No abstract

The coatings produced by an atmospheric plasma spray process (APSP) must be of uniform quality. However, the complexity of the process and the random introduction of noise variables such as fluctuations in the powder injection rate and the arc voltage make it difficult to control the coating quality that has been shown to depend upon mean values of powder particles’ temperature and speed, collectively called mean particles’ states (MPSs), just before they impact the substrate. Here, we use a science-based methodology to develop a stable and adaptive controller for achieving consistent MPSs and thereby decrease the manufacturing cost. We first identify inputs into the APSP that significantly affect the MPSs and then formulate a relationship between these two quantities. When the MPSs deviate from their desired values, the adaptive controller is shown to successfully adjust the input parameters to correct them. The performance of the controller is tested via numerical experiments using the software, LAVA-P, that has been shown to well simulate the APSP.

No abstract

Current techniques for determination of the thickness of coatings for gas turbine parts involve metallographic measurements on sections cut from the coated component. This technique is time consuming and expensive, and only a limited amount of data can be obtained for individual systems. In this paper, initial results are presented for a nondestructive technique using eddy current testing. Measurements have been carried out on flat and curved surfaces with and without thermal barrier coatings, and good agreement has been obtained with metallographic determinations in every case. Preliminary data suggest that a combination of eddy current and ultrasonic techniques may enable degradation behavior to be monitored.

We numerically solve the system of nonlinear and coupled partial differential equations expressing the conservation of mass of species, the total mass, linear momentum, and energy, the k-ε turbulence model for plasma flow, the lumped heat capacity model for particle heating, and Newton’s equations for the particle motion under pertinent initial and boundary conditions. The interaction between the powder particles and the plasma is modeled by considering the drag force the plasma exerts on the particles and vice versa. The effect of particle vaporization as well as that of turbulence modulation on the mean velocity and the mean temperature of particles is also considered. The initial-boundary-value problem has been numerically analyzed by using the recently developed software, LAVA-3DI. The computed results are found to agree well with the test observations reported in the literature.