Effect of rhenium on the brittle fracture threshold of molybdenum

Conclusions

• 1. Addition of rhenium in quantities from 0.5 to 36% into molybdenum does not result in monotonic reduction of the metal cold brittleness threshold in its cast condition (T ^u_b ), as this is usually suggested in technical literature [5, 6, 9].

• 2. In introducing rhenium into molybdenum an increase is observed in the temperature range of transition of cast metal from plastic to brittle state. This increases T ^u_b and reduces T ^l_b with the exception of alloys containing 4–6% Re whose T ^u_b corresponds to T ^u_b of pure molybdenum.

• 3. An increase of T ^u_b in adding rhenium to molybdenum is connected with increased values of σ_0·2 in the higher temperature region of the cold brittleness range, while a reduction of T ^l_b is caused by a marked weakening of the temperature sensitivity σ_0·2.

• 4. The retention of plasticity down to lower temperatures with a high rhenium content (36%) is associated with the additional mechanism of strain-twinning. In alloys with a lower rhenium content (0.5–20%) twinning is not observed.

• 5. At all temperatures below T ^u_b the character of fracture of alloys, regardless of their rhenium content, is brittle, transcrystalline and differs little when the test temperature changes from T ^u_b to T ^l_b . An increase in plasticity during transition from T ^l_b to T ^u_b leads to the appearance in the fracture of traces of a preliminary plastic strain with the general brittle nature of fracture retained. At temperatures above T ^u_b the specimens bend with α=120°C without fracture, consequently, the Mo−Re alloys like pure molybdenum develop no tough fracture.