Ma Mingzhen

Tensile Strength of Zr—Ti Binary Alloy

Zr—Ti binary alloys are prepared using a nonconsumable tungsten electrode under Ti-gettered inert atmosphere (argon). Microstructures are observed mainly as α phase using x-ray diffraction. A tensile test is performed to investigate the tensile strength of a series of Zr—Ti binary alloys at room temperature. The findings indicate that increasing Ti concentration results in an initial increase (50at% of Ti) and then a decrease in tensile strength. The Zr55Ti45 (at%) component exhibits the maximum tensile strength of 1216.68MPa, which is much higher than that of pure Ti (increased by approximately 200%) or pure Zr (increased by approximately 100%). The potential mechanisms for the remarkable tensile strength are solid solution strengthening and grain refinement.

Zr-Cu Amorphous Films Prepared by Magnetron Co-sputtering Deposition of Pure Zr and Cu

ZrxCu100−x amorphous films are prepared on Si (111) substrates by magnetron co-sputtering of pure Zr and Cu. It is found that the glass forming ability (GFA) of the films increases with x when x is in the range from 35 to 65 and with the best glass forming ability at x = 65. It is therefore different from the bulk counterparts, for which only x = 35 and 50 were reported to have high glass forming ability during casting. The structure of the films is sensitive to the substrate temperature and the sputtering argon pressure.

Ab Initio Comparative Study of Zincblende and Wurtzite ZnO

By employing the first-principles pseudopotential plane-wave method, the physical properties of zincblende ZnO are investigated in comparison with those of the common wurtzite structure. Zincblende ZnO is predicted to be a direct gap semiconductor. Compared to the wurtzite structure, the zincblende ZnO is characterized by smaller bandgap and pressure coefficient, larger electron effective mass, increasing static dielectric constants and more covalent bonding. Furthermore, the optical properties including dielectric function and energy loss function of zincblende ZnO were obtained and analysed with some features. These aspects reveal promising applications of zincblende ZnO in optoelectronic devices.

Tensile and compression properties of Zr-based bulk amorphous alloy at different temperatures

Mechanical properties of the Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloy at different temperatures were investigated. The compression test was carried out on a Gleebe-3200 machine at 345 and 375°C, respectively, in the supercooled liquid region. It is shown that decreasing the compressive rate and increasing temperature have a similar influence trend on the compressive behavior of the bulk amorphous alloy. Room and low temperature tensile strengths were tested on the Instron materials testing system. At low temperature, the tensile strength decreased with decreasing of the testing temperature. Hardness measurement indicated that below the glass transition temperature, the hardness decreased with increasing of the annealing temperature and duration time. It, however, increased when the annealing treatment was performed above the glass transition temperature.Mechanical properties of the Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloy at different temperatures were investigated. The compression test was carried out on a Gleebe-3200 machine at 345 and 375°C, respectively, in the supercooled liquid region. It is shown that decreasing the compressive rate and increasing temperature have a similar influence trend on the compressive behavior of the bulk amorphous alloy. Room and low temperature tensile strengths were tested on the Instron materials testing system. At low temperature, the tensile strength decreased with decreasing of the testing temperature. Hardness measurement indicated that below the glass transition temperature, the hardness decreased with increasing of the annealing temperature and duration time. It, however, increased when the annealing treatment was performed above the glass transition temperature.

Formation and Compression Behavior of Two-Phase Bulk Metallic Glasses with a Minor Addition of Aluminum

A remarkable enhancement in room-temperature compressive deformability is realized by the minor-addition of 1.5 at.% Al in ZrTi-based bulk metallic glass. Two amorphous phases are observed by transmission electron microscopy in the Al-containing alloys and this explains the improvement of compression deformability The studies suggest that phase separation might occur in glass forming alloys with a negative enthalpy of mixing.

Undercooling and Unidirectional Solidification of CuNi Alloy Melts

Cylinder-shaped Cu80 Ni20 alloy melt is undercooled and solidified by the combination of the electromagnetic levitation technique and the flux treatment method. Nearly constant temperature gradient of 8-10K/cm is realized for the cylindrical melts with different undercooling levels at the bottom ends. The experimental results reveal that with the increase of the undercooling of the melts from 35 to 220K, the microstructures undergo transition from coarse dendrites to granular grains, unidirectional dendrites, and finally to equiaxed grains.

Influence of temperature and strain rate on hot deformation behavior of Zr50Ti50 alloy in single β field

Abstract The deformation behavior and microstructure of the Zr50Ti50 alloy in β phase field were investigated by isothermal compression tests at temperatures ranging from 700 to 850 °C and strain rates ranging from 0.001 to 1 s−1. The flow curves exhibited typical flow softening. The initial discontinuous yielding behavior was observed at higher strain rates, which was not found in other traditional Zr alloys. The apparent deformation activation energy was calculated to be 103 kJ/mol and constitutive equation describing the flow stress as a function of the strain rate and deformation temperature was proposed. The analysis indicated that the hot deformation mechanism was mainly dominated by dynamic recovery. However, dynamic recrystallization was delayed by dynamic recovery. Thereafter, the processing map was calculated to evaluate the efficiency of the forging process at the temperatures and strain rates investigated and to optimize processing parameters of hot deformation. The optimum processing parameters were found to be 830–850 °C and 0.56–1 s−1 for hot the deformation of Zr50Ti50 alloy in the β phase region.

Temperature rise and flow of Zr-based bulk metallic glasses under high shearing stress

Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected. Shearing force was loaded on Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(Vit.1) BMGs by cutting during the turning of the BMG rod. The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point. The temperature rise caused viscous fluid flow and brought about the deformation of BMGs. This suggested that the deformation of BMGs was derived, at least to some extent, from the adiabatic shear temperature rise.

Effect of Sodium Dodecyl Sulphate and Sodium Bromide Additives on Ni-W Nanocoatings

Nickel-tungsten (Ni–W) coatings were fabricated by electrodeposition method with varying quantities of sodium dodecyl sulphate and sodium bromide to examine the effects of the aforesaid additives on the coatings. The obtained nanocoatings were studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and hardness tester. The hardness, tungsten content and grain size attained a maximum value at current density of 0.15 A/cm²,0.1 A/cm² and 0.1 A/cm², respectively. There was a pronounced impact of both the additives on the microstructure and morphology of the coatings. According to results, there are considerable difference in terms of the impact caused by the additives to the tungsten content, hardness and grain size of the coatings. The obtained results suggest that hardness of coatings is mainly contributed by W content in the deposits.

The structural, elastic, and electronic properties of ZrxNb1?xC alloys from first principle calculations

The structural, elastic, electronic, and thermodynamic properties of ZrxNb1−xC alloys are investigated using the first principles method based on the density functional theory. The results show that the structural properties of ZrxNb1−xC alloys vary continuously with the increase of Zr composition. The alloy possesses both the highest shear modulus (215 GPa) and a higher bulk modulus (294 GPa), with a Zr composition of 0.21. Meanwhile, the Zr0.21 Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states. In addition, the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing.