Mechanical properties of Ti–Nb biomedical shape memory alloys containing Ge or Ga

Mechanical properties of Ti–24 mol% Nb-based shape memory alloys (SMA) containing 3 mol% Ga or Ge were characterized in this paper as a part of our systematic work for the development of β-Ti based biomedical shape memory alloys. The alloys, called TiNbGa and TiNbGe, were produced by severe cold-rolling followed by a solution treatment at 1273 K for 1.8 ks. The apparent phase was β (bcc) at RT in both the alloys. It was revealed by X-ray diffraction pole figure analysis that a {112}_β〈110〉_β recrystallization texture was well developed in TiNbGa. However, a {001}_β〈110〉_β deformation texture still remained in TiNbGe even after the solution treatment. Martensite transformation temperatures were significantly lowered by the addition of Ge, compared to Ga and Al additions. TEM-EDX observation revealed that (Ti, Nb)₅Ge₃ particles are formed in TiNbGe regardless of the solution treatment. The (Ti, Nb)₅Ge₃ particles were judged to be an ineffective strengthener, because significant hardening was not recognized in the flow-stress of TiNbGe. TiNbGa exhibited a large shape recovery of about 2% above RT in the strain–temperature curves during thermal cycles under external stress. The TiNbGe alloy exhibited superelasticity of 3.5% at RT.     

Devitrification of Zr-Ni-Al-Cu-Ti(Nb,Ta) glassy alloys

The devitrification behavior and phase formation in Zr_65-55Ni₁₀Al_7.5Cu_7.5Ti_5-10(Nb,Ta)_5-10 metallic glass have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. It has been found that mutual addition of Ti and Ta/Nb benefits the formation of nanoscale icosahedral phase in the glassy phase on heating and the oxygen content in the alloy makes significant influence on the devitrification behavior of these alloys. At the same time in Nb-bearing alloys and alloys containing 5 at.% Ta icosahedral phase was found to coexist with crystalline one.     

Hydrothermal synthesis of barium titanate fine particles from amorphous and crystalline titania

Barium titanate fine particles of cubic system were synthesized hydrothermally from aqueous barium hydroxide solutions with fine particles of either amorphous or crystalline (rutile) titania in suspension. The mean size of barium titanate particles prepared from amorphous titania ranged from 0.03 m to 0.11 m, depending on hydrothermal conditions. The particle size approximately agreed with the crystallite size (0.04–0.09 m). On the other hand, the mean size of barium titanate particles prepared from rutile titania ranged from 0.2 to 0.7 m, which was about six times as large as the crystallite size. The difference of sizes of barium titanate particles prepared might be ascribed to the difference in dissolution rates of amorphous or crystalline titania particles.Nomenclature mean particle size, m - BT barium to titanium molar ratio - d crystallite size, m - K shape factor appearing in Equation 3 - half value breadth of diffraction peak - lattice strain - Bragg diffraction angle, degree - wave length of X-ray, urn - _g geometric standard deviation defined by 84.1%-size/50%-size in a log normal size distribution     

Mechanical properties of alloys consisting of two ductile phases

A large number of engineering alloys consist of two ductile phases; for example α/β titanium alloys, α/β brasses and dual phase steels. Whenever a material consisting of two or more component phases with different properties is subjected to stress, in general, the phases deform differently. This results in additional interaction stresses and strains and their magnitude depends on such factors as the property difference between phases, and morphology and volume fraction of phases. Due to these complexities, the properties of two-phase materials, in general, cannot be predicted on the basis of simple laws such as the law of mixtures. The aim of this review paper is to describe how the various parameters such as morphology and volume percent of phases affect the mechanical properties of two-phase materials. Such information will be of great use in designing and selecting two-phase materials for various engineering applications.     

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.     

Ambient temperature formation of (Ta,Nb)C and (Ta,Nb)N

A tantalum/niobium concentrate has been mechanically milled with magnesium and either graphite or nitrogen for 100 h. Directly after milling the formation of MgO was evident in both systems, a mixed metal carbide (Ta,Nb)C was also present in the carbon system. A cubic phase, close to that expected for the mixed metal nitride, was found in the powder milled under nitrogen. Annealing of the powders showed the reaction was incomplete with reduced oxide phases present. The carbide/nitride phases were readily separated from the MgO by acid leaching which left powders <5 m in size. The leaching preferentially dissolved the smaller, more highly strained crystallites in both cases.     

