Effect of Pre-Post TIG Welding Heat Treatment on Cast NI Superalloy (original) (raw)
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Metals
Heat-affected zones (HAZs) of Inconel 939 (IN-939) superalloy are susceptible to cracking during welding process. Preventing cracking during the repair welding of turbine components is important. In this study, the effects of heat input and pre-welding heat treatment on the microstructure, mechanical properties and crack formation in tungsten inert gas welding of IN-939 were investigated. The whole specimens were welded using Inconel 625 filler in an Ar atmosphere and characterised by metallographic examinations and hardness measurements. Results showed that the microstructures of IN-939 HAZs were highly susceptible to cracking during welding due to increasing of γ′ volume fraction. All of these cracks appeared in the HAZs and grew perpendicular to the melting zone along the grain boundaries. In this survey, the pre-welding heat treatment and heat input strongly affected the HAZ microstructure and hardness. However, the pre-welding heat treatment with 67% impact was more effective t...
Experiment involves study of change in mechanical properties as a result of post weld heat treatment of shaft & wheel assembly: a component of turbo charger. Processes involved are friction welding to assemble shaft & wheel, stress relief by heating and then induction hardening. During friction welding because of rapid friction, squeezing & solidification of weld joint under high mechanical force, stress introduced in shaft & wheel assembly which in turn reduces service life of component. To minimize the effect of this internal stress and to enhance strength, hence service life of component, it is heat treated. Later component is induction hardened to obtain desired hardness. All the parameters such as heating temperature, Maximum strength & Hardness required after heat treatment were all set taking into account service conditions of shaft & wheel assembly during working of turbocharger in an automobile engine. Strength testing using UTM, Hardness test using Rockwell scale, hardening depth using Nital Test was performed & results analyzed to confirm desired changes in mechanical properties.
Journal of Materials Engineering and Performance, 2022
This study aimed to investigate the effects of tungsten inert gas (TIG) repair welding on microstructure, mechanical properties, and corrosion resistance of Inconel 939. After welding with Inconel 625 filler under argon atmosphere, the microstructure, hardness, tensile strength, and corrosion resistance of the specimens were analyzed. The results showed that the hardness value and corrosion resistance decreased in the heataffected zone and particularly in the fusion zone. These changes were attributed to a decrease in the amount of cÕ phase in the fusion zone, the generation of liquation cracking, and the accumulation of dislocations. Also, the cyclic hot corrosion tests were conducted on the specimens prepared from the base metal and the weldment in a synthetic molten salt environment for 30 h at 900 °C, which corresponds to the operating temperature. The results showed that although the weldment remained unchanged by the end of the test, in contrast, the base metal began to change after initial cycles, and a brittle oxide layer formed on the surface. Finally, the results of hot tensile tests performed at 900 °C showed that TIG welding has limited effects on yield strength and elongation. Welding reduced the yield strength and elongation as much as 4 and 47%, respectively, of those of the BM.
MATEC Web of Conferences
This research work focuses on the mechanical behaviour comparative assessment in conjunction with microstructural evolution characterization of Waspaloy® and Inconel® 718, following TIG and EB welding. Both of the forth-mentioned alloys are precipitation strengthened Ni-based superalloys, widely used in chemical, petrochemical and aerospace industries. More specifically, Waspaloy® is strengthened by the precipitation of the ordered fcc gamma prime intermetallic phase, γ΄ - Ni3(Al,Ti), while Inconel® 718 is mainly hardened by the ordered bct gamma double prime phase, γ΄΄ - Ni3Nb, in addition to γ΄. After both welding processes, samples of the above superalloys were subjected to appropriate post-weld heat treatment, according to SAE Aerospace Material Specifications. The mechanical response of the tested specimens is assessed via uniaxial tensile tests, combined with fractography. Furthermore, the microstructural characterization of TIG and EB welds is conducted by Scanning Electron M...
