Processing and Characterization of Plasma Sprayed Iron Aluminide Coatings

Abstract

Surface modification is a generic term now applied to a large field of diverse technologies that can be gainfully harnessed to achieve increased reliability and enhanced performance of industrial components. Intermetallic compounds find extensive use in high temperature structural applications. The Fe3Al based intermetallic alloys offer unique benefits of excellent oxidation and sulfidation resistance at a potential cost lower than many stainless steels. These are mainly used in heating elements, regenerator disks, wrapping wire, hot gas filters, tooling, and shields. To obtain functional surface coating on machine components exhibiting selected in-service properties, proper combination of processing parameters has to be planned. These combinations differ by their influence on the coating properties and characteristics. Plasma spraying is gaining acceptance as a development of quality coatings of various materials on a wide range of substrates. Coatings made with plasma route exhibit excellent wear, corossion resistance and high thermal shock resistance etc. Iron premixed with 30% aluminium is deposited on mild steel and copper substrates by atmospheric plasma spraying at various operating power level ranging from 11to 21kW . After plasma spraying, the coated materials have been subjected to a series of tests. The particle sizes of the raw materials used for coating (iron with, 30 wt% aluminium powder) are characterized using Laser particle size analyzer of Malvern Instruments make. Thickness of the iron aluminide coatings are measured by using an optical microscope. X-ray diffraction technique is used to identify the different (crystalline) phases present in the coatings. The coating adhesion strength is evaluated by coating pull out method, as per ASTM C- 633 standard. Coated specimens are studied by JEOL JSM-6480 LV scanning electron microscope in order to know the surface and interface morphology. The porosity of the coatings is measured by putting polished cross sections of the coating sample under a microscope using image analyser. Microhardness measurement is done to know the hardness of the optically distinguishable phases by using Leitz Microhardness Tester Solid particle erosion is a wear process where particles strike against a surface and promote material loss. In this work, room viii temperature solid particle (sand) erosion test is carried out by using ASTM G76 standards. Deposition efficiency is evaluated as the important factor that determines the techno-economics of the process. Statistical analysis i.e. Artificial Neural Networks is gainfully employed to simulate property-parameter correlations in a space larger than the experimental domain. It is evident that with an appropriate choice of processing conditions a sound and adherent iron aluminide coating are achievable using iron aluminium powders.