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The electrochemical corrosion and erosion behavior of FeAlCr coating was reported in this article. The FeAlCr coatings were deposited by detonation spray coating system (DSC) by utilizing the gas atomized powder with a nominal composition of Fe-12Al-5Cr at two different pulse frequencies on mild steel (MS) substrate. Feedstock and coatings were characterized using XRD, SEM and elemental mapping. Nanoindentation tests using a Berkovich indenter indicate a hardness of 5.5 GPa and 4.9 GPa for the coatings deposited at 3 Hz and 6 Hz respectively as compared to 1.5 GPa of the substrate. Electrochemical corrosion tests were performed on coated samples in 3.5 wt% NaCl and 2 N H2SO4 media and are compared with the bulk MS substrate. Detonation pulse frequency significantly influenced the coating microstructure and corrosion performance. The coating deposited at a frequency of 6 Hz exhibited higher resistance against electrochemical corrosion in 3.5 wt% NaCl medium than the coating that was deposited at 3 Hz frequency. Solid particle erosion tests performed at room temperature (25 °C) and an impingement angle of 90° (normal incidence) using Al2O3 as the erodent medium demonstrate a higher erosion loss of the coatings than the bulk MS. On the contrary, at a temperature of 400 °C, the coatings exhibited notably better erosion resistance than the MS substrate, illustrating the potential of FeAlCr coatings for high temperature wear-corrosion resistant applications.

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 performance and life of pressure die casting tools and inserts can be improved by providing efficient conformal cooling. These tools are usually made of H13 tool steel, and additive manufacturing offers the freedom to the design and process to incorporate cooling channels. In this work, Selective laser melting (SLM) process investigation was carried out on AISI H13 tool steel with different combinations of laser power and scanning speed to obtain 99.87% theoretical density of the H13 material. Further analysis of the metallurgical and mechanical behavior was carried for as-built additively manufactured (AM) samples, and the properties are compared to those of conventional heat-treated H13 alloy. The AM-built H13 alloy possessed ultrafine supersaturated dendritic microstructure with ultimate tensile strength (UTS) of 1895 MPa and yield strength (YS) of 1550 MPa which are higher than those of the conventional processed AISI H13 tool steel, but with a lower elongation of 10.4%. Post-heat treatment investigations were carried out to achieve the desired microstructure of fine martensite and precipitates of secondary carbides. Tempering curve was generated for AM-built H13 tools steel and compared with conventional standard tempering curve of H13 alloy. Based on the AM process developed and the optimized post-heat-treated procedure, the core pin modified with the conformal cooling channel needed for a pressure die casting application was additively manufactured with the cooling channel and field-tested in an actual industrial environment. It was seen that the AM-built core pin performed much better with a recorded 15–20% reduction in the surface temperature. This resulted in a reduction of the cast part's surface porosity in size and numbers, consequently reducing the number of rejections. The pressure dies casting cycle time decreased by 2 s, increasing productivity. This application is now ready for adoption in the industry.

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 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...

High Tensile Steels such as AISI-4340 is extensively used steel in various engineering sectors such as aerospace, defense, automotive, heavy engineering and power sectors for components such as pinion housing, gears, shafts, connecting rods, propeller shafts, & landing gears of aerospace vehicles etc. Such component faces extensive wear at the contact areas during operation resulting in loss of performance leading to replacement. Directed energy deposition or laser cladding for refurbishment of such components can reduce the cost of replacement and can also be advantageous in countering environmental concerns. In this study, feasibility of using AerMet-100 alloy powder for refurbishment of AISI4340 steel was explored using laser cladding process. A 6 kW diode laser with 6 + 2 axes robot was used for the experimentation where laser clads were generated by melting and depositing the powder that was fed through a powder-feeding nozzle. AerMet-100 clads were found to have good compatibility with the substrate and defect free clads were generated. In order to homogenize the microstructure at Heat Affected Zone, a post-clad heat treatment (PCHT) at 470 °C for 1hr was carried out. The as-cladded microstructure shows lath martensite with retain austenite, whereas post clad heat-treated sample shows slightly reduced retained austenite. Micro-hardness evaluation revealed increased in clad hardness after PCHT due to formation of fine carbides. Micro-tensile test of Post heat-treated clad showed max Tensile stress of 1752 MPa compared to substrate 1240 MPa. It can be concluded that AerMet-100 material can be a potential candidate for repair and refurbishment of AISI4340 steel.

