High temperature performance of molybdenum lanthanum and TZM alloys
Refractory molybdenum has excellent high temperature strength, creep resistance and low thermal expansion coefficient, Good thermal conductivity and corrosion resistance, so it is used in the electrical industry, aerospace industry and energy industry. The use of pure molybdenum is generally limited.It is within its recrystallization temperature (about 1000 ℃), because once molybdenum recrystallization occurs, the harmful impurity yuanqin is easy to concentrate on the equiaxed grain boundary, thus making molybdenum not only lose its excellent high temperature performance, but also greatly reduce its normal temperature performance. Since molybdenum was recognized by people, improving its high temperature use range has always been a goal of scientists.Like other metals, alloying can significantly improve its high temperature performance. Solid solution strengthening and second phase strengthening are the two most typical methods. For solid solution strengthening, the experimental results show that under the condition of keep metal deformable, the possibility of molybdenum alloying extremely limited, in addition to tungsten and rhenium, joined the amount of yuan qin is usually not more than 1% (mass fraction), and one of zirconium, titanium and hafnium are the most effective and commonly used to add elements, representatives of this alloy is Mo20.5 Ti alloy, TZM and T7C alloy, after solid solution strengthening to close to the limit, in order to further improve its heat resistance strength, consider a diffuse distribution of second phase, But because of the high melting point of molybdenum and molybdenum determines all the melting point is lower than molybdenum metal compounds and use of molybdenum metal compounds is impossible to improve the high temperature strength, usually choose molybdenum oxide and carbide to strengthen metal, over the past 20 years, selects the dispersion of rare earth oxides to improve its high temperature strength, typical alloy with lanthanum molybdenum and molybdenum alloy.
