Effect of Si, Pd and La additions on glass forming ability and thermal stability of Zr-Ni-based amorphous alloys

In the present paper, the influence of minor additions of Si, Pd and La with representative atomic sizes on glass forming ability (GFA) and thermal stability of Zr-Ni-based amorphous alloys has been investigated using X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results show that minor additions of La, Pd and Si can improve GFA of Zr-Ni-based alloys and La exhibits the optimum effect on enhancing GFA. The efficient cluster packing model can well explain the correlation between atomic sizes of additional elements and GFA of amorphous alloys. In addition, the relationship of the atomic size between the additional element and Zr has a more important effect on GFA than that between the additional element and Ni. The activation energy for crystallization of the Zr-Ni-based amorphous alloys with Si, Pd and La additions is obviously higher than that of the Zr_66.7Ni_33.3 amorphous alloy, and increases with decreasing distance between neighboring atoms. The thermal stability has a relation with topological short-range ordering of amorphous alloys. The proper addition of small atoms is preferential to enhance thermal stability of amorphous alloys due to stronger short-range ordering. Moreover, the small or intermediate atom addition can produce even better effect on thermal stability than the large atom addition.     

Evaluation of glass forming ability in ternary Ni62(Nb,Ta)38 alloys

The parameter γ¹ we previously defined has been proved to be valid in predicting the better glass former in several binary alloy systems, but is hard to be applied in the multi-component alloys because the phase diagrams of these alloys are usually not well constructed. In the present work, we attempt to extend the application of parameter γ¹ to a ternary alloy system and predict the better glass former in the Ni₆₂Nb_38-xTa_x (x = 5, 10, 15, 20, 25, 30, 35) alloys based on the systematic investigation on the phase evolution from Ni₆₂Nb₃₈ to Ni₆₂Ta₃₈. The prediction has been confirmed by the experimental results, indicating the validity of the parameter γ¹ in the Ni₆₂(Nb, Ta)₃₈ ternary alloys.     

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.     

Sr元素对Mg-Zn-Ca合金非晶形成能力和耐蚀性的影响

为改善Mg-Zn-Ca合金的非晶形成能力,采用铜模喷铸法制备了不同Sr含量的Mg-Zn-Ca-Sr合金,其直径为2和4mm棒材试样。利用XRD、SEM、DSC和电化学测试方法研究了Sr元素对Mg-Zn-Ca合金非晶形成能力和在模拟体液中耐蚀性的影响。结果表明,Mg_(65)Zn_(30)Ca_(5-x)Sr_x(x=0,0.5,1.0,1.5,原子分数%,下同)合金直径为2 mm棒材试样组织均为非晶态,而直径为4mm棒材试样均是由非晶和晶体相(Mg和MgZn相)组成,但晶体相的体积分数和尺寸随着Sr元素添加量的增加而减少,即合金的非晶形成能力提高,其中,Mg_(65)Zn_(30)Ca_4Sr_1合金非晶形成能力最强。电化学腐蚀测试结果表明,随着Sr含量增多,合金的腐蚀电位向正向移动,腐蚀电流密度减小,合金的耐蚀性逐渐增强,2 mm棒材试样中Mg_(65)Zn_(30)Ca_(4.5)Sr_(0.5)合金的耐蚀性最好,直径为4 mm棒材试样中Mg_(65)Zn_(30)Ca_4Sr_1合金的耐蚀性最强。     

Thermodynamics of equilibrium and partitionless solidifications in glass forming binary eutectic alloys

T₀ curves in the phase diagrams have been proven useful to understand thermodynamically glass formation in metallic alloys, emphasizing the importance of the metastable solid solutions crystallized partitionlessly. Here we focus on four typical binary eutectic alloys with distinct glass-forming abilities and interatomic interactions, Ag₆₀Cu₄₀, Sb_17.5Pb_82.5, Au_81.4Si_18.6, and Ni₂₄Zr₇₆. The thermodynamics involved in the liquid–solid solution transition at T₀ temperatures for the alloys of eutectic compositions are quantified, and the validity of the thermodynamic properties is evaluated. The comparison of the melting entropies for the equilibrium and partitionless solidifications reveals a basic relation. Based on the thermodynamics of the equilibrium phases and the solid solutions, an understanding of the glass formation of metallic alloys is proposed.     

