Effect of silver on the glass forming ability of MgCuGdY bulk metallic glasses

Bulk metallic glasses have been synthesized in the Mg_xCu_yAg_zGd₁₀ and Mg_xCu_yAg_zGd₉Y₂ systems by HF melting and injection in conical and cylindrical shape copper moulds in order to determine their critical diameter and to prepare samples for mechanical tests. Silver can be substituted either to the copper or to the magnesium leading to different alloys whose properties have been measured by differential scanning calorimetry (DSC) curves and X-ray analyses. Up to a high diameter (10 mm), they present the structure of bulk metallic glasses. The effect of silver is in general to reduce the glass transition region (ΔT = T_x − T_g) but with an increase of the critical diameter which is not in agreement with glass forming ability (GFA) criteria when choosing ΔT as so, however the γ = T_x/(T_g + T_l) parameter is in agreement with the GFA as the γ parameter is increasing when the critical diameter is increasing. The effect of silver in the gadolinium–yttrium-based alloys is to decrease the ΔT range from 69 K without silver to 40 K with 9 at.% of Ag. Mechanical measurements made by compression tests at room temperature show that these alloys stay brittle with an elastic limit above 800 MPa but with no improvement of plasticity due to silver.     

Ti-Cu基合金玻璃形成能力与力学性能

本文基于“二元共晶混合”法设计Ti-Cu-Ni-Zr合金成分,通过水冷铜模铸造法制备出不同直径Ti-Cu-Ni-Zr合金棒。利用X射线衍射仪(XRD)、差示扫描量热仪(DSC)、万能试验机和扫描电镜(SEM)研究了Ti-Cu-Ni-Zr合金玻璃形成能力和力学性能。结果表明,Ti-Cu-Ni-Zr合金具有较高的玻璃形成能力,其临界直径可达4 mm;Ti-Cu-Ni-Zr合金玻璃形成能力近似相等,而表征玻璃形成能力的热力学参数过冷液相区ΔT_x,参数γ,约化玻璃转变温度T_rg也近似相等。通过对合金力学性能进行研究,结果表明,Ti_32.3Cu_47.6Ni_7.9Zr_12.2和Ti_31.6Cu_48.2Ni_7.7Zr_12.5大块非晶合金分别具有0.7%和0.2%的塑性,而Ti₃₀Cu_49.5Ni_7.2Zr_13.3和Ti_28.55Cu_50.7Ni_6.75Zr₁₄大块非晶合金断裂机制近似为脆性断裂。Ti-Cu-Ni-Zr大块非晶合金塑性越大,其剪切带数量越多且扩展深度越大,反之亦然。另外,对于塑性材料,当锯齿流变振幅越大时,对应样品表面剪切带扩展深度越明显,当锯齿流变振幅越小时,对应样品表面剪切带扩展深度较浅;近似脆性断裂的锯齿流变对应次剪切带萌生,而对于完全脆性大块非晶合金,在应力-应变曲线上并未发现锯齿流变现象,相应的在样品外表面也并未发现次剪切带。     

Formation and mechanical properties of bulk Cu-Ti-Zr-Ni metallic glasses with high glass forming ability

Bulk amorphous Cu52.5Ti30Zr11.5Ni6 and Cu53.1Ti31.4Zr9.5Ni6 alloys with a high glass forming ability can be quenched into single amorphous rods with a diameter of 5 mm, and exhibit a high fracture strength of 2 212 MPa and 2 184 MPa under compressive condition, respectively. The stress—strain curves show nearly 2% elastic strain limit, yet display no appreciable macroscopic plastic deformation prior to the catastrophic fracture due to highly localized shear bands. The present work shows clearly evidence of molten droplets besides well-developed vein patterns typical of bulk metallic glasses on the fracture surface, suggesting that localized melting induced by adiabatic heating may occur during the final failure event.     

