Sanjeev Bhandari

Parametric Study of Slurry-Erosion of Hydroturbine Steels with and without Detonation Gun Spray Coatings using Taguchi Technique

WC-Co-Cr coatings were deposited on some hydroturbine 13Cr4Ni and 16Cr5Ni steels by the detonation-gun spray process. An in-depth characterization of the as-sprayed coating was done using X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) techniques. Microhardness and porosity measurements were also made. The coating was found to have a typical splat-like morphology with some indications of unmelted carbide particles. The XRD results showed the presence of WC as the primary phase along with W2C and Co6W6C as secondary phases. Furthermore, the slurry erosion behavior of the coatings was investigated to ascertain the usefulness of the coatings to reduce the slurry erosion of the steels. The effect of four operating factors viz. the velocity, impact angle, concentration, and particle size on the slurry erosion of coated and bare steels has been studied using a high-speed jet-type test rig. The sand used as an erodent was collected from a power plant to replicate the actual turbine conditions. It has been observed that the given cermet coating can enhance the erosion resistance of the steel. Velocity was found to be the most significant factor affecting the erosion behavior of the coating, whereas it was the erodent particle size in the case of uncoated steel. As evidenced from the SEM images, the platelet mechanism of erosion seemed to be the prominent one, causing the removal of material from the surface of the steel, whereas for the coating, the formation and interlinking of cracks resulted in the removal of material.

Slurry Erosion Behaviour of Detonation Gun Spray Al2O3 and Al2O3–13TiO2-Coated CF8M Steel Under Hydro Accelerated Conditions

Slurry erosion performance of detonation gun (D-gun) spray ceramic coatings (Al2O3 and Al2O3–13TiO2) on CF8M steel has been investigated. Slurry collected from an actual hydro power plant was used as the abrasive media in a high speed erosion test rig. Attempt has been made to study the effect of concentration (ppm), average particle size and rotational speed on the slurry erosion behaviour of these ceramic-coated steels under different experimental conditions. The analysis of eroded samples was done using SEM, XRD and stylus profilometry. The slurry erosion performance of the D-gun spray Al2O3–13TiO2-coated steel has been found to be superior to that of Al2O3-coated steel. Both the coatings showed brittle fracture mechanism of material removal during the slurry erosion exposure.

Slurry Erosion Performance Study of Detonation Gun-Sprayed WC-10Co-4Cr Coatings on CF8M Steel Under Hydro-Accelerated Conditions

In the current investigation, cermet coatings (WC-10Co-4Cr) were deposited on CF8M steel by detonation gun (D-gun) thermal spraying process. Subsequently, the slurry erosion behaviors of the coated and bare steels were investigated using a high-speed erosion test rig. Slurry collected from an actual hydro power plant was used as the abrasive media. Effects of concentration (ppm), average particle sizes and rotational speed on the slurry erosion behaviors of coated and bare steels under different experimental conditions were studied. The analysis of eroded samples was done using SEM and stylus profilometry. Signatures of microcutting, fracture of well-bonded WC grains, and fragmentations were observed on the eroded surface of WC-10Co-4Cr coating, while signatures of formation of plowing, lips, shearing of platelet, formation of crater, and micro-cutting were observed on the eroded surface of CF8M steel.

Slurry erosion studies of hydroturbine steels under hydroaccelerated conditions

Degradation of the hydroturbine components due to slurry erosion is a serious issue, especially for the hydropower plants situated on the rivers originating from Himalayas in India. In the current investigation, slurry erosion performance of two stainless steels (CA6NM and CF8M), which are commonly used in hydroturbine power plants, has been studied. A high-speed erosion test apparatus was used for the studies. Slurry collected from an actual hydropower plant was used as the abrasive media in the test apparatus. The effect of slurry concentration (ppm), average particle size of slurry particles and rotational speed on the slurry erosion behaviour was investigated under different experimental conditions. The analysis of eroded samples was done using scanning electron microscopy (SEM) and stylus profilometry. SEM images showed signatures of formation of lips, ploughing, crater and microcutting on eroded surface of steels.

Slurry Erosion Performance of High-Velocity Flame-Sprayed Ni-20Al 2 O 3 and Ni-10Al 2 O 3 -10TiO 2 Coatings Under Accelerated Conditions

The slurry erosion wear behavior of Ni-20Al2O3 and Ni-10Al2O3-10TiO2 coatings, deposited by high-velocity flame-sprayed technique, has been evaluated in the present investigation. A series of slurry erosion tests were conducted on the deposited surfaces, using an indigenously developed slurry erosion test rig under varying environmental conditions. The effect of identifying operational parameters like rotational speed, average particle size of erodent and erodent concentration on erosion behavior was also evaluated. Surface roughness tester, scanning electron microscope and XRD apparatus were utilized as surface characterization tools, whereas Vickers’s microhardness tester and bond strength tester were employed for mechanical analysis. The SEM observations of eroded specimens were observed to be lying in close proximity to the reported experimental results. Irrespective of the test conditions, Ni-10Al2O3-10TiO2 coating showed better results of slurry erosion performance in comparison with Ni-20Al2O3 coating. Further, each operational test parameter revealed a proportional effect on the erosion rate of both the coatings.

