Surface Modification
Lasers and electron beams can be used as sources of intense heat at the surface for heat treatment, remelting (glazing), and compositional modification. It is possible to achieve different molten pool shapes and temperatures. Cooling rates range from 103 – 106 K s-1. Beneficially, there is little or no cracking or porosity formation.
While the possibilities of heat treating at the surface should be readily apparent, the other applications beg some explanation. At cooling rates in excess of 106 K s-1 eutectic microconstituents disappear and there is extreme segregation of substitutional alloying elements. This has the effect of providing the benefits of a glazed part without the associated run in wear damage.
The alloy composition of a part or tool can also be changed to form a high speed steel on the surface of a lean alloy or to form an alloy or carbide enriched layer on the surface of a high speed steel part. Several methods can be used such as foils, pack boronising, plasma spray powders, powder cored strips, inert gas blow feeders, etc. Although this method has been reported to be both beneficial and stable, it has yet to see widespread commercial use.
Read more about this topic: High Speed Steel
Famous quotes containing the word surface:
“Brave men are all vertebrates; they have their softness on the surface and their toughness in the middle.”
—Gilbert Keith Chesterton (1874–1936)