Microstructural Characterization and Wear Behavior of Nano-Boride Dispersed Coating on AISI 304 Stainless Steel by Hybri
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UCTION
NICKEL-BASED alloys (Ni: 68.4 wt pct, Cr: 17 wt pct, B: 3.9 wt pct, Si: 4.9 wt pct, and Fe: 5.8 wt pct) are often attractive due to their excellent wear and corrosion resistance at ambient and high temperatures due to the dispersion of borides and carbide phases in the microstructure and also because of their relatively low cost.[1–3] In the past, several investigations concerned the development of nickel-based hard surface alloys on steel substrate for improvement of wear and corrosion resistance by both thermal spraying and laser cladding.[4–8] Among all thermal spraying techniques, it was observed that HVOF spraying offered a maximum improvement in hardness due to the development of dense coating.[5] However, presence of inter-splat boundaries and sharp interface imposes limitations on the application of the coating for the components which are subjected to high load.[9] Laser surface engineering is an advanced surface modification technique applied for tailoring the surface microstructure and/or composition of any component, which leads to development of a wear and corrosion resistance surface with a stronger interface.[10–12] In the past, laser surface cladding of nickel-based alloy (NiCrBSi) PRASHANT SHARMA, Senior Research Fellow, and JYOTSNA DUTTA MAJUMDAR, Professor, are with the Department of Metallurgical & Materials Engineering, I. I. T. Kharagpur, Kharagpur 721302, West Bengal, India. Contact e-mail: [email protected]. ernet.in Manuscript submitted July 31, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
was reported to be developed by laser cladding technique, however, was found to consist of micro-cracks attributed to the formation of eutectic borides and silicide phases in the microstructure.[13] In an earlier attempt, a hard and wear resistance nanoborides (of chromium, Cr2B, and nickel, and Ni3B) dispersed composite coating (in c-Ni matrix) was developed on AISI 304 stainless steel by HVOF spray deposition of NiCrBSi.[14] Though there was a substantial enhancement in microhardness (750 to 945 VHN), a very large residual compressive stress was introduced in the coated surface (234.5 MPa). Moreover, presence of a sharp interface and porosities (3 pct) was observed on the coated surface. Furthermore, the microstructures developed by both the HVOF spraying and laser melting are metastable in nature.[9,10] Hence, the stability of the microstructure needs to be studied in detail to ensure the thermal stability of the microstructure. In the current study, the effect of laser surface melting on high velocity oxy-fuel spray deposited nickel-based coating (NiCrBSi) on AISI 304 stainless steel has been conducted and its effect on wear and corrosion resistance properties has been evaluated in details. In addition, the high temperature stability of the as-coated and laser melted surface has been studied by differential scanning calorimetry analysis followed by a detailed phase analysis at room and elevated temperatures.
II.
EXPERIMENTAL
High velocity oxy-fuel (HVOF) spray deposited AISI 304 stainless
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