Tungsten-rhenium-molybdenum alloy rotating anode targets for X-ray tubes
The X-ray tube is the core of all X-ray instruments. The performance of X-ray instrument depends on the quality of X-ray tube to a large extent. Anode target is a very important part of X-ray tube, it directly affects the X-ray emission intensity and the service life of the tube.
With the development of X-ray detection technology, rotating target X-ray tubes with large thermal capacity and strong X-ray output are widely used in the field of medical diagnosis to withstand continuous load or instantaneous high load input. Modern X-ray tubes with high power output apply a high voltage of up to 200KV to the electrons escaping from the incandescent filament during operation. Under the action of high pressure, the escaped electrons bombard the anode target surface at high speed, causing it to produce strong X-rays. However, only about 1% of the input electrical energy to generate X-rays is converted into X-ray energy, while about 99% of the electrical energy is converted into heat energy on the target, so that the local temperature of the focus orbit is above 2600 ° C, and the temperature of the target is above 1300 ° C. Therefore, the material of the rotating anode target for the X-ray tube, in addition to the special function of generating X-rays, the maximum X-ray emission efficiency and the minimum X-ray loss, is also required to have high temperature strength, can withstand large thermal shock, and good heat dissipation performance. Therefore, the development of rotating targets for X-ray tubes with excellent performance has become a common task of material scientists in various countries.
X-ray tube with rotating anode target surface directly subjected to the bombardment of high-energy electron beam to emit X-rays, the local temperature can be as high as 2600℃. Tungsten has a high melting point, high temperature strength, good heat dissipation performance, high atomic number, and can stimulate strong X-rays under electron beam bombardment, so it is usually used as a target surface material. However, because the X-ray tube is intermittent work, when it is cold and hot, the target surface material is easy to crack, and tungsten has a notch-sensitive effect, which is easy to lead to the expansion and deepening of cracks, stripping from the matrix, and damaging the X-ray tube. Adding a small amount of rhenium and other precious metals in tungsten or other transition elements with high melting point and high plat number to form tungsten alloy as a target surface material has better melting loss resistance than pure tungsten target surface layer, preventing the crack of the target surface, ensuring clear imaging, and improving the service life of the X-ray tube. On the other hand, if pure tungsten is used as a target, the weight of the target increases when the diameter is increased to improve the heat capacity of the target due to the large ratio of tungsten. When rotating at high speed, the starting torque increases, the starting time increases, the excitation coil increases, and the bearing load increases, which is very unfavorable to the work of the X-ray tube. At the same time, due to the notch sensitive effect of tungsten, once the crack occurs, it develops rapidly, causing the overall damage of the target. To this end, it is necessary to use a kind of material that can be bonded with tungsten better into one, and can reduce the weight of the target and increase the heat capacity of the target as the matrix, molybdenum specific gravity is about 1/2 of tungsten, specific heat is more than twice of tungsten, and high temperature strength, can be bonded with tungsten into a solid whole, it is commonly used as the matrix material, the diameter of the same molybdenum base tungsten target than pure tungsten target weight reduction of about 1/2, The same weight molybdenum base tungsten target, the heat capacity increased by more than twice, increasing the output power of the target.
