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

Manikandan M

Department of Design and Automation

School of Mechanical Engineering

Vellore Campus

Subramani P

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 hastelloy X is keen to solidification and liquation cracks during fusion welding methods. The microsegregation of Mo &amp; Cr-rich elements at the final phase of solidification process causes the development of secondary precipitates such as M6C, M23C6 carbides, P &amp; σ phases in the fusion zone and these phases act as an origin for initiation of hot cracking during conventional arc welding method. The present study adopts gas tungsten arc (GTA) welding and pulsed current arc welding technique to suppress the segregation of carbide phases using ERNiCrCoMo-1 filler wire. The metallographic results discovered the existence of Mo-rich secondary carbide precipitates in weld zone (WZ) of GTA weldment and no such of Mo-rich carbide precipitates identified in PCGTA weldment. The formation of Mo-rich M6C, Fe2MoC, and Cr2Ti phases were identified in GTA weldment and Ni3Ti, Ni3(Al, Ti) and γ- Co3Ti precipitate phases in PCGTA weldment by X-ray diffraction (XRD) inspection. The tensile strength and impact toughness of PCGTA weldment is better than GTA weldment by 4.18% and 20.18% respectively. The microhardness results also reveal an 8.05% increase in the mean hardness value of PCGTA weldment compared to GTA weldment. The improvement in strength of PCGTA welding is due to the refined microstructure with the absence of microsegregation of Mo &amp; Cr-rich elements. © 2019 The Society of Manufacturing Engineers

Preclusion of carbide precipitates in the Hastelloy X weldment using the current pulsing technique

This research article focuses on the joining of SMO 254 stainless steel by autogenous CO2 Laser beam welding and pulsed current gas tungsten arc welding (PCGTAW) with ERNiCrMo3 filler. The studies proved that full penetration could be achieved on the weld joint of a 5 mm thick plate with a reduced heat input of 120 J/mm in the laser welding while in the case of PCGTAW it was 3032 J/mm. An attempt is made to do a comparative evaluation of the microstructure changes which have occurred owing to welding and thereby the mechanical properties. The studies revealed the lack of deleterious phases in both welding techniques. Presence of grain boundary thickening near the fusion zone and elemental segregation was observed in PCGTAW joints. The residual stress measurements by X-ray diffraction method were executed over the cross-section of the two different weldments. An attempt is made to represent the stresses variation along the weld region, heat affected zone and the base metal graphically. The tensile test validated that in every case the rupture ensued at the base metal and the higher weldment hardness than base metal proves the soundness of the joint. © 2019 The Society of Manufacturing Engineers

Investigations on induced residual stresses, mechanical and metallurgical properties of CO2 laser beam and pulse current gas tungsten arc welded SMO 254

Materials Research Express

Hot corrosion studies of HVOF sprayed carbide and metallic powder coatings on alloy 80A at 900 °C

The air plasma spray process is extensively adopted by many industries because of versatility, cost-effectiveness and good quality of the coatings produced. The present study compares the high-temperature corrosion behavior of air plasma sprayed Cr3C2-25NiCr and NiCrMoNb powders coatings on alloy 80A (Ni80TiAl). The corrosion study was carried out by air and molten salt environment of Na2SO4 + 60%V2O5 under cyclic conditions for 50 cycles at 900 °C. Thermogravimetric analysis was used to analyze the hot corrosion (air and molten salt environments) of uncoated and coated alloy 80A. Microstructure, porosity, thickness, and hardness of the coatings were evaluated in the cross section of the coatings. XRD and SEM/EDS analysis were carried out to evaluate the corrosion product at the end of the 50th cycle. The microstructure shows the coatings are laminar structure with uniform, adherent and dense microstructure with porosity less than 4% and thickness of 150 ± 10 μm. The microhardness of both coatings found to be higher than the substrate. Thermogravimetric analysis shows the air oxidation both coated and uncoated alloy 80A obey the parabolic rate law of oxidation. Uncoated alloy 80A shows the very less weight gain compared to other coated substrates. NiCrMoNb coated with molten salt environment substrates shows the higher weight gain. Also, molten salt environment shows higher mass gain compared to the corresponding air oxidation environment substrates. Presence of NiO, Cr2O3 and spinel oxide NiCr2O4 provides the excellent corrosion resistance in the air oxidation environment both coated and uncoated substrates. The high Mo element content in NiCrMoNb coating is causing more weight gain at 900 °C in molten salt (Na2SO4 + 60%V2O5) environment by forming a volatile MoO3 oxide. The results conclude that NiCrMoNb coating may be used as a protective coating in air oxidation environment and the Cr3C2-25NiCr coating may be used as a protective coating in the molten salt environment. © 2018 Elsevier B.V.

