Sensor technology is becoming more of a production tool to help improve production quality, reliability and reduce manufacturing costs. Combustion sprayed abradable seal products are a family of materials where this technology will be helpful to the applicator and end user. Although these materials have been used for over forty years with wide success in the aerospace and industrial gas turbine industries they can be sensitive to spray process variables. Changes in spray processing conditions during spraying will change the desired microstructure and coating properties. This paper looks at a commercially available combustion powder and how process parameters such as gas flows and powder feed rates affect output process variables such as particle velocity and temperature. This paper will also discuss the importance of understanding the influences that particle temperature and velocity have on coating properties such as hardness, erosion and coating strength. Deposit efficiency of these combustion powders is also measured as a function of particle temperature and velocity. Based on particle temperature and velocity, sensor diagnostic tools can provide warnings about process changes resulting in fast corrective action. The benefits of this sensor technology are the potential for less inspection requirements, improved microstructure control, reduced in-service failures, and less time and labour required for stripping coated components that may not meet specification standards.

Individual particles of various ceramic materials sprayed by water stabilized plasma torch (WSP) were characterized in flight by an optical sensing device DPV-2000. Temperature, velocity, and diameter of individual particles were measured at the center of particle plume and maps of the particle plume cross-section were acquired as well. Plasma jet and consecutively particle plume of the WSP torch is much larger compared to gas stabilized torches and even larger than the maximum span of the DPV-2000 sensing head. In summary, temperatures of particles varied from 2000 to 2600°C and their velocities from 60 to 140 m/s depending on the powder feedstock cut size, particle density, feeding distance, spraying distance, and feed rate. The last three parameters were varied to study their effect on the particle states and their distribution in the plasma jet and to correlate these results with selected properties of the corresponding coating. Some of the spraying parameter effects are difficult to interpret, nevertheless, general trends have been established.

For constant conditions concerning substrate state, feedstock and environment properties of thermal spray coatings depend only on temperature and velocity of particles at impact on the substrate. Two different HVOF spraying guns, the kerosene fuel system Tafa JP5000 with radial powder injection and the ethylene fuel system Sulzer Metco Diamond Jet Hybrid 2700 with axial powder feeding, are characterized concerning the evolution of space resolved velocity and density of particles by LDA. Also influence of process parameter variations is examined. The region of shock diamonds is studied specifically. The influence of different characteristics concerning impact velocity and trajectories on the coatings microstructure is determined by means of optical microscopy and microhardness testing.

An experimental study was conducted to study the effects of properties of in-flight particles on microstructures of coating layers using a wire arc spraying system. In this study, 0.8% carbon steel wires were used for arc spraying and nitrogen gas was used as atomizing gas. Temperature, velocity and distributions of the in-flight particles were measured by DPV2000 for different working conditions. Specimens of spray-footprint were made and microstructures of them were evaluated. As a result, amount of oxide in a coating layer was proved to be related with the temperature of the in-flight particles. Because oxidation of the molten steel particles is an exothermic reaction, higher temperature of the particles during arc spraying means higher area fraction of oxide in the coating layers. For this reason, oxide level is lowest at the central area of spray footprint and it becomes higher as the distance from the center increases. Hardness, porosity and phase are changed according to the distance from the center. Abstract only; no full-text paper available.

Characteristics of in flight particles before they impact on the substrate influence strongly the quality of coating obtained by plasma spraying. Various optical techniques can be used to measure the in-flight particle characteristics; some of these techniques require the use of high- speed two-color pyrometers to collect the light emitted by the particle during the in-flight period when they pass through the measurement volume. However, the intense radiation coming from the plasma can affect the particle thermal radiation and lead to erroneous measurements. This work was dedicated to the study of reflected light coming from the plasma and scattered by the injected particles. To achieve this goal, sprayed particles were analyzed by optical emission spectrometry. The light scattered by the particles was found to influence significantly the measured temperature. This work allows thus the estimation of the accuracy of temperature measurements on particle surface for the thermal spraying process. Abstract only; no full-text paper available.

Amorphous metallic alloys can be produced by rapid quenching from the metallic liquid at sufficient cooling rates to suppress the nucleation and growth of crystalline phases. The cooling rates required depend on the alloy constitution; generally the necessary values are in the order of 106 Ks-1[1]. There has been considerable interest in the manufacture of Fe-based metallic glasses because they possess attractive combinations of properties such as high hardness, good abrasive wear resistance together with enhanced corrosion resistance and good magnetic properties. However, in order to achieve these cooling rates in metallic alloy melts, samples less than 50 ƒÝm thick must be suddenly brought into good thermal contact with an efficient heat sink. Hence, these amorphous alloys are frequently produced in the form of ribbon or powder. An alternative approach consists to employ thermal spraying to deposit the alloys directly onto a substrate, in the form of a protective coating about 200 ƒÝm thick. In this study, FeSi powder was chosen as feedstock material. It is characterized by its good magntic properties [2- 7]. In order to control temperature and velocity of the in-flight particles during the coating deposition, on-line measurement of flame sprayed FeSi particles were performed with high-speed two-color pyrometer used especially for the spray forming process. In the same time, a wide band spectral pyrometer (LAND INFRARED) was used to monitor the coating surface temperature to ensure achieving good cooling rates. X-ray diffraction patterns show that the FeSi coatings structure present a crystalline phase and magnetic measurements indicate the soft ferromagnetic character of this last. Abstract only; no full-text paper available.

In-flight particle analysis via infrared sensing has proven helpful in the development and control of thermal spray processes. The aim of this work is to assess the effect of optical system design on thermal measurement accuracy. Through experimental testing and theoretical analyses, investigators show how variations in optical component sizes, alignments, and arrangements affect the amplitude and shape of sensor voltage waveforms and signal peaks. It is observed that only when photodetectors are in saturation, marked by the trapezoidal shape of their output signals, can they provide information about particle velocity, temperature, and size, and in some cases, even volume distribution. Correlation tests are carried out by means of plasma spraying molybdenum powder. Paper includes a German-language abstract.

This paper describes the development of a diagnostic system that monitors in-flight particle diameters, velocities, and temperatures during thermal spraying. The system is based on a low-cost CCD camera and user-developed software. The camera incorporates a 732 x 282 pixel sensor with high sensitivity in the near IR range where the only radiation is that of the particles. User-developed software modules handle signal processing, image analysis, calibration, and data visualization. In video images, particles appear as light tracks of varying length, width, and intensity, corresponding (respectively) to velocity, diameter, and temperature. A test case in which Cr 2 O 3 powder is sprayed in a plasma jet demonstrates the capabilities of the diagnostic system. Paper includes a German-language abstract.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.