Crystallization kinetics of bulk Cu58.1Zr35.9Al6 alloy

The crystallization kinetics of the bulk amorphous Cu_58.1Zr_35.9Al₆ alloy was examined by differential scanning calorimetry under continuous heating and isothermal annealing. During continuous heating, the activation energy of crystallization was determined to be 383 kJ/mol by Kissinger method. However, on the isothermal annealing, the activation energy was determined to be 459.2 kJ/mol by the Arrhenius method, which was much larger than that obtained from the Kissinger method. The different temperatures at which crystallization occurs are responsible for the discrepancy in the activation energy. The average Avrami exponent of about 3.5 implies that the crystallization process of the bulk amorphous Cu_58.1Zr_35.9Al₆ alloy is diffusion-controlled with a nucleation rate decreasing with time.     

Co基非晶软磁合金的制备与晶化动力学行为研究

采用旋铸急冷工艺在大气环境中制备出Co6.85Fe4Si10B17.5非晶合金带材.XRD分析表明:样品为完全非晶.用DiamondTG/DTA差热分析仪在高纯氩气保护下测量了非晶薄带的等温晶化动力学曲线.采用JMA方程计算出了合金的晶化动力学参数,在不同的晶化温度下,Avrami指数的值在2.11～2.58之间,晶化激活能Ec为113.67 kJ/mol.Co6.85Fe4Si10B17.5非晶合金的晶化方式是初晶型(761、791、803 K)和共晶型晶化(813 K),合金的晶化百分比与退火时间的关系曲线均为S型曲线.     

Structure relaxation and crystallization of Al83Ni10Ce7 metallic glass

Structure relaxation and crystallization of Al₈₃Ni₁₀Ce₇ metallic glass were studied by different scanning calorimetry (DSC) and X-ray diffraction (XRD). According to the DSC scan, it is interesting to find that the second exothermic peak changes with pre-annealing temperatures (below glass transition temperature), suggesting a change in the amorphous structure upon relaxation. Continuous heating crystallization and isothermal crystallization exhibit different crystallization mechanism of the present alloy. fcc-Al and a metastable phase precipitate simultaneously in the first stage crystallization during continuous heating; however, only a metastable phase precipitates during isothermal annealing below glass transition temperature (T_g).     

(Zr0.55Cu0.3Al0.1Ni0.05)98Er2非晶合金制备及其晶化动力学行为

为了研究SAF2507双相不锈钢（SAF2507 DSS）螺旋桨叶片在含硫酸盐还原菌( SRB)和铁氧化菌(IOB)海水中的耐腐蚀性能,提出一种二次急冷淬火成形技术来成形SAF2507 DSS螺旋桨叶片。同时根据螺旋桨叶片在不同二次急冷淬火成形温度下析出相的类型和析出规律,研究螺旋桨叶片在含SRB和IOB海水中的腐蚀性能。结果表明,当二次急冷淬火成形温度在700℃时,螺旋桨叶片表面析出少量的χ相;达到850℃时,χ相停止析出并完全转化成σ相,析出的σ相达到最大值;超过850℃时,析出的σ相开始急剧减少,到950℃时仅有少量的σ相析出。螺旋桨叶片在不同二次急冷淬火成形温度下,腐蚀电流密度、交流阻抗等电化学性能变化规律与螺旋桨叶片表层χ相和σ相的析出规律、以及χ相和σ相自身的耐腐蚀特征相吻合。二次急冷淬火成形温度在750℃-1050℃之间,螺旋桨叶片的耐腐蚀性能随热成形温度的升高呈增强—降低—增强规律变化,850℃时螺旋桨叶片的耐腐蚀性能最差。螺旋桨叶片二次急冷淬火成形后富Fe的表面特征,在SRB+IOB的作用下,螺旋桨叶片表面钝化膜被破坏,导致耐腐蚀性能降低。     

