Erosion-corrosion is a critical problem in marine components and has huge economic impact. In the current study, friction stir processing was utilized for enhancing the erosion-corrosion resistance of SS316L steel, most widely used material for marine applications. Compared to the unprocessed alloy, the friction-stir processed specimen showed nearly 3.5 times and 5 times higher erosion and erosion-corrosion resistance respectively at oblique impingement. In contrast, erosion and erosion-corrosion resistance for processed alloy was 2 times higher at normal impingement. The unusual enhancement in erosion-corrosion resistance was attributed to surface strengthening through grain-size refinement and martensite phase formation. In addition, higher corrosion resistance due to stronger passivation also contributed towards superior performance of the processed alloy. © 2017 Elsevier B.V.

Harpreet Singh Grewal

Mechanical Engineering

(SoE) School of Engineering

Selvam K.

Ayyagari A.

Mukherjee S.

Arora H.S.

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Shiv Nadar University

Wear

Herein, bimodal-reinforced AlCoCrFeNi complex concentrated alloy composite cladding on stainless steel 316L substrate using microwave hybrid processing is synthesized. Detailed microstructural analysis of the claddings shows the presence of cellular structure A2 (disordered BCC) with intermetallics (B2 (ordered BCC) and σ phases) at the intercellular regions. The presence of Cr23C6 is also observed for the reinforced claddings due to the dissociation of the SiC particles. The bimodal-reinforced cladding shows the highest hardness (in excess of 800 HV) and fracture toughness (≈12 MPa√m), followed by micro- and nanocomposite claddings. Under slurry erosion condition, the bimodal composite cladding exhibits 10 times better erosion resistance than stainless steel 316L and nonreinforced cladding (1.5–2 times), respectively, at oblique angle followed by nano- and microreinforced unimodal counterparts. The outstanding performance of the bimodal composite cladding under both test conditions is related to higher hardness, fracture toughness, and resistance to plastic deformation. The detailed analysis of the eroded samples shows microcutting and ploughing as a dominant mechanism at an oblique angle while platelets, cracks, and microindents being the contributing factors for erosion at the normal impact angle. © 2020 Wiley-VCH GmbH

Advanced Engineering Materials

Slurry Erosion–Corrosion of Bimodal Complex Concentrated Alloy Composite Cladding

Thermal spray coatings (TSCs) are widely utilized for limiting degradation of structural components. However, the performance of TSCs is significantly impaired by its inherent non-homogeneous microstructure, comprising of splat boundaries, porosities, secondary phase-formation, and elemental segregation. Herein, we report a simplistic approach for significantly enhancing the corrosion resistance of TSCs. Ni-Cr-5Al2O3 coatings were deposited on stainless steel using high-velocity oxy-fuel technique. The microstructure of as-sprayed coating showed significant inhomogeneities in the form of isolated splats and elemental segregation. The microstructure of developed coatings was modified using a novel processing technique, known as stationary friction processing (SFP). The SFP treatment resulted in complete refinement of coating microstructure with elimination of splat boundaries and pores along with elemental homogenization. The corrosion behavior of as-sprayed and SFP treated coating was evaluated in 3.5\% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. The SFP treatment reduced the corrosion rate of as-sprayed coating by an order of magnitude. Long-time immersion studies showed continuously decreasing impedance of the as-sprayed coating due to the penetration of the electrolyte along the splat boundaries. In contrast, impedance for the SFP treated coating increased with the immersion time due to the removal of all microstructural defects. Copyright © 2020 American Chemical Society.

Fulltext

ACS Omega

Facile and Green Engineering Approach for Enhanced Corrosion Resistance of Ni-Cr-Al2O3Thermal Spray Coatings

In this study, a novel processing technique for microstructural refinement of Ni-Cr-5Al2O3 composite coating developed using high velocity oxy-fuel (HVOF) technique is demonstrated. The processing technique, known as stationary friction processing (SFP) is an adaptation of the well-known friction stir processing (FSP). The as-sprayed coating showed a typical lamellar microstructure along with non-homogeneous elemental distribution. The SFP treatment resulted in significant microstructural refinement with complete elimination of splat boundaries and pores together with fully homogeneous elemental distribution. The performance of as-sprayed and processed coatings was evaluated in slurry erosion, erosion-corrosion and pure corrosion in 3.5\% NaCl solution. At oblique impingement angle, the SFP treated sample showed minimum erosion rate of nearly 0.1 mm3/h which is 3–5 times lower than the as-sprayed coating and the substrate. For normal impingement, the erosion rate of SFP specimen was nearly 30\% lower compared to the as-sprayed coating and the substrate. This is attributed to higher hardness as well as fracture toughness of the SFP treated coating as a result of microstructural refinement. In addition, the SFP treated coating was able to demonstrate superior resistance under erosion-corrosion conditions as well. Further, the processed sample showed lowest corrosion rate of 0.079 μA/cm2, 5–6 times lower than the as-sprayed coating (0.39 μA/cm2). The enhancement in the corrosion resistance of the coating after processing is attributed to complete homogenization of the coating with removal of all splats, splat boundaries, pores and regions of elemental segregation. © 2020 Elsevier B.V.

Surface and Coatings Technology

Structural rejuvenation of thermal spray coating through stationary friction processing

Cavitation erosion remains the primary cause of material degradation in fluid machinery components operating at high speed. Micro-jets/shock waves caused by implosion of bubbles on material surface results in significant material loss and premature failure of the components. The presence of corrosive medium further exuberates this effect, causing rapid degradation. Here, we demonstrate a novel pathway to control cavitation erosion-corrosion by tailoring the surface properties using submerged friction stir processing (FSP), a severe plastic deformation process. FSP parameters were varied over wide range of strain-rates to generate tailored microstructures. High strain-rate processing resulted in nearly single phase fine grained structure while low strain-rate processing resulted in phase transformation in addition to grain refinement. As-received and processed samples were subjected to ultrasonic cavitation in distilled water as well as in corrosive environment of 3.5\% NaCl solution. Individual roles of cavitation erosion, corrosion and their synergistic effects were analyzed. Depending on the microstructure, processed samples showed nearly 4–6 times higher cavitation erosion resistance compared to as-received alloy. Superior cavitation erosion-corrosion resistance of processed samples was attributed to surface strengthening, higher strain-hardening ability and quick passivation kinetics. The results of current study could be potentially transformative in designing robust materials for hydro-dynamic applications. © 2018 Elsevier B.V.

Ultrasonics Sonochemistry

Ultrasonic cavitation erosion-corrosion behavior of friction stir processed stainless steel

Metallurgical and Materials Transactions A

Effect of Strain Rate on the Martensitic Transformation During Plastic Deformation of an Austenitic Stainless Steel

Materials & Design

Microstructure and mechanical properties of friction stir processed AISI 316L stainless steel

International Journal of Corrosion

Effects of Strain Energy and Grain Size on Corrosion Resistance of Ultrafine Grained Fe-20%Cr Steels with Extremely low C and N Fabricated by ECAP

Journal of Materials Engineering and Performance

Effect of Temperature and Chloride Ion Concentration on Corrosion of Passive Films on Nano/Ultrafine Grained Stainless Steels

Applied Surface Science

Improvement in cavitation erosion resistance of AISI 316L stainless steel by friction stir processing

Enhancing the erosion-corrosion resistance of steel through friction stir processing