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In the present study, laser periodic structuring of titanium-based alloy (Ti-6Al-4V) has been carried out using Ti:Sapphire laser with the wavelength of 800 nm and pulse duration of 3 ps and 100 fs with varying peak fluence and scan speed. After laser irradiation, the topography of the surface has been recorded using 3D surface profilometer. Laser surface processing leads to the formation of a periodically patterned surface with the average ablation depth of 37.25 µm-42.13 and average surface roughness of 0.991-1.862 µm as compared to 0.169 µm average roughness of as-received Ti-6Al-4V. In the microstructure, there is presence of fine periodic ripples with an average ripple width of 0.48 µm to 0.54 µm when processed with 3 ps laser and the average ripple width of 0.17 μm in addition to the presence of very fine pits, deposited particle, and oxide dispersed surface when processed with 100 fs laser. The microhardness of the surface is improved (395 VHN-373 VHN ) as compared to 282 VHN of as-received Ti-6Al-4V. There is a significant improvement in the corrosion resistance in terms of a decrease in corrosion rate (0.0037 to 0.0008 mm/year) in laser surface processed sample as compared to as-received Ti-6Al-4V (0.0932 mm/year) in Hank’s solution and also increase in pitting corrosion resistance in terms of increase in critical potential for pit formation (Epit) under a few employed parameters with both 3 ps laser (at a laser fluence of 0.063 J/cm2 and a scan speed of 20 mm/sec) and 100 fs laser (at a laser fluence of 0.63 J/cm2 and at a scan speed of 60 mm/sec).

The present work is directed towards understanding the role of filler addition in laser-MIG hybrid welding (LHW) process as compared with that in autogenous laser welding (ALW) process during welding of 10-mm-thick maraging steel plates. Addition of filler wire is beneficial in improving the edge bridging between the parts to be welded and also in improving the fusion zone microstructure. Single-pass LHW of the 10-mm-thick maraging steel plates was performed using a combination of 3.5-kW CO2 laser and synergic pulse MIG welding power source at a welding speed of 1 m/min. MIG filler wire with reduced solutes such as Mo and Ti contents was used for the LHW process. Simultaneously, double-sided single-pass ALW of similar plates was performed. The role of filler wire addition on the microstructure and mechanical properties of the LHW fusion zone (FZ) was studied and compared with that of ALW FZ. The usage of filler wire resulted in less solutes in the LHW FZ after welding, and hence, the volume fraction of “reverted austenite (RA)” formed during aging was minimized when compared with ALW FZ. During transverse weld tensile testing, the ALW welds yielded higher tensile properties when compared with the LHW weld due to their fine grain structure and high number density of precipitates. Whereas the KIc fracture toughness of the ALW FZ was low with the KIc value of 49.5 MPa√m due to the presence of the high amount of RA as compared with LHW which exhibited the KIc value of 77.5 MPa√m. The study vividly brings out the advantages of LHW process in improving the microstructure of the fusion zone due to the addition of filler wire.

This is the second and final part of a review of the impact of LST on piston rings and cylinder liner tribological characteristics. Part 1 was published in this journal, 2021, 99(5), 231–237, and traced the development of the laser surface texturing process for materials. Part 2 reviews the development and application of the process to piston-cylinder ring liner contact situations. The future directions for automotive tribological research and desirable areas for research goals related to friction, fuel efficiency, emissions are also discussed. The numbering of figures follows on from those in Part 1, and, like Part 1, the complete reference list is given to enable easy concurrent reading of both parts.

The effect of zinc coating on the weld brazability of dissimilar Al–steel joint made by the cold metal transfer (CMT) process using the passive infrared (IR) thermography sensing technique was investigated using a numerical model. The numerical model was developed to understand the heat transfer phenomena during the CMT process. In the developed model, a thin thermally resistive layer (TTRL) was introduced at the interface of the two joining metals in order to manipulate the absence of zinc deposition on the steel sheet. The model could clearly identify the lack of weld deposition. The results were compared with experimental observations. Two cases are considered in this paper. The first study identifies the sensitivity of the IR thermography technique and the second one reveals the resolution in defect detection. The developed 3D model can be used as a tool to identify the defects caused during welding and can provide insights into the online monitoring of cold metal transfer joining process.

