Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

Bulk metallic glasses(BMGs)have been devel-oped in many alloy systems during past decade.Among these systems,rare-earth(RE)metal-basedBMGs are ones of those found earliest and with betterglass forming ability(GFA).For example,La-basedBMGs were the first a…     

Development of bulk metallic glasses based on the Dy-Al binary eutectic composition

A series of dysprosium-based ternary, quadruple, and quintuple bulk metallic glasses （BMGs） based on Dy-Al binary eutectic composition were obtained with the partial substitution of Co, Gd, and Ni elements, for dysprosium. The results showed that the Dy31Gd25Co20Al24 alloy, which had the best glass forming ability （GFA）, could be cast into an amorphous rod with a diameter of 5 ram. The GFA of alloys was evaluated on the basis of the supercooled liquid region width, 7 parameter, the formation enthalpy, and the equivalent electronegativity difference of amorphous alloys. It was found that the eutectic composition was closely correlated with the GFA of the Dy-based BMGs.     

Development and Characterization of Low-Density Ca-Based Bulk Metallic Glasses: An Overview

Ca-based bulk metallic glasses (BMGs) have unique properties and represent a new seventh group of BMGs. Many of them have excellent GFA, which can be related to their efficient atomic packing, low onset driving force for crystallization, and high viscosity (high relaxation time) of the supercooled liquid. The Ca-based glasses have the lowest density and elastic moduli among all BMGs discovered to date. Unfortunately, as many other glasses, Ca-based BMGs are brittle below the glass transition temperature, and they also have marginal oxidation and corrosion resistance. The latter can be improved by proper selection of alloying elements. In this article, we review recent work on the development of low-density Ca-based BMGs and discuss the effect of alloy composition on the thermal, physical, and chemical properties of these glasses. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Glass-Forming Ability for Mg-Cu-Nd Alloys

The glass-forming ability (GFA), thermal stability, and mechanical properties of ternary Mg-Cu-Nd alloys were investigated. The results show that the amorphous structure of about 3 mm in diameter can be obtained in the composition range of 53 to 59 at. pct Mg, 32 to 38 at. pct Cu, and 9 to 11 at. pct Nd. Differential scanning calorimeter (DSC) measurements show that the bulk metallic glasses (BMGs) exhibit distinct glass transition temperature and supercooled liquid region before crystallization. However, the GFA for the present alloys cannot be explained by the existing calculated parameters, while it can be better explained by the strategy for pinpointing the best glass-forming alloys in terms of microstructure evolution. Compared with Mg₅₇Cu₃₃Y₁₀ BMG, Mg-Cu-Nd BMGs show a better fracture strength, which is increased with the copper content for those Nd-containing BMGs. Viscous flow was observed on the fracture surfaces of compressive samples, showing that apparent strengths can be reproducible. The Mg-Cu-Nd BMGs are challengeable in potential application for engineering materials due to their high strength and low cost. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Prediction of Bulk Metallic Glass Formation in Cu–Zr–Ag–Hf System by Thermodynamic and Topological Modeling

Cu based bulk metallic glasses (BMGs) are widely studied because of their high glass forming ability (GFA) and interesting combination of properties such as high strength coupled with good ductility and low cost. With these attributes, Cu based BMGs are being projected as promising materials for practical applications. The process of glass formation in metallic systems is a challenging task and alloys should be cooled from the liquid state at rates faster than a critical cooling rate (R_c) to resist crystallization. Interestingly, composition plays an important role in achieving easy glass formation, which is usually measured in terms of R_c. In the present work, attempt has been made to identify the composition for easy glass formation in Cu based quaternary system by theoretical approach. A GFA parameter P_HS, which is a product of enthalpy of chemical mixing (?H_chem) and mismatch entropy normalized with Boltzmann??s constant (?S_??/k_B) is used to identify the best glass forming composition in Cu?CZr?CAg?CHf system. Further, a new parameter P_HSS, which is a product of P_HS and configurational entropy (??S_config/R) is found to illustrate strong correlation with GFA. An attempt has also been made to correlate P_HSS parameter with critical diameters and R_c using reported data in Cu?CZr?CAg?CHf system.     

