层状结构TiAl基复合材料合成机制与性能研究
发布时间：2018-12-13 10:50
【摘要】：Ti Al基合金作为综合性能优异的新型结构材料可满足航空航天超音速飞行器及汽车发动机对结构减重和高温强度的双重要求。然而Ti Al基合金室温塑性低,成形能力差,传统热轧制方法制备Ti Al基板材相当困难。本文通过设计层状结构和引入Ti B晶须增强相提高Ti Al板材综合力学性能。本文将纯Ti箔和原位自生的Ti Bw/Ti复合材料箔分别与纯Al箔交替堆叠,通过真空热压制备出Ti-Al叠层和(Ti Bw/Ti)-Al叠层,并通过反应热处理合成出具有层状结构的Ti Al板材和Ti Bw-Ti Al复合材料板材。分析了叠层在热处理过程中的相组成及相转变规律,研究了层状结构形成机理,对层状结构Ti Al板材和Ti Bw-Ti Al复合材料板材进行力学性能测试,揭示了强韧化机制与断裂机理。将真空热压获得的界面结合良好的Ti-Al叠层进行660oC的低温反应退火,Ti原子和Al原子不断进行互扩散,生成Ti Al3相,并且Ti Al3相的生长遵循直线生长动力学模式。低温反应退火2h后,材料中的Al完全消耗,获得Ti-Ti Al3叠层。由于低温反应退火时Ti与Al反应扩散速率不同,组织中存在Kirkendall孔洞,生成相Ti Al3为疏松多孔结构。将叠层继续进行1200oC/35MPa/2h高温反应退火,材料中孔洞得到弥合,且Ti和Al继续扩散,反应生成Ti Al和Ti3Al,由于材料成分不均匀,存在贫Al区和富Al区。随着热处理的进行,贫Al区转变为全层片(α2-Ti3Al/γ-Ti Al)层,富Al区形成等轴γ-Ti Al层,最终制备出具有双晶结构的层状Ti Al板材。由于(Ti Bw/Ti)-Al叠层和纯Ti-Al叠层的扩散组元一致,且厚度基本没变,因此对(Ti Bw/Ti)-Al叠层亦采用同种热处理工艺,制备了具有层状结构的Ti Bw-Ti Al复合材料板材,组织由Ti Al层和Ti Bw-rich层交替组成,其中Ti Al层为全层片(α2-Ti3Al/γ-Ti Al)层和等轴γ-Ti Al层交替排列,Ti Bw-rich层为高体积分数的Ti B晶须聚集层。室温拉伸结果表明,层状结构Ti Al板材抗拉强度、室温延伸率较高,层状双晶结构可相互细化组织。层状Ti Bw-Ti Al复合材料板材由于增强相Ti Bw的存在,提高了强度。分析拉伸断口,全层片(α2-Ti3Al/γ-Ti Al)层断裂主要为穿片层断裂和沿片层断裂,等轴γ-Ti Al层主要为穿晶断裂和沿晶断裂。断裂韧性结果表明,层状结构Ti Al板材平行于热压方向的断裂韧性比垂直于热压方向的高,且Ti B晶须的引入提高了韧性。层状结构和Ti B晶须的存在增加了裂纹萌生与扩展的阻力,延长了裂纹扩展的路径,起到了增韧的目的。三点弯曲结果表明,层状结构Ti Bw-Ti Al复合材料板材室温弯曲强度升高,增强相Ti B晶须的引入可提高复合材料的弯曲强度。
[Abstract]:As a new structural material with excellent comprehensive properties, Ti Al alloy can meet the dual requirements of structural weight loss and high temperature strength of aerospace supersonic aircraft and automobile engines. However, Ti Al alloy has low room temperature plasticity and poor formability, so it is very difficult to prepare Ti Al base sheet by traditional hot rolling method. In this paper, the comprehensive mechanical properties of Ti sheet were improved by designing layered structure and introducing Ti B whisker reinforcement phase. In this paper, the pure Ti foil and the in-situ Ti Bw/Ti composite foil are alternately stacked with the pure Al foil. The Ti-Al laminates and (Ti Bw/Ti) -Al laminates are prepared by vacuum hot pressing. Ti Al sheet and Ti Bw-Ti Al composite sheet with layered structure were synthesized by reactive heat treatment. The phase composition and phase transition of laminated layers during heat treatment were analyzed. The formation mechanism of laminated structure was studied. The mechanical properties of laminated Ti Al and Ti Bw-Ti Al composite sheets were tested. The mechanism of strengthening and toughening and the mechanism of fracture are revealed. The interface obtained by vacuum hot pressing was annealed at low temperature with good Ti-Al laminates, and the Ti atoms and Al atoms were continuously diffused to form Ti Al3 phase, and the growth of Ti Al3 phase followed the linear growth kinetics model. After annealing at low temperature for 2 h, the Al in the material was completely consumed and the Ti-Ti Al3 lamination was obtained. Due to the difference of reaction diffusion rate between Ti and Al during low temperature reaction annealing, there are Kirkendall pores in the microstructure, and the formation phase of Ti Al3 is porous. The stacked layers were further annealed by 1200oC/35MPa/2h reaction at high temperature, the pores in the materials were bridged, and the Ti and Al continued to diffuse. The Ti Al and Ti3Al, formed by the reaction resulted from the poor Al region and the rich Al region due to the uneven composition of the material. With the heat treatment, the poor Al region was transformed into a 2-Ti3Al/ 纬-Ti Al) layer, and the Al rich region formed an equiaxed 纬-Ti Al layer. Finally, the layered Ti Al sheet with double crystal structure was prepared. Because the diffusion components of (Ti Bw/Ti)-Al laminates and pure Ti-Al laminates are the same, and the thickness of (Ti Bw/Ti)-Al laminates is basically unchanged, the (Ti Bw/Ti)-Al laminates are also treated by the same heat treatment process. Ti Bw-Ti Al composite sheet with layered structure was prepared. The microstructure was composed of Ti Al layer and Ti Bw-rich layer alternately, in which the Ti Al layer was arranged alternately with 伪 2-Ti3Al/ 纬 -Ti Al) layer and equiaxed 纬 -Ti Al layer. The Ti Bw-rich layer is a high volume fraction Ti B whisker aggregation layer. The tensile results at room temperature show that the laminated Ti Al sheet has high tensile strength and high elongation at room temperature, and the layered double crystal structure can refine each other's microstructure. The strength of laminated Ti Bw-Ti Al composite plate is improved because of the existence of reinforcing phase Ti Bw. By analyzing tensile fracture, the fracture of 伪 2-Ti3Al/ 纬-Ti Al) layer is mainly translamellar and along lamellar fracture, and the equiaxed 纬-Ti Al layer is mainly transgranular and intergranular fracture. The results of fracture toughness show that the fracture toughness of laminated Ti Al sheet is higher than that of perpendicular to hot pressing direction, and the toughness is improved by introducing Ti B whisker. The existence of layered structure and Ti B whisker increases the resistance of crack initiation and propagation, prolongs the path of crack growth, and plays the purpose of toughening. The results of three-point bending show that the flexural strength of laminated Ti Bw-Ti Al composites increases at room temperature, and the flexural strength of composites can be improved by the introduction of Ti B whiskers.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB333
