Microstructure Control and Mechanical Properties of Binary Co–Al Alloys Based on B2 Intermetallic Compound CoAl

Microstructure and mechanical properties are investigated in the binary Co–Al alloys based on B2 intermetallic compound CoAl. The effort is focused on two-phase alloys of the compound with Co primary solid solution in order to impart some ductility to the intrinsically brittle compound. The Co–Al binary phase diagram on the Co-rich side is first examined to confirm the stable phase fields of interest by differential thermal analysis and energy dispersive X-ray spectroscopy. Then the compression tests are carried out on selected two-phase alloys to correlate the 0.2% flow stress as well as compressive ductility with microstructures. Several attempts are also made to refine the microstructure through heat treatments and hot rolling, by which it is found that at least several per cent of compressive plastic strain can be obtained at room temperature in the 72 and 76 at%Co alloys.