Of Mosi <sub> Preparation Of 2 </ Sub>-based Composite Heating Elements And Its High Temperature Performance Study

Based on the fundamental concept of MoSia heat element and the knowledge of alloying and compositing, SiC/Si3N4 reinforced MoSi2 matrix composites are fabricated by Self-propagating High-temperature Synthesis (SHS) technology and different sintering process. The powder fabrication process, adhesive alteration, microstructure, high temperature mechanical property, electrical/heat property and oxidation film have been studied systematically by the means of XRD, electron microscopy, high-temperature three points bending stress etc. The effects of hot pressure sintering, pressureless sintering and in-situ technology on properties have been compared.Many valued results have been obtained in the study. The extent of the SHS reaction of MoSio matrix composite powder is limited by the amount of W and Al element addition. Result shows that the main reaction product is (Mo,W)(Al, Sfh phase, accompanied with a small amount of (Mo,W)5Si3 The relative densities of composite can be highly improved by increasing the sintering temperature and extending sintering time rationally, although alloying and compositing made it difficult in sintering. The addition of alloying element Al contributes to the appearance of liquid sintering, which benefits the improvement of relative density. The strength of hot pressed SiC or Si3N4 particle reinforced MoSi2 matrix composite is twice of that of MoSi2 at room temperature, however, the strength of composites behaved different at high temperature. The strength of SiC particle reinforced (Mo0.8,W0.2) (Al0.3,Si0 7)2 composite behaved desired properties. Due to the reaction of Si3N4 and Al that produce A1N, which is harmful for the strength improvement at high temperature, the SisN4 particles are not suit for being used as reinforcement particles with Al alloying element addition. The oxidation film is produced quickly when the tested composites, with which are added Al, are oxidized during the temperature scope of 600℃-1700℃, whose oxidation rate is greater than others. The "pest" phenomena of Si3N4 reinforced (Mo0.8,W0 2)(A10.3,Si0.7)2 pressureless sintering composite will happen in two hours. Such process is believed being dominated by pore-and-crack priority oxidation mechanism. The increase of defects resulted by the oxidation of Si3N4 provides the opportunity and space of the reaction of alloying Al element. The synergic factor operation increases the process of "pest" phenomena. The electrical resistance property of MoSi2 matrix composite is similar to that of MoSi2, namely, the electrical resistance of MoSi2 matrk composites increases in line with temperature, which is 10%-25% higher than that of pure MoSia.