Rouholah Ashiri, Amir Hosein Asadi, Massoud Goodarzi, Mohammad Saeed Shahriari,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2026)
Abstract
Abstract
In this study, the effect of welding current on the repair welding behavior of the cobalt-based superalloy MAR-M509 was systematically investigated using four cobalt-based filler metals, namely HAYNES-188, HAYNES-25, MAR-M918, and FSX-414, in the Gas Tungsten Arc Welding (GTAW) process. Welding experiments were conducted at five current levels of 50, 60, 70, 80, and 90 A, and the influence of heat input on weld geometry, dilution, microstructural evolution, and hardness distribution was evaluated. Macroscopic observations revealed that insufficient heat input at low current levels resulted in lack of fusion (LOF) defects in some samples, whereas complete penetration was achieved for all filler metals at 80 and 90 A. Dilution generally increased with increasing welding current, indicating a greater contribution of the base metal to the fusion zone under higher heat input conditions. Microstructural investigations showed that increasing the welding current reduced the cooling rate and promoted dendritic growth, leading to increases in dendrite length, primary dendrite arm spacing (PDAS), and secondary dendrite arm spacing (SDAS). In addition, localized liquation phenomena were observed near the fusion boundary under high heat input conditions. Hardness profile analysis demonstrated that the heat-affected zone (HAZ) exhibited the highest sensitivity to thermal variations, and increasing welding current intensified hardness fluctuations due to carbide evolution and localized microstructural heterogeneity. Comparison of the four filler metals indicated that, although the overall trends were similar, the filler metal type significantly influenced dilution behavior, weld geometry, and solidification characteristics. Based on the combined evaluation of penetration, dilution, dendritic growth, and hardness distribution, a welding current of 80 A was identified as the optimum condition, providing the best balance between weld quality and microstructural stability in the repair welding of MAR-M509.
Kh. Ranjbar, A. Firoozi, F. Shahriari Nogoorani, S. F. Ziaee,
Volume 10, Issue 2 (Journal OF Welding Science and Technology 2024)
Abstract
Plain carbon steels are widely utilized in various industrial applications primarily due to their low cost. However, these steels often fall short in terms of mechanical properties and wear resistance. The deposition of hard and wear-resistant coatings on these steels significantly enhances their performance and extends their range of applications. Colomonoy 6, is a nickel-based superalloy, enhance hardness, erosion resistance, wear resistance, and corrosion resistance on the applied surfaces. The study investigated the application of weld overlay using colomonoy 6 on a plain carbon steel, aimed to create a hard and wear-resistant surface. The overlaying processes were performed using plasma transfer arc welding and gas tungsten arc welding under identical conditions. Microstructural characteristics were examined through optical and electron microscopy, and Phase analysis was performed using X-ray diffraction technique. The wear behavior of the weld overlays was evaluated using pin-on-disc wear testing at three different temperatures: 25 °C, 300 °C, and 600 °C, using an alumina pin. The microstructural investigation revealed the formation of dendritic nickel-rich solid solutions and interdendritic carbide and boride phases within the overlays, contributing to improved hardness and wear properties. Results demonstrated that in both overlaying methods, the wear mechanism at room temperature was mild abrasive, whereas at 600 °C, it was plastic deformation, exhibiting a wear track depth of approximately 33-35 μm, and 50-55 μm, respectively. In both overlayed metals, an approximate Vickers hardness number of 600 was measured a 4-fold increase in hardness of substrate. This finding suggests that factors other than hardness, such as microstructural stability and phase distribution at elevated temperatures, play significant roles in wear performance.
A. H. Jafarzadeh, M. S. Shahriari, R. Ashiri,
Volume 11, Issue 2 (Journal OF Welding Science and Technology 2026)
Abstract
Repair welding of nickel-based superalloy Inconel 939, which was under working conditions of 100,000 hours, was performed by gas tungsten arc welding using Inconel 617 filler metal. The main objective of this study is to investigate and analyze the challenges during welding such as irregular distribution of primary MC carbides and crack formation in the heat-affected zone, and also to investigate the effect of post-welding heat treatment cycle on the microstructure and hardness of different weld zones. During welding, a crack of 91 micrometers length was observed in the heat affected zone, which due to the presence of a liquation film and accumulation of carbides around the crack, the crack was categorized as a liquation crack. Then, due to post-welding heat treatment, improvement of microstructural characteristics and hardness of the weld zone, partial melted zone, and heat-affected zone was observed, which resulted in homogenization of the hardness profile of the weld. It was observed that post-welding heat treatment caused the crack formed during welding to grow and spread to reach a length of 386 micrometers, which was classified as a strain-aging crack due to its formation and growth during post-welding heat treatment.
