共查询到19条相似文献,搜索用时 234 毫秒
1.
在非等温转变理论以及非稳态形核理论基础上提出了计算大块非晶合金连续冷却转变曲线和 临界冷却速率的新模型,以用于评估合金的非晶形成能力. 依据此模型对Zr基和Pd基8种合金 进行了计算,计算结果与实验值符合较好. 计算结果表明,影响临界冷却速率的主要因素为 黏度、临界形核功和临界结晶分数. 随着黏度增大,临界冷却速率降低;随临界形核功增大 ,临界冷却速率急剧降低;随临界结晶分数增大,临界冷却速率起初降低较快,达到一定程 度后下降速率趋于缓慢.
关键词:
临界冷却速率
非晶形成能力
大块非晶
连续冷却转变曲线 相似文献
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基于经典结晶理论讨论了非晶合金的晶化动力学因素和晶化热力学因素对玻璃形成能力(GFA)的影响.分析表明,合金的等温转变(TTT)曲线“鼻尖”温度Tn对应的黏度与晶化阻力因子成正比;重新加热时晶化开始温度Tx对应的黏度与晶化驱动力因子成反比.由此得到了新的GFA参数ω0=(Tg-T0)/(Tx-T0)-(Tg-T0)/(Tn-T0),其中Tg为玻璃转变温度,T0为理想玻璃转变温度.统计结果显示,ω0与临界冷却速率具有较高的相关性,R2高达09626.进一步分析表明:新提出的ω0参数可以合理地解释过冷熔体的黏度、脆性、液相稳定性、热稳定性以及Trg、ΔTx、γ、γm、ΔTrg、α、β、δ和φ等参数与GFA的关系.
关键词:
块体非晶合金
黏度
脆性
玻璃形成能力 相似文献
3.
利用水冷铜模铸造法成功制备了Zr65-xCu17.5Al7.5Ni 10Nbx (x=0,2,5)大块非晶合金. X射线衍射、热分析研究结果表 明,Nb的添加显著改变了非晶合金的晶化行为,促进了二十面体准晶相的形成. 各合金的准 静态压缩实验表明,Nb的适量添加有利于提高大块非晶合金的强度和塑性. 其中x=5的大块 非晶合金的抗压强度σb和塑性应变量εp
关键词:
Zr基大块非晶合金
晶化行为
力学性能
耐腐蚀性能 相似文献
4.
利用电磁悬浮无容器处理技术实现了液态五元Zr57Cu20Al10Ni8Ti5合金的深过冷与快速凝固,同时通过分子动力学模拟计算揭示了非晶形成的微观机制.实验发现,凝固组织具有明显的核-壳结构特征,核区为非晶相,壳区主要由ZrCu, Zr2Cu和Zr8Cu5晶体相组成.非晶体积分数随合金过冷度的升高逐渐增大,当达到实验最大过冷度300 K (0.26TL)时,非晶体积分数增至81.3%.由此导出完全非晶凝固所需临界过冷度为334 K. TEM分析显示,过冷度增大并接近临界过冷度时,合金凝固组织中晶体相主要为Zr8Cu5相,而ZrCu和Zr2Cu相的生长被抑制.在达到临界过冷度后,过冷液相的凝固路径由Zr8Cu5结晶生长转变为非晶凝固.此外,合金的晶体壳中存在少量的晶间非晶相,而非晶核中... 相似文献
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通过分析规则熔体的热力学模型,计算了典型金属玻璃的熔体混合焓ΔHmix和混合熵ΔSmix.结合临界冷却速率,归纳出典型金属玻璃形成液体的热力学特性,并提出基于原子尺寸、元素组成以及元素之间混合焓等参数的形成大块金属玻璃的成分判定方法.结果表明,当ΔHmix<-15 kJ·mol-1且ΔSmix>0.6 J·K-1mol-1时,合金易于形成大块金属玻璃.金属玻璃的临界冷却速率Rc具有明显的尺寸效应,其值与熔体的ΔSmix值呈指数关系,可以用Rc=42.24×104exp(-13.91ΔSmix)+19.66粗略判断.运用该方法成功设计并制备出远离原有Zr基大块金属玻璃形成区域(55at%—65at%Zr)的Zr40Al10Ni15Cu35和四元Fe-B基Fe53Co5Nd12B30大块金属玻璃.
关键词:
混合焓
混合熵
大块金属玻璃
玻璃形成能力 相似文献
7.
通过等温示差扫描量热法研究了Zr60Al15Ni25大块非 晶合金的晶化动力学.实验结果表明,晶化过程的孕育期很短,即使在743 K这样低的温度下也不过0.52 min,而放热峰宽(反应整个晶化过程进行的时间)却随退火温度的降低明显增大,这说明了结晶过程是一个晶核长大控制的过程.Avrami指数表明在不同的退火温度,该合金的晶化机制发生了变化.晶化机制的变化是由于合金原子在不同温度下的扩散能力相差很大所致.
关键词:
晶化动力学
60Al15Ni25大块非晶合金')" href="#">Zr60Al15Ni25大块非晶合金
示差扫 描量热法(DSC) 相似文献
8.
用铜模吸铸法获得了直径为5mm的一种新的Pr基大块非晶.与以往其他稀土-过渡金属(RE-TM)大块非晶不同的是,这种新的Pr基大块非晶具有明显的玻璃转变和稳定的过冷液相区,且其玻璃转变温度在目前已知的大块非晶中是最低的,Tg=409K.研究了该大块非晶的玻璃转变动力学,并给出了Kauzmann温度Tk、Vogel-Fulcher温度T0g及脆性参数m等重要参数.
