اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

Effect of a transverse magnetic field on the growth

of equiaxed grains during directional solidification

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

ABSTRACT

The effect of a transverse magnetic field on the growth of equiaxed grains during directional solidification of Al-10wt% Cu alloys was investigated experimentally and numerically. The experimental results show that the magnetic field has a great influence on the size and distribution of equiaxed grains. Indeed, the magnetic field causes refined and coarsen equiaxed grains to distribute on the both sides of the sample, respectively. In-situ synchrotron X-ray imaging shows that a transverse magnetic field induced some force which can act on equiaxed grains and cause the movement of equiaxed grains during directional solidification. Numerical results reveal that the modification of the structure may be attributed to the thermoelectric (TE) magnetic effects produced by the magnetic field. Furthermore, a new method of removing inclusions in molten metal is developed by means of the TE magnetic force.

 

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

Motion of equiaxed grains during directional solidification

under static magnetic field

حرکت دانه های هم محور در حین انجماد جهت دار تحت میدان مغناطیسی استاتیک

ABSTRACT

The in situ and real time observations of the equiaxed grain motion during directional solidification of Al–10 wt% Cu under static magnetic field has been carried out by means of synchrotron X-ray radiography. It was observed that equiaxed grains moved approximately along the direction perpendicular to both the imposed magnetic field and the temperature gradient. Based on the radiographs, the motion of the solid grains was analyzed for various temperature gradients, and it was shown that the trajectories were imposed by the combination of the Thermo-Electric Magnetic forces, induced by the coupling of thermo-electric currents with the permanent magnetic field and the gravity force. The variations of the velocities and sizes of grains during the equiaxed growth under static magnetic field were measured and compared to a simple analytical model for the Thermo-Electric Magnetic forces and the Stokes law. A good agreement was achieved for the deviation angle as a function of the grain diameter, while a large discrepancy was observed for the velocity intensity when the dimensions of the equiaxed grains increased. In the latter case, it was shown that the corrections for both sample confinement and grain morphology were mandatory to explain the very low values of grain velocities.

 

روشی برای مسطح سازی جبهه انجمادی در فن آوری انجماد جهت دار

A method for flattening the solidification fron tindirectional solidification technology

روشی برای مسطح سازی جبهه انجمادی در فن آوری انجماد جهت دار

ABSTRACT

Nonplanar solidification front causes defects in directional solidification process.The transverse temperature gradient,which can bedivided into radial temperature gradient and circumferential temperature gradient,is one of the reason scausing the nonplanar solidification front . This paper presents a method by varying the wall thickness of the mould to decrease the circumferential temperature gradient and hence flatten the solidification front.The equations for calculating the wall thickness were deduced by heat transfer analysis.The optimized mould contour was obtained by solving the equations numerically.It was proved by simulation that the circumferential temperature gradient can be almost reduced by 40%.Furthermore,the starting time difference of solidification at one cross section along the circumferential direction almost reduces by half.Additionally,this paper also researches the influences of parameters of the mould and the furnace etc. on the shape of the mould and the circumferential temperature gradient.The circumferential temperature gradient decreases as the thermal conductivity and the emissivity of the mould increase. And the temperature of the cooling ring impacts little on the circumferential temperature gradient. According to the development trend of the blade manufacturing, this method may be applied widely.