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

By measuring and analyzing the crystallization activation energy (CAE) of Fe-based amorphous alloy Fe79B16Si5 and Fe78B13Si9, it is reconfirmed and further analyzed that the conventional Kissinger method does not conform with the premise of Kissinger equation, namely, samples with different heating rates should keep a constant fraction of transformation at the exothermal peak temperature Tp of DSC thermogram. The XRD equal first peak height (EFPH) method is applied to CAE measurement of Fe-based amorphous alloy for the first time. It is shown again that the EFPH method coincides with the premise of Kissinger equation. The procedure of EFPH method is introduced in detail in this paper. The accuracy in determining CAE of amorphous alloy may be improved by applying the EFPH method. As a result, the mechanism of embrittlement of amorphous alloy may be better elucidated.

Effect of yttrium on thermal stability and crystallization behavior of Nd_(60)Fe_(20)Al_(10)Ni_(10) 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.

THE CRYSTALLIZATION KINETICS OF AN AMORPHOUS Ti-RICHNiTi FILM

The crystallization kinetics of an amorphous Ti-rich NiTi film (Ni 46.34at.%, Ti 53.66at.%)prepared by DC magnetron sputtering was determined by non-isothermal techniques. The activation energy of crystallization and the mean value of the Avrami parameter are 382kJ/mol and 0.85, respectively. The calculated isothermal kinetic curse of amorphous film at 773K coincides with the result of X-ray diffraction.The formation of a Ti2Ni phase is accompanied with the crystallization of Ti-rich NiTi film.

Effects of Zr on crystallization kinetics of Pr-Fe-B amorphous alloys

The effects of Zr on crystallization kinetics of Pr Fe B amorphous alloys have been investigated by DTA and XRD methods. It was found that for Pr 8Fe 86- x Zr x B 6 ( x =0, 1, 2) amorphous alloys, the final crystallized mixture is α Fe and Pr 2Fe 14 B, and the metastable Pr 2Fe 23 B 3 phase occurs during crystallization of Pr 8Fe 86 B 6 amorphous alloy, not during crystallization of Pr 8Fe 86- x Zr x B 6( x =1, 2) amorphous alloys. By analyzing the activation energy of crystallization, the formation of an α Fe/Pr 2Fe 14 B composite microstructure with a coarse grain size in annealed Pr 8Fe 86 B 6 alloy, is attributed to a difficult nucleation and an easy growth for both the α Fe and Pr 2Fe 14 B in the alloy. The addition of Zr can be used to change the crystallization behavior of the α Fe phase in Pr Fe B amorphous alloy, which is helpful to reduce the grain size for the α Fe phase.

EFFECT OF PRE-ANNEALING ON CRYSTALLIZATION KINETICS OF AMORPHOUS Ni-P ALLOYS

The effect of pre-annealing treatment on the crystallization kinetics parameters of amorphous Ni-P alloys has been investigated.Experimental results showed that the crystallization tem- perature,T_p and T_x,the apparent activation energy,E_c,as well as the Avrami exponent for isothermal crystallization,n,decrease significantly,while ΔT_(px)=T_p-T_x increases with the elongation of pre-annealing time at 570 K.

Crystallization kinetics of (Ni_(0.75)Fe_(0.25)_(78-x)Nb_xSi_(10)B_(12)(x=0,5)amorphous alloys

Amorphous ribbons of （Ni0.75Fe0.25）78-xNbxSi10B12 （x = 0, 5） were prepared by a single roller melt-spinning technique in air atmosphere. The crystallization kinetics of the alloys were investigated by means of continuous heating, and the activation energies of the alloys were calculated using Kissinger plot method and Ozawa plot method on the basis of differential thermal analysis data. The crystallization products were analyzed by X-ray diffraction. After the （Ni0.75Fe0.25）78Si10B12 amorphous alloy was annealed at the temperatures 715 and 745 K, a single phase of γ-（Fe, Ni） solid solution with grain sizes of about 10.3 and 18.5 nm, respectively, precipitates in the amorphous matrix. The crystallized phases are γ-（Fe, Ni） solid solution, Fe2Si, Ni2Si, and Fe3B after annealing at 765 K. The （Ni0.75Fe0.25）73NbsSi10 B12 amorphous alloy was annealed at 720, 750, and 800 K; and the crystallization phases, γ（Fe, Ni） solid solution, （Fe, Ni）23B6. Ni31Si12 and Nb2NiB0.16 form simultaneously.

