The mystery of molten metal

• Published in: China foundry 2010-11, Vol.7 (4), p.425-437
• Main Author: Natalia Sobczak Jerzy Sobczak Rajiv Asthana Robert Purgert
• Format: Article
• Language: English
• Subjects: casting defects; high-temperature phenomena; in-situ observation; molten metal
• ISSN: 1672-6421; 2365-9459

Recent advances in scientific understanding of high-temperature materials processing using novel experimental methodologies have shed light on the complex role of surface and interface phenomena. New in-situ studies on molten metal/solid ceramic interactions using a unique experimental complex at the Foundry Research Institute, Krakow, have revealed a number of unusual observations in materials processing at high temperatures. We present some such unusual observations and their explanation with reference to liquid metal processing of Al, Ni, and Ti, and their alloys in contact with oxide ceramics. In particular, we focus on the following aspects： primary oxidation of Al from residual water vapor or oxygen, capillary purification to remove surface oxide, substrate protection by CVD carbon, roughening due to spinel whisker formation, inclusions in castings due to mechanical detachment, floatation due to buoyancy forces, and segregation due to directional solidifciation, modification of the solid surface morphology by metal vapor ahead of the liquid, and the complication due to multi-component alloys melted in crucibles made from complex oxide-based ceramics. In the case of Ti, rapid reactions with oxides result in undesirable volumetric changes that create difficulty in casting high-quality Ti parts, particularly by investment casting. Nanoscale （e.g., colloidal） coatings based on Y2O3 protect crucibles and hold ladles against such attack. Practical insights and recommendations for materials processing emerging from the fundamental studies on high-temperature interfacial phenomena have been described.