High-strength Zr-based bulk amorphous alloys containing nanocrystalline and nanoquasicrystalline particles

Abstract

It was recently found that the addition of special elements leading to the deviation from the three empirical rules for the achievement of high glass-forming ability causes new mixed structures consisting of the amorphous phase containing nanoscale compound or quasicrystal particles in Zr–Al–Ni–Cu–M (M ? Ag, Pd, Au, Pt or Nb) bulk alloys prepared by the copper mold casting and squeeze casting methods. In addition, the mechanical strength and ductility of the nonequilibrium phase bulk alloys are significantly improved by the formation of the nanostructures as compared with the corresponding amorphous single phase alloys. The composition ranges, formation factors, preparation processes, unique microstructures and improved mechanical properties of the nanocrystalline and nanoquasicrystalline Zr-based bulk alloys are reviewed on the basis of our recent results reported over the last two years. The success of synthesizing the novel nonequilibrium, high-strength bulk alloys with good mechanical properties is significant for the future progress of basic science and engineering. © 2000 Published by Elsevier Science Ltd.     

Nanostructured Composite Materials with Improved Deformation Behavior

The recent progress in the development of nanostructured composites is described for Zr‐base multicomponent alloys as a typical example for such materials. These advanced composite materials are attractive candidates for structural as well as functional applications. The combination of high strength with high elastic strain of fully nanocrystalline and glassy alloys renders them quite unique in comparison to conventional (micro‐)crystalline materials. However, one major drawback for their use in engineering applications is the often limited macroscopic plastic deformability, despite the fact that some of these alloys show perfectly elastic‐plastic deformation behavior. To improve the room temperature ductility of either fully nanocrystalline or amorphous alloys, the concept of developing a heterogeneous microstructure combining a glassy or nanostructured matrix with second‐phase particles with a different length‐scale, has recently been employed. This review describes the composition dependent metastable phase formation in the Zr‐(Ti/Nb)‐Cu‐Ni‐Al alloy system, which in turn alters the mechanical properties of the alloys. We emphasize the possibilities to manipulate such composite microstructures in favor of either strength or ductility, or a combination of both, and also discuss the acquired ability to synthesize such in‐situ high‐strength composite microstructures in bulk form through inexpensive processing routes.     

Laser-induced combustion synthesis of Zr–Ti–Al–Ni amorphous-based alloys

Bulk metallic glasses, like many crystalline intermetallics, have large negative enthalpy of mixing among the major constituent elements, and hence are potential candidates of self-propagating high-temperature reaction systems. Based on this characteristic, the laser-induced combustion synthesis (LCS) technique has been applied to fabricate amorphous-containing alloys. In the present paper, we report the LCS of the Zr–Ti–Al–Ni alloys. A series of Zr–Ti–Al–Ni alloys is designed and synthesized by LCS. The LCS products mainly consist of intermetallic phases, but in Zr₅₅Ti_10.8Al_17.1Ni_17.1 and Zr₅₀Ti_21.6Al_14.2Ni_14.2 amorphous phases are found. The hardness and tribology characteristics are closely related to the phase contents. The amorphous phases, ductile and soft, lower the hardness and increase the friction coefficient of the LCS samples.     

Microstructure and mechanical properties of Pt-added and Pd-added Zr-20Nb alloys and their metal release in 1 mass% lactic acid solution

The effects of Pt and Pd addition to a Zr-20Nb alloy on its microstructure and mechanical property, as well as the elution of metals from the alloys in lactic acid solution, were investigated. The microstructure was characterized with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). The mechanical properties were evaluated by a tensile test. The β phase is dominantly observed in the Zr-20Nb as well as in the Pt-added and Pd-added Zr-20Nb alloys. Needle-like microstructures are observed in equiaxed grains in all alloys. Pd addition to the Zr-20Nb alloy suppresses ω phase formation more than Pt addition does. The 0.2% offset yield strength and the ultimate tensile strength of the Pt-added and Pd-added Zr-20Nb alloys increase with the Pt and Pd concentrations. XRD analysis revealed that the lattice parameter of β-Zr in the Pt-added and Pd-added Zr-20Nb alloys decreases with the Pt and Pd concentrations. Pt and Pd solute in β-Zr as a substitutional element and contribute to the increase in the strength by solid solution hardening. The addition of 2Pt and 2Pd to the Zr-20Nb alloy also improves metal elution from the alloys in lactic acid solution.     

