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Mechanical losses consume about 40% of the total energy developed by a typical automotive engine. The piston–cylinder system accounts for 50% of the engine frictional losses, of which 70% to 80% is...

The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with v...

Superhydrophobic surfaces were generated on stainless steel SS 304 substrates, using a combination of physical as well as chemical modification of the surface and tested for use in biomedical applications. Nanosecond pulsed laser was used for physical modification, i.e. creating nanoscaled roughness on the substrates. An additional chemical modification was performed using fluorosilane-based sol-gel nanocomposite coatings to further improve the hydrophobicity. Presently, the key challenge that such surfaces face, is to possess a substantial durability. In this study, a surface activation technique such as plasma pre-treatment was adopted to improve the adhesion of coatings on the laser treated substrates. The coatings deposited using dip coating technique were cured at 150 °C. The surface morphology and the roughness of the processed substrates and the coated samples were characterized using Atomic Force Microscope and Scanning Electron Microscope. The wettability of the surface was monitored and ...

Online (passive) thermographic inspection of overlap joints of aluminium and zinc coated steel sheets made by cold metal transfer weld brazing process was explored. Different experimental trials were conducted for demonstrating the feasibility of thermographic inspection to detect the porosities, improper weld bead and to differentiate the pre weld temperature. The whole process was monitored using infrared cameras in different wavelength region. Image analysis algorithms were developed to reconstruct the thermal images that contain the signatures of the weld defects and to extract the pre weld temperature and its evolution with distance from the centre of the weld torch. Post-weld radiography lends strong support to the observations.

Maraging steel 250 grade plates of 10 mm thickness were welded in single pass using a laser-arc hybrid welding (LHW) setup comprising 3.5 kW CO2 laser and synergic pulse metal inert gas (MIG) welding power source at a welding speed of 1 m/min. The influence of single-pass welding on the bead characteristics, microstructure, and mechanical properties was investigated. The size and volume fraction of reverted austenite was effectively reduced in the fusion zone. Moreover, the width of the heat-affected zones (HAZ) was reduced and the microhardness results did not show significant softening in the HAZ after post weld aging. Tensile testing of the welds in transverse direction showed 97.3% weld efficiency. The fusion zone exhibited KIc fracture toughness of 77.4 MPa√m which was affected by the distribution pattern of reverted austenite. The study vividly brings out the process advantages of LHW for accomplishing thick section welds of maraging steel in single pass with narrow groove and lesser filler wire con...

Laser and laser hybrid welding are among the processes chosen for joining Indian reduced activation ferritic martensitic (INRAFM) steel that will be used for fabrication of Indian test blanket modules (TBMs) to be tested in ITER. In the present study, a 3.5 kW slab CO2 laser in autogenous mode and hybridized mode with MIG were successfully employed to make butt joints in plates 6 mm and 12 mm thick respectively. Initially, bead-on-plate (BOP) experiments were conducted to study the effect of various laser and laser hybrid welding parameters such as laser power, welding speed, MIG torch angle, wire feed rate, composition of torch gas, gas shielding arrangement, stand off, distance between arc and laser, and focal position of the laser with respect to the surface. The resultant weld beads were evaluated for weld penetration, width of the weld, and width of the HAZ. Based on BOP welding studies, parameters were chosen for carrying out butt welding experiments using square butt for 6 mm plates and Y-g...

In the present study, laser welding was carried out with CO2 laser on a 2 mm thick aluminum alloy (6061-T6) sheet to study laser weldability of this heat-treatable aluminum alloy. Screening experiments were performed initially to enumerate the power density requirement for proper coupling of the laser with the material. Bead on plate experiments were conducted to recognize situation under which stable keyhole and welds with minimum defects (porosity and cracks) can be produced. Recognized process window (3 kW power, 4 m/min welding speed, and 18 L/min Helium flow rate) obtained from initial trial was used in butt welding experiment and the resulted weld was characterized by macroscopic and microscopic observation, microhardness study, and tensile test. The microstructure reveals porosity and crack-free welds and hardness data confirmed presence of heat-affected zone (HAZ) and huge drop in overall hardness after welding. After post-weld treatment (aging treatment), the hardness was increased marginally, bu...

India is one of the countries associated with the development and testing of test blanket modules (TBMs) in ITER. Accordingly, India has taken up development of 9Cr-W-Ta reduced activation ferritic...

