Cu_(46)Zr_(46)Al_8块体非晶合金的晶化动力学研究

在连续加热和等温加热条件下,对Cu_(46)Zr_(46)Al_8块体非晶合金的晶化动力学行为进行了研究。在连续加热条件下,非晶合金具有与升温速度相关的非常明显的动力学特征。利用Kissinger方程计算得到的晶化激活能Ex和Ep分别为(355±10)kJ/mol和(403±10)kJ/mol。借助Johnson-Mehl-Avrami (JMA)模型,通过求解等温晶化过程的Avrami指数和局部Avrami指数揭示了非晶合金的晶化机制。这一晶化机制在其晶化激活能与晶化体积分数的关系中得到验证。等温晶化动力学研究表明,Cu_(46)Zr_(46)Al_8块体非晶合金在过冷液相区的晶化为初级晶体相的长大和二级晶化相的形核、长大的共同作用机制。     

基于能量守恒原理的块体非晶合金热加工条件下晶化机制的研究

基于能量守恒法,提出了研究块体非晶合金晶化机制研究的新方法.利用DSC方法和Kissinger式计算了块体非晶合金Zr53.7Ni9.4Cu28.5Al8.4在连续升温过程中的晶化激活能.通过对该块体的激光点热源加热试验,验证了该晶化机制模型的正确性.结果表明,Zr53.7Nig.4Cu28.5Al8.4块体非晶的晶化激活能为220kJ/mol,所提出的方法可定性地用于该块体非晶晶化机制研究.     

加热方式对Zr48Cu36Ag8Al8块体非晶合金晶化机制的影响

采用铜模吸铸法制备了Zr_(48)Cu_(36)Ag_8Al_8块体非晶合金,并利用同步示差扫描量热仪(DSC)对其晶化动力学进行研究。结果表明:通过对不同升温速率下的DSC曲线进行分析,根据Kissinger方程计算获得的Zr_(48)Cu_(36)Ag_8Al_8非晶合金的晶化激活能约为239 k J/mol;而根据经典JMA模型,通过对在过冷液相区内不同温度(703～743 K)的等温DSC曲线进行计算获得的等温晶化激活能为341 k J/mol,造成的差异主要归因于高温区与低温区晶化机制的差异。此外,通过对比晶化产物的组织相貌,还发现不同加热方式组织的生长速率的控制方式不同。     

NiCoNbTi非晶合金晶化行为的研究

采用单辊甩带法制备出(Ni0.5Co0)6Nb25Ti15非晶带材,利用X射线衍射和扫描差热分析对该非晶带材的晶化动力学过程进行研究,并用Kissinger方程计算其晶化激活能.结果表明:(Ni0.5Co0.5)60Nb25Ti15非晶带材在升温过程中晶化过程为一级晶化,且随升温速率的增大,该非晶合金晶化起始温度Tx和晶化峰值温度T0均增大,其晶化激活能为165.714 kJ/mol,晶化峰值激活能为168.357 kJ/mol.(Ni05Co05)60Nb25Ti15非晶带材的晶化为多晶析出的共晶晶化方式.     

预退火处理对非晶Cu-Ti合金晶化过程动力学的影响SCIEI

对非晶Cu_(40)Ti_(60)合金引入一种预退火处理工艺,利用DSC研究了急冷态及预退火处理样品的晶化过程动力学,发现预退火处理使非晶合金的晶化温度、晶化激活能和Avrami指数值下降。由实验结果和理论分析得到了非晶Cu_(40)Ti_(60)合金的形核激活能和长大激活能。     

非晶合金的晶化动力学与初生相的内在联系

通过差示扫描量热法(DSC)研究了Zr60Al15Ni25非晶合金的晶化动力学。X射线衍射(XRD)和能谱(EDS)分析结果表明:Zr60Al15Ni25非晶合金晶化过程中的初生相为复杂三元化合物Al2NiZr6和AlNi4Zr5。非晶合金的有效晶化激活能反映了晶化初生相与非晶相间的结构差异,二者结构差异越大,有效晶化激活能就越高,Zr60Al15Ni25非晶合金的有效晶化激活能高达345 kJ/mol;当合金高温熔体快冷过程中的初生相与非晶合金的晶化初生相一致时,晶化动力学参数能够实际反映合金的玻璃形成能力,相反则不能。     

