弛豫对Zr-Al-Ni-Cu基非晶合金晶化过程的影响

非晶合金的稳定性是制备大块非晶合金的关键，而弛豫后形成的短程有序结构对非晶中的晶体相形核有重要的影响。本文通过差热分析及X射线衍射法研究了预先弛豫处理对Zr60Al8Ni12.5Cu17Si2.5和Zr60Al8Ni10Cu17Si5非晶合金晶化过程的影响。结果表明：预先弛豫处理降低了上述非晶合金的稳定性。Si含量的增加则提高上述非晶合金的稳定性。根据等温转变过程日体相形核孕育期采用Arrhenius公式所确定的晶化激活能更能反映非晶晶化过程及非晶的稳定性。     

Growth and mechanical properties of GeSi bulk crystals

Bulk crystals of Ge_1–xSi _x alloys were grown by the Czochralski technique. Full single crystals were obtained for the alloys of composition 0 < x < 0.15 and 0.9 < x < 1, while single crystal parts near the seeds of ingots provided alloys of intermediate composition. The dislocation velocity and mechanical strength of the GeSi alloys were investigated by the etch pit technique and compressive deformation tests, respectively. In the GeSi alloys of the composition range 0.004 < x < 0.080 the dislocation velocity decreases monotonically with increasing Si content in the temperature range 450–700°C and the stress range 3–24 MPa. In contrast, in the composition range 0.94 < x < 1 the dislocation velocity first increases and then decreases with decreasing Si content in the temperature range 750–850°C and the stress range 3–30 MPa. The velocity of dislocations was determined as functions of stress and temperature. The stress–strain behaviour in the yield region of the GeSi alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress–strain curves of the GeSi alloys of composition 0.94 < x < 1 are similar to those of pure Si at temperatures of 800–1000°C and the yield stress increases with decreasing Si content down to x = 0.94. The yield stress of the GeSi alloys is dependent on the composition, being proportional to x(1 – x). The strengthening mechanism in alloy semiconductors is discussed.     

Mössbauer Study of Nanoscale Crystallization in Amorphous Fe–P–Si Alloys during Annealing

The crystallization behavior of amorphous Fe–P–Si alloys is studied by Mössbauer spectroscopy and physicochemical analysis. The resulting materials are found to contain nanocrystalline particles of complex composition, characterized by a doublet and several sextets in the Mössbauer spectrum. In the alloys containing 6 or 10 at. % Si, crystallization leads to the precipitation of pure Fe, which increases Si mobility and, accordingly, the rate of particle growth.     

Structural characterization and electrochemical behaviour of Fe-Ni-Mo-B Amorphous alloys

A series of amorphous alloys obtained by the “melt-spinning” technique, with variable nickel and molybdenum contents, have been examined. Potentiodynamic anodic and cathodic polarization curves have been obtained for each of these amorphous alloys in various environments (1N HCl, 1N H₂S0₄, 3% NaCl, 1N NaOH).Their electrochemical properties were correlated with the amorphous structure and with their composition, characterized by means of X-ray diffraction and Mössbauer spectroscopy. Surface morphology has been observed by Scanning Electron Microscopy (SEM). The nickel content, in amorphous Fe-Ni_x-Mo₄-B₁₃ (balance iron) alloys enhanced the corrosion resistance in acid (IN H₂SO₄, 1N HCl), neutral (3% NaCl) and alkaline (1N NaOH) environments. The molybdenum content (from 4 to 8.5%) in the amorphous Fe-Ni₂₀-Mo_x-B₁₃ (balance iron) alloys increased the corrosion resistance only in alkaline solutions.In the various environments tested, the corrosion potentials tend to ennoble on increasing the nickel content. While the alloys are in the active state in acid and neutral environments, they are passive in alkaline environments. A correlation has been found between the short range order in the alloys of the Fe-Ni-Mo-B type, of similar chemical composition, and the electrochemical behaviour.     

