Recycling of toasted 431 stainless steel powders in extreme high speed laser cladding (EHLA) – characterization of heat affected powders, deposition efficiency, and coating microstructures.

Extreme high speed laser cladding (EHLA) ‘over-spray’ can lead to substantial powder wastage. Paralleling similar challenges in powder bed fusion technology (PBF), it is desirable to explore the reuse of over-sprayed powders to reduce such wastage. Firm understandings of the properties of heat affected, ‘toasted’ powders and subsequent recycled-powder-cladding microstructures are required to green-light powder recycling.

Herein two ‘431’ martensitic stainless steel powders are tested, with claddings produced from as-received powder and processed, over-sprayed powder. Powder and cladding microstructures are characterized by XRD, optical & electron microscopy, EDS, and EBSD techniques. Large differences in cladding performance are observed between new and over-sprayed powders. One 431 powder displays improvements in deposition efficiency and altered microstructure when compared to its new counterpart. The other 431 powder displays detrimental degradation of cladding performance, with substantial cracking and inconsistent cladding melt-pool profiles. The differences in solidification behaviour of the similar alloys are traced. Benefits and challenges around toasted powder recycling are identified.

The authors acknowledge the support from the Australian Research Council (ARC). The ARC Training Centre in Surface Engineering for Advanced Materials, SEAM, has been funded under the ARC Industrial Transformation Training Centre (ITTC) scheme via Award IC180100005. We are grateful for the additional support of the industrial, university and other organisation partners who have contributed to the establishment and support of SEAM. This work is supported under a Swinburne University Postgraduate Research Award. This work is supported by D&T Hydraulics and Engineering, Mackay.