【作者】 王胜海；

【导师】 边秀房；

【作者基本信息】 山东大学 ， 材料加工工程， 2007， 博士

【摘要】 本文以X射线衍射技术（XRD）、差示扫描量热分析（DSC）、透射电子显微镜（TEM）和高分辨电子显微镜（HRTEM）为主要研究手段，系统地研究了Al-Ni-Mg-Cc合金系的非晶形成规律，并详细研究了Al-Mg-Ce和Al-TM-RE（TM表示过渡族金属元素，RE表示稀土元素）非晶合金的晶化行为，此外，还对Al₈₃Ni₁₀Ce₇非晶合金的结构驰豫行为进行了研究。实验结果表明，通过向Al-Ni-Ce合金系中加入适量的Mg元素，能够在一个较宽的成分范围内获得“准纳米-非晶”合金，其具体成分范围如下：Al₈₂Ni_10-xMg_xCe₈（4≤x≤5）；Al₈₃Ni_10-xMg_xCe₇（2≤x≤4）；Al₈₄Ni_10-xMg_xCe₆（2≤x≤4）。分析认为，Al-Ni-Mg-Ce合金系中“准纳米-非晶”合金的形成主要归因于Mg元素的特殊性质，即Mg与其它组元之间具有较小的负的混合焓。通过对Al₈₄Ni_10-xMg_xCe₆合金系非晶形成能力（GFA）的研究发现，GFA与|△H×S_σ／k_B|成正比，与（T_l-T_m）成反比，并在此基础上，提出一个新的判据Ω=|△H×S_σ／k_B|／（T_l-T_m）来衡量合金的非晶形成能力。其中，△H表示混合焓，S_σ表示错配熵，T_m表示熔化开始温度，T_l表示熔化结束温度，k_B表示波尔兹曼常数。发现在非晶态Al₈₂Mg₁₀Ce₈和Al₈₄Mg₁₀Ce₆合金的晶化过程中，亚稳相Al₉₂Ce₈作为初生相从非晶基体中析出。这一过程明显不同于一般富铝基非晶合金的晶化规律，即fcc-Al作为初生相单独或与其它金属化合物一同在晶化过程的第一阶段从非晶基体中析出。非晶态Al₈₂Mg₁₀Ce₈合金的晶化过程可以归纳如下：在晶化过程的第一阶段，亚稳相Al₉₂Ce₈作为初生相从非晶基体中析出；在晶化过程的第二阶段，亚稳相Al₉₂Ce₈分解成fcc-Al和Al₄Ce相，同时Al₁₂Mg₁₇相也从基体中析出，在此过程中还出现少量未知的亚稳相。晶化的最终产物为fcc-Al、Al₄Ce和Al₁₂Mg₁₇相。非晶态Al_<sub>84Mg₁₀Ce₆合金的连续加热晶化过程类似于Al_<sub>82Mg₁₀Ce₈非晶合金，只是区别于在晶化过程的第二阶段没有出现未知的亚稳相，其晶化过程可简单表示如下：非晶基体→稳相Al₉₂Ce₈+非晶基体→（fcc-Al+Al₄Ce）+Al₁₂Mg₁₇。通过对比Al-Mg-Ce(Al₈₂Mg₁₀Ce₈／Al₈₄Mg₁₀Ce₆)和Al-Mg-Ni-Ce(Al₈₂Mg₆Ni₄Ce₈／Al₈₄Mg₇Ni₃Ce₆／Al₈₄Mg₈Ni₂Ce₆)非晶合金的晶化行为，发现少量的Ni加入到Al-Mg-Ce非晶合金中能够促使fcc-Al作为初生相在晶化过程中从非晶基体中析出。对比Al₈₃Ni₁₀Si₂Ce₅和Al₈₅Ni₁₀Ce₅非晶合金的晶化行为发现，少量Si的加入能够把共晶型晶化的非晶合金Al₈₅Ni₁₀Ce₅转变为初晶型晶化的非晶合金Al₈₃Ni₁₀Si₂Ce₅；对比Al₈₇Ni₇Nd₆和Al₈₇Ni₅Co₂Nd₆非晶合金的晶化行为发现，少量Co替代Ni能够把初晶型晶化的非晶合金Al₈₇Ni₇Nd₆转变为共晶型晶化的非晶合金Al₈₇Ni₅Co₂Nd₆。通过Kissinger方法计算出Al₈₃Ni₁₀Si₂Ce₅、Al₈₅Ni₁₀Ce₅、Al₈₇Ni₇Nd₆和Al₈₇Ni₅Co₂Nd₆非晶合金的晶化激活能分别为191、290、166和221kJ／mol。由此可以看出，Si的加入降低了非晶合金的晶化激活能，即降低了非晶合金的热稳定性；Co的加入增加了非晶合金的晶化激活能，即增强了非晶合金的热稳定性。以DSC测试结果为依据，Al₈₃Ni₁₀Ce₇非晶合金的结构驰豫研究表明，其晶化过程的第二峰随预退火温度的升高（473K-533K）逐渐与第一峰合并在一起；随着预退火温度的进一步升高（533K-553K）又逐渐从第一峰中分离出来。Al₈₃Ni₁₀Ce₇非晶态合金在连续加热条件下和等温退火条件下经历了两种晶化机制。在连续加热条件下，fcc-Al和一种未知亚稳相在晶化过程的第一阶段一同从非晶基体中析出；而在等温退火晶化过程中，一种未知亚稳相单独从非晶基体中析出。更多还原

