Phase stability in high entropy alloys: Formation of solid-solution phase or amorphous phase

The alloy design for equiatomic multi-component alloys was rationalized by statistically analyzing the atomic size difference, mixing enthalpy, mixing entropy, electronegativity, valence electron concentration among constituent elements in solid solutions forming high entropy alloys and amorphous alloys. Solid solution phases form and only form when the requirements of the atomic size difference, mixing enthalpy and mixing entropy are all met. The most significant difference between the solid solution forming high entropy alloys and bulk metallic glasses lies in the atomic size differen ce. These rules provide valuable guidance for the future development of high entropy alloys and bulk metallic glasses.     

Solid solution or amorphous phase formation in TiZr-based ternary to quinternary multi-principal-element films

TiZr-based multicomponent metallic films composed of 3–5 constituents with almost equal atomic concentrations were prepared by cosputtering of pure metallic targets in an Ar atmosphere.X-ray diffraction was employed to determine phase composition,crystalline structure,lattice parameters,texture and crystallite size of the deposited films.The deposited films exhibited only solid solution(fcc,bcc or hcp) or amorphous phases,no intermetallic components being detected.It was found that the hcp structure was stabilized by the presence of Hf or Y,bcc by Nb or Al and fcc by Cu.For the investigated films,the atomic size difference,mixing enthalpy,mixing entropy,Gibbs free energy of mixing and the electronegativity difference for solid solution and amorphous phases were calculated based on Miedema’s approach of the regular solution model.It was shown that the atomic size difference and the ratio between the Gibbs free energies of mixing of the solid solution and amorphous phases were the most significant parameters controlling the film crystallinity.     

Formation of zirconium metallic glass

Bulk metallic glasses are commonly produced by the rapid cooling of liquid alloys. They have emerged over the past decade as a novel class of materials, with attractive properties and technological promise. The bulk metallic glasses so far produced contain three or more component elements. These complex compositions are necessary to frustrate the crystallization of the liquid melt on cooling, but can also lead to phase separation, which is detrimental to the thermal and mechanical properties of metallic glasses. Here we report, using X-ray diffraction measurements, the formation of a bulk metallic glass from elemental zirconium at high static pressures and low temperatures (relative to its melting temperature at atmospheric pressure). Amorphous zirconium can be recovered at ambient conditions and demonstrates a superior thermal stability compared to amorphous alloys, which could lead to new high-temperature applications of amorphous metals.     

Magnetocaloric effect in Er-Al-Co bulk metallic glasses

A series of Er-Al-Co bulk metallic glasses (BMGs) have been prepared by the copper mold casting method. The glass forming ability and magnetocaloric effect (MCE) for these alloys have been investigated. The second-order magnetic transition from para-magnetic to ferromagnetic states takes place at about 9 K. These BMGs exhibit excellent MCE because of their large effective magneton number; Er56Al24Co20 BMG has a maximum entropy change and refrigeration capacity of 16.06 J kg-1 K-1 and 546 J kg-1,respectively...     

Thermodynamic properties and microstructural characteristics of binary Ag-Sn alloys

The liquidus and solidus temperatures and enthalpy of fusion for Ag-Sn alloys are systematically measured within the whole composition range by differential scanning calorimetry (DSC). The measured enthalpy of fusion is related to Sn content by polynomial functions, which exhibit one maximum value at 52 wt%Sn and two minimum values around 21 wt%Sn and 96.5 wt%Sn, respectively. The liquidus slope, the solidification temperature interval, the solute partition coefficient and the entropy of fusion are calculated on the basis of the measured results. The undercoolability of those liquid Ag-Sn alloys solidifying with primary (Ag) solid solution phase is stronger than the other alloys with the preferential nucleation of ζ and ε intermetallic compounds. Morphological observations reveal that peritectic reactions can rarely be completed, and the peritectic microstructures are always composed of both primary and peritectic phases.     

Deformation induced structural evolution in bulk metallic glasses

The structural behavior of binary Cu50Zr50 and ternary Cu50Zr45Ti5 bulk metallic glasses (BMGs) under applied stress was investigated by means of in-situ high energy X-ray synchrotron diffraction. The components of the strain tensors were determined from the shifts of the maxima of the atomic pair correlation functions (PDF) in real space. The anisotropic atomic reorientation in the first-nearest-neighbor shell versus stress suggests structural rearrangements in short-range order. Within the plastic deforma...     