高强度低密度大模量菲晶态Ai—Li合金

利用单辊快速凝固装置制备出高强度、低密度、大楼量的非晶态Ａｌ６１Ｌｉ２．５Ｙ２５Ｎｉ１１．５（ｗｔ－％）合金，其最大拉伸断裂强度、显微硬度和弹性模量分别为１０３９ＭＰａ、４８８ＤＰＮ和９８．７ＧＰａ．与同成分的晶态合金相比，具有较高的电极电位、较宽的电压钝化区，其腐蚀抗力为晶态合金的７倍．在恒加热速率的晶化过程中出现４个晶化峰，晶化激活能的计算表明，Ａｌ６１Ｌｉ２．５Ｙ２５Ｎｉ１１．５非晶合金的晶化过程为一级反应．     

Effect of transition metal (TM) on the crystallization and the magnetic properties of Fe<Subscript>62</Subscript>Co<Subscript>10</Subscript>Si<Subscript>10</Subscript>B<Subscript>13</Subscript>Nb<Subscript>4</Subscript>TM<Subscript>1 </Subscript>melt-spun ribbons

Crystallization and magnetic behavior of melt-spun Fe₆₂Co₁₀Si₁₀B₁₃Nb₄TM₁ amorphous ribbon where TM = Ni, Cr, V, Pd, Pt, Ti, Ta and Zr were examined. The alloy with Pt as transition metal showed the lowest crystallization temperature of 823 K among the studied alloys. Significant increase in crystallization temperature was observed when the atomic radius of the substituted transition metal was varied from that of Pt. High Curie temperature and high saturation magnetization were recognized for the alloys containing Pd, Pt or Ti. The amorphous alloys except the alloys containing Ti or V showed good soft magnetic properties.     

Formation of metastable phases and nanocomposite structures in rapidly solidified Al-Fe alloys

In the present work the structure and morphology of the phases of nanocomposites formed in rapidly solidified Al-Fe alloys were investigated in details using analytical transmission electron microscopy and X-ray diffraction. Nanoquasicrystalline phases, amorphous phase and intermetallics like Al₅Fe₂, Al₁₃F₄ coexisted with α-Al in nanocomposites of the melt spun alloys. It was seen that the Fe supersaturation in α-Al diminished with the increase in Fe content and wheel speed indicating the dominant role of the thermodynamic driving force in the precipitation of Fe-rich phases. Nanoquasicrystalline phases were observed for the first time in the dilute Al alloys like Al-2.5Fe and Al-5Fe as confirmed by high resolution TEM. High hardness (3.57 GPa) was measured in nanocomposite of Al-10Fe alloy, which was attributed to synergistic effect of solid solution strengthening due to high solute content (9.17 at.% Fe), dispersion strengthening by high volume fraction of nanoquasicrystalline phase; and Hall-Petch strengthening from finer cell size (20-30 nm) of α-Al matrix.     

High Strength and Ductile Bulk Quasi‐crystalline Alloys

Quinary Zr‐Al‐Ni‐Cu‐(Ag or Pd) amorphous alloys exhibit a double‐stage devitrification on heating. Primary devitrification leads to the precipitation of nanoscale icosahedral particles with a size from 20 to 50 nm. High nucleation and low growth rates are obtained in a polymorphous mode for the Ag‐containing alloys and a diffusion‐controlled mode for the Pd‐containing alloys. The nanoscale mixed structure alloys exhibit improved strength and ductility as compared to the corresponding amorphous single‐phase alloys.     

Microstructure and mechanical properties of two-phase Cr–Cr2Nb, Cr–Cr2Zr and Cr–Cr2(Nb,Zr) alloys

