This paper investigates the weldability, microstructure and mechanical properties of 5 mm thick Inconel 718 plates obtained by pulsed current gas tungsten arc welding (PCGTAW) using ERNiCu-7, ERNiCrCoMo-1 and ERNiCr-3 fillers. Post weld heat treatment (PWHT) was also carried out at 720 °C/8 h/furnace cooling followed by 620 °C/8 h/air cooling on the weldments. A comparative evaluation based on the microstructure features and mechanical properties of both the as-welded and aged samples were studied. Further this study addressed the combined effect of filler wires and post weld heat treatment on the metallurgical and mechanical properties of the weldments. The studies showed the improvement in tensile strength and drop in impact toughness for all the weldments after direct ageing heat treatment. © 2015 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

Devendranath Ramkumar K

Department of Manufacturing Engineering

School of Mechanical Engineering

Vellore Campus

Arivazhagan N

Jagat Sai R

Santhosh Reddy V

Gundla S

Harsha Mohan T

Saxena V

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 formation of Laves phase in the fusion zone of Inconel 718 welds is considered to be detrimental and requires major attention, as this phase deteriorates the mechanical properties and high-temperature corrosion resistance. This present study addresses the use of current pulsing technique on the gas tungsten arc welding of 5-mm-thick Inconel 718 plates. Nb-free fillers, namely ERNiCrMo-10 and ERNiCrMo-14, are chosen for joining these plates. Microstructure studies revealed the segregation of Mo-rich phases at the inter-dendritic regions of the fusion zone of both the weldments. Further, the occurrence of detrimental Laves phase was minimized while employing Mo-rich fillers. It is inferred from the tensile studies that the fractures occurred in the parent metal for ERNiCrMo-10 filler and at the fusion zone while employing ERNiCrMo-14. Room-temperature Charpy impact studies also affirm that the impact toughness of ERNiCrMo-10 welds is significantly greater than that of ERNiCrMo-14. Hot corrosion studies were performed on the coupons by exposing them to a synthetic molten salt environment comprising Na2SO4 + 60%V2O5 at 800 °C for 50 h. Owing to the presence of higher amounts of Cr2O3 and NiO, both fusion zones exhibited better hot corrosion resistance than the parent metal. The novel outcome of the study reiterates that with the use of current pulsing and Mo-rich fillers, the detrimental phase shall be controlled. © 2017, ASM International.

Journal of Materials Engineering and Performance

Effect of Mo-rich Fillers in Pulsed Current Gas Tungsten Arc Welding of Inconel 718 for Improved Strength and Hot Corrosion Resistance

Journal of Materials Research

Effect of fillers on the microstructure, mechanical properties, and hot corrosion behavior of Nb stabilized austenitic stainless steel welds

In this article, an attempt has been made to investigate the effect of fillers on the pulsed current gas tungsten arc welding (PCGTAW) of Inconel 625 and Inconel 718. Two different Ni-Mo rich fillers namely ERNiCrMo-4 and ERNiCrMo-10 were employed for joining 5 mm thick plates of Ni based super alloys. The deleterious Laves phase was completely suppressed, while using these fillers. Mo rich segregation was observed in the fusion zones for both the fillers without much depletion of Mo in the fusion matrix. Tensile failures were observed at the parent metal of Inconel 718 in both the cases. It was attested from the notch tensile studies that the notch strength ratio was greater than unity, which attested that the weldments were ductile in all conditions. Impact studies showed that the weldments employing ERNiCrMo-10 exhibited better impact toughness at room temperature conditions. Hot corrosion studies were performed on the coupons exposed in the synthetic molten salt environment of 60%Na2SO4–40%V2O5 at 900 °C. Studies showed that both the parent metal Inconel 625 followed by the fusion zone of ERNiCrMo-10 exhibited better corrosion resistance in the high temperature environment. Surface analytical techniques were adopted to investigate the hot corroded species. © 2017 The Society of Manufacturing Engineers

Investigations on the microstructure, tensile strength and high temperature corrosion behaviour of Inconel 625 and Inconel 718 dissimilar joints

The present study addresses the effect of fillers on the microstructure and tensile strength of dissimilar joints of Inconel 625 and UNS S32205 by pulsed current gas tungsten arc welding (PCGTAW) employing ERNiCrMo-10 and ERNiCrMo-14 fillers. This study attested that tensile failure occurred in the fusion zone of the dissimilar joints for both the cases in the as-welded un-peened condition. Double shot laser shock peening (DLSP) was performed on the fusion zone of these PCGTA welds on the cap and root regions of the weldments. It was assimilated that after DLSP on the cap and root regions of the weldments, the yield and tensile strength of the welded joints employing these fillers were improved considerably. Residual stress analysis were carried out on the dissimilar coupons using X-ray Diffraction analysis. The results demonstrated that after subjecting to double sided DLSP, the fusion zones were subjected to compressive residual stresses. The present study articulated that shot peening using low energy laser beam resulted in better tensile strength. © 2016 Elsevier B.V.