Comparitive analysis of the corrosion resistance of H32 5052 Al alloy and galvanized mild steel lap joints fabricated by a) Metal Inert Gas (MIG) Welding-brazing and b) Cold metal transfer (CMT) was done by keeping wire feed rate and welding speed constant. The weld interfaces of 5052 Al and mild steel were characterized using Field emission scanning electron microscopy, X-ray diffraction and nano-indentation measurements. Weight loss tests were done as per ASTM G 67-04 on the lap joints. Results indicated formation of Al-Fe-Si layer at the weld bead-mild steel interface in both the techniques. The layer was found to be Aluminium rich in MIG –braze sample whereas it was iron rich in the CMT sample. The layer thickness was found to be higher in the toe region than the head region in both samples. The Al-Fe-Si layer preferentially dissolved during the weight loss test of the welds. The thickness of Al-Fe-Si layer for MIG-braze welds was greater resulting in higher intergranular corrosion.

In the present study, a galvanized steel and a AA6082 aluminum alloy sheet of 2 mm thick were weld-brazed by applying laser and using 2-mm-diameter solid Al-12% Si filler wire at 2.5 m/min wire feed rate and 2 m/min laser scan speed at varying laser power (4.0, 3.5, 3.0 kW) in flange configuration. The microstructural investigation of the laser weld-brazed joints revealed the presence of two-layered intermetallic compound at steel/braze seam interface. The corresponding x-ray diffraction analysis of the steel/braze seam interface showed the presence of Al-Fe-Si-based ternary intermetallic phases. SEM and EDS analysis of the braze seam revealed the presence of α-Al grains surrounded by Mg2Si phase in the grain boundary region. Fine intermetallic layer was observed at lower heat-input condition. The corrosion performance of the brazed joints was studied with the help of immersion, salt spray, and electrochemical polarization tests in different electrolytes containing NaCl salt. Brazed joints experienced galvanic corrosion during immersed in corrosive media. From the salt spray test, it was revealed that galvanized steel was highly susceptible to corrosion compared to Al-rich phase. The polarization results showed a substantial change in corrosion resistance from steel interface to the brazed region due to the variation in microstructure. The samples brazed with low heat-input showed better corrosion resistance as compared to the joints made with high heat-input. Post-corrosion microstructure revealed intergranular corrosion at the brazed joint along with pit formation.

Additive manufacturing (AM) is an innovative complex shaping technique with unlimited freedom and flexibility in fabrication. Though the majority of AM processes were focused in polymers, it is later extended to metals and very recently to ceramics. Conventional prototyping of ceramics, especially complex parts proceeds through several iterations of design and fabrication of dies, moulds, fixtures etc. which are cost intensive and also time taking to arrive at the final designs. Often the finished parts also needs machining to achieve the micro-features. 3D printing of ceramics with its inherent advantages simplifies above issues especially for fabrication of prototypes leading to the selection of optimum designs in a very short time. Further, as the same infrastructure is based on the printing of ceramic shapes using software generated virtual images it also results in lower cost. In the present study, unlike generally employed UV or visible curable resins to 3D print the green ceramic parts, a new concept of thermally induced gelation of methyl cellulose is used to retain the shape while printing of the parts. In this process, magnesium aluminate spinel paste formulated with 0.25% by weight of methyl cellulose (MC) having optimized rheology was 3D printed simultaneously exposing to the hot air flow close to the MC gelation temperature. Magnesium aluminate spinel test specimens are also shaped using generally practiced slip casting process for the sake of comparison, as slip casting process is not adaptable to fabricate the parts micro-features 3D printed in the present study. The formed parts by both the techniques were pressureless sintered at 1650 °C. 3D printed spinel specimens have shown comparable density, hardness and flexural strength with respect to the slip cast specimens complemented by fractographic analysis.