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。     

Development of FeNiNbSiBP bulk metallic glassy alloys with excellent magnetic properties and high glass forming ability evaluated by different criterions

Fe₃₈Ni₃₈Nb_2.5B_21.5−x−yP_xSi_y (x, y = 1–8) bulk metallic glassy alloys with high glass forming ability and excellent magnetic properties were developed. Bulk samples with maximum diameters of 3 mm are fabricated by copper mold casting method. The glassy alloys have large ΔT_x of 40–70 K. The alloys exhibit excellent magnetic properties like extremely low H_c of 0.5–0.8 A/m, high μ_e of 1.6–2.85 × 10⁴ and comparatively high B_s of 0.6–0.8 T which changes regularly with the content variations of P, B and Si. By ascertaining applicability of the empirical GFA criterions, T_rg, α, β and γ can be used in evaluating the GFA of FeNiBSiPNb system alloys.     

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.     

Structure and transformation behaviour of rapidly solidified Ni–Al–Hf alloys

Rapidly solidified Ni–Al–Hf alloys of ternary eutectic compositions were studied by X-ray diffractometry, transmission electron microscopy and differential scanning calorimetry. Ni₆₆Hf₂₀Al₁₄ amorphous alloy with relatively high Hf/Al ratio showed high tensile strength of 1600 MPa and high thermal stability against crystallization. The formation of a nanoscale metastable intermetallic compound having a body-centered cubic lattice with a lattice parameter of a=1.22 nm was observed in the alloys with higher Al than Hf content. The transformation of an amorphous+metastable cubic mixture to AlNi₃ produces AlNi₃ of the same composition as the AlNi₃ phase formed on rapid solidification. Pm m AlNi₃ phase can dissolve up to 11 at.% Hf.     

Thermodynamic and topological instability approaches for forecasting glass-forming ability in the ternary Al–Ni–Y system

A thermodynamic approach to predict bulk glass-forming compositions in binary metallic systems was recently proposed. In this approach, the parameter γ* = ΔH^amor/(ΔH^inter − ΔH^amor) indicates the glass-forming ability (GFA) from the standpoint of the driving force to form different competing phases, and ΔH^amor and ΔH^inter are the enthalpies for glass and intermetallic formation, respectively. Good glass-forming compositions should have a large negative enthalpy for glass formation and a very small difference for intermetallic formation, thus making the glassy phase easily reachable even under low cooling rates. The γ* parameter showed a good correlation with GFA experimental data in the Ni–Nb binary system. In this work, a simple extension of the γ* parameter is applied in the ternary Al–Ni–Y system. The calculated γ* isocontours in the ternary diagram are compared with experimental results of glass formation in that system. Despite some misfitting, the best glass formers are found quite close to the highest γ* values, leading to the conclusion that this thermodynamic approach can be extended to ternary systems, serving as a useful tool for the development of new glass-forming compositions. Finally the thermodynamic approach is compared with the topological instability criteria used to predict the thermal behavior of glassy Al alloys.     

Effect of copper addition on the glass forming ability of a Fe–Co based alloy

The effect of copper addition on the glass forming ability of Fe₃₆Co₃₆Nb₄Si_4.8B_19.2 bulk metallic glass is studied. With 0.6 at% of copper addition, the critical size of the glassy rod formed is enlarged from 2 to 4 mm. Differential scanning calorimetry (DSC) study shows that the copper addition depressed the phase separation before the eutectic transformation upon cooling. And the crystallization of the alloy with copper addition is carried through three stages upon heating. Energy dispersive spectroscopy study shows that the copper addition reduces the oxygen content of the alloy.     

