Hot tearing susceptibility of Mg-5(Zn + Y)-0.5Zr alloys was predicted based on Clyne-Davies' model. The solidification contraction force curves of Mg-5(Zn + Y)-0.5Zr alloys were obtained by using ...the 'T' type hot tearing permanent-mold were tested. The predicted values of CSC agree well with the measured values of crack volume. The hot tearing susceptibility of the alloys is as follows: Mg-3.75Zn-1.25Y-0.5Zr > Mg-4.29Zn-0.71Y-0.5Zr > Mg-3Zn-2Y-0.5Zr > Mg-2.5Zn-2.5Y-0.5Zr. The phase constitution and fracture morphology of hot tearing regions of the alloys were observed by x-ray diffraction and scanning electron microscopy. The experimental indicated that the type and amount of secondary phase were controlled by Zn/Y ratio. When Zn/Y ratio varies from 1 to 6, the secondary phase changes from W-phase, W + I phases to I-phase. The hot tearing susceptibility of Mg-5(Zn + Y)-0.5Zr alloys increases with increasing Zn/Y ratio from 1 to 3 due to the increasing of solidification temperature range, the increasing of the grain size and the decreasing of the amount of remaining liquid. Further increased Zn/Y ratio from 3 to 6, the hot tearing susceptibility decreases because the solidification temperature range decreases and the quasicrystal I-phase enhances the intergranular bonding force.
The solidifcation behavior of AISI DC 53 cold work tool steel was investigated by means of a cooling curve and its frst derivative. Copper and sand wedge-shaped molds were used to obtain various ...solidifcation rates. To reveal the cooling rate degree during solidifcation, the secondary dendrite arm spacing of the steel alloy was examined by scanning electron microscopy (SEM). The solidification rates of each section for both wedge steel samples were calculated by means of the secondary dendrite arm spacing using a research-based empirical relation from the literature. Experiment results revealed that at the tip region of the cast specimen in the copper wedge-shaped mold, the carbide size was 7–8 μm, where the solidifcation rate was approximately 4,830 °C·s
−1
. The greatest carbide size obtained in the upper region of the sand cast wedge-shaped specimen was 250–270 μm.
Two soils spiked with lead at different rates were stabilised/solidified using Portland cement and fly ash at different soil:binder ratios, and tested for their setting time, unconfined compressive ...strength, leachability and durability. A performance threshold approach was used in order to identify optimal management options for the products of the S/S treatment. Results show that soil texture, percentage of binders and lead concentration play an important part in the treatment, significantly influencing the performance of the resulting products in terms of curing, compressive strength and durability. Pb soil concentrations higher than 15000 mg kg
−1
were found to heavily reduce the applicability of the treatment requiring the maximum amount of binder in order to satisfy the performance criteria. The performance of sandy soils was shown to be limited by setting time and UCS features due to the retardation of the hydration reactions and also by its leaching behaviour, whereas for silt-clayey soils the critical parameter is the mechanical resistance.
In order to clarify the causing mechanism of center cavity in the cast of high Cr steel, the casting experiment of cylindrical ingot in 1 ton scale and the analysis of thermal elastic-plastic stress ...and strain were carried out. Moreover in relation to these results, the influence of Cr and C concentration on the generation of center cavity was discussed with tensile strength just below the solidus temperature and solidification contraction of the specimens. As the result, though both center line cracks and shrinkage holes were observed in the center cavity of high Cr steel, difference of solidification contraction between specimens was not much. The primary factor of center cavity was proved to be cracking caused by thermal stress under the lower tensile strength just below the solidus temperature associated with the increase of the ferrite amount which should be influenced by Cr and C concentration. Therefore, it was indicated that laying compressive stress on the final solidification part was effective to reduce center cavity in the high Cr and low C steel.