Nonequilibrium phases in rapidly quenched Co-C-Si and Ni-C-Si alloys

It has been found that the rapid quenching of Co-C-Si and Ni-C-Si alloys results in the formation of an amorphous phase in the range above 10 at% C and 12 to 23 at% Si in the Co-C-Si system, and a nonequilibrium ordered b c c phase with a lattice parameter of 0.2744 nm in the range above 4 at% C and 15 to 21 at% Si in the Ni-C-Si system. Since the interaction between cobalt and carbon is repulsive, the glass formation in the high metalloid concentration range in the Co-C-Si system is thought to be attributed to a strongly attractive interaction between metalloid atoms (carbon and silicon). Crystallization temperature and Vickers hardness of the amorphous alloys are in the range of 671 to 708 K and 833 to 942 diamond pyramid number (DPN) respectively. Furthermore, the amorphous alloys exhibit a soft ferromagnetism and the Curie temperature, saturated magnetization under an applied field of 100 Oe, coercive force and permeability at 1 kHz are 395 to 432 K, 4.33 to 5.50 kG, 0.031 to 0.210 Oe and 31 000, respectively, in the as-quenched state. The effective permeability of (Co_0.94Fe_0.06)_67.5C_12.5Si₂₀ amorphous alloy is higher than that of Co₆₇Fe₄Si₁₉B₁₀ amorphous alloy with zero magnetostrain at frequencies above 200 kHz. Accordingly, the Co-C-Si amorphous alloys newly found in the present work are very attractive as a soft ferromagnetic material with good characteristics in the high frequency range.     

Fe-Si-B amorphous alloys with high silicon concentration

Amorphous phase formation with good ductility has been found in Fe-Si-B ternary alloys with high silicon concentration using a melt-spinning technique. The formation range of these amorphous alloys is in the range 0 to 29 at % silicon and 5 to 26 at % boron, being much wider than the previously reported range (0 to 19 at % silicon and 10 to 26 at % boron). The crystallization temperature (T _x) and Vickers hardness (H _v) of the Fe-Si-B amorphous alloys containing more than 19 at % silicon increase significantly with increasing boron content, while the increase in silicon content causes a decrease inT _x andH _v. TheT _x andH _v of Fe₆₆Si₂₈B₆ alloy with the highest silicon concentration are 740 K and 500 DPN, respectively. The decreases inT _x andH _v with silicon content are interpreted owing to the increase in the contribution of the repulsive interaction between silicon and silicon against the attractive interactions between iron and silicon or boron. Furthermore, the silicon-rich amorphous phase has been found to crystallize by the almost simultaneous precipitation of the two equilibrium compounds of Fe₃Si and Fe₂B, Fe₂Si_0.4B_0.6 or Fe_4.9Si₂B.     

Electrocatalytic behavior of Ni-based amorphous alloys for hydrogen evolution

Ni-based amorphous alloys were synthesized by rapid quenching from the melt, using a planar flow technique. Their amorphous nature and thermal stability were studied by X-ray diffraction and differential scanning calorimetry. The electrocatalytic activity of the as-quenched amorphous alloys with respect to the hydrogen evolution reaction (HER) in alkaline water electrolysis was studied in relation to the alloy composition. The kinetic parameters of the HER were evaluated by cyclic voltammetry and impedance spectroscopy techniques in 6 M KOH at room temperature. The electrocatalytic activity of the amorphous alloys was found to depend on the alloy composition. It was obtained that molybdenum containing amorphous alloys (Ni–Mo–B) showed a superior electrocatalytic activity in the HER compared to Ni–(Nb,Ta)–B and Ni–Si–B, as Ni_66.5Mo_28.5B₅ revealed considerably lower charge transfer resistance and higher exchange current density than Ni₆₃Mo₂₇B₁₀. The results have to be attributed to an improved intrinsic activity of the Ni–Mo–B alloys compared to the other Ni-based glasses.     

Mechanical properties of ductile Fe-Ni-Zr and Fe-Ni-Zr (Nb or Ta) amorphous alloys containing fine crystalline particles

Melt-quenched Fe_60–80Ni_10–30Zr₁₀ and Fe₇₀Ni₂₀Zr_10–x (Nb or Ta) _x (x2 at %) alloy ribbons with the duplex structure consisting of amorphous and bcc phases were found to exhibit hardness and tensile strengths higher than those of the totally amorphous alloys. The volume fraction of the bcc phase was intentionally allowed to alter in the range 0% to 60% by changing the composition and sample thickness. The bcc phase has an average particle size of 75 nm for the Fe-Ni-Zr alloys and 50 nm for the Fe-Ni-Zr-Nb alloys, and the lattice parameter is much larger than that of pure -Fe because of the dissolution of large amounts of zirconium, niobium and/or tantalum. The hardness and tensile strength of the duplex alloys increase with amount of bcc phase and reach about 880 DPN and 2580 MPa, which are higher by about 20% to 30% than those of the amorphous single state, at an appropriate volume fraction of bcc phase. As the volume fraction of the bcc phase increases further, the duplex alloys become brittle and the tensile strength decreases significantly. The enhancement of strength was considered to be due to the suppression of shear slip caused by fine bcc particles dispersed uniformly in the amorphous matrix. It was thus demonstrated that an optimum control of melt-quenched structure results in the formation of ductile Fe-based amorphous alloys containing fine crystalline particles.     

