【作者】 孙民；

【导师】 柳林；

【作者基本信息】 华中科技大学 ， 材料学， 2005， 硕士

【摘要】 本论文利用X 射线衍射分析仪（XRD）、光学显微系统（OM）、扫描电子显微镜（SEM）及能谱分析仪（EDX）、透射电子显微镜（HRTEM）、示差扫描量热仪（DSC）、差热分析仪（DTA）、电液伺服万能材料试验机和电化学设备等实验手段系统研究了不同添加量的Nb、Ta 元素替代Zr 后对Zr₆₅Cu_17.5Ni₁₀Al_7.5 大块非晶合金的结构、热稳定性、晶化行为、压缩力学性能及电化学行为的影响。采用电弧熔炼/水冷铜模吸铸法制备出直径3mm 的Zr_65-xCu_17.5Al_7.5Ni₁₀Mx （M=Nb, Ta） （x=0¹0at%）块体合金。XRD 和金相实验结果表明,含有少量Nb 和Ta 的合金基本为单一非晶相,而较高Nb、Ta 含量的合金则为非晶合金基复合材料。选择不同添加元素和不同添加量形成的非晶合金基复合材料中析出的晶体形态不同。DSC 和DTA 的实验结果表明,Nb 和Ta 的添加都在一定程度上降低了合金过冷液相区热稳定性。在添加相同含量的情况下,含Ta 合金的热稳定性高于含Nb 合金。少量Nb 和Ta 的添加导致合金的晶化模式由单步晶化变为多步晶化。同时,随着Nb、Ta 含量的增加,合金的晶化潜热ΔH 值亦逐渐降低。首次在Zr₆₅Cu_17.5Al_7.5Ni₁₀大块非晶合金中用Nb、Ta 元素取代少量的Zr 元素获得了二十面体准晶相,并发现添加元素在准晶相和紧邻非晶基体相中的含量不同,而且所得二十面体准晶相的晶面间距随着Nb 或Ta 含量的增加而减小。压缩力学性能结果表明,适量Nb 和Ta 的添加均能显著提高Zr₆₅Cu_17.5Al_7.5Ni₁₀合金的塑性和强度。其中,Zr₆₀Cu_17.5Al_7.5Ni₁₀Nb₅大块非晶合金具有最大的塑性应变量和较高的强度,达到6%和1741MPa; 而Zr₅₅Cu_17.5Al_7.5Ni₁₀Ta₁₀非晶合金基复合材料则具有最高的强度及较高的塑性应变量,两者的值分别为1920MPa 和4%。分析认为,Zr₆₀Cu_17.5Al_7.5Ni₁₀Nb₂ 等“塑性”大块非晶合金与Zr₅₅Cu_17.5Al_7.5Ni₁₀Ta₁₀ 非晶合金基复合材料可能以不同的方式影响剪切带行为进而提高材料的整体塑性。电化学实验结果表明,Nb 和Ta 的添加能显著提高Zr 基大块非晶合金在0.3N 的NaCl 水溶液中的临界点蚀电位。由于相界面的存在,非晶基复合材料的抗点蚀能力低于含Nb 或Ta 量较低的大块非晶合金。其中,Zr₆₀Cu_17.5Al_7.5Ni₁₀Nb₅大块非晶合金的钝化电流密度比1Cr18Ni9Ti 不锈钢低了三个数量级,而点蚀电位则高了0.343V。更多还原

【Abstract】 In this dissertation, the effect of substitution of Zr with Nb and Ta on structure, thermal stability, crystallization behavior, compressive mechanical and corrosion properties of the as-cast Zr₆₅Cu_17.5Ni₁₀Al_7.5 bulk metallic glass were investigated using X-ray diffraction （XRD）, optical microscopy （OM）, scanning electron microscopy （SEM） coupled with energy dispersive X-ray detector （EDX）, differential scanning calorimetry （DSC）, differential thermal analysis （DTA）, mechanical testing system, high resolution transmission electron microscopy （HRTEM） and electrochemical polarization.. Bulk Zr_65-xCu_17.5Al_7.5Ni₁₀M_x （M=Nb, Ta） （x=0¹0at%） alloys with a diameter of 3mm were prepared by copper mold casting. XRD patterns and SEM observation show that the substitution of Zr with a small amount of Nb or Ta does not change the amorphous nature of obtained alloys. However, if Nb or Ta content reaches a certain lever, bulk metallic glass matrix composites containing crystalline phases will be formed. The morphologies and amount of the precipitates in the amorphous matrix varies with the content of Nb or Ta. DSC and DTA analyses reveal that the thermal stability of Zr₆₅Cu_17.5Al_7.5Ni₁₀M_x （M=Nb, Ta） decreases with the increase of Nb or Ta content. For the same content of Ta and Nb, the Ta-bearing alloy exhibits a higher thermal stability as compared to the Nb-bearing alloy. Moreover, the addition of Nb or Ta changes the exothermic mode of the base BMG from single stage to multiple stages. In addition, the enthalpy ?H for crystallization decreases with the increasing Nb or Ta concentration. It is verified in the first time that the first-stage exothermic reaction for alloys containing 2at% and 5at% Nb or Ta corresponds to the formation of icosahedral quasicrystals, and the following ones to the phase transformation of the quasicrystals into the stable phase Zr₂Cu compound. Besides, composition analysis on partially quasicrystallized samples demonstrates that Nb mainly located in quasicrystals, indicating Nb promote the formation of quasicrystals. Furthermore, the quasilattice distance of the quasicrystal varied with different Nb or Ta contents. Study on the compressive mechanical behavior and fracture feature reveal that the plasticity and strength of the base alloy are enhanced by the addition of appropriate amount of Nb and Ta. Among the alloys obtained, the Zr₆₀Cu_17.5Al_7.5Ni₁₀Nb₅ bulk metallic glass exhibits the largest plasticity with a value of 6% and superior strength of about 1741MPa. On the other hand, the Zr55Cu17.5Al7.5Ni10Ta10 bulk metallic glass matrix composite exhibits the highest strength of 1920MPa and distinct plasticity of about 4%. It is believed that the ductile bulk metallic glasses （for example, Zr60Cu17.5Al7.5Ni10Nb2） may follow a different deformation mechanism from the Zr55Cu17.5Al7.5Ni10Ta10 bulk metallic glass composite as far as the improvement in general plasticity is concerned. In some cases, the crystalline particles gained in the metallic glass matrix composite are too small for efficient interaction with shear bands, and ther is no improvement of the mechanical properties compared to the monolithic base glass. The corrossion behavior of Zr-Cu-Al-Ni-Nb/Ta alloys was examined by electrochemical polarization measurements in 0.3N NaCl solution at 20℃. It is found that the addition of Nb or Ta could effectively increase the pitting potentials of the base bulk metallic glass. However, the pitting potential decreases once crystalline phases are formed when Nb or Ta has reached a certain level due to that the interfaces between crystalline phase and amorphous matrix can be easily attacked during anodic polarization. It is particularly pointed out that the Zr60Cu17.5Al7.5Ni10Nb5 bulk metallic glass exhibits the highest critical pitting potential and lowest passive current. The corrosion resistance of the BMGs in the present study is much better than 1Cr18Ni9Ti stainless steel.更多还原