Understanding extreme high-speed laser material deposition: Characterisation, modelling and bonding mechanisms

Extreme high-speed laser material deposition (EHLA), a novel coating and additive manufacturing technique, has attracted scholarly and industrial attention since its inception in 2017. Although similar to laser cladding, EHLA is uniquely known for its substantially low heat input into the substrate during the deposition process, where the substrate can largely avoid being melted. In this work, the bonding mechanisms of EHLA are comprehensively studied by parameter optimisation, characterisation and numerical modelling. Taguchi design of experiment was used to explore the full range of key processing parameters for EHLA. Microscopic analyses revealed sharp coating/substrate interface with minimal elemental mixing or heat affected zone. Numerical modelling was used to rationalise the temperature and chemical species fields, which conferred the solid-state diffusion behaviour of the coating and substrate during the rapid fusion and cooling process. Miniaturised mechanical testing was performed to validate the bonding strength between the deposited coating and the substrate. This study formed a mechanistic understanding and a predictive model for optimising processing conditions suitable for untested material/substrate combinations using the EHLA process. • Defectless coating of alloy 625 was successfully deposited on SS316L substrate using EHLA. • The bonding between coating and substrate remained intact until 40% engineering strain. • The bonding mechanisms in the optimal case is attributed to solid state diffusion dominant. • A numerical model with a predictive capability is established to guide unknown coating and substrate choices.