Crystallization kinetics of (Ni_(0.75)Fe_(0.25))_(78-x)Nb_xSi_(10)B_(12)(x=0,5) amorphous alloys

Amorphous ribbons of (Ni0.75Fe0.25)78-xNbxSi10B12（x=0,5） were prepared by a single roller melt-spinning technique in air atmosphere. The crystallization kinetics of the alloys were investigated by means of continuous heating,and the activation energies of the alloys were calculated using Kissinger plot method and Ozawa plot method on the basis of differential thermal analysis data. The crystallization products were analyzed by X-ray diffraction. After the (Ni0.75Fe0.25)78-xNbxSi10B12 amorphous alloy was annealed at the temperatures 715 and 745?K,a single phase of γ-（Fe,Ni） solid solution with grain sizes of about 10.3 and 18.5?nm,respectively,precipitates in the amorphous matrix. The crystallized phases are γ-（Fe,Ni） solid solution,Fe2Si,Ni2Si,and Fe3B after annealing at 765?K. The (Ni0.75Fe0.25)78-xNbxSi10B12 amorphous alloy was annealed at 720,750,and 800?K; and the crystallization phases,γ-（Fe,Ni） solid solution,（Fe,Ni） 23 B6,Ni 31 Si 12 and Nb2NiB 0.16 form simultaneously.

Study on Annealing Embrittlement of Fe-B-Si Amorphous Alloy

The law and activation energy of annealing embrittlement for three kinds of popular Fe B Si amorphous alloys have been studied. For comparison, the crystallization activation energy (CAE) of these alloys was measured by XRD equal first peak height method and conventional Kissinger method. The structural relaxation activation energy (SRAE) of these alloys was measured by Curie temperature method or internal friction method. Through the comparison and analysis of the activation energies of annealing embrittlement, crystallization and structural relaxation, the related influencing factors on annealing embrittlement of Fe based amorphous alloys are elucidated.

INVESTIGATION ON CRYSTALLIZATION KINETICS OF Pd-Cu-Si GLASS

The crystallization kinetics of Pd-Cu-Si glass was studied by means of diferential scanning calorimetry-Ⅱ.According to Kissinger peak shift methd and Arrhenius equation,the apparent activation energy was calculated.The crystallization kinetics follows Johnson- Mehl-Avrami equation with n=3.0 within 0.15<x<0.85.In isothermal treatment,the concepts of local Avrami exponent and local activation energy have been introduced into Pd-Cu-Si system for understanding the isothermal crystallization process.

Thermal stability of Zr_(55)Al_(10)Ni_5Cu_(30)bulk amorphous alloy during continuous heating and isothermal annealing

The crystallization behavior of Zr 55 Al 10 Ni 5Cu 30 (mole fraction, %) bulk amorphous alloy during continuous heating and isothermal annealing was investigated. The results show that there exists a first order exponential decay relation between the characteristic temperatures and the heating rates during continuous heating process. The activation energy for glass transition E g and that for crystallization E p and E x during continuous heating were evaluated by Kissinger plots. In addition, there is a second order exponential decay relation between the annealing temperature and the corresponding crystallization time during isothermal annealing. The isothermal activation energy obtained by Arrhenius equation increases as crystallization proceeds, indicating the sufficient stability of the residual amorphous structure after initial crystallization.