Amorphous alloys resistant to corrosion in artificial saliva solution

The tailoring of new corrosion-resistant alloys with specific properties has recently been performed mostly by the sputter deposition technique. The aim of this work was to investigate corrosion resistance of aluminum–tungsten (Al–W) amorphous alloys in artificial saliva solution, pH=5.5, based on the electrochemical methods of cyclic voltammetry and linear polarization. Thin alloy films were prepared on a sapphire substrate by magnetron codeposition. Completely amorphous films were obtained in the Al₈₀W₂₀–Al₆₇W₃₃ composition range. Amorphous Al–W alloys exhibit very high corrosion resistance due to their homogeneous single-phase nature. The passive films spontaneously formed at their surface are uniform with characteristics of an insulator film and prevent corrosion progression in the bulk in a very demanding oral environment. The mechanism of increasing resistivity of Al–W alloys to pitting corrosion and generalized corrosion has been discussed in the view of increasing tungsten content in the alloy. Considering these exceptional corrosion properties and microhardness which falls in the range 7.5±1.6 Pa, Al–W alloys represent promising materials for dental applications.     

Compositional range,thermal stability,hardness and electrical resistivity of amorphous alloys in Al-Si (or Ge)-transition metal systems

An amorphous single phase was found to be formed in wide compositional ranges in rapidly solidified Al-Si-transition metal (M) and Al-Ge-M alloys. The compositional ranges are in the range from 12 to 53 at. % Si or Ge and 8 to 23% M and Al-Si-Co and Al-Ge-Fe alloys have the widest glass-formation ranges. Because the interaction between aluminium and silicon or germanium atoms is thought to be repulsive from the immiscible equilibrium phase diagrams, the glass formation is probably due to an attractive interaction of M-Si (or Ge) and Al-M pairs. Hardness, H _v, and crystallization temperature, T _x, increase with increasing M content and the highest values reach 1120 DPN and 715 K, while the change with silicon or germanium content is much smaller for H _v and is hardly seen for T _x. Additionally, the H _v and T _x have maximum values for Al-Si (or Ge)-M (M=Cr, Mn or Fe), decrease with the decrease and increase in the group number of M element and are the lowest for Al-Si (or Ge)-Ni alloys. The compositional dependence is interpreted under the assumption that T _x and H _v of the aluminium-based amorphous alloys are mainly dominated by the attractive interaction of M-(Si or Ge) and Al-M pairs. Room-temperature resistivity, _RT, increases in the range of 220 to 1940 cm with increasing silicon or germanium and M contents. The change in _RT with the group number of M elements shows a maximum phenomenon for manganese. It has thus been clarified that the characteristics of the Al-Si-M and Al-Ge-M amorphous alloys have the different compositional dependence as compared with those for conventional metalmetalloid amorphous alloys, probably because of the unusual interaction among the constituent elements.     

Microstructure and solidification behavior of Cu–Ni–Si alloys

The microstructure and solidification behavior of Cu–Ni–Si alloys with four different Cu contents was studied systematically under near-equilibrium solidification conditions. The microstructures of these Cu–Ni–Si alloys were characterized by SEM and the phase composition was identified by XRD analysis. The phase transition during the solidification process was studied by DTA under an Ar atmosphere. The results show that the microstructure and solidification behavior is closely related to the composition of Cu–Ni–Si alloys. The microstructure of Cu–Ni–Si alloys with higher than 40% Cu content consists of primary phase α-Cu(Ni, Si) and eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si).When the Cu content is about 40%, only the eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si)) is present. DTA analysis shows there are three phase transitions during every cooling cycle of alloys with higher than 40% Cu content, but only one for 40% Cu content. Cu–Ni–Si alloy with 40% Cu solidifies by a eutectic reaction, but Cu–Ni–Si alloys with higher than 40% Cu content solidify as a hypoeutectic reaction.     

