【作者】 张雪；

【导师】 黄陆军；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2023， 硕士

【摘要】 Ti₂AlNb合金具有高比强度、低弹性模量和热膨胀系数、优异的抗蠕变性能和高温抗氧化性能。作为一种金属间化合物,Ti₂AlNb合金的塑性仍无法满足新一代飞行器的要求,限制了Ti₂AlNb合金在航空航天以及汽车发动机领域的广泛应用。针对该难题,本研究采用低能球磨+真空热压烧结的制备方法,通过Ti B₂与Ti原位自生反应形成（Ti,Nb）B增强相,制备出具有优异性能的（Ti,Nb）B/Ti₂AlNb复合材料,提高复合材料的塑性。本文以Ti₂AlNb合金为基体,Ti B₂粉末为增强相原料,采用热力学分析、烧结致密化动力学计算与实验相结合的方式探索热压烧结工艺,通过低能球磨混粉和热压烧结成功制备出了网状结构（Ti,Nb）B/Ti₂AlNb复合材料,并采用SEM、TEM、EBSD等分析方法和力学性能测试,对复合材料的组织演变机理、拉伸性能、高温蠕变性能以及变形断裂机理进行了分析和阐释。结合热力学分析、烧结致密化动力学计算及试验结果,获得最佳的热压烧结工艺参数:在1300℃/35 MPa/2 h下进行热压烧结,复合材料组织均匀,增强相反应完全,复合材料的致密度可以达到99.5%,与计算结果一致。组织分析表明（Ti,Nb）B/Ti₂AlNb复合材料组织中生成纳米级的（Ti,Nb）Bw以及沿网状边界分布的α₂相,并与基体存在特定的位向关系,随增强相含量的降低,反应越完全;网格内部的基体由O相和B2相交替分布,增强相含量的增加可以有效细化基体组织。增强相含量为0.125wt.%时,（Ti,Nb）B/Ti₂AlNb复合材料室温抗拉强度较Ti₂AlNb合金提高了9.2%,延伸率提高458%,三点弯曲测试结果显示抗弯强度、弯曲塑性和弯曲断裂功得到提高。随增强相含量降低,复合材料强度和塑性呈现先升高后降低的趋势,此复合材料相较于Ti₂AlNb合金,其抗弯强度和弯曲应变量分别提高9.3%和66.7%。对复合材料变形行为分析显示增强相的引入增大了材料变形集中程度,材料主要通过增强体载荷转移作用、细晶强化、（Ti,Nb）B准连续网状分布实现强韧化。增强相含量为0.125wt.%时,（Ti,Nb）Bw Ti₂AlNb复合材料650℃、700℃和750℃的抗拉强度分别为794.5 MPa、743.6 MPa和699.4 MPa;延伸率分别为14.1%、12.1%和12.8%;相比于合金,在保持同等强度的同时,塑性分别提高50%、42.4%和47.1%。降低测试温度发现,复合材料在500～600℃下抗拉强度比合金高,延伸率分别提高66.0%、59.8%和84.9%。（Ti,Nb）B/Ti₂AlNb复合材料在不同温度下与T合金的高温抗拉强度保持相等水平下,高温塑性得到大幅度提高,（Ti,Nb）B/Ti₂AlNb复合材料蠕变性能相较于Ti₂AlNb合金有所下降,蠕变过程主要由位错攀移控制,同时有晶界扩散机制。更多还原

【Abstract】 Ti₂AlNb alloy has high specific strength,low modulus of elasticity and coefficient of thermal expansion,excellent creep resistance and high temperature oxidation resistance.As an intermetallic compound,the plasticity of Ti₂AlNb alloy still cannot meet the requirements of a new generation of aircraft,which limits the wide application of Ti₂AlNb alloy in aerospace and automotive engine fields.In order to solve this problem,the preparation method of low-energy ball milling+vacuum hot pressing sintering was used to form（Ti,Nb）B reinforced phase by the in-situ autogenesis reaction of Ti B₂and Ti,and the（Ti,Nb）B/Ti₂AlNb composite with excellent performance was prepared to improve the room temperature plasticity of the composite.Taking Ti₂AlNb alloy as the matrix and Ti B₂powder as the raw material for the reinforced phase,this paper explores the hot pressing sintering process by combining calculation and experiment,and successfully prepares the network structure（Ti,Nb）B/Ti₂AlNb composite by low-energy ball milling powder mixing and hot pressing sintering,and analyzes and explains the microstructure evolution mechanism,tensile properties,high temperature creep properties and deformation fracture mechanism of the composite by SEM,TEM,EBSD and other analysis methods and mechanical property tests.Combined with thermodynamic analysis,sintering densification kinetic calculation and test results,the best hot pressing sintering process parameters were obtained:hot pressing sintering at 1300°C/35 MPa/2 h,the composite structure was uniform,the reinforcement phase reaction was complete,and the density of the composite could reach 99.5%,which was consistent with the calculation results.Tissue analysis showed that nanoscale（Ti,Nb）Bw andα₂phases distributed along the network boundary were generated in the tissues of（Ti,Nb）Bw/Ti₂AlNb composites,and there was a specific site relationship with the matrix,and the more complete the reaction was with the decrease of the content of the enhanced phase.The matrix inside the grid is alternately distributed by O phase and B2 phase,and the increase of enhanced phase content can effectively refine the matrix structure.When the reinforced phase content was 0.125wt.%,the room temperature tensile strength of（Ti,Nb）B/Ti₂AlNb composite was increased by 9.2%compared with Ti₂AlNb alloy,and the elongation increased by 458%,and the three-point bending test results showed that the bending strength,bending plasticity and bending fracture work were improved.Compared with Ti₂AlNb alloy,the strength and plasticity of the composite increased by 9.3%and 66.7%,respectively.The analysis of the deformation behavior of the composite showed that the introduction of the reinforced phase increased the deformation concentration of the material,and the material was mainly strengthened and toughened by the reinforcement load transfer,fine grain strengthening,and（Ti,Nb）B quasi-continuous network distribution.When the reinforced phase content was 0.125wt.%,the tensile strength of（Ti,Nb）Bw/Ti₂AlNb composites at 650°C,700°C and 750°C were 794.5MPa,743.6MPa and 699.4MPa,and the elongation was 14.1%,12.1%and 12.8%,respectively.Compared with the alloy,while maintaining the same strength,the plasticity is increased by 50%,42.4%and 47.1%,respectively.Reducing the test temperature,it was found that the tensile strength of the composite material was higher than that of the alloy at500～600°C,and the elongation increased by 66.0%,59.8%and 84.9%,respectively.The creep properties of（Ti,Nb）B/Ti₂AlNb composites are greatly improved compared with Ti₂AlNb alloys when the high-temperature tensile strength of Ti₂AlNb alloys is maintained at the same level at different temperatures,and the creep properties of（Ti,Nb）B/Ti₂AlNb composites are reduced compared with Ti₂AlNb alloys,and the creep process is mainly controlled by dislocation climbing,and there is a grain boundary diffusion mechanism.更多还原