La_2O_3添加对MgAl_2O_4-CaAl_4O_7-CaAl_(12)O_(19)复合材料烧结行为的影响

Effect of La_2O_3 addition on sintering behavior of MgAl_2O_4-CaAl_4O_7-CaAl_(12)O_(19) composite

为适应材料轻量化的发展需要,在1 400~1 600℃温度下开发了MgAl_2O_4-CaAl_4O_7-CaAl_(12)O_(19)(MACA2-CA6)复合材料,并考察了La_2O_3添加对该复合材料烧结行为、显微结构和力学性能的影响。结果表明,La_2O_3添加剂优先固溶到MA-CA_2-CA_6复合材料组成晶相CA_6中,促使CA_6相发生晶格畸变,有效抑制了CA_6晶粒沿基面的异常长大,其形貌由片状向等轴状趋势转变,促使MA-CA_2-CA_6复合材料制备过程中由于CA_6晶粒异常长大而导致的多孔网状显微结构得以有效消除,因此也极大地改善了Mg^(2+)的扩散条件,在一定程度上间接促进了MA晶粒的发育,有效促进了MA-CA_2-CA_6复合材料的烧结。经1 200℃预烧、1 600℃保温2h烧成后,当La_2O_3的添加量为4wt%时,MA-CA_2-CA_6复合材料试样的显气孔率由19.2%下降至6.1%,体积密度由2.78g/cm^3上升至3.18g/cm^3,制得了MA、CA_2、CA_6晶相呈现交织分布、显微结构致密、有利于其力学性能改善的La_2O_3/MA-CA_2-CA_6复合材料,经1 200℃预烧、-1 600℃保温2h烧成后的4wt% La_2O_3添加试样,其冷态抗压强度由317 MPa增加到了501 MPa。

In order to adapt the demands for the lightweight of materials,MgAl2O4-CaAl4O7-CaAl12O19（MA-CA2-CA6）composite was developed at 1 400-1 600℃ by addition of La2O3 micro powder,and the effect of La2O3 addition on sintering behavior,microstructure and mechanical properties of the composite was discussed.The results show that the added La2O3 dissolves to the CA6 phases of MA-CA2-CA6 composite,causing the lattice distortion of CA6 crystal,and the abnormal grain growth rate of CA6 to be decelerated,resulting in a more equiaxed morphology instead of anisotropic growth to platelet structure,thereby further contributes to the elimination of pores located between the initial plate-like CA6 grains.The disappearance of the platelet structures is favorable to Mg^2＋ diffusion and thus indirectly promotes the development of MA grains,so the sintering activity of MA-CA2-CA6 composite is comprehensively promoted.As a result,the dense microstructure is obtained,with the apparent porosity decreases from 19.2%to 6.1% and the bulk density increases from 2.78 g/cm^3 to 3.18 g/cm^3 after presintering at 1 200℃and sintering at 1 600℃ for 2 hby addition of 4 wt% La2O3.In addition,a texture microstructure of the crystalphase,which includes MA,CA2 and CA6,is observed in the typical back-scattered electron（BSE）images of microstructures with 4 wt% La2O3 content La2O3/MA-CA2-CA6 composite samples sintered at 1 600℃for 2 h,which is considered to be favorable to improve the mechanical properties of MA-CA2-CA6 composite,and the cold compressive strength increases from 317 MPa to 501 MPa after presintering at 1 200℃ and sintering at 1 600℃ for 2 h by addition of 4 wt% La2O3.