Effect of Si on the Glass Formation and Magnetic Properties of High-Iron Fe–Zr–Si Alloys

High-iron Fe–Zr–Si amorphous ribbons were fabricated through the melt-spun technique. Then, the effects of Si content on the glass-forming ability and magnetic properties of Fe_90?xZr₁₀Si_x (x =?1, 2, 3, 4, 5, 10) alloys were investigated. Results showed that the amorphous structure only formed in an alloy composition of 3 at.% Si. Moreover, α-Fe(Si) and Fe₃Zr phase appeared gradually when Si was added. Fe₈₇Zr₁₀Si₃ alloy is a unique amorphous structure in Fe_90?xZr₁₀Si_x ribbons. The peak temperatures of the two crystallization stages were 464 and 600 ^°C. The saturation magnetization (M_s) values of the alloys ranged from 91.2 to 132.3 emu/g, and all had an initial increase before decreasing and their coercivity (H_c) values increased with increased Si content. The Fe₈₇Zr₁₀Si₃ amorphous alloy exhibited a low H_c value of approximately 39.1 A/m, which shows good magnetic properties in the as-quenched state. After annealing, the M_s of the amorphous sample considerably improved, particularly reaching 165.3 emu/g at 600 ^°C.     

Amorphization behaviour in mechanically alloyed Ni—Ta powders

Amorphization behaviour of NixTa100–x alloy powders synthesized by mechanical alloying mixtures of pure crystalline Ni and Ta powders with a Spex high energy ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. This range is larger than amorphous alloys prepared by the rapid-quenching process or by electron-gun deposition technique. A supersaturated nickel solid solution formed for Ni-rich composition. The thermal stability has been investigated by differential thermal analysis. The crystallization temperature of amorphous Ni—Ta powders was proportional to the Ta content, and the activation energy of amorphous Ni—Ta powders exhibited a maximum near the eutectic composition. It is found that the amorphization rate at the early stage of the mechanical alloying process was faster in the intermediate compositions than those at both Ni- and Ta-rich compositions.     

Deposition of amorphous Fe-Zr alloys by magnetron co-sputtering

In the last decades, amorphous metal alloys were under intensive research because of their specific properties. Furthermore, amorphous magnetic metallic alloys, also known as metallic glasses, are important because of their application in electronic industry, information technology, recording media, etc. [Shen J, Kirschner J. Surf. Sci. 2002;500:300-322; Bass J, Pratt Jr WP. Physica 2002;B321:1-8; Dugaev VK, Vygranenko Yu, Vieira M, et. al. Physica 2003;E16:558-562]. Fe_1−xZr_x amorphous films co-condensed by magnetron sputtering were studied. X-ray diffraction methods were applied for studying a glass forming range vs. the composition of the elements. Electrical properties of the samples were measured by so-called four-probe and Van der Pauw methods. The surface morphology was investigated by SEM. The results show that amorphous Fe_1−xZr_x alloys with 1.5 nm crystallites could be synthesized by magnetron co-sputtering on the substrates at room temperature when the alloy's composition was Fe_0.91Zr_0.09 with a very smooth surface. The grain size of alloys decreased increasing the Zr concentration. The resistivity of the thin films of these alloys depends on the crystalline size and structure.     

Crystallization studies on amorphous AI-Y-Ni and AI-Y-Cu alloys

AI₈₃Y₁₀Ni₇, AI₈₀Y₁₀Ni₁₀ and AI₈₀Y₁₀Cu₁₀ alloys were studied by the rapid solidification processing route. The glass-forming ability was found to decrease in the order of alloys mentioned above. Differential scanning calorimetry (DSC) of these amorphous alloys showed that the amorphous phase in AI-Y-Ni alloys has a higher thermal stability when compared to that in AI-Y-Cu alloys. A four-stage crystallization sequence could be identified for the AI-Y-Ni amorphous alloys. Even though the AI₈₀Y₁₀Cu₁₀ alloy showed four exothermic peaks in the DSC study, a definite crystallization sequence could not be arrived at due to the coexistence of many crystalline phases along with the amorphous phase in the melt-spun condition.     

Soft magnetic amorphous Fe–Zr–Si(Cu) boron-free alloys

Amorphous Fe₈₀Zr_xSi_20−x−yCu_y boron-free alloys, in which boron was completely replaced by silicon as a glass forming element, have been prepared in the form of ribbons by using the melt quenching technique. X-ray diffraction and Mössbauer spectroscopy measurements revealed that the as-quenched ribbons with the compositions with x = 6–10 at.% and y = 0, 1 at.% are fully or predominantly amorphous. Differential scanning calorimetry (DSC) measurements allowed the estimation of crystallization temperatures of the amorphous alloys. Soft magnetic properties have been studied by the specialized rf-Mössbauer technique. Since the rf-collapse effect observed is very sensitive to the local anisotropy fields it was possible to evaluate the soft magnetic properties of the amorphous alloys studied. The rf-Mössbauer studies were accompanied by conventional measurements of hysteresis loops from which the magnetization and coercive fields were estimated. It was found that amorphous Fe–Zr–Si(Cu) alloys are magnetically very soft, comparable with those of the conventional amorphous B-containing Fe-based alloys.     

