【作者】 侯赵平；

【导师】 叶枫；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2009， 硕士

【摘要】 本文针对c-BN和B₄C难烧结致密化,通过SiAlON生成过程产生的液相来降低c-BN的烧结温度,在较低的温度下实现c-BN的致密化,对于B₄C材料,通过添加Si在高温产生液相来实现B₄C的致密化,采用放电等离子烧结法制备c-BN/SiAlON和含Si的B₄C基复合材料。系统研究了成份和烧结工艺对复合材料力学性能和摩擦磨损性能的影响,探讨了复合材料的强化及磨损机理。研究结果表明,采用粒径为0.5¹μm的c-BN,c-BN/Y-α-SiAlON和c-BN/Yb-α-SiAlON复合材料的在1550℃/50MPa/5minSPS烧结过程中,75wt%以上的c-BN发生c-BN→h-BN转变,c-BN加入抑制α-SiAlON的形成,且随着c-BN含量的增加,抑制作用增大。当采用粒径为2⁴μm的c-BN时,c-BN在液相烧结过程中未发生相变,c-BN粒径为2⁴μm的20wt%c-BN/Yb-α-SiAlON复合材料的硬度达到了21.586GPa。采用粒径为2⁴μm的c-BN时,c-BN/β-SiAlON复合材料的力学性能随着c-BN含量的增加先增加后减小。10wt%c-BN/β-SiAlON维氏硬度和抗弯强度达到最大值,达到了15.4GPa和432MPa。随着c-BN含量的继续增加,复合材料力学性能下降,主要是由于c-BN增加降低了材料的致密度。SEM分析表明:复合材料的力学性能提高的主要原因是:c-BN的加入阻碍裂纹扩展导致裂纹偏转。在载荷为20N的干摩擦下, 20wt%c-BN/Yb1510E2复合材料,与Yb1510E2相比,摩擦系数和磨损率都升高,主要是由于Yb1510E2陶瓷为摩擦化学反应和粘着磨损;而20wt%c-BN/Yb1510E2主要为表面疲劳磨损和磨粒磨损。对于磨损方式主要为表面疲劳磨损和磨粒磨损的c-BN/β-SiAlON复合材料摩擦系数随着c-BN含量的增加而减小,而磨损率随着c-BN含量的增加而增大,这主要是由于c-BN与基体结合弱,在摩擦磨损的进行,c-BN含量高的试样磨损量大,与摩擦副的接触面积也大,摩擦系数随之会降低。添加Si粉可以显著提高B₄C的致密度和力学性能,当Si含量为8wt%时,在1800℃/50MPa/5minSPS烧结后,相对密度可以达到99.78%,维氏硬度和抗弯强度达到最高,分别为41.83GPa,654MPa。随着Si含量的增加,硬度有所下降,主要是由于生成的SiC硬度低于B₄C硬度。添加Si后复合材料力学性能提高的主要原因是:①致密度的提高;②晶粒细化;③S iC的韧化作用。XRD分析表明,含Si试样的B₄C晶格常数增大,这是由于Si取代B₄C结构中C-B-C原子链的C原子并且Si可能会进入B₄C晶体结构的空隙位置,而且置换出来的C会与Si继续反应生成SiC相。在载荷为20N的干摩擦下,Si含量为4wt%、6wt%、10wt%的B₄C复合材料的摩擦系数在整个试验过程中一直以较大的幅度波动,其波动范围为0.3⁰.6,这主要是由于随着摩擦磨损的进行,润滑膜和氧化膜相互交替;Si含量为8wt%的B₄C复合材料的摩擦系数曲线在整个试验过程比较平滑,其摩擦系数为0.2;且磨损率最低,为1.75109×10^-6mm^-3/N·m,这是由于在摩擦磨损过程中生成了H3BO3和Si（OH）4润滑膜。根据摩擦系数和磨损表面分析可知,纯B₄C和含Si的B₄C复合材料在室温下干磨损机理为摩擦化学反应和化学诱导断裂。更多还原

