FABRICATION AND PROPERTIES OF NEW OXIDE-BASED COMPOSITE FIBERS (MIGL)AND HEAT-RESISTANT MATERIALS REINFORCED WITH THEM

The use of a molybdenum substrate in the shape of a microrope permits an increase in the crystallization rate of oxide fibres, resulting in a significant decrease in the fibre cost. Some variants of the method are now disclosed. As-grown fibres contain both an oxide component, wh ich can be considered as a matrix for the composite fibre, and molybde num wire as a reinforcement. In order to measure the room-temperature strength of the fibres, a new version of the fibre fragmentation test was developed. Interpretation of the test results is made without any assumptions about the strength distribution function of the fibre. The test results are presented in terms of a dependence of the fibre stre ngth on the remaining effective length of the fibre. High-temperature strength properties of these novel fibres were estimated by testing co mposites reinforced with them. When making composites with a heat-resi stant nickel-based matrix by using a routine liquid-phase fabrication method, a significant portion of the molybdenum wire is dissolved in t he matrix alloy. It is therefore mainly the oxide component that serve s as a reinforcement in the matrix. Preliminary evaluation of the high -temperature strength of the oxide fibre shows that there is a need to optimize the microstructure and fabrication parameters of the fibres in order to achieve strength values the same as those for monocrystall ine and eutectic fibres at temperatures above 1000 degrees C. Neverthe less, even at the present stage of development of the fibre technology , the high-temperature strength of composites with nickel superalloy a nd Ni3Al-based matrices looks very promising. The analysis of creep ru pture properties based on preliminary experiments and corresponding me chanical models offers the prospect of developing heat-resistant compo sites by using MIGL fibres and advanced alloys as the matrix materials . The operating temperature (i.e. for a creep rupture stress of about 150 MPa) can vary between 1100 and 1200 degrees C depending on the par ticular application. (C) 1998 Elsevier Science Ltd. All rights reserve d.