Multiphase-Field Modeling of Micropore Formation in Metallic Alloys
- PDF / 2,052,472 Bytes
- 4 Pages / 593.972 x 792 pts Page_size
- 51 Downloads / 250 Views
on of defects such as microporosity limits the mechanical properties of cast parts. They are induced by both solidification shrinkage and gas segregation that occur concomitantly during the solidification, in the mushy zone.[1] Most advanced models of microporosity formation solve at the scale of the process average conservation equations for the evolution of the solid fraction, the flow of interdendritic liquid, and the partitioning and diffusion of gases during solidification.[2–7] During its growth, the pressure inside the pore exceeds that of the surrounding liquid due to capillarity forces between liquid and gas. Therefore, to close the problem mathematically, a so-called pinching model, i.e., a mathematical expression relating the radius of curvature of the pore–liquid interface to a microstructural parameter (e.g., solid fraction) is required.[3,7–9] For a spherical pore, this relationship is straightforward; however, in reality, due to numerous contacts with the solid phase, pores take a complex and highly tortuous shape. Local
HOSSEIN MEIDANI, formerly Ph.D. Student with the Computational Materials Laboratory, Institute of Materials, Ecole Polytechnique Fe´de´rale de Lausanne, 1015 Lausanne, Switzerland, is now Dev. Engineer with the Thermal Transverse Technologies (TTTM), Alstom (Switzerland), Brown Boveri Str. 7, 5401 Baden, Switzerland. Contact e-mail: [email protected] ALAIN JACOT, Senior Scientist, is with the Computational Materials Laboratory, Institute of Materials, Ecole Polytechnique Fe´de´rale de Lausanne, and also with the Calcom ESI SA, Parc Scientifique, PSE-A, 1015 Lausanne, Switzerland. MICHEL RAPPAZ, Professor, is with the Computational Materials Laboratory, Institute of Materials, Ecole Polytechnique Fe´de´rale de Lausanne. Manuscript submitted April 14, 2014. Article published online November 11, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
mean curvatures as high as 0.2 lm1 have been measured in aluminum alloys by X-ray tomography (XRT), which correspond to overpressures as high as 400 kPa in the pore with respect to the surrounding liquid,[10] that can directly affect the pore size and fraction. Different pinching models have been proposed which all share simplifications of the pore shape[3,7–9]; still, these assumptions are not backed with an extensive study of the pore morphology. To address this issue, Felberbaum and Rappaz performed XRT observations and studied pores in solidified Al-Cu alloys.[10] Curvature distribution on the pore–liquid interface is of interest since it plays an important role on the way the pore grows. The XRT observations were performed on solidified samples, and thus the regions of eutectic composition were assimilated to locations of the last liquid to solidify. However, unfortunately, the limited resolution of XRT did not allow for accurate curvature estimations on those locations. Calculating the curvature distribution all over the pores surface, Felberbaum et al. found that the majority of surface patches where the mean curvature, H = 0.5(j1 + j2), is positive
Data Loading...