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。     

Effect of P on glass forming ability,magnetic properties and oxidation behavior of FeSiBP amorphous alloys

The effect of P on the glass forming ability, soft magnetic properties and oxidation behavior of Fe₇₈B₁₃Si_9-xP_x (x = 0–7) amorphous alloys were investigated. It is found that the proper introduction of P, can effectively improve the glass forming ability and stability of supercooled liquid region. Fe₇₈Si₄B₁₃P₅ BMG, which exhibits high saturation flux density of 1.56 T, was readily made into rod sample with a diameter of 1.5 mm under air casting atmosphere. P bearing alloys also exhibit excellent soft magnetic properties containing low coercivity of 1.7–2.7 A/m, and high effective permeability of 8200–12,200. Slight oxidation can further improve the coercivity to a lower value of 1.1 A/m and the higher effective permeability to 11,900 for the alloys with P content no more than 3 at. %. Excessive addition of P may deteriorate the glass forming ability, soft magnetic properties and oxidation behavior. Magnetic domain revealing the magnetization process of the amorphous ribbons were characterized to explain the effect of P on magnetic properties and oxidation behavior.     

Evaluation of glass forming ability of alloys

Key step of exploiting a new type BMG (Bulk Metallic Glass) is quickly judging GFA (Glass Forming Ability) of the alloys. The mole melting heats of BMGs are calculated using the weighted averages principle. The reliability and limitation of Trg criterion for CFA are discussed. The reason why Trg of BMGs is larger than 0.5 is discussed. Two new criteria for GFA, △Hmg and △Gg, are proposed. GFA sequence of BMGs is calculated using the △Hmg criterion, the result agrees with that of A. Inoue and the Rc criterion. Furthermore, as an example, the Rc of the alloys developed by Chuang DONG et al is calculated using the △Hmg and △Gg. The ascending sequence of these alloys calculated with the △Hmg criterion agrees with that of Chuang DONG et al. On the contrary, the result by the △Gg criterion is in contrary with Chuang DONG et al, indicating that the △Hmg criterion is better and more convenient than the △Gg criterion. Calculation showed that the optimum △Hmg iS -15.16 k J/mol.     

Effect of Ce addition on the microstructure and damping properties of Cu–Al–Mn shape memory alloys

The effect of rare earth element Ce addition on the microstructure, martensitic transformation, mechanical properties and damping behavior of the Cu–Al–Mn shape memory alloys (SMAs) had been investigated. It is shown that the Ce addition makes the grain refinement and affects the martensitic transformation temperature. The tensile strength and the ductility of the Cu–Al–Mn alloys can be enhanced by the Ce addition. Damping capacity tan δ of the martensite for the Cu–Al–Mn–Ce alloys is strain amplitude dependent. The Ce addition has obvious effects on the damping properties of the martensite. With the increase of the Ce content, the damping capacity increases initially and then decreases.     

Glass forming ability and crystallization of Zr-Cu-Ag-Al-Be bulk metallic glasses

The glass forming ability of Zr₄₆Cu_37.64−xAg_8.36Al₈Be_x (x = 0, 6 and 10 at.%) bulk metallic glasses (BMGs) were significantly improved by Be addition. The critical size of amorphous rods can be over 35 mm diameter. The high GFA achieved is mainly due to the decrease of melting point and liquidus temperature, and suppression of the formation of crystalline phases during solidification from liquid state. The high stabilization with supercooled liquid regime of 115 K was found for the BMG with x = 10 at.%. Two independent exothermic events happen in x = 0 and 6 at.% BMGs, corresponding to the formation of primary crystalline phases Cu₁₀Zr₇ and AgZr, then transforming to final stable crystalline phases Zr₂Cu and AlCu₂Zr. However, in the x = 10 at.% BMG, the precipitation of primary phases and transformation to final stable phases are within the first exothermic event and the AlCu₂Zr phase is totally suppressed.     

Synthesis and characterization of amorphous Zr-based alloys with Ta and W additions

A reference Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ bulk metallic glass as well as a number of alloys obtained by addition of refractory elements Ta or W (combined with Sn) to the main Zr–Cu–Al–Ni system were elaborated by mould casting, twin roll casting and planar flow casting. The chemical compositions were chosen according to empirical rules, and as combinations of the binary eutectics for strongly interacting elements, taking into account the corresponding enthalpies of mixing. Optical microscopy, X-ray diffractometry, differential thermal analysis, differential scanning calorimetry, scanning electron microscopy and tensile mechanical testing were used to characterize the fully and partially obtained amorphous materials. Correlation of glass forming ability, thermodynamic parameters, crystallization behaviour and mechanical properties with chemical composition and production technology is discussed.     

