共查询到19条相似文献,搜索用时 187 毫秒
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研究了Pd40Ni40P20合金在重力(1g)及微重力(μg)条件下凝固组织中溶质原子的分布.与重力条件相比,微重力条件下凝固的样品组织中,初生相的P含量较低,而Pd的含量较高;共晶区域内的平均P含量较高而平均Pd含量较低.深入分析初生树枝晶一次枝晶间距L与冷却率υ以及固液界面前沿液相中溶质综合输运系数D的相互关系,发现地面条件下的固液界面前沿液相中溶质综合输运系数D1g比空间的Dμg大1.7倍.
关键词: 相似文献
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基于金属熔体结构的遗传性, 激光熔池的快速熔凝导致粉末的晶化状态可能会对最终成形件的晶化产生重要影响, 理清其影响规律对于制备大块非晶合金具有重要意义. 本文选取等离子旋转电极法所制粉末和1000 K退火态粉末为沉积材料, 采用激光立体成形技术沉积Zr55Cu30Al10Ni5块体非晶合金, 考察了粉末中已有晶化相对熔池及热影响区晶化行为的影响. 结果发现, 原始粉末组织由非晶相及粗大的Al5Ni3Zr2相组成; 当激光线能量较低时, 相应熔覆层的熔池和热影响区皆含有Al5Ni3Zr2相; 随着线能量的提高, 熔池中Al5Ni3Zr2相消失, 保持了非晶态, 但热影响区晶化加重, 并有大量Al5Ni3Zr2相析出; 当采用退火态粉末时, 即使线能量较小, 相应熔覆层仍主要由非晶构成, 几乎无Al5Ni3Zr2相析出. 这是由于原始粉末在退火时其微观结构发生重排, 与Al5Ni3Zr2相关的原子短程/中程有序结构减少, 导致已沉积层非晶区的热稳定性提高, 不利于Al5Ni3Zr2相析出. 可见, 提高线能量将会加剧非晶沉积体的晶化, 而粉末中的Al5Ni3Zr2团簇相状态对Zr55Cu30Al10Ni5合金沉积层的晶化有重要影响. 相似文献
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用X射线衍射法研究了(Fe0.1Co0.55Ni0.35)78Si8B14金属玻璃在常压下及20kbar高压下晶化过程中的析出相及析出过程。结果表明在上述压力下晶化过程都分成两个阶段,分别对应于初级晶化和共晶晶化。在常压下,初级晶化时析出fcc-Co晶体,而共晶晶化对应着Ni31Si12和(FeCoNi)3(SiB)相的析出。随着回火温度的增高或时间的延长,(FeCoNi)3(SiB)相逐渐转变为(FeCoNi)23B6相。20kbar高压下的晶化析出过程与常压下不同的是:提高了晶化温度,在共晶晶化阶段出现了Co2B相。此外,压力还阻止(FeCoNi)23B6相的形成。从热力学和动力学的角度讨论了压力对金属玻璃晶化过程的影响。
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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
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本文研究了Pd43.5Ni43.5P13合金在20m落管中的过冷行为。下落过程中凝固的液滴为直径在0.2—2.5mm范围的小球。对样品进行了X射线衍射测量、扫描电子显微镜观察和X射线能谱微区成分分析。结果表明当样品在1.8×104Pa的氮气中凝固时得到了近单相的Pd-Ni-P过饱和固溶体。这一事实表明样品中可能发生非分解凝固。此外,在8.0×104Pa氮气中凝固的样品发现非晶相与固溶相共存,说明样
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作为潜在的功能及结构材料,高熵非晶合金在凝聚态物理和力学领域引起广泛的研究兴趣.高熵非晶合金宏观力学性能与微观结构非均匀性之间的关联是当前重要的科学问题之一.本文选取非晶形成能力良好的Pd42.5Cu30Ni7.5P20非晶合金和Pd20Pt20Cu20Ni20P20高熵非晶合金作为模型体系,借助于动态弛豫行为及应力松弛实验建立了温度和物理时效对非晶合金高温变形机制与微观结构非均匀性之间的关联.研究结果表明Pd基非晶合金表现出“肩膀峰”β弛豫形式.玻璃转变温度以下物理时效非晶合金体系原子移动性导致β弛豫肩膀峰往更高的温度迁移.在应力松弛过程中,由于高构型熵的引入降低吉布斯自由能,这是高熵非晶合金具有较高激活能的原因.高熵非晶合金更难被激活,需要突破更高的能量势垒.物理时效时间增加,高熵非晶合金流变单元更小,这也得益于多主元高熵非晶合金慢扩散效应.高熵非晶合金激活体积的改变在物理时效下应力松弛... 相似文献
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The phase transitions in Pd40Ni10Cu30P20 bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffaction measurements
with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous
at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous
transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the
melt differed from the primary phase crystallized from the starting amorphous solid upon heating suggesting there existed
a distinct mechanism in two cases. 相似文献
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Sun Liling Wu Tianjiao Wang Wenkui Zhang Jun Utsumi Wataru Okada Taku 《中国科学G辑(英文版)》2005,48(2):716-722
The phase transitions in Pd40Ni10Cu30P20 bulk metallic glass (BMG) have been studied under high pressure and high temperature (HP & HT) by X-ray diffaction measurements
with synchrotron radiation source. We found that the BMG underwent a phase transitions of amorphous-crystalline-amorphous
at 10 GPa upon heating. The parallel experiments were carried out at 7 GPa, while we did not observe the amorphous-crystalline-amorphous
transitions by increasing temperature. Quenching the melted BMG at 7 GPa, it was found that the phase crystallized from the
melt differed from the primary phase crystallized from the starting amorphous solid upon heating suggesting there existed
a distinct mechanism in two cases. 相似文献
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本文研究了Pd40Ni40P20块状非晶在4 GPa及常压下的晶化过程。得到了时间-温度转变图。结果表明:高压下样品的晶化温度明显升高,压力对原子的长程扩散及相分离熔体的粘性流动均有抑制作用。在接近熔点进行高压退火时,获得了单相过饱和固溶体。其晶体结构为面心立方。 相似文献