Laser brazing of aluminum 6082 to galvanized steel was carried out with different laser power followed by mechanical and microstructural characterization. Hardness, tensile and low cycle fatigue tests were conducted for mechanical property evaluation, while microstructural analyses were consisted of optical microscopy, SEM and XRD studies. Microstructures revealed the presence of different eutectics at the inter-dendritic region, whereas, ternary Al-Fe-Si and binary iron-rich intermetallics were at the steel interface. Asymmetrical hardness profile throughout the braze joint with lowest value in the brazed region was noted. The sample, brazed with 4 kW laser power, showed best tensile strength, and failed through the base material. Low cycle fatigue tests showed cyclic stabilization at lower strain amplitudes. Fatigue failure occurred in the brazed region and exhibited fatigue striations, flow lines and intergranular cracking.

Thermally-sprayed tungsten carbide (WC)-based cermet coatings have been widely used for a large variety of wear resistance applications. More recently, these coatings are being used as an alternative to hard chrome plating, especially in the aerospace and automotive industries. Utilizing the automated spray systems and the commercial availability of spray grade powders with different compositions, the WC-based cermet coatings that are conventionally used for wear protection are now being extended for simultaneous corrosion protection. Therefore, the corrosion behavior of various WC-based cermet coatings as a function of matrix composition, feedstock type and deposition technique exposed to a variety of corrosion mediums has been critically reviewed. The corrosion mechanisms of WC-based cermet coatings studied using various analytical tools have also been comprehensively discussed. The interrelationship between the microstructural integrity and the corrosion behavior has been critically assessed. Further, the influence of pre- and post-treatments to improve the overall corrosion resistance of the coatings has also been highlighted.

Partial replacement of steel by Aluminium (Al) alloys is a promising approach adopted by automotive sector to improve fuel efficiency without compromising on the strength. However, this results in the generation of dissimilar welds of Al alloys and steel. Understanding the corrosion behavior of Al alloys–steel welds as a function of welding parameters is critical in the successful application of such alloys. The present study reports the intergranular corrosion behavior of T6 heat-treated AA6061 Al alloy-galvanized mild steel lap joints, welded by metal inert gas welding–brazing technique as a function of different welding parameters, viz. weld speed (4-6 m/min) and wire feed rate (0.8-0.9 m/min), following ASTM G 67-04. Weld characterization was performed by field emission scanning electron microscopy (FESEM), x-ray diffraction and nano-hardness measurement. Results indicate heavy dissolution and metal loss at the interface. A high volume fraction of Al-Fe intermetallics was precipitated at the weld interfaces, resulting in high hardness and higher localized corrosion. The thickness of Al-Fe intermetallic layer increased with increasing wire feed rate and lower weld speed which enhanced the severity of galvanic and intergranular corrosion.

Laser micromachining is an advanced machining process in which machining is achieved by focusing a laser beam to melt and vaporize the material. The primary aim of this work is to fabricate a control grid for an electron gun using laser micromachining. Initially, line scribing and 2D profiling experiments are performed on a 130-μm molybdenum plate to compare the surface quality and material removal rate of nanosecond and femtosecond lasers. The effects of laser processing parameters such as average power, repetition rate, and the feed rate on the width, depth, material removal rate, and cut quality of both the nanosecond and femtosecond lasers are studied. During micromachining using the nanosecond laser, melting and recasting of the metal around the machined sites are observed, resulting in the formation of heat-affected zone. During machining using the femtosecond laser, ultrafast laser pulses are used, which result in the absence of heat-affected zone. The surface roughness obtained using the femtosecond laser for creating a 2D profile is 0.187 μm, while using the nanosecond laser, the roughness value obtained is 1.89 μm. The femtosecond laser is used to successfully machine the 3D profile of the control grid, adopting the optimized parameters obtained from the line scribing and 2D profiling experiments. The average width of the grid line was measured as 149.89 μm which is very close to the required dimension of 150 μm.

