Effects of switching over from gas tungsten arc welding (GTAW) to pulsed current gas tungsten arc welding (PCGTAW) on the quality of joints produced in Hastelloy C-276 material were investigated. Welding was carried out both by autogenous mode and using ERNiCrMo-3 filler wire. Microstructures of weld joints produced with and without current pulsing were studied using optical and scanning electron microscopy. Microsegregation occurring in GTAW and PCGTAW joints was investigated using energy dispersive X-ray spectroscopy (EDS). Strength and ductility of weld joints produced with and without pulsing were evaluated. The results show that pulsing results in refined microstructure, reduced microsegregation and improved strength of weld joints. Secondary phase(s) noticed in GTA weldments were found to be absent in PCGTA weldments. Autogenous PCGTA weldments were found to be the best in terms of: (i) freedom from microsegregation, (ii) strength and (iii) freedom from unwanted secondary phases. © 2014 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

Manikandan M

Department of Design and Automation

School of Mechanical Engineering

Vellore Campus

Arivazhagan N

Department of Manufacturing Engineering

Rao M.N

Reddy G.M.

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Journal of Manufacturing Processes

The pulsating current approach in <a href="https://www.sciencedirect.com/topics/engineering/tungsten">tungsten</a> <a href="https://www.sciencedirect.com/topics/engineering/inert-gas">inert gas</a> (TIG) welding is adapted for joining <a href="https://www.sciencedirect.com/topics/engineering/hastelloy">Hastelloy</a> C-276. <a href="https://www.sciencedirect.com/topics/engineering/microstructure">Microstructure</a> examination revealed the absence of micro-segregation while employing UNS N06022 filler. Due to the prevalence of <a href="https://www.sciencedirect.com/topics/engineering/high-tensile-stress">higher tensile stresses</a> in the un-peened conditions, tensile failures were observed in the weld regions of both the joints irrespective of fillers. Low <a href="https://www.sciencedirect.com/topics/engineering/energy-engineering">energy</a> <a href="https://www.sciencedirect.com/topics/engineering/laser-shock-peening">laser shock peening</a> without coating (LSPwC) was carried out on the weld zones on both the sides of the joints with the pulse densities 2500 and 7500 pulses per cm2. This <a href="https://www.sciencedirect.com/topics/engineering/laser-surface-treatment">laser surface treatment</a> had remarkably increased the <a href="https://www.sciencedirect.com/topics/engineering/tensile-strength">tensile strength</a> of the welded joints by shifting the location of tensile failures well away from the fusion zones for all the cases. Similarly, a considerable increase is observed in the <a href="https://www.sciencedirect.com/topics/engineering/notch-toughness">notch toughness</a> of both the joints in the LSPwC condition. The enhancement in tensile strength and notch <a href="https://www.sciencedirect.com/topics/engineering/impact-toughness">impact toughness</a> of the welds could be ascribed to the <a href="https://www.sciencedirect.com/topics/engineering/compressive-residual-stress">residual compressive stresses</a> induced which were then confirmed by Sin2ψ method in <a href="https://www.sciencedirect.com/topics/engineering/x-ray-diffraction">X-ray diffraction</a> (XRD) technique.

Journal of Materials Processing Technology

Effect of low energy laser shock peening on the mechanical integrity of Hastelloy C-276 welds

Microsegregation of alloying elements is prone to hot cracking in the weldment of alloy C-276. The formation of topologically close packed phases P and µ is largely responsible for the hot cracking. The present study articulates the effect of laser shock peening (LSP) to improve the metallurgical and mechanical properties of the weld joint. The weld joint was fabricated by pulsed current gas tungsten arc welding (PCGTAW) using an ERNiCrMo-3 filler wire. LSP without coating was carried out on the cap surface of the weldment. Microstructural studies were carried out to compare the as-welded and laser-peened microstructure on the fusion zone. The results show that a fine equiaxed dendritic structure was observed in both conditions. EDS analysis was carried out to evaluate the microsegregation of alloying elements. EDS analysis indicates that there are no secondary intermetallic phases. X-ray diffraction analysis was carried out to evaluate the phase change and crystallite size in the as-welded and laser shock peened fusion zone. The result shows 48.99% reduction in crystallite size after LSP. Hardness and tensile strength results indicate there is a consequential increase in laser shock peened specimen compared with as-welded specimen. © 2018, Indian Academy of Sciences.

