Mechanical Properties of Incoloy 908 — An Update

Abstract

Incoloy 908 is a nickel-iron base superalloy with its coefficient of thermal expansion and mechanical properties optimized for use in Nb₃Sn superconducting magnets. Thermoelastic, tensile, fatigue crack growth, fracture toughness,and Charpy impact properties, and the results of conduit pressurization tests are summarized for base and weld metal.A limited number of stress rupture tests were also performed in air. The average yield strength (0.2% offset) for the solution annealed and aged base metal is 1200 MPa at 4.2 K. The fracture toughness,K_IC, is greater than 230 MPa√m at 4.2 K. The fatigue behavior at 4.2K is comparable to austenitic stainless steels. Fatigue crack growth rates are a factor of three lower at 4.2 K than 298 K and are independent of heat treatment. At 4.2 K, the 20% cold-work-then-aged material has a 20% higher yield strength and a 10% higher ultimate tensile strength. Gas tungsten arc weld (GTAW) metal with or without Incoloy 908 filler metal exhibited comparable yield and about 10% lower tensile strength when compared with that of the base metal after a 200 hour age at 650^°C. Fracture toughness, tensile elongation and Charpy absorbed energy were about 40% of those of the base metal. Leak-before-break behavior was observed in an internal pressurization test at room temperature for a geometry identical to that of the US-Demonstration Poloidal Coil conduit. The stress rupture performance is better than other low COE alloys of a similar type to that of Incoloy 908.

Supported by the U.S.-DOE Grant DE-FG02-91ER-54110.