WRe/TZM composite material
Tungsten-rhenium (WRe) alloys are alloys composed of tungsten and rhenium elements. Tungsten has the advantages of high melting point, excellent high-temperature performance, high atomic number, and can excite strong X-ray under high-energy electron beam bombardment. However, as a target, pure tungsten has the following disadvantages: there is a notch sensitive effect, the crack is easy to further expand and deepen, and then cause the target failure. The recrystallization temperature of rhenium is higher than that of tungsten. Therefore, rhenium in Tungsten-rhenium alloy can significantly reduce the plastic-brittle transition temperature of tungsten, improve the mechanical properties of tungsten at high temperature, and inhibit crack propagation. Therefore, tungsten-rhenium alloy is a common target surface material for rotating anode target of CT machine.
TZM(titanium zirconium molybdenum) alloy has high melting point, high strength, high elastic modulus, small linear expansion coefficient, low vapor pressure, good electrical and thermal conductivity, excellent corrosion resistance and good high temperature mechanical properties, so it is widely used in many fields. Such as rocket nozzle, nozzle throat lining, torpedo engine valve body, gas pipeline, CT machine X-ray tube anode target matrix. Because Tungsten and Molybdenum can form W/Mo solid solution, the joint performance of WRe/TZM composite is good, so the advantages of WRe alloy and TZM(titanium zirconium molybdenum) alloy are integrated.
The scanning part of CT equipment mainly includes X-ray tube, detector and scanning frame. X-ray tube is one of the core components of CT machine, and the rotating anode target in X-ray tube produces X-ray when subjected to high-energy electron beam bombardment, which is a wearing part and needs to be replaced regularly. According to statistics, more than 50% of the damage of X-ray tubes is caused by the failure of the anode target. This is because during the working process of X-ray tubes, more than 99% of the energy is converted to heat energy, and only 1% of the energy is converted to X-ray. The local temperature of the anode can even reach 2600℃. Therefore, the target surface material of X-ray tube is required not only to have the ability of producing high-quality X-ray, but also to have the characteristics of high temperature resistance, high thermal shock resistance and good heat dissipation performance. Therefore, WRe alloy is usually selected as the target surface material, TZM(titanium zirconium molybdenum) alloy and graphite as the matrix support materials.
The preparation methods of rotating anode target include powder metallurgy, chemical vapor deposition, hot pressing welding, etc. Among them, powder metallurgy is the most convenient, and hot isostatic pressing or hot pressing sintering is used to prepare double-layer WRe/TZM composite materials. However, due to the large difference in melting points between the two, the density is difficult to meet the requirements. At present, most rotary anode targets are prepared by powder prepressing, high-temperature sintering (1800℃ ~ 2200℃), hot forging, annealing and other processes. The process is complicated and the cost is high.