In the present study, laser-brazed AA6082 to DX56-galvanized steel joints were investigated to understand the influence of process parameters on joint strength in terms of intermetallic layer formation. 1.5-mm-thick sheet of aluminum alloy (AA6082-T6) and galvanized steel (DX56) sheet of 0.7 mm thickness were laser-brazed with 1.5-mm-diameter Al-12% Si solid filler wire. During laser brazing, laser power (4.6 kW) and wire feed rate (3.4 m/min) were kept constant with a varying laser scan speed of 3.5, 3, 2.5, 2, 1.5, and 1 m/min. Microstructure of brazed joint reveals epitaxial growth at the aluminum side and intermetallic layer formation at steel interface. Intermetallic layer formation was confirmed by EDS analysis and XRD study. Hardness profile showed hardness drop in filler region, and failure during tensile testing was initiated through the filler region near the steel interface. As per both experimental study and numerical analysis, it was observed that intermetallic layer thickness decreases with increasing brazing speed. Zn vaporization from galvanized steel interface also affected the joint strength. It was found that high laser scan speed or faster cooling rate can be chosen for suppressing intermetallic layer formation or at least decreasing the layer thickness which results in improved mechanical properties.

This work presents a detailed microstructure-property correlation of high power diode laser nitrided titanium based on its dendrite and martensite microstructures, structural phase and microhardness. For the laser nitrided titanium, cooling rate was estimated for the first time using empirical power law relationship by considering the martensite width and dendrite arm spacings and the results were validated by analytical thermal model. A processing window was formulated for laser gas nitriding of titanium by relating the experimental parameters such as laser processing parameters, nitrogen gas pressure and titanium nitride phases. The novelty of this work is demonstration of laser nitriding of titanium in laminar flow nitrogen gas environment using a simple acrylic container setup that avoids design and fabrication of a complex gas nozzle delivery system. In this setup, a thin transparent acrylic sheet was used as optical window instead of expensive quartz glass, to transmit high power diode laser beam at 980 nm wavelength to irradiate the substrate work piece in a closed container. This simple laser nitriding technique has created characteristic golden colored TiN surface with high surface hardness. Dendrite and martensite microstructures of the laser nitrided titanium were analyzed by optical and FESEM microscopy. EDAX analysis revealed the presence of nitrogen in laser nitrided titanium and X-ray diffraction confirmed the TiN phases. The microhardness of laser nitrided titanium is six times higher than its substrate.

The paper presents an integrated model of artificial neural networks (ANNs) and non-dominated sorting genetic algorithm (NSGAII) for prediction and optimization of quality characteristics during pulsed Nd:YAG laser cutting of aluminium alloy. A full factorial experiment has been conducted where cutting speed, pulse energy and pulse width are considered as controllable input parameters with surface roughness and material removal rate as output to generate the dataset for the model. In ANN–NSGAII model, back propagation ANN trained with Bayesian regularization algorithm is used for prediction and computation of fitness value during NSGAII optimization. NSGAII generates complete set of optimal solution with pareto-optimal front for outputs. Prediction accuracy of ANN module is indicated by around 1.5 % low mean absolute % error. Experimental validation of optimized output results less than 1 % error only. Characterization of the process parameters in pareto-optimal region has been explained in detail. Significance of controllable parameters of laser on outputs is also discussed.

Three integrated ANN-GA, ANN-SA and ANN-Quasi Newton methodology has been developed and implemented according to the following way to determine optimised input parameter setting for maximum welding strength during laser-MIG hybrid welding of aluminium alloy plates. Finally, significance of optimised parameters has been determined by ANOVA. Variation of welding strength with individual process parameters have been tested through main effect plots and interaction plots. Three soft computing based integrated models such as, ANN-GA, ANN-SA and ANN-Quasi Newton have been developed.Those models predicted and optimised welding strength during hybrid CO2 laser-MIG welding process.Best ANN architecture (3-11-1 network) predicts welding strength with mean absolute percentage errors less than 2%.ANN-GA shows best optimisation performance with only 0.09% experimental validation error.Welding speed shows maximum influence on welding strength and an increase in welding speed decreases welding strength. In this paper, artificial neural networks (ANNs), genetic algorithm (GA), simulated annealing (SA) and Quasi Newton line search techniques have been combined to develop three integrated soft computing based models such as ANN-GA, ANN-SA and ANN-Quasi Newton for prediction modelling and optimisation of welding strength for hybrid CO2 laser-MIG welded joints of aluminium alloy. Experimental dataset employed for the purpose has been generated through full factorial experimental design. Laser power, welding speeds and wires feed rate are considered as controllable input parameters. These soft computing models employ a trained ANN for calculation of objective function value and thereby eliminate the need of closed form objective function. Among 11 tested networks, the ANN with best prediction performance produces maximum percentage error of only 3.21%. During optimisation ANN-GA is found to show best performance with absolute percentage error of only 0.09% during experimental validation. Low value of percentage error indicates efficacy of models. Welding speed has been found as most influencing factor for welding strength.