【Abstract】 In this paper, the glass-forming ability （GFA） of the Al-Ni-Mg based amorphous alloys, the crystallization behaviors of Al-Mg-Ce and Al-TM-RE amorphous alloys and the structure relaxation of Al₈₃Ni₁₀Ce₇ amorphous alloy have been systematically investigated by using the X-ray diffractometer （XRD）, differential scanning calorimetry （DSC）, transmission electron microscopy （TEM） and high-resolution transmission electron microscopy （HRTEM）. It has been found that the proper addition of Mg can promote the formation of nanoglassy alloy in the Al-Ni-Ce system in a relative wide composition range (Al₈₂Ni_10-xMg_xCe₈, 4≤x≤5; Al₈₃Ni_10-xMg_xCe₇, 2≤x≤4 and Al₈₄Ni_10-xMg_xCe₆, 2≤x≤4). The origin of the formation of nanoglassy alloy can be interpreted in terms of the small negative heat of mixing between Mg and other constituents.The investigation of GFA in the Al₈₄Ni_10-xMg_xCe₆ amorphous alloys indicated that the GFA should be in direct proportion to |ΔH×S_σ/k_B | and in inverse proportion to （T_l-T_m）. Thus, based on this assumption, a new criterion is proposed to beΩ= |ΔH×S_σ/k_B|/（T_l-T_m） to evaluate the GFA. Here,ΔH, S_σ, k_B, T_m and T_l represent the mixing enthalpy, mismatch entropy, Boltsmann constant, the initial melting point and the final melting point, respectively.The crystallizations of Al₈₂Mg₁₀Ce₈ and Al₈₄Mg₁₀Ce₆ amorphous alloys indicate that a non-equilibrium phase Al₉₂Ce₈ precipitates in the first crystallization stage, which is quite different from the crystallization of common Al-based amorphous alloy, characteristic of primary crystallization of fcc-Al or eutectic crystallization of fcc-Al and compounds. With the Ni additions to the Al₈₂Mg₁₀Ce₈ and Al₈₄Mg₁₀Ce₆ amorphous alloys, primary crystallization of fcc-Al occurs in the Al₈₄Mg₇Ni₃Ce₆ and Al₈₄Mg₈Ni₂Ce₆ amorphous alloys.The crystallization of Al₈₂Mg₁₀Ce₈ amorphous alloy consists of two stages. A metastable phase Al₉₂Ce₈ precipitates in the first crystallization stage. With increasing temperature, the metastable phase Al₉₂Ce₈ is beginning to decompose into fcc-Al and Al₄Ce phases in the second crystallization stage; and at the same time, Al₁₂Mg₁₇ phase pricipitates from the amorphous matrix. It should be noted that an unknown metastable phase emerges in the second crystallization stage. The final crystalline precipitations consist of fcc-Al, Al₁₂Mg₁₇ and Al₄Ce phases. The crystallization process of Al₈₄Mg₁₀Ce₆ amorphous alloy is simmlar to that of Al₈₂Mg₁₀Ce₈ amorphous alloy, which can be summarized as follow: amorphous→metastable phase Al₉₂Ce₈ + amorphous→（fcc-Al+Al₄Ce） + Al₁₂Mg₁₇. The only difference between the crystallizations of Al₈₂Mg₁₀Ce₈ and Al₈₄Mg₁₀Ce₆ amorphous alloys is that no unknown metastable phase appears in the second crystallization stage of Al₈₄Mg₁₀Ce₆ amorphous alloy.A small addition of Si can transform a eutectic crystallization (Al₈₅Ni₁₀Ce₅) to a primary crystallization (Al₈₃Ni₁₀Si₂Ce₅); while, a small addition of Co can transform a primary crystallization (Al₈₇Ni₇Nd₆) to a eutectic crystallization (Al₈₇Ni₅Co₂Nd₆). Based on the Kissinger method, the activation energy for crystallization of the Al₈₃Ni₁₀Ce₅, Al₈₅Ni₁₀Ce₅, Al（87）Ni₇Nd₆ and Al₈₇Ni₅Co₂Nd₆ amorphous alloys are determined to be 191, 290, 166 and 221 kJ/mol, respectively. It can be found that the activation energy for crystallization decreases with Si addition; while, the activation energy for crystallization increases with Co addition. Namely, the thermal stablity decreases with Si addition; while, the thermal stablity increases with Co addition.According to the DSC scan, it is interesting to find that the second exothermic peak gradually decayed with increasing the pre-annealing temperature from 473K to 533K; while, with further increasing the pre-annealing temperature up to 553K, the second peak gradually enhanced. This behavior suggests a change in the amorphous structure upon relaxation. Continuous heating crystallization and isothermal crystallization exhibit different crystallization mechanisms of the present alloy. Fcc-Al and a metastable phase precipitate simultaneously in the first crystallization stage during continuous heating; however, only a metastable phase precipitates during isothermal annealing below glass transition temperature （Tg）.更多还原