二次急冷淬火成形SAF2507双相不锈钢螺旋桨在SRB+IOB海水中的腐蚀行为

为了研究SAF2507双相不锈钢（SAF2507 DSS）螺旋桨叶片在含硫酸盐还原菌(SRB)和铁氧化菌(IOB)海水中的耐腐蚀性能,提出一种二次急冷淬火成形技术来成形SAF2507DSS螺旋桨叶片。同时根据螺旋桨叶片在不同二次急冷淬火成形温度下析出相的类型和析出规律,研究螺旋桨叶片在含SRB和IOB海水中的耐腐蚀性能。结果表明,当二次急冷淬火成形温度在700℃时,螺旋桨叶片表面析出少量的χ相;达到850℃时,χ相停止析出并完全转化成σ相,析出的σ相达到最大值;超过850℃时,析出的σ相开始急剧减少,到950℃时仅有少量的σ相析出。螺旋桨叶片在不同二次急冷淬火成形温度下,腐蚀电流密度、交流阻抗等电化学性能变化规律与螺旋桨叶片表层χ相和σ相的析出规律、以及χ相和σ相自身的耐腐蚀特征相吻合。二次急冷淬火成形温度在750～1050℃之间,螺旋桨叶片的耐腐蚀性能随热成形温度的升高呈增强-降低-增强规律变化,850℃时螺旋桨叶片的耐腐蚀性能最差。螺旋桨叶片二次急冷淬火成形后富Fe的表面特征,使得在SRB+IOB的作用下,螺旋桨叶片表面钝化膜被破坏,导致耐腐蚀性能降低。     

Zr57Cu15.4Ni12.6Al10Nb5块体非晶合金晶化行为研究

用示差扫描量热仪（DSC）研究了Zr57Cu15.4Ni12.6Al10Nb5块体非晶合金的匀速升温晶化与等温晶化的晶化行为。在匀速升温晶化方式下，用Kissinger法与Ozawa法获得了块体非晶合金的激活能，对第一晶化峰分别为320．5kJ／mol和316．6kJ／mol，对第二晶化峰分别为324．5kJ／mol和320．5kJ／mol。该非晶合金的晶化表现出明显的动力学效应。在等温晶化方式下，用Johnson-Mehl-Avrami方程获得了晶化的Avrami指数为1．61，表明非晶合金的晶化受原子扩散控制。     

HRTEM study of crystallization of Zr–Cu–Ni metallic glass

Employing differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM), the micromechanism for crystallization of Zr₇₀Cu₂₀Ni₁₀ metallic glass under isothermal annealing conditions has been investigated. It is found that the relationship between the annealing temperature and the peak position, incubation time and ending time in the isothermal annealing DSC traces of Zr₇₀Cu₂₀Ni₁₀ metallic glass obeys a first-order exponential function. However, the time–temperature transformation curves of Zr₇₀Cu₂₀Ni₁₀ metallic glass at different crystallized volume fractions can be well fitted by a second-order exponential function. It is observed that at the initial crystallization stage some ordered atomic clusters precipitate first, acting as nucleation sites and facilitating the subsequent crystallization process, and the crystal growth process mainly proceeds through the atomic depositing on the previously formed crystals. This behavior confirms that the new micromechanism for crystallization of amorphous alloys proposed by Lu and Wang can also be applied to the new series of zirconium based amorphous alloys.     

Zn38Mg12Ca32Yb18大块金属玻璃的晶化动力学行为

采用差示扫描量热分析仪,研究了Zn38Mg12Ca32Yb18 大块金属玻璃的在等时和等温状态下的晶化动力学行为。在等时条件下,不同的理论模型来分析特征温度的名义激活能。研究结果表明,采用Kissinger模型,Flynn-Wall-Ozawa 模型和Augis-Bennett模型计算的名义激活能相互吻合。再者,采用Johnson-Mehl-Avrami模型分析了等温过程中晶化转变动力学机。The Avrami 指数 n 的分布区间介于 3.25 到 4.12之间. 我们发现,在等温晶化过程中采用Arrhenius 方程计算得到的激活能比在等时晶化过中采用Kissinger 方程的激活能要大,这可能是由于等温退火过程中能垒比等时晶化过程中的要高所引起的。     

Zr－Al－Ni－Cu大块非晶合金的变温晶化行为研究

研究了Zr-Al-Ni-Cu大块非晶合金在连续升温过程中的晶化行为。结果表明，随升温速度的加快，特征温度Ts，Tx，Tp均向高温区移动，晶化热焓增加，过冷温度区间扩大，并且峰值温度Tp对应的晶化体积分数减少。利用Kissinger曲线和Doyle曲线法计算合金的变温晶化激活能E，结果表明，晶化激活能随晶化过程的进行，其值先增加后降低，并且在晶化即将结束时，晶化激活能急剧降低。采用Kissinger曲线计算晶化激活能，由于特征温度在不同的加热速度下对应的晶化体积分数发生变化，从而导致了激活能计算值的偏大。     