Composite materials obtained by adding particles to the metallic matrix (MMCs) have made remarkable progress in its development and applications in automotive and aerospace industries in recent ...decades. Among them the most current application is MMCs with zinc and aluminum matrix. The present work is focused on the study of the effect of the directional heat extraction on the alumina distribution inside the zinc-aluminum matrix and on the columnar – to – equiaxed (CET) phenomenon in samples directionally solidified. The ZA-27 alloy was reinforced with ceramic-particulates of alumina (Al2O3) and then vertically directionally solidified. The following parameters were measured: cooling rates, temperature gradients, interphase velocities. And the influence of heat transfer on the solidification microstructure of the MMCs was analyzed. Experimental results include transient metal/mould heat transfer coefficients, secondary dendrite arm spacings and particle distribution as a function of solidification conditions imposed by the metal/mould system. The results about the conditions for the CET in MMCs are compared with those obtained in directional solidification of Zn-Al alloys.
The preparation and solidification of metallic droplets attract more and more attention for their significance in both engineering and scientific fields. In this paper, the preparation and ...characterization of Sn-based alloy droplets using different methods such as atomization and consumable electrode direct current arc (CDCA) technique are reviewed. The morphology and structure of these droplets were determined by optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The solidification behavior of single droplet was systematically studied by means of scanning calorimetry (DSC), and the nucleation kinetics was also calculated. In particular, the development of fast scanning calorimetry (FSC) made it possible to investigate the evolution of undercooling under ultrafast but controllable heating and cooling conditions. The combination of CDCA technique and ESC measurements opens up a new door for quantitative studies on droplet solidification, which is accessible to demonstrate some theories by experiments.
A cellular automaton (CA) model to predict the formation of grain macrostructure during solidification has been implemented and the coupling between the microscopic and the macroscopic submodels has ...been investigated. The microscopic submodel simulates the nucleation and growth of grains, whereas the macroscopic solves the heat conduction equation. The directional solidification of an Al-7 wt. (%) Si alloy was simulated, enabling the calculation of the temperature and solid fraction profiles. The calculated temperature was used to obtain the solid fraction profile by an application of Scheil equation. This solid fraction disagrees with that calculated in the micro-macro coupling of the model, although this coupling is completely based on Scheil equation. Careful examination of the discrepancies shows that it is a result of the undercoolings for nucleation and growth of grains and also of the interpolations of enthalpy change and temperature from the finite volume mesh to the CA cell mesh.
The grain-aligned Tb
x
Dy
1−
x
(M
y
Fe
1−
y
)
1.9 (
x=0.50, 0.30,
y=0.05, 0.10, 0.15, M=transition metal) giant magnetostrictive materials with the size of
Φ(6∼15)×(150∼200) mm have been produced ...using a newly developed directional solidification apparatus. The magnetic properties of
λ
s = 1820 ppm and
d
33=1.1 ppm/Oe (under the compressive pressure of 12.5 MPa) have been obtained in Tb
0.5Dy
0.5(Fe
0.95)Mn
0.05)
1.9 alloy under the alloy by drawing it down to the cooling zone at the speed of 12 mm min
−1 and heat treating the alloy at 950°C for 6∼8 h. XRD studies reveal a 110 crystallographic alignment in the directionally solidified Tb
0.5Dy
0.5(Fe
0.95MN
0.05)
1.9 alloy. A transducer designed to work in underwater sonar system has been developed by using this material. It has an resonance frequency of 2.4 kHz, emission current sensitivity of 170 dB, mechanical quality factor of 3 and an electro-acoustic efficiency of 43%.
The nonequilibrium distribution coefficient (
k
neq) as a function of solid-liquid interface velocity and orientation was investigated for a spin-1 Ising model for binary alloys using Monte Carlo ...computer simulations. The crystal structure and thermodynamic properties were chosen to correspond to bismuth doped silicon with
k
eq = 7 × 10
−4. Values for
k
neq were obtained for several orientations of the solid/liquid interface, including (1 1 1) and (0 0 1). For the same growth velocity,
k
neq was found to be greatest for solid/liquid interfaces parallel to the (1 1 1) plane. The orientation dependence is related to variations in the kink site density at the interface. The simulation results are compared with experimental results reported by Aziz et al.
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