Laser Surface Alloying, Cladding / Laser based Additive Manufacturing

We have restarted this work since 2015. Between 1996 and 2002, the work done was part of my Ph.D. at the Indian Institute of Science, Bangalore.

The localized nature of laser heat source provides a unique technique to modify the surfaces for enhanced mechanical properties. The ability to control the laser resolidification velocities and composition of the melt pool by optimizing the process conditions gives the opportunity to manufacture desired phases on surfaces of most metals and alloys. Several classes of materials are under study using Laser Cladding and Surface Alloying

Cladding Schematic

Bearing alloy coatings

Bearing alloys contain dispersions of soft phase in a hard matrix. Immiscible systems such as Aluminium-Bismuth, Aluminium-Silicon-Bismuth, Copper-Bismuth, Aluminium-Tin etc., form candidate materials for bearing alloys as the Bismuth, Tin etc., precipitate as globules in the matrix that is much harder. Such a dispersion can be achieved on the surface of desired materials using laser surface alloying. The high laser scan speeds can simulate high growth rates during solidification and yield fine dispersions of soft phase in relatively hard matrix.

Al-Bi Clad

Microstructure of aluminium laser surface alloyed with bismuth. Bismuth is seen as white phase.

Computational modelling

The computational model developed for welding can be modified to obtain heat, momentum and species distribution during laser surface remelting. The thermal parameters thus obtained could be used to perform several microstructure predictions. One such study is to obtain the size distribution of bismuth particles during laser suface remelting of Al-Bi hyper monotectic alloys clad on aluminium substrate. The model involves homogeneous nucleation applicable for immiscible (critical) systems, diffusional growth and collision and coalescence due to convection in the melt pool. The model successfully describes the nature of size distribution (asymmetric, with a tail) and the average size as a function of remelting speed for the case of aluminium-bismuth studied.

size distribution

References

Please Note that the soft copies of the papers are subject to copyright restrictions of the respective publishers.