Preparation And Properties Of A New NiCrFeAl(hBN)-YSZ Composite Thermal Protective Coating

In this paper,taking TC11 titanium alloy for aero-engine compressor as the research object,a NiCoCrAlY+YSZ+NiCrFeAl-hBN（NYN-hBN）composite coating,prepared by thermal spraying technology,was designed with various protective functions such as heat insulation,wear resistance and corrosion resistance.The NiCoCrAlY coating,as the bonded coating at the bottom,had a great impact on resistance to high-temperature oxidation,and at the same time,it effectively alleviated the thermal mismatch between the ceramic coating and TC11 titanium alloy matrix as the transitional layer.YSZ ceramic coating as an intermediate layer mainly played a role in heat insulation.NiCrFeAl-hBN surface layer mainly played a multi-functional protective role.For the contrastive study,the commonly used NiCoCrAlY+YSZ+NiCrFeAl-hBN（NYN-hBN）coating was prepared at the same time.The research details were as follows:1.Taking the surface Rockwell hardness,bonding strength and surface roughness of the coating as the judgment indexes,the preparation parameters of plasma-sprayed NiCoCrAlY+YSZ coating and oxyacetylene flame sprayed NiCrFeAl-hBN coating were orthogonally optimized,and the prepared coatings after optimizing the parameters were experimentally verified.The outcome stated that the bonding hardness of that composite coating,designed with optimized parameters,was 10.3 MPA,which was nearly 45%higher than that before optimization.The optimized surface Rockwell hardness was 54.9 HR15Y with more moderate hardness.2.The erosion resistance,wear resistance and electrochemical corrosion resistance of NYN-hBN coating and NYN-Be coating prepared by the optimal process were compared and studied at room temperature.The results showed that the erosion resistance of NYN-hBN coating was better than that of NYN-Be coating and that the erosion rates of the two coatings were the highest when the erosion angle was 60°at room temperature,which were 1.60×10^-3and 1.85×10^-3,while the NYN-hBN coating decreasing by 13.5%compared with the NYN-Be coating.Besides,at room temperature,the wear rate of NYN-hBN coating was0.0007 mm³/（N·m）,which was significantly lower than that of NYN-Be coating（0.0015mm³/（N·m））.The wear mechanism of both coatings was abrasive wear.When the self corrosion potential was similar,the self corrosion current density of NYN-hBN coating was(8.57×10^-6A/cm²),significantly lower than that of NYN-Be coating(3.54×10^-5A/cm²),showing better electrochemical corrosion resistance.3.The experimental results of mechanical properties and thermal shock resistance under thermal environment showed that the hardness value of NYN-hBN coating changed little after holding at 600℃for different times,and it had good thermal stability.In the friction and wear experiment temperature from 100℃to 600℃,the wear rate of NYN-hBN coating had the trend of rising at the first and then turning to declining.In addition,the wear mechanism of that coating steadily altered from abrasive wear to adhesive wear.The minimum wear of the table at 600℃was 0.00268 mm³/（N·m）.The maximum wear rate at300℃was 0.0031 mm³/（N·m）.Based on the analysis with Abaqus,the life span of NYN-hBN coating during the thermal cycle of heating at 800℃and air cooling was 567times;the number of thermal vibrations was 219 times in the 800℃heating-water cooling experiment.