Preparation, microstructure and mechanical properties of Zr-based bulk amorphous alloys containing tungsten

A new Zr-based bulky amorphous alloys containing W are designed and prepared by using the combined technique of jet and water-cooled copper mold casting. XRD, DSC and SEM analysis are conducted to investigate the microstructure, the supercooled liquid region ΔT_x (=T_x−T_g), and thermal stability of the new bulk metallic glass system. The effects of the addition of W and the increase of Cu content on the glass forming ability (GFA) and thermal stability are discussed. Compressive experiments were also carried out to study the Young's modulus, compressive fracture strength and elongation of the new alloys. The fracture characterization and mechanism of the new bulk amorphous alloys are discussed in detail.     

Zr基大块非晶合金的超塑性成形性能

研究了Zr41.25Ti13.75Ni10Cu125Be22.5大块非晶合金的过冷温度区域范围、时间-温度-转变曲线及其在过冷温度区域的力学行为,并在此基础上,对精密凸轮零件进行了模锻成形实验,分析了不同温度和应变速率对成形结果的影响.结果表明:Zr41.25T13.75Ni10Cu12.5Be22.5大块非晶合金在635.6～710.4 K的过冷区域范围内,其应变速率敏感系数接近1,具有良好的超塑性性能;较理想的超塑性成形温度为653～668 K,应变速率为5.0×10-4～5.0×10-3s-1.在温度为668 K、应变速率为5.0×10-4s-1的工艺条件下,非晶合金的可成形时间大于1000 s,最大流动应力小于70 MPa.     

Mechanical properties of Al-based metal matrix composites reinforced with Zr-based glassy particles produced by powder metallurgy

Al-based metal matrix composites consisting of pure Al reinforced with different amounts of mechanically alloyed Zr₅₇Ti₈Nb_2.5Cu_13.9Ni_11.1Al_7.5 glassy powder were produced by powder metallurgy, and their mechanical properties were investigated by room temperature compression tests. The samples were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region in order to take advantage of the viscous flow behavior of the glassy powder. Compression tests show that the addition of the glass reinforcement increases the strength of pure Al from 155 to 250 MPa, while retaining appreciable plastic deformation with a fracture strain ranging between 70% and 40%. The yield strength and the elastoplastic deformation of such composites containing a high volume fraction of glassy particles were accurately modeled using a shear lag model and a self-consistent effective medium approach. Finally, the fracture characteristics of the reinforcing particles were rationalized using a proposed fracture criterion.     

冷-热处理对Zr基块体非晶合金结构和性能的影响

传统晶态材料构件或装备在低温环境中会出现可动部分卡死、龟裂、特性改变甚至脆性断裂等现象。低温极端条件如温度突变、高应变速率冲击等对材料性能带来的不利影响严重制约了其在低温极端环境领域的应用。块体非晶合金在低温条件下具有强度更高塑性更好的特殊性能,在极地科考以及航空航天等极端条件下具有极大的应用优势。本文以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)₉₇Tm₃块体非晶合金为研究对象,研究冷-热处理时间对块体非晶合金的结构、力学性能和腐蚀性能的影响。结果表明,当处理时间由30 min延长到90 min时,试样的晶化体积分数从2.3%增加到4.0%,屈服强度由1701 MPa增加到1810 MPa。在3.5 wt.% NaCl溶液中,合金具有较小的自腐蚀电流密度与较大的电化学阻抗,这意味着经冷-热处理后的块体非晶合金具有优异的耐腐蚀性能。本研究为块体非晶合金在低温极端环境领域的应用提供了强有力的理论支撑。     

Cast bulk glassy alloys:fabrication,alloy development and properties

Metallic glasses represent an interesting group of materials as they possess outstanding physical, chemical and mechanical properties compared to their crystalline counterparts.Currently, with well designed compositions it is possible to cast liquid alloys into the glassy state at low critical cooling rates from 100 K·s-1 to 1 K·s-1 and in large critical sample sizes up to several centimeters, which significantly enhances the promise for possible applications as advanced engineering materials.This paper reviews the development of (ZrCu)-based bulk metallic glasses with large sizes by copper mold casting and their unique properties.Additionally, the ex-situ and in-situ second phases reinforced BMG composites with large plasticity are also presented.     

