Zhong Ming Ren

Investigation on Properties of the Silica Ceramic Cores for the Hollow Blades Prepared by the Conversion of the Silicon Resin

The working conditions of the ceramic cores are extremely harsh with the development of the preparation technology and improvement of the use conditions in the hollow blades, which brings forward high request for the preparation and properties of the ceramic cores. In this paper, silica ceramic powders were firstly coated by the silicon resin. The obtained composite powders were used to prepare the ceramic cores by the dry pressing method. And the phase compositions, microstructure and properties of the ceramic cores with the sintering temperatures were investigated. The results showed that the composite powders prepared by the coating showed good formability. The sintering temperature promoted the formation of the cristobalite. With the increase of the sintering temperature, the porosity of ceramic cores gradually decreased, the shrinkage rate and bulk-density increased. The prepared ceramic cores at 1250°C had highest bend strength of 19.25Mpa.

Magnetic Field-Induced Granular Pearlite at Early Stages of Phase Transformation

ffects of high magnetic fields (HMF) up to 19.81T on pearlite phase transformation are studied by examination of the microstructures of a Fe-0.47C-2.3Si-3.2Mn (wt %) alloy partially isothermally processed above the eutectoid temperature. The results show that granular pearlite (GP) can be obtained at earlier transformation stages. The evolution of the granular pearlite is always accompanied by the formation of lamellar pearlite. TEM analysis reveals the existence of sub-grain boundaries within GP colonies and indicates that the nucleation of ferrite matrix in GP belongs to multiple nucleation mechanism. Most of carbides at the early stage of pearlite formation are found to precipitate at the α/γ interface--the growing front of ferrite phases, and some of coarse carbides can further develop into thin lamellar cementite.

Three Numerical Simulation Methods on Dynamic Free Surface Deformation Simulation of a Sessile Drop

The problem of free surface deformation is involved in variable fields ranging from material processing to metallurgy. In order to investigate the transient evolution of fluid field and free surface deformation numerically, three numerical simulation methods are proposed among which one is based on level set method, the other two are based on moving mesh method. Afterwards, a benchmark problem of sessile droplet is chosen to test and verify each numerical method. A comparison of each numerical result and experimental result shows a good agreement between each other. Comparison and discussion of three numerical methods are made in the end.

Variation of Surface Tension of Water in High Magnetic Field

The surface tension of water in high magnetic fields up to 10T was investigated with aid of the high-magnetic-field tensiometer (HMFT). It was found that the surface tension of water linearly varied with the magnetic field intensity and increased by 0.48mN/m or 0.65% in 10T. The increase of the surface tension of water could be attributed to the increase in the number and stabilization of the hydrogen bonds in the magnetic field.

Enhancement of Faceted Growth of Primary Al3Ni Phase in High Magnetic Field

Faceted growth of primary Al3Ni phase in the hypereutectic Al-Ni alloy in a high magnetic field was investigated. It was found that faceted growth of primary Al3Ni phase was enhanced in the presence of the magnetic field. However, the fibrous to granular transition of Al-Al3Ni eutectics occurred. The undercooling of primary and eutectic phases during solidification was measured using differential thermal analysis. It was showed that the undercooling of primary phase was hardly changed but that of eutectics markedly increased in the magnetic field. According to Cahn theory of crystal growth, the critical driving force was used to satisfactorily explain the morphology transition in the magnetic field.

A Numerical Framework for Free Surface Flow and Wettability Based on Arbitrary Lagrange-Eulerian Method

A mathematic model based on moving mesh Arbitrary Lagrange-Eulerian (ALE) is developed to solve incompressible fluid flow concerned with the free surface and wettability. A mercury sessile drop with different wetting angles is chosen to validate this method. Besides, two more extensive applications called electrowetting-on-dielectric (EWOD) and transferred drop are numerically simulated and compared with previous researchers work in order to demonstrate its efficiency.

Relationship between F Value and Slag Entrapment in Mold with Electromagnetic Brake

An experimental device is designed to control slag entrapment of molten steel with ElectroMagnetic Brake(EMBR). Mercury was taken to simulate the liquid steel flow in the mold. The factors which affect slag entrapment with EMBR are studied, such as position of magnets, distribution of magnetic flux density and submerged depth of Nozzle. Experimental results show that the posibility of power entrapped by liquid steel was smallest as magnetic flux density B=0.3T, meanwhile, it was found that F value decreases with increasing immersion depth. Indeed, the occurrence probability of the slag entrapment decreases while d=45 mm (d is distance from the centre of SEN to the centreline of magnetic core.) instead of d=25 mm. The submerged depth within 30~50 mm are suitable to the level fluctuation in EMBR conditions in this experiment.

Research of the Morphology and Distribution of the Primary Silicon in Al-18Si Alloy under a Gradient High Magnetic Field

A gradient high magnetic field effected significantly the morphology and distribution of the primary silicon grains in Al-18Si alloy. Experimental studies shew that in the gradient high magnetic field the primary silicon phase grains, which are large plate-like or five-star-like in the case of solidification without magnetic field, are accumulated on the top of the specimen and refined remarkably with the morphology of polygonal or nodular shapes when the alloy solidifies from the semisolid state. In the segregated layer of the silicon, the distribution of the silicon grains is homogeneous. The size of the primary silicon grains decreases and the grain number density rises with the increase of the magnetic strength maintaining the magnetization force unchangeable. It seems that the high magnetic field influences the diffusion of silicon. Theoretical models have been proposed to explain the refining and the distribution of the silicon grains.

Kiss-Point Position Control of Solidification Layer and Process Optimization for Twin-Roll Casting of Magnesium Alloys

The solidification and process optimization for twin-roll casting of magnesium alloys have been studied. Effects of roll speed, roller diameter, setback length and strip thickness on the position of the solidification front and the surface quality of strip were analyzed through experiments. A kiss-point model which considers the strip thickness, set-back length and roll speed was established to optimize process and enhance the surface quality of magnesium alloy strip. Results showed that the twin-roll casting process could be effectively stabilized and optimized under the direction of the model, and the defectless magnesium alloy strip was obtained.

Physical Simulation on the Liquid Metal Flow in FC-Mold of Slab Continuous Casting

The flow state and velocity distribution of liquid metal in the FC-Mold and the influence rules by the magnetic flux density have been investigated when electromagnetic brake adopted, applying mercury as medium to simulate molten steel in the continuous casting process. The velocity measurement has been completed by the Ultrasonic Doppler Velocimeter (UDV) under various magnetic distribution and the influence laws of magnetic flux density on the liquid metal flow in the mold has been analyzed. The experimental results indicate that, when the upper and lower magnetic flux density is 0.18T and 0.5T respectively, a preferable control effect can be obtained, not only the free surface fluctuation can be compressed, but also a plug flow can be rapidly formed.