Co77.5Si13.5B9非晶合金的制备与非等温晶化动力学效应

采用旋铸急冷工艺在大气环境中制备出了Co77.5Si13.5B9非晶合金带材。X射线衍射（XRD）和透射电镜（TEM）分析表明样品为完全非晶。用差热分析仪测量了非晶薄带的热稳定性参数Tg,Txi,Tpi,加热速度分别为5,10,15,35,55,75,95 K.min^-1。分析了合金的非等温晶化动力学行为,计算了两个析晶峰的晶化表观激活能。研究发现：不同升温速率的DTA曲线表明非晶合金的晶化过程为两步晶化,在连续加热条件下,随升温速率的加快,Co77.5Si13.5B9非晶合金的特征温度Tg,Txi,Tpi均向高温区移动,说明其玻璃转变和晶化行为均有动力学效应。当分别采用晶化开始温度和两个峰值温度时,所得非晶合金的激活能并不是一稳定值。Ozawa方法计算出的激活能值与Kissinger法计算出的结果是一致的。非晶态Co77.5Si13.5B9合金的晶化百分比与退火温度和退火时间的关系曲线均呈S型曲线,随加热速度的增加,非晶合金的晶化百分比与温度的关系曲线向高温处移动,晶化百分比与时间的关系曲线则向时间缩短的方向移动。     

(Ni0.75Fe0.25)70Zr8Si10B12非晶合金非等温晶化行为研究

采用旋铸急冷工艺在真空条件下制备出(Ni0.75Fe0.25)70Zr8Si10B12合金条带.经X射线衍射(XRD)分析表明样品为完全非晶.用Diamond TG/DTA差热分析仪在高纯氩气保护下测量了非晶薄带的热稳定性参数玻璃转变温度Tg、晶化起始温度Txi、晶化峰值温度Tpi.选用不同的升温速率,即10,20,30,40 K·min-1研究其晶化行为.结果表明,随升温速度的增大,特征温度Tg,Txi,Tpi均向高温区移动,其玻璃转变与晶化行为都与加热速率有关,均具有动力学效应.应用Kissinger法与Ozawa法研究了(Ni0.75Fe0.25)70Zr8Si10B12非晶合金的非等温晶化动力学行为.计算了不同特征温度下的激活能E、频率因子,用Kissinger法和Ozawa法计算的激活能结果是一致的.     

非晶合金Cu77Ni8Sn8P7的玻璃转变和晶化激活能

通过对非晶合金Cu_(17)Ni_8Sn_8P_7的初淬和退火态进行DSC分析(差动扫描量热分析),得到多种加热速度下的玻璃化温度及晶化温度,用Henderson提出的变温动力学方法计算了非晶合金在晶化开始温度和蜂值温度下的转变激活能,并确定了非晶合金玻璃转变激活能的方法。最后讨论了转变激活能和温度的关系,并估算了晶化过程中成核和生长的激活能。     

Cu46Zr44Al5Nb5块体非晶合金的晶化行为研究

通过磁悬浮熔炼-水冷铜模吸铸法制备了Cu46Zr44Al5Nb5块体非晶合金,并研究其变温晶化行为和等温晶化行为,运用Kissinger法和FWO法分别计算出各特征激活能和阶段激活能,考察了不同加热速度下晶化体积分数和晶化温度、晶化激活能的关系,并绘制了TTT曲线并计算非晶形成的临界冷却速率。结果表明,运用Kissinger法得到玻璃转变激活能E g为231.96 kJ·mol-1、晶化初始激活能E x为351.39kJ·mol-1、晶化峰的激活能E p为401.36 kJ·mol-1,Cu46Zr44Al5Nb5BMG具有良好的热稳定性,由TTT曲线计算非晶形成的临界冷却速率约为3.985 K·s-1。晶化类型主要为扩散控制的共晶型转变,随着晶化量的增大,阶段激活能呈减小的趋势。初始晶化阶段的晶化温度较高,主要是形核和微小晶粒的长大,需要克服较大的能量势垒,而随着温度的降低,晶粒的不断形成,晶化过程演变为主要以形核为主,所需要克服的能量势垒相应减小。在T x+100℃等温晶化退火,析出Cu10Zr7和AlCu2Zr共晶相,随着保温时间的延长,析出相的尺寸和体积分数逐渐增加。     

