预氧化处理对反应烧结碳化硅微观结构和弯曲强度的影响

本文提出了一种简单有效的预氧化处理方法,用来强化反应烧结碳化硅(RBSC),研究了800~1 300 ℃预氧化处理对其微观结构和力学性能的影响,探究了含不同尺寸压痕裂纹的材料在氧化前后残余弯曲强度的变化规律。结果表明,随着氧化温度的升高,RBSC的室温强度和Weibull模数均存在先下降后上升,然后再下降的趋势,主要原因是不同温度氧化后的RBSC表面形貌不同。在1 200 ℃下预氧化2 h,RBSC的弯曲强度和Weibull模数都明显变大,强度提升了19.9%,Weibull模数由7.3提升到11.8。然而,800 ℃低温氧化不完全和1 300 ℃高温氧化反应过于强烈均会导致弯曲强度和Weibull模数下降。在最优氧化条件(1 200 ℃氧化2 h)下,含压痕裂纹(载荷20 N)的RBSC试样的残余弯曲强度在氧化后由201.1 MPa提高到324.2 MPa,强化机理是高温氧化生成的SiO₂能够消除材料表面缺陷和微裂纹。

Effect of Pre-Oxidation on Microstructure and Flexural Strength of Reaction Boned Silicon Carbide

In this paper, a simple and effective pre-oxidation treatment method is proposed to strengthen reaction boned silicon carbide (RBSC). The effects of different temperature oxidation treatments from 800 ℃ to 1 300 ℃ on its microstructure and mechanical properties were investigated. Changes of residual flexural strength of materials with different sizes of pre-cracks before and after oxidation were also investigated. The results show that with the increment of the oxidation temperature, the strength and Weibull modulus of RBSC have a tend to first decrease, then increase, and then decrease again, mainly due to the different surface morphologies after oxidized at different temperatures. The flexural strength and Weibull modulus of RBSC increase significantly after pre-oxidized at 1 200 ℃ for 2 h, the strength increase by 19.9%, and the Weibull modulus increase from 7.3 to 11.8. However, both the incomplete oxidation at low temperature of 800 ℃ and the excessively strong oxidation reaction at high temperature of 1 300 ℃ lead to the decrease of flexural strength and Weibull modulus. Under the optimal pre-oxidation condition at 1 200 ℃ for 2 h, the residual flexural strength of RBSC specimen with indentation cracks (load of 20 N) increase from 201.1 MPa to 324.2 MPa after oxidation. The strengthening mechanism is that the SiO₂ generated by high temperature oxidation eliminates the microcracks and defects of the material on the surface.