Formation and investigation of plasma gradient coating with upper hafnium oxide layer
The relevance of the research is caused by the need to increase the operating temperature and thermocyclic resistance of the thermal barrier coating to protect heat-stressed details of aircraft and rocket technology against overheating, as well as for thermal insulation of sealing sectors of drillin...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | Russian |
| Published: |
Tomsk Polytechnic University
2018-11-01
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| Series: | Известия Томского политехнического университета: Инжиниринг георесурсов |
| Subjects: | |
| Online Access: | http://izvestiya.tpu.ru/archive/article/view/2102 |
| Summary: | The relevance of the research is caused by the need to increase the operating temperature and thermocyclic resistance of the thermal barrier coating to protect heat-stressed details of aircraft and rocket technology against overheating, as well as for thermal insulation of sealing sectors of drilling columns for drilling wells in rocks. The main aim of the research is formation of nanostructured gradient coating with an upper layer of hafnium oxide, that has a gradient of chemical composition and coefficient of thermal expansion, by the method of plasma spraying in vacuum. Objects of the research are three-layer coatings and gradient nanostructured coatings with the upper layer of hafnium oxide. Hafnium oxide is an attractive ceramic component of thermal barrier coating due to its high chemical, mechanical stability and its elevated temperatures of phase transitions. Methods: scanning electron microscopy, X-ray microanalysis, X-ray diffraction and thermal analysis. Results. Three-layer nanostructured coatings with the thickness up to 120 µm containing layers of NiCoCrAlY, ZrO 2 -7 %Y 2 O 3 , HfO 2 -9 %Y 2 O 3 and gradient nanostructured coatings NiCoCrAlY - (ZrO 2 -7 %Y 2 O 3 + NiCoCrAlY) - ZrO 2 -7 % Y 2 O 3 - (ZrO 2 -7 %Y 2 O 3 + HfO 2 -9 %Y 2 O 3 ) - HfO 2 -9 %Y 2 O 3 were obtained. It is shown that a mixing layer with a thickness of ~5 µm is formed in a three-layer coating at the interface of ZrO 2 -7 %Y 2 O 3 and HfO 2 -9 %Y 2 O 3 layers. It characterizes the average microparticle size in the coating. The ceramic layer of gradient coatings is uniform and has a holistic structure. The hafnium oxide layer is characterized by a cubic modification, (ZrO 2 -7 %Y 2 O 3 + HfO 2 -9 %Y 2 O ) layer by pseudocubic modification, and the ZrO 2 -7 %Y 2 O 3 contains predominantly a tetragonal phase. Thermal analysis of the upper layer of hafnium oxide showed the presence of an exothermic reaction in the temperature range of 1300...1600 °C, accompanied by a mass loss of 2 %, that may be related to the partial release of the stabilizing oxide from the hafnium oxide lattice, its redistribution, a decrease in defectiveness and internal stresses in the coating. X-ray diffraction method showed the preservation of the cubic structure of hafnium oxide after thermal analysis with a decrease in the lattice parameter a. |
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| ISSN: | 2500-1019 2413-1830 |