Materials Science and Engineering: A

Influence of laser peening on the tensile strength and impact toughness of dissimilar welds of Inconel 625 and UNS S32205

Segregation of Mo is one of the most detrimental problems associated with the welding of super-austenitic stainless steels. The present study articulates the effects of fillers on the microstructure and mechanical properties of pulsed current gas tungsten arc (PCGTA) welded joints of AISI 904L. Four different fillers namely ERNiCrMo-4, ERNiCrMo-10, ERNiCrMo-14 and ERNiCu-7 were employed for joining 5 mm thick plates of AISI 904L. Efforts had been taken to investigate the effect of filler wires on the segregation of Mo in the fusion zone. Studies attested to the retention of Mo in the dendritic regions while employing Ni-Mo rich fillers. Evidently, Mo in the fusion zones was comparatively greater than that in the parent metal. Microstructure studies revealed the formation of unmixed zones at the weld interface while employing these fillers. Migrated grain boundaries were prominent in the fusion zone of ERNiCu-7 weldments. Tensile studies demonstrated that failures occurred at the parent metal of AISI 904L irrespective of fillers employed. Charpy V-notch studies showed that the impact toughness at the cap zones of the weldments was superior to the root regions for all the cases of the weldments. Also, the welded coupons were subjected to cyclic hot corrosion studies at 650 °C in a synthetic molten salt mixture containing K2SO4 + 60% NaCl for 50 cycles. The corrosion studies attested that the fusion zone employing ERNiCrMo-14 exhibited better corrosion resistance than the other fillers and also the parent metal employed in the study. Surface analytical techniques were employed to investigate the hot corroded species. © 2016 The Society of Manufacturing Engineers

Effects of filler metals on the segregation, mechanical properties and hot corrosion behaviour of pulsed current gas tungsten arc welded super-austenitic stainless steel

The effect of post-weld heat treatments on the microstructure and mechanical properties of friction welded joints of alloy 718 was studied in the present work. Alloy 718 rods were friction welded with two prior heat treatments - solution treatment and solution treatment and aging. Solution treatment was done at 995 °C for 1 h. Aging was done at 720 °C for 8 h followed by furnace cooling to 620 °C and holding at 620 °C for 8 h followed by air cooling. After friction welding, the joint samples were subjected to two types of post-weld heat treatments - direct aging (aging after welding, the same aging treatment mentioned above) and solution treatment and aging. Electron back scattered diffraction technique and transmission electron microscopy were used to study the development of microstructure. Hardness and tensile properties of the weld joints were evaluated. In the as-welded condition, samples welded with prior solution treatment and aging condition exhibited lower hardness at the weld zone and inferior tensile properties compared to the base material due to the dissolution of strengthening precipitates in the weld zone. On the other hand, formation of fine grains due to dynamic recrystallization led to higher hardness at the weld zone compared to the base material welded with prior solution treatment condition. Solution treatment and aging post-weld heat treatment resulted in an abnormal grain growth in the weld zone and thermomechanically affected zone. Owing to the formation of strengthening precipitates, solution treatment and aging post-weld heat treatment resulted in a significant increase in tensile strength of joint samples compared to that of as-welded friction weld joints. However, solution treatment and aging post-weld heat treatment done on friction weld joint samples with prior solution treatment or solution treatment and aging heat treatment condition resulted in inferior tensile properties compared to those of samples subjected to direct aging post-weld heat treatment. This may be attributed to grain coarsening that occurred during the post-weld solution treatment. Therefore, direct aging after welding is the recommended post-weld heat treatment for friction welded alloy 718 joints as compared to solution treatment and aging after welding. © 2013 Elsevier Ltd.

Materials and Design

Effect of post-weld heat treatments on microstructure and mechanical properties of friction welded alloy 718 joints

The detrimental laves formation in fusion zone during welding of Inconel 718 is controlled with compound current pulsing technique along with helium shielding gas. Also solid solution filler wire is used to minimize the niobium segregation. Welds were produced in 2mm thick sheets by GTA welding process and subjected to the characterization techniques. The results show, refined fusion zone microstructure, reduced amount of laves phase, minimum niobium segregation and softer fusion zone in the as welded condition. © (2012) Trans Tech Publications.

Materials Science Forum

Laves phase control in inconel 718 weldments

Welding Metallurgy and Weldability of Nickel-Base Alloys

The effects of improvement in stress rupture properties of Inconel 718 gas tungsten arc welds using current pulsing are described. The use of current pulsing resulted in significant refinement of the fusion zone solidification structure, with improvement in Laves morphology. The current pulsing method also reduced the extent of Nb segregation during weld metal solidification. The results show that presence of needle-like δ-phase in excessive amounts is detrimental for stress rupture properties in wrought alloy 718.

Journal of Materials Science

Improvement in stress rupture properties of inconel 718 gas tungsten arc welds using current pulsing

The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties. © 2004 Institute of Materials, Minerals and Mining. Published by Maney on behalf of the Institute.

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