High-speed laser cladding, as an advanced surface engineering technology, offers significant advantages in improving material properties and repairing damaged components. However, due to the complexity of process parameters and changing environmental factors, high-speed laser cladding can encounter various quality issues in practical applications. This article systematically reviews the common issues and causes in high-speed laser cladding, providing insights for process optimization.

1. Coating Bonding and Metallurgical Defects

In high-speed laser cladding, the quality of the bond between the coating and the substrate directly affects the service performance. The following are typical bonding-related defects:

1.1 Peeling

Peeling refers to the detachment of the coating from the substrate surface. The primary cause is that the substrate did not form an effective melt pool, leading to poor metallurgical bonding between the powder and the substrate. In high-speed laser cladding, low power, excessive powder, and high scanning speed can hinder melt pool formation. Additionally, contamination such as oil or electroplated layers on the workpiece surface can also prevent proper bonding.

1.2 Cracks

Cracks are common defects in high-speed laser cladding, often related to thermal stress concentration and material mismatch. Cracks are more likely to occur when the substrate has high hardness (e.g., after quenching or carburizing), fatigue layers, or when the powder has high hardness and large shrinkage rates. Cracking sensitivity is particularly high when using nickel-based powders or in multi-layer laser cladding.

1.3 Porosity

Porosity significantly reduces the coating’s density and corrosion resistance. In high-speed laser cladding, the causes of porosity are diverse, including rust or oil on the substrate, impurities or moisture in the powder, unstable powder flow, excessive powder, insufficient power, or high scanning speed.

2. Coating Surface Quality and Morphological Issues

2.1 Excessive Floating Powder and Lack of Metallic Luster

This issue severely affects the surface quality after high-speed laser cladding. It may result from excessive powder, low power, high scanning speed, high nozzle height, small laser spot size, or contamination of optical lenses, causing incomplete powder melting and poor wetting.

2.2 Pitting After Grinding

Pitting is typically caused by incomplete melting of the powder or insufficient melting. This issue is common in processes with low power, excessive powder, or high scanning speed, which are typical manifestations of poor powder-energy matching in high-speed laser cladding.

2.3 Diagonal Wrinkles on the Coating

These morphological defects are usually related to an overheated melt pool and are more likely to occur when the power is too high, the melt pool temperature is too high, or the powder is excessively liquefied. This can affect the appearance and dimensional accuracy of the high-speed laser cladding part.

3. Powder Feeding and Process Stability Issues

3.1 Powder Adhesion to the Nozzle

Powder adhesion to the nozzle can disrupt the powder flow, affecting the stability of high-speed laser cladding. The causes include excessive powder ejection, increased nozzle temperature, low nozzle working distance, or rough or contaminated nozzle surfaces. Properly offsetting the cladding head can help mitigate this issue.

3.2 Powder Clogging

Powder clogging directly interrupts the high-speed laser cladding process. Common causes include delayed cleaning of adhered powder, poor powder flowability, moisture or impurities in the powder, and uneven powder distribution in multi-feed systems.

3.3 “Hissing” Noise During Cladding

Abnormal noise during the cladding process often indicates a problem in the process. It may be caused by powder contamination, moisture, or dirty substrates. High power density can lead to metal vaporization in the melt pool, producing noise and affecting the corrosion resistance of the laser cladding coating.

3.4 Spark Splashing During Cladding

Severe spark splashing can compromise process safety and coating quality. It typically occurs when the scanning speed is too high, power density is too high, the power and powder feeding are mismatched, or the gas flow is too large, representing excessive energy input in the high-speed laser cladding process.

3.5 Unstable Powder Flow Leading to Uneven Coating

Stable powder flow is essential for achieving a uniform high-speed laser cladding coating. Instability in powder flow is often caused by worn scrapers, blocked powder feeding channels, insufficient gas flow, poor powder feeder seals, or air leaks in powder feeding pipes.

3.6 Reduced Cladding Efficiency (Thinner Coating)

Reduced efficiency signifies a deterioration in the system’s condition. Possible causes include contamination of protective lenses, worn scrapers, improper working distance, worn powder holes causing rougher powder flow, or a decrease in laser power.

4. Συμπέρασμα

High-speed laser cladding is a technology that demands precise control over its process parameters. The occurrence of the aforementioned issues is often closely related to parameter matching, equipment status, and material management. A systematic understanding of the causes of these defects is crucial for achieving high-quality high-speed laser cladding and expanding its application. By continuously optimizing the process and strengthening process monitoring, the stability and yield of high-speed laser cladding can be effectively improved.