Surface Alloying of Tool Steels by Laser or Electron Beam Melting

Abstract

Lasers have been used for some years for surface hardening, cutting and welding [1,2]. Surface melting, glazing or alloying has however not received much attention until recently [2]. The various possibilities were first outlined by KEAR and coworkers [3]. The aim is to coat the surface with an appropriate alloy and melt it into the surface, thereby producing a surface with improved properties, for example high hardness, good abrasive resistance and corrosion resistance. The possible application or service life of a component could thus be extended relatively cheaply. The use of a Laser or Electron Beam offers further advantages. The energy density of such a beam can be extremely high ∼ 10⁵ W/mm² and is sufficient to heat the surface at a rate of 10⁷ – 10⁹ K/sec [4]. Unless the beam is moved at a sufficient rate the surface layer would evaporate. By moving the beam over the surface the liquid layer is quenched by the mass of the substrate. Cooling rates lie in the range 10⁴ – 10⁷ K/sec [4]. This rapid rate of cooling can produce fine crystalline and supersaturated or even amorphous surface layers. Amorphous layers are of necessity thin and hence of only limited use in technical applications. On the other hand the fine crystalline layers, which may be supersaturated are of fundamental interest and considerable technological importance.