Epitaxial laser metal forming: analysis of microstructure formation

Epitaxial laser metal forming (E-LMF) is presented as a new cladding technique which combines the advantage of near-net-shape manufacturing with a close control of the solidification microstructure. E-LMF is a process where metal powder is injected into a molten pool formed by controlled laser heating. Laser surface treatment has the advantage that heat input is very localised, thus leading to large temperature gradients. This is used, in unison with closely controlled solidification velocities, to stabilise the columnar dendritic growth, thereby avoiding nucleation and growth of equiaxed grains in the laser clad. It is possible with this technique to deposit a single crystal clad by epitaxial growth onto a single crystal substrate. In this paper, the microstructure obtained by E-LMF is analysed by scanning electron microscopy (SEM), optical microscopy (OM) and indexing electron backscattered diffraction (EBSD) patterns. In particular, the grain structure formation in the deposit during the process and the influence of a subsequent heat treatment on precipitation and recrystallisation is characterised.