Zr-Cu-Ni-Al-Nb大块非晶合金的晶化行为、力学性能及电化学腐蚀行为的研究

利用水冷铜模铸造法成功制备了Zr_65-xCu_17.5Al_7.5Ni ₁₀Nb_x (x=0，2，5)大块非晶合金. X射线衍射、热分析研究结果表 明，Nb的添加显著改变了非晶合金的晶化行为，促进了二十面体准晶相的形成. 各合金的准 静态压缩实验表明，Nb的适量添加有利于提高大块非晶合金的强度和塑性. 其中x=5的大块 非晶合金的抗压强度σ_b和塑性应变量ε_p 关键词： Zr基大块非晶合金 晶化行为 力学性能 耐腐蚀性能     

Electrical resistivity and glassy behaviour in crystalline metallic alloys

Positional disorder due to loss of translational symmetry is suggested as being responsible for most of the concentration dependence of the electrical resistivity of certain disordered transition metal alloys. It is then argued that in such cases the existence of tunneling states should be observable at low temperatures. Measurements of the thermal conductivity on Ti_0.67V_0.33 between 0.06 and 10 K confirm this conjecture.     

Fracture mechanisms in bulk metallic glassy materials

We find that the failure of bulk metallic glassy (BMG) materials follows three modes, i.e., shear fracture with a fracture plane significantly deviating from 45 degrees to the loading direction, normal tensile fracture with a fracture plane perpendicular to the loading direction, or distensile fracture in a break or splitting mode with a fracture plane parallel to the loading direction. The actually occurring type of failure strongly depends on the applied loading mode and the microstructure of the material. Extensive evidence indicates that the Tresca fracture criterion is invalid, and for the first time, three fracture criteria are developed for isotropic materials with high strength, such as advanced BMGs or the newly developed bulk nanostructural materials.     

Measuring surface and bulk relaxation in glassy polymers

We present a comprehensive study of gold nanoparticle embedding into polystyrene (PS) surfaces at temperatures ranging from T _g + 8 K to T _g − 83 K and times as long as 10⁵ minutes. This range in times and temperatures allows the first concurrent observation of and differentiation between surface and bulk behavior in the 20nm region nearest the free surface of the polymer film. Of particular importance is the temperature region near the bulk glass transition temperature where both surface and bulk processes can be measured. The results indicate that for the case of PS, enhanced surface mobility only exists at temperatures near or below the bulk T _g value. The surface relaxation times are only weakly temperature dependent and near T _g , the enhanced mobility extends less than 10nm into the bulk of the film. The results suggest that both the concept of a “surface glass transition” and the use of glass transition temperatures to measure local mobility near interfaces may not universally apply to all polymers. The results can also be used to make a quantitative connection to molecular dynamics simulations of polymer films and surfaces.     

A.C. conductivity of bulk glassy chalcogenides

The a.c. conductivity of amorphous Se, Se₉₀Ge₁₀, Se₇₅Ge₂₅, As₂Se₃, As₂S₃, and As₄₅Te₄₀Ge₁₅ has been measured at room temperature in the 20 MHz–35 GHz range. The results display a contact effect we explicit. For the six materials, the conductivity is roughly proportional to ω^s with $\text{s}{}^{\mathrm{\approx }}\text{1}$ up to the microwave region (no saturation is observed). The experimental results are analysed with regard to the electronic and the atomic contributions but a better estimate of some parameters is necessary to confirm any model.     

块体非晶合金的韧塑化

块体非晶合金因其独特的原子结构而具有许多优异的力学性能,成为近年来材料领域的研究热点之一,但是由于其在变形过程中的室温脆性和应变软化等关键问题一直制约着其实际工程应用.为解决此问题,块体非晶合金领域的研究者们提出了多种方案,包括通过在非晶合金中调控其内禀特性如弹性常数、结构不均匀性,通过外加手段改变其应力及缺陷状态,通过外加和内生的方法在非晶基体中引入晶态增强相等方式,获得了一系列力学性能优异的块体非晶合金及其复合材料.特别是利用"相变诱导塑性"(transformation-induced plasticity,TRIP)概念研制出的块体非晶合金复合材料,同时具有大的拉伸塑性和加工硬化能力.本文围绕块体非晶合金的韧塑化这个关键科学问题,对单相非晶及非晶复合材料的韧塑化方案及机理进行了综述,着重介绍了TRIP韧塑化块体非晶合金复合材料的制备、性能、组织调控及韧塑化机理等,并对此领域的未来发展进行了展望.     

Universal conductivity variation in glassy Zr-M alloys

Temperature dependence (3–300 K) of the electrical conductivity in a number of amorphous Zr_1?xM_x alloys (M = Cu, Ni, Co and Fe, 0.19 < x < 0.71) has been analysed in some detail. Like in some other alloys with a high electrical resistivity, the conductivity varies as T at lower temperatures (T < 80 K) and √T at higher temperatures. A new feature observed is that the ratio of the coefficients of a low temperature T and a high temperature √T conductivity variation is practically constant for allalloys. Therefore a universal conductivity-temperature curve can be constructed for all amorphous Zr_1?xM_x alloys with the resistivity higher than 150 μohms cm. These results are consistent with the effects of incipient localisation and indicate that the electron-phonon coupling determines the conductivity variation.     

Magnetic behaviour ofCuAuFe alloys

The magnetic properties of Cu_99-xAu_xFe₁ alloys (x=12, 37 and 50.7 ats) have been investigated over the temperature range 4.2–70 K using low field AC magnetic susceptibility measurements and mössbauer spectroscopy. All alloys exhibit spin glass behaviour at low temperature with freezing temperatures T_f-5.7–7.6 K. Results of analysis of the high temperature (T3 T_f) Curie-Weiss behaviour are compared with those obtained from analysis of the broadly distributed 4.2 K Mössbauer spectra.     