Ni60Nb(20-x)TaxTi15Zr5系列非晶合金性能研究

采用X射线衍射(XRD)、示差扫描量热分析(DSC)、显微硬度测量、四点探针测量电阻法和动态极化曲线法,研究了Ni60Nb(20-x)TaxTi15Zr5 系列非晶合金的结构、热稳定性、力学性能、导电性和耐腐蚀性能.研究表明随着Ta含量的增加,合金的热稳定性、力学性能、耐腐蚀性能变好,对导电性影响不大.当Ta完全代替Nb时性能最优,具有宽过冷液相区(67K),很高的显微硬度(1100HV)和电阻率(220μΩ·cm),很低的钝化电流密度(0.01A/m2).     

Mechanical properties and deformation behaviour of some zirconium-nickel amorphous alloys

A series of zirconium-nickel alloys have been melt-spun under identical conditions to produce partly crystalline and fully amorphous ribbons. The mechanical properties: hardness and fracture strength of these ribbons have been determined. The deformation and fracture behaviour in bending and tension have been studied and the effect of the crystalline particles on the deformation and fracture processes has been examined. The structure of the deformation defects has also been investigated.     

Study of the in vitro corrosion behavior and biocompatibility of Zr-2.5Nb and Zr-1.5Nb-1Ta (at%) crystalline alloys

The in vitro corrosion behavior and biocompatibility of two Zr alloys, Zr-2.5Nb, employed for the manufacture of CANDU reactor pressure tubes, and Zr-1.5Nb-1Ta (at%), for use as implant materials have been assessed and compared with those of Grade 2 Ti, which is known to be a highly compatible metallic biomaterial. The in vitro corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements, as a function of exposure time to an artificial physiological environment (Ringer’s solution). Open circuit potential values indicated that both the Zr alloys and Grade 2 Ti undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Zr-1.5Nb-1Ta alloy and that this oxide has better corrosion protection characteristics than the ones formed on Grade 2 Ti or on the Zr-2.5Nb alloy. EIS study showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film presents on the metals surface, improving their resistance with exposure time, presenting the highest values to the Zr-1.5Nb-1Ta alloy. For the biocompatibility analysis human osteosarcoma cell line (Saos-2) and human primary bone marrow stromal cells (BMSC) were used. Biocompatibility tests showed that Saos-2 cells grow rapidly, independently of the surface, due to reduced dependency from matrix deposition and microenvironment recognition. BMSC instead display a reduced proliferation, possibly caused by a reduced crosstalk with the metal surface microenvironment. However, once the substrate has been colonized, BMSC seem to respond properly to osteoinduction stimuli, thus supporting a substantial equivalence in the biocompatibility among the Zr alloys and Grade 2 titanium. In summary, high in vitro corrosion resistance together with satisfactory biocompatibility make the Zr-2.5Nb and Zr-1.5Nb-1Ta crystalline alloys promising biomaterials for surgical implants.     

Mechanical properties of Al2O3--SiC composites containing various sizes and fractions of fine SiC particles

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Mechanical properties of Al2O3--SiC composites containing various sizes and fractions of fine SiC particles

Abstracts are not published in this journal     

Effect of crystalline properties on coercive force in iron acicular fine particles

Crystallographic properties and their size dependence in acicular fine particles of iron prepared by reduction from-FeOOH were investigated by transmission electron microscopy and compared with magnetic properties. Although both larger particles with an average needle length of 0.5m and smaller ones of 0.2m length have single domain configuration, the former are crystal lographicaIly polycrystalline while the latter are single crystal with a [100] axial orientation, an easy magnetization direction of iron. The coercive force, principally yielded by external shape anisotropy, is higher in smaller particles in spite of their inferior axial ratio. The intrinsic magnetocrystalline anisotropy is inferred to be the most responsible to give rise to this further increase of coercive force. The experimentally obtained values of magnetic properties are also compared with the theoretical estimation, which results semi-quantitatively in good accordance.     

Mechanical properties and microstructure of bioactive ORMOSILs containing silica particles

We synthesized organically modified silicate (ORMOSILs) gels with colloidal silica (CS) (AEROSIL®) starting from polydimethylsiloxane (PDMS), tetraethoxysilane (TEOS) and calcium nitrate (Ca(NO₃)₂·4H₂O) through sol–gel processing. Dynamic mechanical analysis indicated that relative height of the tanδ peak at about −100 °C increased with an increase in the relative content of the inorganic components. This peak growth was accounted for by the relative increase in PDMS–colloidal silica particle interactions. The colloidal silica could control the mechanical behavior of the hybrids. The gel of a specific composition could deposit apatite within 3 days of soaking in the simulated body fluid (SBF), since it included many calcium ions on the surface.     

