3D-C/SiC复合材料的高温拉伸性能

Tensile Performance of 3D-C/SiC Composites at High Temperature

研究了 3D C/SiC复合材料从室温到 15 0 0℃真空条件的拉伸性能。试验材料用T30 0碳纤维编织为三维四向编织体 ,编织角为 2 2° ,用CVI法在 95 0℃～ 10 0 0℃沉积热解碳界面层、SiC基体。最终得到纤维体积分数约为4 0vol%、热解碳界面层厚度约 0 .2 μm和空隙率为 17vol%的复合材料 ,表面SiC涂层厚度为 5 0 μm。试验在超高温拉伸试验机上进行 ,真空度为 10 -3 Pa ,夹头位移速率为 0 .5 95mm/min。结果表明 ,拉伸应力 应变曲线是非线性的 ,大部分拉伸曲线基本由三段折线组成 ,对应着三段模量。第一阶段的模量和基体裂纹饱和应力对应的应变εsa 基本不随温度的升高而改变 ;第二和第三阶段的模量、损伤开始应力σmc、基体裂纹饱和应力σsa、断裂应力σf 和损伤开始应变εmc随温度有相似的变化规律 ,即随温度升高而增加 ,在 110 0℃ ～ 130 0℃范围内出现最大值 ,尔后随温度增加而下降 ;但是断裂应变的变化规律正好与此相反。试样机械加工后 ,由于残余应力部分得到松弛 ,并去除了表面SiC涂层开裂后引起的应力集中 ,因此材料断裂强度和断裂应变明显升高。高温和室温的拉伸断裂应变小于0 .6 % ,不能有效地松弛材料切口处的应力集中。测量了拉伸过程中试样的电阻相对变化率 。

The tensile mechanical performance of 3D-C/SiC from room temperature to 1500 ℃ have been investigated. The preform fabricated with T300 carbon fibers which are woven into 3-dimemsion 4-direction structure with 22 weaving angles. CVI method deposited pyrocarbon and SiC matrix at 950℃～1000 ℃. The composites contained 40 vol% fiber and 17 vol% porosity. The thickness of the pyrocarbon on fiber is about 0.2 μm and SiC coating thickness 50 μm on specimens surface .Experiments were carried out at super-high-temperature tensile machine with 10 -3Pa vacuum degree and 0.595 mm/min clamp moving speed. Result shows that tensile stress-strain curve is not linear, most of them consist of 3 zigzags corresponding to different modulus. The first stage′s modulus E 1, matrix crack saturate strain ε saare primarily constant with the increment of the temperature. The second and third stage′s modulus E 2and E 3, matrix start crack stress σ mc, crack saturate stress σ sa, fracture stress σ fand matrix start crack strain ε mchave the same tendency, all of those increase as the temperature elevated and have maximum value at 1100 ℃～1300 ℃, but decrease when temperature is higher than 1300 ℃. The fracture strain ε f is at opposite tendency. After grinding specimen, due to the residual stress relaxation and ruling out the stress concentration influence of surface SiC cracking, the tensile fracture strength and strain have increased obviously. All specimens′ fracture strain are less than 0.6%, it can not relax stress concentration at notch. In tensile procedure, curve′s changeable tendency of the electrical resistance relative variation versus. Load resemble to that of the tensile stress-strain curve.