Study on improving properties of molybdenum and molybdenum alloy
Improving the properties of molybdenum and molybdenum alloy is an inevitable way to expand the application field and meet the increasing performance requirements. A series of researches on high performance molybdenum and molybdenum alloys have been carried out at home and abroad.
1. Molybdenum single crystal
In order to improve the low temperature plasticity of molybdenum and eliminate the grain boundary, single crystal was prepared. High purity single crystal with oxygen content of 1ppm was prepared by zone melting method by electron bombardment and electron beam heating. The uniform elongation was 5% at 4.2K. Molybdenum single crystal bars and tubes with a diameter of 10 ~ 30 × 200 ~ 300 mm have been produced as materials for atomic power generation.
2. Harmful elements control
The low temperature plasticity of molybdenum is due to the segregation of harmful gases at grain boundaries. The results show that oxygen is the most harmful element to increase the transition temperature from brittleness to plasticity for molybdenum. If the oxygen content of sintered molybdenum is more than 30ppm, it is not malleable. By adding A1 and B as deoxidizers, the oxygen content of molybdenum is reduced and the plasticity is improved.
3. Doped molybdenum
After deep processing and recrystallization annealing at high temperature, the creep resistance and sag resistance of the wires are excellent. In recent years, this technology has been applied to the forming of molybdenum sheet. The second phase of dispersion strengthening is La2O3 and other fine rare earth oxide particles. The optimum content of La2O3 is 1%. The recrystallization temperature of the alloy with this content is higher than that of TZM alloy, showing excellent heat resistance. At room temperature, it shows excellent impact resistance compared with pure molybdenum plate.
4. Strengthening and toughening of carbide dispersed particles
The equiaxed recrystallization catalysis of molybdenum is inevitable, but the recrystallization temperature of molybdenum alloy dispersed by tungsten carbide can be increased, which makes it difficult to recrystallize. The typical dispersion strengthening particles are tic, ZrC and HFC. The recrystallization temperature of mo-0.5tic can reach 2170k, which is obviously higher than that of other alloys. The impact test shows that the brittle plastic transition temperature of Mo tic alloy as rolled is 200 ~ 220K lower than that of TZM alloy, and has excellent low temperature plasticity and stability of microstructure at high temperature. The high temperature stress deformation curve shows that the high temperature strength of Mo HFC is twice that of TZM at 1873K and quadruple at 2013k.
5. Internal nitriding treatment
Internal nitriding means that the nitrogen atoms diffused from molybdenum nitrides preferentially combine with titanium or wrong atoms to form nitrides by utilizing the difference of formation energy between molybdenum nitrides and titanium or wrong nitrides. The ultra-fine second phase dispersion particles of internal nitriding are used to improve the recrystallization temperature, low-temperature plasticity and high-temperature strength. After nitriding, the brittle plastic transition temperature is similar to that of rolling state, but obviously lower than that of recrystallization state, which is due to the formation of fine microstructure after nitriding treatment.
