【作者】 崔晓；

【导师】 祖方遒；

【作者基本信息】 合肥工业大学 ， 材料加工工程， 2013， 博士

【摘要】 鉴于大块非晶合金（BMGs）的优异性能及应用前景，近半个世纪以来，人们在不断地尝试开发新的合金系统及新的制备工艺，并从非晶合金固体—深过冷液相—平衡与过热液相的物理性质与结构角度探索玻璃形成能力（GFA）的本质。尽管在GFA判据及成分选择的经验准则方面取得了瞩目的进展，对玻璃形成能力本质的认识及新型非晶合金设计准则上仍需不断求索。本文以多组具有不同GFA的多元合金系（CuZr-基、LaCe-基、La-基等）为研究对象，以电阻法、内耗温度/频率谱等为主要手段探索了诸多合金升、降温过程电子输运特性、内耗性质，并以所获得的现象和规律为依据，探讨了这些特性与玻璃形成能力的依存关系和内在本质，进而从新的角度尝试提出了GFA判据及非晶合金设计准则，并进一步验证了其有效性。此外，本文以实验揭示了CuZr二元非晶合金熔体发生温度诱导结构转变的可能；据此，探索了不同状态熔体GFA的差异，以及所获非晶样品的晶化行为和产物的变化；对此，论文还依据相竞争的认知探讨了液-固及固态转变过程的物理机制，并制备出目前临界尺寸最大的CuZr二元非晶合金。本文主要结论和创新点总结如下：1、非晶合金升温过程内耗测试结果表明，在玻璃转变温度之前，非晶合金的内耗值Q-1及相对模量M变化不大，发生玻璃转变时，其相对模量M发生明显的下降，材料由滞弹性转变为粘弹性，相应地内耗Q-1开始明显上升，并随之逐渐形成内耗峰，随后Q-1开始开始下降直至晶化结束。这种起始于玻璃转变而终止于晶化结束的内耗峰，表明非晶合金内耗峰包含了玻璃转变和晶化转变过程。“内耗-温度”峰的明显特征为：在同一加载频率下，升温速率越高，峰温越高，且峰值也越大；内耗峰的峰值随频率上升而降低。2、通过对不同非晶合金的内耗-温度谱、频率谱的研究，提出并验证了一种以内耗技术确定非晶合金晶化温度Tx的方法：在内耗-温度（升温）曲线中，非晶合金的Tx可通过对Q-1-T曲线上内耗-温度峰左侧的拐点温度（dQ-1-dT曲线的峰值温度）来表征。通过对一系列具有不同GFA的非晶合金进行的内耗研究结果发现，拐点内耗值与GFA之间存在着某种相关性：对于相同或相近合金系，GFA越好的合金，拐点内耗值越高。3、在本文研究所涉及的非晶合金系范畴内，从室温到Tg之前某一特定温度的升温中，非晶固体呈负的电阻率温度系数。将该区间数据按lnσ—1/T进行拟合结果表明，总体符合σ=σ0exp（ΔE/kBT）物理模型，即包含有对应于Mott的无序半导体电子传输机制，表明在升温过程中非晶合金由“定域态”受热激发而跃迁到“扩展态”，从而电阻率降低。4、基于电子输运性质提出了判断非晶合金玻璃形成能力新的判据，定义两个与电子输运性质有关的新参数：比电阻率（ρr=ρamor/ρcrystal）和储存电阻率（Δρ=ρamor-ρcrystal）。研究结果表明，对于相同或相近非晶合金系，ρr和Δρ的值越大，GFA越好。以该判据作为GFA的评判标准，通过元素替代法研究了Zr₅₇Cu₂₀Al₁₀Ni₈Ti_5-xAg_x（x=0,1,2,3,4,5）非晶合金的GFA随Ag含量的变化规律。电阻率实验结果表明，Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅非晶合金具有最大的ρr和Δρ值，说明该合金具有最高的玻璃形成能力。通过铜模吸铸法得到了具有最大形成尺寸为20mm且具有高强度高塑性的Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅大块非晶合金。5、基于Cu₆₄Zr₃₆合金的非晶形成竞争相为Cu₁₀Zr₇相的认知，通过用Ti替代7.5%的Zr元素得到的新合金在铜模吸铸过程中，使得Cu₁₀Zr₇相的析出被完全抑制且新合金的非晶形成竞争相变成Cu₅₁Zr₁₄相，如愿地使合金GFA得以增强。Cu₅₀Zr₅₀合金的非晶形成竞争相为CuZr相，通过电阻率实验对Cu₅₀Zr₅₀非晶合金进行连续升降温测试发现：CuZr相仅能在高于988K的温度下存在，在冷却过程中将会分解为Cu₁₀Zr₇相和CuZr2相，然而该分解过程具有117K的温度滞后性。分析认为，滞后温度的存在对制备非晶复合材料的过程中对稳定CuZr相有重要的作用。6、前人对非晶合金制备的熔体条件多以不同过热温度进行试探，而本文则以作者专门搭建的高精度、高真空、高温熔体电阻测试系统为手段，事先探明了Cu₅₀Zr₅₀及Cu₆₄Zr₃₆合金熔体在特定温区的结构敏感量电阻率的异常行为（并辅以DTA热分析验证），进而基于其信息探索了熔体状态与合金GFA及非晶晶化行为的相关性。结果表明（：1）通过电阻方法发现Cu₅₀Zr₅₀及Cu₆₄Zr₃₆两种合金熔体在高于液相线300⁴00K温度范围内出现了异常温度变化行为，提示此合金熔体发生了温度诱导的液-液结构转变，这一现象和推测得到了DTA热分析结果的验证；（2）根据不同熔体状态的区间选择合适的温度制备了一系列非晶薄带，连续升温模式下的电阻率和DSC测试结果表明，熔体过热温度越高，所制备的非晶合金的GFA和热稳定性越好，且由于在不同熔体状态下制备的非晶薄带在晶化过程中晶化相的析出过程明显不同；（3）发生熔体结构转变后，通过喷铸制备的Cu₅₀Zr₅₀锥形块体非晶的最大形成尺寸由2mm提高到了3mm、通过喷铸制备的Cu₆₄Zr₃₆锥形块体非晶的最大形成尺寸由1mm提高到了2.5mm。更多还原

【Abstract】 Owing to the unique property and application prospect of bulk metallic glasses （BMGs）, inrecent half a century, reseachers are trying to explore new alloy systems and new preparationtechnology continuously, and exploring the essence of glass forming ability （GFA） from physicalproperties of BMG solids-supercooled liquid-equilibrium and overheat liquid. At present, there aregreat progresses on GFA criteria and the empirical rules on selecting compositions of BMGs.However, the acquaintance of the essence of GFA and designing rules of new BMGs still needcontinuously exploring.Multicomponent alloy systems （CuZr-based, LaCe-based, and La-based） with different GFAare selected in this paper, by means of heating and cooling, the temperature behaviors of internalfriction property, electron transport property （resistivity） of BMGs with different GFA are explored,and