Toughening Effect and Oxidation Behavior of MoSi2 -ZrO2 Composites

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0980-II05-35

Toughening Effect and Oxidation Behavior of MoSi2 -ZrO2 Composites Karin Gong1, Yiming Yao1, Mats Sundberg2, Xin-Hai Li3, Erik Ström2, and Changhai Li1 1 Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden 2 Kanthal AB, Hallstahammar, SE-734 27, Sweden 3 Siemens Industrial Turbomachinery AB, Finspong, SE-612 82, Sweden Abstract Toughening effect of ZrO2-particles in MoSi2-based materials is one of the important toughening mechanism. In this work, the influence of particle size and volume percentage of unstabilized ZrO2addition on toughening in MoSi2-matrix composites was studied. The measured data revealed that the fine particle size, < 1 m, with certain volume percentages around 20% gave more effective toughening results. The tested materials were prepared by two different sintering processes: pressureless sintering (PLS) and PLS + Hipping sintering. The results on sintered density, RT-hardness and RT-toughness indicated that the PLS process could be a practical and economical method for producing MOSi2-ZrO2 composites in industry. Oxidation behavior of MoSi2-ZrO2 composites was also studied in the work. Clearly, the ZrO2-addition made the oxidation resistance of the composites worse than that of monolithic MoSi2, which means that a low ZrO2-addition should be used in the composites, as far as an acceptable toughening effect was reached. Introduction Structural materials used under oxidizing and aggressive environments at temperatures above 1000 ºC have drawn special attention from materials scientists. The choice of materials is limited to the silicon-based structural materials. And, MoSi2 is presently considered as one of the promising materials due to its high melting point (2030ºC) and excellent high temperature oxidation resistance. MoSi2 as an intermetallic material, one major problem, which has impeded its usage as high temperature structural materials, is poor ductility and toughness below brittle-to-ductile transition temperature, around 1350ºC [1]. Addition of alloying elements into MoSi2 may lead to solid solution strengthening and improved toughness of MoSi2. Clearly, the alloying effects depend on the solid solubility of the added alloying elements. The solid solubility of transition metal elements in MoSi2 have been systematically studied [2-10] with these alloying process. So, the alloying additions have been found to have a limited toughening effect on MoSi2. Further progress depends on the development of engineered composite materials. At the end of 1980´s, Mcdonnell Douglas Research Laboratories (MDRL) [11] reported that MoSi2-matrix is compatible with most of the selected ceramic reinforcements up to a reasonable application temperature; say 1700 °C. Lately, works [12-22] have clearly demonstrated that ZrO2toughening effect may be employed to improve MoSi2-based materials significantly. In 1992, Petrovic et al. [18] indicated that the presence of an unstabilized ZrO2 particle phase in MoSi2/ZrO2 composites increased the room tempe