Surface modification of Zr-based bulk amorphous alloys by using ion irradiation

Surfaces of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈M₂ (M = Er and Gd) bulk amorphous alloys were modified by irradiation with energetic singly charged argon (Ar⁺) ions. Samples of both the alloys were irradiated with 2.17 × 10¹⁷ argon ions of 10 keV energy. As cast and ion irradiated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Mechanical properties like Vicker's hardness, nanohardness, elastic modulus and elastic recovery were measured. Considerable increase in elastic modulus and hardness was observed because of ion irradiation in these alloys. The ion irradiated samples of the [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Er₂ alloy showed better properties as compared to [Zr_0.65Cu_0.18Ni_0.09Al_0.08]₉₈Gd₂ alloy. CuZr₂ phase was detected in ion irradiated alloys by XRD and confirmed by EDS. The range of Ar⁺ ions was found to be approximately 9.3 ± 5.4 nm in both alloys.     

含锆铝合金的力学性能和强化机理

研究了高强铝合金的力学性能与Zr含量的关系，计算了合金的各种强化因素值。研究发现：合金的抗拉强度巩和屈服强度如σ0.2均随Zr含量的增加而增大，增幅分别达到11．8％和12．6％；合金延伸率δ在Zr添加量不高时随Zr含量的增加而增大，在Zr含量为0．06％时出现峰值，随后合金延伸率δ逐渐稳定在8％左右。结合合金显微特征，合金强化机理主要包括晶粒细化、颗粒弥散强化及形变强化，在Zr含量为0．16％的合金中相应的强化值分别为21.35和14MPa.     

Production and mechanical properties of aluminum alloys with dispersed nanoscale quasicrystalline and amorphous particles

By the dispersion of nanoscale quasicrystalline and amorphous particles in Al phase, new Al-based alloys with good mechanical properties were developed in a high Al concentration range of 93–95 at.% for Al−Cr−Ce−Co, Al−V−Fe, Al−Ti−M and Al−Fe−Cr−Ti alloy systems. The Vickers hardness of a melt-quenched (MQ) Al_84.6Cr_15.4 alloy with almost a single icosahedral quasicrystalline phase (QC) was 710. The addition of Ce and Co in the Al−Cr binary alloys was effective for the extension of the concentration range of the QC to a lower solute concentration range. The fracture strength (σ_f) increased to 1340 MPa for the MQ Al_94.5Cr₃Ce₁Co_1.5 alloy in which the particle size and volume fraction were approximately 40 nm and 70%, respectively. The σ_f of the MQ Al₉₄V₄Fe₂ alloy was 1390 MPa and the particle size and volume fraction were about 10 nm and 50%, respectively. Similarly, σ_f of the MQ Al₉₃Ti₄Fe₃ alloy was 1320 MPa and the particle size and volume fraction were about 11 nm and 30%, respectively. Power metallurgy (P/M) Al₉₃Fe₃Cr₂Fe₂ alloy with dispersed nanoscale QC exhibited ultimate tensile strength (σ_UTS) of 660 MPa, 0.2 % proof stress (σ_0.2) of 550 MPa, plastic elongation (ε_P) of 4.5%, Young's modulus (E) of 85 GPa, Vickers hardness (Hv) of 192 and specific strength (σ_UTS/ρ) of 2.20×10⁵ Nm/kg at room temperature and σ_UTS of 350 MPa, σ_0.2 of 330 MPa and ε_P of 1.5% at 573 K. The QC structure in the P/M Al₉₃Fe₃Cr₂Ti₂ alloy remained almost unchanged even after annealing for 720 ks at 573 K and good wear resistance against S50C steel was also maintained for the extruded alloy tested at sliding velocity of 0.5 to 2 m/sec. These mechanical properties are promising for the future extension of the new Al-based alloys to practical materials. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Zr基非晶合金多孔材料的制备与性能

