Sustainable iron aluminide-based laser claddings

Abstract

Since 3 % of the world’s total energy consumption (16 EJ) is used to remanufacture worn parts, the potential for emission reduction which is important to tackle climate change is enormous. Thus, alternative materials with significantly reduced environmental impacts, omitting critical raw materials must be found. For wear protection, especially at higher temperatures, Co, Cr and Ni are often used, which are critical raw materials with a comparatively high environmental impact. Thus, the major goal of this study is to provide sustainable alternatives for high-temperature wear protection which meet all four approaches reducing a material’s carbon footprint: i) product light-weighting, ii)improvements in the production, iii) intensive use and lifetime extension, iv) enhanced recycling. Having a closer look at possible materials as high-temperature wear protection conforming these rules, iron aluminides are a good alternative, yielding ~8.4 kg CO2eq/kg compared to 13.8 kg CO2eq/kg of high-Cr-alloyed cast steels, Ni-base alloys (~20-22 kgCO2eq/kg) or Co-base alloys (31-39 kg CO2eq/kg). Since iron aluminides provide low density, the light-weighting measure to reduce the impact is met. To improve the production, laser metal deposition was used to deposit iron aluminide claddings which enables a local functionalisation of a surface. To improve the lifetime increasing the comparatively low hardness of Fe3Al (260 HV10) and wear resistance, strengthening with different alloying elements was performed. Here, an Fe3Al matrix was chosen, strengthened with different measures. Strengthening with Si, C and Ti+B led to low hardness levels <500 HV10 at 20 °C but stable hardness up to 600 °C –due to low hardness and hard phase content abrasives are incorporated into the surface, leading to a self-protection effect (mechanically mixed layer) and thus low wear rates of 0.01–0.05 mm3/m up to 700 °C. Precipitation strengthening with borides and carbides led to hardness levels of ~800 HV10 providing sufficient wear resistance up to 700 °C with wear rates between 0.03 and 0.05 mm3/m. To improve the lifetime and enhance recycling,up to 70 vol.% recycled hard metal scrap and sustainable TiC cermets were used to reinforce the Fe3Al matrix leading to hardness levels of 1100 HV10 at RT and with 70 vol.% reinforcement with a stable plateau up to 700 °C, entailing excellent wear rates of 0.04-0.05 mm3/m up to these temperatures. In summary, all developed claddings are equally performant or outperform currently used high-temperature wear protection solutions with high amounts of Cr, Co and Ni but with environmental impact reduction of over 60% for GWP100 compared to Co-based wear protection solutions.