Structural stability and non-catalytic nucleation inhibition effect of Si–Zr–B mould coating on undercooled superalloy melt

Abstract

The investment moulding technique was first adopted to prepare a SiO2–ZrO2–B2O3 (Si–Zr–B) substrate layer on the inner surface of the mould, by employing SiO2 glass dust and ZrO2 powder, SiO2–ZrO2 sol, and analytical grade H3BO3 as refractory material, binder, and softening agent, respectively. Then using sol–gel processing, seven layers of Si–Zr–B film of the same formula as the aforementioned Si–Zr–B substrate layer were compounded with the substrate layer step by step. After glassing treatment at 850°C for 60 min, this film transformed into a glass lined coating. It was shown from X-ray diffraction analysis that, after holding it at a temperature of 1500°C for 30 min, the amount of crystallinity in the Si–Zr–B coating was about 1–3% (vol.-%). Finally, the undercooling experiment showed that a large undercooling (up to 140 K) was achieved in a DD3 (Ni–Cr–Mo–Al–Ti–Co–W) single crystal superalloy melt in this coated mould. So it is concluded that a Si–Zr–B coating has got a good structural stability at high temperature and provides ideal non-catalytic nucleation inhibition for an undercooled superalloy.