采用液态金属渗流法制备直径为6 mm 的Zr基块体多孔非晶合金,采用扫描电镜(SEM)和X射线衍射仪(XRD)分析多孔材料的结构、形貌、断口特征和相组成,同时对多孔非晶合金的孔隙结构和力学特点进行分析.结果表明:采用CaC2作为孔隙支撑材料,能够制备出孔隙分布均匀、孔隙直径为0.2～0.8 mm的多孔非晶合金,其密度和孔隙率分别为3.57 g/cm3和47%.压缩力学性能实验表明:该多孔非晶合金的应力-应变曲线具有锯齿状变化规律,应力逐渐降低,其最大强度和应变分别为383 MPa和18.6%,应变量远大于单相非晶合金的应变量.     

Environmental properties of Zr-based metallic glasses and nanocrystalline alloys

Zr-Cu-Ni-Al belongs to the best glass forming systems known; these glasses are suitable as precursor material for nanocrystalline alloys. For an application as hydrogen storage materials for example it is of great interest to know more about these metastable materials in regard to their environmental properties. Corrosion as studied by a salt spray test or anodic polarization in aqueous solutions exhibit a rather high sensitivity with no significant differences between the amorphous and nanocrystalline state. Hydrogen charging was performed electrochemically in a glycerine-phosphoric acid electrolyte. In Zr-Cu-Ni-Al alloys absorption kinetics and storage capacity were found to be very similar for the amorphous and the nanocrystalline phase. In the nanocrystalline alloy consisting mainly of a fcc (big cube) phase with a NiTi₂ type structure a hydrogen induced amorphization was observed. Oxidation of metastable Zr-based materials in air was studied below the glass transition temperature at 360°C by thermogravimetry. Oxidation resistance was found to improve very significantly from the amorphous to the nanocrystalline microstructure. The scales formed on both materials consist mainly of columnar ZrO₂ with diameter in the nanometer range; Probably including the other metals as a nanocrystalline solid solution.     

Formation and mechanical properties of Ni-free Zr-based bulk metallic glasses

Glass formation and mechanical properties of Zr–Al–Co–Cu–Ag bulk metallic glasses (BMGs) were investigated. The glass-forming ability (GFA) of Zr₅₅Al₂₀Co₂₀Cu₅ alloy is significantly improved with minor addition of Ag, indicating by the impressive increase of the critical diameter of glass formation from 5 mm for Zr₅₅Al₂₀Co₂₀Cu₅ to 16 mm for (Zr_0.55Al_0.20Co_0.20Cu_0.05)₉₇Ag₃ and (Zr_0.55Al_0.20Co_0.20Cu_0.05)₉₅Ag₅ alloys. The Zr–Al–Co–Cu–Ag BMGs exhibit high compressive strength of 2160–2280 MPa and distinct plasticity of 0.6–2.5%. The Zr-based BMGs with outstanding GFA and mechanical properties as well as low-level cytotoxicity elements are expectative for industrial and biological applications.     

Mechanical behaviour of alloys containing heterogeneously distributed particles: modelling with Delaunay triangulation

Non-shearable precipitates and second-phase particles are efficient obstacles to dislocation motion that have an important effect on the strength and creep resistance of many materials, in particular oxide-dispersion-strengthened alloys. When the obstacles are clustered, the material cannot be considered as a homogeneous medium. Modelling its mechanical behaviour by means of constitutive laws requires an additional step of homogenisation. We propose here a new method based on the Delaunay triangulation of the obstacle distribution and compare it with a previously developed technique based on the Voronoi tessellation. The Delaunay triangulation is considered to be a better representation of local particle arrangement. It is shown that the softening effect of particle clustering is accentuated in the Delaunay triangulation approach.     

