Two-dimensional simulation is performed for an annular-shaped plasma torch using argon gas under different operating currents and torch-substrate distances. The mathematical model is based on the conservation equations of mass, momentum, and total energy for gasdynamics and the steady-state Maxwell's equations for electrodynamics. Suspension carrying zirconium particles are axially injected into plasma flow and their trajectories and heating histories are analyzed with the Lagrangian method. A simplified model is used to simulate the evaporation of suspension droplets and the emergence of solid particles. The numerical results show that current streamlines are sharply bent at an intersection area between anode and cathode plasma jets. In-flight particles are strongly heated in the intersection area. An increase in operating currents results in shortening the length of currents and moving the curvature area further upstream. The numerical results also indicate that the particle impacting positions on a substrate get closer to its center as the operating current gets larger and the torchsubstrate distance becomes narrower. Furthermore, the numerical results suggest that setting an operating current to higher values, which leads to an increase in particle impacting velocity, is suitable for impacting particles with molten state on thesubstrate.
The corrosion resistance of a thermally sprayed coating was evaluated by the combined cycle corrosion test (CCT) ; the coating was formed on a steel substrate by a flame spraying with the Al-5Mg-0.15Ca alloy comprising 5 mass% of Mg, 0.15mass% of Ca and the balance Al. Two types of samples that was different in the thickness of the coating, 50 μm and 100 μm were prepared. The samples were subjected to the CCT after giving a cross-cut to the steel substrate on the coating. After finishing the certain period of the CCT, the cross-sectional distribution of elements and phases across the coating of the tested samples was examined by SEM-EDX and EBSD analysis. Red rust-spots appeared on the samples after subjecting them to the CCT for 6000 h, regardless of the level of the coating thickness; they developed on a white-rust layer formed on the coating nearby where the cross-cut had been given. The SEMEDX analysis showed that the part of the white-rust layer was covered with the thin layer of a corrosion product, which was estimated as calcium carbonate.