【作者】 邢辉；

【导师】 孙坚；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 博士

【摘要】 本文利用透射电子显微术研究了两种钛合金: TNTZO合金（Ti-23Nb-0.7Ta-2Zr-1.2O at.%）和Ti-Mo合金的微结构,并结合理论计算对TNTZO合金的塑性变形机制进行了分析验证,最后采用电子能量损失谱研究了Ti-Mo合金中各相的模量。具体工作分为以下两个部分:一、TNTZO合金的形变微结构及塑性变形机制的研究本文首先通过理论计算证明,TNTZO合金中位错的可动性很高,易于在合金中开动和滑移。EBSD和TEM分析表明冷旋锻TNTZO合金具有沿旋锻轴向的<110>丝织构,因此冷旋锻TNTZO合金中所观察到的由细小纤维状组织交织而成的大理石纹状组织产生于体心立方金属在张应力主导的外加应力下沿<111>{110}, {112} or {123}位错的双滑移或多滑移导致的晶粒面应变方式的变形。[100]和[111]晶带轴方向的高分辨电子显微分析表明冷旋锻TNTZO合金中存在着柏氏矢量为1/2<111>的位错;不同变形量压缩变形的TNTZO合金的衍衬分析也表明合金塑性变形缺陷主要是1/2<111>位错。退火TNTZO合金中很容易观察到位错阵列和亚晶的存在,可以推测这些位错来源于塑性变形过程。用高分辨透射电镜在塑性变形后的TNTZO合金中进一步观察到<111>{112}机械孪生和应力诱导ω相变,ω相和β基体的位向关系是, ,惯习面是,这不同于热诱导ω相的惯习面。机械孪生和应力诱导的ω相变都是由{112}面上<111>方向的剪切应力诱发的。<111>{112}机械孪生和应力诱导的ω相变的形成可以用位错机制来解释。最后采用第一性原理对不同Nb含量钛合金的不稳定层错能分别进行了理论计算,验证了当电子浓度趋于4.2时,单位位错可以分解产生为1/12<111>或1/6<111>分位错,易于形成孪晶和ω相。二、Ti-Mo合金的相组成、结构和弹性模量的测定本文首先利用透射电镜研究了Mo含量分别为6⁹%的Ti-Mo合金在固溶处理后的相组成和微结构:Ti-9%Mo中的相组成为β、α"和ω相,Ti-8%Mo中的相组成为β、α"相,Ti-7%Mo和Ti-6%Mo中的相组成均为α′、α"相;α"相的点阵常数与合金成分有关;α"相和β基体的位向关系为:[100]_β// [100]_α", ;α"相内存在{111}_α"型孪晶;非热ω相和β基体之间的位向关系为:。其次用电子能量损失谱测量了同一Ti-8%Mo合金中β和α"两种不同相的模量,结果显示α"相的弹性模量比β相高19%;还测量了Mo含量分别为8²0%的Ti-Mo合金中β相的模量,结果显示不同Mo含量的合金中β相的模量随Mo含量的增加呈升高趋势。最后利用电子能量损失谱测量了Ti-8²0%Mo合金中β相的Ti L_2,3边的强度。结果显示随着Mo含量的增加,Ti元素L_2,3电离峰的强度逐渐降低,这说明Ti原子3d轨道中空穴数减少,电子数增多, Ti、Mo原子间结合力增强,合金稳定性升高,因此β相的模量也随之增加。这为低模量Ti-Mo合金的设计提供了一种思路:尽可能选择低Mo含量,并在避免α"相的生成时获得单相β相。更多还原

【Abstract】 In this dissertation, the microstructure of TNTZO （Ti-23Nb-0.7Ta-2Zr-1.2O at. %） alloy and Ti-Mo alloy was investigated by Transmission Electron Microscopy （TEM）. Then integrated with calculation, the mechanism of plastic deformation in TNTZO alloy was theoretically analyzed. Additionally a new method to measure modulus of materials by means of Electron Energy Loss Spectrum （EELS） was discussed with Ti-Mo alloy as sample. Specific study mainly included two parts as follows:Ⅰ. Study on the microstructure and mechanism of plastic deformation in TNTZO alloyThe elastic property and structure of dislocation in Gum Metal are investigated by anisotropic elastic theory and high-resolution transmission electron microscopy （HRTEM）. The results show that the elastic energy coefficients for the 1/2<111> perfect dislocations nearly equal to zero as the shear modulus along <111>{110}, {112}, {123} when the valence electron number e/a reaches 4.2, which implies a low intrinsic critical resolved shear stress for dislocation glide. HRTEM observations further revealed 70.53°dislocations in Gum Metal after severe cold working. The substantial plastic deformation is considered to originate from the conventional dislocation mechanism, rather than from the dislocation-free mechanism in Gum Metals.{112}<111> mechanical twinning and stress-induced omega transition were further observed by high-resolution transmission electron microscope in TNTZO after deformation. The orientation relationships between theωphase andβparent matrix are and , and the habit plane of for the stress-inducedωtransition is different from that of often observed for the thermalωtransition. Both mechanical twinning andωtransition arise from the shear along <111>{112}. A dislocation mechanism for mechanical twinning and stress-inducedωtransition was discussed additionally.Ⅱ. Study on the phase composition、microstructure and measurement of elastic modulus in Ti-Mo alloyThe phase composition and microstructure of Ti-Mo alloy （with Mo content about 6⁹% respectively） after solution treatment was firstly investigated: The lattice constants ofα" phase varied linearly with Mo content; orientation relationships betweenα" andβparent matrix are [100]_β// [100]_α" and ;α" type twinning exits inα" phase; orientation relationships between nonthemalωphase andβparent matrix are , and .Sequentially a new method to measure micro modulus was discussed. The modulus of differentα" and in Ti-8%Mo alloy was measured and a change law about modulus ofβphase with Mo content in three alloys （Ti-8²0%Mo）was expected to obtain. The results show the elastic modulus ofα" phase is higher than that ofβphase by 19% in same alloy and modulus ofβphase of different alloys increased with higher Mo content. Finally Ti L2,3 edge intensity ofβphase in Ti-8²0%Mo alloy was measured using EELS. The results show the ionization peak intensity of Ti L2,3 decreased gradually due to hybrid between d-orbits of Ti and surrounding Mo atoms.更多还原