【作者】 古向阳；

【导师】 刘燕萍；

【作者基本信息】 太原理工大学 ， 机械设计及理论， 2011， 硕士

【摘要】 Ti-Al系合金具有低密度,良好的高温强度、抗蠕变和抗氧化能力,其密度只是Ni基高温合金的一半,因而常用作Ni基高温合金低温段的候选材料,是航天、航空飞行器理想的新型高温结构材料。但由于其硬度低,耐磨性较差,在用作滑动部件(如活塞锁,连杆轴及导杆等)时,容易与对磨材料粘着产生磨损,限制了其应用范围。很多学者在实验上对如何改善Ti-Al系合金的硬度和耐磨性都进行了研究,并取得了一定的成功,如Cr的合金化作用对硬度、耐磨性等的改善起到了主要作用等。但其微观强化机理和微观扩散原理目前尚不清楚,因此如何从原子层次上对其进行模拟并加以解释显的尤为重要。本文采用第一性原理对含Cr、V的Ti-Al系合金进行了研究。首先,基于第一性原理研究了合金元素Cr、V对Ti-Al系合金电子结构的影响,计算了含Cr、V的Ti-Al系合金的总能量、形成能、给合能和力学性能,从理论上解释了在Ti-Al系合金中固溶合金元素Cr后其性能得到改善的原因,并通过电荷密度和态密度的分布探讨Cr、v对Ti-Al系合金的微观作用机理。研究结果表明：合金元素Cr、V在Ti4Al4和Ti4Al12中固溶时都占据了Ti原子的位置,Cr固溶于Ti4Al4和Ti4Al12后的结构稳定性随着Cr含量的增加而增加；V固溶于Ti4Al4和Ti4Al12后的结构稳定性随V含量的增加而减小,而实际实验中固溶的V是微量的,因此微量V的溶入对复合化合物的稳定性影响不明显；微量的合金元素Cr、V就能较大幅度地提高Ti-Al系合金的力学性能(包括杨氏模量E、切变模量G和体模量B),而材料的强度与切变模量G和杨氏模量E密切相关,G和E的值越大,材料的强度越高,耐磨性能越好。其次,本文还对搭建的Ti-Al系合金(100)面进行晶体结构优化,系统地研究Cr、V在Ti-Al系合金(100)面中的扩散情况,并从电子结构角度分析了Cr、V在Ti-Al系合金中的强化机理,从理论上解释了表面Cr、V合金化后Ti-Al系合金性能得到改善的原因。当单个Cr或V原子向Ti5Al5和Ti5Al15中扩散的时候,其优先占据第二层Ti原子的位置,且占据第二层Ti原子时的结构稳定性最好；当两个Cr或V原子向Ti5Al5和Ti5Al15中扩散的时候,它们优先同时占据第二层和第三层Ti原子的位置,且同时占据第二层和第三层Ti原子时的结构稳定性最好。并通过分析得出：在Ti-Al系合金中添加合金元素Cr后,使Cr3d轨道上的电子、Al3p轨道上的电子和Ti3d轨道上的电子相互杂化,结合能力变强；添加合金元素V后,使V3d轨道上的电子、Ti3d轨道上的电子和Al3p轨道上的电子相互杂化,结合能力增强。更多还原

【Abstract】 Ti-Al alloys is deal new-type heat structural material in aerospace and aviaTion aircraft, being used as Ni base superalloy low-temperature segment of the candidate materials, because of its properTies of low density department, good contravariance and oxidaTion resistance etc. But it is easy to sTick with grinding materials produced wear and limits its applicaTion scope when it is acted as sliding parts(such as the piston lock, the connecTing rod shaft and guide bar). The reason is its properTies of low hardness and poor wear resistance. Much research was studied on how to improve the Ti-Al alloy of department of hardness and abrasion resistance in the experiment, and has been achieved some successes. For example, Cr’s alloying effect plays a main role to improve Ti-Al alloy of department of hardness and abrasion resistance. But its microscopic strengthening mechanisms and microcosmic diffusion principle is unclear. So how to simulate and expound this phenomenon from its atomic level is parTicularly important.The research of Ti-Al alloys with Cr、V addiTions was studied using the first-principle. Firstly, the electronic structures of Ti-Al alloys with Cr、V addiTions were studied using the first-principle. The total energy, formaTion energy, cohesive energy, the charge density and Density of statess were calculated, and explained the reason that the mechanical property was improved after infiltraTion chromium in Ti-Al alloys in terms of theory. The microscopic mechanism of Ti-Al alloys with Cr and V was explored through the charge density and Density of states distribuTion. The results of the study indicate that alloying element Cr and V occupied Ti atomic posiTion when being doped in Ti4Al4 and Ti4Al12. As the alloying element Cr content increasing, the structure stability increased after Cr was doped in Ti4Al4 and Ti4Al12. But it decreased after V was doped. The doping of V is trace in actual experiment, so the influence of the structure stability of composite compounds is not obvious. The department of mechanical properTies of Ti-Al alloys that included Shear modulus G, Young’s modulus E and Body modulus B were greatly improved by the trace of alloying element Cr and V. The material of strength is closely related to Young’s modulus E and Shear modulus G, the bigger of the value of G and E, the strength of the material and the better of the wear-resisTing performance.Secondly, the crystal structure opTimizaTion of the building of the Ti-Al alloy (100) plane was also studied. The department of the diffusion of the Ti-Al alloy (100) plane with Cr and V was systermaTically studied. The strengthening mechanisms of Ti-Al alloy with Cr and V were analyzed from the electronic structure. The reason of the properTies improving of Ti-Al alloy with Cr and V was explained in theory. The alloying element Cr or V priority occupied second Ti atomic posiTion when it doped in Ti5Al5 and Ti5Al15, and their structures’ stability was best. The two alloying elements Cr or V preferred simultaneously occupied the second and third floor Ti atomics’posiTion when their doped in Ti5Al5 and Ti5Al15, and their structures’stability was best. The reason through analyzing is that the addiTion of Cr in the alloys enhanced reciprocal hybridizaTion of Cr(3d)、Al(3p) and Ti(3d), while V in the alloys enhanced reciprocal hybridizaTion of V(3d、Ti(3d) and Al(3p), and the alloys’binding capacity increased.更多还原