Fulltext

Sādhanā

Surface modification technique to enhance metallurgical and mechanical properties of alloy C-276 weldment by laser shock peening without coating

This research article examines the metallurgical and mechanical behavior of twenty-first-century nickel-based superalloy 686. The weld joints were produced with ERNiCrMo-4 and ERNiCrMo-14 filler wires by continuous current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) mode. Optical and scanning electron microscope (SEM) analyses were performed to evaluate the microstructure of welded joints. PCGTAW weldments showed refined microstructure, narrower weld bead and minimum heat-affected zone compared to GTAW. SEM analysis revealed the presence of secondary phases in the interdendritic regions of GTA and PCGTA weldments made of ERNiCrMo-4 and GTA ERNiCrMo-14 fillers. Energy-dispersive X-ray spectroscopy examination was also performed to assess the microsegregation of alloying elements in the weldments. The results proved nonexistence of microsegregation in the case of PCGTA weldments made by ERNiCrMo-14 filler. However, segregation of alloying element Mo was noticed in other weldments. Strength and toughness of the weld joints were evaluated by conducting tensile and Charpy impact tests. The refined microstructure with the absence of microsegregation obtained in the PCGTA welding made with ERNiCrMo-14 filler wire resulted in the higher strength and toughness than other weldments. © 2018, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Improvement of Metallurgical and Mechanical Properties of Gas Tungsten arc Weldments of Alloy 686 by Current Pulsing

Electron Beam Welding (EBW) was performed on the highly corrosion resistance superalloy 686. The present research work investigates the metallurgical and mechanical properties of the weld joint fabricated by Electron Beam Welding technique, and the results are compared with the base metal. Optical and Scanning Electron Microscope (SEM) analysis were carried out to study the structural properties of the weld joint. The fine equiaxed dendritic structure was revealed in the Center Fusion Zone (CFZ). The columnar dendrite was noticed in the Transition Fusion Zone (TFZ). Energy-dispersive X-ray spectroscopy (EDS) analysis results show that segregation of Mo and W were noticed in the sub-grain boundary. X-ray diffraction analysis (XRD) confirmed the presence of Mo and W rich phases in the weldment. Tensile testing was carried out to evaluate the strength and ductility of the weld joint. The result revealed that the weld strength was equal to the base metal strength. The presence of Mo and W-rich intermetallic phase reduced the ductility and toughness of the weld joint compared to base metal. Bend test confirmed the defect-free weld joint that was achieved in the Electron Beam Welding technique. The corrosion rate of base metal and EBW weldment are calculated in the synthetic seawater environment with the help of Potentiodynamic polarization experiment, and corrosion rate is measured with Tafel’s interpolation technique. The corrosion test result shows that the resistance of EBW weldment is lesser than base metal corrosion resistance because of the microsegregation of alloying elements in the interdendritic region. © 2018, Indian Academy of Sciences.

Investigation of metallurgical and mechanical properties of 21st century nickel-based superalloy 686 by electron beam welding technique

Alloy 80 A is prone to hot cracking during conventional arc welding process. Microsegregation of alloying element Cr lead to the formation of M23C6 carbide phase during solidification of fusion zone, and it contributes to hot cracking. The current study employs different welding techniques and filler wires to minimize the microsegregation. The weldments were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques using filler wires 263 and ERNiCrMo-3. Scanning electron microscope (SEM) reveals the existence of secondary phase in the interdendritic region for all the weldments. Energy dispersive X-ray spectroscopy (EDS) analysis reports that PCGTAW eliminates microsegregation of Cr precipitate and suppress Nb and Mo precipitates better when compared to GTAW. X-ray Diffraction (XRD) analysis indicate the presence of M23C6 Cr and Mo-rich carbide phase in GTA weldment of 263 filler wire. Whereas in PCGTAW, NiCrCoMo phase is observed. In both GTAW and PCGTAW of ERNiCrMo-3, the intermetallic phases Ni8Nb and Cr2Ti are observed. The tensile test was conducted to assess the strength and ductility of the weldments. The results of the PCGTAW weldments have improved compared to their respective GTAW weldments. © 2018 The Society of Manufacturing Engineers

Development of welding technique to suppress the microsegregation in the aerospace grade alloy 80A by conventional current pulsing technique

Inconel 718 (2 mm thick) was welded using argon and helium gas shielded tungsten arc welding process with a filler metal. Both constant current and compound current pulse modes were applied and the cooling rates calculated. The dependence of Laves phase formation, dendrite arm spacing and niobium segregation ratios in fusion zone on the nature of shielding gases and current was studied. The maximum instantaneous weld cooling rate was achieved for the combination of Helium shielding gas and compound current pulse mode. This ultimately resulted in reduction of laves phase, segregation of niobium and dendrite arm spacing in the fusion zone. © 2013 Elsevier B.V. All rights reserved.

Journal	Data powered by TypesetJournal of Manufacturing Processes
Publisher	Data powered by TypesetElsevier BV
ISSN	1526-6125
Open Access	No