| TC11 titanium alloy, which is an α+β type bi-phase thermal treatment strengthening titanium alloy, is widely used in engine compressor disks,blades,rotors and other aerospace parts due to a series of excellent properties such as low density, high strength and stable microstructure. TC11 titanium alloy can be used under temperature of 500℃ for a long time but it will oxide at a elevated temperature, leading to the limitation of the scope and the environment of its applications. The thermal insulation of TC11 titanium alloy have always been achieved by using materials with low thermal conductivity or thermal control system, which increasing the size of the structure in the systems. Therefore, one can conclude that the investigation and development of structure-compact thermal-insulating technique is of great importance.Based on principles of optics and method of magnetron sputtering, this work designed multilayers with high reflectivity of near-infrared light on TC11 titanium alloy substrates to achieve the purpose of heat insulation and anti-oxidation. Firstly, the properties of oxide films (ZrOx, AlOy, MgOz) and metalloid films (TiAIN, TiAlCr) are studied under different sputtering deposition conditions. Based on the research results, the preparation process is optimized and multilayers samples with high reflectivity of near-infrared light are obtained. Six types of multilayers samples are aquired:TC11/ZrOx (AlOy, ZrOx)2, TC11/ZrOx (MgO2, ZrOx)2, TC11/TiAlN/ZrOx (AlOy ZrOx)2, TC11/TiAlN/ZrOx (MgOz, ZrOx)2, TC11/TiAlCr/ZrOx (AlOy, ZrOx)2, TC11/TiAlCr/ZrOx (MgO2, ZrOx)2.Here the subscripts x,y and z are used to describe the stoichiometric ratio of the oxide films and the superscript 2 means the number of repeated cycles of alternate sputtering oxide films is 2. Thicknesses, refractivitives, transmittances and reflectivities of the films are measured by level gauge, film thickness measurement apparatus and ultraviolet-visible-near infrared spectrophotometer while thermal insulation and anti-oxidation properties of multilayers are tested by the self-designed thermal insulation test device. The main results are as follows:(1) Monolayer oxide films (ZrOx, AlOy, MgO2) and metalloid films (TiAIN, TiAlCr) are deposited on silicons, glasses and titanium alloy TC11 substrates respectively. The optimal conditions for both types of films are determined:Oxide thin films gained best integrated performances under the condition of Ar gas flow 30sccm, O2 flow 5 sccm, sputtering power 150 w, target distance 10 cm and deposition temperature 500℃.As for TiAIN films and TiAlCr films, the optical conditions are Ar gas flow 30sccm, N2 flow 30 sccm, deposition temperature 500℃ but hte optimal air pressure are 0.5 Pa and 1.0 Pa respectively. Under their optimal preparation technology conditions, the transmittance of oxide films are all beyond 90% and the refractivity of ZrOx film, AlOy film and MgOz films are 2.04,1.56 and 1.66 at the wavelength of 3139 nm respectively. The reflectivity of TiAIN film and TiAlCr film are 27.06% and 64.47% respectively.(2) Six different types of multilayer films were deposited on the TC11 titanium alloy substrates, including TC11/ZrOx(AlCy ZrOx)2, TC11/ZrOx (MgOz, ZrOx)2, TC11/TiAlN/ZrOx (AlOy, ZrOx)2, TC11/TiAlN/ZrOx (MgO2, ZrOx)2, TC11/TiAlCr/ZrOx (AlOy, ZrOx)2 and TC11/TiAlCr/ZrOx (MgOz, ZrOx)2. The morphology structure and compositions of the multilayer films are analyzed, the reflectivities of these multilayer films are tested and the averagevalusa are 61.53%,61.26%,65.46%,64.87%,71.87% and 69.98% respectively.(3) Heat-insulating properties of these multilayer films are tested by the self-designed thermal insulation test device under the condition of Furnace temperature 650℃. the results indicate that the central temperature of the back of TC11 sample without reflective multilayers is 325℃ while the central temperature of the back of TC11 sample with reflective multilayers is between 260℃-275℃. After period heat insulation test 5 times, the central temperature of the back of the uncoated TC11 sample, TC11/ZrOx (AlOy, ZrOx)2 sample and TC11/ZrOx (MgO2, ZrOx)2 sample increase to 346℃,304℃ and 311℃ respectively, which means the heat insulation effect deceases after period heat insulation test, and their reflectance also show a decreasing trend.(4) The anti-oxidation study was carried out on TC11/TiAlN/ZrOx(AIOy, ZrOx)2 and TC11/TiAlN/ZrOx(MgO2, ZrOx)2 multilayer films at 750℃, and it was also carried out on TC11/TiAIN/ZrOx(AlOy, ZrOx)2 and TC11/TiAlN/ZrOx(MgOz, ZrOx)2 multilayer films at 850℃. The results show that multilayer films can have good protection for titanium alloy substrate under the two kinds of temperature with formations of the thinner oxide layer. Besides, alumina membrane film shows better antioxidant property than the Sample with magnesium oxide film, which can be explained by the mismatch of expansion coefficient between magnesium oxide film and the substrate, leading to the peeling of film. |
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