the relationship and essence between GFA and above mentioned property are discussed based onthe phenomenon and laws. For further, new GFA criterion and designing principle are tried toproposed, and the effectivenesses are tested. Besides, the possibility and mechanism of temperatureinduced structure transition of CuZr binary alloy melt was explored, and the possibility of the effectsof melt temperature on GFA （critical diameter） of BMGs was also studied, meanwhile, the differenceof crystallization behavior and crystallization products of BMGs with different melt temperature isanalyzed.Based on the above results, the physical mechanism of liquid-solid transition andsolid-solid transition are discussed based on the understanding of phase competition, and new CuZrbinary BMGs with largest critical diameter are successfully prepared. The main conclusions andinnovation points are summarized as follows:1. The internal friction results of BMGs on heating condition reveal that the internal frictionvalue （Q-1） and relative modulus （M） have no significant changes before glass transition. Wheneverglass transition appears, the relative modulus decrease obviously which means the material changesfrom anelastic to visoelastic. Accordingly, Q-1begining to increase, and internal friction peak willappear after crystallization, afterwards, the internal friction tend to decrease until the end ofcrystallization. The internal friction peak which starts from glass transition and ends with the final ofcrystallization implies that internal friction peak includes both glass transition process andcrystallization process. The obvious characteristic of “Q-1-T” can be summarized as follows: with thesame vibration frequency, the higher the heating rate the larger the internal friction peak temperature;the internal friction peak value decrease with the increase of frequency.2. By studying the Q-1-T spectrum and frequency spectrum of different BMGs, a new methodfor determining the crystallization temperature of BMGs is proposed: on the Q-1-T curve, Txcan be determined from the inflexion which locates on the left side of internal friction peak （the peaktemperature of d Q-1-dT curve）. By studying internal friction behaviors of a series BMGs withdifferent GFA, the results reveal that there exist certain relationships between GFA and the internalfriction value of inflexion: For BMGs with same base alloy, the higher the GFA, the larger theinternal friction value of inflexion.3. For the BMGs that have been studied in this paper, on heating from room temperature to acertain temperature before glass transition temperature, the temperature coffecient of BMGs isnegative with the temperature elvating. By fitting the electrical conductivity according to lnσ—1/T,the result is well in accordance with the physical model:σ=σ0exp（ΔE/（k BT））, e. g.,corresponding to the electron transport mechanism of semiconductor which proposed by Mott: theelecton which is bounded in the “localized state” can jump to the “extended state” as a result ofthermal activation which will cause the decrease of the resistivity.4. Owing to the special electron transport property of BMGs, new GFA criterions which relatewith