Roles of Co element in Fe-based bulk metallic glasses utilizing industrial FeB alloy as raw material

A series of Fe-based bulk metallic glasses were fabricated by a conventional copper mold casting method using a kind of Fe-B industrial raw alloy. It is found that Fe-B-Y-Nb bulk metallic glass with 3 at% of Co addition possesses the best glass forming ability, thermal stability, hardness, magnetic property and anti-corrosion property. The hardness test result indicates a synchronically trend with glass-forming ability parameters. The excellent glass-forming ability and a combination of good mechanical and functional properties suggest that the alloys in this work might be good candidates for commercial use.     

Formation and biocorrosion behavior of Zr-Al-Co-Nb bulk metallic glasses

Ni-and Cu-free Zr-Al-Co-Nb glassy alloys with different Nb and Co contents were synthesized by melt spinning and copper mold casting.The effects of Nb addition to partially replace Co in the Zr55Al20Co25 glassy alloy on the glass-forming ability,thermal properties,in-vitro biocorrosion behavior and surface wettability of the metallic glasses were investigated.Although addition of Nb up to 5 at.% slightly decreased the supercooled liquid region and the glass-forming ability(GFA),the alloys could be casted in a bulk glassy rod form with diameters up to 3mm.The Zr-Al-Co-Nb glassy alloys were spontaneously passivated with low passive current densities in phosphate buffered saline and Hanks’ solution.Substitution of "toxic" Co by Nb is effective in improved the corrosion resistance of the Zr-Al-Co glassy alloy.Water contact angle measurements showed that Nb addition increased the hydrophilicity of the glassy alloys,which may enhance cell adhesion of the alloys in biomedical applications.     

Zr基大块非晶的研究

利用射流成型法制备出Ｚｒ５２．５Ｃｕ１４．６Ａ１１０Ｔｉ５大块非晶,该合金系统具有很强的玻璃形成能力和宽的过冷区,其玻璃转化温度Ｔｇ＝６５０．６３Ｋ,晶化温度Ｔｘ＝７２１．９０Ｋ,过冷区△Ｔｘ＝Ｔｘ－Ｔｇ＝７１．２７Ｋ,Ｖｉｃｋｅｒ硬度为５５８ｋｇ／ｍｍ＾２,压缩断裂强度１７３０ＧＰａ,弹性模量８２ＧＰａ,观察其断口有大量纹络状河流花样,并有融化的液滴存在,该合金系统大的玻璃形成能力应归功于合金组     

Cu-Zr-Ag-Al非晶的晶化动力学研究

利用差示扫描热分析法(DSC)和X射线衍射仪(XRD),并借助Kempen模型和Kissinger方程,研究了不同加热速率下Cu45 Zr45 Ag7Al3非晶合金晶化过程及非等温晶化动力学.在连续加热条件下,随升温速率的加快,Cu45Zr45Ag7Al3非晶合金的特征温度Tg,Tx和Tp均向高温区移动,且过冷液相区间扩大.计算了该合金的激活能,分别为Eg=431.1kJ/mol,Ex=307.2 kJ/mol和Ep=339.5 kJ/mol;并计算出相应的Avrami指数n(分别为5.2和1.9),表明该非晶合金的晶化是以界面控制的多晶型晶化为主.     

Deformation induced structural evolution in bulk metallic glasses

The structural behavior of binary Cu50Zr50 and ternary Cu50Zr45Ti5 bulk metallic glasses (BMGs) under applied stress was investigated by means of in-situ high energy X-ray synchrotron diffraction. The components of the strain tensors were determined from the shifts of the maxima of the atomic pair correlation functions (PDF) in real space. The anisotropic atomic reorientation in the first-nearest-neighbor shell versus stress suggests structural rearrangements in short-range order. Within the plastic deformation range the overall strain of the metallic glass is equal to the yield strain. After unloading,the atomic structure returns to the stress-free state,and the short-range order is identical to that of the undeformed state. Plastic deformation,however,leads to localized shear bands whose contribution to the volume averaged diffraction pattern is too weak to be detected. A concordant region evidenced by the anisotropic component is activated to counterbalance the stress change due to the atomic bond reorientation in the first-nearest-neighbor shell. The size of the concordant region is an important factor dominating the yield strength and the plastic strain ability of the BMGs.     

Magnetocaloric effect in Er-Al-Co bulk metallic glasses

A series of Er-Al-Co bulk metallic glasses (BMGs) have been prepared by the copper mold casting method. The glass forming ability and magnetocaloric effect (MCE) for these alloys have been investigated. The second-order magnetic transition from para-magnetic to ferromagnetic states takes place at about 9 K. These BMGs exhibit excellent MCE because of their large effective magneton number; Er56Al24Co20 BMG has a maximum entropy change and refrigeration capacity of 16.06 J kg-1 K-1 and 546 J kg-1,respectively,under the field of 50 kOe (10 kOe=795.775 kA/m) indicating that these BMGs are potential candidate magnetic materials for hydrogen liquefaction.     