The microstructures and mechanical properties of binary and ternary Cr-based alloys containing Nb, Zr, or both Nb and Zr, have been studied in both the as-cast and annealed conditions. The level of alloying in each instance was targeted to lie below, or approximately at, the maximum solubility in chromium. The as-cast microstructures of these alloys consisted of Cr-rich solid solution surrounded by small amounts of interdendritic Cr–Cr₂X eutectic structure. Annealing at 1473 K resulted in solid-state precipitation of the Cr₂X Laves phase in the Cr–Nb and Cr–Nb–Zr alloys, but not in the Cr–Zr alloys. The binary Cr₂Nb phase consisted of an extensively twinned ({111}<112> twins) C15 structure whereas the presence of Zr modifies its appearance substantially; the twinned C15 structure persists. Oxides were occasionally present and their compositions were qualitatively determined. Vickers hardness primarily depended upon the volume fraction of the Cr₂X Laves phase present. Age hardening due to solid-state precipitation of Cr₂X Laves phase within the Cr-rich matrix was observed in the Nb-containing alloys. The room temperature bend strength of the alloys was strongly affected by the presence of grain-boundary Cr₂X phase. It is considered that porosity as well as oxides in the alloys also lowers their bend strength.     

Structure and mechanical properties of Ti-Al-Si-N protective coatings deposited from separated plasma of a vacuum arc

Protective coatings of the Ti-Al-Si-N system have been deposited from vacuum arc by sputtering a cathode of composition 78Ti-16Al-6Si in nitrogen. The coatings of the Ti-Al-Si-N system have been studied using X-ray diffraction analysis to examine phase compositions and substructure, atomic force microscopy to analyze the topography, X-ray fluorescence to define the chemical composition, and nanoindentation to measure hardness and elastic modulus. It has been found that as the nitrogen pressure in the deposition chamber increases, in the Ti-Al-Si-N system the transition from nanocrystalline (to 0.04 Pa) to nanocomposite (0.04–0.66 Pa) and X-ray amorphous (0.66–1.1 Pa) coatings takes place, and at a pressure of 2.7 Pa, the amount of the crystalline phase abruptly increases again. The highest mechanical characteristics and thermal stability have been shown by a coating having the nanocrystalline structure and nanocomposite coatings with a low content of amorphous phase, whose hardness attains 47 GPa.     

Nb–Al–N thin films: Structural transition from nanocrystalline solid solution nc-(Nb,Al)N into nanocomposite nc-(Nb,Al)N/a–AlN

Structures and mechanical properties of thin films of the Nb–Al–N system produced by magnetron sputtering of targets from niobium and aluminum in the Ar–N₂ atmosphere have been studied. It has been shown that as the aluminum concentration increases, the structure of a thin film transforms from the nanocrystalline into the nanocomposite one, which consists of nanocrystallites of solid solutions in a matrix of amorphous aluminum nitride. Hardness, elastic modulus, and yield strength of Nb–Al–N thin films have been studied by nanoindentation in the mode of continuous control of the contact stiffness. It has been found that the transition of the structures of Nb–Al–N thin films from the nanocrystalline to the nanocomposite structures results in an increase of hardness and decrease of elastic modulus due to the formation of a thin amorphous interlayer between grains of nanocrystallites. A high hardness to elastic modulus ratio of Nb–Al–N nanocomposite thin films indicates that the films are a promising material for wear-resistant coatings.     

Comparison of the structure and properties of equiatomic and non-equiatomic multicomponent alloys

A series of equiatomic and non-equiatomic Fex(NiCrCo)_100?x (at.-%, x?=?25, 45, 55, 65, 75 and 85) multicomponent alloys were prepared and studied. With the increase in x, the phase structure of the alloys evolves from a single FCC phase (x?=?25, 45 and 55), to a mixture of FCC and BCC phases (x?=?55) and finally to a single BCC phase (x?=?65 and 75). As a result, the BCC-structured alloys have much higher strength and hardness than the FCC-structured alloys. The existing VEC criteria are unable to predict the FCC-BCC phase transition in these alloys.     

High temperature magnetic properties of mechanically alloyed Fe–Zr powder

We report the preparation and characterization of amorphous/non-equilibrium solid solution Fe_100 − xZr_x (x = 20–35) alloys by mechanical alloying process. The microstructure and magnetic properties of milled powders have been studied as a function of Zr substitution. The effective magnetic moment of as-milled powders decreases as concentration of Zr is increased. Thermomagnetization measurements confirmed that the Fe₈₀Zr₂₀ sample exhibits two clear magnetic phase transitions due to the co-existence of an amorphous phase and a Fe rich non-equilibrium solid solution. All the other samples exhibiting an amorphous structure showed a single magnetic phase transition with Curie temperature of ~ 570 °C,which did not vary much with different composition. The Curie temperature of the mechanically alloyed powders is noticeably higher than those of melt-spun amorphous ribbons.     