ON THE CRYSTALLIZATION OF AMORPHOUS Ni-BASE ALLOY

本文研究了非晶态Ni_(83)Cr_7Fe_3Si_4B_3合金在动态加热及等温热处理条件下的晶化过程。结果表明,对于动态加热及等温热处理两种情况,镍基非晶态合金的晶化过程相同,结晶相没有发生变化。但是,在动态加热条件下,初始晶化主要是成核结晶,而在等温热处理晶化过程中晶粒长大起主要作用。     

非晶态合金延─脆转变过程原子热激活运动特征

在等温和连续加热条件下测定了非晶态合金的脆化激活能。在两种加热条件下，非晶态合金对应于延－脆转变临界点的激活能数值非常接近，说明开始发生延－脆转变时受到相同的阻碍势垒，退火脆化与原子的热激后运动密切相关。实验结果还表明，脆化激活能随脆化程度的增大而单调升高并与脆化过程不同发展阶段相对应，是非晶态合金延－脆转变过程中原子热激活运动的两个基本特征非晶态合金的退火脆化不是具有恒定激活能的单一激活过程。     

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.     

La62Al15.7(Cu,Ni)22.3块体非晶合金的晶化行为

利用等温和变温晶化退火的方法对铜模吸铸La62Al15.7(Cu,Ni)22.3块体非晶合金的晶化行为进行了研究.结果表明,La62Al15.7(Cu,Ni)22.3块体非晶合金晶化过程分为3级,不同阶段的晶化产物分别为 La、Al3La和富Cu、Ni的未知相;非晶合金的驰豫激活能和3级晶化激活能的关系为:Eg相似文献   

Microstructure evolution in nanocrystalline NiTi alloy produced by HPT

A slightly Ni-rich nano-NiTi alloy, deformed by high-pressure torsion (HPT) was investigated. By HPT, almost complete amorphization of initial B2 NiTi is obtained. Crystallization and microstructure evolution during isothermal treatment were investigated by differential scanning calorimetry (DSC) and transmission electron microscopy.The DSC signals observed during continuous heating experiments indicate an unusually large separation between the crystallization and the growth stages. A detailed analysis of the evolution of the enthalpy release upon annealing reveals reproducibly non-monotonous trends with annealing time that cannot be explained solely by growth of crystalline volume fractions. The size of nanocrystals increases dramatically after annealing for 5 h. The effective activation enthalpies for stress relaxation (along with crystallization) and grain growth were estimated at 115 and 289 kJ/mol, respectively. The results are discussed with respect to the intricate interdependencies between synthesis and thermal processing pathways and the evolution of the nanoscale microstructure.     

Additivity rule,isothermal and non-isothermal transformations on the basis of an analytical transformation model

In the present work, the “additivity rule” was proved to be compatible with an analytical transformation model assuming mixed nucleation (with site saturation and continuous nucleation as two extremes), for some specified conditions. Combining the analytical model with numerical calculations, it is practicable to allow a conversion of continuous heating or cooling transformation (CHT or CCT) data into isothermal transformation data (TTT), and also a conversion of TTT data into CHT or CCT data, under a restrictive assumption of constant cooling or heating rate. From a comparative study between TTT and CHT data, the effective activation energy was found to increase and decrease, respectively, as compared with that before the CHT–TTT and TTT–CHT conversions; the growth exponent was proved to hold almost invariably, independent of the conversions. Real applications in the crystallization of amorphous Mg–Ni alloy and in the gamma–alpha massive transformation in Fe–Mn alloy show that the above conclusions are reasonable.     