Strain localization and premature splitting in the vicinity of outer heat affected zone is a major concern in the formability performance of laser welded similar material dual phase (DP) steels during stretch forming. Hence, the present work aims at evaluation of limiting drawing ratio (LDR) of tailor welded blanks (TWBs) fabricated using two dissimilar material combinations of DP and interstitial free (IFHS) steels using laboratory scale deep drawing test. Finite element models of deep drawing of parent materials and TWBs were developed incorporating anisotropy of sheet metals and non-homogenous properties of the weld zone. The numerical simulations were performed incorporating theoretical forming limit diagram (FLD) to predict LDR, thinning development and failure location. The LDR of both the TWBs was lower compared to that of parent metals due to non-uniform plastic deformation with localized thinning failure at cup bottom in the weaker material side. The failure propagated along a direction parallel and close to weld line as observed in experimental results. The global forming performance of different TWBs was characterized and compared in terms of formability ratio from the deep drawing, limiting dome height and Erichsen cupping test data. It was found that the extent of decrease in formability due to increase in strength ratio was not so severe in deep drawing process unlike stretch forming process. It was also proposed through rigorous finite element studies that LDR of TWBs could be improved with restricted weld movement by shifting the initial weld line position, and the same was validated through deep drawing experiments.

In this work, joining of aluminium alloy AA6061-T6 to Interstitial Free steel using pulsed gas metal arc welding process has been attempted. The effect of different surface conditions of steel (viz, galvanized, galvanealed and uncoated) and gap between the sheets on braze joint formation have been investigated. Galvanized steel surface showed good bead width, joint formation and lap shear strength compared to the other two combinations. Interface gap has not affected the wetting behaviour significantly but presence of a gap of 300 μm or so helped in escape of zinc vapour during the process there by avoiding formation of any crevice or macroporosity in the joint. Features and properties of the joint are characterized by metallography, fractography, energy dispersive spectroscopy (EDS) and lap shear tests. Load carrying capacity of Al-Galvanized steel was highest (222 N/mm of seam length) compared to other combinations, aided by better wetting due to presence of Zn on the surface and minimum porosity due to interfacial gap provided during brazing.

Transparent polycrystalline Magnesium Aluminate Spinel (MgAl 2 O 4 ) specimens were formed by colloidal slip casting (SC) and uniaxial powder compaction (UDP) routes using powder with identical properties. SC and UDP formed specimens which were pressureless sintered and further subjected to hot isostatic pressing to eliminate the residual porosities and to achieve the transparency. SC samples exhibited better transmission compared to UDP samples. Mechanical properties were found to be lower by 10–15% for UDP samples and are complemented by the total fracture energy release rate ( J c ) and J R – δ curves. Finally, the optical and mechanical properties were correlated with the processing routes.

Austenitic stainless steels find extensive applications in engineering and structural parts requiring inherent corrosion resistance. The main objective of this study is to achieve good quality butt joint in 2.5-mm thick 304 grade Stainless Steel. The joint quality is quantified in terms of weld-bead dimensions. The main issue that manufacturers face is controlling the input process parameters, to get a good quality joint, with required weld bead geometry under controlled thermal distortion. The objective of this work is to select proper input process parameters that would result in desirable weld-bead profiles with minimal heat input. The critical process parameters influencing laser-welding were found using response surface methodology technique. The results proved that the developed model could efficiently predict the responses. The criteria demonstrated a possible reduction in top width of weld bead with enhanced depth of penetration, which automatically envisaged an increase in aspect ratio. A two-factor five-level criteria design was used for predicting the optimized parameters by performing multi-response optimization. Among them, the third criterion has shown a significant decrease in heat input and it was chosen as the best-optimized parameter.

