Utilization of a carbon-dioxide laser to form an amorphous metallic layer on gray cast iron with various amount of boron

This study was conducted to examine the capability of a medium-powered carbon-dioxide laser to form an amorphous metallic layer on the surface of a ferritic gray cast iron in order to improve the wear and corrosion resistance of engineered components. Boron was used as an alloying element for the retardation of nucleation and for the formation of the amorphous metallic layer. Homogenization heat treatment was followed by vacuum emission spectroscopy, which provided the quantitative information related to the chemical composition prior to the laser processing. The laser parameters were chosen and they were examined experimentally to identify the optimum conditions for the process. The characteristics of the laser-formed layer on the surface of specimens were determined by chemical testing, x-ray diffraction techniques, scanning electron microscopy, and electron diffraction techniques to substantiate the formation of the metallic glass layer and examine its features. Micro-hardness examination was used to determine the hardness profile of the generated layer at the heat-affected zone. Metallographic examination provided such information as the surface condition, the depth of the fusion zone, and any defects caused by the process. The test results led to the conclusion that the carbon-dioxide laser, with medium power output within a certain range of operation, is capable of forming metallic glass structures on the surface of gray cast iron, alloyed with boron. In such a process, the laser must operate at the pulse mode generating a pulse with short width and long dwell time. In addition, the boron content of the sample should be in the range of 3.8 (eutectic point) to 4.17 percent by weight. The hardness measurement of the untreated surface showed a notable increase in the hardness of the specimen containing two percent boron. The micro-hardness examination of the laser-treated area revealed that the treatment caused a further increase in the micro-hardness of the specimens. Electron Diffraction Spectro-Analysis of the laser heat treated zones did not conform to the structures predicted by the iron-carbon-boron and iron-carbon-silicon ternary diagrams. The laser treated surfaces produced a super-saturated structure with a high hardness and good resistance to corrosion. (Abstract shortened with permission of author.