An investigation of laser dressing of metal-bonded diamond blades is reported. The influence of laser irradiation on the diamond particles and bond material was reported, and the bonding material w...

Laser drilling of precise holes in thermal barrier coated Ni based superalloys has been studied. The interplay between various hole geometrical features such as hole shape, taper, barrelling, undercut, etc. and laser parameters such as pulse energy, pulse width and pulse repetition rate have been examined. The hole diameters are seen to follow a linear dependence on the incoming laser power densities for pulse width up to 2·0 ms. However, such a linear dependence was not observed for a pulse width of 3·0 ms. It was found that high pulse energy and short pulse width (high power density) gave crack free recast layer, whereas low pulse energy and longer pulse width (low power density) gave microcracks in the heat affected layer of superalloy. The significant barrelling observed in IN718 material at low power density values is due to multiple reflection of the incident beam from the cavity in combination with plasma formation at the evaporation front and trapping of the incident radiation causing exce...

Transparent ceramics, a new class of advanced functional materials, find diverse applications in strategic and civilian sectors owing to its unique combination of mechanical and transmission properties. Technological advancements in ceramic powder synthesis, shaping and sintering have made it possible to tailor the microstructural, mechanical and optical property relationships in case of advanced transparent ceramic materials. Transparent ceramic materials are classified broadly as visible, mid wave and long wave infrared regions. The transparent ceramic systems, which are explored currently, include transparent alumina (as polycrystalline submicron alumina and single crystal sapphire (Al2O3)), aluminium oxynitride (AlON), spinel (MgAl2O4) and zinc sulphide (ZnS) ceramics. This review summarizes the status of the development of these ceramics and a case study on transparent zinc sulphide samples developed by chemical vapour deposition (CVD) followed by hot isostatic pressing (HIP). Physicochemical, therma...

Modified 9Cr–1Mo steel plates of 6 mm thickness have been laser welded using CO2 laser. The effects of beam intensity and overall heat input (168-1500J/mm) on the bead characteristics, microstructure and mechanical properties of the welds have been investigated by varying the laser welding parameters such as laser beam mode, power and welding speed. The microhardness survey carried out on the welds after post-weld heat treatment did not reveal any soft zones in the intercritical heat affected zone for welds made with a heat input of up to 420 J mm−1. The tensile strengths of the welds were comparable to that of the base material. Charpy impact tests on subsize specimens revealed that the welds have good toughness. δ-Ferrite was observed in the fusion zone of the welds made at heat input of 700 J mm−1 and above, the content of which increased with the increased heat input.

Improving wear resistance of rails has a direct impact on the performance of rail–wheel system in railroad technology. Enhancement of sliding wear resistance at curved track, where factors such as adhesion, high slip ratios and contact fatigue act at contact patch of rail–wheel system, is particularly desirable. In the present investigation, influence of laser surface modification on sliding wear performance of a pearlitic rail steel (used in Indian railways) under two different conditions, namely, laser hardening (without any melting involved) and laser melting (with thin surface layer melting), has been studied under laboratory conditions. Before sliding wear testing, the effect of laser scanning speed on the treated layer depth has been optimised, utilising a 9 kW CO2 laser system. Sliding wear tests were carried out using a pin-on-disc device, with laser treated and untreated pearlitic rail steel discs and sliding pins made of wheel steel material, tungsten carbide (WC) and high speed steel (H...

An experimental Al–Cu–Li–Mg–Ag–Zr type alloy in the form of 13.7 mm thick plates was studied for its fusion characteristics using gas metal arc welding (GMAW) and pulsed gas metal arc welding (P-GMAW). High copper 2319 filler of 1.6 mm diameter was used. The burn-off characteristics of 2319 filler wire in GMAW and P-GMAW were experimentally determined, including the relation between pulse current and pulse duration for the desired one-drop detachment per pulse (ODPP) condition and feasible range of pulse parameters. The effect of welding parameters on bead geometry and shape relationships was investigated through beadon-plate experiments in the welding current range above the spray transition current. Reasonably good weld beads were obtained in P-GMAW at currents as low as 194 A and welding speeds of 45 cm min–1. P-GMAW yielded significantly higher weld penetration compared to GMAW.