Materials Amorphized by Laser Irradiation

Abstract

That lasers can be used to melt and quench metallic alloys was realized some time ago [1], but active exploitation of the method has started only recently. Most of the present activities fall into one of two categories, namely work with scanned lasers [2] and work with pulsed lasers [3]. In the first group, a continous beam, typically from a high-power CO2 laser (a few 100 W to several kW), is scanned across a bulk metal workpiece, sometimes covered with a thin coating. In this process, often referred to as “laser glazing”, the coating and/or part of the bulk metal is molten by the beam and subsequently resolifies as the beam moves on. Sharply focussed beams must normally be used to overcome the high reflectivity of metals in the far infrared, but extended areas of a workpiece can be treated by applying partially overlapping line scans. Scanning velocities are usually limited by the absorbed power and range from tens of cm/s to a few m/s. Cooling rates in a scanned-laser heated surface region are comparable to those of mechanical quenching up to about 106 K/s—and enable glass formation only for easy glass formers [2], For all its technological potential, no physically new phenomena have been observed with laser glazing.