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.

M. Kamaraj

Department of Metallurgical and Materials Engineering

Characterization techniques

CURRENT PULSE

CURRENT PULSING

FILLER WIRE

Fusion zones

GTA WELDING

GTAW

Inconel-718

KEY WORDS- INCONEL 718

LAVES-PHASE

NIOBIUM SEGREGATION

SHIELDING GAS

THICK SHEETS

Weldments

Helium

Industrial engineering

Production engineering

Welding

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Materials Science Forum

Abstract: The micro-segregation of niobium and Laves phase formation during Gas Tungsten Arc (GTA) welding of alloy 718 were studied by employing different cooling techniques which resulted in weld cooling rates ranging from 43.2 °C/s to 508.7 °C/s. The weld cooling rates were achieved by the combinations of modified pulse wave form, argon and helium shielding gases, copper heat sink and liquid nitrogen cooling. A combination of compound current pulse (CCP) waveform with helium shielding and liquid nitrogen cooling resulted in lesser niobium segregation and discontinuous, finer Laves particles in the interdendritic regions compared to that of the conventional constant current GTA weld metal. This process yielded better ageing response and improved high temperature mechanical properties of the weldments. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Materials at High Temperatures

High temperature mechanical properties of cryogenically cooled alloy 718 weldments

The microsegregation in alloy 718 fusion zone during gas tungsten arc welding affected the aging response and the mechanical properties. The average weld cooling rate was enhanced in gas tungsten arc (GTA) welding process by employing liquid nitrogen during the process. The combination of in-process and external cooling methods reduced the microsegregation of Nb in alloy 718 fusion zone. Detailed characterization of the weld microstructures in the as-welded and the direct aged conditions was conducted. The dendritic structure have been refined to a level of 10-20 μm dendrite arm spacing and Laves particle sizes ranging from 0.04 to 1.43 μm due to the enhanced weld cooling rate. Similarly, the average Laves volume fraction was reduced from 45 to 0.1 % when compared to the conventionally cooled GTA welding process. The microsegregation was quantified through the computed solidification time through the DSC analysis and the volume fraction of the eutectic phases. It was found that the solidification time was reduced significantly from 2.499 s to as low as 0.36 s with the liquid nitrogen-cooled GTA welding process. The microhardness survey revealed an improved aging response of the fusion zone. [Figure not available: see fulltext.] © 2016, International Institute of Welding.

Welding in the World

Effect of enhanced cooling on microstructure evolution of alloy 718 using the gas tungsten arc welding process

Microstructural characterization of alloy 718 fusion zone welded with both solid solution and age hardenable filler metal has been done. The microsegregation and the aging response were studied by employing three levels of weld cooling rate. Gas Tungsten Arc welding process was used. The fusion zone of solid solution filler metal has been responding to the aging treatment due to the weld process conditions and weld metal chemistry. However the weld metal composition was modified due to the higher molybdenum (Mo) content in solid solution filler metal. The effect of this modification on the phase reaction temperatures was studied and the same was compared with the conventional filler metal. © 2014 Elsevier Inc.

Materials Characterization

Laves phase in alloy 718 fusion zone - Microscopic and calorimetric studies

The interdendritic Laves phase and the microsegregation have been investigated in Alloy 718 fusion zone cooled with liquid nitrogen during welding. Conventional GTA welding process was employed with modified waveform and two types of shielding gas and filler metal (solid solution and age hardenable). The weld cooling rate was enhanced using liquid nitrogen cooling during Gas Tungsten Arc welding process. The resultant fusion zone microstructures were characterized using the metallurgical tools. Dendrite remelting phenomenon was observed from the optical micrographs. It was found that the enhanced cooling rate with liquid nitrogen reduced the interdendritic phases which were confirmed in both the electron microscopic and the X-ray diffraction analysis. The elemental mapping in scanning electron microscope-energy dispersive spectral analysis also confirmed the reduced microsegregation. The dendrite arm spacing was reduced from the range of 15-54 μm (CCPHE-CCAR, conventional) to 3-17 μm (CCPHE-CCAR, liquid nitrogen cooled) for the employed process variables. The computed weld cooling rate was found to be enhanced from seven to fifteen times than the conventional welding process. © 2014 Elsevier B.V.

Journal of Materials Processing Technology

Microstructural characterization of liquid nitrogen cooled Alloy 718 fusion zone

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.

Effect of weld cooling rate on Laves phase formation in Inconel 718 fusion zone

Journal of Materials Science Letters

Laves phase in superalloy 718 weld metals

Welding Journal

Effect of Nitrogen on Solidification Cracking Resistance in ERNiCr-3 Weld Metal

Science and Technology of Welding & Joining

Residual stresses in P91 steel electron beam welds

10.4028/www.scientific.net/msf.710

Thesis Eleven

Reviews : Max Horkheimer, Between Philosophy and Social Science: Selected Early Writings, translated by G.F. Hunter, M.S. Kramer, and J. Torpey (MIT Press, 1993)

Laves phase control in inconel 718 weldments

Journal	Materials Science Forum
ISSN	02555476
Open Access	No