关键词:
大块非晶
玻璃转变
脆性参数m 相似文献
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Woyun Long Xueqiong OuyangZhiwei Luo Jing LiAnxian Lu 《Physica B: Condensed Matter》2011,406(3):503-507
Amorphous Zr50Al15−xNi10Cu25Yx alloy powders were fabricated by mechanical alloying at low vacuum with commercial pure element powders. The effects on glass forming ability of Al partial substituted by Y in Zr50Al15Ni10Cu25 and thermal stability of Si3N4 powders addition were investigated. The as-milled powders were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimeter. The results show that partial substitution of Al can improve the glass forming ability of Zr50Al15Ni10Cu25 alloy. Minor Si3N4 additions raise the crystallization activation energy of the amorphous phase and thus improve its thermal stability. 相似文献
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Debdutta Lahiri Surinder M. Sharma Ashok K. Verma B. Vishwanadh G. K. Dey Gerhard Schumacher Tobias Scherb Heinrich Riesemeier Uwe Reinholz Martin Radtke S. Banerjee 《Journal of synchrotron radiation》2014,21(6):1296-1304
Short‐range order has been investigated in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 metallic glasses using X‐ray absorption spectroscopy and ab initio molecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass‐forming abilities (Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity. 相似文献
13.
以1at% Ag元素分别等量替代Zr57Cu20Al10Ni8Ti5金属玻璃的各个组元,利用差示扫描量热升温分析获得不同试样的热力学参数,并结合不同尺寸(Φ8,Φ10,Φ12)吸铸试样的X-射线衍射分析结果,考察、验证元素替代后合金的实际玻璃形成能力及热稳定性的变化规律.经比较发现,Ag替代Ti元素,其玻璃形成能力显著提高(直径实际增大4 mm),同时热稳定性也明显改善,且临界冷却速率也明显降低,而Ag替代其他组元却无明显规律.针对玻璃形成能力的相关数据比较分析表明,本文结果未显示符合其Inoue的尺寸准则,混合焓判据也未显示出明显符合的现象.通过对堆垛密度的计算发现,1 at% Ag替代Ti元素后使金属玻璃体系内部的堆垛密度增加.通过动力学分析,从晶化激活能、晶化反应速率常数两方面探讨了元素替代对玻璃形成能力和热稳定性的作用机理. 相似文献
14.
The temperature dependence of Gibb's free energy difference (ΔG), entropy difference (ΔS) and enthalpy difference (ΔH) between the undercooled melt and the corresponding equilibrium solid phases of bulk metallic glass (BMG) forming melts has been proved to be very useful in the study of their thermodynamical behavior. The present study is made by calculating ΔG, ΔS and ΔH in the entire temperature range Tm (melting temperature) to Tg (glass transition temperature) for three Zr-based samples of BMGs: Zr57Cu15.4Ni12.6Al10Nb5, Zr41.2Ti13.8Ni10Cu12.5Be22.5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8. The study is made on the basis of Taylor's series expansion and a comparative study is also performed between the present result and the result obtained in the framework of expansions proposed by earlier workers, and also with the experimental results. An attempt has also been made to study the glass forming ability for BMGs. 相似文献
15.
Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5? x Pd x (x?=?0???17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x?=?5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x?=?17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x?=?5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x?=?17.5). 相似文献
16.
The spinodal decomposition of a deeply undercooled metallic liquid Zr41.2 Ti13.8Cu12.5Ni10Be22.5 between 800 and 700 K is analysed in the framework of the theory of Cahn and Hilliard for continuous cooling, and the wavelength with maximum amplification is predicted, using as input parameters thermodynamic values gained in experiments. Electron microscopical studies show the microstructure of glass forming alloys Zr41.2Ti13.8Cu12.5Ni10Be22.5. The as‐cast material exhibits a two phase mixture of amorphous regions with different compositions. Evidence for spinodal decomposition is given, and the computed maximum‐amplitude wavelength corresponds well with the one found in the experiments. 相似文献
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B. Reinker M. Dopfer M. Moske K. Samwer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):359-364
Dynamic calorimetric measurements are performed for the quaternary metallic glass Zr65Al7.5Cu17.5Ni10 in order to analyse the dependence on different heating rates for the glass transition temperature Tg. We compare two different temperature programs used for sample relaxation, to estimate the influence of the thermal history
on Tg. A lower limit for the glass transition temperature Tg was calculated according to two different models based on the fact, that width and temperature of the glass transition depend
on the experimental time scale set by the heating rate: One model assumes a Vogel-Fulcher-Tammann type behaviour, as used
to describe more or less “fragile” glass formers and the other assumes an Arrhenius-like behaviour, which is related to “strong”
glass formers. The values obtained from both models differ by about 80K. From additional absolute specific heat capacity measurements
we calculate the Kauzmann temperature TK, as a lower limit for the temperature of the glass transition from thermodynamic aspects. Comparing TK with the temperature values obtained from the two evaluation models we can classify the quaternary metallic glass Zr65Al7.5Cu17.5Ni10, to behave more like a “strong” glass former.
Received: 23 January 1998 / Received in final form and Accepted: 31 August 1998 相似文献
19.
Ti42.5Zr7.5Cu40Ni5Sn5 bulk metallic glass with a critical diameter of 4 mm was fabricated by the conventional copper mould casting method. The
supercooled liquid region ΔT
x, reduced glass transition temperature T
rg, γ parameter, and δ parameter of the alloy were measured to be 63.9 K, 0.561, 0.393, and 1.400, respectively, implying that the alloy has an
excellent glass-forming ability. The bulk metallic glass exhibits high compressive fracture strength of 2162 MPa with distinct
plastic strain of 0.9%. The fracture surface consists mainly of vein-like patterns, typical of bulk glassy alloys.
Supported by the Program for New Century Excellent Talents in University of China and the National Natural Science Foundation
of China (NSFC)(Grant No. 50771040) 相似文献