electron transport property are proposed: reduced resistivity （ρr=ρamor/ρcrystal） and storageresistivity （Δρ=ρamor-ρcrystal）. The results of resistivity measurements of a series BMGs reveal that thehigher the GFA, the larger the value of ρrand Δρ. Taking the electron transport criterion of BMGs asthe guiding principle of GFA, glass forming ability of Zr₅₇Cu₂₀Al₁₀Ni₈Ti_5-xAg_x（x=0,1,2,3,4,5）BMGs with respect to Ag content are studied by element substitution. The results of resistivitymeasurements reveal that Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅BMG has the largest ρrand Δρ, it implies thatZr₅₇Cu₂₀Al₁₀Ni₈Ag₅BMG has the best GFA. By preparing Zr₅₇Cu₂₀Al₁₀Ni₈Ag₅BMG using coppermould casting method,20mm rod with fully amorphous structure and high strength and plasticitycan be cast.5. Based on the understanding of Cu₁₀Zr₇phase which always competing on the glass formationof Cu₆₄Zr₃₆BMGs, by substituting7.5%Zr with Ti, the precipitation of Cu₁₀Zr₇phase can be fullyrestrained for the new alloy on copper mould casting process, and the competing crystal phase onglass formation the the new alloy change into Cu₅₁Zr₁₄. The competing crystal phase on glassformation of Cu₅₀Zr₅₀BMG is CuZr. By examing the resistivity behavior with continuous heatingand cooling, we found that CuZr phase only exist in the temperature region of higher than988K, andit will decompose into Cu₁₀Zr₇and CuZr2on cooling, however, there exists large temperaturehysteresis of117K on decomposition process. It was believed that the hysteresis temperature isimportant for stabilizing CuZr phase on preparing BMG based composites.6. There are many reports about the effect of overheating on glass formation of BMGs, however,in the present paper, resistivity measurements of CuZr binary alloy melts on overheating conditionare performed on a special high accuracy, high vacuum melt resistivity measuring system. Abnormal temperature behaviors of Cu₅₀Zr₅₀and Cu₆₄Zr₃₆alloy melts are observed using resistivitymeasurement （proved by DTA results）. Based on the results of melt state, the relationships betweenmelt state and GFA/crystallization behavior are explored. And the results are shown as follows:（1）Abnormal temperature behaviors of the melt in the temperature region of300⁴00K higher than theliquid temperature which implies that temperature induced liquid-liquid structure transition appeared,and this phenomenon was proved by DTA results;（2） Several overheating temperatures are selectedaccording to the different region of the melt state and metallic glass ribbons with different melt statewere prepared using single melt spinning method. Experimental results of resistivity and DSCmeasurements based on continuous heating mode reveal that elevating the overheating temperatureof alloy melts can improve the GFA and thermal-stability of CuZr binary BMGs, and crystallizationbehavior of CuZr binary BMGs are various for the CuZr binary BMGs with different meltstate.relevant melt state;（3） As liquid-liquid structure transition occurs, the critical diameter of theCu₅₀Zr₅₀cone shape sample is improved from2mm to3mm, and the critical diameter of the Cu₆₄Zr₃₆cone shape sample is improved from1mm to2.5mm.更多还原