【作者】 秦振华；

【导师】 吕书林； 郭威；

【作者基本信息】 华中科技大学 ， 材料工程， 2020， 硕士

【摘要】 Ti非晶合金独特的长程无序结构使其具有高比强度、大弹性极限、较好耐腐蚀等优异性能,在航空航天、生物医疗等领域具有潜在的应用价值。但Ti基非晶合金玻璃形成能力较低及其室温脆性断裂特征限制了它的应用。为了改善其室温塑性,研究者们通过引入第二相来制备非晶复合材料。B2相增强Ti非晶复合材料不但塑性变形能力较高,而且由于B2相在变形过程中发生的马氏体相变使其具有明显的加工硬化现象,这消除了非晶合金应变软化缺陷。但析出的B2相尺寸较大且分布不均,不利于进一步提高其力学性能。元素Ta和Mo作为亚稳B2相稳定化元素,可同时改善基体的玻璃形成能力（GFA）、改变微观组织结构,提高其室温塑性。本文选用具有B2相析出能力的Ti基非晶合金复合材料作为基体合金,通过分别添加0-3%原子百分比的元素Ta和Mo,详细研究了元素微添加后的复合组织及性能的变化,以及添加元素含量对组织及性能的影响规律。利用X射线衍射（XRD）、扫描电子显微镜（SEM）分析元素Ta和Mo的添加对Ti基块体非晶复合材料微观组织结构的影响。结果表明,随着Ta含量增加,B2相由片状分布变为球形颗粒状分布,B2相体积分数减小,非晶相体积分数增加。而随着Mo含量增加,除了B2相外还有其他结晶相析出。利用差示扫描量热仪（DSC）分析了元素Ta和Mo的添加对Ti基块体非晶复合材料的玻璃形成能力和热性能的影响。结果表明,随着Ta含量增加,块体非晶复合材料及全非晶薄带过冷液相区热稳定性和玻璃形成能力均有所提高,根据相关公式计算的等效原子尺寸差异（δ）、混合焓(ΔH_mix)以及等效电负性差异（Δχ）计算结果,等效原子半径尺寸差异δ和负的混合焓ΔH_mix在减小,但电负性Δχ在增加,电负性Δχ的提高会增加原子间的吸引力,形成一些原子对,抑制了合金熔体凝固时原子的扩散,有利于非晶的形成,故玻璃形成能力的提升主要是由于电负性的增加。然而Mo的添加却降低了玻璃形成能力,根据电子判据Δh的计算结果,是由于Δh的减小导致。利用电子万能试验机（Zwick）进行单轴室温压缩试验。结果表明,随着Ta含量增加,块体非晶复合材料塑性降低,但屈服强度明显增加,这与非晶相的体积分数增加有关。更多还原

【Abstract】 Due to its unique long-range disordered structure,Ti-based amorphous alloy has excellent properties such as high specific strength,large elastic limit,good corrosion resistance,so it has potential application values in aerospace,biomedical and other fields.However,the weak glass-forming ability and the room-temperature brittleness of Ti-based amorphous alloys limit its applications.In order to improve their plasticity at room temperature,researchers have prepared amorphous composites by introducing a second phase.Not only is the plastic deformability of Ti amorphous composites enhanced by B2 phase,but also the pronounced work-harding phenomenon can be observed because of the the martensitic transformation of B2 phase during the deformation,which eliminates the work-softening effect of amorphous alloy.But the precipitated B2 phases are large in size and unevenly distributed,which is not conducive to improving further improving its mechanical properties.Ta and Mo,which can be used as stabilizers of metastable phase B2,can improve the glass forming ability（GFA）,change the microstructure and increase the room-temperature plasticity.In this paper,Ti-based amorphous alloy composites with the precipitation ability of B2 phase were selected as the matrix alloy.By adding Ta and Mo with 0-3%atomic percentage respectively,the changes of the composite structure and properties after minor additions and the influence of added elementary content on the microstructure and properties were studied in detail.By using X-ray diffraction（XRD）and scanning electron microscope（SEM）,the effect of Ta or Mo minor addtions on microstructure of Ti-based bulk metallic glass composite have been discussed.The results show that,with increasing Ta content,the distribution and morphology of the cubic B2 phase have been changed from big platelike distribution to spherical granular distribution,with the volume fraction of B2phase decreasing and the volume fraction of amorphous phase increasing.But with minor addtions of Mo,the crystal precipitates have not only B2 phase,but also other crystal phase.It has been studied about the effects of Ta or Mo minor addtions on the glass-forming ability（GFA）and thermal properties of Ti-based bulk metallic glass composite by using differential scanning calorimetry（DSC）.The results show that with increasing Ta content,the thermal stability of the supercooled liquild and the GFA of Ti-based bulk metallic glass composite and the whole amorphous thin ribbons have been improved.According to the calculation results of equivalent atomic size differences（δ）,mixing enthalpies(ΔH_mix)and equivalent electronegativity differences（Δχ）,the negative mixing enthalpies(ΔH_mix)and equivalent atomic radius size differences（δ）are decreasing,but the electronegativity（Δχ）is increasing.The improvement of electronegativity,which can increase the attraction between atoms,form some atomic pairs and inhibit the diffusion of atoms during the solidification of alloy melt,will facilitate the formation of amorphous alloy.So the improvement of glass-formation ability is mainly due to the increase of electronegativity.But its GFA of the amorphous thin ribbons by minor addtions of Mo has been decreased.According to the calculation results of the electronic criterionΔh,it is caused by the decrease ofΔh.The compression tests at room temperature by the electronic universal testing machine have indicated that,with increasing Ta content,Ti-based bulk metallic glass composites have showed a lower plasiticity,but the yield strength increases obviously.This is related to the increase of the volume fraction of the amorphous phase.更多还原