Glass-Forming Ability of Mg–Cu–Ni–Gd Bulk Metallic Glasses with High Strength

The glass-forming ability (GFA) of Mg–Cu–Ni–Gd alloy system was evaluated using copper mold casting. A three-dimensional composition map of Mg–Cu–Ni–Gd system with GFA over 6 mm was revealed, confirming that the Ni addition decreased the GFA of Mg–Cu–Gd system. The maximum Ni tolerance was about 6 at.% for the Mg–Cu–Ni–Gd BMGs with GFA over 6 mm. The compressive tests displayed that the Ni addition as small as 3.45 at.% could result in higher strength for the Mg–Cu–Gd BMGs. The Mg–Cu–Ni–Gd system with small Ni content can be balanced candidates for the Mg-based BMGs with both acceptable GFA and high strength.     

Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd Bulk Metallic Glasses with Potential for Biomedical Applications

Ti₄₇Cu_38−xZr_7.5Fe_2.5Sn₂Si₁Ag₂Pd_x (x = 1, 2, 3, and 4 atomic percent, at. pct) bulk metallic glasses (BMGs) with potential for biomedical applications were fabricated by copper-mold casting. The Ti-based BMGs exhibited high glass-forming ability (GFA) with critical diameters of 4 to 5 mm and a supercooled liquid region over 50 K, though the high contents of Pd slightly decreased the GFA. The additions of 2 and 3 at. pct Pd benefited the improvement of plasticity, and the resultant BMGs showed the relatively low Young’s modulus of about 100 GPa, high compressive strengths of 2174 to 2340 MPa, and compressive plastic strain of around 4 pct. The addition of Pd also decreased the passive current density and increased the pitting potential of the Ti-based BMGs in the Hank’s solution, leading to the enhanced bio-corrosion resistance of the BMGs. Furthermore, the cell adhesion, viability, and proliferation behaviors revealed that the present Ti-based BMGs possess as good biocompatibility as that of the Ti-6Al-4V alloy. These results demonstrated the potential of the Ti-Cu-Zr-Fe-Sn-Si-Ag-Pd BMGs as biomedical materials.

     

Formation, Crystallization Behavior, and Soft Magnetic Properties of FeCSiBP Bulk Metallic Glass Fabricated Using Industrial Raw Materials

Formation of pseudo-binary Fe-C-Si-B-P bulk metallic glasses (BMGs) with good glass-forming ability (GFA) and soft magnetic properties prepared using industrial pig-iron and P-Fe alloys as raw materials was investigated. It was found that the GFA could be enhanced by tuning the content of carbon, and fully glassy rods with a maximum diameter of 2?mm were obtained in the Fe_77.3C_5.9Si_3.3B_4.8P_8.7 alloy. The crystallization behavior and its effects on the soft magnetic properties of the Fe_77.3C_5.9Si_3.3B_4.8P_8.7 alloy were analyzed. The superior magnetic properties, coupled with large GFA and low cost of raw materials, make the current Fe-based BMGs promising for potential applications in electric industries.     

[(Fe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>)<Subscript>0.75</Subscript>B<Subscript>0.20</Subscript>Si<Subscript>0.05</Subscript>]<Subscript>96</Subscript>Nb<Subscript>4</Subscript> Metallic Glasses with Small Cu Additions

Recently, (Fe-Co)-B-Si-Nb bulk metallic glasses (BMGs) were produced. Such BMGs exhibit high glass-forming ability (GFA) as well as good mechanical and magnetic properties. These alloys combine the advantages of functional and structural materials. The soft magnetic properties can be enhanced by nanocrystallization. To force the nanocrystallization, small content of Cu was added to the starting composition. In this article, {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100–x Cu _x glassy alloys (x = 1, 2, and 3) were chosen for investigation. The GFA and the thermal stability of these alloys were evaluated. The effects of crystallization during heat-treatment processes on the phase evolution and the magnetic properties, including M _s , H _c , and T _c , in these alloys were investigated. The phase analyses were done with the help of the X-ray diffraction patterns recorded in situ by using the synchrotron radiation in transmission configuration.     

