Selection method of mechanical testing equipment for ultra-high temperature structural ceramics

2017-06-01

With the rapid development of my country's aviation and aerospace technology, engine and turbine blade materials are developing in the direction of being more resistant to high temperatures, lighter and stronger. Among them, C-SiC composite structural materials have become one of the many domestic materials due to their excellent performance. It is the research object of universities and scientific research institutes, and high-temperature mechanical testing equipment is one of the indispensable technical conditions in the scientific research process.

When selecting test equipment, the following influencing factors should be comprehensively analyzed in order to make a more reasonable and complete design plan, thereby reducing manufacturing costs.

【Refer to 2700℃ high temperature vacuum mechanical test system】

1. Temperature range:

When selecting equipment, you should first clarify the actual operating temperature. Its working temperature is mostly 600 to 2000°C. Its limit temperature can be designed according to 2200°C. If you choose according to the limit temperature of 2500°C, you need to increase the size of the furnace cavity and change the temperature. Partial structure, replacement of components that can withstand higher temperatures, and the space of the testing machine must also be increased accordingly, thus increasing the procurement cost.

2. Equipment functions

Tensile, compression, bending, and shear tests in high-temperature environments can all be completed on this set of equipment. Since there are no national standards for such tests to follow, the sample specifications should be as small as possible in physical size while meeting the requirements, so as to facilitate Reduce manufacturing costs.

3. Heating method

For high-temperature vacuum systems in this temperature range, there are two types of heating elements to choose from: 1) graphite 2) W alloy. When the test object is C-based composite material or C-SiC composite material, there are free ions in the high-temperature cavity. C can chemically react with W alloy to form tungsten carbide, which causes cracks in the heating element. The cracks extend to the depth of the heating element and cause brittle fracture. Therefore, high-strength graphite can only be selected as the heating element.

4. Vacuum unit

Vacuum unit options include molecular pumps, diffusion pumps, and mechanical pumps. Because the heating element in the furnace cavity is graphite and the insulation material is carbon felt, both are highly volatile materials. However, the molecular pump has poor anti-pollution ability, so it can only choose the combination of diffusion pump + mechanical pump. It can also be equipped with a Roots pump to increase the pumping speed and speed up the work rhythm.

5. Environmental vacuum degree

Because the highly volatile materials in the furnace cavity are large in volume and continue to evaporate during the test, the working vacuum is on the order of 10-2Pa.

6. Temperature measurement method

The theoretical measurement range of the tungsten-rhenium thermocouple can reach 2300°C. In actual application, the discrete type becomes larger after exceeding 1830°C, and the high-temperature brittleness of the tungsten-rhenium thermocouple causes large losses. Therefore, a two-color colorimeter + thermocouple combination is selected. Method of measuring temperature.

7. High temperature fixture

The clamp material can be made of C-C composite material and W alloy material. C-C composite materials are easy to obtain, have good processing properties, and have high high-temperature strength. They are particularly suitable for manufacturing compression and bending fixtures. W alloy clamps have the advantage of high temperature and high strength, but are difficult to process accurately and suffer from chemical reactions between high temperature and free C. However, they can still be used as clamp materials for long periods of time.

8. Deformation measurement

When conducting mechanical property tests in high-temperature environments, the deformation measurement is much more complicated than in room temperature environments: the test process cannot be directly observed with the naked eye.