Deformation-induced phase development in a cobalt-based superalloy during monotonic and cyclic deformation

ULTIMET ® alloy is a metastable face-centered-cubic (FCC) material that undergoes a deformation-induced phase transformation to a hexagonal-close-packed (HCP) phase. In-situ neutron-diffraction measurements were made at room temperature to study the phase transformation during monotonic tensile deformation to a total strain of 16% (890 MPa) and also during strain-controlled cyclic deformation with a total strain range of Δ ε=2.5% up to 500 fatigue cycles. The HCP phase developed with increasing strain during the monotonic-loading experiment, while, during the fatigue deformation, the HCP phase continuously developed with each loading cycle. Transmission electron microscopy was also performed on monotonically loaded specimens in order to complement the neutron-diffraction results.