反复熔炼对Zr基大块非晶合金玻璃形成能力的影响

研究了反复熔炼对Zr60Al15Ni25和Zr65Al7.5Ni10Cu17.5合金的玻璃形成能力的影响。DSC分析表明，随着熔炼次数的增多，Zr60Al15Ni25非晶合金的玻璃转变温度和晶化开始温度都提高，而Zr60Al7.5Ni10Cu17.5非晶合金的特征温度基本没有发生变化。Zr60Al15Ni25合金的熔化焓由于反复熔炼而降低，在热力学上有利于非晶相的形成。根据反复熔炼对铸锭凝固组织进而对合金熔体中的短程序的影响，讨论了玻璃形成能力的变化及原子间的结合力对短程序尺寸的影响，分析了2种合金对反复熔炼处理的敏感性的不同。     

Effect of the volume fraction of the ex-situ reinforced Ta additions on the microstructure and properties of laser-welded Zr-based bulk metallic glass composites

To investigate the effect of the volume fraction of the ex-situ reinforced Ta additions on the weldability of Zr–Cu–Ag–Al bulk metallic glass composites (BMGCs), in this study, different Ta contents (0–6 vol%) of BMGCs are welded using the Nd:YAG pulsed laser technique with preselected welding parameters. After welding, the microstructure (including the parent material (PM), weld fusion zone (WFZ) and heat-affected zone (HAZ)), mechanical and thermal properties of the test samples are investigated.The test results show, for all BMGC welds, the micro-sized Ta particles in the PM, WFZ and HAZ to be covered by a crystallized interfacial layer (IL), ZrCu. For both un-welded and laser-welded BMGCs, as the Ta contents increase, the glass transformation temperature (T_g) increases, which in turn reduces the glass formation ability (GFA) indices, ΔT_x, γ and γ_m. However, when compared to that of un-welded BMGC, the GFA index, ΔT_x, of the laser-welded BMGCs is slightly improved. However, the γ, and γ_m of the BMGC welds seem not to be affected.In addition, due to the characteristics of the rapid thermal cycle of the laser welding process, two smaller sizes of Ta, nano-sized (mainly on the surface of WFZ) and sub micro-sized Ta, are found in the WFZ. These sub-micro-sized Ta particles normally locate near the micro-sized Ta, which tends to slightly reduce the hardness in this area.Furthermore, an increase in the volume fraction of Ta (0–6 vol%) in the BMGCs does not encourage the formation of the harmful crystalline phase in the amorphous matrix after the laser welding process. It is observed that, other than the IL (ZrCu) on the micro-sized Ta particles, no other type of crystalline is observed in the amorphous matrix of the laser-welded BMGCs.     

Effects of minor Cu and Si additions on glass forming ability and mechanical properties of Co-Fe-Ta-B Bulk metallic glass

Effect of Cu and Si substitutions for Co and B on the glass forming ability (GFA) of Co_(43-x)Cu_xFe₂₀Ta_5.5B_(31.5-x)Si_y (x=0-1.5 and y=5-10) were systematically investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, and differential scanning calorimetry. In order to evaluate the contribution of copper and silicon, appropriate amounts of copper and silicon were individually introduced to the base alloy composition. By using the effects of copper and silicon together, significant enhancement was obtained and the critical casting thickness (CCT) of the base alloy was increased three times from 2 mm to 6 mm. Moreover, mechanical properties of the alloys were examined by compression tests and Vickers hardness measurements. The compression test results revealed that the glassy alloys having enhanced GFA shows high strength of about 3500-4000 MPa. In addition, existence of (Co,Fe)₂B and (Co,Fe)_20.82Ta_2.18B₆ crystalline phases in glassy matrix influences the hardnesses of the alloys compared to monolitic glassy structure having hardness of about 1200 Hv.