Microstructure and mechanical properties of novel Ni–Cr–Co-based superalloy GTAW joints

Abstract

Recently, a novel Ni–Cr–Co-based superalloy has been developed in China, exhibiting exceptional overall characteristics such as favorable mechanical properties at 800 °C, resistance to corrosion and oxidation, as well as remarkable welding capabilities. In this paper, the welding sample of the novel superalloy was prepared using the gas tungsten arc welding (GTAW) method. The conclusion indicates that the GTAW technique can be utilized to fabricate high-quality weld joints filled with superalloy wire. A segregation phenomenon exists between the core and boundary of the dendrite in the fusion zone. The interface of the joints is effectively fused without any separate area. There is an abundance of co-crystallization occurring between the weld metal and the base metal. Besides, the joint has been tested at room temperature (20 °C) and high temperature (800 °C) for its ultimate tensile strength (UTS). The UTS of the joint is 11780 MPa and 781Mpa at 20 °C and 800 °C, respectively. Moreover, the positions of the fractures in the two cases are different. At 20 °C, the fracture location is in the base metal, while at 800 °C, the fracture location is inside the fusion zone. The SEM analysis of the fracture indicates that at 20 °C, the joint's tensile fracture surface exhibits transparent mixed fracture mode, and there are numerous small dimples; at 800 °C, the dimple on the fracture surface of the joint disappeared, replaced by the feature of smooth fracture along the dendrites.

Keywords

• New cast superalloy
• GTAW
• Microstructures
• Mechanical properties