Micromechanical and Electrophysical Properties of Al 2 O 3 Nanostructured Dielectric Coatings on Plane Heating Elements
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MICROMECHANICAL AND ELECTROPHYSICAL PROPERTIES OF Al 2O 3 NANOSTRUCTURED DIELECTRIC COATINGS ON PLANE HEATING ELEMENTS Z. A. Duryahina,1 T. M. Kovbasyuk,1, 2 S. A. Bespalov,3 and V. Ya. Pidkova1 By using the ion-plasma discharge system, an Al 2O 3 dielectric layer with nanoscale structure is formed on a plane heating element made of AMg2 aluminum-magnesium alloy. The sprayed Al 2O 3 layer consists of two sublayers with a total thickness of 13–15 µm and grain sizes of 4–306 nm. The surface roughness is equal to 50–60 nm. For the adhesion coefficient HSC ∼ 1, the Meyer microhardness of the Al 2O 3 layer is equal to 0.788 and the Young modulus is equal to 75.433 GPa. Keywords: heating element, plasma spraying, dielectric layer, microstructure.
At present, the so-called film heating elements efficiently replace the existing element base of electric heating devices with extended functional elements. Due to the alternative location of relatively thin dielectric and resistant layers on the metal substrate, it becomes possible to guarantee the uniform distribution of temperature over the surface, high adhesion, and a constant heat flux on the contact surface of heat exchange.
The first stage in the creation of plane heating elements is the deposition of dielectric layers on the metal substrate. As the most extensively used methods for the formation of these layers, we can mention the resistive evaporation in a vacuum and the ion-plasma (HF-cathodic and HF-anodic) methods. The possibilities of the first method are restricted due to the high temperature of evaporation of the major part of oxides. Thus, in particular, the melting temperature of aluminum oxide is equal to 2030°C and the temperature at which the pressure of vapor is equal to 10 –2 mmHg (start of evaporation) is equal to 1800°C.
The HF-magnetron (reactive) method enables one to get almost all types of dielectric films formed by oxides, nitrides, oxynitrides, etc. The main disadvantage of the films formed by the HF-cathodic and HF-magnetron methods is the appearance of high mechanical stresses, which leads to a sharp decrease in the electric strength. In what follows, we study the electrophysical and micromechanical properties of Al 2O 3 dielectric coatings produced with the help of an ion-plasma discharge system. In the course of formation of dielectric layers, it is important to guarantee their reliable adhesion to the substrate because the violations of the integrity of the layer decrease its operational reliability. Since these coatings are used as the functional layers of plane heating elements, we note that the state of the surface of the outer layer of Al 2O 3 (its roughness and the number of defects) affects the quality of the resistive layer formed on this surface. 1 2 3
“L’vivs’ka Politekhnika” National University, Lviv, Ukraine.
Corresponding author; e-mail: [email protected].
Presidium of the Ukrainian National Academy of Sciences, Kiev, Ukraine.
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 52, No. 1, pp. 51–55, January–Februar
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