Papers by Keyword: Bulk Amorphous Alloy

Abstract: The Zr-Cu-Al bulk amorphous (BA) alloys, which have no long-range ordered structure, possess various properties such as high strength and toughness with compositional dependence. In the present study, in order to estimate the natures of local structure change and relaxation behavior of hyper-eutectic BA alloys during annealing, positron annihilation measurements and density measurement have been performed for hyper-eutectic Zr-Cu-Al BA alloys with annealing. The enthalpy relaxation and structural relaxation was also measured by differential scanning calorimetry (DSC) measurement. These results show that the relaxation process of free volume containing in hyper-eutectic BA alloys is different from that in hypo-eutectic alloys.

Abstract: The electrical resistivity of three kinds of Zr-based bulk amorphous alloys as a function of continuous increasing temperature was measured by the direct current four-probe method. Combining with Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis, the correlation between the electrical resistivity and structural evolution of these amorphous alloys has been demonstrated. The experimental results showed that three amorphous alloys all had a small negative temperature coefficient of resistivity (TCR<-10^-4 K^-1) before crystallization. Little change of the electrical resistivity related with the glass transition process was observed, while the electrical resistivity decreased sharply once the crystallization occurred. The onset of crystallization determined by the electrical resistivity measurement was far lower than that by DSC. The different stages of crystallization behavior could be evidently identified by the change of the electrical resistivity.

Abstract: In order to investigate very high cycle fatigue properties of Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloy, rotating bending fatigue tests were conducted at room temperature by using 5 different series of Zr₅₅Al₁₀Ni₅Cu₃₀ alloy. The differences of material processing conditions are manufacturer, product year, material size and minimum diameter of specimen. Although all specimens fractured from surface, duplex S-N characteristics were observed for each series of the material. Time strength distributions at N=10⁴ for short life region and at N=10⁷ for long life region were well approximated by normal distribution. The entire S-N property accepting the normalized stress amplitude by the time strength at N=10⁴ or N=10⁷ has shown more clearly duplex S-N characteristics. In addition, P-S-N properties were also estimated from the standard deviation of time strength distributions at N=10⁴ or N=10⁷. Based on the observation of fracture surface by scanning electron microscope (SEM), it is confirmed that every fracture surface was consisting of typical three regions such as multi-facet region, stable crack growth region and instantaneous fracture region.

Abstract: For enhancing wear property of Fe-based bulk amorphous alloys as structural materials, We investigate effects of Cr or Mo compositions on wear and mechanical behaviors of FeCSiBPMo and FeCSiBPAlCr system bulk amorphous alloys which are suction-cast into a copper mold by arc melting in an argon atmosphere using a suction casting technique. X-ray diffraction, differential scanning calorimeter and Scanning electron microscopy were used to observe the microstructure and surface morphologies. Cr-Fe or Mo-Fe substitutions led to a dramatic increase in the glass transition temperature as well as the supercooled liquid region. After the wear test, the mass loss of both BAAs decreased remarkably at higher element. Nanoindentation results indicate that with an increase of the Cr or Mo compositions, the hardness and elastic modulus increased in both BAA samples. These results suggest that wear behaviors of the BAAs corresponded to change in hardness, which means that fracture morphologies of worn surface are strongly dependent on surface hardening with high Cr or Mo content.

Abstract: A new bulk amorphous alloy, Y₃₆Nd₂₀Al₂₄Co₂₀, with a diameter of 5 mm was successfully fabricated by the method of equiatomic substitution for the Y element in Y₅₆Al₂₄Co₂₀ amorphous alloy. The values of the supercooled liquid region ∆T_x(=T_x-T_g ), the reduced glass transition temperature T_rg (=T_g/T_l) and the parameter γ (=T_x/(T_g+T_l)) for Y₃₆Nd₂₀Al₂₄Co₂₀ bulk amorphous alloy are 60K, 0.605 and 0.415, respectively. The critical cooling rate of the Y₃₆Nd₂₀Al₂₄Co₂₀ bulk amorphous alloy was determined to be 40 K/s, providing an indication that this alloy has a high glass-forming ability.

Abstract: This paper reports laser remelting of crystalline Cu based alloys in order to produce amorphous layer on the surface. The as prepared Cu based master alloy ingots were imbedded in a metallic sinking with Wood metal to assure the good thermal conductivity during the laser treatment. The laser remelting of a thin surface layer and a subsequent rapid cooling of it was performed using impulse and continuous mode of Nd:YAG laser. In respectively the impulse mode the laser power and the interaction time were 1.5; 2 kW and 20÷100 ms. In the continuous mode the laser power was 2 kW, and the laser scan speed was 80÷120 mm/s. The characterization of the microstructure of surface layer was performed by XRD, scanning electron microscopy and microhardness measurements.

Abstract: The aim of our research was to comparatively examine Ni content surface layers on amorphisable Cu base alloy produced by different laser surface treatments. Laser surface treatment (LST) techniques, such as laser surface melting, laser alloying and laser cladding, provide a wide range of interesting solutions for the production of wear and corrosion resistant surfaces. [1,2] With LST techniques, the surface can be: i) coated with a layer of another material by laser cladding, ii) the composition of the matrix can be modified by laser alloying. [3] Two kinds of laser surface treatment technologies were used. In the case of coating-melting technology a Ni content surface layer was first developed by galvanization, and then the Ni content layer was melted together with the matrix. In the case of powder blowing technology Ni3Al powder was blown into the layer melted by laser beam and Argon gas. LST was performed using an impulse mode Nd:YAG laser. The laser power and the interaction time were 2 kW and 20÷60 ms. The characterization of the surface layer microstructure was performed by XRD, scanning electron microscopy and microhardness measurements.

Abstract: In this paper CuZrAl amorphous alloys with different Al content were prepared by centrifugal casting. The master alloy ingots were prepared by arc melting the mixture of the constituents on a water cooled copper boat in argon atmosphere. Wedge-shaped samples were prepared from the ingots by centrifugal casting into copper mold. The microstructure of the samples was examined by Scanning Electron Microscope (SEM) and the phases were analyzed by X-ray diffractometry (XRD) to define the amorphous fraction.

Abstract: The fracture surface morphology of Fe76Ni2Si9B13 bulk amorphous alloys failed in compression at temperatures from 4.2 to 300 K was investigated. The samples were prepared by the explosive compaction technique from amorphous powder. It has been found that fracture stress decreases with temperature from 300 to 4.2 K. In this temperature range, the brittle failure prevails. The failure propagates across particles and along particle boundaries too. The fracture micromorphology is riverlike pattern with fine dimples.

Abstract: The paper makes a review about the opportunity, forming conditions and obtaining methods of bulk amorphous alloys and their properties. There are also presented the experiments regarding the obtaining and characterization from mechanical and chemical point of view of some alloys from Fe70 (Cr5-x Nix)5 Ga4 P13 Si5 C3 ( x = 0,1,2,4) family, pointing out the negative effect of the nickel on their resistance characteristics.