Thermal spray techniques have been extensively used to deposit coatings of varying compositions on a variety of industrial components for life enhancement under wear and corrosion prone environments at ambient and high temperatures. A number of components used in power generation systems most commonly encounter high-temperature erosion–corrosion. This review article briefly summarizes various thermal spray techniques and coating characteristics that are relevant to erosion–corrosion applications followed by detailed discussion on the erosion–corrosion fundamentals and testing methods. Further, ambient and high-temperature erosion–corrosion behavior of WC- and CrC-based cermet coatings and oxide coatings have been investigated, compared, analyzed and presented. Based on the analysis of results reported so far, the methodologies to enhance the erosion–corrosion resistance of coatings have been proposed both for ambient and high temperature applications. The future scope of work that needs to be explored to contribute further developments has also been identified and presented.

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.

In the present work, laser weld-brazing experiments were performed to produce aluminum to galvanized steel joints in lap and flange configuration. Tests were carried out using Al-12 % Si eutectic filler wire for joining of AA6082 -T6 with galvanized steel with varying laser power and keeping other parameters (wire feed and laser scan speed) constant. Microstructural characteristics of the laser brazed joints, studied by SEM, revealed cast structure in the brazed zone. Intermetallic formed at the steel interface was non-uniform. From the hardness results, it was noted that the brazed region exhibits lower hardness compared to the base material. The wetting length was improved with increasing filler wire rate, which in turn improved the strength of the brazed joint in both the configuration (lap and flange). At 4 kW laser power, flange configuration sample has failed in AA6082 whereas, in case lap joint, failed in the heat affected zone of AA6082.

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.

Cold metal transfer welding, a low-heat input process, was employed to weld-braze 6061-T6 aluminium alloy to galvanized interstitial free steel using Al–Si-based (4043 and 4047) filler wires in lap fillet configuration. The effects of current pulsing and filler composition on interface morphology and joint strength were investigated. Pulsing, as well as Si content in the filler, affected the interfacial intermetallic compound layer morphology and joint strength. The detailed micro-area X-ray diffraction studies of seam/steel interface revealed the presence of binary (Al–Fe type) and ternary (Al–Fe–Si type) intermetallic phases for joints made with 4043 and 4047 filler, respectively. Lap shear tests proved that joints made with 4047 filler having ternary intermetallic phases were stronger and fractured in the braze seam. However, joints made with 4043 filler having binary intermetallic phases recorded interfacial failure at lower loads than joints made with 4047 filler. Therefore, the type and morphology of the interfacial intermetallic compounds were found to influence the joint performance.

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.

Laser brazing technique was employed to weld-braze 2 mm thick galvanized steel to 5083 aluminum alloy in flange joint configuration using 2 mm diameter solid AlSi12 (AA4047) filler wire. Experiments were performed at various wire feed rates (2.0–3.6 m/min) with constant laser power (3.5 kW), scan speed (2.5 m/min) and spot size (1.7 mm). The microstructural observation of the etched specimens under SEM showed cast structure at the brazed zone and a two-layered (planar and needle structured) interface towards the galvanized steel. HAZ was observed at the aluminum side. The selective Energy-dispersive X-ray spectroscopy (EDS) point analysis and X-ray diffraction technique were used to study the interface and the results confirmed that the planar and needle structures are comprised of ternary Alx-Fey-Siz and binary Alx-Fey intermetallic phases respectively. From hardness testing, both the base material, i.e., AA5083and galvanized steel are found to be harder than brazed zone. In case of nano-indentation testing, intermetallics have shown higher hardness values compared to base materials. The joint strength increased with increasing wire feed rate and recorded interfacial failure. Fatigue life of the laser brazed joints at lower stain amplitude is better with increasing wire feed rate and are in close range to the aluminum base material (AA5083) value. Fatigue tested specimens recorded brazed zone failure and revealed flow lines, intergranular cracking and typical fatigue striations.

