© 2012 AMAE DOI: 01.IJMMS.02.01. AMAE Int. J. on Manufacturing and Material Science, Vol. 02, No. 01, May 2012 41 A Comparative Study on Direct and Pulsed Current Gas Tungsten Arc Welding of Alloy 617 E. Farahani 1 , M. Shamanian 2 , F. Ashrafizadeh 2 1 Pars Oil & Gas Company (POGC)/Inspection Engineering Department, Tehran, Iran Email: Emad.Farahani@gmail.com 2 Isfahan university of technology/Department of materials engineering, Isfahan, Iran Abstract— the aim of this article is to evaluate the mechanical and microstructure properties of Inconel 617 weldments produced by direct current electrode negative (DCEN) gas tungsten arc welding (GTAW) and pulse current GTAW. In this regard, the micro structural examinations, impact test and hardness test were performed. The results indicated that the joints produced by direct mode GTAW exhibit poor mechanical properties due to presence of coarse grains and dendrites. Grain refining in pulse current GTAW is reason of higher toughness and impact energy than DCEN GTAW. Further investigations showed that the epitaxial growth is existed in both modes that can strongly affect the mechanical behavior of the joints in heat affected zone (HAZ). Index Terms - Alloy 617, Welding, Pulsed Current, Microstructure, Grain Refining. I. INTRODUCTION Super alloys are divided into three groups including iron, nickel and cobalt alloys. Inconel is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium based super alloys. Inconels retain their mechanical properties at high temperature applications where many kinds of steels are susceptible to creep as a result of thermally-activated deformation [1-4]. Alloy 617 (UNS N00617- ASTM B 166), a solid solution nickel-based alloy, has a face-centered-cubic (FCC) crystal structure, widely used in the high temperature applications because of its excellent high temperature corrosion resistance, superior mechanical properties, good thermal stability and superior creep resistance [4-6]. The microstructure and phase stability of Inconel 617 alloy were investigated by researchers [7]. They showed that M 23 C 6 carbides can be formed after high temperature exposures (in the range of 649ÚC –1093ÚC). Presence of 1 wt% aluminum also strengthens the matrix by forming Ni 3 Al inter metallic compound which slightly improves the mechanical properties at 650ÚC –760ÚC. However, the major role of aluminum and chromium additions is to improve the oxidation and carburization resistance at high temperatures [8]. The corrosion behavior [9, 10] and high temperature properties [8, 11-14] of Inconel 617 have been previously investigated in the literature. It should be mentioned that welding processes are essential for the development of virtually manufactured Inconel products. However, the papers which deal with the investigation of Inconel 617 weldments are a few. However, the microstructure of dissimilar Inconel 617/ 310 stainless steel produced by gas tungsten arc welding . (GTAW) has beeninvestigated [4] Pulsed current GTAW (PCGTAW), developed in the 1950s, is a variation of constant current gas tungsten arc-welding (CCGTAW) which involves cycling of the welding current from a high level to a low level at a selected regular frequency. The high level of the pulsed current is selected to give adequate penetration and bead contour, while the low level of the background current is set at a level sufficient to maintain a stable arc. This permits arc energy to be used efficiently to fuse a spot of controlled dimensions in a short time. It decreases the wastage of heat through the conduction into the adjacent parent material [15, 16]. In contrast to CCGTAW, during PCGTA, the heat energy required to melt the base material is supplied only during peak current pulses (for brief intervals of time). It allows the heat to dissipate into the base material leading to a narrower heat affected zone (HAZ). The PCGTAW has many specific advantages compared to CCGTAW, such as enhanced arc stability, increased weld depth to width ratio, refined grain size, reduced porosity, low distortion, reduction in the HAZ and better control of heat input. In general, the PCGTAW process is suitable for joining thin and medium thickness materials, e.g. stainless steel sheets, and for applications where metallurgical control of the weld metal is critical [17]. PCGTAW of super alloys is scanty in the reported literatures, but some researchers have evaluated the effect of pulsed current parameters on corrosion and metallurgical properties of super-duplex stainless steel welds [15]. In addition, PCGTAW of Ti–6Al–4V titanium alloy, AA 6061 aluminum alloy and 304L austenitic stainless steel have been also reported in the previous papers [18-20]. However, PCGTAW of Inconel 617 has not been reported in the literature. The aim of this study is to investigate the micro structural and mechanical properties of Inconel 617 welds produced by GTAW and PCGTAW using Inconel 617 filler metal. II. EXPERIMENTAL PROCEDURE A. Materials Inconel 617 alloys were cut and machined in the form of 11mm × 110mm × 150mm plates. The solution annealing treatment was performed at 1175ÚC for 1 h and then the samples were cooled in turbulent air. The Inconel welds were 1