非晶Pr8Fe86B6合金的晶化动力学

用差热分析（DTA），结合X射线衍射（XRD）研究了非晶Pr8Fe86B6合金的晶化动力学。结果表明：该非晶Pr8Fe86B6合金的晶化相为α－Fe固溶体和Pr2Fe14B金属间化合物，通过对两相晶化激活能的分析得出：α－Fe相的激活能在晶化初期变化不大，当其体积分散大于8％时，其晶化激活能开始减小，而Pr2Fe14B相的激活能随其体体积分数的增加而减小，且α－Fe相较Pr2Fe14B相容易易化析出。     

电脉冲退火处理对Fe-Si-B非晶原子结合力的影响

非晶态合金Fe78Si9B1 3样品经短时超短脉冲电流处理 ,发生了结构弛豫 ,用DTA方法及Kissinger方程计算非晶样品的晶化激活能 ,用穆斯堡尔谱学方法研究了试样在电脉冲处理后的无反冲分数的变化 .结果表明 ,随脉冲电流密度和脉冲频率的增加 ,样品的晶化激活能降低 ,穆斯堡尔无反冲分数下降 ,表明原子间结合力随电流密度和脉冲频率的增加趋向降低     

铜模吸铸与高能球磨制备Zr46Cu46Al8非晶合金的组织结构及晶化动力学研究

采用铜模吸铸法制备出直径3 mm的Zr₄₆Cu₄₆Al₈块体非晶合金, 利用高能球磨法获得了不同粒径的合金粉体, 通过X射线衍射仪、示差扫描量热仪、扫描电镜等测试手段及热力学计算方法, 研究了制备方法对非晶合金组织结构及晶化动力学的影响。结果表明, 块体合金和粉体合金均可获得完全非晶结构; 块体非晶合金玻璃转变和晶化过程具有明显的动力学效应; 单因素变量法制备非晶粉体的最佳参数为: 转速300 r·min-1, 球料比30:1, 球磨时间15 h; 相同条件下, 除过冷液相区外, 块体非晶合金热力学参数普遍高于非晶粉体, 且晶化放热更剧烈; 随着加热速率增大, 二者热力学参数均向高温区移动, 过冷液相区的宽度也逐渐增加; 块体非晶合金和非晶粉体的特征温度表观激活能数值相近, 块体非晶态合金的表观激活能较非晶粉体高, 热稳定性更优。     

块体Pd77.5Cu6Si16.5非晶合金的晶化动力学研究

应用变温条件下的JMA方程和Kissinger方程研究长体Pd77.5Cu6Si16.5非晶合金的晶化动力学行为。计算了其玻璃转变温度Tg，晶化起始温度Tx，晶化峰值温度Tpl的激活能E，频率因子和Avrami指数等晶化动力学参数。并将这些参数与非晶条带的相应参数做对比，发现一些描述晶化过程的参量发生了变化。实验结果表明，块体非晶合金的原子活动性小于传统非晶条带，而具有更宽的过冷液相区。     

锆基大块非晶合金的非等温晶化动力学效应

采用非等温差示扫描量热法(DSC)研究了锆基非晶合金Zr60Al15Ni25、Zr65Al10Ni10Cu15的晶化动力学.结果显示,随着升温速率的加快,这两种非晶合金的特征温度Tg、Tx、Tp均向高温区移动,且过冷液相区逐渐加宽,表明非晶合金的玻璃化转变和晶化均具有动力学效应.分别采用Kissinger法和Ozawa法计算各非晶合金的激活能,两种方法的计算结果相近.从激活能数据得出,两种锆基非晶合金的热稳定性均较强;与非晶合金Zr60Al15Ni25相比,Zr65Al10Ni10Cu15虽较难形成玻璃化转变和开始晶化,但其晶化一旦开始则随后的过程反而更容易进行.     

