High-Quality High-Material-Usage Multiple-Layer Laser Deposition of Nickel Alloys Using Sonic or Ultrasonic Vibration Powder Feeding

Abstract

Laser-based metal deposition has been considered and applied as one of the most promising techniques for repairing high-value aerospace components such as turbines and vanes. Low component distortion and minimum heat input are the main advantages of laser-based alloy deposition techniques. The currently used laser deposition techniques are based on the gas delivery of metallic powders to the laser-generated melt pool. Despite efforts in improving delivery nozzle designs, the powder usage efficiency is still not 100 per cent, with some powders ejected from the deposition points, and powder feeding cannot be rapidly switched on and off to synchronize with laser-firing actions; this causes wastage of high-cost superalloy materials and contamination of the work environment. To mitigate this process deficiency, a gas-free vibration powder delivery system has been developed. The system uses sonic or ultrasonic vibration to exert a distributed driving force on the powder and to assist its delivery to the laser-generated melt pool. Three different configurations (off-axial, coaxial, and multiple-stream) were designed and evaluated. The initial problems encountered were instability of the powder flowrate owing to jamming and mass variations. Through various stages of design and optimization, the powder flowrate from these nozzles was found both to be highly stable and to have fast dynamic responses to the electrical control signals. Experiments on the deposition of various alloy materials including Inconel 718 were carried out with a 1.5 kW diode laser, a 1 kW single-mode fibre laser, and a 7 kW multimode fibre laser. They showed that 100 per cent deposition efficiency can be achieved by using the developed vibration delivery system. The deposition quality in terms of the surface roughness, microstructure, and porosity was also much improved in comparison with gas delivery laser deposition techniques. In addition, a high-volume material deposition rate at 3.31 kg/h has been demonstrated.