The research of wear and corrosion-resistant properties of laser coatings with strengthening phase

One of the most promising methods of spraying protecting coating is the laser coating with strengthening phases, alloying or modifying elements. The purpose of this study is the creation of composite wear and corrosion resistant coatings by additive technology of laser coating for oil and mining industries. The possibility of obtaining complex coating with a strengthening phase is shown. Two variants of coating were considered. Variant 1: support plate made of 12Х18Н10Т stainless steel was cladded with sublayer made of Ni + Cr powder, afterwards the upper cladding layer made of Х23Н5М3ГС steel of Cr-Ni-Мn system was formed with various content of strengthening WC phase in the form of VK-12 powder. Variant 2: support plate made of carbon steel was cladded with four layers of self-fluxing cladding powder PS-12NVK-01 of Ni-Cr-Fe / WC system with addition of nanomodification of powder TiN + Y2O3 + Cr + Fe. The specialists established the dependence of microstructure, structural-phase components and micro hardness of cladded layer from the quantity of WC strengthening phase. The various content of WC strengthening phase (from 10 to 30 %) does not influence the micro hardness of the upper layer significantly – it’s average value is ≈ 700 HV The laser influence on powder mixture leads to partial deterioration of WC strengthening phase, which leads to chemical reaction of tungsten cobalt powder and stainless steеl with formation of complex intermetallic compounds and carbides. Small addition of nanosized modifier TiN + Y2O3 (0,1 % of weight) in a composite mixture with coating power PS-12NVK-01 allows increasing the hardness of protective coating by 1.4, and wear-resistance – by 2 times in comparison to the coatings with similar characteristics, obtained without nanomodifying additions.

High Temperature Corrosion Behaviors of 20G Steel, Hastelloy C22 Alloy and C22 Laser Coating under Reducing Atmosphere with H2S

High-temperature corrosion behaviors of 20G steel, Hastelloy C22 alloy and C22 laser coating was evaluated by corrosion mass gain measurements at 450 °C. The corrosive atmosphere is 0.2 vol% H2S–0.1 vol% O2–N2, which simulated the severe high-temperature corrosion environment occurred under low-NOx combustion in pulverized-coal furnaces. Experimental results showed that the corrosion resistance of the C22 laser coating and the C22 alloy was obviously better than 20G steel. Furthermore, it should be noted that the C22 laser coating fabricated in this study displayed a higher corrosion resistance than the commercial C22 alloy although they had the same chemical composition. The severe pitting corrosion was observed in 20G steel with the corrosion products consisting of FeS2, Fe2O3 and Fe3O4. The C22 alloy and C22 laser coating exhibited the uniform corrosion and their main corrosion products were NiS2, CrS and a small amount of chromium and manganese oxides.

A Novel Method of Laser Coating Process on Worn-Out Cutter Rings of Tunnel Boring Machine for Eco-Friendly Reuse

Cutter rings form an integral part of tunnel boring machines (TBM). These cutters are deployed in various hard rock tunneling projects. The life of the cutter rings governs the economics of tunneling significantly. This paper presents a novel methodology to enhance hardness and wear resistance of used worn out disc cutters in TBM for eco-friendly reuse. Disc cutters are mainly made of H13 tool steel. To improve the hardness and wear resistance, a layer of tungsten carbide is coated on the used cutter rings. Considering the long operating hours of TBM, cutter rings get worn out due to severe interaction with the hard rock both in compression and rolling mode. Replacement of the cutter-ring is costly, and quite a time consuming and cumbersome job. Refurbishment is always a better option and laser cladding is a novel technique for enhanced life of cutters. It increases the hardness and wear resistance of the cutters to a considerable extent. Cladding is carried out with the help of a laser beam. In this method, a layer of nanoparticles of tungsten carbide powder is deposited on the worn-out surface of the cutters. For carrying out the investigation, different coating parameters are selected based on the central composite design (CCD). With different capacities of laser, a total of 13 samples were prepared at various scanning speeds varying between 200 to 300 mm/min and a level of laser power varying between 100 to 200 W. The coating is critically inspected by various means such as an optical microscope, FESEM, and EDS. Hardness testing was accomplished by Vicker’s hardness testing machine. Wear testing was carried out with the aid of pin on disc setup. The results shows an asymmetrical behavior between the yield parameters (hardness and wear rate) and process parameters (scanning speed and laser power). The hardness values increased from 16% to 95%. A correlation test was conducted between the hardness and wear rate. The results depict a clear negative correlation between them, indicating the advantage of laser coating for reducing cutter ring wear in TBM.