The chemical environment and mechanical environment of aeroengine and gas turbine turbines are very harsh. The huge stress generated by the rotation speed of 6000~30000 rpm requires the turbine materials to have excellent mechanical properties. In the more than 70 years since the advent of gas turbine engines, advances in material science and the application of cooling measures have made the temperature resistance of high-temperature components of engines significantly improved.
At present, titanium alloys are mostly used for the manufacture of cold-end parts, while the manufacture of hot-end parts uses a large number of nickel-based alloys, adding rare refractory metals such as rhenium and hafnium, which make them have excellent temperature resistance and stiffness strength properties. Advances in material science make it possible for future engines to use light heat-resistant materials, including intermetallic compounds and metal-based composite materials (composites composed of metals or alloys as the matrix and reinforcements such as fibers, whiskers, and particles).
The turbine blades of the large turbofan engine in active use are manufactured by single crystal growth. The single crystal has reliable mechanical properties, excellent fatigue strength and creep resistance (plastic deformation under high temperature and high strain environment). The equiaxed crystal structure has good mechanical properties in all directions; oriented crystal turbine blades have improved mechanical properties in the longitudinal axis direction; single crystal turbine blades have superior mechanical properties in the longitudinal axis direction and improved heat resistance.
The characteristics of ceramic materials are hardness, oxidation resistance and high temperature resistance. In the future, if its impact resistance can achieve technological breakthroughs, it will be very suitable for making high temperature turbine blades.
Turbine blade surface coating technology
In order to improve the high-temperature creep strength and resistance to high-temperature oxidative corrosion required by the blade, one of the methods is to use surface coating technology to provide protection. There are two main types of coatings currently in use: diffusion coatings and cladding coatings. The typical composition of the diffusion coating is protective Al2O3, Cr2O or SiO2 (the numbers are all subscripts). The typical composition of the coating is MCrAlY, which can be prepared by physical vapor deposition or plasma spraying.
According to some data, the oxidation resistance of the vapor-deposited NiCoCrAlY composite coating is 1.5 times that of the single aluminide coating, and the vacuum plasma sprayed NiCoCrAlY+ (Si, Hf) coating is 5 times that of it. Hf and Si can improve the adhesion of alumina and delay the thickening of the scale.
The ceramic thermal barrier coating is used as the thermal insulation layer of the turbine air-cooled cooling blades. For example, the zirconia coating can reduce the surface temperature of the high-temperature alloy by 100~200 degrees Celsius. If it is applied to the third generation single crystal alloy combined with advanced cooling technology, it can The temperature is reduced by 350 degrees Celsius, which is expected to greatly increase the temperature of the engine before the turbine.
The vapor deposited ceramic coating (EB-PVD) produced by electron beam evaporation can provide a columnar ceramic structure. It has an order of magnitude improvement in flaking life compared to plasma sprayed coatings. For example, the PWA142 blade adopts the PWA73 coating of physical vapor deposition method to improve the corrosion resistance and oxidation resistance of the blade, and it will not have a deleterious effect on tensile, long-term creep and high-cycle fatigue performance levels.