Papers by Author: Yan Qing Su

Abstract: Effects of parameters on the stability of silicon melt pool in cold crucible continuous casting were discussed. The results indicate that the extinguishing of induction heating is mainly caused by the side wall feeding, low superheat degree and volume of the pool. The hot melt splashes are caused by the higher input power and uncompletely melted silicon of the dome top surface. The pool was shown to be stabilized as the raw materials were fed in the center area of the dome surface, the superheat degree and volume of the pool were properly increased, the pool was controlled in the effective heating range of the coil and the input power was set properly

Abstract: The effects of technical parameters on initial silicon melting in cold crucible continuous casting were studied. These parameters include the materials, the shape and the position of the base, the mass of the silicon that set on the top of the base. Through experimental and theoretical analysis, the optimized parameters were finally given: the base graphite with obconical shaped should be put at the level of the second turn of the coil, and the initial silicon with 10g should be put on the base. The mechanism of these parameters affecting on the initial melting are discussed and revealed.

Abstract: In this study, Ti46Al0.5W0.5Si ingots were directionally solidified by a near-rectangular cold crucible under different process parameters. These process parameters include the electromagnetic stirring, the crucible configuration and the molten drop, all of them have important effect on the S/L interface. The effects of the parameters on the solid/liquid (S/L) interface morphology were investigated, and the mechanisms of the parameters influencing the S/L interface were discussed and revealed. Results showed that the typical S/L interface of the ingots was presented as a curved ‘W-type’ shape. The uneven temperature distribution in the front of the solidified interface is the main reason for a curved S/L interface. Further, the requirements for obtaining a planar S/L interface in the process of cold crucible directional solidification were given, which provided a guide for the future work.

Abstract: This paper gives a detailed study of temperature distribution on Ti46Al0.5W0.5Si alloy directionally solidified by cold crucible. Based on experiment and numerical calculation, the heating process under different power was investigated, and the operating efficiency of cold crucible was roughly calculated. Further, the temperature field of Ti46Al0.5W0.5Si alloy under high power was numerically calculated, the finite element model predicted the temperature distribution at different moment. The results give a significance guide on cold crucible directional solidification.

Abstract: A square shaped silicon ingot was cast by cold crucible continuous casting. The grain growth behaviors during different growth stages were investigated. In the first, grains nucleate at the base surface in the centre and in the three phase junction at periphery, and then grow upwards and inclined upwards separately. In the second, grain grow competitively, two distinguished zones are formed. In the final, a cap is formed on the liquid free surface, and precipitates are present.

Abstract: The ingot of Ti47Al alloy was prepared by a newly developed rapid directional solidification, the microstructure and compressive properties of the ingot was observed and tested. The results show that the macrostructure consisted mainly of coarse columnar grains parallel to the axial direction, with the size of 0.5mm wide and 10mm in length. The direction of lamellar is almost perpendicular to the growth direction in the longitudinal section and no dendritic core is found. The average ultimate compressive strength of the specimens with grain growth parallel/perpendicular to the compressive direction is 1233.3 and 861.7 MPa respectively. The fracture mode for specimens with grain growth parallel to the compressive direction exhibits predominantly translamellar fracture, however, that for specimens with grain growth perpendicular to the compressive direction exhibits predominantly delamenation or interlamellar fracture.

Abstract: In the article this is a new way to prepare Ti-6Al-4V alloy rod and blade by metal mold vacuum suction casting. The effects of hydrogen on the suction casting is also studied. It is found that the alloy melt can be sucked up easily by the mold and has a better fluidity because of H2. Hydrogen can make the electrical current for suction casting decrease sharply compared with the electrical current in Ar. Hydrogen can refine the grain size of the alloy rod and blade. Compared with the unhydrogenated specimen, the peak stress of the hydrogenated specimens increase about 20%, because hydrogen decreases the volume fraction and size of shrinkage porosity.

Abstract: Microstructure evolution of peritectic Al-25at.%Ni alloy during directional solidification with pulling velocity ranging from 2 to 500m/s is investigated. The directional solidified alloy is composed of Al3Ni2, Al3Ni phase and eutectic (Al3Ni+Al) phase. When pulling velocity ranges from 2 to 5m/s, Al3Ni phase grows into an integral matrix. Majority of primary Al3Ni2 is consumed by peritecti reaction and transformation behind the peritectic interface with pulling velocity ranging from 2 to 20 m/s. While pulling rate increases, major Al3Ni phase direct solidifies from liquid. With cooling rate increasing, Al3Ni2 phase content firstly decreases and then increases, while the Al3Ni phase content decreases throughout.

Abstract: A novel precision casting technique for TiAl based alloy was described in this work, called the permanent mold suction casting technology，and the blades of Ti-47Al-2Si、Ti-47Al-2W-0.5Si、Ti-47Al-2W-0.5Si -0.5B were get by this technology. The structures of these blades were studied. The results of this study indicate that microstructure is sensitive to heat treatment and composition. The average grain size is 30 um before heat treatment. The grain size of TiAl based alloy is grossed by heat treatment at 1573 for 5h and furnace cooling, especially Ti-47Al-2Si. The addition of boron, the grain size of Ti-47Al-2W-0.5Si-0.5B is smaller than Ti-47Al-2W-0.5Si. The γ-TiAl based alloys have equiaxed grain in cross section, but the surface microstructure of γ-TiAl based alloys have more fine equiaxed grain than inside due to high cooling rate of mold.

Abstract: The microstructure evolution of Ti-Al peretectic system in transient stage and steady state in directional solidification was predicted via theoretical analysis. The solute distribution controlled by diffusion at and ahead the solid-liquid interface will determine whether the properitectic and peritectic phases can nucleate and grow ahead of the opposing solid phase. The formation of banding structure is possible in a certain composition range. At the steady state, a microstructure selection map was set up based on interface response function model. The microstructure of TiAl alloys with different aluminum content was studied with Bridgman directional solidification method. Some evidence in the experiment has been found to support the theoretical prediction.