Praveen Kumar

Hardness and wear behaviour of electroless Ni–B coatings

Depth-dependent hardness variation of dimethylamine borane-reduced electroless Ni–5u2005wt-%B deposits has been examined using the nanoindentation technique. The deposits were characterised using ICP-OES, FESEM, XRD and DSC for evaluating the composition, morphology, structure and phase transformation behaviour, respectively. Coatings were also analysed for hardness and wear resistance. The surface of the as-plated deposit exhibits a typical nodular morphology. DSC traces show the presence of a single exothermic peak at 313°C conforming to its phase transformation. X-ray diffraction pattern of as-prepared deposit contains a mixture of amorphous and sharp microcrystalline nickel peaks. Heat-treated coating exhibits improved hardness and wear resistance. Depth-dependent nanohardness profile of as-deposited film neither obeys Nix–Gao nor the Lam–Chong model of indentation.

Review on the machining characteristics and research prospects of conventional microscale machining operations

ABSTRACT The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of work stations have enabled microscale machining operations to acquire an edge over other fabrication techniques in various applications such as aerospace, instrumentation, automotive, biomedical, etc. The literature is filled with works done by researchers working in this domain. A significant contribution comes from the works which have been published during the period 1998–2014. The focus of these studies has primarily been on conventional and nonconventional micromachining techniques. Since nonconventional machining operations such as microelectrical discharge machining, laser machining, etc., are not compatible with traditional workpiece materials, conventional micromachining techniques such as micromilling and microdrilling are generally used. However, as of today, there has been no revision on the state of the-art in this field to serve as a reference for the experienced researcher and as a handbook for the newcomer. In this review, we have attempted to summarize the current state of understanding on this topic. A variety of issues which are representative of micromachining operations are critically analyzed and presented. Conventional micromachining operations have been compared with their nonconventional counterparts with respect to performance characteristics such as burr formation, surface integrity, etc., and their advantages and shortcomings have been listed. Meticulous efforts have been taken to address the key challenges faced in typical micromachining operations. Taking the convenience of the reader into consideration, we have presented a birds-eye view of the various micromachining operations and simulation studies as performed in the last decade. In the last few years, diamond turning operations have gained more importance and are particularly used for machining composite materials and superalloys. This paper gives an insight into these operations apart from providing an outlook for future growth and development of micromachining technology.

Wettability of Y2O3: A relative analysis of thermally oxidized, reactively sputtered and template assisted nanostructured coatings

The wettability of reactively sputtered Y2O3, thermally oxidized Y-Y2O3 and Cd-CdO template assisted Y2O3 coatings has been studied. The wettability of as-deposited Y2O3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y2O3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y2O3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y2O3 and thermally oxidized Y-Y2O3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y2O3 coatings, the surface roughness was improved by depositing a thin film of Y2O3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y2O3 (54 mJ/m2) and thermally oxidized Y-Y2O3 coatings (43 mJ/m2) compared to the Cd-CdO template assisted Y2O3 coating (7 mJ/m2).

Mechanical micro-drilling of nimonic 80A superalloy using uncoated and TiAlN-coated micro-drills

ABSTRACT Micro-drilling is a complex mechanical machining process. Micro-drilling experiences an early tool damage which is a major drawback for nickel-based superalloy. This paper examines the wear condition on the micro-tool cutting edge, surface roughness of machined holes, and hole diameter analysis in micro-drilling of Nimonic 80A, using two types of micro-drills (uncoated and TiAlN coated) with 0.79u2009mm diameter. Micro-drilling tests, using cutting speed (Vc), feed rate (fz), and the micro-drill diameter as experimental parameters were carried out to bring out the best optimized machining conditions in micro-drilling of Nimonic 80A. Wear on the tool cutting edge and burr height occurring at the entrance of drilled holes were measured at constant period to give the lastingness of micro-drill. Quality of holes were analyzed in terms of surface roughness inside the hole and the hole diameter after every five drilled holes. The result obtained from the above analysis showed that TiAlN-coated micro-drill performs way better than the uncoated micro-drill in terms of wear, surface roughness, hole quality, and burr. Thus, the above performed study gives the knowledge to select micro-tool for machining of Nimonic 80A which could be useful in the aerospace industry.

Fabrication of broadband quasi-omnidirectional antireflective surface on glass for photovoltaic application

In this paper, we have demonstrated a simple and cost effective HF-vapor phase etching method to fabricate the broadband quasi-omnidirectional antireflective surface on glass substrate. Both-sides etched sodalime glass substrates under optimized conditions showed a broadband enhancement in the transmittance spectra with maximum transmittance as high as ~97% at 598u2005nm. FESEM results confirmed the formation of a graded nanoporous surface, which lowers it refractive index. The etched surface exhibited excellent AR property over a wide range of incidence angles (8°-48°), which is attributed due to the formation of graded porosity. Silicon solar cell covered with plain glass showed Isc of 0.123A and efficiency of 8.76%, while it showed Isc of 0.130A and efficiency of 9.2% when it was covered by etched glass. Furthermore, it exhibited an excellent anti-soiling property as compared to plain glass. All these results show its strong potential in the photovoltaic application.