高尺寸稳定性的MgAl_(2)O_(4)/MgO复合陶瓷型芯的制备

Preparation of MgAl_(2)O_(4)/MgO-based Composite Ceramic Core with High Dimensional Stability

以镁铝尖晶石(MgAl_(2)O_(4))为原料,制备了新型MgAl_(2)O_(4)/MgO复合陶瓷型芯。用X射线衍射仪(XRD)分析了样品的相组成,并用扫描电子显微镜(SEM)观察了陶瓷型芯的表面及断面微观形貌。结果表明,陶瓷型芯中的主晶相为镁铝尖晶石,次晶相为方镁石,镁铝尖晶石为陶瓷型芯骨架,骨架大颗粒之间填充有细方镁石颗粒。性能测试表明,添加镁铝尖晶石可抑制氧化镁的液相烧结,降低收缩率,同时可以显著提高陶瓷型芯的显气孔率和高温尺寸稳定性。含有60%镁铝尖晶石的MgAl_(2)O_(4)/MgO复合陶瓷型芯显气孔率为38.24%、收缩率为1.99%、室温抗弯强度为25.9 MPa、热膨胀率仅为1.61%。溶出实验结果表明,所制备的MgAl_(2)O_(4)/MgO复合陶瓷型芯能在温和条件下溶出,不对铸件造成化学腐蚀及机械损伤:在溶出液为20%有机弱酸乙酸溶液中,90℃溶出6 h后,型芯能够完全塌陷成粉末。

A new type of MgAl_(2)O_(4)/MgO-based composite ceramic core was prepared with magnesium-aluminum spinel(MgAl_(2)O_(4))as raw material.The phase compositions of the new ceramic core were analyzed via X-ray diffraction(XRD).The microstructures of the surface and cross-section of the ceramic core were characterized by Scanning Electron Microscopy(SEM).The results show that the main crystal phase in the ceramic core is magnesium-aluminum spinel,and the secondary crystal phase is periclase.The skeleton of the ceramic core is magnesium-aluminum spinel,filled with fine magnesium oxide particles.Performance tests confirmed that the addition of magnesium aluminum spinel can inhibit the liquid phase sintering of magnesium oxide,thereby reducing the shrinkage rate.Meanwhile,the apparent porosity and high-temperature dimensional stability of the ceramic core are significantly improved.The MgAl_(2)O_(4)/MgO-based composite ceramic core with 60%magnesium-aluminum spinel showed an apparent porosity of 38.24%,a shrinkage rate of 1.99%,a flexural strength of 25.9 MPa and a thermal expansion rate of 1.61%.The removal experiments results show that the prepared MgAl_(2)O_(4)/MgO-based composite ceramic core can be dissolved under mild conditions.This dissolution method does not cause chemical corrosion and mechanical damage to the casting.The core can completely collapse into powder after being removed at 90℃for 6 h in 20%organic weak acid acetic acid solution.