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A Ni-P solid solution phase was obtained by quenching of melts under a pressure of 4.5 GPa. This was considered as a metastable high pressure phase. Despite the lack of thermodynamic parameters for Ni80, P20 alloy under pressure, the degree of undercooling, nucleation frequency and crystal growth velocity were calculated. We conclude that metastable phases with the same composition as the melting phase, such as supersaturated solid solution phase and amorphous phase, are easily prepared by high-pressure quenching. 相似文献
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G. E. Abrosimova N. S. Afonikova N. P. Kobelev E. L. Kolyvanov V. A. Khonik 《Physics of the Solid State》2007,49(11):2099-2103
The effect of heat treatment over the range from room temperature to 500°C on the elastic properties of a bulk amorphous Pd40Cu30Ni10P20 alloy was studied. It is shown that the increase in the shear modulus under crystallization of the alloy is two-staged and that the most significant increase in the modulus occurs at the second stage. The obtained results are compared to the x-ray structural data. It is also found that the density characteristics of the as-cast material change very slightly during the transformation from the amorphous to the crystal state, with the density decreasing slightly due to crystallization. 相似文献
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A.?V.?Lysenko S.?A.?Lyakhov V.?A.?Khonik M.?Yu.?Yazvitski? 《Physics of the Solid State》2009,51(2):221-225
The shear viscosity is measured under conditions of isochronous (linear) heating below the glass transition temperature of
the Pd40Cu40P20 metallic glass, which is characterized by the polymorphic crystallization into the Pd2Cu2P tetragonal phase with a lower density than the initial glass. It is shown that the rate dependence of the shear viscosity
can be interpreted as a result of the irreversible structural relaxation by analogy with the case of the previously studied
metallic glasses despite the unusual ratio of the densities of the material in noncrystalline and crystalline states. 相似文献
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The evolution of the structure of an amorphous Ni70Mo10P20 alloy during annealing in the temperature range from 673 to 873 K is studied using x-ray diffraction and transmission electron
microscopy. It is found that a previously unknown metastable phase forms during crystallization of the amorphous Ni70Mo10P20 alloy. The morphology of the newly formed crystals is studied, the space group and the lattice constant are determined, and
the atom positions for the phase that forms are proposed. It is found that the metastable phase is a phosphide whose composition
is close to (Ni(Mo))3P. We established that, as the temperature or the duration of annealing is increased further, the metastable phase turns into
the equilibrium Ni3P phase. The orientation relations between the metastable and equilibrium phases are determined. 相似文献
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Measurements of electrical resistivity after low temperature fast neutron irradiation are made for amorphous Pd80Si20 and Pd80Ni2Sl18 and then Pd80Si20 annealed at 230°C and 360°C, and the isochronal annealing curves are obtained. The resistivity increase of Pd80Si20 annealed at 360°C is about 10 times larger than that of amorphous alloys and no defined annealing stage is observed in amorphous alloys and Pd80Si20 annealed at 360°C. For amorphous Pd80Si20, about 60% of the resistivity increase by irradiation remains after annealing up to room temperature and these are discussed by the structural relaxation. 相似文献