Single-crystal laser deposition of superalloys: processing-microstructure maps

The transformation hardening of steel surfaces by laser beams—I. Hypo-eutectoid steels

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.

Epitaxial laser metal forming: analysis of microstructure formation

The solution of a traveling distributed heat source on a semi-infinite plate provides information about both the size and the shape of arc weld pools. The results indicate that both welding process variables (current, arc length and travel speed) and material parameters (thermal diffusivity) have significant effects on weld shape. The theoretical predictions are compared with experimental results on carbon steels, stainless steel, titanium and aluminum with good agreement. 25 references, 23 figures, 1 table.

Temperature fields produced by traveling distributed heat sources

https://iopscience.iop.org/article/10.1016/S1468-6996(01)00047-X/pdf

Columnar to equiaxed transition in solidification processing

A thermal analysis for laser heating and melting materials is derived for a Gaussian source moving at a constant velocity. The resulting temperature distribution, cooling rate distribution, and depth of melting are related to the laser spot size, velocity, and power level. As the power is increased to heat the liquid above the boiling point, a transition to deep penetration welding is described. Calculations are presented for 304‐stainless steel which are in agreement with experiment.

H. E. Cline

Papers

Heat treating and melting material with a scanning laser or electron beam