A novel combinatorial approach to the development of beta titanium alloys for orthopaedic implants

In recent years there has been a significant thrust directed towards the development of novel implant alloys based on β-Ti. Two recently developed and promising biocompatible β-Ti alloys are Ti–35Nb–7Zr–5Ta and Ti–29Nb–4.6Zr–13Ta. While both these alloy compositions, based on the quaternary Ti–Nb–Zr–Ta system, are promising, there is still a tremendous scope for improvement in terms of alloy design in this and other systems via optimization of alloy composition and thermo-mechanical treatments. Here a novel combinatorial approach has been used for the development of implant alloys with optimized compositions and microstructures. Using directed laser deposition, compositionally graded alloy samples based on the Ti–Nb–Zr–Ta system have been fabricated. These samples have been heat-treated to affect different microstructures in terms of the volume fraction and distribution of the α phase in the β matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these samples to construct a database relating the composition and microstructure to the mechanical properties. These databases have been used to train and test fuzzy-logic based neural-network models for predicting the mechanical properties. The trained models have also been used to predict the influence of different alloying additions on the hardness and modulus. These predictions have subsequently been verified by detailed experimental characterization, shedding light on the factors influencing the strength and modulus in these alloys. Such modeling approaches for the development of novel implant alloys can be highly beneficial since they offer the possibility of identifying promising compositions without the necessity for extensive experimental test cycles.     

激光诱导燃烧合成Zr-Ti-Al-Ni合金

根据等电子浓度和等原子尺寸判据设计了四种Zr Ti-Al-Ni系合金,并用激光诱导燃烧合成的方法制备了材料研究发现,其合成产物主要由金属间化合物和Ti/Zr固溶体组成,在成分Zr55Ti1o 8Al171Ni17 1和Zr50Ti21 6Al14 2Ni14 2中还出现了非晶相.合成产物的硬度和摩擦磨损特性与相组成有密切的关系,非晶含量越大,合金硬度值越低,平均摩擦系数越高.     

Microdomain atomic structure of Zr50Pd40Al10 metallic glasses and its formation mechanism

Zr-based Zr_50Pd_40Al_10 metallic glasses has not only crystalline phases of about 5 nm in diameter but also amorphous phases. In this work, the radial distribution functions(RDFs) of amorphous structure of Zr_50Pd_40Al_10 metallic glasses were firstly measured by electron diffraction, and then Reverse Monte Carlo(RMC) optimization accompanied by density functional theory(DFT) calculations. The amorphous structure has not only short-range order but also good medium-range order. In the RDFs of its amorphous structure, the first and the second peaks are located at 2.96 ? and 4.79 ?, respectively. Partial radical distribution functions(PRDFs) show that the contributions of the first and the second nearest-neighbor distances of various atom pairs to the G(r) peak values, and the first nearest-neighbor distances of Pd–Zr and Zr–Zr atom pairs are the sources of main G(r) peak values between 2? and 6?. The competition mechanism for generating the Pd_25Zr_55 Al_20 amorphous phase and the intermetallic crystalline phase Pd_11Zr_9 is associated with the differences of atomic radius, the proportion, and the melting point of different atoms, as well as the heat of mixing between atoms, leading to an equilibrium state of the two phases. Accordingly, a composite system with intertwined nanocrystals and amorphous phases is in turn formed, and improves the stability of the material.     

Multiscale characterization of nanostructured Al–Si–Zr alloys obtained by rapid solidification method

Properties of engineering metallic alloys (e.g., fracture toughness, corrosion resistance) are often limited by the presence of primary intermetallic particles which form during conventional solidification. Rapid solidification brings about much more homogenous amorphous and/or nanocrystalline structure with reduced density of primary particles. Rapidly solidified thin ribbons obtained by melt spinning are usually considered as intrinsically homogenous. However, due to different cooling conditions at the wheel surface and on the side exposed to the ambient environment, structure of such ribbons may vary significantly across its thickness. The materials studied in this study were 30–40 μm thickness ribbons of nanocrystalline hyper- and hypo-eutectic Al–Si–Zr alloys produced by melt-spinning method. Transmission electron microscopy and high resolution scanning transmission electron microscopy were used to characterize the structure homogeneity across the ribbons. Thin foils for transmission observations were prepared by focused ion beam system. Microstructural observations confirmed nanocrystalline character of Al–Si–Zr alloys. However, these observations revealed inhomogeneity of the structure across the ribbon width.     