Effect of infiltrating time on interfacial reaction and properties of tungsten particles reinforced Zr-based bulk metallic glass composites

The tungsten particles reinforced Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5) (Vit 1 alloy) bulk metallic glass composites (BMGCs) were prepared by the melt infiltrating casting method with the infiltrating time of 1,5 and 10 min,respectively.The changes of interfacial reaction and compression properties of the bulk metallic glass composites with different infiltrating times were studied.Results show that with the increase of infiltrating time,tiny nanocrystals are generated at the interfacial boundary of tungsten particles and the amorphous matrix,and the size of tiny crystals increases with the infiltrating time.When the infiltrating time is 10 min,polygonal crystals with a larger size are also generated within the amorphous matrix.The compressive strength of the composites also increases with the infiltrating time.When the infiltrating time is 10 min,the compressive strength of the composite reaches 2,030 MPa and the compression strain is 44%.The fracture morphology of the composite materials is in a vein-like pattern and the melting phenomenon is found on the fracture surface.In addition,the density of the shear bands during the compressive tests of the composite materials increases with the infiltrating time.     

Influence of fluxing in the preparation of bulk Fe-based glassy alloys

Fe-based master ingots, with composition [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄, have been prepared by arc-melting and subsequently purified using the fluxing technique. Rods, with diameters from 1 to 2.5 mm, ribbons and wires with a maximal diameter of 200 μm have been produced from these purified master ingots. The amorphous structure, thermal stability, hardness and magnetic properties of the specimens were studied. In particular, we show by high-energy synchrotron X-ray diffraction that the rods are fully amorphous up to a maximal diameter of 2 mm. Moreover, the [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄ glassy alloy exhibits high hardness (HV = 1050) combined with good soft-magnetic properties (H_c = 63 A/m).     

Zr-based bulk glassy alloy with improved resistance to stress corrosion cracking in sodium chloride solutions

In order to evaluate stress corrosion cracking (SCC) susceptibility of Zr-based bulk glassy alloys and develop the BGAs with low susceptibility to SCC, the SCC behaviour of Zr₅₀Cu₄₀Al₁₀, Zr₅₀Cu₃₀Al₁₀Ni₁₀ and hypoeutectic Zr₇₀Cu₆Al₈Ni₁₆ BGAs in various environments including sodium chloride solution has been investigated using a slow strain rate technique at an initial strain rate of 5 × 10⁻⁶ s⁻¹. It is found, for the first time, that the Zr₇₀Cu₆Al₈Ni₁₆ BGA has no susceptibility to SCC in a 0.5 M NaCl solution. On the other hand, Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Al₁₀Ni₁₀ BGAs are highly susceptible to SCC in the NaCl solution, although they are not susceptible to SCC in de-ionized water, phosphate buffer, 0.5 M Na₂SO₄ and 0.5 M NaNO₃ solutions. The possible cause of the high susceptibility to SCC in the NaCl solution for the Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₀Al₁₀Ni₁₀ BGAs is discussed.     

Zr基大块非晶合金的微区变形及力学性能

利用纳米压痕仪、扫描电镜等研究了Zr基大块非晶合金在纳米压痕条件下的变形及力学性能。Zr基大块非晶合金在纳米压头作用下以弹性-塑性方式变形，载荷-位移曲线及压痕周边多重剪切带(堆起或波纹状)的特征证明了塑性变形的存在。冷却速度、第二相及退火等因素影响非晶合金的压痕硬度HV和弹性模量E，冷却速度小的试样或部位(如试样中心)的HV，E值略高；离第二相(W丝)越近，HV，E值越高；退火处理提高非晶的HV，E值，同时退火与第二相还明显改变压痕周边的变形状态及塑性变形量的大小，退火显著减小塑性变形量，使压痕周边凹陷，而第二相使压痕堆起消失。对塑性变形机理进行了初步分析。