RAPID SOLIDIFICATION FOLLOWING LASER MELTING OF PURE METALS .2. STUDY OF POOL AND SOLIDIFICATION CHARACTERISTICS

Various solidification parameters, like solid/liquid temperature gradient, cooling rate, nature of latent heat release, and pool characteristics, i.e. rate of change of width, depth and maximum velocity of the pool, are studied for rapid solidification following laser melting of aluminium and steel. For a fixed laser radius (i.e. 2.0 mm), the studies are carried out with various beam power densities between 10(8) and 10(9) W m-2. There is melting (i.e. 'post-melting') even after the laser is removed and the amount of post-melting is related to the amount of superheat of the pool. From the solid/liquid interface temperature gradient and the cooling rate, it is shown that the microstructure of the solidified material is very fine and the microstructure at the top of the pool is always finer than that at the bottom.