Ch Radhakrishna

Electric arc welding

Electron beam welding

Fillers

Metallographic phases

Microanalysis

Niobium

Scanning electron microscopy

Segregation (metallography)

Solutions

Welds

DELTA PHASE

Dendrites

Electron probe microanalysis

Gas tungsten arc

Homogenization treatment

Laves phase

POST WELD HEAT TREATED CONDITIONS

superalloys

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

Laves phase in superalloy 718 weld metals

Journal of Materials Science Letters

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

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

Superalloys 718, 625 and Various Derivatives (1991)

The Effect of Laves Phase on the Mechanical Properties of Wrought and Cast + HIP Inconel 718

Journal	Journal of Materials Science Letters
Publisher	Kluwer Academic Publishers
ISSN	02618028
Open Access	No