Phase transformation analysis at high temperature of permendur alloys by using neutron diffraction

Time-of-flight (TOF) neutron diffraction measurements were performed to analyze the phase transformation temperatures and phase fractions in the intercritical region of a permendur alloy with a Co composition reduced to about 25%, and with solute Mn and C. By comparing neutron diffraction patterns during heating and cooling, it was confirmed that the phase transformation temperature during cooling shifted to lower temperature. When observing phase transformation at high temperatures by neutron diffraction measurements, it is necessary to consider the change in diffraction intensity due to the Debye-Waller factor with temperature change. In this study, the influence of the Debye-Waller factor was experimentally defined, and the phase fraction in the intercritical region was analyzed using the intensities of strongest reflection corrected with the influence of the Debye-Waller factor. As a result, the change in phase fraction was successfully analyzed with a time resolution of 10 seconds during heating. Moreover, the theoretical phase transformation temperatures of the equilibrium state were compared with those of the non-equilibrium state, and the differences between the two were verified. The theoretical phase transformation temperatures in equilibrium state were found to deviate significantly from the non-equilibrium phase transformation temperatures observed in the neutron diffraction measurements. (author)