In the modern world, surface engineering technologies have been playing an important role to overcome in-service degradation of ferrous and non-ferrous materials. In this context, the primary objective of this article is to comprehensively review the corrosion behaviour of protective coatings deposited through different surface engineering technologies namely (a) Thermal spray techniques such as plasma spray, high velocity oxy-fuel spray, detonation spray and cold spray; (b) Electrolytic processes including anodizing, hard anodizing, hard chrome plating, electroplating, pulse electrodeposition and micro arc oxidation; (c) Physical vapour deposition techniques namely magnetron sputtering and cathodic arc; (d) sol-gel coatings; and (e) laser materials processing on a variety of non-ferrous materials. The process-structure-property-performance aspects of these coatings are critically reviewed which indeed was the basis for their industrial adaptation in textile, naval, automotive, aerospace, mobile communications, power generation, energy management, electronics and strategic sectors. The critical strategies and challenges associated with each processing technique and the resultant corrosion behaviour were highlighted. In addition, the future R&D direction in each of the aforementioned processes and materials were identified and discussed.

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, a high intensity, precise, flexible and clean heat source is used as a manufacturing tool in several industrial sectors. With the advent of more robust, energy efficient, cheaper and low footprint lasers such as fiber lasers, laser based manufacturing is increasing rapidly. Laser based processes can be classified into macro processes (cutting, welding, cladding, alloying, drilling, brazing) and micro processes (micro texturing, scribing, micro drilling etc.) depending on the scale of effects induced during the process. The Centre for Laser Processing of Materials (CLPM) at ARCI, established about 15 years ago has been carrying out R&D on several processes for application in industry. Some of the recently developed industrial applications such as laser micro texturing of automotive components, laser deposition based repair of pressure die casting dies, laser brazing of aluminium alloys to steel, laser hardening of bearing steels and laser metal additive manufacturing are presented here.

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 ...

In the present work, a high-strength composite steel structure developed by imparting laser surface hardening treatment on a low-carbon low-Manganese automotive steel sheet has been comprehensively analysed. The layered composite steel structure has been successfully developed by re-engineering the surface of the steel using diode laser hardening treatment up to a depth of 250–300 µm through its thickness. Hardness at the treated surface improved by 150% to that of its base due to formation of a mixture of hard phases constituting martensite and bainite along with retained ferrite. Indeed, coupling EBSD technique with Weibull distribution of various phase fractions determined by image quality helped analyse microstructure effectively. The tensile property of the layered composite steel sheet was found to yield significant improvements in both Yield Strength (YS) (40–44%) and Ultimate Tensile Strength (UTS) (19–21%) due to sandwich effect of composite layer constituting hardened layer and soft base accomplished by a strengthening mechanism associated with rule of mixtures concept. In fact, Young’s modulus of the composite steel sheet, determined from slope of tensile stress–strain diagram was found to be convergent with ultrasonic test result. Additionally, the crystallographic texturing effects of the hardened layer and untreated base measured using standard XRD technique re-confirmed their influence on Young’s Modulus and r-bar values obtained.

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.

In the present work, a C-Mn low carbon automotive steel sheet has been used for laser surface hardening treatment. The steel sheet has been successfully surface hardened using high power diode laser up to certain depth (250–300 µm) to make layered composite structure through its thickness. The microstructure of the treated layered steel sheet have been evaluated by different characterization techniques such as optical microscopy, scanning electron microscopy, X-ray diffraction. The hardness at the treated surface improved significantly (133–145% increase as compared to base hardness) due to formation of harder phases, which are identified as a mixture of martensite, bainite and prior-ferrite using EBSD technique. The tensile property of the layered steel sheet was also evaluated and found to yield significant improvements in both Yield Strength (YS) (25–40%) and Ultimate Tensile Strength (UTS) (20%) due to the sandwich effect of a composite layer constituting hardened layer and base accomplished by a strengthening mechanism associated with rule of mixtures concept. Correspondingly, the Young's modulus of the layered steel sheet determined from the slope of tensile stress-strain diagram was also found to be consistent with ultrasonic test results. Additionally, the crystallographic texturing effects of the hardened layer and untreated base measured using standard XRD technique re-confirmed their effect on Young's Modulus and r-bar values obtained.