【Abstract】 To improve the sinterability of cubic Boron Nitride and Boron carbide, SiAlON and Si were added into c-BN and B₄C, respectively, to supply transient liquid phase during the sintering. c-BN/SiAlON and B₄C ceramic composites with high density were fabricated at low sintering temperature by SPS. The effect of composition and preparation process on the mechanical and wear properties of composites, the toughening mechanism and wear mechanism were studied.When the particle size of c-BN which used is 0.5¹μm, c-BN/α-SiAlON composites were prepared by spark plasma sintering. Over 70% c-BN had transformed to h-BN during the sintering at 1550℃for 5min. The added c-BN inhibited the formation ofα-SiAlON, and the role of inhibition enhanced with the increasing of the content of c-BN. On the contrary, when using the larger size of c-BN （2⁴μm）, c-BN didn’t transforme to h-BN during the same sintering condition. The obtained Vickers hardness of the 20wt%c-BN/Yb-α-SiAlON composites could reach 21.586GPa.The Vickers hardness and the flexural strength of the c-BN /β-SiAlON composites with the c-BN size of 2⁴μm increased with the increasing c-BN content. The composites containing 10wt% c-BN possessed the maximum mechanical properties. The HV and flexural strength are 15.4GPa and 432MPa, respectively. It is attributed to the crack deflection caused by c-BN particles. Subsequently, the mechanical properties decreased with the increasing c-BN content due to the low density.Wear tests were carried out under non-lubricated condition with load of 20N. Compared with the Yb1510E2, the 20wt%c-BN/Yb1510E2 composite showed the appreciably bigger friction coefficient and wear rate. It is due to the different wear modes. The wear modes of the Yb1510E were tribochemical wear and adhesive wear, the wear modes of the 20wt%c-BN/Yb1510E2 were surface fatigue wear and abrasive wear. The predominant modes c-BN/β-SiAlON composites are surface fatigue wear and abrasive wear, their the friction coefficient decreased with the increasing of the content of c-BN, in contrast, the wear rate of the c-BN/β-SiAlON composites increased with the increasing of the content of c-BN. It is due to the weak bonding strength between c-BN and the matrix, which resulte in the higher wear volume for the composites with higher c-BN content. The higher wear colume also increased the area of the composites contacted with the friction pair, hence decrease the friction coefficient.The density and mechanical properties of B₄C composites increased with the increasing silicon content. The B₄C composites with 8wt% Si could obtain the highest relative density and mechanical properties in the investigated B₄C based composites. Its Vickers hardness and the flexural strength are 41.83GPa, 654MPa, respectively. Subsequently, the mechanical properties decreased with the increasing Si content, probably due to the Hv of the SiC is lower then the Hv of the B₄C. It is concluded that the improvement of mechanical properties is due to:①the high relative density;②grain refinement;③grain boundary strengthening and crack deflection caused by SiC particles. The phase composition was studied by the means of XRD. The results showed that the lattice parameters of boron carbide for the specimens containing Si were bigger than those for pure boron carbide specimen. It is due to the fact that silicon solid solute into by replacing the carbon atoms belong to C-B-C atomic chain and solute into the interstices in the B₄C structure as interstitial atoms, leading to the increase of the lattice parameters, and the SiC was synthesized by in-situ reaction between the carbon atoms replaced by the Si atoms and Si.Wear tests on B₄C composites were carried out under non-lubricated condition with load of 20N, the results show that the friction coefficient of the composites with the Si content of 4,6,10wt% were fluctuating between 0.3 and 0.6 as function of the sliding distance. It is due to the alternate of lubricating film and oxidized film. When the Si content was 8wt%, the curve of the friction coefficient was gentle and minimum wear rate could be obtained, its friction coefficient and wear rate was 0.2, 1.75109×10^-6mm^-3/N·m, respectively. Because of the formation of the H3BO3 and Si（OH）4. The predominant wear mode of pure B₄C and the B₄C composites was tribochemical wear.更多还原