| 大块非晶形成及抑制形核机理研究 | |
| Alternative Title | STUDY ON FORMING PROCESS OF BULK METALLIC GLASS AND MECHANISM OF NUCLEATION INHIBITION |
| 李会强 | |
| Subtype | 博士 |
| Thesis Advisor | 杨院生 |
| 2007-02-06 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料加工工程 |
| Keyword | 大块非晶 真空吸铸 模拟计算 熔体自由能 界面能 原子团簇 非稳态形核 |
| Abstract | 论文采用数值方法模拟大块非晶合金制备过程并从熔体自由能、原子团簇、界面能以及动力学因素(如粘度以及冷却速率)的影响等几方面，从抑制形核入手研究大块非晶形成机理，大块非晶制备过程的凝固模拟表明，Zr65Al7.5Ni10Cu17.5合金试样心部和顶部有晶相析出，最大晶相分数为0.014。并且试样底部出现温度回升现象，回升后的温度达到695K；模拟计算得到制备Zr65Al7.5Cu17.5Ni10大块非晶的浇注温度应低于1350K，试样直径应小于45mm，浇注速度应大于4.29m/s。针对大块非晶合金特征建立了熔体自由能计算模型，应用该模型得到了成分三角形中Zr基大块非晶合金体系的自由能分布，计算表明目前已知的Zr-Al-Ni-Cu大块非晶合金均位于自由能较低的成分区域内。建立了大块非晶合金熔体原子团簇统计力学模型，原子团簇的出现导致液相自由能降低，只含Zr2Ni原子团簇，在xNi=0.35自由能下降约4000J/mol；而同时存在Zr2Ni和ZrNi时，在xNi=0.40下降8000 J/mol。综合考虑界面内能和界面熵以及液相/晶相成分对界面能的影响，建立了大块非晶合金界面能模型。对Zr-基合金系的计算结果表明界面能较高的区域与目前已知的容易形成非晶的成分范围相符。对于Zr66Al8Cu7Ni19合金的计算表明，在过冷条件下，熔体中原子团簇和界面处溶质再分配导致界面能增加约0.045-0.07 J/m2。对Zr66Al8Ni26合金计算表明，由于熔体中原子团簇的出现，形核率明显降低约6个数量级。此外，较大的冷却速率亦导致形核率明显降低，当冷却速率为103Ks-1，Pd82Si18合金熔体的形核率峰值为104mol-1s-1；当冷却速率为102.5Ks-1，Zr65Al7.5Ni10Cu17.5合金熔体的形核率峰值降低至105mol-1s-1。 |
| Other Abstract | The numerical method is employed to simulate the preparation process and investigate the mechanism of the nucleation inhibition with the effects of the Gibbs energy, clusters and interfacial energy, as well as the parameters for the dynamics such as viscosity and the cooling rate being considered.The suction casting of the bulk metallic glass formation is modeled and simulated. The results show that temperature at the bottom of the sample firstly drops and then rises back to 695K which is rather higher than the glass transition temperature. The crystalline phase precipitates in the center of the sample. The crystalline fraction reaches the highest value of 0.014 in the center of the sample. And the casting temperature should be lower than 1350K, the diameter of sample should be smaller than 45mm and the filling velocity should be lower than 4.29m/s.A new Gibbs energy model is developed by taking into account the characteristic of the bulk metallic glasses melts. With this model the Gibbs energy distributions within the compositions of Zr-based systems are obtained, and the well-known Zr-Al-Ni-Cu glass alloys are all in the composition regions with lower Gibbs energy.A Gibbs energy model of glass melt with multi-clusters is presented based on the statistical mechanism. The Gibbs energy drops about 4000J/mol at xNi=0.35 if the effect of cluster Zr2Ni is considered or about 8000 J/mol at xNi=0.40 if both of clusters Zr2Ni and ZrNi are taken into account.A new model for the interfacial energy of glass alloys is developed with the non-structural approach by investigating the effect of the enthalpy, the entropy and the compositions of liquid/crystal. The obtained higher interfacial energy regions of the Zr-based alloys are in good coincidence with the composition ranges with higher glass-forming ability. To Zr66Al8Cu7Ni19 alloy the interfacial energy increases about 0.045-0.07J/m2 due to the existence of clusters and the solution redistribution.The computed results for Zr-based bulk metallic glass alloys show that the nucleation rate of Zr66Al8Ni26 drops about 106 due to the existence of the clusters. Additionally, the higher cooling rates also lower the nucleation rate; To Pd82Si18 the peak value of nucleation rate falls to 104mol-1s-1 when the cooling rate increases to 103Ks-1. As the cooling rate reaches 102.5Ks-1, the peak value of nucleation rate of Zr65Al7.5Ni10Cu17.5 decreases to 105mol-1s-1. |
| Pages | 110 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/16908 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 李会强. 大块非晶形成及抑制形核机理研究[D]. 金属研究所. 中国科学院金属研究所,2007. |
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