Study On Pyro-Joining Of SiC Ceramic And Its Composites By Precursor And Ceramic-Metal Joining By Fgm

Joiningsofseveralceramicsandcomposites(SiC,CandCf/SiC)athightemperatureviaprecursor (silicone resin, SR249) -infiltration-pyrolysis process and in-situ nano-ceramicgrains reinforced ceramic-metal (SiC-Ti) gradient materials for joining of ceramic andmetal have been firstly studied in this dissertation. The curing and pyrolysis of precursorSR 249, the joining process, the structures and the properties of the joints have beenstudied by infrared spectroscopy (IR), thermoanalysis (TA), element analysis, X-raydiffraction (XRD), scanning electron microscope (SEM), and transmission electronmicroscope(TEM).The curing and pyrolysis of precursor SR249 have been firstly studied systematically.The curing process of SR249 is accomplished by eliminating Si-OH to form the structureofSi-O-Si.High cross-link degree reticulation structure increasesthe stabilityand ceramicyieldathightemperature.Thecuringtemperatureinfluencestheceramic yieldremarkably.Thetemperatureof250℃isappropriateforobtaininghighercross-linkdegreeandceramicyield.ThestateofSR249influences theceramicyield.Theceramic yieldofpureSR249is89.3%. The cured SR249 transforms into Si-O-Si structure at high temperature. C, SiO2and SiC are amorphous in the pyrolysis production treated at 800℃and 1000℃. Crystalgrains appearat 1200℃. PartsofSi-O-Si ceramics aredecomposedtoSiOandCObeyond1400℃. The structure and the composition of the pyrolysis production are altered atdifferent temperatures. The content of the atom Si bonded with O gets fewer neverthelessthat of the atom Si bonded with C higher while the precursor is heated up.Meanwhile, thechange of the content of free C has the tendency of getting lower.The structure of Si-O-Chasthecapabilityofkeepingstabilizationuntil1400℃.The pyrolysis kinetics of SR249 is studied in the dissertation. The pyrolysis of SR249includes three stages.The apparent activation energyof the first stage is23.32kJ/mol. Thepyrolysis mechanism function of this stage is Avrami-Erofeev equation. The rate ofpyrolysisreactioninthisstageiscontrolledbyrandom nucleation.Si-CandC-Crupturetoform small-molecular gas in this stage.The apparent activation energyof the second stageis 196.95kJ/mol. The pyrolysis mechanism function of the second stage is...