Tungsten-chromium coatings on reduced activation ferritic/martensitic steels prepared by laser melting deposition process

Abstract Tungsten-chromium alloys are promising plasma facing materials in future fusion reactors considering the loss of coolant accident (LOCA). A laser melting deposition (LMD) additive manufacturing technique has been used in this study to deposit 90W-10Cr coatings on reduced activation ferritic/martensitic (RAFM) steels. The results show that the coatings have metallurgical bonding with the RAFM steel substrates. The W-steel joint have graded transitions of compositions, microstructures, and phases along the deposition direction due to the dilution effects of the substrates, which are beneficial to reduce thermal stresses of W-steel joints. Pores and cracks are seen in the coatings prepared using different process parameters. Low and high input energy densities can both lead to pore formations due to the combined effects of lack of fusion, residual of delivered gas, and evaporations of low melting point elements. Cracking is driven by the internal stress during LMD process and liquation of binding matrix. Fe7W6 intermetallics are mainly formed near the bonding boundaries of W-steel joint, showing a dispersed distribution either scattered in the matrix or surrounding the scattered W particles. The top and mid-top regions of coatings have unique microstructures showing W particles embedded in Cr-Fe based matrix, which are supposed to have reliable performance both during the operations of reactors and the LOCA.