantly reduced by 46.65%. Based on the L9 (34) orthogonal experiment and GRA, five optimized plasma spraying schemes are proposed, i.e., microhardness optimality, porosity optimality, environmental optimality, greenness optimality, and enhanced greenness optimality. The verification shows that the enhanced greenness optimality of plasma spraying is improved by 11.83% compared with the greenness optimality. In this study, we propose a method to evaluate and improve the greenness of plasma spraying both in environmental and mechanical performance through the integration of LCA and GRA, which can be adopted to optimize the spraying process parameters in real sustainable production.