Production of Si55 Al20 Fe10 Ni5 Cr5 Zr5 bulk amorphous alloy by hot pressing

Abstract

The temperature dependence of the relative density was examined for a Si₅₅ Al₂₀ Fe₁₀ Ni₅ Cr₅ Zr₅ alloy which was produced by hot pressing of the amorphous powder during heating up to various temperatures under a critical pressure of 1·5 GPa through a heating/pressing cycle. The density of the compacts increased with increasing temperature and reached a maximum near the crystallisation temperature of 698 K. The relative density of the compacts reached 98·3% at the critical condition of 1·5 GPa and 687 K. The hardness value of the bulk specimen was 940 HV(10 gf, 0·098 N), corresponding to that of the amorphous ribbon. Exposure to higher temperatures resulted in the precipitation of the crystalline phase. The present results indicate that Si based alloys can be produced in a compact form with a low fraction of voids by hot pressing the amorphous powder.     

Formation of amorphous Ni-Zr alloy powder by mechanical alloying of intermetallic powder mixtures and mixtures of nickel or zirconium with intermetallics

Mechanical alloying was used to synthesize Ni_xZr_1–x alloys from mixtures of intermetallic compound powders, and also from mixtures of intermetallic compound powders and pure elemental powders. The mechanically alloyed powders were amorphous in the range 0.24 x 0.85. This range is larger than amorphous alloys produced by the melt-spinning technique and mechanical alloying of elemental crystalline powders. Two-phase mixtures of the amorphous phase and the corresponding crystalline terminal solid solution were formed in the range 0.10 x 0.22, and x=0.90. It is found that the morphological development during mechanical alloying of these powders is different from mechanical alloying using only pure ductile crystalline elemental powders. The thermal stability has been investigated. The enthalpy and activation energy of crystallization for Ni-Zr amorphous powders prepared by mechanical alloying are lower than those for melt-spun samples of the same composition. The crystallization temperature of the mechanically alloyed Ni-Zr amorphous powders is higher than that of meltspun samples in the composition range Ni₂₀Zr₈₀ to Ni₃₃Zr₆₇ and Ni₄₀Zr₆₀ to Ni₆₀Zr₄₀. The presence of tiny crystallites as nucleation centres and high oxygen levels in the mechanically alloyed amorphous alloys might be responsible for the differences in crystallization behaviour. A new crystalline metastable phase was observed during crystallization studies of Ni₂₄Zr₇₆ amorphous powder.     

The structure and thermal stability of mechanically alloyed Ni-Nb-Zr amorphous alloys

Ni₈₀Nb₂₀, Ni₆₀Nb₄₀, Ni₄₀Nb₆₀, Ni₆₀Nb₂₀Zr₂₀ and Ni₆₀Zr₄₀ amorphous alloys were prepared by mechanical alloying. The structure and thermal behaviour of the amorphous alloys were studied by X-ray diffractometry and differential scanning calorimetry and were compared to corresponding melt spun materials. In Ni-Nb amorphous alloys the mean nearest-neighbour distance and the thermal stability both increase with increasing Nb content. Substitution of Nb by Zr in Ni₆₀Nb₄₀ amorphous alloy also increases the mean nearest-neighbour distance, but reduces the thermal stability.     

Tensile strength,ductility and fracture of magnesium-silicon alloys

Tensile tests were performed between 293–573 K in order to investigate the mechanical properties of cast and extruded Mg-Si alloys. For the cast materials, Mg-high Si ( 10 wt%) alloys showed lower values of the highest tensile strength at temperatures up to 373 K, as compared to pure Mg and Mg-low Si (<10 wt%) alloys, whereas the strength at 573 K increased with increasing Si content. The addition of aluminum and zinc to the alloys was effective in increasing the strength. The fact that the Mg-high Si alloys showed lower strength than the Mg-low Si alloys was because a high volume of Mg₂Si embrittled the Mg-Si alloys. Microstructural investigations revealed that the particles of Mg₂Si were coarse for the cast materials and fracture of the particles was caused by deformation. The mechanical properties of the cast materials were improved by hot extrusion. Microstructural refinement by hot extrusion was responsible for the improvement of the mechanical properties.