Multipass cold rolling and resultant mechanical properties of a Cr-containing nickel aluminide

Abstract

The difficulties encountered in fabricating Ni3Al-based intermetallic alloys into final structural components, due to their limited workability as a result of their inherent high yield strength and low ductility at elevated temperatures, are an important issue that have restricted the commercial applications of these materials. The Osprey spray deposition process is capable of delivering near-net-shape preforms, thereby avoiding the technical problems related to the hot working of these materials, e.g. hot rolling of slabs. The present work concerns an investigation of the cold rollability of a chromium-containing Ni3Al intermetallic alloy produced with the Osprey process. The sliced preform with a thickness of 7 mm was successfully cold rolled through multipasses into sheets with a thickness of 0.7 mm and a good surface finish. The material has been found to have a high working hardening rate at room temperature. The maximum total reduction permissible without resulting in rolling defects is 30%. Thus, for larger reductions, intermediate annealing between rolling passes is necessary and it has been optimized to be at 1100°C for one hour. The repeated cold rolling and the recrystallization occurring during intermediate annealing change the initial microstructural features and grain size of the Osprey-spray-deposited material. The cold-worked and annealed intermetallic sheets with a thickness of 0.7 mm have a yield strength of 570 and 730 MPa and a elongation value of 33 and 7%, at room temperature and at 700°C, respectively. Fractography shows a transition from the transgranular fracture mode at low temperatures to the intergranular fracture mode at temperatures above 650°C.