Kinetics of crystallization process for bulk glass forming Zr-base alloys

The crystallization kinetics of Zr₆₅Ni₁₀Cu_17.5Al_7.5 (alloy I) and Zr_52.5Ni_14.6Cu_17.9Al₁₀Ti₅ (alloy II) are investigated. Two-stage crystallization takes place during continuous heating of the glassy alloy I, resulting in the transformation of the glass to the metastable α-Zr-solid solution and Zr-base quasicrystals with an activation energy of 309 KJ/mol in the first-stage and the formation of Zr₂Cu compound and the stable α-Zr-solid solution with an activation energy of 227 KJ/mol in the second-stage. For alloy II, one-stage crystallization with an activation energy of 333 KJ/mol occurs during continuous heating of the glass, resulting in the formation of Zr₃Al and α-(Zr,Ti)-solid solution. Based on the DSC data and calculations, both the alloys go through with three stages of crystallization mechanism during isothermal annealing, i.e. (1) surface nucleation and growth, (2) three-dimensional nucleation and growth, and (3) crystal growth. The TEM observation on Zr_52.5Ni_14.6Cu_17.9Al₁₀Ti₅ alloy is in good agreement with the calculations.     

Curie temperature behaviour at relaxation and nanocrystallization of Finemet alloys

Dependence of Curie temperature (Tc) on time and temperature of annealing for Finemet-type amorphous alloys is studied by DSC. Structural relaxation of an amorphous phase at annealing is accompanied by increase of Tc. The σ-shaped time dependencies, however, are not characterized by the definite final value of Tc: long-term annealing of amorphous phase results in continuation of slow increase of Tc for every temperature. Apparent values of activation energy of relaxation were evaluated from the Tc time–temperature dependencies. It is found that the average value of activation energy increases with progress of the relaxation process. Correlation of the Tc data with structural alterations reflects redistribution of components in amorphous phase during annealing. Further increase of the annealing temperature results in precipitation of α-Fe(Si) nanograins in an amorphous matrix, that accompanied by gradual degradation of corresponding to Tc heat capacity peak. DSC measurements of Tc allow to detect the starting moment of amorphous phase crystallization.     

Decomposition of the supersaturated solid solutions at the stage of coalescence under conditions of passage from dislocation-controlled to volume diffusion

The microstructure and thermal stability of multilayered Co/Zr amorphous films differing in the composition and thickness of individual layers have been studied. The range of the amorphous-phase existence was shown to be determined by both the chemical composition of films and thicknesses of individual layers. The critical thickness of cobalt layers which corresponds to the nucleation of a crystalline phase is 22–24 Å. A model of an island layered structure of multilayered Co/Zr amorphous films is suggested. Changes in the structure and phase composition of multilayered Co/Zr amorphous films caused by isothermal annealing have been studied. The temperature of the onset of crystallization (T _x) is shown to decrease from 460 to 380°C as the thickness of Co layers increases from 12 to 18 Å. The effect of annealing in the course of continuous heating on the specific saturation magnetization of the multilayered Co/Zr amorphous films has been studied. The effect of irreversible increase in the specific saturation magnetization was found for the first time at temperatures below the temperature of the onset of crystallization. A conception of a diffusion character of the structural relaxation and crystallization processes is used to interpret the results obtained.     

Cu64Zr36非晶合金的晶化动力学

利用单辊急冷法制备了CH64Zr36非晶合金，使用盐浴等温退火并用DSC和XRD研究了其晶化过程、玻璃转变和晶化动力学。结果表明：CH64Zr36非晶合金的晶化过程为：非晶一非晶＋Cu10Zr7→Cu10Zr7＋CuZr2。该合金的玻璃转变和晶化激活能分别为433．7kJ／mol和603kJ／mol。     

Zr-Ti-Cu-Ni-Be大块非晶合金等温晶化过程相分离研究

利用差示扫描量热法(DSC)和透射电镜(TEM)对Zr41.2Ti13.8Cu12.5Ni10Be22.5(at％)大块非晶合金的等温晶化过程和析出相进行了研究。结果表明，大块非晶合金在等温晶化过程中表现出多阶段相析出行为，并且在不同的晶化阶段，析出相也有所不同。在第1个晶化阶段，析出相主要是体心四方(b.c．t)结构的Zr2Cu相；而在晶化的第2个阶段，晶化相主要为简单六方结构的ZrBe2相。从一定程度上证实了Zr41.2Ti13.8Cu12.5Ni10Be22.5大块非晶合金在发生晶化时会形成富Zr区和富Be区，即有相分离的趋势。XRD测试的结果也证实了非晶合金在发生完全晶化时，主要的晶化产物为Zr2Cu和ZrBe2相。