Quantitative microstructural analysis was carried out to determine the size and volume fraction of strengthening phases: gamma double prime (γ″) and gamma prime (γ′); in additively manufactured (AM) Inconel 718 (IN718) with an emphasis on the utilization of Nb for γ″ formation during aging treatment. Powder bed fusion AM (PBF-AM) technique was used to generate coupons using indigenously synthesized IN718 alloy powder. Microstructural studies using transmission electron microscope (TEM) and small angle x-ray scattering (SAXS) were carried out on powder bed fusion-additive manufactured (PBF-AM) coupons in as-built condition (as processed) and in three different heat-treated conditions: solutionizing at three different temperatures (980, 1030 and 1080 °C) followed by double aging treatment. As-built microstructure consists of dendritic structure accompanied with Nb segregation along the interdendritic regions resulting in the formation of a Nb rich interdendritic phases dispersed within the interdendritic Nb-rich γ matrix. The inhomogeneous Nb distribution resulted in preferential precipitation of coarse δ during solutionization at 980 °C and further coarse γ″during direct aging and aging subsequent to solutionizing at 1030 °C. As-cast structure and related elemental segregation got modified during solutionization at 1080 °C and resulted homogeneous γ″ precipitation. Though the average size of γ″precipitates remained same in all aged samples, volume fraction increased with increasing solutionization temperature. SAXS studies were carried out on PBF-AM as well as conventionally produced wrought samples with the similar heat treatment conditions and confirmed that PBF-AM built IN718 aged samples solutionized at 1030 °C and 1080 °C resulted in γ″ precipitates with average precipitate size and volume fraction similar to that of the wrought-IN718 sample solutionized at 1080 °C.

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...

Sol–gel derived multilayered solar selective coatings were generated on AISI SS 321 substrates using Ag-TiO 2 as the cermet layer, titania and silica as the dielectric layers with high and low refractive indices respectively. The phase compositions of the individual layers were independently confirmed using grazing angle incidence X-ray diffraction, which was corroborated by X-ray photoelectron spectroscopic analysis. Thickness of the layers was measured using variable angle spectroscopic ellipsometry. The solar absorbance was measured over the UV–Vis-NIR wavelength range. Thermal emissivity was determined using FTIR spectroscopic analysis. The durability of the coatings was ascertained using accelerated corrosion testing methods as well as by measuring the optical properties after thermal cycling experiments. The promising nature of hexavalent chrome-free, environmental friendly, multilayered solar selective coating was ascertained with respect to amenability to scale-up.

In the present work, the dry sliding wear behaviour of electrodeposited Ni-W/SiC nanocomposite coatings after heat treatment was studied. For that purpose, Ni-14 (at%) W/SiC composite coatings with varying proportion of β-SiC particle content were deposited using pulsed current electrodeposition and subsequently heat-treated at 500 °C in vacuum. The coatings were analysed for its structure, surface topography, particle content in coating and inter-particle spacing. The mechanical properties of coatings were evaluated and correlated with SiC content in the respective coating. Sliding wear tests under dry condition were carried out (at room temperature) against WC-Co disc using pin-on-disc configuration. It has been observed that the mechanical properties of nanocomposite coatings follow the rule of mixtures (ROM). The wear rate of the nanocomposite system has demonstrated a linear relationship with the inter-particle spacing of SiC particles embedded in the Ni-W matrix. Specific wear rate and friction coefficient of nanocomposite coatings were rationalised through a mathematical model based on the inverse rule of mixtures (I-ROM).

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.

This study reports a detailed investigation of the microstructure and mechanical properties (wear resistance and tensile strength) of hardened and tempered AISI H13 tool steel substrate following laser cladding with AISI H13 tool steel powder in as-clad and after post-cladding conventional bulk isothermal tempering [at 823 K (550 °C) for 2 hours] heat treatment. Laser cladding was carried out on AISI H13 tool steel substrate using a 6 kW continuous wave diode laser coupled with fiber delivering an energy density of 133 J/mm2 and equipped with a co-axial powder feeding nozzle capable of feeding powder at the rate of 13.3 × 10−3 g/mm2. Laser clad zone comprises martensite, retained austenite, and carbides, and measures an average hardness of 600 to 650 VHN. Subsequent isothermal tempering converted the microstructure into one with tempered martensite and uniform dispersion of carbides with a hardness of 550 to 650 VHN. Interestingly, laser cladding introduced residual compressive stress of 670 ± 15 MPa, which reduces to 580 ± 20 MPa following isothermal tempering. Micro-tensile testing with specimens machined from the clad zone across or transverse to cladding direction showed high strength but failure in brittle mode. On the other hand, similar testing with samples sectioned from the clad zone parallel or longitudinal to the direction of laser cladding prior to and after post-cladding tempering recorded lower strength but ductile failure with 4.7 and 8 pct elongation, respectively. Wear resistance of the laser surface clad and post-cladding tempered samples (evaluated by fretting wear testing) registered superior performance as compared to that of conventional hardened and tempered AISI H13 tool steel.

