Problems Associated with Hydraulic Turbines

Surf. Topogr.: Metrol. Prop.

et al. 2021

This study aims to develop cavitation erosion-resistant clads on stainless steel (SS-316) using the microwave cladding technique. Ni-based alloy powder (EWAC) was reinforced with tungsten carbide (10% by wt) powder to obtain composite clads. The cladding process was carried out in a domestic microwave applicator of 2.45 GHz frequency with 900 W power. The microstructure, crystal structure (phase identification and quantification), and microhardness of the developed clad were investigated with scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), and Vickers microhardness tester, respectively. It was found that the deposited clad has a uniform thickness of ∼520 μm, and the microstructure mainly consists of equally dispersed and agglomerated carbides in cellular like Ni-Matrix. XRD analysis reveals that the composite clad was composed of various intermetallic, carbide, and oxide phases. The EWAC + 10WC clad (625 ± 81 HV0.3) has a hardness ∼3.5 times higher than the stainless steel substrate (195 ± 15 HV0.3). The cavitation erosion behavior of the SS-316 and EWAC + 10WC clad was examined by using a vibratory cavitation test apparatus. The parametric cavitation erosion testing was conducted according to the Taguchi L9 orthogonal array (OA) to study the effects of variations in amplitude (AMP), immersion depth (ID), and standoff distance (SOD) on mass loss in SS-316 and composite clad. The parametric study results show that SOD was the most influential test parameter, followed by AMP and ID. SOD contributes more than 50% in the mass loss of SS-316 and clad specimens, whereas AMP and ID contribution was around 32%–37% and 7%–11%, respectively. The developed EWAC + 10WC clad performed ∼6.7 times better than the SS-316. Nevertheless, the SS-316 and EWAC + 10WC clad specimens got severely damage in the form of pits, craters, plastic deformation, lip formation, impingement marks, and secondary cracks.

Section: Introductionmentioning

confidence: 99%

Parametric optimization and analysis of cavitation erosion behavior of Ni-based + 10WC microwave processed composite clad using Taguchi approach

Surf. Topogr.: Metrol. Prop.

et al. 2021

“…The ensuing collapse of these cavities generates micro-jets and high-pressure shock waves, resulting in material erosion [3]. Moreover, to meet the demand for increased energy requirements nowadays, hydraulic systems need to operate at higher speeds and pressures, which increases the severity of cavitation erosion [4]. Because of the involvement of special attack features, such as impulsiveness, randomness, stress localization, and repetitiveness, the cavitation phenomenon becomes unique, which needs to be studied independently [5].…”

Section: Introductionmentioning

confidence: 99%

Microwave cladding of NiCrSiC-5Al₂O₃ on austenitic stainless steel to improve cavitation erosion resistance

Surf. Topogr.: Metrol. Prop.

et al. 2021

The current investigation aimed to study the cavitation erosion performance of the microwave synthesized NiCrSiC-5Al 2 O 3 composite clad with a 900 W power multimode domestic microwave applicator of 2.45 GHz frequency. The clads were deposited on the austenitic grade stainless steel, namely AISI-316. The as-deposited composite clad's microstructure, crystal structure, porosity, microhardness, and flexural strength were examined. Cavitation erosion study was done using the vibratory cavitation method at varying standoff distance (SOD)-(0.5 mm, 1 mm, 1.5 mm) and vibration amplitude (AMP)-(40 μm, 50 μm, 60 μm), keeping other parameters constant. The results had shown that the deposited NiCrSiC-5Al 2 O 3 composite clad exhibited 1.20% porosity, 489.16±47.95 HV 0.3 microhardness, 264.91±4.5 MPa flexural strength, and performed 3.5 times much better than the AISI-316 in terms of cavitation resistance. The least weight loss occurred at 1.5 mm SOD and 40 μm AMP, where the highest weight loss was observed at 0.5 mm SOD and 60 μm AMP. The erosion mechanism of the NiCrSiC-5Al 2 O 3 composite clad surface was observed as plastic deformation followed by surface fatigue; the clad surface was eroded in the form of pits, craters, impingement marks, secondary cracks, and plastically deformed lips.

“…In the case of hydropower plants, hydraulic turbine and its components get severely damaged by cavitation (pits formation due to vapour bubbles explosion near the surface of the component) and silt or sediment erosion. 7 The components of the hydraulic turbine are manufactured from austenitic and martensitic stainless steel. 8 However, stainless steel has a variety of applications in other industries, e.g.…”

Section: Introductionmentioning

confidence: 99%

Influence of microwave heating on metallurgical and mechanical properties of Ni-40Cr₃C₂ composite clads in the context of cavitation erosion resistance characteristics

Proceedings of the Institution of Mechanical Engineers, Part C:

et al. 2020

Surface modification is one of the most reliable solutions for protecting the material damage in hydraulic turbines due to cavitation phenomena. However, the conventional coating/cladding process has many drawbacks like high porosity, weak adhesion strength, and poor fracture toughness. In contrast, the cladding process with microwave hybrid heating can overcome these limitations. Hence, this study aims to develop the microwave processed composite clad of Ni-based alloy with 40% Cr3C2 (by wt.) on SS-316 substrate in the domestic microwave oven of 2.45 GHz frequency and 900 W power. The selection of the material system for this study was based on mitigating the effect of cavitation erosion. The thorough metallurgical and mechanical characterization of the developed composite clad was done. Microstructural characterization using scanning electron microscopy revealed that the developed composite clads had a uniform thickness of 600 µm and free from interfacial cracks and visible pores (measured porosity ∼1.67% – as per ASTM B276). Uniformly dispersed hexagonal and stripe type carbides precipitate in the Ni-based alloy matrix of the composite clad was observed through scanning electron microscopy images. X-ray diffraction analysis shows that various hard carbides (SiC, Ni3C, Cr3Ni2SiC, Cr7C3, and NiC) and intermetallic (Ni3Fe, Ni2Si, and Cr3Si) phases were formed during microwave heating. The microhardness, flexural strength, fracture toughness of the Ni-40Cr3C2 clads were evaluated. The results reveal that the composite clad possesses microhardness = 605 ± 80 HV0.3 (∼3 times SS-316), flexural strength = 813.23 ± 16.2 MPa, and fracture toughness = 7.44 ± 0.2 MPa√m. The appropriate value of these properties makes this composite clad suitable for cavitation erosion resistance application.