NUCLEATION AND GROWTH ACTIVATION ENERGIES DURING CRYSTALLIZATION OF AMORPHOUS ALLOYS (Ⅰ)——CALCULATION METHOD

A new method is developed for the determination of activation energies for nucleation (E_n) and for growth of nuclei (E_g) during crystallization of amorphous alloys. This method is based on the crystallization kinetics theory and the experimental results of the variation relationships of local activation energy E_c(x) and local Avrami exponent n(x) with the crystallized volume fraction (x) during crystallization of an amorphous Ni-P alloy. Calculation results of E_n and E_g in the case of crystallization of the amorphous Ni-P alloy by this method show that this method is not only simple in the experimental procedures, but also accurate in the quantitative results.

用Kissinger方法测定非晶材料晶化激活能时应注意的问题

应用 Kissinger方法测定非晶材料晶化激活能时应确保所选温度对应的晶化分数相差不大 ,否则将会引入较大误差。以 Ni Ti非晶薄膜为例对此作了讨论。

Influence of Water Pollution on MIC of Stainless Steel 304L

Crystallization kinetics of Pr 8Fe 86 x Zr x B 6 ( x =0, 1, 2) amorphous alloys was studied by DTA and XRD methods. The experimental results showed that the crystalline phases of Pr 8Fe 86 B 6 alloy are composed of α Fe phase, Pr 2Fe 23 B 3 and Pr 2Fe 14 B, when crystallization temperature is below 900 ℃. The activation energy of α Fe phase remains relatively constant about 306.09 kJ/mol, as the crystalline fraction of α Fe phase is below 8 %. At the beginning of crystallization, the activation energy of Pr 2Fe 23 B 3 and Pr 2Fe 14 B phases are 510.85 kJ/mol and 725.97 kJ/mol, respectively, and then the activation energy of three phases declines with increasing the crystalline fraction. The crystallization behavior of α Fe and Pr 2Fe 14 B essentially results in the formation of a α Fe/Pr 2Fe 14 B composite microstructure with a coarse grain size in annealed Pr 8Fe 86 B 6 alloy, which is attributed to a difficult nucleation and an easy growth for both the α Fe and Pr 2Fe 14 B in the alloy. Zr can be used to change the crystallization behavior of the α Fe phase in Pr Fe B amorphous alloy, which is helpful to the formation of the α Fe/Pr 2Fe 14 B nanocomposite microstructure with a fine grain size for the α Fe phase in the alloy.

NUCLEATION AND GROWTH ACTIVATION ENERGIES DURING CRYSTALLIZATION OF AMORPHOUS ALLOYS (Ⅱ)——RELATIONSHIP BETWEEN MICROSTRUCTURE OF AMORPHOUS STATE AND TEMPERATURE

By using the new method for determination of activation energies for nucleation andgrowth (E_n & E_g) developed in Part Ⅰ of this work, the E_n and E_g of some pre--annealedamorphous Ni--P alloys, as well as those of the as--quenched Ni--P glass within differenttemperature ranges are measured and studied. The results show that the values of E_n and E_gare closely related to the microstructure of amorphous alloys and the annealing temperature.The higher the ordering in the amorphous alloys, the smaller the values of E_n and E_g; thehigher the annealing temperature, the greater the E_n and E_g values. By means of the newlydeveloped crystallization micromechanism, such an experimental phenomenon which is diffi-cult to understand from the classical crystallization mechanism is reasonably explained.

不同尼龙的等温结晶行为研究

对比研究了4种不同尼龙(PA)-PA56、PA66、PA510、PA610的等温结晶行为。利用Avrami法对5个不同温度下的4种PA的结晶动力学进行分析。结果表明:4种PA的结晶能力各不相同,结晶速率从大到小依次为PA66、PA56、PA510、PA610;结晶活化能绝对值也差异较大,其中PA56比PA66高,PA610比PA510高;Avrami指数n基本都分布在2~3。

