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Rhenium is known to improve the ductility and toughness of molybdenum at the 42-47 wt % level. Recent work has claimed that recrystallized, dilute Mo-Re alloys, i.e., 11-13 wt % Re, also show improved ductility by comparison with recrystallized unalloyed Mo. This recent work, incorporating data on ductility, as well as data on strength, hardness, modulus and chemical composition, has been critically examined. Based on this re-evaluation, the present authors feel that improved recrystallized properties in Mo-Re alloys, by comparison with unalloyed Mo, have yet to be conclusively demonstrated. Also, the use of room temperature tensile ductility as a guide to comparative ductility and toughness in alloys is convenient but limited. Obviously, strain rate has a major influence on ductility in BCC metals. In order to demonstrate that recrystallized, dilute Mo-Re alloys have superior properties compared to recrystallized unalloyed Mo, the notched and unnotched ductile-to-brittle transition temperature should be determined as a function of strain rate as should fracture toughness parameters. It is most important that such evaluations are carried out on alloys that meet fundamental criteria related to chemical composition. Specifically, the ratios of impurity levels of C to O have to meet established minimum levels since an imbalancemore » of these elements is known to lead to brittle behavior in Mo. Failure to recognize this effect can result in misleading conclusions regarding ductility in Mo alloys.« less |