Co对Nd-Fe-Al大块非晶合金的晶化行为和磁性能的影响

采用示差扫描量热法(DSC)，X射线衍射(XRD)和振动样品磁强计(VSM)研究了Co对Nd—Fe-Al大块非晶合金的非晶形成能力，晶化行为和磁性能的影响。结果表明：加入Co元素后可以显著提高Nd—Fe-Al大块非晶合金的非晶形成能力以及提高合金的居里温度。Nd60Fe30-xAl10Cox(z=0、5、10)大块非晶合金在室温有较高的内禀矫顽力，具有硬磁性。内禀矫顽力随着Co含量的增加变化不大．但是饱和磁化强度和剩磁则随着Co含量的增加有所下降。Nd60Fe3-xAl10Cox(x=0、5、10)大块非晶合金具有的硬磁性能来自于非晶相。合金少量晶化后，磁性能变化不大。完全晶化后合金的硬磁性迅速消失。     

Effects of crystalline particles on mechanical properties of strip-cast Zr-base bulk amorphous alloy

Effects of crystalline phase particles formed in a strip-cast Zr-base bulk amorphous alloy on strength, ductility, and fracture toughness were investigated by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope chamber. The compressive and fracture toughness test results indicated that strength, ductility, and fracture toughness of the strip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5 vol.%) of hard, brittle crystalline particles. According to the in situ microfracture observation, crystalline particles were easily cracked under low stress levels, acted as blocking sites of shear band or crack propagation, and provided initiation sites of multiple shear bands. Thus, the improvement of mechanical properties in the strip-cast alloy could be explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles.     

Mechanical properties of Nb2O5 and Ta2O5 prepared by different procedures

We have studied the mechanical properties of niobium pentoxide and tantalum pentoxide ceramics prepared by a conventional ceramic processing technique and by exposure to high-intensity light (HIL). The results demonstrate that, after HIL exposure in an optical furnace, the niobium pentoxide and tantalum pentoxide ceramics possess enhanced microhardness and improved mechanical properties (strength, fracture toughness, and brittle microstrength) owing to the formation of fractal micro- and nanostructures. With increasing exposure intensity, the strength of the Nb₂O₅ and Ta₂O₅ ceramics increases.     

Oxidation-reduction reactions of CeMO4+x (M = Ta or Nb) phases

Phase equilibrium methods, single crystal and powder x-ray diffraction analyses, thermogravimetric analysis and magnetic susceptibility measurements were utilized to define subsolidus phase relations $\text{in air}$ for the systems cerium oxide - Ta₂O₅ and cerium oxide - Nb₂O₅. Stoichiometric CeTaO₄ is stable in air (P_O2 = 0.21 atm) only above 1265°C. At 1265°C, the reversible reaction, $\text{3}\text{CeTaO}{}_4\text{+}\text{1}\text{2}\text{?}$CeTa₃O₉ + 2CeO₂ is established. If CeTaO₄ is quenched to room temperature and $\text{reheated}$ below 1000°C, or, if the material is rapidly cooled from above 1265°C to below 1000°C it absorbs oxygen according to, . The x parameter is variable and temperature dependent. Using a thermal microbalance, three distinct complex reaction series involving a homogeneity range in x were established, (a) 0.50 ≥ × ≥ 0.48 (<350°–600°C), (b) 0.17 ≥ × ≥ 0.06 (600°–950°C), (c) 0.40 ≥ × ≥ 0.34 (950°-room temperature). CeNbO₄ (not isostructural with CeTaO₄) also absorbs oxygen below ≈700°C in air to yield CeNbO_4+x materials.     

Mechanical behaviour of partially crystallized amorphous alloys

Deformation and fracture of partially crystallized Ni₅₅Pd₃₅P₁₀ amorphous alloys have been investigated. The samples with a few percent crystallization show a fracture stress (175 kg mm⁻²) and apparent Young's modulus (19.5×10³kg mm⁻²) greater than those completely amorphous or partially crystallized 50%. On the other hand, the fracture strain of the former are lower than those of the two latter. A simulated model with mixtures of carborundum powder with grease, shows accord with morphological and mechanical aspects of the partially crystallized alloys. As expected, microcrystals embedded in an amorphous material act as obstacles to plastic flow.