Papers by Keyword: Solidification Rate

Abstract: This paper presents the experimental investigation conducted on ADC12 cast alloy. The main objective of the research is to investigate the effect of 1.5%La addition with different cooling rate on microstructure and hardness value of ADC12 cast alloy. The Ceramic Mold with different thickness dimensions was use to obtained different cooling rate. The Si structure became modified by increase the cooling rate of base alloy. With La addition the Si size observed smaller area than base alloy when the cooling rate increases. In addition, the higher cooling rate and La addition improves the hardness specially at lower thickness with La addition.

Abstract: Microstructure of the arc-melted Cr-20at%Nb alloy solidified in different positions was investigated using optical microscope (OM) and scanning electron microscope (SEM). The results show that fully coupled eutectic was developed at the bottom of the ingot and then the eutectic experienced a columnar to equiaxed transition due to the decrease of G/V ratio (G the thermal gradient and V the solidification rate) with increasing the solidification distance. A novel lamellar structure was observed in the middle side of the arc-melted ingot, which may form by means of the eutectoid reaction of C14-Cr₂Nb→C15-Cr₂Nb+Crss. With the increase of the solidification distance from the middle side to the top side, the primary Cr₂Nb phase underwent a nonfaceted to faceted transition.

Abstract: The influence of performance is difference along with the change content of chloride ion through the experimental study, so it is necessary to carry on the analysis of the reaction mechanism in blend. At the base of dissemination mechanism and solidification mechanism, the thorough research can be conducted about chloride ion is cured by cement-fly-ash-flushed-by-seawater. The contrast analysis about the dissemination and solidification of chloride ion in base-materials will be researched through microscopic experimental and the analysis of solidification rate. The best chloride ion content can be discovered from the research that it can obtain the best dissemination-solidification and make the influence of performance to be smallest. The dissemination-process of chloride ion in fly-ash-flushed-by-seawater is from the surface of fly-ash-flushed-by-seawater to the interior of cement-gelatin, it is different from internal addition method, and it is proposed for the first time in this what simulate the fly-ash-flushed-by-seawater by soaking fly-ash by the solution of NaCl.

Abstract: Transient temperature fields of directional solidification of Al-Ni-Co alloys were studied by employing finite element method. Temperature gradient at solidification front and solidification rate was analyzed under different pouring temperature of molten steel. The results show that with different initial pouring temperatures of molten steel, individual ratio of temperature gradient at solidification front to solidification rate soars up in the initial stage of solidification, then varies within 2000-6000°C•s•cm-2, and finally plunges down and goes together when the solidification thickness reaches 5-6cm. Simulation result is consistent with the production reality. Numerical simulation results can provide an available reference for process optimization of directional solidification of Al-Ni-Co alloys.

Abstract: Ni₃Si compound is one of the excellent high temperature structural materials, because it possesses the attributes of high melting point, high strength, low density, excellent oxidation resistance at elevated temperatures, and magnificent corrosion resistance in acid environments, particularly sulfuric acid solutions, while the application of this compound is limited due to poor ductility at ambient temperatures and lack of fabricability at high temperatures. The incorporation of a ductile phase into the intermetallic materials has become an attractive means to modify the ductility. In this paper Ni-Ni₃Si hypoeutectic in situ composites are obtained by Bridgman directional solidification technology. Microstructure of the Ni- Ni₃Si hypoeutectic in situ composites are regular lamellar eutectic structure at the lower solidification rates, whereas eutectic cells or dendrites can be found with the increase of the solidification rate, due to the increase of the composition undercooling. Moreover, the directional solidification mechanism was investigated as well.

Abstract: This paper presents the results of an investigation on the interrelationship between thermophysical properties, processing conditions and primary dendrite arm spacing for a nickel-base superalloy. The research was realized for CMSX-4, directionally solidified in a Bridgman furnace. For a systematic, fast and cost-efficient investigation numerical finite element models were applied. The numerical model, composed of thermophysical material data, geometric data and boundary conditions, was calibrated and experimentally validated. Microstructural parameters of the castings were determined for a broad range of processing conditions and varying thermophysical properties in order to study general influences. Withdrawal speed, furnace temperature, enthalpy of fusion, solidification range, heat conductivity and specific heat were varied accordingly. The primary dendrite arm spacing is predominantly influenced by withdrawal speed and furnace temperature, but shows only a weak dependency on thermophysical properties.

Abstract: In this paper, the structure and composition of multicrystalline silicon ingots prepared by directional solidification with different pulling rates were analyzed to investigate the effect of pulling rate on the multicrystalline silicon ingot. The results showed that the lower pulling rate will make the site taking place constitutional supercooling move to the upper part of ingots and make the high purity area become larger. Lowering the pulling rate will decrease the impurity effective segregation coefficient and the solid-liquid interface curvature.

Abstract: Laser surface alloying of Ni-Co electroplated steel using 900 W CW CO2 laser to develop Fe-Ni-Co alloy on the surface is reported. Fe-Ni-Co alloys of different compositions are produced by varying the working speed from 0.25 m/min to 3m/min and laser spot size from 0.6 mm to 5mm. The development of microstructure in the melted zone is analysed in terms of composition variation and cooling rate. The microhardness of newly formed alloys reported here are three times higher as compared to base metal. Martensite is observed in the laser modified zone.

Abstract: Carbides in HSS roll were studied systematically. The results showed that there were two kinds of carbides in HSS roll, 1st and 2nd carbides. 1st eutectic carbides included the chrysanthemum-like MC mainly consisting of V and the plate-like M2C rich in Mo. 2nd carbides were complex carbides, concentrating Fe, Cr, Mo and V elements. The morphology, distribution and alloy concentration of the 1st eutectic carbides were studied using OM, SEM and EDS. During heat treatment, evolution of the 1st eutectic carbides was analyzed. It was found that the MC carbides had no change in morphology, components and distribution, while the M2C carbides decomposed to M6C and MC. In order to improve the properties of HSS, a method of increasing solidification rate was defined to refine the eutectic carbides. After refinement, the eutectic carbides distributed both along the grain boundaries and inside the grains.

Abstract: Co-base superalloys have been applied in the stationary compoents of gas turbine owing to their excellent high temperaure properties. The stationary Co-base alloy components are generally manufactured by casting. Solidification behavior of the alloy is an important factor in the selection of casting parameters. In the present study, solidification microstructure and carbide formation behaviors were studied by directional solidification. Directional solidification experiments were carried out at the solidification rates of 0.5 ~ 150µm/s with the Co-base superalloy ECY768. Between the dendrites just below the final freezing temperature, MC carbide and M23C6 carbide were found. It was identified that the script or blocky carbides were Ta or W-rich MC carbide, and the lamellar carbides were Cr-rich M23C6 eutectic carbides. The solid/liquid interface morphology clearly showed that freezing of the Cr-rich eutectic carbide occurred just after the script type MC carbide.