Optimization of Molybdenum Brittleness through Rhenium Alloying

Molybdenum (Mo) and Rhenium (Re) each possess unique chemical and physical properties that make them ideal as alloys to increase strength, hardness, electrical conductivity, and resistance to corrosion and wear. When these two metals are combined with each other to Molybdenum Rhenium their individual attributes are significantly enhanced.

Rhenium augments the comprehensive properties of molybdenum at both high and room temperatures, increasing its recrystallization temperature, weldability, and radiation resistance, and thus expanding the alloy’s functionality and value in the aerospace, heating equipment, electronic technology, and nuclear reactor industries, among others.


Molybdenum Rhenium Role in Ductile-Brittle Transition

Rhenium is renowned for its ability to decrease the ductile-to-brittle transition temperature of molybdenum. When the fraction of rhenium in MoRe alloys reaches 51%, their transition temperature can drop to -2540°C, making Re the most effective alloying element for optimizing the ductile-brittle characteristics of Mo.

Rhenium’s hexagonal, close-packed (hcp) structure and high melting point make it readily soluble with molybdenum and doesn’t occur the ductile-brittle transition at room temperatures. Sintered Mo25Re and Mo50Re alloys show no significant cracks, even after 25% deformation at high temperatures. Even more impressive, when the content of rhenium increases to 35%, the MoRe alloy resists cracking even at room temperature and after deformation of greater than 90%.


Molybdenum Rhenium’s Distinct Impurity Behavior and Electron Distribution

While common impurities (MoO2, MoReO4) occur in the MoRe alloy, they are less likely to precipitate or disperse to the grain boundaries. In addition, two other major impurities C (carbon) and O (oxygen), are far more soluble with the MoRe alloy than with pure molybdenum, resulting in lower amounts of molybdenum carbides and oxides segregating to the grain boundaries. Also, the pattern of electron distribution in the MoRe alloy is different from that of pure molybdenum. The addition of rhenium makes the atomic bonds in the alloy’s electron distribution less directional, inhibiting the shift from metallic bonds to covalent bonds, reducing low-temperature brittleness.