Effect of Er on properties of Zr-based bulk metallic glasses

(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x?=?0～6) bulk metallic glasses were fabricated by copper mould suction casting method, and the effect of Er on properties was studied. The compressive plastic strain (ε_p) and compressive strength (σ_max) at room temperature increases first and then decreases with the increase of Er content. The compressive plastic strain (ε_p) of the specimen is 35.1% when x?=?2.6, which is about eight times than that of the specimen with x?=?0. The compressive strength (σ_max) is 2513?MPa, which is much higher than that of the specimen with x?=?0. It indicates that Zr-based bulk metallic glasses could be strengthened and toughened by adding Er. The thermal stability decreases gradually and the glass-forming ability increases first and then decreases with the increase of Er content.     

Effect of Pd on GFA and Thermal Stability of Zr-based Bulk Amorphous Alloy

The effect of Pd addition on the glass-forming ability and thermal stability of the Zr55Al10Cu30Ni5-xPdx (x=0, 1, 3, 5 at. pct) alloys upon copper-mold casting has been investigated. The structure, thermal stability and microstructure were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), respectively. It was identified that a new bulk amorphous alloy with the larger supercooled liquid region Tx of 100 K is obtained with substituting Ni by 1 at. pct Pd. Furthermore, the origins that thermal stability and GFA change with increasing of Pd have also beer discussed.     

Microporosity reduction in modified RR2072 single crystal superalloys

Abstract

The effect of the addition of grain boundary strengthening elements (carbon, hafnium) on the microporosity of an experimental single crystal superalloy RR2072 has been investigated. Quantitative examination showed that the volume fraction of microporosity decreased in the alloys modified by these additions, and the reduction was associated with MC phase/carbon distribution and/or high hafnium content. Excessive carbon (i.e. >0.05 wt-%), however, did not reduce microporosity as efficiently as expected. Detailed analysis has revealed that carbon atoms, whether they stay in MC carbides or in the matrix as interstitial atoms, cause lattice expansion and thus reduce volume contraction during solidification. This mechanism is responsible for microporosity reduction in the carbon bearing alloys. Based on this mechanism of interstitial induced lattice expansion, theoretical calculation is consistent with experimental results. In the carbon and hafnium bearing material, however, high hafnium is another important reason for the reduction of microporosity.     

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.     

Microstructure and magnetocaloric effects in partially amorphous Gd55Co15Al30−xSix alloys

In order to clarify the phase components and further improve the glass-forming ability of Gd₅₅Co₁₅Al₃₀ alloy, substitution of Al with Si was adopted. Although the X-ray powder diffraction experiment indicated an amorphous structure of the Gd₅₅Co₁₅Al_30−xSi_x (x = 1, 2, 3) alloys, precipitation of crystalline Gd₂Al phase was evident from the energy-dispersive spectroscopy, selected-area diffraction, and magnetization measurements. The magnetocaloric effect of Si substituted alloys is lower than that of Gd_52.5Co_16.5Al₃₁ alloy with a similar composition and full amorphous structure, which is ascribed to the presence of antiferromagnetic Gd₂Al phase whose magnetic entropy change is lower.     

Effect of rare-earth elements on the microstructural characterization in rapidly quenched thermally strengthened aluminium alloys

The influence of rare-earth elements on the microstructural features of rapidly solidified Al93.3-xFe4.3V0.7Si1.7Mmx(x=0, 0.5, 1.0, 3.0, 6.0) alloy was systematically studied by differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and energy dispersive X-ray analysis. Experimental results show that there are different type of phase transformation depending on mischmetal (Mm) concentration. For Al87.3Fe4.3V0.7Si1.7Mm6.0 metallic glass, a shoulder was observed on the high-angle side of the main peak in the X-ray diffraction patterns due to quenched-in aluminium nuclei and a prepeak resulting from Mm–Mm pairs. By means of particle extraction analysis, it has been proved that the -Al13(Fe, V)3Si phase existing in as-cast Al–Fe–V–Si alloy is wholly or partly inhibited for Al93.3-xFe4.3V0.7Si1.7Mmx (x=0.5, 1.0, 3.0) crystalline alloys. In addition, a new phenomenon has been reported that the lattice parameter of as-quenched Al–Fe–V–Si–Mm alloys decrease with increasing Mm content; the "cell lessening effect". This effect is presumably due to the results of composite interactions between rare-earth elements and alloy elements.     

