At present, Huirui has launched a series of research in the field of single-crystal laser repair. The key process parameters for controlling single crystal or directional crystallization are to control the cooling rate and temperature gradient of the molten pool. The cooling rate determines the shape of the molten pool, and the temperature gradient determines the crystal growth direction when the molten pool solidifies. Both process parameters can be captured and measured in real-time through melt pool monitoring and image processing methods.

As the aviation industry continues to improve its requirements for aero-engine performance and thrust-to-weight ratio, the operating temperature of the hot-end components of aero-engines has further increased, and the performance requirements for alloys have become higher and higher. Nickel-based high-temperature alloys are gradually turning to single crystals with better high-temperature properties. Development, such as Rene N5, CMSX-4, DD432, etc., has now developed to the fifth generation of nickel-based single-crystal superalloys. The operating temperature of each generation of superalloys is approximately 25°C higher than the previous generation. Along with the development of materials come challenges to the manufacturing process. How to use direct metal deposition technology to realize the repair and direct molding of single crystal parts has gradually become a research hotspot. How to ensure the properties of single crystal during the repair and molding process? Avoiding the formation of miscellaneous crystals is the biggest challenge. This requirement can be achieved using laser cladding technology.

Research shows that electron microscopy EBSD scanning of the cross-section of a single-layer clad single-crystal alloy material shows that most of the lower area of the cladding layer can form a directional crystal structure that continues the epitaxial growth of the substrate crystal (the blue area in the figure below, the color represents the crystallization growth direction);
Miscellaneous crystal structures (colored areas) with different directions will be formed on the upper surface of the cladding layer;
From the above observations, it can be concluded that during multi-layer cladding, the cladding layer must have sufficient penetration depth to remelt the miscellaneous crystal area of the next layer to form a continuously growing single crystal or directional crystal structure.

The picture below shows the EBSD scanning picture of the cross-section of a single crystal material with 10 layers of continuous cladding (the color represents the growth direction of the single crystal). The organizational structure formed under three different laser process conditions. Among them, the structure formed under (c) conditions is similar to that of the substrate. A multi-layered single-crystal structure with continuous and consistent crystal directions.

Huirui laser cladding single crystal material technology achievements

At present, Huirui has launched a series of research in the field of single-crystal laser repair. The key process parameters for controlling single crystal or directional crystallization are to control the cooling rate and temperature gradient of the molten pool. The cooling rate determines the shape of the molten pool, and the temperature gradient determines the crystal growth direction when the molten pool solidifies. Both process parameters can be captured and measured in real-time through melt pool monitoring and image processing methods.

Nickel-based powder materials were used to conduct experiments on DD432 and achieved good results, and process development tests were conducted on single crystal blades of DD432. There are certain differences in the thickness of various parts of the single crystal blade tip. The thicker it is, the more difficult it is to perform directional epitaxy. This is mainly because the greater the thickness of a single cladding layer, the stricter the process requirements, and the smaller the process window. After process optimization research, the following laser cladding single crystal material results have been achieved:

1. The maximum single-pass cladding width is 1.8mm, and the continuous stacking can reach a height of 10mm;
2. The single-layer thickness can be adjusted within the range of 0.15~0.5mm;
3. The amount of miscellaneous crystals on both sides is less than 10%;
4. The high-temperature tensile performance of the bonding interface at 800°C reaches 91% of that of the base material, and the strength of the cladding layer is not less than 91% of that of the base material.

Single crystal blade cladding case

The appearance of the cladding layer is smooth and dense, with no defects such as cracks and holes visible to the naked eye. Since two different processes are used in the cladding process, a relatively obvious junction area is formed at the junction of the cladding processes.