Method and Process Development of Advanced Atmospheric Plasma Spraying for Thermal Barrier Coatings

Over the last few years, global economic growth has triggered a dramatic increase in the demand for resources, resulting in steady rise in prices for energy and raw materials. In the gas turbine manufacturing sector, process optimizations of cost-intensive production steps involve a heightened potential of savings and form the basis for securing future competitive advantages in the market. In this context, the atmospheric plasma spraying (APS) process for thermal barrier coatings (TBC) has been optimized. A constraint for the optimization of the APS coating process is the use of the existing coating equipment. Furthermore, the current coating quality and characteristics must not change so as to avoid new qualification and testing. Using experience in APS and empirically gained data, the process optimization plan included the variation of e.g. the plasma gas composition and flow-rate, the electrical power, the arrangement and angle of the powder injectors in relation to the plasma jet, the grain size distribution of the spray powder and the plasma torch movement procedures such as spray distance, offset and iteration. In particular, plasma properties (enthalpy, velocity and temperature), powder injection conditions (injection point, injection speed, grain size and distribution) and the coating lamination (coating pattern and spraying distance) are examined. The optimized process and resulting coating were compared to the current situation using several diagnostic methods. The improved process significantly reduces costs and achieves the requirement of comparable coating quality. Furthermore, a contribution was made towards better comprehension of the APS of ceramics and the definition of a better method for future process developments.     

Effects of formulation variables on surface properties of wood plastic composites

Degree of surface quality of wood plastic composites (WPCs) is a function of both raw material characteristics and the manufacturing variables. The WPC panels comprised of different panel densities (800, 950, 1000, and 1080 kg/m³), wood flour contents (50, 60, 70, and 80 wt.%), wood flour sizes (<0.5, ?0.5 to <0.8, 0.8–1, and >1 mm), and hot-pressing temperatures (190 and 210 °C) were manufactured using a dry blend/flat-pressing method under laboratory conditions. The surface smoothness of the WPC panels improved with increasing WPC density, plastic content, and hot-pressing temperature while it deteriorated with increasing wood flour size. The reduction in the particle size of the WF resulted in a more compact structure on the WPC surface. In general, the wettability of the samples increased by increasing surface roughness.     

Insights into the reliability of different thermal conductivity measurement techniques: a thermo-geological study in Mære (Norway)

Thermal response tests (TRTs) are used to measure the effective thermal conductivity in boreholes. The results serve as a basis for the dimensioning of commercial ground-source heat pump installations with closed loop systems. The study evaluated the reliability of TRTs performed in winter by comparing two TRTs carried out under very different winter weather conditions. A third TRT elucidated the influence of convection in wells with a higher heat input. Rock cores were analysed for quartz content and these results and the laboratory-measured thermal conductivity data were compared with the TRT results. This highlighted the importance of the distribution and orientation of minerals in the rock, and that a high quartz content does not necessarily give high thermal conductivity values. It is concluded that winter TRTs give useful results if additional temperature loggers are installed in anticipated fracture zones to detect groundwater flow and to survey the effect of infiltrating water.     

A Framework for Recognizing the Simultaneous Aspects of American Sign Language

The major challenge that faces American Sign Language (ASL) recognition now is developing methods that will scale well with increasing vocabulary size. Unlike in spoken languages, phonemes can occur simultaneously in ASL. The number of possible combinations of phonemes is approximately 1.5×10⁹, which cannot be tackled by conventional hidden Markov model-based methods. Gesture recognition, which is less constrained than ASL recognition, suffers from the same problem. In this paper we present a novel framework to ASL recognition that aspires to being a solution to the scalability problems. It is based on breaking down the signs into their phonemes and modeling them with parallel hidden Markov models. These model the simultaneous aspects of ASL independently. Thus, they can be trained independently, and do not require consideration of the different combinations at training time. We show in experiments with a 22-sign-vocabulary how to apply this framework in practice. We also show that parallel hidden Markov models outperform conventional hidden Markov models.     

Thickness-controlled hydrophobicity of fibrous Parylene-C films

Fibrous Parylene-C films with tilted columnar morphology were deposited with a physicochemical version of the oblique-angle deposition (OAD) technique. Advancing contact angles increased from 103.9° (smooth hydrophobic surface) to 168.5° (rough superhydrophobic surface) as the thickness of the film increased from ∼ 100 nm to ∼ 60 μm, reflecting changes in the morphology of the top surface. Treatment with oxygen plasma can render these fibrous films completely water wettable. These techniques allow tailoring of surface wettability to meet the demands of specific biomedical applications.     

A grain-scale study of spall in brittle materials

The evolution of spall for a brittle material is investigated under variance of anisotropy, grain boundary fracture energy, and loading. Because spall occurs in the interior of the specimen, fundamental studies of crack nucleation and growth are needed to better understand surface velocity measurements. Within a cohesive approach to fracture, we illustrate that for anisotropic materials, increases in the fracture energy cause a transition in crack nucleation from triple-points to entire grain boundary facets. Analysis of idealized flaws reveals that while crack initiation and acceleration are strong functions of the fracture energy, flaws soon reach speeds on the order of the Rayleigh wave speed. Finally, simulated surface velocities of spalled configurations are correlated with microstructural evolution. These fundamental studies of nucleation, growth, and spall attempt to link atomic separation to the macroscopic spall strength and provide a computational framework to examine the evolution of spall and the impact on the simulated surface velocity field.