Materials Science and Technology, 2013
Microstructural, mechanical and weldability aspects in the similar and dissimilar welds of alloy 718 and alloy 500 nickel based superalloys have been investigated. Alloy 500 weld metal showed high tendency of titanium to the segregation. Coalescence of the microvoids led to propagation of hot solidification microfissures. The alloy 718 weld metal displayed the formation of Nb rich low melting eutectic type morphologies, which can reduce the weldability. The microstructure of dissimilar weld metal with dilution of 65 wt-% displayed semideveloped dendritic boundaries. The less segregation and decrease in the low melting eutectics caused less susceptibility of dissimilar weld to solidification cracking. The segregation elimination phenomenon has occurred in the heat affected zone of alloy 500. In the partially melted zone, remelted and resolidified regions have been observed. These locations provided sites for nucleation of liquation cracks. For the alloy 718 heat affected zone, dissolution of c0-Ni 3 Nb needle-like precipitations has taken place. It was the chief reason for sharp decline of the microhardness. The heat affected zone of alloy 500 revealed intense liquation cracking, in which the crack is initiated at the partially melted zone. The hot liquation cracking in the heat affected zone of Alloy 718 was observed as a result of c0-Ni 3 Nb dissolution.
Advances in Mechanical Engineering, 2015
This work describes a post-weld heat treatment for a precipitation-hardened nickel alloy. Inconel X-750 is a nickel-based superalloy for gas tungsten arc welding processes. The materials were heat-treated in two steps: solution and aging. The post-weld heat treatment variables examined in this study included post-weld heat treatment temperatures of 705°C, 775°C, and 845°C and post-weld heat treatment time of 2-24 h in 2-h increments. The resulting materials were examined using the full factorial design of experiments to determine the resulting material hardness and observed with optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy in the fusion zone and heat-affected zone. The results show that a longer post-weld heat treatment time corresponds to larger g 0 precipitates and a smaller amount of Cr 23 C 6 at the grain boundaries, which can decrease the overall hardness. The post-weld heat treatment analysis indicates that an increase in the amount of g 0 results in better mechanical properties for particles with octagonal shapes and a small size. A factorial analysis, which was conducted on the relationship between the post-weld heat treatment temperature and time to the hardness of the fusion zone, had a 95% confidence level.
Cracking susceptibility after post-weld heat treatment in Haynes 282 nickel based superalloy
Acta Metallurgica Sinica (English Letters), 2013
This paper presents a study of the standard post-weld heat treatment (PWHT) behaviour of autogenous laser welded γ' age-hardenable precipitation strengthened nickel based superalloy Haynes 282 (HY 282). The study involves a careful and detailed microstructural characterisation as well as an analysis of the weld cracking susceptibility during welding and Gleeble thermo-mechanical physical simulation. Various factors that could influence post-weld cracking in superalloys weld were experimentally examined. Our microstructural examination of the as-solution heat treated (SHTed) material and the thermo-mechanically refined grain material shows that intergranular heat affected zone (HAZ) cracking is observable in only the as-welded SHTed material. There was no indication of post-weld heat treatment cracking in all welded materials. Our conclusion, in this study, is that the chemistry of superalloy HY 282 which aids the preclusion/ formation of deleterious solidification microconstituents during welding as well as its relatively slow aging kinetics enhances its resistance to PWHT cracking.
Microstructural Analysis of Linear Friction-Welded 718 Plus Superalloy
JOM, 2014
superalloy was examined after linear friction welding (LFW) and after standard postweld heat treatment (PWHT). The liquid phase reaction of secondphase precipitates, which are known to constitutionally liquate during conventional fusion welding, was observed in the thermomechanically affected zone (TMAZ) of the welded material. These phases included MC-type carbides, Ti-rich carbonitrides, and d phase precipitates. This observation is contrary to the general assumption that LFW is a completely solid-state joining process. However, unlike conventional fusion welding processes that cause heat-affected zone liquation cracking in 718 Plus and many other superalloys, the LFW process did not cause cracking in 718 Plus superalloy despite the liquation of precipitates. This absence of cracking during joining is attributed to the applied compressive stress during the forging stage of the LFW process. Also, no cracking was observed after PWHT, although PWHT resulted in a microstructure that had a nonhomogeneous distribution of precipitates in the weld and the TMAZ.