本文编号：2376417
[Abstract]:As a new structural material with excellent comprehensive properties, Ti Al alloy can meet the dual requirements of structural weight loss and high temperature strength of aerospace supersonic aircraft and automobile engines. However, Ti Al alloy has low room temperature plasticity and poor formability, so it is very difficult to prepare Ti Al base sheet by traditional hot rolling method. In this paper, the comprehensive mechanical properties of Ti sheet were improved by designing layered structure and introducing Ti B whisker reinforcement phase. In this paper, the pure Ti foil and the in-situ Ti Bw/Ti composite foil are alternately stacked with the pure Al foil. The Ti-Al laminates and (Ti Bw/Ti) -Al laminates are prepared by vacuum hot pressing. Ti Al sheet and Ti Bw-Ti Al composite sheet with layered structure were synthesized by reactive heat treatment. The phase composition and phase transition of laminated layers during heat treatment were analyzed. The formation mechanism of laminated structure was studied. The mechanical properties of laminated Ti Al and Ti Bw-Ti Al composite sheets were tested. The mechanism of strengthening and toughening and the mechanism of fracture are revealed. The interface obtained by vacuum hot pressing was annealed at low temperature with good Ti-Al laminates, and the Ti atoms and Al atoms were continuously diffused to form Ti Al3 phase, and the growth of Ti Al3 phase followed the linear growth kinetics model. After annealing at low temperature for 2 h, the Al in the material was completely consumed and the Ti-Ti Al3 lamination was obtained. Due to the difference of reaction diffusion rate between Ti and Al during low temperature reaction annealing, there are Kirkendall pores in the microstructure, and the formation phase of Ti Al3 is porous. The stacked layers were further annealed by 1200oC/35MPa/2h reaction at high temperature, the pores in the materials were bridged, and the Ti and Al continued to diffuse. The Ti Al and Ti3Al, formed by the reaction resulted from the poor Al region and the rich Al region due to the uneven composition of the material. With the heat treatment, the poor Al region was transformed into a 2-Ti3Al/ 纬-Ti Al) layer, and the Al rich region formed an equiaxed 纬-Ti Al layer. Finally, the layered Ti Al sheet with double crystal structure was prepared. Because the diffusion components of (Ti Bw/Ti)-Al laminates and pure Ti-Al laminates are the same, and the thickness of (Ti Bw/Ti)-Al laminates is basically unchanged, the (Ti Bw/Ti)-Al laminates are also treated by the same heat treatment process. Ti Bw-Ti Al composite sheet with layered structure was prepared. The microstructure was composed of Ti Al layer and Ti Bw-rich layer alternately, in which the Ti Al layer was arranged alternately with 伪 2-Ti3Al/ 纬 -Ti Al) layer and equiaxed 纬 -Ti Al layer. The Ti Bw-rich layer is a high volume fraction Ti B whisker aggregation layer. The tensile results at room temperature show that the laminated Ti Al sheet has high tensile strength and high elongation at room temperature, and the layered double crystal structure can refine each other's microstructure. The strength of laminated Ti Bw-Ti Al composite plate is improved because of the existence of reinforcing phase Ti Bw. By analyzing tensile fracture, the fracture of 伪 2-Ti3Al/ 纬-Ti Al) layer is mainly translamellar and along lamellar fracture, and the equiaxed 纬-Ti Al layer is mainly transgranular and intergranular fracture. The results of fracture toughness show that the fracture toughness of laminated Ti Al sheet is higher than that of perpendicular to hot pressing direction, and the toughness is improved by introducing Ti B whisker. The existence of layered structure and Ti B whisker increases the resistance of crack initiation and propagation, prolongs the path of crack growth, and plays the purpose of toughening. The results of three-point bending show that the flexural strength of laminated Ti Bw-Ti Al composites increases at room temperature, and the flexural strength of composites can be improved by the introduction of Ti B whiskers.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB333
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