CVD diamond coated silicon nitride self-mated systems : tribological behaviour under high loads

Friction and wear behaviour of self-mated chemical vapour deposited (CVD) diamond films coating silicon nitride ceramics (Si3N4) were investigated in ambient atmosphere. The tribological tests were conducted in a reciprocal motion ball-on-flat type tribometer under applied normal loads up to 80 N (~10 GPa). Several characterisation techniques - including scanning electron microscopy (SEM), atomic force microscopy (AFM) and micro-Raman studies - were used in order to assess the quality, stress state and wear resistance of the coatings. In addition, a novel method is presented to estimate the wear coefficient of the diamond coated flat specimens from AFM and optical microscopy (OM) observations of the wear tracks

Power Losses and Heat Extraction in a Stator with Directly Air-Cooled Laminated Windings

This paper explores and assesses power loss generation and heat extraction in a stator with directly air-cooled laminated winding. An electrical machine winding made of an electric conducting sheet, which have slotted structure for accommodating a magnetic core, is denoted a laminated winding. A space is introduced between the conducting sheets so that the heating power is removed right where it is created. Explicit to the laminated windings, the conductors with smallest cross section and highest dc resistance have also limited cooling. Since these conductors are closest to the air-gap they become subject to induced power losses. An electrical machine with folded air-cooled laminated winding is built and evaluated. The paper demonstrates on how the thermal management of the stator segments is evaluated and adjusted during the manufacturing process. The power loss estimation of the prototype machine reveals significant discrepancy between the measurements and the calculation of known power losses at no load condition compared to short-circuit conditions. Conjugate heat transfer models are developed to evaluate the coolant flow distribution and heat dissipation in the direct air-cooled laminated windings

Structural Characterization and Corrosion Behavior of Stainless Steel Coated With Sol-Gel Titania

Sol-gel titania films were prepared from hydrolysis and condensation of titanium (IV) isopropoxide. Diethanolamine was used as chelant agent in titania synthesis. 316L stainless steel substrates were dipcoated at three different withdrawal speeds (6, 30, and 60 mm/min) and heated up to 400 °C. Thermogravimetry and differential thermal analyses of the titania gel solution evinced a continuous mass loss for temperatures up to 800 °C. The transition of anatase to the rutile phase begins at 610-650 °C, being the rutile transformation completed at 900 °C. The thicknesses of the films were determined as a function of the heat treatment and withdrawal speed. It was observed that their thicknesses varied from 130 to 770 nm. Scanning electron microscopy images of the composites revealed the glass-like microstructure of the films. The obtained sol-gel films were also characterized by energy dispersive spectroscopy. The chemical evolution of the films as a function of the heating temperature was evaluated by Fourier transform infrared spectroscopy (specular reflectance method). After performing the adhesion tests, the adherence of the titania films to the stainless steel substrate was excellent, rated 5B according to ASTM 3359. The hardness of the ceramic films obtained was measured by the Knoop microindentation hardness test with a 10 g load. We observed that the titania film became harder than the steel substrate when it was heated above 400 °C. The corrosion rates of the titania/steel composites, determined from potentiodynamic curves, were two orders of magnitude lower than that of the bare stainless steel. The presence of the sol-gel titania film contributed to the increase of the corrosion potential in ca. 650 mV and the passivation potential in ca. 720 mV