Chemical composition dependence of atomic oxygen erosion resistance in Cu-rich bulk metallic glasses

The effect of atomic oxygen(AO) on the surface oxidation of several typical Cu-based bulk metallic glasses(BMGs) was studied in the present work.The AO source using in this study is generated by discharge plasma type ground simulation equipment.The AO erosion/oxidation resistances of the amorphous alloy samples were assessed based on the analysis of mass loss,surface color and microstructure.It is found that these Cu-based BMGs possess good AO erosion/oxidation resistance and their resistance to AO erosion/oxidation strongly depends on the chemical composition.For the samples containing more Ag and/or Cu,the AO erosion/oxidation resistance is weaker.The present result is important for designing new metallic glasses using as space materials.     

Centimeter-scale-diameter Co-based bulk metallic glasses with fracture strength exceeding 5000 MPa

Co48-xFexCr15Mo14C15B6Er2 (x = 2.5 and 5) bulk metallic glasses (BMGs) with critical size (dc) up to 15 mm in diameter were synthesized by copper mold casting. Co43Fe5Cr15Mo14C15B6Er2 BMG has a wide supercooled liquid region (84 K) and ultrahigh fracture strength exceeding 5000 MPa,which is the highest value for reported metallic glasses with dc exceeding 1 cm. Furthermore,the Poisson ratio,Young modulus,shear modulus and bulk modulus of this alloy were evaluated to be 0.31,217 GPa,82 GPa and 214 GPa,respectively. The ideal configurational entropy of Co48-xFexCr15Mo14C15B6Er2 (x = 0 and 5) has been calculated. The introduction of the similar element Fe in the Fe-free Co-Cr-Mo-C-B-Er alloy will be beneficial to increasing the ideal config-urational entropy and depressing the critical cooling rate to achieve greater glass-forming ability. The combination of superior glass-forming ability and ultrahigh fracture strength makes the present Co48-xFexCr15Mo14C15B6Er2 (x = 2.5 and 5) BMGs promising candidates as advanced structural materials.     

非晶态合金(Fe_(100-x)M_x)_(83)B_(17)和Zr_(100-x)M_x的杨氏模量

用超声波脉冲透射技术获得了三元非晶态合金(Fe_(100-x)M_x)_(83)B_(17)和二元非晶态合金Zr_(100-x)M_x的声速,并确定了它们的杨氏模量。对于前者合金元素M指Cr,Mo,W,Zr和Co;对于后者指Fe,Ni和Co。文中讨论了声速与组分的原子百分数含量x之间的关系,并讨论了近程有序,合金元素密度以及不同尺寸原子之间的随机堆砌引起的致密化等对声速的影响。     

Solid solution strengthening in multicomponent fcc and bcc alloys:Analytical approach

Based on virtual solvent concept, novel methods are developed to determine interatomic distance, atomic size misfit, and elastic modulus misfit in multicomponent alloys with components having the crystal structure differing from that of the alloy. The combination of the different methods results in a number of models to calculate solid solution strengthening. These models are assessed with view point of the best fit to experimental data. The models giving the most reliable strengthening prediction can be used for an evolutionary design of strong and stable multicomponent alloys.     

Deformation behavior during nanoindentation in Ce-based bulk metallic glasses

Recently, bulk metallic glasses (BMGs) have at- tracted a great deal of attention due to their extremely high strength, improved wear resistance and excellent corrosion resistance[1-7]. However, it is known that their structural applications are currently…     

二元胶体的熵驱动相变

利用二元胶体的硬球模型,讨论了胶体的熵驱动相变机制,排斥体积发挥了重要作用,增加小球的自由体积,导致系统的平移熵增加,同时系统的混合熵减少,随着溶液浓度增加,必须保证小球有足够的平移熵,导致系统相分离的发生,溶液呈现宏观有序.     

多组元AlxTiVCrMnFeCoNiCu高熵合金的室温力学性能

依据多组元高混合熵合金的合金设计理念,设计了一族九组元AlxTiVCrMnFeCoNiCu高熵合金,并研究了该合金系室温力学性能.结果表明:(1)合金系具有超过1.3GPa的断裂强度,其中AlTiVCrMnFeCoNiCu合金达2.4GPa,同时AlTiVCrMnFeCoNiCu和Al2TiVCrMnFeCoNiCu两种合金还具有一定的压缩塑性;(2)合金系枝晶和枝晶间隙区均具有很高的显微硬度,且随Al含量的提高而近线性提高;(3)固溶强化机制、纳米相弥散强化机制和面心立方/体心立方相转变使得合金系具有很高的断裂强度和显微硬度.