Enhancing strength-ductility in fine-grain Mo[sbnd]re alloy fibers

Super-high strength (∼ 2.4 GPa) is obtained in fine-grain Mo[sbnd]Re alloy with ignorable ductility at room temperature, which is attributed to fine grain size and high stress concentration induced by thermal-mechanical processing. The processing-induced stress could not fully release at 800 °C annealing for 1 h. The second σ phases precipitating at 1100 °C annealing without obvious spheroidization in columnar grains, providing a comprehensive match between strength (1.25 GPa) and ductility (20 %) at room temperature. Strength remarkably drops after annealing at 1400 °C and 1500 °C with ductility nearly unchanged. Both strength and ductility decrease obviously after annealing at 1600 °C and 1800 °C. The average grain size in 1800 °C annealed sample is nearly twice as in 1600 °C annealed one. Enhanced strength in as-deformed fibers is dominated by fine grain-strengthening, although a large amount of soft [110] texture occurs. Excellent match between strength and ductility may be attributed to the recovery and [112] texture that happens in 1100 °C annealed fiber. What is more, nano-meters σ particles are detected along grain boundaries in 1100 °C annealed fiber, providing an extra strengthening route. In other annealed fibers, the growth of grain size leads to the decrease in strength.