Understanding the Effect of Oxygen on the Glass-Forming Ability of Zr55Cu55Al9Be9 Bulk Metallic Glass by ab initio Molecular Dynamics Simulations

Oxygen (O) is an inevitable impurity in bulk metallic glasses (BMGs) and its influence over the glass-forming ability (GFA) of BMGs is a longstanding controversy. The present ab initio molecular dynamics (AIMD) simulations indicate that the GFA decreases upon introducing 0.78 at. pct O in the amorphous Zr₅₅Cu₅₅Al₉Be₉ (at. pct), while examining the evolution of atomic configurations and kinetic properties in BMGs. This study includes a comprehensive analysis using pair correlation function (PCF), bond pair analysis (BPA), and Voronoi polyhedra construction. It is concluded that the incorporation of O leads to a decline in the closely packed icosahedral polyhedrons, where the atom O is coordinated with Be and Zr in the first nearest shell to form the O-centered clusters with enhanced ordering. Mean square displacement (MSD) analysis also shows that the trace O could induce remarkable acceleration of atomic mobility, therefore increasing crystallization tendency of the Zr₅₅Cu₅₅Al₉Be₉ alloy. The present results illuminate the role of O in the metallic glass-forming process and reveal the underlying role of O in the GFA of the Zr-Cu amorphous alloys.

     

The Effect of Purification on the Glass-Forming Ability of a Pd-Cu-Si Alloy

The copper mold casting method is now commonly used for preparing bulk metallic glasses (BMGs). In the present work, it was found that, by employing the copper mold casting method, Pd_77.5Cu₆Si_16.5 (at. pct) glassy rods with 1-mm diameter could be prepared, while the ?2-mm Pd_77.5Cu₆Si_16.5 casting rod possesses some crystalline phases embedded within the glass matrix, confirming that the critical size of the glassy alloy is about 1?mm. By melt purification with fluxing treatment, the critical size of the glassy rod prepared by copper mold casting is increased to 4?mm. Based on thermal property analysis, it was found that melt purification by the fluxing method can greatly enhance the thermal stability and increase the glass forming ability (GFA) of the Pd-Cu-Si alloys. The as-prepared ?4-mm Pd-Cu-Si glassy rod exhibits a reduced glass transition temperature (T _rg ) of 0.599, a supercooled liquid region (??T) of 74?K (74?°C), and a ?? parameter of 0.419.     

Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au _x Si₁₇Cu_75.5–x Ag_7.5 (x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature (T _g ) and crystallization temperature (T _x ) decreased with increasing Au content. The ultralow T _g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength (σ _c,f ), Young’s modulus (E), and Vicker’s hardness (H _v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T _g and T _x , and mechanical properties, i.e., σ _c,f , E, and H _v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.     

Effect of Solute Contents of Al-Ni-Sr Alloy on Glass Forming Ability and Thermal Stability

Glass forming ability (GFA) and structural characterization of a new amorphous Al-Ni-Sr alloy melt spun were investigated on the theory of the factors for the glass formation. The GFA was varied with the ratio of Ni to Sr in detail and successful amorphous phase dispersed with 2 ～ 5 nm precipitates was prepared from Al-Ni5-Sr3. Thermal stability and crystallization behavior of the amorphous phase were determined by continuous and isothermal heating technique on DCS, resulting that the crystallization occurs by the growth of fcc Al nanocrystals on the preexistent nuclei.     

