Tej Pratap

1. Nickel-based superalloys such as Hastelloy C-276 are extensively employed in aerospace, petrochemical, marine and power-generation industries owing to their exceptional corrosion resistance, mec...

High contact stress, load, and speed significantly deteriorates the tribological performance of grey cast iron, leads to shorter component life cycle. Heat treatment coupled with coating may significantly enhance component lifespan and tribological performance due to change in substrate physiochemical properties. Thus, this work focused on the influence of heat treatment at 900°C, followed by rapid water quenching, then deposition of DLC and AlCrN coatings. Further, the surface morphology, microstructure, and worn behavior during micro-scratch and tribotest were analyzed. The DLC coating showed highest reduction in friction coefficient (COF) compared to AlCrN due to its high hardness by 36.3, 21.2, and 16.9% under applied load 40N, 80N, and 120N, respectively. A deep abrasion wear was found on the AlCrN coating, whereas a fine wear mark was observed on the DLC coating under all applied load, owing to least COF and chemically inert behavior of DLC. Although AlCrN exhibits relatively higher wear due to surface defects and its brittle nature compared to DLC but its highest hardness helps in reducing COF from untreated substrate highlighting the role of heat treatment in reducing COF. DLC has superior performance compared to AlCrN for volumetric wear, by reducing wear volume loss of about 9.94%, 5.76%, and 5.29% under static loads of 40N and 80N, and progressive loads of 20–120N, respectively whereas material adhesion was more prominent for AlCrN as confirmed from worn surface morphology.

Surface texturing and its topography significantly affect the tribological performance and lifecycle of automotive components at elevated temperature, fluctuating load and speeds. Engineered surfaces using laser-induced texturing is most promising approach to address these concern by varying texture morphology, orientation and roughness. Therefore, the present study propose fabrication of seven distinct textures namely, chevron, triangles with vertex along sliding length (TAL) and width (TAW), rectangular (RT), square (ST), staggered circle (SCT), and circle (CT) by variation in texture shapes and orientation keeping constant density, pitch and depth on grey cast iron (GCI) for cylinder liner piston ring pair (CLPRs) application. Laser-induced texturing increases the areal roughness and microhardness due to variation in scanning strategy and grain refinement. Lowest COF is observed for moderate load of 80N and sliding velocity of 0.2 m/s. RT shows highest reduction in frictional coefficients (COF) and friction force (FF) of around 26.6% compared to base due to least bulge and stabilized film thickness whereas TAL has lowest. Chevron has highest roughness, bulge height, microhardness, least mass loss and most wear prone surface. Worn morphology indicates textures were intact and wear mechanics related to topographical parameters.

Shorter component life cycle and emission due to high friction wear of reciprocating components like cylinder liner–piston rings are the main concerns in an engine and generally addressed through different surface modifications. Protruded multi-shaped textures are getting wider popularity nowadays to address these issues. Therefore, the present study proposes an effective fabrication of five distinct laser textures, namely, protruded circular, staggered circular, rectangle, square, and hexagon textures on grey cast iron with variable morphology and contact footprint for prolonged life and tribological performance under SAE 10W-30 lubrication. Five-axis flexi nanosecond ytterbium pulsed laser with optimum process parameters with laser power of 60 W, scanning speed of 2134 mm/s, frequency of 450 Hz, jump speed of 7015 mm/s, and pulse duration of 120 ns was used to fabricate all the textures. Surface morphology of the fabricated textures confirms the quality and accuracy of the fabricated textures. Laser irradiation increases microhardness, whereas protrusions provide lubricant retention along with higher load-carrying ability. Moreover, tribological results confirm the protrusions are favourable in reducing coefficient of friction (COF), frictional force (FF), wear, and mass loss compared to normal surfaces and conventional dimpled textures. Protruded staggered circular texture exhibited the highest reduction of around 38% in COF and FF, compared to base surface, whereas protruded square texture showed the highest reduction in mass loss. It attributes the fact of protrusion dimensions, depth, and fracture of protruded sections also contributed towards improved tribological performance.

