Авіаційно-космічна техніка та технологія (Nov 2018)
RESEARCH OF THE EFFECT OF DOPING ON THE TEMPERATURE COEFFICIENT OF THE LINEAR EXPANSION OF COATINGS
Abstract
The effect of doping with yttrium-containing ligatures on the thermal coefficient of the linear expansion of sealing coatings is studied. KHA-82 coating was taken as the base material for the research. It is used in the aircraft engines produced by Motor Sich JSC. This coating contains nickel (base), silicon, aluminium, and solid lubricants (graphite and boron nitride). To enhance the physical-mechanical properties of the coating, an yttrium-containing ligature was added to the size prepared by the serial process. Three different compositions of the ligature with varying content of yttrium were studied, namely Ni-Y is composition No.1, Y is composition No. 2, Co-Ni-Cr-Al-Y is composition No. 3, and KHA-82 is composition No. 4. The coatings were applied onto specially prepared samples by a gas-flame technique. Analysis of the volumetric and possible structural phase changes in the material of the coatings under consideration was carried out on the Shevenar differential dilatometer. It was found out that during the first heating within 650-700° C, there is a change in the shape of the dilatometric curve. Recurring heating also causes the change in the trajectory of the dilatometric curve. The obtained result is probably related to the development of the oxidization processes, appearance of intermetallide phases, and changes in the porosity of the coatings during the first and recurring heating. Reduction of the pore space is beneficial in terms of energy as it is accompanied by the reduction of free surface, which in its turn can trigger the development of phase changes that are connected with the formation of oxide, nitride, and intermetallide inclusions. The smallest difference in the shape of dilatometric curves is observed in the coating of composition No. 3, which is presumably due to the fact that double spinels with a more compact structure are formed in the structure of the material obtained. The estimation of the difference in the temperature coefficient of the linear expansion of the base and coating materials indicates an insignificant difference in these values that can be reduced if the suggested yttrium-containing ligatures are added.
Keywords