Chaotic properties of quantum transport in Ni-Nb-Zr-H glassy alloys

We analyzed the dynamic evolution of an ensemble of electrons performing macroscopic resonant tunneling for room-temperature millimeter-sized Coulomb oscillation in Ni-Nb-Zr-H glassy alloys as a function of the cluster size and boundary length using a one-dimensional Kronig-Penny model with a stepwise potential. The reflection coefficient showed a stagnant chaos around a narrow torus for a superlattice with a cluster size of 0.55 nm and a boundary distance of 0.23 nm. The transmission and reflection coefficients showed stationary chaotic behavior in periodic units with decreasing boundary distance rather than increasing cluster size.     

Superparamagnetic-like behaviour of magnetic alloys

The effect of antiferromagnetic interaction on a binary Ising ferromagnetic alloy A_pB_1?p is studied based on cluster-variational method and assuming either J_AB or J_BB or both exchange interactions to be of antiferromagnetic type. In a ferromagnetic state the moment saturates to a value much lower than its full value. Within the temperature interval where moment saturates, the system exhibits superparamagnetic-like behaviour. The induced moment becomes a function of $\text{h}\text{T}$ only, and the zero-field susceptibility follows Curie law. The incomplete saturation of moment persists up to a large value of $\text{h}\text{T}$. The short-range order parameter at T = 0 is much less than that of homogeneous ferromagnet.     

Exchange bias in bulk Ni-Mn-In-based Heusler alloys

The crystal structure and exchange bias of the bulk Heusler alloys Ni₅₀Mn_50−xIn_x with 14.5?x?15.2 have been investigated using X-ray diffraction and magnetization measurements, respectively. Magnetic measurements were performed with SQUID magnetometry after samples were zero-field cooled and field cooled (FC) in positive magnetic fields up to H=50 kOe, from a temperature T=380 K. Three temperatures of the phase transitions, T₁<T_M<T_C, and a shift of the FC (50 kOe) magnetic hysteresis loops up to 120 Oe at 5 K have been detected for all samples. The exchange bias field (H_E) was almost constant for intermediate In concentrations 14.8<x<15.2, and sharply decreased to about 20 Oe on the borders of this concentration interval (x?14.5; 15.2?x). The changes of H_E have been related to changes in the ratio of T₁ to T_M: the overlapping of transitions at T₁ and T_M (for x=14.8, and 15.2) results in a decrease in H_E.     

The Invar behaviour of iron-nickel-platinum alloys

The ordering temperatures of alloys in the quasi-binary section Fe₃(Ni_xPt_1−x) have been determined experimentally, and are found to be consistent with theoretical predictions. Lattice constants and expansion coefficients vary smothly between Fe_0.75Ni_0.25 and Fe_0.75Pt_0.25 and are basically in agreement with the predictions of the Weiss 2_γ state theory except in a region very close to Fe_0.75Pt_0.25. The effect of heat treatments below the ordering temperature is placed in an overall context of competing phase transformations, which can also be used to rationalise conflicting views on the existence of Fe₃Ni, and the role of ordering on the Invar effect in general.     

The formation of glassy alloys by irradiation with intense proton beams

Using a 50 ns pulse of an intense proton beam 1.5 J cm^–2 of energy was deposited in a 1 m thick surface layer of glass forming alloys. In Fe₈₀B₂₀, the formation of a glassy surface layer of 1.9 m thickness was observed by x-ray diffraction. Etching experiments performed with alloys containing phosphorus yielded similar results. Applying a mask technique amorphous and crystalline zones were structured with a resolution of better than 2 m.On leave from Central Electronics Engineering Research Institute, Pilani, Rajasthan, India     

Kondo behaviour in hydrogenated Pd-Co alloys

Pd-Co-H_x alloys with x in the 0.75 range present resistivity minima as a function of temperature typical of Kondo behaviour. It is found that the concentration x is a critical factor for these observations and several explanations are proposed.     

Magnetoelastic behaviour in amorphous FePGa alloys

Temperature dependences of Young's modulus and saturation magnetization, linear and forced volume magnetostriction were measured for FePGa amorphous alloys. A discussion concerning the influence of linear magnetostriction, forced volume magnetostriction and magnetic ordering on the changes of E(T) function was made. It was found that annealing of the sample decreases the linear magnetostriction contribution increasing the other two contributions at the same time.     

Magnetic behaviour of AuFe and NiMo alloys

We study the electronic structure and a mean-field phase analysis based on the pair–pair energies derived from first-principles electronic structure calculations of AuFe and NiMo alloys. We have used the tight-binding linear muffin-tin orbitals-based augmented space recursion (TB-LMTO-ASR) method to do so. We investigate different behaviours of the two alloy systems by mapping the problems onto equivalent Ising models and then discuss the magnetic phase diagrams using the calculated pair energies. All three phases: paramagnetic, random ferromagnetic and spin glass, have been studied.     

The magnetic behaviour of diluted CrAl alloys

Magnetic susceptibility as a function of temperature of binary CrAl alloys containing 0.7,1.07,1.35,1.59, 1.79,1.98, 2.18, 2.84, 3.74 and 4.36 at %A1 is investigated. Aluminium, by alloying, acts on the Néel temperature of pure chromium giving rise to a complicated phase diagram. The bahaviour of the magnetic susceptibility as a function of temperature, in the ordered phase, for the samples containing 1.28, 2.18 and 2.84 at %A1 is found to be temperature independent. In the paramagnetic region, for the samples containing between 1.07 and 2.84 at %A1, it is found a decrease of the magnetic susceptibility as a function of temperature.