Enhanced glass forming ability and refrigerant capacity of a Gd55Ni22Mn3Al20 bulk metallic glass

In this work, a small amount of Mn was added to a Gd₅₅Ni₂₅Al₂₀ glass forming alloy, as a replacement for Ni, and a Gd₅₅Ni₂₂Mn₃Al₂₀ bulk metallic glass (BMG) was obtained by suction casting. Its glass forming ability (GFA) was characterized by X-ray diffraction and differential scanning calorimetry, and its magnetic properties were measured using a magnetic property measurement system. It is found that the minor Mn addition can significantly improve both the GFA and the magnetocaloric effect (MCE) of the alloy. The refrigerant capacity (RC) of the BMG can reach a high value of 825 J kg⁻¹ under a field of 3979 kA/m, which is about 29% larger than that of a Gd₅₅Ni₂₅Al₂₀ BMG. The effect of the minor Mn addition on the GFA and MCE of the BMG was investigated in the study.     

微量元素对Cu-Zr-Al块体金属玻璃形成能力及力学性能的影响

研究微量元素Ag、Ti、Ga、Ni和Sn对Cu55Zr38Al7铜基块体金属玻璃形成能力及力学性能的影响。结果表明:添加2%(摩尔分数)的Ag、Ti或Ga均可以提高Cu55Zr38Al7合金的玻璃形成能力;用6%的Ag替代Cu,玻璃棒的临界直径可从2 mm增加到4 mm;因此,替代化学性质相似的元素或者扩大合金系的原子尺寸范围对提高玻璃形成能力具有显著的效果;然而,添加微量元素均不同程度地降低Cu-Zr-Al金属玻璃的硬度。断口表面形貌显示;微量相似元素替代影响基体在压缩过程中剪切带的繁殖;在微量元素替代的伪四元铜基块体金属玻璃中,2%Ti和2%Ag替代可分别获得最大压缩强度2 163 MPa和最大压缩应变8.7%。因此,通过添加微量元素可以调谐金属玻璃的玻璃形成能力和力学性能。     

Zr-Co(Cu)-Al bulk metallic glasses with optimal glass-forming ability and their compressive properties

The formation of bulk metallic glasses (BMGs) in the ternary Zr₅₆Co₂₈Al₁₆ and quaternary Zr₅₆Co_28–xCu_xAl₁₆ (x=2, 4, 5, 6, 7, mole fraction, %) glassy alloys was investigated via the copper mold suction casting method. The main purpose of this work was to locate the optimal BMG-forming composition for the quaternary ZrCo(Cu)Al alloys and to improve the plasticity of the parent alloy. The X-ray diffractometry (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) were used to investigate the glassy alloys structure and their glass forming ability (GFA). In addition, the compression test, microhardness, nano-indentation and scanning electron microscopy (SEM) were utilized to discuss the possible mechanisms involved in the enhanced plasticity achievement. The highest GFA among Cu-containing alloys was found for the Zr₅₆Co₂₂Cu₆Al₁₆ alloy, which was similar to that of the base alloy. Furthermore, the plasticity of the base alloy increased significantly from 3.3% to 6% for the Zr₅₆Co₂₂Cu₆Al₁₆ BMG. The variations in the plasticity and GFA of the alloys were discussed by considering the positive heat of mixing within Cu and Co elements.     

Unusual volume change associated with crystallization in Ce-Ga-Cu bulk metallic glass

In the general concept of crystallization kinetics, the amorphous solid with a number of open spaces transforms into a thermodynamically stable crystal, being denser than the corresponding amorphous phase. However, we unambiguously show that Ce₇₀Ga₆Cu₂₄ bulk metallic glass (BMG) exhibits volume expansion together with the density decrease upon crystallization in sharp contrast to other amorphous materials. This anomalous behavior is found to be explained by the formation of structurally loose interfaces among crystallites in the crystalline Ce₇₀Ga₆Cu₂₄ in addition to the disappearance of Ce-concentrated densely-packed local structure originally located in the amorphous matrix of BMG.     

Zr_(56.6)Cu_(17.3)Ni_(12.5)Al_(9.6)Ti_4块体非晶合金的玻璃形成能力

采用低纯度的原料,通过电弧熔炼铜模铸造法制备了直径达10mm的Zr56.6Cu17.3Ni12.5Al9.6Ti4非晶合金圆棒。该合金玻璃转变温度tg=385.8℃,晶化温度tx=464.2℃,过冷液相区温差Δtx=78.4℃,约化玻璃温度trg(tg/tmL)=0.62。以基于DTA的合金凝固点偏移的方法确定该合金的临界冷却速度Rc=7.1℃/s,低于商业合金Vit.105合金的临界冷速(约为10℃/s)。楔形试样对比结果显示:Zr56.6合金试样中的非晶组织区域明显大于Vit.105合金的,预示前者具有较好的实际玻璃形成能力。以上结果表明,Zr56.6Cu17.3Ni12.5Al9.6Ti4合金是Zr Al Ni Cu Ti系中玻璃形成能力最强的合金之一。     

