Influence of High Current-Density Impulses on the Stress-Strain Response and Microstructural Evolution of the Single Crystal Superalloy CMSX-4

Abstract

Owing to the low formability of single-crystal nickel-based materials, single-crystal components are typically cast. Subsequently, a multi-stage heat treatment is carried out in order to partially compensate the dendrite segregation and to stabilize the precipitated gamma'-phase. Such components possess a high resistance to creep at elevated temperatures. Since it is known that electrical impulses can be used to increase the formability of various materials, the potential of an electrical high current-density impulse treatment was evaluated for forming of the high strength nickel-based superalloy CMSX-4. Heat treated and pre-deformed specimens were loaded in compression and subjected to short pulses with a high-current density of 2.3 kA/mm(2). Depending on the microstructural state, the material demonstrated work hardening or softening as a consequence of the impulse treatment. In addition, experiments were carried out on crept specimens to test whether the current-impulse treatment can be used to reverse creep-related segregation of alloying elements (raft formation). It was possible to observe a change in the concentration of the elements in the gamma/ gamma'-phase transition following the current-impulse treatment. In particular, a local increase in the gamma-forming elements Cr, Co and a decrease in the gamma'-forming elements Ta, Ti was observed after the impulse treatment.