Epitaxial laser metal forming: analysis of microstructure formation

Epitaxial laser metal forming (E-LMF) is presented as a new cladding techni que which combines the advantage of near-net-shape manufacturing with a clo se control of the solidification microstructure. E-LMF is a process where m etal powder is injected into a molten pool formed by controlled laser heati ng. Laser surface treatment has the advantage that heat input is very local ised, thus leading to large temperature gradients. This is used, in unison with closely controlled solidification velocities, to stabilise the columna r dendritic growth, thereby avoiding nucleation and growth of equiaxed grai ns in the laser clad. It is possible with this technique to deposit a singl e crystal clad by epitaxial growth onto a single crystal substrate. In this paper, the microstructure obtained by E-LMF is analysed by scanning electr on microscopy (SEM), optical microscopy (OM) and indexing electron backscat tered diffraction (EBSD) patterns. In particular, the grain structure forma tion in the deposit during the process and the influence of a subsequent he at treatment on precipitation and recrystallisation is characteriscd. (C) 1 999 Elsevier Science S.A. All rights reserved.