The present study reports the effect of laser parameters on the microstructure, and consequently, the wear resistance of laser surface engineered (hardening and melting) AISI H13 tool steel (in hardened and tempered condition) substrate. The microstructure of the laser surface hardened zone consists of ultrafine mixed carbides (M 23 C 6 , M 7 C 3 , MC or M 2 C) dispersed between martensite laths. On the other hand, a laser surface melted microstructure comprises retained austenite, martensite, transformed ledeburite and fine carbides precipitated in the inter-dendritic zone. Microhardness of the laser surface engineered zone is significantly enhanced to as high as 670–810 VHN as compared to 480–500 VHN of the as received quenched and tempered substrate and decreases along vertical depth from the surface until a narrow soft zone at the interface with a typical hardness of 440 VHN. Laser surface melting yields a higher hardness level (770 ± 10 VHN) as compared to that after laser surface hardening (660 ± 10 VHN). Wear resistance of laser surface engineered samples (evaluated both by ball-on-disk and fretting wear testing equipments) shows a significant improvement as compared to that in hardened and tempered condition. Due to an increased hardness, surface melting shows superior resistance to wear both under fretting as well as ball on disk wear testing conditions. A marginal improvement in corrosion resistance was also recorded in laser surface engineered samples due to microstructural/compositional homogenization introduced by laser surface engineering.

Tailor-Welded Blanks (TWBs) are obtained by welding together sheets of same or different metals of different thicknesses to produce a single blank prior to subjecting it to a forming process. Designers nevertheless need to overcome the difficulty faced in the forming of TWBs due to material property changes in the two parent metal sheets which is leading to weld line shift. The present work is aimed at studying the formability behavior of TWBs of two different steels viz. Interstitial free steels and Dual phase steels with respect to laser welding and Tungsten inert Gas welding. The formability of the TWBs and the base materials has been studied for differential strengths and analyzed with the help of LS Dyna Non-linear Finite element software. From the results, it was found that the weld shift can be altered by varying the strength parameters of the parent materials.

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.

In the present study, laser cladding of AISI H13 tool steel powder has been undertaken on hardened and tempered AISI H13 tool steel components using a 6 kW fiber coupled diode laser both in continuous wave and pulsed mode with coaxial powder feeder to explore the possibility of reclamation/refurbishment of large AISI H13 tool steel components. Laser parameters in terms of laser power, processing speed and powder feed rate have been optimized to achieve acceptable clad-substrate integrity with optimum deposition height and width without any surface cracks and porosity. A detailed study of the effect of post-cladding heat treatment (both by laser assisted surface heating and conventional tempering at 550 °C) on the microstructure, phase aggregate, crystallite size, micro-strain and residual stress was carried out. Subsequently, the microhardness of the clad zone was evaluated. Pulsed laser cladding (heat input controlled) with 50 Hz frequency and 50% duty cycle with 10 ms ON-time developed a microstructure comprising martensite, retained austenite and mixed carbides. The maximum improvement in hardness (considered as a convenient index of strengthening) by laser cladding reached up to 650 VHN, which is about 45% higher than the hardness of hardened and tempered substrates. Post-cladding tempering at 550 °C for 2 h led to the development of uniform microstructure without fine carbide precipitated along grain boundaries or inter-dendritic regions taking the hardness to 600–650 VHN level. Laser reheating (tempering) of the clad zone with a 1000 W laser power showed a more refined microstructure with maximum hardness up to 680–700 VHN. Residual stress, developed on the surface after laser cladding, was compressive in nature and measured higher in magnitude after pulsed laser cladding. Magnitude of this residual compressive stress marginally decreased after post-cladding tempering either by conventional or laser assisted route. Thus, the novelty of the present study lies in the continuous or pulsed mode laser cladding assisted reclamation of AISI H13 hot working dies with similar composition powder, followed up with conventional or laser assisted tempering, leading to the development of about 45% higher hardness (than as hardened and tempered conditions) and retention of residual compressive stress on the surface after cladding.