Mechanical properties of advanced nickel aluminides

Abstract

The mechanical properties of two nickel aluminide alloys have been studied over a range of temperatures. Testing included tensile, impact, and fracture toughness testing. The wrought alloy was studied in cold-worked and cold-worked plus annealed conditions. The cast alloy was studied in the as-cast condition. At room temperature, the annealed wrought alloy showed good tensile properties and fracture toughness. The cold-worked material had much higher strength, but the fracture toughness was reduced. At 650°C both the cold-worked and the annealed conditions showed reduced toughness. The cast alloy showed acceptable tensile properties and fracture toughness at room temperature, and good tensile properties at 650°C. However, the fracture toughness was reduced at the higher temperature. Impact testing showed relatively little effect of temperature. Interganular fracture for the wrought alloy, and interdendritic fracture for the cast material were found to be responnsible for the low toughness observed at 650°C. The availability of oxygen to the freshly exposed metal at the strained crack tip is believed to cause oxygittlement of the grain boundaries, and thus intergranular fracture for the wrought alloy, and interdendritic failure for the cast material.