Crack-free tungsten coating on ODS plate via a modified laser-based additive technique: Offset laser cladding

A modified laser-based additive manufacturing technique, offset laser cladding was introduced to achieve dense tungsten coating on an oxide dispersion-strengthened (ODS) substrate as a plasma facing material (PFM). Different from ordinary direct energy deposition (DED) which leads to incomplete melting of tungsten and excessive melting of ODS substrate, the offset laser cladding technique can achieve complete melting of tungsten while substrate melting is suppressed. Experimental conditions (i.e., laser power, scanning speed, powder size, offset distance and injection powder nozzle setting) were carefully calculated using two validated simulation models to minimize the consumption of valuable experimental resources. Tungsten coating using the offset laser cladding in an open chamber condition showed that dense coating was achieved with a pore size of 1-2 mu m. The result is comparable to that of vacuum plasma spray (VPS) tungsten coating which requires a high-level vacuum chamber. A thin interface layer (2-5 mu m) was formed between the tungsten coating and ODS substrate that can alleviate thermal damage due to a large thermal expansion coefficient difference. While a small amount of surface melting was involved, the microhardness test revealed that the ODS substrate was insignificantly affected by laser heating during the offset laser cladding.