As one of the most important application technologies for laser surface modification, laser cladding technology can greatly improve the performance and life of materials or parts using a high-energy laser beam to change the performance of the workpiece surface.
The main process of laser cladding
(1) Pre-set powder method: The pre-set powder method mainly places the coated powder evenly on the surface of the substrate through bonding or spraying. During laser cladding, the cladding powder and the matrix material melt simultaneously under the action of laser energy, and the molten coating quickly cools under the absorption of heat of the matrix material to form a metallurgical bond.
(2) Synchronous powder feeding method: Synchronous powder feeding refers to laser cladding through automatic powder feeding equipment, sending the cladding powder into the melting pool, and completing synchronous powder feeding. This powder feeding method is uniform in the cladding layer, high working efficiency, and easy to achieve automatic control.
New parts modification
Through laser cladding technology, a special performance coating is clad in a designated area of the workpiece surface, which can improve the surface performance of the workpiece, and make important parts have super wear-resistant and corrosion-resistant characteristics, greatly extending the service life of the parts.
After the production of ball valves in the chemical industry, the surface of the cladding layer is modified. The thickness of the cladding layer is required to be 1.2mm, without defects such as pores and cracks, and has high corrosion resistance. The cladding layer hardness is above 55HRC.
Repair of old parts
In the petrochemical industry, equipment is in a harsh working environment for a long time, which can easily lead to severe corrosion and wear of parts, and even the complete scrapping of large and expensive parts. Laser cladding technology makes it possible to repair some expensive parts and inconvenient replacement parts. The repaired parts will have twice the strength of the original parts, saving the company the cost of purchasing new parts.
Components that often have problems in chemical equipment include valves, pumps, impellers, journals, roulettes, bushings, bearing shells of large rotors, etc. After the ball valves and shaft parts in the chemical industry fail, the thickness of the cladding layer is required to be 1mm, and defects such as pores and cracks are not allowed, and they have certain corrosion resistance. The hardness of the clad layer is above 50 HRC.
Difficulty in application
1. The process parameters of the cladding process are uncontrollable factors
The process parameters of laser cladding technology play a decisive role in the mechanical properties and microstructure of the cladding layer. The main technical parameters during the cladding process include laser energy, spot size, cladding speed, preheating temperature, overlap size, powder feeding method and powder feeding speed, etc. , and many technical parameters affect and restrict each other. At present, the parameters used by various scientific research and production institutions are mainly based on empirical data and lack theoretical basis.
2. Cracking defects in the cladding layer
During laser cladding, the cladding area melts rapidly under the action of laser light and then solidifies quickly. Since the physical shrinkage properties of the cladding powder and the matrix material are slightly different, when the cladding area cools rapidly, the cladding layer is limited by the inherent elements of the cold matrix, resulting in endogenous tensile stress. When the endogenous tensile stress exceeds the limit that the cladding layer can withstand, cracks will occur on the cladding surface, which is an important indicator that affects the cladding quality.
