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Research On Preparation And Properties Of ZrO2/?Al2O3-Y2O3? Coatings Derived By Sol-gel Process On TC11 Alloy

Posted on:2018-04-01Degree:MasterType:Thesis
Country:ChinaCandidate:Y B YaoFull Text:PDF
GTID:2321330536987740Subject:Materials science
Abstract/Summary:PDF Full Text Request
TC11 titanium alloy has been widely used in aerospace field,such as air compressor wheel,blade and so on due to its advantages of high specific strength,middle temperature performance and high corrosion resistance.But with the engine thrust weight ratio increases,the compressor operating temperature is higher than the heat resistance temperature?500 °C?of TC11 alloy,and the alloy will be easily oxidized and become embrittle,thereby significantly reducing the service life of the engine blade.In order to solve this problem,the Al based coatings were prepared on TC11 alloy by sol-gel technique,and the effect of coating on the oxidation resistance at high temperature was studied systematically.ZrO2/?Al2O3-Y2O3?coating was successfully prepared on the surface of TC11 alloy by sol-gel spin coating technique.The surface of the coating was uniform and compact,with a thickness of about 10 ?m.The fitting data of the oxidation kinetics curve at 700 °C for 100 h showed that he oxidation rate of coated samples was 0.02695 mg·cm-2·h-1,which reduced the oxidation rate of the matrix by more than 90%.Although both the main components of the oxide layer were Al2O3 and rutile TiO2,but the content of Al2O3 in the oxide layer of coated sample was much higher than that of the blank sample.At the same time,the heat shock experiment at 700 °C shows that the spallation occurs in blank sample after 15 cycles,and the coating sample is up to 55 cycles.In order to further improve the thermal shock resistance of ZrO2/?Al2O3-Y2O3?coating,the TC11 alloy was treated with phosphoric acid of 30 wt.%.After sintering at 800 °C,the TiP2O7 layer formed on the surface of the alloy is metallurgical bonding with the substrate,whose porous characteristics of the surface provides favorable conditions for the sealing of the sol layer.The results of oxidation and thermal shock test at 700 °C show that the coating can not only improve the high-temperature oxidation resistance of the substrate,but also the thermal shock resistance of the composite is up to more than 85 times.The mechanism of high temperature protective coating mainly consists of the following parts.The homogeneous and dense structure characteristics of the coating reduced oxygen pressure on alloy surface and inhibit O diffusion,and the formed TiP2O7 layer not only has more excellent thermal adaptation than ZrO2,but also produced the " effect of rich Al and poor Ti " to promote the selective oxidation of Al,thus increased the high temperature oxidation resistance and thermal shock resistance.The coating can provide the long-term and effective high temperature protection for TC11 alloy,which has certain significance to improve the service life and reliability of the engine compressor blade.
Keywords/Search Tags:TC11 titanium alloy, sol-gel technology, ZrO2/?Al2O3-Y2O3? coating, weak phosphoric acid sintering process, high temperature oxidation, thermal shock
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