Numerical Simulation On Residual Stress Of High Velocity Air-Fuel Flame Sprayed Fe-Based Amorphous Coatings

In this paper, pre-processing software ICEM is used to demarcation mesh, and CFD software FLUENT is used to simulate the HVAF thermal spray process, which takes Kermetico Company’s AK-07 spraying system sprayed Fe41Co7Mo14C15B6Y2 amorphous coatings for reference. The heat transfer coefficient on the substrate and near wall temperature of the flow field analysis is exported to design the Finite Element program by parametric design language of ANSYS software. The moving heat source model of the spraying is established based on the birth-death technique, and coating temperature field and residual stress are calculated. Parameters used in the simulation process such as spraying speed, spraying distance, powder diameter, powder feeding rates are obtained by experimental method. K-type thermocouples are employed to measure temperatures of test points in the substrate, the coating thickness was measured by metallographic method, and the analytical model for predicting thermal residual stresses in multilayer coating systems is adopted to calculate coating residual stress in order to validate the reliability of numerical simulation results. Simulation results of coating temperature field showed reasonably good agreement with the experimental data. Deviation of 36 temperature peaks of 4 measuring points within 15%. Compare simulation results and theoretical calculation results of coating residual stress field,result display that deviation of stress value within 15% of 9 stress values among 48 maximum stress values and the maximum deviation is 29.24%.The effect of different spray gun type and different powder diameter on particle temperature and velocity is studied. The results show that the larger the particle diameter, the lower the particle temperature and velocity. When particle diameter is between 25um-30 um, the particle temperature is between1350-1500 K and the particle velocity is between 410-460 m/s. The particle temperature and velocity increases with the increasing of barrel length. When barrel length is 2 and 2L, particle temperature are all about 1400 K. The simulated particle velocity of 2L type is 40m/s higher than that of the 2L type one.The Influence of different air-fuel ratio and different fuel flow rate in flow field,temperature and velocity of particles are studied, respectively. Under the condition that barrel type is 2L and particle diameter is 25 um, remaining propane flow is 145 SLPM unchanged, when air-fuel ratio is 3.3, particle temperature is the highest, reaching1430 K, particle velocity reaches maximum 445m/s. Remaining air-fuel ratio is 3.2, withthe increasing of propane flow, particle temperature raises monotonically. When the propane flow is 140 SLPM, particle temperature reaches the melting point of the material 1388 K. When the propane flow is higher than 140 SLPM, the upward trend is obvious.The effect of particle temperature, spraying layer, convection conditions on coating residual stress is studied. Shear stress at the interface between the coating and the substrate is increased and Compressive stress in X and Y direction is reduced with the number of layers of spray increased. Residual stress is monotonically increased with the increasing of particle temperature. The trend is increased when the particle temperature exceeds 1600 K. During the process of spray, the tensile stress and compressive stress at the interface between the coating and the substrate is decreased if the convection heat transfer is larger.