Relationships between tensile deformation behavior and microstructure in Ti–Nb–Ta–Zr system alloys

Ti–Nb–Ta–Zr system alloys are receiving more attention for biomedical material component applications. However, the deformation behavior of the Ti–Nb–Ta–Zr system has not been evaluated to date. Therefore, the deformation behavior of Ti–Nb–Ta–Zr alloys with different Nb contents was investigated in this study.The behaviors of loading–unloading stress–strain curves of Ti–20Nb–10Ta–5Zr and Ti–25Nb–10Ta–5Zr air-cooled after final heating of the manufacturing process are similar to that obtained in metastable β type titanium alloys that have the shape memory effect. Therefore, the shape memory effect was expected in Ti–20Nb–10Ta–5Zr and Ti–25Nb–10Ta–5Zr alloys. The elastic deformation of Ti–30Nb–10Ta–5Zr disobeyed Hooke's law. However, stress or strain-induced martensite (SIM) is not observed on the loading–unloading stress–strain curve. The deformation mechanism of Ti–25Nb–10Ta–5Zr changes with varying its microstructure. In Ti–25Nb–10Ta–5Zr air-cooled after final heating, the microstructure consisted of an ω phase in a β phase. The stress for inducing martensite in a β phase, σ_M, was nearly equal to the yielding stress, σ_y. Therefore, stress-induced martensitic transformation and movement of dislocations occurred together. In Ti–25Nb–10Ta–5Zr water-quenched after final heating of the manufacturing process, the microstructure consisted of a single β phase, where σ_M is lower than σ_y. Therefore, stress-induced martensitic transformation occurred before yielding.     

Microstructural evolution and strengthening mechanisms in Ti–Nb–Zr–Ta,Ti–Mo–Zr–Fe and Ti–15Mo biocompatible alloys

The microstructural evolution and the strengthening mechanisms in the two quaternary alloys, TNZT (Ti–34Nb–9Zr–8Ta) and TMZF (Ti–13Mo–7Zr–3Fe), and one binary alloy, Ti–15Mo, have been investigated. In the homogenized condition both the quaternary alloys exhibited a microstructure consisting primarily of a β Ti matrix with grain boundary α precipitates and a low volume fraction of primary α precipitates while the binary alloy showed single-phase microstructure with large β grains. On ageing the homogenized alloys at 600 °C for 4 h, all the alloys exhibited the precipitation of refined scale secondary α precipitates distributed homogeneously in the β matrix. However, after ageing while the hardness of TMZF marginally increased, that of the TNZT and Ti–15Mo alloys decreased. Furthermore, the modulus of TNZT decreased while other two alloys showed opposite trends. TEM studies indicate that there is initially a B2 ordering in TNZT that is destroyed after ageing causing a reduction in both hardness and modulus of this alloy. Also in Ti–15Mo, dissolution of ω precipitates on ageing causes the hardness to reduce, while the precipitation of secondary α causes an increase in the modulus. Using these examples, the important influence of thermal processing on the property–microstructure relationships in orthopaedic alloys for implant applications will be highlighted.     

Er对ZrCuNiAl非晶合金结构、力学性能、热稳定性及非晶形成能力的影响

以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x=0,0.5,1,1.5,2,2.5,3,原子分数,下同)系块体非晶合金为研究对象,通过改变微量元素Er的含量来研究Er对非晶合金的结构、力学性能、热稳定性及非晶形成能力的影响。结果表明:添加Er元素所制备出的试样都是完全非晶结构的合金。随着Er含量的增加,各试样的弹性模量呈现出先增大后减小,压缩塑性应变呈台阶式上升,x=0,x=0.5,x=1试样的塑性应变在4%的范围内波动;x=1.5,x=2,x=2.5试样的塑性应变在11%的范围内波动;x=3试样的塑性应变最高,其值为23.19%,弹性模量为37.76GPa,屈服强度为1604MPa,抗压强度为2068MPa,断裂强度为2060MPa;随着Er含量的增加,锆基非晶合金的热稳定性和非晶形成能力均先减小后增大。