Molybdenum alloy single crystal electron beam zone melting experiments as follows:
By electron beam zone melting method of high purity metals, affecting purification factors: raw materials, focusing system parameters, vacuum melting, purification times, purification rate, melting power and process systems. Wherein the degree of vacuum in order to purify, frequency and speed of the main parameters.
(1) Focusing system parameters
Selection can cause narrowing of the molten zone electron beam focusing system parameters are cultivating zone melting crystal prerequisite for melting fine specimens are extremely sensitive to power variations reflect. Zone melting, the use of a narrow molten zone purity of the product obtained by the system using wider than high melting zone. However, due to the concentration of the molten zone exclusion miscellaneous increases rapidly and makes the molten zone is harder exclude impurities, thus requiring a corresponding increase in the speed to make up for a certain lack of purification. Generally, once melted using a large molten zone, repeatedly melting a narrow molten zone.
(2) Smelting and melting power system
According to the literature, the use of electron beam zone melting purification, the sample before the first penetration, often need to go through several purification, electron beam power increase progressively, each successive melt a thin layer of the sample, the purpose is not to destroy the vacuum, after the bombardment of current into the melting zone is more stable.
(3) Purification of the number
According to reports, the electron beam zone melting purification of the product with the number of the specific resistance increases with the increase, resulting hardness decreased significantly, but then stabilized to a certain value, this is because the distribution of impurities in the product tends to limit value , and then continue to increase the number of purification will not have much effect. Experimental results showed that: in the choice of a suitable purification rate under the premise of a single crystal and crystal surface depends largely on the success rate of the first melt. Fine specimen heat melted easy to bend, soften, thereby center offset, not for a second melt.
(4) Purification Vacuum
Purification of the electron beam vacuum degree of purity of the product melt is very significant. Currently more advanced equipment are equipped with ultra-high vacuum systems for the purity of the product to a higher value. Tedmon, Rose and Iawley have that: For preparation of nitrogen, oxygen content of 0.001% or less, that must the vacuum to 1.33 × 10-4Pa, otherwise difficult to achieve the desired effect.
(5) Purification Speed
Purification rate is a key factor affecting the quality of purification, which directly affect the product purity and product distribution of the residual impurities. Calverley, Tedmon Rose and the residual impurities have been tested for the distribution, they found that: When the purified faster, the entire specimen is more evenly distributed impurities; slower when purified, the residual impurity concentration in the test the distribution of the sample is less than the end of the head-end.
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