Surface and Coatings Technology

High-temperature corrosion behaviour of air plasma sprayed Cr3C2-25NiCr and NiCrMoNb powder coating on alloy 80A at 900 °C

Even though Nickel based superalloy (alloy 600) exhibits high corrosion resistance at elevated temperatures, the main limitation of this alloy is the formation of Cr-depleted zones in the grain boundary regions. In this regard, there is a constant demand for the reduction of Cr-depleted (sensitization) zones towards various applications. In order to achieve this, the present work is focussed on the fabrication of weld joints by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) using the filler wires such as ERNiCr-3, ERNiCrMo-3, and ERNiCrMo-14 to avoid sensitization. The fabricated materials were analyzed by optical and scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The macro examination of these welded materials clearly reveals the presence of defect-free weld joints. As per the results from the microstructural analysis, the rapid cooling was achieved in the pulsed current technique, and subsequently, the equiaxed dendrites were observed in the fusion zone. EDS analysis showed the presence of Nb-rich (MC) carbide phases near the joints fabricated by filler wires i.e. GTA ERNiCr-3 and ERNiCrMo-3 indicating the preferential formation of Nb-carbide over Cr-carbide. In a similar way, Mo-rich M23C6 phases were observed near the joint fabricated by the filler wire, GTA ERNiCrMo-14. There was no microsegregation observed during the fabrication through the PCGTA welding technique. © 2017

Development of welding technique to avoid the sensitization in the alloy 600 by conventional Gas Tungsten Arc Welding method

Alloy 686 is a highly corrosion resistant 21st-Century Nickel based superalloy derived from Ni-Cr-Mo ternary system. The alloying elements chromium (Cr) and molybdenum (Mo) are added to improve the resistance to corrosion in the broad range of service environment. The presence of a higher percentage of alloying elements Cr and Mo lead to microsegregation and end up with hot cracking in the fusion zone of Nickel-based superalloys. However, there is scanty of information regarding the welding of alloy 686 with respect to the microsegregation of alloying elements. The present study investigates the possibility of bringing down the microsegregation to cut down the formation of secondary phases in the fusion zone. The weld joints were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed current gas tungsten arc welding (PCGTAW) with ERNiCrMo-10 filler and without filler wire (autogenous) mode. The microstructural properties of the weld joints were studied with optical and Scanning Electron Microscope (SEM). The joints fabricated by pulsed current (PC) technique shows refined microstructure, narrower weld bead and practically no heat affected zone (HAZ). Scanning Electron Microscope demonstrates the presence of secondary phases in the interdendritic regions of GTAW case. Energy Dispersive X-ray Spectroscopy (EDS) analysis was carried out to evaluate the microsegregation of alloying element. The results show that the segregation of Mo noticed in the interdendritic zone of GTAW both autogenous and filler wire. Tensile and Impact tests were done to evaluate the strength, ductility, and toughness of the weld joints. The results show that the PCGTA helps to obtain improved strength, ductility and toughness of the weld joints compared to their respective GTAW. Bend test did not lead to cracking irrespective of the type of welding adopted in the present study. © 2017 Elsevier B.V.

Materials Science and Engineering: A

Development of welding technology for improving the metallurgical and mechanical properties of 21st century nickel based superalloy 686

Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and l has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties. © The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg 2014.

Fulltext

Acta Metallurgica Sinica (English Letters)

Improvement of Microstructure and Mechanical Behavior of Gas Tungsten Arc Weldments of Alloy C-276 by Current Pulsing

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.

Journal	Data powered by TypesetJournal of Manufacturing Processes
Publisher	Data powered by TypesetElsevier BV
ISSN	1526-6125
Open Access	0