| High temperature titanium alloy has a wide application value in aerospace engine fields due to its advantages of low density,excellent high temperature strength and high temperature creep resistance.At present,titanium alloy components are developing towards complex,thin-walled and large-scale,which creates a huge development space for the application of cast titanium alloy.However,the cast high-temperature titanium alloy can only be widely used at 450?-500?in China,which has a significant gap with foreign countries under the application condition of 600?.Therefore,the development of cast titanium alloy which can withstand 600?has become a bottleneck restricting the development of high-speed aircraft in China.At the same time,the working conditions of aerospace engine components are very bad,which also put forward higher requirements for the oxidation resistance,wear resistance and mechanical properties.Therefore,Ti-1100 alloy is selected as the research object in this paper.The effects of Nb content(0.5,1.0,1.5,2.0 wt.%)on the microstructure,high temperature oxidation property,friction and wear property and tensile property of as cast and heat-treated Ti-1100 alloy are systematically studied.The results show that:Nb does not change the microstructure of as-cast Ti-1100 alloy.The microstructure of as-cast Ti-1100 alloy is still widmanst?tten structure with basket weave characteristic.With the increase of Nb content,the thickness of?-lamellae decreases first and then increases,and the grain size of Ti-1100-1.0Nb alloy is the smallest.With the increase of vacuum annealing temperature,the size of primary?-lamellae is becoming wider and the number of secondary?-lamellae is increasing.There are silicide precipitates in the?phase layer of high Nb(1.5 wt.%,2.0 wt.%)alloy,and the number of silicide increase with the increase of vacuum annealing temperature.Nb element can effectively improve the high temperature oxidation resistance of as-cast alloy,and the oxidation kinetics curve furrows the parabolic rule.Ti-1100-1.0Nb alloy showed the best high temperature oxidation resistance at 650?,700?and 750?,and the weight gain after 100 hours oxidation was 0.44 mg/cm2,0.54 mg/cm2 and 1.46 mg/cm2,respectively.The weight gain at 700?and 750?improved 23%and 232%,compared to that at 650?.In the process of high temperature oxidation,excessive Nb(1.5 wt.%,2.0wt.%)can promote the external diffusion of Al,Mo,Si and other alloy elements to form various oxides.High oxidation temperature and Nb content can promote the formation of Al2O3 on the oxidation surface.The Al2(Mo O4)3 oxide particles were found for the first time for Ti-1100-1.5Nb alloy oxidation at 650?and 750?.With the increase of Nb content,the room temperature wear rate of as-cast Ti-1100 alloy increases first and then decreases.The 1.5Nb titanium alloy has the worst wear performance.With the increase of wear temperature,the wear resistance of the alloy increases significantly,and the wear mechanism changes from abrasive wear,adhesive wear to oxidation wear.The high temperature friction oxide layer is mainly composed of Fe2O3 and Ti O2.After vacuum annealing at 1000?,the wear rate of titanium alloy increased by 4.7-8.1%compared with the as-cast Ti-1100-x Nb alloys,and the wear resistance decreased significantly.Nb can increase the tensile strength of as-cast Ti-1100 alloy at room temperature and high temperature,while the elongation decreases.Fracture mechanism of room temperature tensile is cleavage transgranular fracture,while that of high temperature tensile is quasi cleavage fracture and microporous aggregation fracture.The tensile strength of Ti-1100 alloy at 600?is less affected by Nb.When tensile at room temperature,the crack is easy to propagate along the direction perpendicular to the?phase;when tensile at high temperature,the crack is easy to propagate along the direction parallel to the?phase.Under the action of tensile stress,micropores tend to nucleate and grow at the?/?interface. |
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