Superplastic Forming And Fes Of Nano-structured Si₂N₂O-Matrix Ceramics

The SI₂N₂O-Si₃N₄and SI₂N₂O-Sialon nanoconposites are fabricated by hot presssintering of amorphous nano-sized silicon nitride powder. The superplastic properties andsuperplastic forming rules are researched by experiment and finite element simulation.Nanostructured SI₂N₂O-Si₃N₄and SI₂N₂O-Sialon is sintering by two mixing powders.For the first kind of mixing powder method, in the sintering condition of1600℃for60min, the relative density of the sintering material is98.2%, and the average graindiameter is less than280nm. But when the sintering temperature is less than1700℃, theaverage grain size is less than500nm. For the second kind of mixing powder method,when the sinitering temperature is less than1600℃, SI₂N₂O-Sialon can be fabricated,whose diameter is less than100nm, which is a typical nanomaterial.During the tensile test, when the temperature is1550℃, the maximum extensibilityof SI₂N₂O-Si₃N₄is65%and the flow stress is less than20MPa. When the speed rate ofpunch is0.1mm/min,0.2mm/min and0.5mm/min respectively, the spherical parts can beformed. The forming rules are derived in the axial and radial dimension changing forsuperplastic deep-drawing forming of Si₃N₄ceramic by experiment investigate and FEM.During the tensile test of the SI₂N₂O-Sialon, when in the temperature is1550℃andthe strain rate is4.7104s-1, the maximum extensibility is110%. The superplasticextrusion of as sintered material was investigated. The parts can be formed at1550℃with a high velocity of1mm/s and a big extrusion ratio of3.57. The extrusion force vsstroke curve and the distribution of stress vs strain at different temperatures were obtainedby finite element similation. The superplastic forming rules were observed by compare thesimulated results with experimental results，which indicates that SI₂N₂O-Sialon parts canbe formed by superplastic forming technology.