氮气气氛下Al对SiC-MgAl2O4复合材料物相和结构演变的影响

以SiC、MgAl₂O₄细粉为主要原料,分别添加质量分数为1%、3%、5%、7%、9%和12%的金属Al,置于流动氮气中,在1 500 ℃下保温5 h烧成得到SiC-MgAl₂O₄复合材料,对烧后试样进行XRD、SEM及EDS分析。结果表明,1 500 ℃高温烧结后,材料体系发生一系列复杂反应,试样中物相均以β-SiC、MgAl₂O₄、氮化物和sialon相为主。部分金属Al在高温下氮化形成氮化铝,并参与sialon相和MgAlON形成的反应。尖晶石则转变为富铝尖晶石和MgAlON两相共存。随着Al含量的增加,尖晶石中固溶铝含量达到极限时,析出α-Al₂O₃。Al含量的增加使得结合相Si-Al-O-N的形貌发生变化,由板带状向板柱状过渡,最终发育成形貌较为清晰的板层状。经SEM-EDS分析,sialon相中固溶一定量的Mg元素,为sialon多型体Mg-sialon相。

Effect of Al on Phase and Structure Evolution of SiC-MgAl2O4 Composites under Nitrogen Atmosphere

SiC-MgAl₂O₄ composites were fabricated in flowing nitrogen for 5 h at 1 500 ℃, using SiC and MgAl₂O₄ powders as well as various mass fraction of 1%, 3%, 5%, 7%, 9% and 12% aluminum powders as the raw materials. The sintered samples were analyzed by XRD, SEM and EDS. The results show that a series of reactions occur in the material system after sintering at 1 500 ℃. β-SiC, MgAl₂O₄, nitride and sialon as the main phases are detected in all the sintered samples. Aluminum is partially nitridated at high temperature to form aluminum nitride and participate in the reaction of sialon and MgAlON formation. The spinel is transformed into two phases coexisting with aluminum-rich spinel and MgAlON. With the increase of aluminum content, α-Al₂O₃ can be precipitated when the solid-solute aluminum in spinel reaches to the content limit. Moreover, as the aluminum content increases, the morphology of the Si-Al-O-N phase changes from slab-band shape to slab-columnar shape, and eventually develops a clearer plate layer shape. A certain amount of Mg element is dissolved in the sialon phase by SEM-EDS analysis, which is considered as the sialon polymorph of Mg-sialon phase.