On the microstructural refinement in commercial purity Al and Al-10 wt% Cu alloy under ultrasonication during solidification

Physical grain refinement is examined under high-intensity ultrasonication during solidification in commercial purity Al (CP-Al) and binary Al-10wt.% Cu alloy melts cooled naturally in air and compared against chemical inoculation using Al-5Ti-1B grain refiner. The coarse dendritic unrefined base microstructure was completely replaced with a fine equiaxed grain structure in the case of either inoculation or ultrasonication. However, ultrasonication produced more effective refinement over chemical inoculation with a two-fold and eight-fold increase in the grain density in CP-Al and Al-10%Cu alloy, respectively. While combining chemical inoculation with ultrasonication produced the finest grain structure in CP-Al, no further improvement over ultrasonication was noted for the Al-10%Cu alloy. Noticeable reduction in nucleation undercooling, of similar magnitude to chemical inoculation, was observed under ultrasonication. Cooling curve observations indicate strongly enhanced heterogeneous nucleation under ultrasonication. It appears that although nucleation potency could be higher under chemical inoculation, more nucleation events are favoured under cavitation

Progress in research on cold crucible directional solidification of titanium based alloys

Cold crucible directional solidification (CCDS) is a newly developed technique, which combines the advantages of the cold crucible and continuous melting. It can be applied to directionally solidify reactive, high purity and refractory materials. This paper describes the principle of CCDS and its characteristics; development of the measurement and numerical calculation of the magnetic field, flow field and temperature field in CCDS; and the CCDS of Ti based alloys. The paper also reviews original data obtained by some scholars, including the present authors, reported in separate publications in recent years. In Ti based alloys, Ti6Al4V, TiAl alloys and high Nb-containing TiAl alloys, have been directionally solidified in different cold crucibles. The crosssections of the cold crucibles include round, near rectangular and square with different sizes. Tensile testing results show that the elongation of directionally solidified Ti6Al4V can be improved to 12.7% from as cast 5.4%. The strength and the elongation of the directionally solidified Ti47Al2Cr2Nb and Ti44Al6Nb1.0Cr2.0V are 650 MPa/3% and 602.5 MPa/1.20%, respectively. The ingots after CCDS can be used to prepare turbine or engine blades, and are candidates to replace Ni super-alloy at temperatures of 700 to 900 °C

Electromagnetic characteristics of square cold crucible designed for silicon preparation

In the present work, the strength and distribution of electromagnetic field in the square cold crucible that designed for casting multicrystalline silicon were measured and analyzed by using a small coil method. The results show that in the perpendicular direction the maximum of magnetic flux density (B) appears at the position slightly above the middle of the coil, and then B attenuates toward both sides, and decreases more to the bottom of the crucible. In the horizontal direction, from the edge (corner) to the center, B firstly decreases gradually, and then slightly increases in the center. While along the inner sides of the crucible, the distribution is relatively uniform, especially in the effective acting range. B increases with the increasing of the input power. Moving the coil to the top of the crucible, B increases and the effective acting range of the electromagnetic field becomes bigger. For the coils with different turns, the five turns coil can induce the highest magnetic flux density

Effect of power parameter and induction coil on magnetic field in cold crucible during continuous melting and directional solidification

Bottomless electromagnetic cold crucible is a new apparatus for continuous melting and directional solidification; however, improving its power efficiency and optimizing the configuration are important for experiment and production. In this study, a 3-D finite element (FE) method based on experimental verification was applied to calculate the magnetic flux density (Bz). The effects of the power parameters and the induction coil on the magnetic field distribution in the cold crucible were investigated. The results show that higher current intensity and lower frequency are beneficial to the increase of Bz at both the segment midpoint and the slit location. The induction coil with racetrack section can induce greater Bz, and a larger gap between the induction coil and the shield ring increases Bz. The mechanism for this effect is also discussed

Microstructure evolution during directional solidification of 2009Al/SiCp at different pulling velocities: Modeling and Experiment

The cellular automaton-lattice Boltzmann method-immersed moving boundary coupled model is established to study the microstructure evolution during the solidification process of 2009Al/SiCp. After several model benchmarks, the natural convection of liquid phase and its effect on particle settlement under different pulling velocities were studied firstly. The results showed that at higher pulling velocity, the particle decelerates downward before contacting with dendrite front due to intensified natural convection. At lower pulling velocity, the particle decelerates gradually until a change in direction and upward movement. As the particle approach the tip of the dendrite, the particle experiences a brief upward movement before contacting the dendritic front. Then the convection induced by particles has an impact on the distribution of solutes in the liquid phase. It has been observed that at lower pulling velocity, there is a significant difference in solute distribution at the solidification front. The primary reason for this phenomenon is the higher solute concentration near the solidification front at lower pulling velocity, rather than the higher liquid phase flowing rate. Finally, our model investigated the microstructure evolution process during the directional solidification process of 2009Al/SiCp at different pulling velocities. The results indicate a good agreement between the simulation results and experiment observations

Microstructure evolution and mechanical properties of vanadium-bearing Ti–22Al–26Nb alloys obtained by controlled cooling from a single B2 region

To investigate the role of Vanadium element in Ti2AlNb-based alloy, Ti–22Al–26Nb-xV (x = 0, 2, 8) alloys were cooled from the B2 single-phase temperature (1300 °C) at controlled process parameters. The isothermal preheating in the B2 single-phase zone contributes to the homogenization of microstructure and the elimination of micro-segregation in subsequent microstructure evolution. Two typical microstructures after temperature-controlled cooling experiments can be obtained: B2+O two-phase and α2+B2+O three-phase microstructures. The effects of Vanadium content and cooling rate on phase transformation and microstructure evolution were analyzed. The crystallographic relationship between B2, α2 and O phases was identified as follows: {011}B2/β//{0001}α2, B2/β//α2, {110}B2/β//{001}O, B2/β//O, {0001}α2//{001}B2/β, α2// O. Last, the compression tests of these heat-treated samples were performed, and the microstructure-dependent mechanical properties were discussed

A novel method towards improving the hydrogen storage properties of hypoeutectic Mg-Ni alloy via ultrasonic treatment

Ultrasonic treatment has great contributions on modifying the morphology, dimension and distribution of constituent phases during solidification, which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys. In this research, ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni (at.%) alloy. Due to ultrasonic treatment, the microstructure of as-cast alloy is significantly refined and homogenized. Ascribing to the increased eutectic boundaries and shortened distance inside α-Mg for hydrogen atoms diffusion, the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively, especially at lower temperature. The peak desorption temperature reduces from 392.99 °C to 345.56 °C, and the dehydriding activation energy decreases from 101.93 kJ mol−1 to 88.65 kJ mol−1. Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms. Owing to the refined primary Mg, a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2 colonies impinging, resulting in the enhancement of hydrogenation rates and capacities