一种新的Cu基大块非晶合金非等温晶化动力学研究

采用铜模吸铸法制备了Cu56.4Zr31.02Ti6.58Al6大块非晶合金(BMGs),并利用X射线衍射仪(XRD)、透射电子显微镜(TEM)和同步示差扫描量热仪(DSC)等手段对其晶体结构、晶化激活能和晶化机制进行了研究。利用y(a)和z(a)判据检测了不同晶化模型对于该BMGs初始晶化相晶化过程的适用性。结果显示:该BMGs初晶晶化产物为Cu10Zr7相,Starink-Zahra模型可以很好地描述其晶化机制。拟合参数λi不为零,故晶化过程中软碰撞作用不可忽视;Avrami指数n由2.5减小为2.3,其晶化过程为连续形核过程中伴随着晶核受扩散控制的三维方式长大,且形核速率不断减小。     

Pd_(82)Si_(18)非晶合金等温晶化动力学研究

采用高速单辊旋淬法制备了Pd_(82)Si_(18)非晶薄带,通过X射线衍射仪、透射电镜表征了非晶合金的物相结构,利用差示扫描量热仪(DSC)结合Johnson-Mehl-Avrami(JMA)模型对非晶合金的等温晶化动力学进行研究,使用Arrhenius公式计算了描述晶化过程不同阶段的局域激活能。结果表明:晶化过程的Avrami指数n值为2.5,表明该等温晶化过程主要依靠一维界面长大;晶化激活能随着晶化分数的变化而变化,晶化激活能E_c(α)范围为333.8 kJ/molE_c(α)343.8 kJ/mol,较大的晶化激活能表明Pd_(82)Si_(18)非晶合金具有良好的热稳定性。     

Al_(88)Co_4Y_6Er_2非晶合金的晶化动力学效应

采用单辊旋淬法制备了Al_(88)Co_4Y_6Er_2铝基非晶合金,运用差示热分析技术研究非晶合金晶化动力学性能。采用Ozawa方法计算了Al_(88)Co_4Y_6Er_2非晶合金晶化激活能,得到初始晶化激活能Ex1是370.6kJ·mol-1。同时发现Al_(88)Co_4Y_6Er_2非晶合金的晶化百分比与温度的关系曲线均呈"S"型曲线,并且随着升温速率的增加,对应的非晶合金"S"型曲线依次向高温移动。此外,在初次晶化过程中晶化激活能(Ea)随晶化体积分数(x%)的增加呈线性递减趋势。     

Zr43Cu50Al7块体非晶合金的结构弛豫和晶化研究

在不同加热速率下应用差示扫描量热法(DSC)研究了Zr43Cu50Al7块体非晶合金的结构弛豫现象和晶化行为,得到了满意的晶化曲线.由晶化曲线得到弛豫峰与玻璃转变温度(Tg)、晶化起始温度(Tx)和晶化峰温度(Tp).Zr43Cu50Al7非晶合金的过冷液相区ΔTx达76.2 K,具有较强的玻璃形成能力.对所得到的弛豫峰作了初步的研究,并运用Kissinger法和Deloy法分别计算出玻璃转变激活能Eg、晶化起始激活能Ec、晶化峰的激活能Ep和晶化阶段激活能Ex.结果表明Zr43Cu50Al7块体非晶合金具有良好的热稳定性.     

