材料期刊网

选用20％CoO和80％Al_2O_3配成的CoO孕育剂,对铸造镍基高温合金涡轮叶片,是一种有效的孕育剂。CoO和Al_2O_3粉末混匀,在1300℃下煅烧2h后,成为在α-Al_2O_3颗粒表面上沉积蓝色CoO·Al_2O_3尖晶石层。浇铸过程中,铸造镍基高温合金中如C,Cr,V,Ti,Al等活泼元素还原CoO,生成面心立方晶系的金属Co.因其结晶结构和晶格常数与基体高温合金相近,就能促进叶片表面晶粒细化。在生产实践中,应该避免生成SiO_2的“白霜”,并注意合理降低浇铸温度和提高模壳焙烧温度。

The CoO inoculant composed of 20% CoO and 80% Al_2O_3 (fused alumina) is an effective nucleator to the cast nickel-base superalloy blades. After calcining CoO and Al_2O_3 powders under 1300℃ for 2h, CoO.Al_2O_3 spinel was formed on the surface of alumina particles. It has been detected by EMPA that metallic Co of fcc crystal structure deposites on the surface due to that the CoO.Al_2O_3 spinel reduced by certain active elements contained in the cast nickel-base superalloys at elevated temperature. This is checked with the relative stabilities of the oxides of Ti, Cr, Al contained in the alloy with CoO. This was also verified by the pure Ni blades for which there was no effect at all. Because of the similarity of the crystal structure and the lattice constants of the metallic Co and the superalloy, the Co particles can act as nucleators refining the grains. In production practice, if SiO_2 is precipitated in local area of inner surface of mould and so the inoculant particles were covered with it, the nucleation effect is markedly reduced. In order to prevent the metallic Co remelting back, lower pouring temperature is preferred; and to enhance the reduction of CoO.Al_2O_3, higher heating temperature of mould is desirable.