Thermal spray coatings are widely used for addressing erosion problems in fluid machineries. However, the presence of splat boundaries, non-homogeneous microstructure and element segregation limits their performance. In this study, we developed Ni-Cr-40Al2O3 coatings on stainless steel (SS316L) substrate using high-velocity flame spray followed by post-processing using friction stir processing. The performance of as-sprayed and processed coatings was evaluated in slurry erosion, erosion–corrosion and pure corrosion in 3.5\% NaCl solution. As-sprayed coating showed lower erosion and erosion–corrosion resistance compared to stainless steel. Friction stir processing resulted in significant microstructure refinement concurrent with enhanced hardness and fracture toughness of the developed coating. At oblique impingement angle, the processed coating showed nearly 30\% to twofold higher erosion and erosion–corrosion resistance compared to stainless steel substrate. During pure erosion at normal impingement, both as-sprayed and processed coating showed higher volume loss. However, during erosion–corrosion at normal impingement, the processed coating was able to demonstrate similar volume loss as that of the substrate. In addition, the processed coating showed significant improvement in the corrosion performance as well. The study showed that friction stir processing could be a promising pathway to unravel the deleterious effects of inherent non-homogeneities in thermal spray coatings. © 2019, ASM International.

Harpreet Singh Grewal

Mechanical Engineering

(SoE) School of Engineering

Harpreet Singh

Rani M.

Perumal G.

Roy M.

Singh H.

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Shiv Nadar University

Journal of Thermal Spray Technology

<p>Hydro machinery components such as turbines, pipes, guide vanes, and pumps suffer from severe slurry erosion caused by the abrasive particles entrained in working fluid. In the current work, an array of systematic slurry erosion tests were executed to study the influence of impact angle on slurry erosion rates of Ni-SiC based composite claddings developed on SS 316&nbsp;L through microwave hybrid heating. Various microstructural and mechanical characterizations such as micro and nano-indentation, x-ray diffraction (XRD), and scanning electron microscopy (SEM) were performed on the developed claddings. The claddings contain 5&nbsp;wt.\% of SiC particles of different size fractions from nano to micro (unimodal) and combination of both in the matrix (bimodal). Slurry erosion studies were performed on the developed claddings at different impingement angles. The claddings exhibited good metallurgical bonding with the substrate without any pores throughout. The developed claddings exhibited high hardness and elastic modulus compared to the substrate material. A significant improvement in the erosion resistance of the claddings was observed with the addition of bimodal sized SiC secondary particles. The enhanced erosion resistance of the claddings could be attributed to the higher fracture toughness and hardness of the developed coating. Among the developed coatings, the bimodal sample with 5\% SiC claddings showed at least two times better erosion resistance than hydro-turbine steel at almost all the impact angles. SEM studies performed on the eroded samples showed micro-cutting and plowing as the main modes of material removal at lower impact angles. © 2021, Springer Nature B.V.</p>

Silicon

Slurry Erosion Resistance of Microwave Derived Ni-SiC Composite Claddings

In the current study, surface modification of austenitic stainless steel, SS316L, was done using friction stir processing. The strain rates during processing were varied over a wide range by using two different tool rotational speeds of 388 rpm and 1800 rpm. The processing was done at two different conditions of: (i) ambient cooling and (ii) submerging in liquid bath maintained at 0 °C. Friction stir processing resulted in significant grain refinement from 22 μm for the as-received alloy to 0.67 μm for the sample processed at 388 rpm under submerged cooling condition. A relationship between the final recrystallized grain size and Zener-Holloman parameter was developed as Z=72.84/d. Deformation texture for processed specimens showed strong strain rate and temperature dependence. Sample processed at high temperature and low strain-rate showed copper-type texture while low temperature and high strain-rate promoted brass-type texture. Hardness of processed specimens showed an increase while elastic modulus decreased after processing which is explained by texture evolution during processing. Tribological properties of processed specimens were evaluated using reciprocating wear tests and slurry erosion tests. The processed samples showed significant improvement in the wear and erosion resistance and were found to have strong correlation with the flow work given as hardness to elastic modulus ratio. © 2017 Elsevier B.V.

Materials Chemistry and Physics

Structural refinement in austenitic stainless steel by submerged friction stir processing

Industrial Lubrication and Tribology

Slurry erosion behavior of plasma sprayed coating on turbine steel

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

Synergistic effect of Al2O3/TiO2 reinforcements on slurry erosion performance of nickel-based composite coatings

Materials Research Express

Influence of microwave hybrid heating on the sliding wear behaviour of HVOF sprayed CoMoCrSi coating

Defence Technology

Evaluating location specific strain rates, temperatures, and accumulated strains in friction welds through microstructure modeling

Post-processing of Ni-Cr-Al2O3 Thermal Spray Coatings Through Friction Stir Processing for Enhanced Erosion–Corrosion Performance