Well-aligned nitrogen-doped carbon nanotube (N-CNTs) film was fabricated on silicon substrate by thermal chemical vapor deposition process with varying the growth temperature. The effect of growth temperature on morphology, microstructure and crystallinity for the growth of N-CNTs was studied. At all growth temperatures, the bamboo-like morphology of graphene layers with compartments in CNTs were observed in transmission electron microscope micrographs. The doping level and the type of nitrogen-related moieties were determined by X-ray photoelectron spectroscopy analysis. The compartment distance decreases with increase in nitrogen doping level in hexagonal graphite network. The increase in nitrogen doping level in N-CNTs will lead to decrease in crystallinity and in-plane crystallite size. Field emission study of nitrogen-doped carbon nanotubes grown at optimum parameters showed that they are good emitters with a turn-on and threshold field of 0.3 and 1.6 V/μm, respectively. The maximum current density was observed to be 18.8 mA/cm2 at the electric field of 2.1 V/μm. It is considered that the enhanced field emission performance of doped nanotube is due to the presence of lone pairs of electrons on nitrogen atom that supplies more electrons to the conduction band.

The development of nanostructured, hard, and wear-resistant composite coating of Al2O3, TiB2, and TiN on low carbon steel (AISI 1025) substrate by combined self-propagating high-temperature synthesis (SHS) and laser surface alloying (LSA) has already been communicated in the author’s previous publications. The coefficient of friction of the coating (with WC-Co as counterbody) is also found to have reduced substantially with the presence of free hexagonal boron nitride (hBN) in it. The occurrence of free hBN has been made possible by putting excess hBN in the precursor mixture which is supposed to undergo combined SHS and LSA. This has also been reported in one of the previous publications. This reduction in coefficient of friction is achieved at a cost of a marginal reduction in the microhardness as well as the specific wear rate as the free hBN in the coating matrix causes some softening. Laser post-treatment causes distinct enhancement in the microhardness and wear resistance of the coating while augmenting the favorable effect of free hBN on the coefficient of friction.

In the present work, an attempt has been made to study the slurry erosion properties and operating erosive wear mechanisms of Co-based Stellite 6 and Ni-based Colmonoy 88 coatings, and also to list the conditions at which maximum and minimum erosion rates occur. Laser surface alloying (LSA) has been done on 13Cr-4Ni steels with commercial Co-based Stellite 6 and Ni-based Colmonoy 88 powders. Slurry erosion tests have been conducted on LSA-modified steels for a constant slurry velocity of 12 m/s and for a fixed slurry concentration of 10 kg/m3 of irregular, sharp-edged SiO2 particles with average sizes of 375 and 100 ?m and at impingement angles of 30, 45, 60, and 90 deg. A mixed (neither ductile nor brittle) mode of erosion behavior for Stellite 6 coatings and a brittle mode of erosion behavior for Colmonoy 88 coatings were observed when these materials were impacted with particles with an average size of 375 ?m, whereas only a brittle mode of erosion was observed for both Stellite 6 and Colmonoy 88 coatings when impacted with particles with an average size of 100 ?m. Mainly, chip formation, chip fracture, microcutting, plowing, and crater lip and platelet formation were observed for Stellite 6 coatings and progressive fracture of carbides, carbide pullout and carbide/boride intact were observed for the case of Colmonoy 88 coatings. � 2009 The Minerals, Metals & Materials Society and ASM International.

In this paper, hybrid laser-arc welding process has been studied based on the relative position of the laser and the arc (i.e. laser-leading and arc-leading arrangement) and, the effects of welding parameters, such as the laser power, arc current, arc voltage and the welding speed on the weld bead were investigated. The study indicates that the welding direction has a significant effect on the weld bead and weld pool behaviour. The result shows that laserleading configuration shows better bead characteristics when compared to arc-leading configuration. This is because in the laser-leading case molten metal flow is inward, while in the arc-leading case the metal flow is outward leading to variation in solidification front resulting in lack of synergic effects of both processes.