Impacting particle temperature monitoring during plasma spray deposition

Abstract

Instrumentation for monitoring the thermal history of individual plasma sprayed particles as they impact on a substrate is described. A double-wavelength fibre optic temperature sensor is focused on a small spot on the substrate surface to record the cooling rate of particles impacting on this region. Discrimination against in-flight particles intersecting the pyrometer field of view is obtained by a second fibre optic sensor viewing the same spot at an angle and working in coincidence with the first sensor. Typical recorded thermograms are presented and interpreted with reference to a numerical thermal propagation model.

Thermal contact resistance between plasma-sprayed particles and flat surfaces

“…It could also be due to errors in the pyrometric readings caused by the assumption that the splat was a gray body. The accuracy of the temperatures obtained by this method was ±100°C [15]. Lee et al [25] have shown a mathematical model capable of estimating the rate of heat transfer from droplets on a high temperature wall.…”

“…Higher temperatures will produce stronger signals, increasing the signal to noise ratio, and reducing the observed oscillations. It has been shown that, in general, the accuracy of temperature measurements obtained by the two-color pyrometry method is ±100°C [15]. Table 1 shows average values of the experimental temperatures at the maximum extent and the experimental cooling rate of molybdenum on non-heated glass.…”

“…2(a)), with dimensions of 30 lm by 150 lm and 30 lm by 300 lm, were used to detect the thermal radiation of the in-flight particles. The radiation was used to calculate the temperature of the in-flight particle [15]. The largest slit (slit e in Fig.…”

“…The photodetector had a response time smaller than 0.1 ls [14]. The ratio of the radiation intensity at the chosen wavelengths (referred to as D 1 and D 2 , respectively) was used to calculate the particle and splat temperatures with an accuracy of ±100°C [15]. Fig.…”

“…High-speed, two-color pyrometry has been used to obtain splat temperature variation during impact of plasmasprayed particles [13][14][15]. In this method, radiation emitted by the spreading splat is recorded at two different wavelengths; assuming gray-body emission, the splat temperature is calculated from the ratio of the intensities of radiation collected.…”