Influence of gas boriding on corrosion resistance of Inconel 600-alloy

Abstract

Purpose: The aim of this study was to analyse the corrosion behaviour of gas-borided layers produced on Inconel 600-alloy. Two types of the borided layers were produced: fully borided and partially borided layer. The results obtained for gas-borided specimens were compared to untreated Inconel 600-alloy. Design/methodology/approach: In this paper, gas boriding in N2-H2-BCl3 atmosphere was applied to produce the boride layers on Inconel 600-alloy. This process was carried out at 910°C (1193 K) for 2 h. Microstructure observations were carried out using a light microscope. The hardness measurements were performed using a Vickers method under a load of 0.981 N. In order to evaluate the corrosion resistance, the immersion corrosion test in a boiling solution of H2O, H2SO4 and Fe2(SO4)3 was used. Findings: The gas-borided layers consisted of a mixture of nickel borides (Ni3B, Ni2B, Ni4B3, NiB) and chromium borides (CrB, Cr2B). The high thickness of compact boride layer (76-79 μm) as well as high hardness (up to 2061 HV) were obtained. Based on corrosion resistance tests it was found that in case of untreated sample the strong intergrannular attack was observed. Whereas the corrosion behavior ofgas-borided Inconel 600-alloy was more complicated and resulted from the surface condition. Research limitations/implications: The obtained results indicated that gas-boriding in N2-H2-BCl3 atmosphere could be a suitable corrosion protection if the whole surface would be covered with boride layer. Practical implications: The parameters of gas boriding in N2-H2-BCl3 atmosphere used in this study (temperature of 910°C for 2 h) allowed to produced layers of a higher thickness in comparison with other acceptable method of boriding e.g. powder-pack boriding. Originality/value: Based on the results it was found that gas-boriding in N2-H2-BCl3 atmosphere is a suitable method to protect Inconel 600-alloy from corrosion.