Introduction: Understanding Laser Cladding and Crack Formation

Laser cladding, an advanced surface modification technology, has widespread applications in industrial repair and remanufacturing. However, cracks often form in the cladded layer during the actual processing, mainly due to improper process control, significantly affecting the quality and performance of the workpiece. This article discusses the causes of cracks and presents key measures to suppress crack formation in laser cladding.

During the laser cladding process, the workpiece is rapidly heated under the high-energy laser beam, with heating rates reaching 10⁶ to 10⁷ K/s. The surface temperature of the base material can instantly exceed 10⁵ K, and it is then rapidly cooled in the presence of inert gases such as argon. Due to differences in the thermal expansion coefficient, elastic modulus, and other physical properties between the base material and the cladded layer, this sudden temperature change induces significant thermal stress. When the stress exceeds the yield limit of the cladded layer, cracks are formed. Therefore, effectively controlling the thermal behavior and material compatibility during the laser cladding process is critical in preventing crack formation.

How to Systematically Suppress Cracks in Laser Cladding

To systematically reduce cracks in laser cladding, the following three strategies are proposed:

1. 열처리 제어

Heat treatment plays a key role in regulating the stress state in laser cladding. First, preheating the base material to a temperature of 200–400°C significantly reduces the temperature gradient between the base material and the cladded layer, slowing down the cooling rate and thereby decreasing thermal stress concentration. After the laser cladding process, a slow cooling treatment or stress-relief annealing process should be applied to promote the release of stresses within the cladded layer, further preventing crack formation and expansion.

2. 원료 관리

The choice of materials directly impacts the success of the laser cladding process. For the base material, high-quality smelted materials with uniform composition and minimal porosity and inclusions should be selected to ensure a good bond with the cladded layer. For powder materials, alloy powders with good toughness should be chosen, and elements such as B, Si, and C must be carefully controlled. Although B and Si have certain slag-forming abilities, if they are not removed in time, they can form inclusions, which increase crack sensitivity. While C enhances hardness and wear resistance, excessive content can significantly increase brittleness. Additionally, when adding reinforcing phases such as WC or TiN, their proportions should be precisely controlled to prevent stress concentration caused by local enrichment of elements. It is also recommended to pre-treat the powder before laser cladding, such as vacuum-heating at 200°C for 2 hours to remove moisture and volatile substances, which improves the cladding quality.

3. Cladding Process Control

Optimizing the laser cladding process parameters is an effective way to suppress cracks. First, it is essential to control the powder feeding rate and maintain the single-layer cladding thickness in the range of 1.0–1.5 mm to avoid stress concentration caused by uneven layer thickness. Using a line laser spot for laser cladding is recommended to increase the single-pass cladding width and improve heat distribution. Additionally, fine-tuning the laser power, scanning speed, and spot diameter is necessary to ensure that the powder reaches its optimal melting state and results in a uniform and dense cladded layer. Finally, the entire laser cladding process should be conducted in a protective atmosphere to prevent oxidation and contamination, ensuring the quality of the cladded layer.

Conclusion: Enhancing Laser Cladding Success Through Comprehensive Strategies

In summary, by utilizing a combination of heat treatment control, material optimization, and fine-tuning process parameters, the success rate of laser cladding can be significantly improved, and cracks can be effectively suppressed. These strategies will promote the wider application of laser cladding technology in high-precision manufacturing, further enhancing its role in various industrial sectors.