Mechanical Properties of a Boron Added Superalloy at 4K and Magnetic Effect

Abstract

Magnetic effects on tensile and fracture properties of an aged superalloy containing boron (base composition similar to Incoloy 908) were investigated in liquid helium. Heat treatments at 980 0 C for Ih and at 650 0 C for 200 h were performed in a vacuum furnace at FZK under observation of an in-situ oxygen emf sensor. Tensile and fracture tests were performed at the University of Tokyo with and without an 8 tesla magnetic field generated with a solenoid-type superconducting magnet. Three extensometers were attached concentrically to a round bar specimen to avoid an effect of bending during measurement of Young's modulus and fracture toughness JR' Calibration of these extensometers was carried out under zero and an 8 tesla magnetic field. An effect of the magnetic field on the load cell was observed from Young's modulus of commercially pure Ti measured using these extensometers. Fracture tests were conducted by the novel JEIT fracture test (J evaluation on tensile test) and usual CT test. No magnetic effect on Young's modulus of the superalloy was observed. Magnetic effects on fracture toughness could not discussed by CT tests, tests, owing to early unstable fracture. The results of JEIT tests showed that a magnetic effect on fracture toughness is small if any. Scattering, however, was fairly large and the number of measurement was not enough. Therefore, more detailed future works are needed to confirm a magnetic effect on fracture toughness.