Fe41Co7Cr15Mo14Y2C15B6大块非晶合金的变温晶化动力学研究

采用差热分析法(DTA)研究了具有高玻璃形成能力的Fe41Co7Cr15Mo14Y2C15B6块体非晶合金的变温晶化动力学.由热分析曲线得到玻璃转变温度Tg、晶化起始温度Tx和晶化峰值温度Tp1、Tp2,这些特征温度具有明显的动力学效应.运用Kissinger法和Ozawa法分别计算出不同升温速率下该Fe基块体非晶合金的玻璃转变激活能Eg、晶化激活能Ex与激活能Ep1、Ep2.采用Kissinger方法和Ozawa方法解释了此大块非晶合金具有高的热稳定性的热力学机制.     

Non-isothermal nano-crystallization kinetics in amorphous Ni55Nb35Si10 alloy

The non-isothermal crystallization kinetics of Ni₅₅Nb₃₅Si₁₀ amorphous alloy, prepared by mechanical alloying, was studied using differential scanning calorimetry. The amorphous alloy showed one-stage crystallization on heating, which led to the formation of nano-intermetallic crystals in amorphous matrix. The apparent activation energy for the crystallization of the alloy, determined by the Kissinger equation, was relatively high (468 kJ/mol), indicating that this amorphous alloy has high thermal stability. Changes in the activation energy during the crystallization process, were also evaluated by iso-conversional methods. The results showed that it decreases slowly from the beginning to crystallized fraction α=0.35 and it remains almost constant to the end of the process. The nano-crystallization mechanism for the non-isothermal crystallization of the amorphous alloy was explained by determining Avrami exponents. Transmission electron microscopy studies revealed the microstructural modification of amorphous alloy via nano-crystallization during annealing. The results suggest that the nucleation rate decreases with increasing time and the crystallization mechanism is governed dominantly by a three-dimensional diffusion-controlled growth. A predictive equation was obtained based on the Sestak?Berggren autocatalytic model to describe quantitatively the non-isothermal crystallization kinetics.     

Crystallization of amorphous NiTiCu thin films

The effect of copper additions (1.3 at%) on the crystallization of amorphous nickel-titanium thin films was explored. Using differential scanning calorimetry (DSC), the overall activation energy and crystallization temperatures were found to be similar to pure NiTi. However, in situ transmission electron microscopy (TEM) showed the nucleation and growth behaviors were markedly different. NiTiCu exhibited a lower nucleation rate, suggesting a higher activation energy in comparison to NiTi. The large grains in NiTiCu microstructures are consistent with a lower growth activation energy. These data suggest copper additions create higher interfacial energies. This paper presents experimental measurements that corroborate this mechanism.     

Determination of activation energy for crystallizations in Ni–Sn–P amorphous alloys

The effect of plastic deformation on the crystallization kinetics of the ternary Ni–Sn–P amorphous alloy coatings prepared by electroless plating was investigated by using differential scanning calorimetry. It was shown that the effective crystallization activation energy of the amorphous coatings is pronouncedly affected by the plastic deformation, indicating a decreasing tendency with deformation. And, accordingly, this leads to the decrease of crystallization temperature. Analyses were presented to discuss the possible mechanism for the notable effects of plastic deformation on the crystallization kinetics of the amorphous coatings.     

Modification of the Ti<Subscript>40</Subscript>Cu<Subscript>36</Subscript>Zr<Subscript>10</Subscript>Pd<Subscript>14</Subscript> BMG Crystallization Mechanism with Heating Rates 10-140 K/min

The article presents investigations of Ti₄₀Cu₃₆Zr₁₀Pd₁₄ bulk metallic glass crystallization process heated with the rates of 10, 60, 100 and 140 K/min. High heating rates experiments were performed in a new type of differential scanning calorimeter equipped with a fast responding thermal sensor. Phase composition and microstructure were studied with x-ray diffraction and transmission electron microscopy. The observed crystallization proceeded in two separate steps. Applied high rates of heating/cooling resulted in the crystallization of only one CuTi phase, replacing typical multi-phase crystallization. The microstructure after crystallization was polycrystalline with some amount of amorphous phase retained. Kinetic parameters were determined with the use of the Kissinger and Friedman iso-conversional analysis and Matusita–Sakka iso-kinetic model. The kinetic analysis supplies results concerning autocatalytically activated mechanism of primary crystallization with decreasing activation energy and small density of quenched-in nuclei, in good agreement with previous structural investigations. The mechanism of secondary crystallization required dense nuclei site, increasing activation energy and large nucleation frequency. The amorphous phase of Ti₄₀Cu₃₆Zr₁₀Pd₁₄ BMG revealed high thermal stability against crystallization. Application of high heating rates in DSC experiments might be useful for the determination of mechanism and kinetic parameters in investigations of metallic glasses crystallization, giving reasonable results.     

