Industry

Laser cladding is a new type of local surface treatment method and one of the surface modification technologies with the greatest potential for future industrial applications. It has significant technical and economic benefits. In the aviation maintenance industry, its application is roughly reflected in the following aspects:

Laser fusion forming is used for part repair

Laser cladding technology has had a direct impact on the repair of aircraft, with advantages including automated repair processes, low thermal stress and thermal deformation, etc. As people expect the lifespan of aircraft to be continuously extended, more complex repair and maintenance processes are needed. Components such as turbine engine blades, impellers and rotating air sealing gaskets can be repaired through surface laser cladding strengthening. For instance, when laser cladding technology is used to repair cracks in aircraft components, some non-penetrating cracks usually occur in thick-walled parts, and the crack depth cannot be directly measured, making other repair techniques ineffective. Laser cladding technology can be adopted. According to the crack conditions, multiple grinding and flaw detection are carried out to gradually remove the cracks. The grooves after grinding are filled with a multi-layer cladding process of laser cladding and powder addition, and the damaged structure can be reconstructed and its service performance restored.

The working conditions of turbine blades in aero engines are extremely harsh. Therefore, nickel-based and cobalt-based superalloy materials with excellent performance but very high prices and complex manufacturing processes are adopted, resulting in high costs. For instance, the average price of a single domestic ordinary blade can reach over 10,000 yuan, and some blades of imported models can even cost tens of thousands of US dollars. However, due to the effects of wear, impact, high-temperature gas and thermal fatigue, turbine blades are prone to various crack defects. Because of the particularity of blade materials and manufacturing processes, crack repair is extremely difficult. As a result, a large number of blades are scrapped because they cannot be repaired, causing huge positive losses. Laser cladding technology can be well applied to the surface repair of turbine blades.

The following picture shows the application of laser cladding to a damaged turbine blade, repairing the blade tip to its original height. During the cladding process, the laser beam forms a very shallow molten pool at the top of the blade, while metal powder deposits at the top of the blade to form weld beads. Under the numerical control of the computer, the solder beads are stacked layer by layer, causing the cladding layer to grow. The picture shows the appearance of the blade to be ground. For comparison, the right picture shows the blade welded by hand, which must undergo additional post-processing. The top of the blade needs to undergo electrical discharge machining to expose the voids formed during the cooling process, but laser cladding eliminates these repair works, thereby significantly reducing time and cost.

2. Laser cladding technology is used for surface modification of aviation materials

Many important surface properties such as hardness, wear resistance, corrosion resistance, impact resistance, oxidation resistance, and heat resistance all depend on the physical and chemical properties of the metal material's surface. The main causes of aircraft structural failure, such as corrosion, wear and fatigue damage, almost always start from the surface of the parts and gradually lead to damage and destruction. Titanium alloys and aluminum alloys are widely used in modern aircraft manufacturing. Titanium and titanium alloys have high specific strength, excellent corrosion resistance, and good high-temperature resistance, which can reduce the weight of the aircraft body and increase the thrust-to-weight ratio. The disadvantages of titanium alloys are their low hardness and poor wear resistance. The hardness of pure titanium is 150 to 200HV, while that of titanium alloys usually does not exceed 350HV. In many cases, a dense oxide film forms on the surface of titanium and titanium alloys, which serves to prevent corrosion. However, when the oxide film breaks, the environment is harsh, or crevice corrosion occurs, the corrosion resistance of titanium alloys will be greatly reduced.

To prevent parts working in high-speed, high-temperature, high-pressure, heavy-load, corrosive medium and other environments from being scrapped due to local surface damage, improve the reliability of parts and extend their service life, countries around the world are researching and applying various surface engineering technologies to enhance the surface performance of parts. Traditional surface modification techniques, such as various spray coatings. Due to the poor interlayer adhesion and the limitations of low equilibrium solubility and poor solid-state diffusibility, the application effect of coatings and the like is not ideal. The emergence of high-power lasers and broadband scanning devices has provided a new and effective means for surface modification of materials. Among various laser beam treatments, laser cladding is a new coating surface modification technology with relatively high economic benefits. It can prepare high-performance and valuable cladding layer surfaces on low-cost substrates, thereby reducing material costs, saving precious and rare metal materials, lowering energy consumption, and extending the service life of metal parts. The laser cladding device is shown in the figure. The one in the upper picture is the synchronous powder feeding method, and the one in the lower picture is the preset coating method.

The microhardness of the titanium alloy surface after laser cladding is 800-3000HV. Surface strengthening of aluminum alloys by laser cladding technology is an effective method to solve problems such as poor wear resistance and easy plastic deformation of aluminum alloy surfaces. Compared with other surface strengthening methods, this method features metallurgical bonding between the strengthened layer and the aluminum substrate, with high bonding strength. The thickness of the cladding layer reaches 1 to 3mm, with a very fine structure. The cladding layer has high hardness, good wear resistance, and strong load-bearing capacity, thus avoiding cracks caused by strain imbalance between the soft substrate and the reinforcing layer. In addition, by cladding high-performance ceramic coatings on the surfaces of titanium alloys and aluminum alloys, the wear resistance and high-temperature resistance of the materials can be significantly enhanced.