碳化硅陶瓷因其强度高、硬度高、热导率高、高温性能稳定等优异性能，被广泛应用在重工业、核能、航空航天等领域。但纯碳化硅陶瓷难以满足高比强度、高韧和高强之要求。本文通过无压烧结制备SiC/B₄C复合陶瓷试样，研究了B₄C添加量、粘结剂、烧结制度对试样力学性能及微观形貌影响规律，以此优化配方和制备工艺，并在此基础上研究了β-SiC补强增韧机理，制备出了高温性能优异的SiC/B₄C复合陶瓷。

配方优化研究表明：当B₄C添加量为20%时，B₄C颗粒弥散分布，对SiC晶粒形成钉扎作用，其断裂韧性和抗弯强度较纯碳化硅陶瓷分别提高了4.57%和9.50%；而添加量超过20%时，B₄C形成连续相，硬度增加，但强韧性下降。以酚醛树脂（PF）和聚乙烯醇（PVA）作粘结剂时，当PF:PVA比例为3:2时，造粒粉振实密度最高为1.42 g/cm³，致密度达95.45%，断裂韧性值高达3.15 MPa·m^1/2。

烧结制度研究表明：保温温度低于2100 ℃，试样致密性差，整体性能低；2100 ℃时晶粒细小，试样的断裂韧性和抗弯强度分别为2.97 MPa·m^1/2和276 MPa；2250 ℃时，试样中SiO₂增加，出现了B₂O₃特征衍射峰，晶粒过分长大，断裂韧性和抗弯强度分别为2.07 MPa·m^1/2，233 MPa（下降了30.2%和13.4%）；在2100℃时保温120 min时，试样的综合性能最好，抗弯强度最高为312MPa，断裂韧性为3.08 MPa·m^1/2，硬度为27.46 GPa。

        添加β-SiC发现：当β-SiC加入量为0~40%时，β-SiC主要向6H-SiC转变，晶型转变导致体积膨胀，有利于试样的致密化，同时晶体中形成的少量微裂纹源有利于消耗裂纹扩展的能量，提高了试样断裂韧性；当β-SiC加入量为40%时，试样的致密度提高到97.60%，力学性能最佳，硬度、抗弯强度和断裂韧性分别为28.58 GP a、3.88 MPa·m^1/2和342 MPa。β-SiC加入量为60%~80%时，主要向4H-SiC转变，晶体结构被破坏，微裂纹数量过多，强度和韧性变差。

Silicon carbide ceramics are widely used in heavy industry, nuclear energy, aerospace and other fields due to their excellent properties such as high strength, high hardness, high thermal conductivity, and stable high-temperature performance. But pure silicon carbide ceramics are difficult to meet the requirements of high specific strength, high toughness and high strength. In this paper, the SiC/B₄C composite ceramic samples were prepared by pressureless sintering. The influence of the amount of B₄C, binder, and sintering system on the mechanical properties and microscopic morphology of the samples was studied in order to optimize the formulation and preparation process. The mechanism of β-SiC reinforcement and toughening was studied, and SiC/B₄C composite ceramics with excellent high temperature properties were prepared.

The formulation optimization study shows that when the amount of B₄C added is 20%, the B₄C particles are dispersed and form a pinning effect on the SiC grains, and their fracture toughness and flexural strength are increased by 4.57% and 9.50% respectively compared to pure silicon carbide ceramics; and When the addition amount exceeds 20%, B4C forms a continuous phase and the hardness increases, but the strength and toughness decrease. When using phenolic resin (PF) and polyvinyl alcohol (PVA) as a binder, when the ratio of PF:PVA is 3:2, the tap density of the granulated powder is 1.42 g/cm³, the density is 95.45%, and the fracture The toughness value is as high as 3.15 MPa·m^1/2.

The sintering system research shows that: the sinering temperature is lower than 2100 ℃, the sample has poor compactness and low overall performance; the grain size is small at 2100 ℃, the fracture toughness and bending strength of the sample are 2.97 MPa·m^1/2 and 276 MPa; At 2250 ℃, the SiO₂ in the sample increased, and the characteristic diffraction peak of B₂O₃ appeared. The grains grew excessively. The fracture toughness and flexural strength were 2.07 MPa·m^1/2 and 233 MPa, respectively (a decrease of 30.2% and 13.4%); When kept at 2100℃ for 120 minutes, the comprehensive performance of the sample is the best, the highest bending strength is 312 MPa, the fracture toughness is 3.08 MPa·m^1/2, and the hardness is 27.46 GPa.

Adding β-SiC found that when the amount of β-SiC added is 0~40%, β-SiC mainly transforms to 6H-SiC, and the crystal form transformation leads to volume expansion, which is conducive to the densification of the sample, and a small amount formed in the crystal The micro-crack source is beneficial to consume the energy of crack propagation and improve the fracture toughness of the sample; when the amount of β-SiC added is 40%, the density of the sample increases to 97.60%, the mechanical properties are the best, the hardness, bending strength and The fracture toughness was 28.58 GP a, 3.88 MPa·m^1/2 and 342 MPa, respectively. When the amount of β-SiC added is 60%~80%, it mainly changes to 4H-SiC, the crystal structure is destroyed, the number of micro cracks is too large, and the strength and toughness become poor.