Al_(86)Ni_5Y_7Er_2非晶合金的晶化动力学研究

采用单辊旋淬法制备了Al86Ni5Y7Er2非晶合金,通过差示扫描量热(DSC)技术研究非晶合金晶化动力学性能,计算得到合金平均晶化激活能,得到平均晶化起始激活能Ex是146.4kJ·mol-1、第一晶化峰值平均激活能Ep1是183.8kJ·mol-1、第二晶化峰值平均激活能Ep2是247.7kJ·mol-1、第三晶化峰值平均激活能激活能Ep3是228.2kJ·mol-1。结果表明Al86Ni5Y7Er2非晶合金具有较好的热稳定性。     

Problem and Improvement of Kissinger Method──New Method on Measuring Crystallization Activation Energy of Amorphous Alloy

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非晶态高炉渣的非等温析晶动力学研究

 采用差示扫描量热法(DSC)对非晶态高炉渣的析晶过程进行研究,得出不同升温速率下非晶态高炉渣析晶过程的DSC曲线,并根据动态DSC曲线用Kissinger法求出了析晶反应的活化能、反应级数及动力学方程中的指前因子等参数,建立了非晶态高炉渣析晶反应动力学的数学模型。实验所用非晶态高炉渣的析晶反应活化能为376.466 kJ/mol,该反应为一级反应。非晶态高炉渣的DSC曲线在1130~1310 K的温度区间内呈现出单一的晶化放热峰,峰顶温度、析晶温度和反应级数随升温速率的提高而提高。     

Kinetic study on the non-isothermal crystallization of Gd53Al24Co20Zr3 bulk metallic glass

Gd-based bulk metallic glass has drawn strong attention because of its large magnetic entropy changes. Thermal stability of metallic glass is a very important issue for its application. In the paper, crystallization behavior of Gd53Al24Co20Zr3 bulk metallic glass was investigated using non-isothermal differential scanning calorimetric (DSC) technique. Attention was given to the analytic details. The crystallized volume fractions as a function of temperature were derived from the DSC signals, where heat capacity change between amorphous phase and crystalline phase was considered. The local activation energies at different crystallized volume fraction were estimated using Doyle-Ozawa and Agrawal methods. The results suggested that the Doyle-Ozawa equation was appropriate to get local activation energy due to its simplicity and accuracy. The local activation energy depended on the crystallized volume fraction. Function reflecting crystallization mechanism was also deduced. The crystallization mechanism of the Gd-based bulk metallic glass was discussed.     

17-4PH钢连续加热奥氏体化的动力学

研究了17-4PH钢连续加热条件下的相变行为。结果表明,17-4PH钢在连续加热条件下,相变临界点Ac1、Ac3都随加热速率的加大而提高,转变温区也相应向高温扩展。奥氏体转变量与温度的关系呈S形,转变速率df/dt非定值且存在一个峰值。通过Kissinger法计算,确定17-4PH不锈钢的奥氏体化相变激活能为47.3kJ/mol。     

A study of nonisothermal tempering kinetics in plain 9Cr 1Mo steel

The present study elaborates the behavior of tempering reaction of nuclear grade plain 9Cr 1Mo martensitic steel investigated under a constant heating rate imposed by a high temperature heat flux differential scanning calorimeter (DSC). The heating rate imposed is varied from 1 to 30 K min^?1. The inflection in the baseline which occurs during the tempering reaction namely, martensite (α′) to ferrite (α) + chromium carbide (M₂₃C₆) around 873 K is identified in the DSC profile as the typical tempering onset temperature. The DSC profiles are used to characterize the extent of carbide precipitation under different heating rates. The analysis of the kinetics of tempering reaction is performed using Kolmogorov-Johnson-Mehl-Avrami (KJMA) model to extract the kinetic parameters. In addition, the Kissinger method of obtaining apparent activation energy (Q_eff) is also attempted. The value of the Q_eff obtained using both of the models are in good agreement and suggest that bulk diffusion of chromium in iron lattice could be the rate controlling mechanism in the tempering of 9Cr-steels. The effect of tempering reaction is also supported by metallographic studies.     