Fe_(61)Co_(10)Zr_5W_4B_(20)块体非晶合金的晶化行为与力学性能研究

采用铜模吸铸法制备Φ2mm的Fe_(61)Co_(10)Zr_5W_4B_(20)块体非晶合金,采用XRD、SEM、DSC、硬度和压缩实验研究了非晶合金的结构组织、热稳定性、晶化特征、硬度和压缩性能。该块体非晶合金表现出二级晶化,其玻璃转变温度为561.1℃,晶化温度为619.0℃,第一晶化峰温度为632.6℃,第二晶化峰比之高约117℃;用Kissinger和Ozawa方法获得的玻璃转变激活能分别为595.1kJ/mol,578.7kJ/mol,晶化激活能分别为413.9kJ/mol,407.4kJ/mol;非晶合金的晶化行为比其玻璃转变表现出更为明显的动力学效应;非晶合金的显微硬度为1207HV,压缩强度为1707.6MPa,呈典型的脆性断裂,断口中光滑区与脉状花纹区并存。

Ni-P非晶薄膜晶化相与相变动力学的XRD分析

用原位XRD技术分析了连续加热过程中电沉积Ni-P薄膜晶化与相变行为．通过定量分析,确定出不同温度下各相的析出量,由此计算出各相的晶化与相变激活能以及晶化结晶度．结果表明, Ni-P非晶薄膜的晶化与相变行为与薄膜中P的含量有关．在晶化过程中出现了四种亚稳相即NiP,Ni2P,Ni12P5及Ni5P2．计算得到:亚稳相NiP,Ni2P及稳定相Ni3P的相变激活能分别为133±15,172±19及190±20 kJ／mol;单个析出相的相变激活能低于Ni-P合金晶化激活能和Ni原子的自扩散激活能．

ZrCuNiAlTi块体非晶合金的变温晶化行为

研究了Zr56.6Cu17.3Ni12.5Al9.6Ti4(at.%)块体非晶合金连续升温过程中的晶化行为。结果表明,随着升温速度的增加,特征温度Tg,Tx,Tp1,Tp2均向高温区移动,特征温度与升温速度的关系可以用一次指数衰减关系拟合。采用Kissinger法和Ozawa法分别计算了特征温度对应的激活能Eg,Ex,Ep1,Ep2。由于不同升温速度下特征温度对应的晶化体积分数几乎不变,因而,采用Kissinger法计算结果与Ozawa法的计算结果呈现一致性。Eg,Ex,Ep1,Ep2之间的大小关系为:Eg≈Ep1≈Ep2<Ex。

硼粉热特性研究

为了研究硼粒子在不同气氛下热特性,采用TGA/DSC和高压DSC对晶体硼粉和无定形硼粉两种形态,在纯氮、纯氧、空气以及氧氮混合(1∶1)气氛和3种压强下进行热分析实验;利用Kissinger法和Ozawa法计算得到无定形硼在空气气氛下的动力学参数。试验结果表明,纯氮气氛下,无定形硼与氮气会发生反应,其反应速度缓慢,放热量小。无定形硼比晶体硼的氧化反应初始温度低,氧化反应更快且更完全。不同氧气浓度条件下,随着氧气浓度的提高,无定形硼反应起始温度提前,反应速率加快,反应更彻底。增加氧气压强,可降低初始反应温度,加快反应速率,提高反应放热量。最终计算得到无定形硼在空气气氛下的活化能E、指前因子A和反应速率常数K。

水雾化制备Fe-Si-B-C非晶软磁粉末及其晶化过程的研究

采用水雾化方法制备了Fe-Si-B-C四元非晶合金粉末。研究了粉末的粒度分布、相结构、微观形貌、热稳定性以及基本软磁性能,并通过Kissinger峰移法计算了其晶化时所需的激活能。结果表明,通过水雾化方法制备的Fe-Si-B-C四元软磁粉末的粒度分布合理;粒径小于38μm的粉末为完全非晶结构,且粉末表面光滑,内部成分均匀;非晶粉末的初始结晶温度为542.15℃,且升温过程中存在2个晶化放热峰;2个晶化反应对应的晶化激活能分别为463.92 k J/mol和910.21 k J/mol;粉末的饱和磁感应强度和矫顽力分别为1.08 T和111.4 A/m。