Investigation of gas porosity in laser melted gray iron

Gray iron is one of the most common, versatile materials used today in the manufacturing world because it is inexpensive, yet strong and durable. If certain deficiencies in iron, specifically corrosion and wear in some applications, could be cost-effectively eliminated, then expensive alloys or composite materials would not be needed for some applications. Existing technology to improve the hardness and wear performance of iron has shown mixed results. A new technology, laser processing, is currently under development and shows great promise. Porosity is an identifiable problem when laser processing iron. Porosity, in general, can be traced to several sources. Some of the possibilities are shrinkage, trapped gases, material evaporation, and chemical reactions producing gases. In the case of laser melted iron, one reaction in particular is of interest. The oxidation of carbon in air is theorized to be a primary contributor to the porosity. Therefore this study investigates this hypothesis in order to verify the effect of oxygen on laser processed iron. For a specific set of processing conditions, inert shielding gases (nitrogen and argon) are compared with air to investigate the environmental effects, in particular the presence of oxygen, on the porosity. In addition, if oxygen is a problem, the possibility of using a deoxidizer to reduce porosity is considered. Titanium is chosen to be coated onto the gray iron to investigate this hypothesis. The current study investigates surface re-melting and alloying with titanium on gray iron. The results are presented quantitatively and qualitatively through metallurgical evaluation, gas chromatography, x-ray diffraction, SEM analysis, and microprobe analysis.