Effect of yttrium on thermal stability and crystallization behavior of Nd60Fe20Al10Ni10 amorphous alloys

The effect of yttrium on the thermal stability and crystallization behavior of Nd-Fe-Al-Ni amorphous alloys was investigated using X-ray diffraction （XRD）, differential scanning calorimeter （DSC）, and transmission electron microscopy （TEM）.The results indicated that the as-cast Nd60Fe20Al10Ni10-xYx（X=-0, 2） amorphous alloys were fabricated with some quenched-in crystals, which could be restrained by Y. With the effect of yttrium, both the crystallization temperature and exothermic peak shifted to higher temperatures, illustrating that the thermal stability could be improved. The addition of Y changed the crystallization process and final crystallization results. Moreover, the crystallites in the amorphous matrix became more homogeneous and smaller. Meanwhile, Y was useful for the passivation of oxygen in chemistry and restrained the negative effect of oxygen. The activation energies of the start of crystallization and peaking were 1.21 and 1.16 eV, respectively, according to the Kissinger equation.     

CCT and TTT Diagrams to Characterize Crystallization Behavior of Mold Fluxes

The isothermal and non-isothermal experiments were performed to construct the continuous cooling transformation （CCT） and temperature time transformation （TTT） diagrams of four industrial mold fluxes through visual observations in an experimental apparatus based on the single hot thermocouple technique （SHTT）. The results of the CCT diagrams indicate that ① the crystallization temperature of mold fluxes lowers as the cooling rate increases, ② the mold fluxes have larger critical cooling rate, higher crystallization temperature, and less onset time of crystallization when the basicity increases or the viscosity decreases, ③ the influences of the melting points of the mold fluxes on their crystallization tendency are not significant. Isothermal tests show that the onset time of crystallization decreases at first, and then increases, and finally represents a ＂C＂ shape with increasing isothermal temperature. The TTT diagrams of four industrial mold fluxes were divided into two separate ＂C＂ shape regions. The crystal phase of C20A selected was analyzed by X-ray diffraction, which is cuspidine （Ca4 Si2 O7F2 ） over I 100 ℃ and calcium silicon oxide fluoride （Ca2SiO2F2） below 1 100℃. When compared with the TTT diagram, the CCT diagram can provide a more realistic estimate of the critical cooling rate of the mold fluxes. Thus, both the CCT and TTT diagrams can unambiguously describe the crystallization phenomena of the mold fluxes.     

Precipitation kinetics in Al-Si-Mg/TiB2 in-situ composites

Al-7Si-0.3Mg-TiB₂ in-situ composites were made by the salt-metal reaction i.e., the reaction of K₂TiF₆ and KBF₄ salts with the molten alloy. The kinetics of the formation of intermediate metastable precipitates in the process of Mg₂Si formation in Al-7Si-0.3Mg-TiB₂ in-situ composites with three different amounts of TiB₂ particles (2.5, 5 and 10 wt.%) were studied using differential scanning calorimeter (DSC) and also compared with the Al-7Si-0.3Mg base alloy. Kissinger analysis of non-isothermal DSC scans at various heating rates was carried out to evaluate the activation energies associated with the precipitation processes. The metastable precipitates were characterized by taking the solutionized samples to their respective DSC peak temperatures at a particular heating rate and the samples were then observed under a transmission electron microscopy. It was found that there is a decrease in the activation energies of the GP zones with increase in TiB₂ content.     

Crystallization Kinetics of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses (BMGs) have been devel-opedrecentlyin many multi-component metal systems .These BMGs exhibit unique properties such as highstrength,high elastic li mit ,high corrosion resistanceand wear resistance , and low coercivity etc . Sincethe…     

热冲压硼钢非等温奥氏体相变动力学模型

 利用Gleeble-3500热模拟试验机对热冲压硼钢进行了线膨胀试验,得到了不同加热速度下硼钢奥氏体化动力学曲线;研究了加热速度对相变过程的影响,结果显示,加热速度越高,获得相同体积分数的奥氏体所需的时间越短,且奥氏体开始转变温度升高,当加热温度介于[Ac1]和[Ac3]时,奥氏体体积分数转变速度随着加热温度的升高先增大后减小。根据奥氏体形核长大理论,考虑加热速度的影响,建立了非等温条件下热冲压硼钢的统一奥氏体相变动力学模型。利用遗传算法确定并优化了硼钢奥氏体化动力学模型中的材料常数,所得材料常数确定的相变模型能够较好的描述硼钢连续加热过程线膨胀曲线,并能够较好地预测硼钢在不同加热速度下的奥氏体体积分数。