Hot end component repair Process is a very complex technology, which is generally present in aero-engines. The basic repair process of the damaged hot-end components in aero-engines includes pre-repair inspection and analysis, differentiation, finishing, damage recognition, recovery heat treatment, treatment of damaged parts, welding, post-weld profile size restoration, post-weld quality Inspection, coating from scratch, etc. The following will introduce several possible cases of damage to the hot end components in aero-engines and the methods of repair.

1. Crack

Crack is one of the main damage forms of engine hot end components failure after long-term operation, and its correction methods mainly include two categories: fusion welding correction and brazing correction. The fusion welding process is flexible, but the fusion welding correction can easily lead to new cracks in the weld seam and heat-affected zone of the hot-end components, and the deformation is large. The whole brazing correction is heated, and the deformation of the parts is small. However, if the brazing method is used to correct the crack of the hot end part, the problem of crack preparation must be solved first, because there is an oxide film in the crack, and the liquid solder cannot be wet and spread. Crack finishing now mainly uses fluorocarbon finishing and mechanical grinding. According to different crack finishing methods and structural characteristics, corresponding correction techniques have been developed abroad and applied in engineering.

2. Wear

Wear is mainly caused by contact surface conflict, vibration or long-term operation, including blade tip wear and blade crown wear. The wear of the blade tip causes the gap between the working blade and the sealing ring to be too large, and the thrust of the engine decreases. New corrosion-resistant metal must be re-surfacing at the blade tip. It is difficult to meet the application requirements of the blade by using the general fusion welding method. This is because the working blades are generally made of high-quality high-temperature alloys and have a complex profile. When the fusion welding method is used, the weld or heat-affected zone is always accompanied by the occurrence of hot cracks. Therefore, the welding heat input must be strictly controlled and the appropriate filler metal selected. The Canadian company Liburdi has developed an automatic precision welding system that can realize the complete integration of the entire process, including fixtures, robot systems, visual measurement systems, filling materials, and control of welding parameters. Through reasonable heat management and process control to reduce heat input, the occurrence of welding emblem cracks is reduced.

The presence of oxygen and sulfur in the gas leads to thermal corrosion and other damage on the surface of the hot-end components operating at high temperatures, which seriously affects the normal operation of the components. For this kind of surface, large-scale damage can be corrected by brazing or laser surface overlay.

Brazing is a cost-effective process for correcting large areas of surface damage on components. The main principle is to combine large-void brazing with diffusion treatment, and through the use of appropriate filler metal and the combination of diffusion process, the modification part arrangement, function and size can meet the requirements of engine application.

For the blade, because the large-scale damage on the blade is mostly on the upper part of the blade body, rather than at the blade root part where the strength is required to reach 100% of the base material, the application of the brazing method is wider. The laser surface surfacing method corrects large-scale damage caused by corrosion. Its principle is similar to the brazing method, that is, the laser is used as the heat source, supplemented by corrosion-resistant filler metal, and the surface of the component is surfacing, and the weld bead is stacked. After defending, machining is carried out to restore the size of the profile.

3. Creep shrinkage

The microstructure of the hot-end components that have been operated for a long time at high temperature changes, such as Y' phase coarsening, grain boundary changes, grain boundary carbide structure changes, and precipitation brittleness remain stable, resulting in a decrease in the creep strength of the hot-end components and the structure showing creep. It becomes microporous, which eventually leads to the formation of internal cracks and failure. When the part is not damaged by the second stage creep in high temperature operation, but only precipitates carbides or carbides along the grain boundary. At the same time, its creep function can be recovered only by normal solution treatment. However, when the load-bearing parts (such as rotor blades) have been in operation for a long time, the alloy has been in the second stage of creep, and the Y' phase has grown together in the structure, and creep shrinkage or micro-cracks have occurred to varying degrees. , it is necessary to use hot isostatic pressing (HIP) to restore its creep performance. HIP can make internal defects (casting pores, creep cracks, cavities, etc.) more merged and restore the original high temperature durability and fatigue characteristics of raw materials. Because its temperature is higher than that of general solution treatment, it can also further homogenize the arrangement elements and avoid the occurrence of harmful phases. If HIP is combined with welding correction, the matrix and weld will be arranged more finely, and the correction effect will be better.