Thermal Stability and Crystallization Kinetics in Y-Based Metallic Glasses

The glass-forming ability (GFA) and thermal stability of Y_56–x Sc _x Al₂₄Co₂₀ (0 ≤ x ≤ 18) alloys produced by melt spinning and suction casting have been investigated. The results show that the addition of a Sc element improves the GFA of Y-based metallic glasses, and the Y₄₁Sc₁₅Al₂₄Co₂₀ alloy has a reduced glass transition temperature T _rg (=T _g /T _l ) as large as 0.641. A new bulk metallic glass (BMG), Y₄₁Sc₁₅Al₂₄Co₂₀, with a diameter of 5 mm was successfully fabricated. The superior GFA after the Sc addition can be attributed to the ability of Sc to effectively alleviate the detrimental effect of oxygen as well as appropriate atomic-size mismatch and large negative heat of mixing among constituent elements. Crystallization kinetic studies show that the activation energies for the Y₄₁Sc₁₅Al₂₄Co₂₀ BMG are E _g  = 4.92 eV and E _x  = 3.18 eV, for the glass transition and crystallization, respectively, which are the highest in all known rare-earth (RE)–based BMGs. The values of the fragility parameter m for the Y₅₆Al₂₄Co₂₀ and Y₄₁Sc₁₅Al₂₄Co₂₀ BMGs are 72 and 42, respectively. The significant decrease in m implies that the GFA and the thermal stability increase with the addition of Sc in the Y₅₆Al₂₄Co₂₀ alloy. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

等离子喷涂制备铁基非晶合金涂层的结构及其耐腐蚀性能的研究

选用铁基非晶合金粉末(含有Cr,Mo,Ni,P,B,Si)采用等离子喷涂方法在Q235低碳钢和不锈钢基体上制备合金涂层,通过金相显微镜、X射线衍射和扫描电子显微镜研究分析了涂层的相组成和显微结构。研究结果表明:该涂层与基体结合紧密,涂层均匀致密度高,涂层主要由非晶组成;涂层由变形成条带状的粒子相互搭接而成,其中含有少量未熔粒子和氧化物。所制备的铁基非晶涂层气孔率约2.5%,硬度为750～850 HV0.1。通过在H_2SO_4、HCl和NaOH溶液中进行浸泡腐蚀和三电极电化学分析,表明该涂层具有优异的耐腐蚀能力。     

Zr-Cu薄膜生长及力学性能的分子动力学模拟

根据磁控溅射实验条件, 采用分子动力学方法, 在Si(100)面上模拟沉积了三种Zr_xCu_100-x(x=50, 70和90)合金薄膜.通过计算径向分布函数(RDF)及X射线衍射(XRD)分析了沉积薄膜的形貌结构, 并探讨了玻璃形成能力和五重局部对称性之间的关系.最后研究了沉积薄膜的力学性能, 及薄膜厚度对拉伸过程的影响.研究结果表明: Zr-Cu合金玻璃形成能力与五重局部对称性之间存在一定的相关性, 沉积玻璃薄膜比晶体薄膜表现出更好的延展性, 其中Zr₅₀Cu₅₀沉积玻璃薄膜比近共晶成分玻璃薄膜(Zr₇₀Cu₃₀)具有更大的拉伸强度; 沉积薄膜存在一定的尺寸效应, 薄膜相对厚度越小, 其拉伸强度越大.      

Effect of Oxygen on Microstructure Evolution and Glass Formation of Zr-based Metallic Glasses

The effect of oxygen on the microstructure evolution and glass formation of Zr-based bulk metallic glasses(BMGs)was studied in detail.It was found that oxygen did not form oxides or dissolve in glass matrix,but induced the precipitation ofα-Zr which has the high affinity and solubility of oxygen in the Zr-based bulk metallic glass(ZrBMG).With the precipitation ofα-Zr,the remaining melts contain much lower oxygen content and have strong glass formation,resulting in the formation ofα-Zr/BMG composite.The findings provide an important insight into the mechanism of the oxygen on glass formation,and give us a useful guideline to avoid the oxygen detrimental for designing new BMGs.     

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65Cu25Gd10 bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter （DSC） was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA. The mechanism of the GFA decrease was also discussed.     

Primary Transformation Kinetics in Zr-Al-Ni-Cu-Pd Bulk Metallic Glass Correlated with Relaxation State

The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10^?9 m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs.