Mg–Y–Cu bulk metallic glass prepared by mechanical alloying and vacuum hot-pressing

We have studied the amorphization behavior of Mg_85−xY₁₅Cu_x (x=20–40) alloy powders synthesized by mechanical alloying technique. The as-milled powders were mainly amorphous after 10 h of milling. The thermal stability of these Mg_85−xY₁₅Cu_x glassy powders was investigated by differential scanning calorimeter (DSC). The ranges of Tg, T_x and ΔT_x are around 430–459, 467–497, and 30–46 K, respectively. The Mg₄₉Y₁₅Cu₃₆ glassy powders exhibit the largest supercooled region of 46 K. The amorphization behavior of Mg₆₁Y₁₅Cu₂₄ was examined in details. Amorphous phases gradually became dominant after 7.5 h of milling and fully amorphous powders formed at the end of milling. The thermal stability of Mg₆₁Y₁₅Cu₂₄ glassy powders was similar to that of melt-spun Mg₆₀Y₁₅Cu₂₅ amorphous alloys. Mg₆₁Y₁₅Cu₂₄ bulk metallic glass with homogeneously embedded nanocrystalline precipitates was successfully prepared by vacuum hot pressing. It was found that the applied pressure during consolidation could enhance the thermal stability and prolong the existence of amorphous phase inside Mg₆₁Y₁₅Cu₂₄ powders.     

New ternary Ni–Ta–Sn bulk metallic glasses

A new ternary Ni-base bulk metallic glass (BMG) system, Ni–Ta–Sn, was explored. There exists a wide BMG forming regime, in at.%, 33<Ta<38 and 2<Sn<9 with cast BMG rods of at least 1 mm diameter. The crystallization temperature being among the highest in Ni-based BMGs, 762–671 °C decreases with Sn content. These BMGs have wide super-cooled liquid region 57–61 K. They show high hardness, typically HV∼1000, and a compressive fracture strength 856–1192 MPa. The elastic strain limit is 0.0237–0.0266. The potentiodynamic studies in a solution of 12 M HCl show a passivation current density about 0.18 A m⁻² for Ni₅₈Ta₃₆Sn₆ BMG in the anodic region revealing a good corrosion resistance.     

机械合金化及真空烧结法制备TiC/Ti材料

采用机械合金化真空烧结法制备TiC/Ti复合材料,利用激光粒度分析仪、SEM和XRD研究了球磨时间及烧结工艺对TiC/Ti复合材料断裂形貌、微观组织及力学性能的影响。结果表明,将球磨10 h的复合粉末冷压成形,真空烧结到1580℃,保温3 h,可获得综合性能较好的TiC/Ti复合材料,烧结样品的致密度、抗弯强度、硬度分别为91.68%、32.79 MPa和72.3 HRA。     

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns.     

块体非晶合金Cu58Zr20Ti20Mo2的形成与力学性能

用铜模吸铸法获得直径3 mm的Cu58Zr20Ti20Mo2块体非晶合金,采用X射线衍射仪、示差扫描量热仪、压缩实验及扫描电镜等研究其结构、热稳定性、压缩性能及断口形貌。Mo的引入有利于非晶的形成,该非晶合金表现为两级晶化行为,玻璃转变温度为422.6℃,晶化起始温度为453.4℃;其压缩应力—应变曲线呈近似线性关系,不存在塑性变形阶段,为脆性断裂,断裂强度为1 720 MPa,变形量为3.4%,断口形貌为清晰的脉状河流花纹;含少量晶态相的Cu57Zr20Ti20Mo3非晶合金仍为脆性断裂,断裂强度为1 546 MPa,变形量为3.3%,断口形貌呈混乱的脉状河流花纹,且有类似液滴的小球形貌。     

Formation and characterization of mechanically alloyed Ti–Cu–Ni–Sn bulk metallic glass composites

In the present study, amorphous Ti₅₀Cu₂₈Ni₁₅Sn₇ and its composite powders reinforced with 4, 8, and 12 vol.% of W additions were prepared by mechanical alloying. After 5 h of milling, amorphous powders with homogeneously dispersed W nanoparticles were synthesized. The as-milled Ti₅₀Cu₂₈Ni₁₅Sn₇ and composite powders were then consolidated by vacuum hot pressing into disc compacts with a diameter and thickness of 4 and 10 mm, respectively.The structure of the as-milled powders and consolidated compacts was characterized by X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. While the thermal stability was examined by differential scanning calorimeter (DSC). In addition, the mechanical property of the consolidated BMGs was evaluated by Vickers microhardness tests. The experimental results showed that W nanoparticles ranged from 20 to 200 nm were embedded within the amorphous matrix. The presence of W nanoparticles did not dramatically change the glass formation ability of amorphous Ti₅₀Cu₂₈Ni₁₅Sn₇ powders. While the thermal stability of amorphous powders differed from those of its composites. A significant hardness increase with W additions was noticed for consolidated composite compacts.     

机械合金化制备AgCu20Ni2合金的组织和性能

研究了机械合金化诱发AgCu20Ni2过饱和合金粉末的形成及粉末冶金方法制备AgCu20Ni2合金的过程,对获得的AgCu20Ni2合金的组织和物理性能关系进行了分析,探讨了制备工艺和冷压变形对合金综合性能的影响。结果表明：采用高能球磨30 h,可获得纳米晶的过饱和合金粉末;合金粉末制备的AgCu20Ni2合金由富Ag的基体α相和均匀分布的析出β相构成,析出相界面结构能有效阻碍基体中位错的运动,强化效果明显。合金断口的SEM、EDS分析表明,AgCu20Ni2合金的断裂类型为韧性断裂。     

Friction joining of Ti40Zr25Ni3Cu12Be20 bulk metallic glass

Joints with fully amorphous structure can be obtained by selecting proper friction time and rotational speed. The optimum strength of the joint is close to that of the base bulk metallic glass (BMG), demonstrating a perfect bonding. Based on the analysis of the temperature distribution during the friction welding, an equation mentioning the critical friction time for retaining amorphous structure has been established. The experimental results prove the validity of the equation. Moreover, the temperature distribution in the friction interface has been studied by numerical simulation, aiming to provide a better understanding of the friction welding process and the microstructure in the interface. The simulation results further confirm the availability of the calculation results, thus can be helpful for designing the process parameters using other BMG systems.     

Spark plasma sintering of (Ti0.9W0.1) C powders prepared by mechanical alloying

Nanocrystalline (Ti_0.9W_0.1)C powder with a diffraction crystallite size of about 10 nm was synthesized by mechanical alloying. The formation of (Ti_0.9W_0.1)C carbide was detected by XRD measurements and microscopic observation. The sintering of these powders by a spark plasma sintering (SPS) at different temperatures were also studied. The results show that the maximum hardness was obtained for more relative density materials, meanwhile, the grain size is large. The micro-hardness and the relative density of the powder milled for 10 h and sintered at 1200 °C for 5 min under 100 MPa reach, respectively, 2978 HV and 98.35%.     

Deformation in a Zr57Ti5Cu20Ni8Al10 bulk metallic glass during nanoindentation

Nanoindentation experiments of a Zr₅₇Ti₅Cu₂₀Ni₈Al₁₀ bulk metallic glass were performed with indentation loads ranging from 200 to 2000 μN. Both the indentation hardness and the reduced contact modulus decreased with the increase in the indentation load due to the propagation of shear bands underneath the indenter – the occurrence of a softening effect. The ratio of the indentation hardness to the reduced contact stiffness was a function of the reciprocal of the indentation depth. Based on the concept of diffusion-induced stresses, a one-dimensional constitutive relation between the change of the excessive free volume and the flow stress was proposed. The indentation-size effect as observed in the indentation tests was explained through the consideration of the contribution of the strain gradient in the constitutive relation.     

Formation and properties of two-phase bulk metallic glasses by spark plasma sintering

Using a mixture of the gas-atomized Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 and Fe₇₃Si₇B₁₇Nb₃ glassy alloy powders, we produced the two-phase bulk metallic glass (BMG) with high strength and good soft magnetic properties as well as satisfying large-size requirements by the spark plasma sintering (SPS) process. Two kinds of glassy particulates were homogeneously dispersed each other. With an increase in sintering temperature, density of the produced samples increased, and densified samples were obtained by the SPS process at above 773 K. Good bonding state among the Ni- and Fe-based glassy particulates was achieved.     

Interface structure and properties of a brass-reinforced Ni59Zr20Ti16Si2Sn3 bulk metallic glass composite

Interfaces between a Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ bulk metallic glass (BMG) and crystalline brass reinforcements were characterized using transmission electron microscopy and nanoindentation. An interfacial layer with a thickness of ∼50–100 nm was observed in the composite prepared by warm extrusion of gas atomized powders. Microstructural characterization and chemical analysis suggest that the formation of interfacial layer was caused by interdiffusion between the BMG and brass during the warm extrusion. Nanoindentation in the vicinity of BMG–brass interfaces does not cause interface decohesion or crack formation, suggesting a strong interface bonding. Apparently, the resultant interfacial layer not only enhances interfacial bonding but also provides a buffer zone to prevent the catastrophic shear band propagation in the BMG matrix.     

Spark plasma sintering consolidation of nanostructured TiC prepared by mechanical alloying

Spark plasma sintering technique was used for the consolidation of nanostructured titanium carbide synthesized by mechanical alloying in order to avoid any important grain growth of the compact materials. The TiC phase was obtained after about 2 h of mechanical alloying. Towards the end of the milling process (20 h), the nanocrystalline powders reached a critical size value of less than 5 nm. Some physical and mechanical properties of the consolidated carbide were reported as a function of the starting grain size powders obtained after different mechanical alloying durations. The crystalline grain size of the bulk samples was found to be increased to a maximum of 120 nm and 91 nm for carbides mechanically alloyed for 2 h and 20 h respectively. The Vickers hardness showed to be improved to about 2700 Hv for a maximum density of 95.1% of the bulk material.     

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。     

Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses（BMGs） with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry（XRD）. The thermal stability was examined by differential scanning calorimetry（DSC）. Zr49Cu46Al5 alloy shows a glass transition temperature, Tg, of about 689 K, an crystallization temperature, Tx, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy（TEM）. The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46,5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5A15 alloy is larger than that of Zr49Cu46Al5 alloy.     

新型铜基块体非晶合金Cu55-xZr37Ti8Inx的制备及性能

利用铜模吸铸法合成Cu—ZrTi—In非晶棒。块体非晶合金Cu50Zr37Ti8In5的△瓦值最大,为66K。从原子尺寸大小和热力学角度分析在铜基非晶合金中添加适量In元素后能够提高其非晶形成能力的原因。在所测的块体非晶合金Cu55．Zr37Ti8Inx（x≤〈5）,Cu52Zr37Ti8In3表现出最高的抗压强度（1981MPa）和最佳的塑性,其在压缩断裂前的总塑性变形量约为1．2％。     

Cu50 Zr42 Al8块体金属玻璃的组织和力学性能

采用悬浮熔炼-铜模吸铸法制备了Cu50Zr42Al8块体金属玻璃,研究了其楔形试样的组织演变.随着熔体凝固过程中冷却速度的变化,楔形试样中存在表面全非晶区,中心晶体区以及二者之间的过渡区域,并确定Cu50Zr42Al8块体金属玻璃临界尺寸为4.8 mm.分别考察了φ4 mm铸态完全非晶棒和φ5 mm非晶复合棒的力学性能.φ4 mm非晶棒的压缩断裂强度,弹性应变和塑性应变分别为2260 MPa,2.0%,0.4%,几乎没有塑性变形.而φ5 mm铸态非晶复合棒的屈服强度、断裂强度分别为1670MPa、1849 MPa,弹性应变和塑性应变分别为1.6%和1.9%.非晶基体中存在的马氏体相CuZr和正交晶相Cu10Zr7的竞争影响了非晶复合棒的最终力学行为.     

A comparative study on characteristic relaxation in Ce65Al10Cu20Co5 and Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glasses and supercooled liquids

The relaxation behaviors of Ce₆₅Al₁₀Cu₂₀Co₅ and Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 (Vit4) bulk glass-forming supercooled liquids were investigated by frequency-dependent heat capacity measurements on a temperature-modulated differential scanning calorimetry (TMDSC) apparatus. The relaxation behaviors of the investigated samples were well described by Kohlrausch–Williams–Watts (KWW) function. The temperature dependences of characteristic relaxation time of the glass-forming liquids were fitted by Vogel–Fulcher–Tamman (VFT) equation. The derived fragility index m shows that Ce₆₅Al₁₀Cu₂₀Co₅ (m = 31) liquid is a stronger liquid than Vit4 (m = 42). The sizes of cooperatively rearranging region (CRR) for Ce₆₅Al₁₀Cu₂₀Co₅ and Vit4 liquids were estimated to be 1.6 and 1.4 nm, respectively.     

Difference in compressive and tensile fracture mechanisms of Zr59Cu20Al10Ni8Ti3 bulk metallic glass

The compressive and tensile deformation, as well as the fracture behavior of a Zr₅₉Cu₂₀Al₁₀Ni₈Ti₃ bulk metallic glass were investigated. It was found that under compressive loading, the metallic glass displays some plasticity before fracture. The fracture is mainly localized on one major shear band and the compressive fracture angle, θ_C, between the stress axis and the fracture plane is 43°. Under tensile loading, the material always displays brittle fracture without yielding. The tensile fracture stress, σ_F^T, is about 1.58 GPa, which is lower than the compressive fracture stress, σ_F^C(=1.69 GPa). The tensile fracture angle, θ_T, between the stress axis and the fracture plane is equal to 54°. Therefore, both θ_C and θ_T deviate from the maximum shear stress plane (45°), indicating that the fracture behavior of the metallic glass under compressive and tensile load does not follow the von Mises criterion. Scanning electron microscope observations reveal that the compressive fracture surfaces of the metallic glass mainly consist of a vein-like structure. A combined feature of veins and some radiate cores was observed on the tensile fracture surfaces. Based on these results, the fracture mechanisms of metallic glass are discussed by taking the effect of normal stress on the fracture process into account. It is proposed that tensile fracture first originates from the radiate cores induced by the normal stress, then propagates mainly driven by shear stress, leading to the formation of the combined fracture feature. In contrast, the compressive fracture of metallic glass is mainly controlled by the shear stress. It is suggested that the deviation of θ_C and θ_T from 45° can be attributed to a combined effect of the normal and shear stresses on the fracture plane.     

Pd20Pt20Cu20Ni20P20 high-entropy alloy as a bulk metallic glass in the centimeter

A Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ bulk metallic glass (BMG) with a high-entropy (HE) alloy composition and a maximum diameter of 10 mm was fabricated by fluxed water quenching. The system and composition of the Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ alloy were determined from a prototype ternary Pd₄₀Ni₄₀P₂₀ BMG in accordance with two strategic alloy designs of (1) HE alloy defined by an equi-atomic alloy with five or more elements and (2) exchangeability of the constituent elements with a similar chemical nature in the periodic table. Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HE-BMG had a supercooled liquid range of 65 K and a reduced glass transition temperature of 0.71. Successful formation of Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HE-BMG is significant to develop new alloys for HE alloys and BMGs.