INVESTIGATIONS ON DRY SLIDING AND EROSION WEAR OF MICROWAVE INDUCED WEAR RESISTANT SURFACES

Abstract

Stainless steel (SS-304) is one of the most widely used engineering materials owing to it excellent corrosion resistance. Stainless steel is inherently poor in wear and erosive resistance though excellent in corrosion resistance. The conventional way to tackle the problem is to design a new wear resistant material. But it may not be a cost effective solution. Hence a pragmatic approach can be modification of the functional surface so that stainless steel can sustain aggressive environments. Cladding is one of the most commonly used pragmatic surface modification techniques in which the chemistry of the target surface is changed with a material of desired properties. In the present work a novel processing technique, microwave heating, has been explored to enhance the surface properties of the stainless steel using Inconel 718. Inconel 718 is one of the most widely used Fe-Ni based superalloy. Attributed to high strength, excellent corrosion and wear resistance, excellent fatigue and creep resistance make it an ideal material to be used in high temperature applications like gas and steam turbines, nuclear reactors, rocket engines etc. Volumetric heating nature of microwaves with principles of hybrid heating have been exploited to develop Inconel 718 cladding on stainless steel surfaces at 900 W at 2.45 GHz. Clads were developed due to partial melting and dilution of the substrate and complete melting of powder particles. Approximately 1 mm thick dads were developed, which were further characterised using XRD, FE-SEM, EPMA, porosity analysis using Dewinter Material Plus software tool (version 4.2) and measurement of Vicker's microhardness. The functional characterisation of cladding was carried out in terms of dry sliding wear test and erosive wear test (air jet erosion). The XRD of the clad reveals formation of various strengthening phases of Ni3Ti and Ni3Al. The diffraction patterns also reveal formation of FeNi phase indicating dilution of the substrate. The microstructure reveals that there is metallurgical bonding between cladding and substrate. Clads were found virtually free from cracks. Clads were further investigated using EPMA to investigate the distribution of various elements across the clad. Nearly uniform distribution of nickel and chromium was observed. Microhardness study was also carried out; the microhardness profile was approximately uniform. The average microhardness in the clad recorded was 572±22 H. The sliding wear characteristics of the clad were analysed on standard pin-on-disc arrangement. Clads exhibit significant resistance to wear owing to strengthening phases formed during cladding. The erosive wear tests were carried out on dads as per ASTM G76 standard. Results indicate improved erosive performance of dads owing to the dense microstructure and hard phases like chromium carbides formed during microwave cladding.