Abstract:

Using the mixture of SiO 2 glassdust and ZrO 2 powder as refractory material, SiO 2-ZrO 2 sol as binder and H 3BO 3 as softening agent, a substrate layer was prepared on the inner surface of the mold by adopting shell-molding technique, where the SiO 2-ZrO 2 sol was the product of the hydrolyzing-condensation reaction at 35℃ for 180 min in the precursor solution with the mole ratio of 3H 2O, 4C 2H 5OH, 0.11 ZrOCl 2·8H 2O and 1 Si(OC 2H 5) 4, respectively. Then adopting sol-gel processing, proper layers of SiO 2-ZrO 2-B 2O 3 thin film with the same composition as the substrate layer was compounded with the substrate layer step by step. After dipping-class heat treatment and glassing treatment at 800℃ for 60 min, this film transformed into the SiO 2-ZrO 2-B 2O 3 glass coating. Furthermore, after holding the coating at a temperature of 1500℃ for 30 min, the amount of crystalline is about 1%~3%(vol%). Finally, an undercooling experiment showed that high undercooling of DD3 single crystal superalloy up to 140K was achieved in this coating mold. Based on the classical nucleation theory, the wetting angle corresponding to the largest undercooling achieved in the inhibitive coatings, θ*, was calculated. It is found that they are far less than the measured one between coating and alloy melt. This phenomenon further proves that not only the SiO 2-ZrO 2-B 2O 3 coating has good high-temperature structure stability, but also it is an ideal inhibitive nucleation coatings for DD3 single crystal superalloy melt.

Key words: DD3 sing le cr ysta l super allo y, underco oling, coating, nucleat ion inhibit ion