Study On Preparation Of Whisker And Chopped Fiber Reinforced SiC-Si₃N₄ Matrix Composites By Reactive Sintering

Fiber reinforced ceramic matrix composites will be widely used in aerospace,defense industry,nuclear energy and other fields,because of its high specific strength,high modulus,high temperature resistance,radiation resistance and other excellent performance.However,the higher preparation cost and longer preparation time limit the extensive application of continuous fiber reinforced ceramic matrix composites.In this paper,whiskers and chopped fiber reinforced SiC-Si₃N₄ matrix composites were prepared by reactive sintering process on the basis of the relatively low cost of whiskers and chopped fibers.The preparation technology of whisker and chopped fiber reinforced SiC-Si₃N₄ matrix composites was studied.Silicon carbide whisker reinforced SiC-Si₃N₄ matrix composites were prepared by solid-phase ball milling,warm-pressing forming,pyrolysis carbonization and reaction sintering.The effects of cold isostatic pressing pressure,sintering additives content,phenolic resin content and silicon carbide whisker content on the structure and properties of silicon carbide whisker reinforced SiC-Si₃N₄ matrix composites were investigated.When the cold isostatic pressing pressure increases from 0 to 200MPa,the flexural strength of the composites is increasing.Y₂O₃ and Al₂O₃ as sintering additives will promote the densification of ceramics,When the content of sintering additive increased from 0 to 12wt.%,The density of the composites increased and the flexural strength increased first and then decreased.When the content of phenolic resin increased from 10wt.%to 25wt.%,The density and flexural strength of composites decreased.When the content of silicon carbide whisker increased from 0 to 26wt.%,The flexural strength and density of composites increased first and then decreased.The chopped basalt fiber and chopped carbon fiber reinforced SiC-Si₃N₄ matrix composites were prepared by the method of stacking.Basalt fiber reinforced SiC-Si₃N₄matrix composites sintered at 1450?,the basalt fiber is melted and decomposed,then the ceramic can not be enhanced.The chopped carbon fibers are evenly distributed in the matrix by a layered form.Chopped carbon fiber reinforced SiC-Si₃N₄ matrix composites were prepared by solid-phase ball milling,warm-pressing forming,pyrolysis carbonization and reaction sintering.The effects of chopped carbon fiber content and sintering temperature on the structure and properties of composites were investigated.The flexural strength and density of composites increased first and then decreased when the content of chopped carbon fiber increased from 0 to 12wt.%.Carbon fiber in the sintering process will react with Si to produce SiC,weakening the fiber enhancement effect.When the sintering temperature increased from 1450?to 1600?,the flexural strength and density of the composites increased first and then decreased.Increasing the sintering temperature promotes the sintering of the ceramic matrix.Chopped boron nitride?BN?fiber reinforced SiC-Si₃N₄ matrix composites were prepared by solid-phase ball milling,warm-pressing forming,pyrolysis carbonization and reaction sintering.The effects of chopped BN fiber content on the structure and properties of composites were investigated.Chopped BN fiber dispersion is better than chopped carbon fiber.When the content of chopped BN fiber increases from 0 to12wt.%,The flexural strength and density of composites increase first and then decrease.Chopped SiC fiber reinforced SiC-Si₃N₄ matrix composites were prepared by solid-phase ball milling,warm-pressing forming,pyrolysis carbonization and reaction sintering.The effects of the content of chopped SiC fiber and the sintering temperature on the structure and properties of composites were investigated.When the content of chopped SiC fiber increases from 0 to 12wt.%,The flexural strength and density of composites increase first and then decrease.When the chopped SiC fiber content is3wt.%,The composites have higher mechanical properties,whose flexural strength,porosity and density are were 120.45MPa,12.98%and 2.231g/cm³,respectively.When the sintering temperature is increased from 1450?to 1600?,the flexural strength and density of the composites decrease first and then increase.Chopped SiC fibers will gradually decompose with the increase of sintering temperature,and the strengthening effect is also weakened.The addition of chopped fiber can improve the hardness and thermal conductivity of ceramics.The hardness of chopped silicon carbide fiber reinforced SiC-Si₃N₄ matrix composites was 50HRB,which was higher than that of 32HRB without fibers.The thermal conductivity of SiC-Si₃N₄ matrix composites reinforced by chopped BN fiber is8.145 W/?m·k?,while the thermal conductivity is only 3.021W/?m·k?when fiber is not added.