冷却-加热对CaO-Al2O3-SiO2系玻璃析晶动力学的影响

以CaO-Al2O3-SiO2系玻璃为研究对象,采用Ozawa方程、Kissinger方程和JMA修正方程研究了冷却方式和加热温度对玻璃析晶动力学的影响。结果表明:化学组成相同的玻璃,冷却速度和加热温度对其析晶活化能E、Avrami指数n和析晶速率指前因子ν都有影响,但加热温度对析晶活化能E的影响更大,并在750℃出现极大值现象。通过玻璃析晶试验发现:冷却速度和加热温度对微晶玻璃主次晶相的析出没有影响,主、次晶相分别是钙长石和榍石。冷却速度和加热温度对析晶活化能E的影响主要来源于析出主、次晶相的比例不同。     

Effect of preannealing on crystallization process of amorphous Sm5Fe80Cu1Si5B3C2.5Zr3.5 alloy

In the view of crystallization activation energy of amorphous alloy,the mechanism of coarse grain in annealed Sm5Fe80Cu1Si5B3C2.5ZR3.5 amorphous alloy was analyzed.It reveals the e4ffect of preannealing on the process crystallization.The results show that preannealing can be used to change the crystallization behavior of the α-Fe phase in the Sm5Fe80Cu1Si5B3C2.5Zr3.5 amorphous alloy,whick is helpful for forming α-Fe phase grains;and it is not large for Sm2Fe17Cx phase.     

Al1.49Si1.45Zr0.26(TiCaMg)0.37O6.43非晶的非等温晶化动力学

采用非等温差示扫描量热分析方法,结合X射线衍射和红外光谱,研究了Al1.49Si1.45Zr0.26(TiCaMg)0.37O6.43非晶晶化动力学.结果表明:非晶在1223～1273 K附近发生了四方氧化锆的析出反应,析晶活化能为518～538 kJ/mol;在1423～1473 K附近发生了莫来石和方石英的析出反应,其析晶活化能为522～545 kJ/mol,且氧化锆的存在能有效地降低莫来石的析晶活化能.     

INVESTIGATION ON CRYSTALLIZATION KINETICS OF Pd-Cu-Si GLASS

The crystallization kinetics of Pd-Cu-Si glass was studied by means of diferential scanningcalorimetry-Ⅱ.According to Kissinger peak shift meth(?)d and Arrhenius equation,theapparent activation energy was calculated.The crystallization kinetics follows Johnson-Mehl-Avrami equation with n=3.0 within 0.15相似文献   

ZrCuAlSi大块非晶合金变温晶化行为

利用铜模吸铸法制备Zr46.3Cu43.3Al8.9Si1.5(at%)大块非晶合金,利用示差扫描量热(DSC)仪研究合金连续升温过程中的晶化行为,利用Kissinger方法计算其特征温度表观激活能,利用Doyle方法计算其局域激活能。结果表明,Zr46.3Cu43.3Al8.9Si1.5大块非晶合金具有良好的热稳定性。利用Kissinger方法计算得到其玻璃转变激活能Eg为395.4kJ/mol、晶化起始激活能Ex为343.2kJ/mol、晶化峰的激活能Ep为343.0kJ/mol。Doyle方法计算其局域激活能表明,其晶化过程中,激活能明显越过一能量势垒后,再呈现逐渐减小的趋势。