Laser cladding with coaxial powder feeding is one of the new ponent to improve performance of its surface. In the process, processes applied to produce well bonding coating on the com- the clad material is transported by the carrying gas through the coaxial nozzle, generating gas-powder flow. The powder feeding process in the coaxial laser cladding has important influence on the clad qualities. A 3D numerical model was developed to study the powder stream structure of a coaxial feeding nozzle. The predicted powder stream structure was well agreed with the experimental one. The validated model was used to explore the collision behavior of particles in the coaxial nozzle, as well as powder concentration distribution. It was found that the par- ticle diameter and restitution coefficient greatly affect the velocity vector at outlet of nozzle due to the collisions, as well as the powder stream convergence characteristics below the nozzle. The results indicated a practical approach to optimize the powder stream for the coaxial laser cladding.
LIU HaoHE XiuLiYU GangWANG Zhong BinLI ShaoXiaZHENG CaiYunNING WeiJian
Thermal fatigue is the typical failure mode of high-temperature combustion chamber components used in power plants and in the aerospace and transportation industries [1-3]. With growing demand for good performance and high reliability, thermal fatigue is becoming a serious problem. The thermal working conditions of combustion chamber components include start-stop cycles and routine working cycles simultaneously [4,5]. The former refer to large temperature changes, with the amplitude of 200℃-500℃ and time period of several hundred seconds that are responsible for low-cycle fatigue （LCF） damage. The latter correspond to low temperature amplitudes of 20℃-60℃, with time period of milliseconds, and are responsible for high-cycle fatigue （HCF） damages.
To better understand the physical processes of multi-pulse laser drilling,this study investigates the keyhole evolution and its driving mechanism in a time-resolved observation system.The evolution characteristics suggested a two-phase process of rapid penetration followed by moderate penetration.As revealed in the ejection and vaporization behavior,the keyhole evolution was dominated by ejection and vaporization during the rapid and moderate penetration stages,respectively.In a single laser-pulsed drilling experiment,the driving mechanism itself was found to be affected by the dimensionless laser power density.The effect of dimensionless laser power density on depth increment was then discussed by comparing the experimental observations with numerical simulation results.The results further confirmed the driving mechanism of the keyhole evolution.The results in this paper are useful for understanding the driving mechanism of the keyhole evolution during multi-pulse laser drilling.