Extrusion properties of a Zr-based bulk metallic glass

The extrusion behavior of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 °C. The metallic glasses were fully extruded without crystallization and failure within the range of T = 395-415 °C under strain rates from 5 × 10^− 3 s^− 1 to 5 × 10^− 2 s^− 1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.     

Microstructural stability of rapidly quenched Al---Fe---Mo alloys

We investigated the microstructural stability of rapidly quenched Al-8%Fe-2%Mo alloys by measuring the evolution of thermoelectric power during ageing between 300 °C and 500 °C, and by transmission electron microscopy and small-angle X-ray scattering observation. Four stages of evolution were found corresponding to the evolution of the solid solution and S-phase into a final incoherent generalized precipitation. The addition of Mo does not delay this evolution but gives a more homogeneous microstructure.     

Age hardening of rapidly quenched Al-Zr-B alloys

Ternary alloys from the Al-Zr-B system were prepared as thin foils by a rapid quench technique. These foils were annealed isothermally as well as isochronally at various temperatures (150 to 550° C). The microstructures show that at high temperature, the grain growth is significantly retarded by the grain boundary pinning of boride precipitates. A strong age hardening is also a characteristic phenomenon in these alloys. It is found that microstructure and microhardness largely depend upon the zirconium/boron ratio of the alloy, indicating that the ratio determines the types of compounds occurring in this alloy system. It appears that in these alloys, high concentration of boron and the low ratio of zirconium/boron together yield stable precipitates at high temperatures.     

Devitrification of rapidly quenched Al-Cu-Ti amorphous alloys

X-ray diffraction, transmission electron microscopy and differential scanning calorimetry were carried out to study the transformation from amorphous to icosahedral/crystalline phases in the rapidly quenched Al₅₀Cu₄₅Ti₅ and Al₄₅Cu₄₅Ti₁₀ alloys. In the present investigation, we have studied the formation and stability of amorphous phase in Al₅₀Cu₄₅Ti₅and Al₄₅Cu₄₅Ti₁₀ rapidly quenched alloys. The DSC curve shows a broad complex type of exothermic overlapping peaks (288- 550†C) for Al₅₀Cu₄₅Ti₅ and a well defined peak around 373†C for Al₄₅Cu₄₅Ti₁₀ alloy. In the case of Al₅₀Cu₄₅Ti₅ alloy amorphous to icosahedral phase transformation has been observed after annealing at 280†C for 73 h. Large dendritic growth of icosahedral phase along with α-Al phase has been found. Annealing of Al₅₀Cu₄₅Ti₅ alloy at 400†C for 8 h results in formation of Al₃Ti type phase. Al₄₅Cu₄₅Ti₁₀ amorphous alloy is more stable in comparison to Al₅₀Cu₄₅Ti₅ alloy and after annealing at 400†C for 8 h it also transforms to Al₃Ti type phase. However, this alloy does not show amorphous to icosahedral phase transformation.     

Mechanical behavior of Zr-based bulk metallic glasses

Bulk metallic glasses have a very high corrosion resistance and mechanical strength. Bulk metallic glasses show elastic-perfectly plastic behavior with an extended region of elastic strain (≈ 2%). But at room temperature their macroscopic plasticity is weak even though a local plastic strain is observed in shear bands. A relaxation analysis allowed studying micro-mechanisms of plastic deformation and estimating the apparent activation volume (≈ 2000 ų). __________ Translated from Problemy Prochnosti, No. 1, pp. 167–170, January–February, 2008.     

The potential of Zr-based bulk metallic glasses as biomaterials

Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.