A thermodynamic approach to assess glass-forming ability of bulk metallic glasses

According to the Gibbs free energy difference between liquid and crystal, a thermodynamic glass-forming ability(GFA) parameter related to characteristic temperatures, onset crystallization temperature(T_x) and liquidus temperature(T_l), was proposed for evaluating the GFA of bulk metallic glasses(BMGs). The new parameter defined as ω=T_l(T_l+T_x)/(T_x(T_l−T_x)) has good correlation with the critical section thickness(Z_c) of Ca-Mg-Cu BMGs. Being verified by the glasses data, including oxide glasses, which were used to validate the former GFA parameters, ω is one of the most reliable and applicable GFA parameters among T_rg (=T_g/T_l), γ(=T_x/(T_l+T_g)), α (=T_x/T_l), δ (=T_x/(T_l−T_g), and so on. Finally, predicting GFA of Cu-Ag-Zr-Ti and Cu-Zr-Ti-Al BMGs using ω was compared with the experimental results.     

Synthesis, thermal stability and properties of [(Fe1−xCox)72Mo4B24]94Dy6 bulk metallic glasses

A series of [(Fe_1−xCo_x)₇₂Mo₄B₂₄]₉₄Dy₆ (x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature (T_g) 860 K and crystallization temperature (T_x) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature (T_l). The [(Fe_0.8Co_0.2)₇₂Mo₄B₂₄]₉₄Dy₆ alloy showed the largest supercooled liquid region (ΔT_x = T_x − T_g = 92 K), reduced glass transition temperature (T_rg = T_g/T_l = 0.622) and gamma parameter (γ = T_x/(T_g + T_l) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm² was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61-61.78 A m²/kg and coercivity in the range of 222-264.2 A/m, which might be suitable for application in power electronics devices.     

Y、Gd、La和Ce对Zr(-Ti)-Cu-Ni-Al非晶形成能力和力学性能的影响

为了控制Zr(-Ti)-Cu-Ni-Al非晶合金中的O含量,进而改善其玻璃形成能力和力学性能,本研究基于稀土元素与O的强相互作用,向合金中添加Y、Gd、La和Ce等元素。使用铜模浇铸制备非晶合金,利用DSC、XRD和TEM对其非晶形成能力和微观结构进行分析,通过压缩试验和SEM对其力学性能及断裂方式进行表征。结果表明:Y的添加对合金的非晶形成能力具有较大的提升,在相对较低真空的气氛下,可制备出直径10mm以上的块体非晶,抗压缩断裂强度达1950 MPa。     

Saturated magnetization and glass forming ability of soft magnetic Fe-based metallic glasses

Saturated magnetization (B_s) and glass forming ability (GFA) are two important attributes of soft magnetic metallic glasses (MGs), both of which are affected by the local short-range order in amorphous structures. Based on the notion of free electron transfer, we propose a set of simple rules for the calculation of B_s from the chemical composition of soft magnetic Fe-based alloys. Through the comparison of the experimentally measured B_s and theoretically calculated B_s, we show that the soft magnetic Fe-based MGs can be generally categorized into two types: one has its GFA correlated positively with the ferromagnetic weakness and the other has its GFA correlated negatively with the ferromagnetic weakness. Finally, the structural mechanisms behind these correlations are discussed.     

Glass formation,thermal and mechanical properties of ZrCuAlNi bulk metallic glasses

The glass forming ability, thermal and mechanical properties of some ZrCuAlNi bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, D_c, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔT_x, and reduced glass transition temperature T_rg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ～40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s^?1, obtaining a elastic modulus of ～83 GPa, total deformation of ～5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.     

