Transformation toughening of MoSi_2 with incorporation of PSZ by means of CVI

本研究旨在利用相变增韧制备高强度ZrO_2/MoSi_2复合材料。采用化学气相渗透（CVI）法在部分烧结MoSi_2中引入ZrO_2。为了获得复合材料制备工艺和微观结构的基础知识，在没有添加氧化物的情况下沉积了ZrO_2。观察了退火后ZrO_2的显微结构，讨论了实现相变增韧的最佳退火条件。结果表明：1）采用金属有机物（MO）浸渍法制备的ZrO_2包覆MoSi_2晶粒均匀; 2）浸渍后的ZrO_2均为非晶态，需要进行后退火处理。在空气中1073 K、3.6ks退火后的ZrO_2由直径为10 nm的等轴晶组成。3）复合材料的硬度是通过ZrO_2向MoSi_2的转变而提高的，最大硬度可达20 GPa。维氏硬度压痕表明，合金具有较高的韧性，并发生相变增韧。

This study was intended to fabricate high strength ZrO_2/MoSi_2 composites, which took advantage of transformation toughening. Chemical-Vapour-Infiltration(CVI) method was adopted for incorporation of ZrO_2 into partially sintered MoSi_2. In order to obtain fundamental knowledge for fabrication process and the microstructure of the composites, ZrO_2 were deposited with no additive oxides. Microstructures of post-annealed ZrO_2 were observed and the optimum annealing conditions for realizing transformation toughening were discussed. The following results were obtained.1) Fine MoSi_2 grains were well-covered with CVI-ZrO_2 by using Metal-Organic(MO) precursor.2) The infiltrated ZrO_2 were all amorphous, therefore post-annealing treatment was required. The post annealed ZrO_2 at 1073K for 3.6ks in air consisted of equi-axed grains of several 10nm in diameter. Existence of monoclinic ZrO_2 was observed and this microstructure suggests the limitation of annealing conditions.3) Hardness increase was realized by increase of ZrO_2 into MoSi_2 and maximum hardness of 20GPa was obtained in the composites. High toughness was recognized by Vickers indentation and occurrence of transformation toughening was realized.