Bioinspired protruded textures with variable surface morphology and characteristics are getting worldwide popularity due to their wider applications. Among them controlled wettability for different materials through bioinspired textures is very essential to reduce the adhesion, bacterial contamination and growth, and drug delivery application. Even, identification and efficient fabrication of favorable bioinspired protrusions with optimum parameters are comparatively complex from normal textures through any material processing methods due to their complex shapes, form accuracy and dimensions. Therefore, this work targets the fabrication of four different types of protruded bioinspired textures namely, fish scale, protruded square, protruded circular, Python scale (snake) textured surface on biomedical grade Ti-6Al-4V titanium alloy for controlling the wettability using femtosecond laser surface texturing (LST). The optimum process parameters for the machining of Ti-6Al-4V were set as a temporal width of 350 fs, output power of 5.5 W, wavelength of 1030 nm, scanning speed of 100 mm/s and pulse rate of 500 KHz and three repetitions for all the texture types. To examine the effect of texture type, perimeter of all the fabricated textures was kept constant. Further, effect of varying perimeters was also analyzed for perimeter ranges from 300 to 500 µm. Surface morphology and characteristics were also analyzed for the measurement of texture consistency, dimensions and composition which was also related to the wettability results examined by static contact angle of the sessile drop method. Wetting of fish scale texture is decreased with increasing perimeter whereas of all other textures, wettability is going to be improved significantly.

The worldwide increase in demand for automotive sectors requires improved components life cycle, fuel economy and emission control. However, the occurrence of high temperature and variable loading on contact surfaces of internal combustion (IC) engine causes excessive friction results into reduced component life cycle, degrades emission level and fuel economy too. A small improvement in tribological performance and oil sealing through surface modification can able to enhance the functional performance of IC engine components significantly. Hence, in this work, a detailed discussion on the comparison of different hybrid surface modification techniques such as coatings, textures, and nanoparticles can work synergistically to improve the tribological performance of IC engine components. The process capabilities, limitations, and their effect on tribological performances of IC engine components are also presented. An analysis of surface texture parameters such as geometry, dimension, motion parameters, surface roughness, and oil transport mechanism is done to know the effects on the performance of the IC Engine. Further, the hybridization of different processes with nanoparticles (metallic, metallic oxides, carbon nanoparticles) is briefly presented. Finally, the effect of modified surface chemistry and characterization such as asperity, topography, microhardness, residual stress, and adhesive strength characteristics is also related to the tribological performances of IC engine components.

Prediction of crater shapes with high accuracy in electrochemical discharge machining plays a significant role in the formation of micro-array on non-conductive materials. In this work, a finite-element method-based thermal model is developed by applying three different heat fluxes such as Gaussian, Constant, and Parabolic to predict the crater shapes on the soda-lime glass substrate. The comparative study of crater shapes reveals that a hemispherical crater is formed with Gaussian and Parabolic heat flux, while the cylindrical crater is formed for Constant heat flux due to the differences in the nature of heat distribution within the glass substrate. Further, material removal rate (MRR) and heat-affected zone (HAZ) are also estimated for Gaussian heat flux as it gives the most suitable crater shape. Parametric simulation is done by considering the supply voltage as a variable parameter and finding that MRR is significantly higher at 60 V compared to 45 V, whereas the increase in HAZ is very small.

Surface modification is the science of manipulating surface morphology and interfacial properties and also plays a vital role in biomedical implantation. A few of the interfacial properties are biocompatibility, protein adsorption, wettability, cell proliferation, collagen, etc. These properties depend on surface modification strategies and significantly impact the implant response within the host body. Generally, the corrosion, surface wear, and degradation in the physiological environment limit the application of different biomaterials and can address through various surface modification strategies. These surface modifications developed over the years to improve the morphology and interfacial properties to meet the specific functional surface application in biomedical implantation. It can be done through surface roughening, patterning/texturing, coating with different materials, and hybrid modification. Further, the process development for bio-medical application, process capabilities, limitations, challenges, and characterization aspects are correlated to identify the effectiveness of different surface modification strategies. Finally, various innovative biomedical applications and surface characteristics are also present with future scope in the direction of surface modification for biomedical implantation.