Single-Layer Deposits of Nickel Base Superalloy by Means of Selective Laser Sintering
Single layer deposits consisting of Mar-M 247 powder were consolidated on Alloy 718 polycrystalline flat sheets by means of the Selective Laser Melting (SLM) technique. The deposition process consisted in selectively fusing a powder bed precompacted using of an insulating non-wettable mask trough. The mask-powder-substrate arrangement was pre-heated inside a processing chamber under high vacuum. An inertreducing atmosphere was applied, and a focused Nd:YAG laser beam was then raster scanned at high speed along the contour of the trough, providing energy to induce a melting front to propagate along the powder as well as over the surface of the plate. As the laser beam moved forward a solidification front was left behind with a metallurgical bond between the substrate and the deposited layer. Optical microscopy revealed that epitaxial growth occurred in the  direction from the melted substrate to about half the height of the deposits. Above that height, the  dendritic front bowed towards the  direction. A dendritic-equiaxed transition appeared near the free surface of the deposit. These results indicate that the SLM technique could have potential application for growing single crystal structures as well as in repairing damaged or worn turbine blades.