Pulsed Nd-YAG laser welding characteristics of Inconel 718 sheet material (2 mm thick) were investigated. Welds were subjected to three different post-weld heat treatments: direct aging, 980 °C solution treatment + aging (980STA), and 1080 °C solution treatment + aging (1080STA). Weld microstructures and room temperature tensile properties were evaluated. Weld tensile properties in direct aged condition were found to be inferior in relation to the base metal due to the presence of Nb-rich brittle intermetallic Laves phase in fusion zone microstructure. Solution treatment at 980 °C was found to result in considerable dissolution of Laves phase, leading to some improvement in weld properties, though not to the level of base metal. The treatment was also found to result in precipitation of needle-like δ-phase around partially dissolved Laves particles. Solution treatment at 1080 °C was found to result in complete dissolution of Laves phase, but also in significant grain coarsening in the base metal, which led to considerable deterioration in base metal properties. © 2004 Elsevier B.V. All rights reserved.

Janaki Ram G D

Department of Metallurgical and Materials Engineering

Aging of materials

dissolution

Heat treatment

Laser Beam Welding

Laser pulses

microstructure

Neodymium lasers

Precipitation (chemical)

Tensile properties

Thermal effects

Welds

ALLOY 718

LAVES PHASES

NB SEGREGATION

POST-WELD HEAT TREATMENTS

Sheet metal

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IIT Madras

Journal of Materials Processing Technology

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 present work deals with the effects of pre- and post-weld heat treatments on microstructure and mechanical properties of alloy 718 friction weld joints. Prior to friction welding, alloy 718 rods were subjected to two types of heat treatments - solution treatment (ST) and solution treatment followed by aging (STA). In the as-welded condition, samples welded with prior ST condition exhibited higher hardness in the weld zone compared to the base material in ST condition and this is attributed to grain refinement due to dynamic recrystallization. Samples welded with prior STA condition exhibited decreased hardness in the weld zone and room temperature tensile properties in relation to the base material in STA condition. It is due to dissolution of γ″ (Ni 3Nb) phase as the temperature measured at weld zone was found to be 1118°C. In order to retrieve the hardness and room temperature tensile properties, friction weld joints were subjected to direct aging (DA) treatment. A significant increase in hardness was observed in the weld zone after direct aging for both samples welded in ST and STA conditions. This is attributed to the grain refinement due to dynamic recrystallization and formation of precipitates by the DA treatment. © 2012 Elsevier B.V.

Materials Science and Engineering A

Microstructure and mechanical properties of friction welded alloy 718

Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle and elliptical) in controlling Nb segregation, Laves formation and stress rupture behaviour of Inconel 718 electron beam welds are studied. Effects of various post-weld heat treatments on stress rupture behaviour are compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous and fine Laves In the interdendritic regions compared with other welds and unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited longer rupture life than unoscillated beam welds in both solution treated and aged and directly aged conditions. © 2007 Institute of Materials, Minerals and Mining.

Science and Technology of Welding and Joining

Effects of electron beam oscillation techniques on solidification behaviour and stress rupture properties of Inconel 718 welds

Autogenous full penetration electron beam welds were made on alloy 718 with and without beam oscillation technique. Weldments were subjected to two types of post-weld heat treatments: direct aging (DA) and solution treatment at 980°C followed by aging (STA). When the welds were prepared using different heat inputs in the welding processes with and without beam oscillation, the influence of beam oscillation could not be studied in isolation but the coupled effect of heat input and beam oscillation was studied. Laves particles were finer in size and lower in amount in unoscillated welds compared with those in beam oscillated welds subjected to DA condition, δ phase needles were observed around Laves particles in the welds subjected to STA condition. The amount of Laves particles was less and that of δ phase was more in unoscillated welds compared with those in beam oscillated welds subjected to STA condition. Unoscillated weldments exhibited longer fatigue lives compared with beam oscillated weldments in both DA and STA conditions owing to less amount of Laves In the former. Weldments In STA condition had longer lives compared with those in DA condition. The role of δ phase needles in fatigue life could not be identified. © 2006 Institute of Materials, Minerals and Mining.

Coupled effect of heat input and beam oscillation on mechanical properties of alloy 718 electron beam weldments

This work examines the influence of post-weld heat treatment (PWHT) on the fusion zone microstructure, and mechanical properties of electron beam (EB)-welded alloy 686. Comparative studies have been made on weld microstructure and tensile properties of the weldments both in as-welded and post-welded heat-treated conditions. PWHT consists of direct aging (DA/480°C for 3 h) and solution treatment (ST, 980°C for 1 h) followed by ageing and finally, homogenizing treatment (HT, 1200°C for 1 h) followed by DA and ST. The secondary topologically closed packed (TCP) phases formation, their distribution and microsegregation characteristics are studied with the aid of scanning electron microscope (SEM) analysis. Energy-dispersive X-ray spectroscopy (EDS) is also performed to estimate the microsegregation of alloying elements in the dendritic core and interdendritic regions of the weldments. The result shows that there is no significant change in the microstructure of DA and solution-treated sample as compared to the as-welded sample. The microstructure of HT sample was entirely different from those of as-welded and other HT samples. The SEM/EDS analysis illustrates the presence of secondary TCP phases (σ, P and μ) in the as-weld, DA and ST condition, whereas HT weldments did not show the presence of TCP phases. Tensile test results show higher tensile strength in ST condition whereas homogenization samples show higher ductility compared with others. © 2019, Indian Academy of Sciences.

Fulltext

Sādhanā

Effect of post-weld heat treatment on the microstructure and tensile properties of electron-beam-welded 21st century nickel-based super alloy 686

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	Journal of Materials Processing Technology
ISSN	09240136
Open Access	No