【作者】 王珊珊；

【导师】 康福伟；

【作者基本信息】 哈尔滨理工大学 ， 材料学， 2018， 硕士

【摘要】 Ti Al基合金具有密度小、比强度高、比刚度高等优良特性而备受关注,成为具有突出研究及应用价值的新一代轻质高温结构材料,在高超音速飞行器及热防护材料等方面应用前景广泛。然而其与生俱来的本征脆性及高温氧化等问题限制了它在大尺寸优异薄板等材料方面的应用。粉末冶金特别是预合金粉末技术可消除铸造缺陷,为制备薄板提供优异原材料,因此,获得高纯低氧球形气雾化粉末和制备高性能粉末冶金板材是进一步扩大Ti Al基合金应用范围的关键。本文以气雾化工艺制备的Ti43.5Al5Nb1V1Y预合金粉末为原料,采用真空热压烧结进行致密化。利用金相显微镜（OM）、激光粒度分析仪、配有BSE模式及EDS能谱仪的扫描电子显微镜（SEM）、透射电镜（TEM）及X射线衍射仪等分析方法,对气雾化工艺制备的预合金粉末颗粒、真空热压烧结组织及高温变形组织进行表征分析,利用Gleeble-3500热物理模拟试验机在变形温度1050℃-1200℃、应变速率0.001 s^-1-0.5 s^-1及变形量50%的条件下对该合金进行等温热圧缩模拟实验。研究结果表明,气雾化工艺制备的Ti43.5Al5Nb1V1Y预合金粉末颗粒细小,球形度较高,真空热压烧结的Ti43.5Al5Nb1V1Y合金组织致密,表面形貌平整无孔洞,微观组织细小均匀,内部形貌呈近γ组织特征,主要由γ相、α2相及YAl2相组成。流变应力变化与变形温度T及应变速率ε（5）分别成反比例和正比例关系,流变应力曲线初期均呈现明显的加工硬化特征,相比于其他合金,该合金的动态再结晶曲线特征更明显。根据Arrhenius关系,计算材料常数α、β、n、A及Q值,构建真空热压烧结Ti43.5Al5Nb1V1Y合金的本构方程。真空热压烧结Ti43.5Al5Nb1V1Y合金的热变形激活能为320.861 k J/mol,构建的峰值应力本构关系模型实验值与计算值吻合良好。Ti43.5Al5Nb1V1Y合金塑性变形的主要软化机制是动态再结晶,变形主要取决于γ相,在所有变形条件下均出现明显的DRX,动态再结晶γ晶粒的尺寸与变形温度的变化成正比、与应变速率的变化成反比,Ti43.5Al5Nb1V1Y合金的失稳主要方式为开裂,基于Prasad失稳准则和DMM模型构建真应变为0.5时Ti43.5Al5Nb1V1Y合金的热加工图,温度1080℃-1200℃、应变速率0.0015 s^-1-0.04 s^-1是变形的理想区域。更多还原

【Abstract】 TiAl-based alloys have drawn increasing attention due to their excellent properties,such as low density,high specific strength,high specific stiffness,etc..They have developed into a novel candidate of light high temperature structural materials in a wide array of applications,like hypersonic aircraft and thermal protection materials.However,inherent brittleness and high temperature oxidation of TiAl-based alloys have extremely limited their applications as large size excellent thin sheets,and so on.The powder metallurgy,especially the pre-alloyed powder technology,can eliminate casting defects and provide excellent raw materials.Therefore,obtaining high-purity low-oxygen spherical gas atomized powder and preparing powder metallurgy sheets with superior performance would be the key to further expand the application range of TiAl-based alloys.In this paper,Ti43.5Al5Nb1V1Y pre-alloyed powders,which were densified by vacuum hot-pressing sintering,were prepared by gas atomization process.OM,laser particle size analyzer,SEM with BSE mode and EDS spectra,TEM,X-ray diffraction and other analytical methods were used to characterize and analyze the pre-alloyed powders,Ti43.5Al5Nb1V1Y alloys after the vacuum hot-pressing sintering and Ti43.5Al5Nb1V1Y alloys after high temperature deformation.Isothermal hot compression simulation tests for Ti43.5Al5Nb1V1Y alloys were carried out at the conditions of deformation temperature of 1050 ℃-1200 ℃,strain rate of 0.001 s^-1-0.5 s^-1 and deformation of 50 % by Gleeble-3500 thermal physical simulation tester.The results show that the Ti43.5Al5Nb1V1Y pre-alloyed powders prepared by the gas atomization process have fine particle size and high sphericity.The compact macrostructure of Ti43.5Al5Nb1V1Y alloy prepared by vacuum hot-pressing sintering is dense and the surface morphology is flat without pores.The microstructure is uniform and the internal microstructure is nearly γ microstructure characteristics,mainly composed of the γ phase,α2 phase and YAl2 phase.The changes of flow stress were inversely proportional and proportional to the deformation temperature and strain rate,respectively.The initial strain flow curves show obvious work hardening characteristics,and compared to other alloys,the dynamic recrystallization curve features of the alloy were more obvious.According to the Arrhenius relation,the material constants α,β,n,A and Q are calculated and the constitutive equation of the vacuum hot-pressing sintering Ti43.5Al5Nb1V1Y alloy is established.The thermal deformation activation energy of the vacuum hotpressing sintering Ti43.5Al5Nb1V1Y alloy is 320.861 k J/mol.The experimental data of the constitutive model of peak stress are in good agreement with the calculated values.The Ti43.5Al5Nb1V1Y alloy deformation depends mainly on the γ phase.The dynamic recrystallization is the main softening mechanism of the Ti43.5Al5Nb1V1Y alloy.Dynamic recrystallization γ grain size is proportional to the change of deformation temperature and inversely proportional to the change of strain rate.Cracking is the main instability method for Ti43.5Al5Nb1V1Y alloy.When true strain is 0.5,the hot processing map of Ti43.5Al5Nb1V1Y alloys is based on the Prasad instability criterion and Dynamic Material Model,and the ideal deformation conditions are deformation temperatures of 1080 ℃-1200 ℃ and strain rates of 0.0015 s^-1-0.04 s^-1.更多还原