The Mystery of Molten Metal

摘要

Recent advances in scientific understanding of high-temperature materials processing using novelrnexperimental methodologies have shed light on the complex role of surface and interface phenomena. New in-situ studies onrnmolten metal/solid ceramic interactions using a unique experimental complex at the Foundry Research Institute, Krakow,rnhave revealed a number of unusual observations in materials processing at high temperatures. We present some suchrnunusual observations and their explanation with reference to liquid metal processing of Al, Ni, and Ti, and their alloys inrncontact with oxide ceramics. In particular, we focus on the following aspects: primary oxidation of AI from residual waterrnvapor or oxygen, capillary purification to remove surface oxide, substrate protection by CVD carbon, roughening due tornspinel whisker formation, inclusions in castings due to mechanical detachment, floatation due to buoyancy forces, andrnsegregation due to directional solidification, modification of the solid surface morphology by metal vapor ahead of the liquid,rnand the complications due to multi-component alloys melted in crucibles made from complex oxide-based ceramics. In therncase of Ti, rapid reactions with oxides result in undesirable volumetric changes that create difficulty in casting high-quality Tirnparts, particularly by investment casting. Nanoscale (e. g. , colloidal) coatings based on Y_2O_3 protect crucibles and holdingrnladles against such attack. Practical insights and recommendations for materials processing emerging from the fundamentalrnstudies on high-temperature interfacial phenomena have been described.