High-temperature tribological studies of plasma-nitrided tool steels

ABSTRACT During hot forging/forming operations, the die surface and near surface region is subjected to severe wear. The failure of dies originates from the surface region. In this research work, plasma nitriding was done on two hot forming tool steels namely AISI H11 and AISI H13. The aim is to develop a hard and wear resistance surface required for hot forming operations. The mechanical and microstructural properties of the developed nitrided layer were critically examined. Thereafter the tribological characteristics of the untreated and plasma-nitrided specimens were studied on high-temperature pin-on-disc tribometer under the constant load of 25 N, sliding speed 0.5 m s−1, sliding distance of 1500 m at different temperatures ranging from room temperature to 600°C. The results showed that the main wear mechanisms is predominantly adhesive at room temperatures and 200°C and a combination of adhesive and abrasive at elevated temperatures (400°C and 600°C).

Performance Analysis of CA6NM Hydro-Turbine Steel Under Accelerated Conditions by Using an Indigenously Developed Slurry Erosion Tester

The assessment of slurry erosion performance of materials under real service situations is often a difficult task. This is due to the intertwined nature of various influential parameters such as slurry concentration, impact velocity, properties of abrasive media, flow characteristics etc. However, real service situations can be simulated in a laboratory test rig by performing the accelerated erosion testing of materials. A slurry erosion tester is generally employed to discriminate the slurry erosion behavior of different materials. The complicated design, inadequate slurry flow, etc. are the main problems that are generally encountered during the slurry erosion testing and thus the data generated have limited application for quantitative analysis. In the present work, a simple design of slurry erosion test rig has been proposed, having several advantages, such as, better control over slurry flow, simultaneous testing of six specimens and time saving feature etc. in comparison with the documented setups. Further, commissioning of the present test rig was carried out by determining the effect of slurry related parameters (rotational speed, average particle size and slurry concentration) on the erosion behavior of CA6NM steel. The obtained results were sufficient to validate the capability of the proposed tester to capture the traditional responses of erosion behavior being observed in the test material.

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

Various aspects such as development, experimentation, and analysis have been covered in the present work to examine the behavior of test coatings under slurry erosion. The primary objective of the present study was to establish the specific mass loss from the test coatings under various slurry environmental conditions and highlights the importance of the addition of alumina in improving the slurry erosion resistance of Ni-TiO2 coating. To attain this objective, two powder compositions, viz. Ni-20TiO2 and Ni-15TiO2-5Al2O3 were deposited onto the CA6NM grade hydro-turbine steel using high velocity frame spray process. The microstructural characterization of the coatings was done by employing surface roughness tester, scanning electron microscope/energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques, whereas mechanical analysis was carried out using micro-hardness and bond strength tester. The slurry erosion tests were performed using an indigenously fabricated high speed slurry erosion test rig at different levels of rotational speed, average particle size of erodent, and slurry concentration in order to explore their effects on slurry erosion performance of test coatings. The slurry erosion results, as well as scanning electron microscope observations of eroded specimens, revealed higher slurry erosion resistance of Ni-15TiO2-5Al2O3 coating in comparison with Ni-20TiO2 coating. Furthermore, each operational parameter was found to have a proportional effect on specific mass loss in case of both the coatings.

A Novel Insight into Slurry Erosion Performance of Some Nickel, Alumina, and Titania Based Thermal Spray Coatings: A Review

An ideal coating system is generally considered as an appropriate combination of significant hardness and toughness. In the past investigations, the potential of various hard phases, as well as tougher candidates have been already explored. Some of these works related to slurry erosion, using nickel, alumina and titania as a coating candidate has been reviewed in the present study. The study is aiming towards investigating the effect of these coating candidates on the slurry erosion performance of a coating system. The review revealed a significant improvement in the coating properties (mechanical and microstructural) as well as coating performance with the application of the investigated coating materials.

Vibration Analysis of Rotor Bearing Housings Considering Unbalancing in Two Planes

Unbalancing and misalignment are the most possible causes of machine vibrations. An unbalanced rotor always causes more vibration and generates excessive force in the bearing area and reduces the life of the machine. Understanding and practicing the fundamentals of rotating shaft parameters is the first step in reducing unnecessary vibration, reducing maintenance costs and increasing machine uptime. By the term two planes here, we mean that two rotors are used for the analysis of unbalanced vibrations. If only one rotor is used, then this system is called a single-plane system. In this paper, experimental studies were performed on a 2 rotor dynamic test apparatus to predict the vibration spectrum for rotor unbalance. Two rotor bearings were used in the experiments. The rotor shaft velocities were measured at rotor speed of 30 Hz using an accelerometer and a dual channel vibration analyzer (DCVA) under the balanced (baseline) and unbalanced conditions. The experimental frequency spectrum was also obtained for both baseline and unbalanced condition under different unbalanced forces. The experimental results of balanced and unbalanced rotors are compared at two different rotor locations.