【作者】 马中锋；

【导师】 何顺荣；

【作者基本信息】 合肥工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 非晶合金在热力学上处于亚稳态,受热时会发生晶化,这种晶化使得非晶合金原有的结构和性能消失,从而影响到非晶合金的工程应用。因此,非晶合金的热稳定性和晶化动力学研究具有重要的理论和实际意义。本文以三种大块非晶合金Zr60Al15Ni25,Zr65Al10Ni10Cu15,Zr52.5Al10Ni10Cu15Be12.5为研究对象,利用X射线衍射法(XRD)和差示扫描量热法(DSC)等实验手段系统地研究了锆基大块非晶合金的热稳定性及其晶化动力学。主要研究方法及结论如下:(1)利用铜模吸铸法制备了两种大块非晶合金Zr65Al10Ni10Cu15和Zr52.5Al10Ni10Cu15Be12.5,并运用X射线衍射法研究了他们的相变规律。结果表明,Zr65Al10Ni10Cu15合金在683K时开始晶化,晶化相分别为四方相Zr2Cu、简单六方相Zr6NiAl2,面心立方相Zr2Ni,四方相Zr5Al3和斜方晶相Ni10Zr7;Zr52.5Al10Ni10Cu15Be12.5大块非晶合金在748K时开始晶化,晶化相分别为六方相ZrBe2、斜方晶相ZrNi、四方相Zr2Al3和单斜晶相ZrCu,表明Be元素的添加提高了Zr65Al10Ni10Cu15的晶化温度,阻止了四方相Zr2Cu和简单六方相Zr6NiAl2在低温条件下的析出,提高了热稳定性。通过等温DSC分析,Be元素的添加能够延迟四元非晶合金Zr65Al10Ni10Cu15的晶化时间,并且五元非晶合金具有较大的晶化热焓,说明五元非晶合金在晶化过程中放出更大的热量。运用JMA(Johnson-Mehl-Avrami)方程,计算得到Be元素添加前后两种非晶合金的Avrami指数分别为1.575~1.953和1.712~1.898,说明两种非晶合金具有相似的晶化机制,同为受扩散控制的形核率随时间增加而下降的晶化机制;Zr52.5Al10Ni10Cu15Be12.5和Zr65Al10Ni10Cu15的晶化激活能分别为431.7kJ/mol和213.1kJ/mol,前者比后者高23%,这也说明Be元素的添加提高了四元非晶合金的热稳定性。(2)利用铜模吸铸法制得Zr60Al15Ni25大块非晶合金,运用差示扫描量热法结合X射线衍射法研究了它的变温晶化行为。通过Kissinger方法求得合金的相变激活能Eg、Ex、Ep分别为539.9kJ/mol、213.1kJ/mol、261.2kJ/mol,表明Zr60Al15Ni25大块非晶合金具有很好的热稳定性;原位XRD研究了Zr60Al15Ni25的晶化行为,发现Zr原子在低温状态下的扩散困难迟滞了两三元相Zr6NiAl2和Zr5Ni4Al的析出,从而提高了合金热稳定性。计算了合金在不同退火温度下的结晶度,在晶化初期,由于原子活性较小,扩散与重排困难,结晶度较低;随着温度的进一步升高,原子扩散系数增大,大量的晶核从非晶基体中析出,结晶度迅速变大;在高温状态下,因为剩余非晶相越来越少,温度对结晶度的贡献变小。(3)分别通过铜模吸铸法和甩带法制备了Zr65Al10Ni10Cu15块体和条带非晶合金,运用恒速升温DSC研究了不同制备工艺对其热稳定性的影响。研究发现,与快淬的条带非晶相比,块体非晶表现为更低的Tg和Tx值,但具有较宽的过冷液相区ΔTx。分别运用Kissiger法和Doyle法计算了两种制备状态下Zr65Al10Ni10Cu15非晶合金的相变激活能,结果表明条带非晶具有更高的玻璃转变和晶化激活能,说明条带非晶合金具有更好的热稳定性。更多还原

【Abstract】 Amorphous alloys are metastable on thermodynamics, which will crystallize as be heated. Their original structures and properties will disappear due to crystallization, the disappearance will influence their engineering application. So the study of their thermal stability and crystallization kinetics wil be of great importance. In this thesis, the thermal stability and crystallization kinetics of bulk amorphous alloys Zr60Al15Ni25, Zr65Al10Ni10Cu15 and Zr52.5Al10Ni10Cu15Be12.5 have been systema- tically investigated by X-ray diffraction method (XRD) and differential scanning calorimetry( DSC). The main experimental results and conclusions are listed as follows:(1) Plate-like Zr65Al10Ni10Cu15 and Zr52.5Al10Ni10Cu15Be12.5 bulk amorphous alloys have been prepared by suction casting into a copper mold. The effect of Be addition on thermal stability and crystallization behavior of Zr65Al10Ni10Cu15 bulk amorphous alloy has been investigated by XRD combined with isothermal DSC. XRD results shows that it will crystallize at 683K, with the formation of tetragonal phase Zr2Cu, hexagonal Zr6NiAl2, face-centred cubic Zr2Ni, tetragonal Zr5Al3 and orthorhombic Ni10Zr7. Zr52.5Al10Ni10Cu15Be12.5 bulk metllic glass crystallizes at 748K and leads to the formation of hexagonal ZrBe2, orthorhombic ZrNi phase, tetragonal phase Zr2Al3 and orthorhombic ZrCu, the delay of crystallization of the latter can explain that the addition of Be will enhance the stability of Zr65Al10Ni10Cu15 bulk amorphous alloy. By isothermal DSC analysis, we found that Be addition to the master alloy can increase the incubation period, and the crystallization enthalpy after Be addtion is larger than its master alloy, which indicates that it will release more energy in the crystallization course of the new alloy. By using JMA equation, Avrami exponent n can be got with the value of 1.575~1.953 and 1.712~1.898 for the two alloys, it can be found that they crystallize in the same crystallization mechanisms, namely, controled by diffusion and nucleation rate decreases with time. The activation energy are 431.7kJ/mol for Zr52.5Al10Ni10Cu15Be12.5 bulk amorphous alloy, 23% higher than the master alloy, which also indicates the Be addition to Zr65Al10Ni10Cu15 can improve its thermal stability.(2) Bulk amorphous alloy Zr60Al15Ni25 has been produced by suction casting into a copper mold. Its thermal stability and crystallization behavior have been investigated by XRD and DSC. Phase transformation activation energy Eg, Ex and Ep calculated by Kissiger method are 539.9kJ/mol, 213.1kJ/mol and 261.2kJ/mol, and it shows that Zr60Al15Ni25 bulk amorphous alloy possesses of high thermal stability. In-situ XRD analysis indicates that the difficulty to form ternary phases Zr6NiAl2 and Zr5Ni4Al is the main reason for its high thermal stability. By calculating its degree of crystallinity at different temperatures, we have discovered that it would tend to smaller values at low temperatures, but it would rise rapidly with temperature; crystallization efficiency would decline at higher temperatures because of the less available amorphous phase.(3) The bulk and ribbon samples of Zr65Al10Ni10Cu15 amorphous alloys have been prepared by suction-casting in a copper mold and single roller melt-spinning technique. Their thermal stability has been investigated by DSC. The results indicate that the bulk amorphous alloy has lower Tg and Tx, but a wider supercooled liquid regionΔTx. Using Kissinger and Doyle plots, phase transformation activation energy can be evaluated. It showed that amphous ribbon has larger glass transition and crystallization activation energy, which explains the ribbon possesses higher thermal stability in comparison to the bulk sample.更多还原