超高速定向凝固条件下钴基高温合金特性的研究

On Direcitonal Solidification Cobalt Base Superalloy (P.R.C.K10) at Superhigh Cooling Rate

利用最新研制的超高梯度定向凝固装置,研究了钴基高温合金的成分偏析及机械性能的变化,实验结果表明:其机械性能有较大提高,试样拉伸断口表现为高韧性穿晶断裂,裂纹起源于碳化物边缘.

Up to now, researches have succeeded in raising temperature gradient just ahead of the solidifying S / L interface to about 100℃ / cm during alloy solidificaion. The authors' many years of research lead them to the belief that mechanical properties can be significantly improved by pushing temperature gradient much higher. The authors have succeeded in developing an experimental setup that can provide a temperature gradient of as high as 1300℃ / cm. This paper presents results of our research on directional solidification of cobalt base superalloy (known as K-10 in P.R.China) under the condition of superhigh cooling rate. The primary and secondary dendrite spacings of K10 become less than one fifth and one eighth respectively of those obtainable with conventional 100℃/ cm temperature gradient; microsegregation is almost completely eliminated. As can be expected the mechanical properties are greatly superior to those obtainable with 100℃/cm: at 1073 K, creep repture strength increases from 167 MPa to 196 MPa or 18%; rupture life is raised from 10 h to 30 h or by 200%; the reduction of cross sectional area increases from 12% to 52%; specific elongation from 17% to 46%. It can be seen from Fig.6 that, as temperature gradient is raised, there are always corresponding improvements of mechanical properties of K-10. The authors also conducted fractography and obtained consistent results. When K-10 has superfine columnar structure obtained with 1300 ℃ / cm temperature gradient, its fracture mechanism becomes different and is high-toughness transcrystalline fracture, craze originates at edge of carbides.