Improvement of corrosion resistance in NaOH solution and glass forming ability of as-cast Mg-based bulk metallic glasses by microalloying

The influences of the addition of Ag on the glass forming ability (GFA) and corrosion behavior were investigated in the Mg-Ni-based alloy system by X-ray diffraction (XRD) and electrochemical polarization in 0.1 mol/L NaOH solution.Results shows that the GFA of the Mg-Ni-based BMGs can be improved dramatically by the addition of an appropriate amount of Ag;and the addition element Ag can improve the corrosion resistance of Mg-Ni-based bulk metallic glass.The large difference in atomic size and large negative mixing enthalpy in alloy system can contribute to the high GFA.The addition element Ag improves the forming speed and the stability of the passive film,which is helpful to decrease the passivation current density and to improve the corrosion resistance of Mg-Ni-based bulk metallic glass.     

Role of yttrium in glass formation of Ti-based bulk metallic glasses

Starting with Zr of two different purities, Ti-based bulk metallic glasses (BMGs) with a nominal composition of Ti40Zr25Cu12Ni3Be20 were prepared. The effect of the addition of yttrium at levels of 0.2 at.%, 0.4 at.%, 0.5 at.%, 0.6 at.%, and 1 at.% on the glass forming ability (GFA) of the alloy has been investigated by means of metallography, X-ray diffraction, and differential scanning calorimetry. Experimental data in-dicates that high impurity content dramatically reduces the glass forming ability. Microalloying with 0.5 at.% Y is effective in suppressing the crystalline phase formation and alleviating the detrimental effect of oxygen in the low-purity alloy. On the contrary, in the alloy contain-ing high-purity element, the effective yttrium addition is less than 0.4 at.%. The results indicate that the beneficial effect of the optimum dopants is mainly due to scavenging the oxygen impurity via the formation of innocuous phase.     

Magnetic and magnetocaloric properties of ternary Gd-Co-Al bulk metallic glasses

Bulk metallic glasses (BMGs) with compositions of Gd₅₅Co_xAl_45−x (15 ≤ x ≤ 30) and Gd₆₀Co_yAl_40−y (15 ≤ y ≤ 30) were synthesized by an injection casting technique. Temperature dependence of magnetization of the BMGs indicates that their Curie temperatures can be tailored between 96 and 143 K by varying Gd and Co concentration. The magnetic entropy changes of the BMGs are greater than 9.0 J/kg K except for the Gd₅₅Co₃₀Al₁₅ glass that exhibits a reduced magnetization due to its large Co content. The relative cooling powers of the BMGs are greater than those of any other crystalline compounds and decrease with the increasing Co content.     

Effect of Ni on the formation and thermal behavior of NdA1Co metallic glasses

Nd60Al10Co30-xNix (x=0,5,10 and 15 at.pct) metallic glasses have been prepared using single-spinner and suck-casting method,and characterized using X-ray diffra...     

Anomalous packing state in Ce-Ga-Cu bulk metallic glasses

Formation mechanism of bulk metallic glasses (BMGs) with high glass-forming ability (GFA) has been a long-standing subject in the field of solid state physics. To highlight the GFA-associated local atomic structure, element-specific positron annihilation spectroscopy was conducted for recently discovered ternary Ce₇₀Ga_xCu_30-x (x = 6–13; at.%) BMGs. We succeeded in identifying the packing structure under the condition of ambient pressure, in which Ce atoms are concentrated more than that in Ce crystal. This anomalous glassy state is most efficiently formed at the Ga concentration of ∼10%, where the best glass-forming ability (GFA) is experimentally observed. First-principles computer simulation results suggest that this anomalous packing structure is associated with Ce-4f electron delocalization in the Ce-Ga-Cu BMGs. The findings provide unambiguous evidence for the relationship between the packing-efficient local structure and the GFA.     

Nd对块体Mg-Cu-Y-Nd非晶合金玻璃形成能力的影响

在非真空熔炼条件下采用工业纯原材料和负压铜模吸铸法制备Mg65Cu25Y10-xNdx(x=0,2,4,6,8,10)棒状试样,利用差示扫描量热(DSC)和X射线衍射(XRD)等方法分析Nd对Mg-Cu-Y-Nd非晶合金玻璃形成能力的影响。结果表明:Nd的含量(x)为0,4,6成分的合金试样具有完全非晶态组织,且x=4时具有最大的玻璃形成能力,其约化玻璃转变温度(Trg)为0.592,过冷液相区宽度(ΔTx)高达66 K;当x为2,8,10时,由于合金成分明显偏离共晶成分,玻璃形成能力降低,试样只含有少量非晶,且主要呈晶体组织特征。