SiCw/BAS复合材料的显微结构及力学性能的研究

本文采用热压烧结法制备出致密的SiC_w增强BAS玻璃陶瓷基复合材料．结果表明,BAS基体晶化后获得以钡长石为主晶相和莫来石为次晶相的复相BAS玻璃陶瓷．晶须的加入对BAS基体有显著的强韧化效果,加入30vol％SiC_w可使材料的室温抗弯强度和断裂韧性分别由基体的156MPa和1．40MPa·m^1/2提高到356MPa和4．06MPa·m^1/2．TEM观察结果表明,晶须／基体界面结合良好,无界面反应物和非晶层的存在．断口形貌和压痕裂纹扩展路径的SEM观察结果表明,复合材料的主要增韧机制为裂纹偏转、晶须的拔出和桥接．     

Csf/BAS玻璃陶瓷复合材料的制备及其力学性能研究

为了提高钡长石(BAS)玻璃陶瓷的力学性能,采用轧膜成型、热压烧结方法制备出纤维分布均匀的致密短碳纤维增强BAS玻璃陶瓷基复合材料(Csf/BAS).采用X射线衍射分析,扫描电子显微镜、透射电子显微镜观察及三点弯曲法与单边开口梁法研究了纤维含量对复合材料组织及力学性能的影响.研究表明:Csf对BAS玻璃陶瓷有良好的强韧化效应.体积分数为30%Csf/BAS复合材料的室温抗弯强度及断裂韧性分别为255 MPa和3.45 MPa.m1/2,其主要的韧化机制为裂纹偏转、纤维的拔出与桥接.用摩尔分数25%Sr代替Ba实现了基体的六方→单斜相的完全转变,进一步提高了复合材料的力学性能.     

ZrB2颗粒增韧B4C陶瓷的原位合成

采用机械混合法无压烧结原位合成ZrB2/B4C陶瓷复合材料,研究了ZrB2含量对复相陶瓷主要性能的影响,分析了复相陶瓷的增韧机理.结果表明,当ZrB2的体积分数为16%时,相对密度最大约为94%,维氏硬度为39.5 GPa,抗折强度为320 MPa,断裂韧性为3.10 MPa·m1/2.由B4C基体和ZrB2颗粒热膨胀系数不匹配引起的裂纹偏转是ZrB2/B4C复相陶瓷增韧的主要原因.     

添加β-Si3N4棒晶对氮化硅陶瓷力学性能的影响

将由自蔓延燃烧合成法制备的β—Si3N4棒晶加入到α-Si3N4起始原料中,研究了热压烧结氮化硅陶瓷力学性能的变化.随棒晶添加量的增加,材料的韧性提高,抗弯曲强度下降.与不加棒晶相比,加入8wt％的β-Si3N4棒晶可使陶瓷的韧性从4.0MPa·m1/2提高到6.7MPa·m1/2.断口形貌和压痕裂纹的显微结构观察表明,韧性的提高源于长柱状晶粒的拔出和裂纹的偏转.     

基体合金种类对SiCw／Al复合材料拉伸性能的影响

对SiCw/LD2、SiCw/LC9复合材料进行了热挤压加工并沿其纵向进行了拉伸对比试验。结果表明:SiCw/LD2的抗拉强度为590MPa,而SiCw/LC9复合材料的抗拉强度高达750MPa。SEM分析发现,上述两种复合材料均为切应力作用下的韧窝形断口,但SiCw/LD2的断口有明显的晶须拔出。低于临界长径比的晶须被拔出是SiCw/LD2断裂的主要形式;高于临界长径比的晶须被拉断是SiCw/LC9断裂的主要形式;基体合金的不同导致了复合材料具有不同的晶须临界长径比,这也是SiCw/LC9复合材料较SiCw/LD2复合材料有更高抗拉强度的根本原因。     

SiCw增强B4C陶瓷复合材料的制备与性能研究

以Si粉为烧结助剂,采用真空热压烧结工艺制备B4C-SiCw陶瓷复合材料.将不同含量的SiCw与B4C和Si混合,制得的复合粉体在1850℃、60MPa下真空热压烧结,研究了SiCw含量对复合材料力学性能的影响,并借助X射线衍射、扫描电镜分析了复合材料的物相组成和微观结构.研究结果表明:分散处理后的SiCw可以有效地提高复合材料的力学性能,当晶须含量为10％(质量分数)时,弯曲强度和断裂韧性达到最大值,分别为468 MPa和5.70 MPa·m1/2.复合材料中SiCw的拔出使复合材料的弯曲强度及断裂韧性得以提高.     

添加TiB2对Ti-B-C复相陶瓷性能的影响

在1800℃,35MPa的条件下热压烧结B4C/Ti(摩尔比1:3),得到了TiB2/TiC陶瓷材料.材料的弯曲强度和断裂韧性分别为454MPa和8.4MPa·m1/2.当材料中添加不同含量的TiB2时,发现显微结构中有棒晶出现,经X射线分析为TiB2.添加5%(体积比)TiB2时,复合材料的弯曲强度和断裂韧性分别高达540MPa和10.8MPa·m1/2;而添加20%TiB2时,复合材料的弯曲强度和断裂韧性下降到357MPa和8.19MPa·m1/2.经扫描电镜观察,添加5%TiB2的材料中棒晶数量明显,长度在10～40μm,气孔较少;而20%TiB2材料中的棒晶发育不充分,数量较少,并且存在大量的气孔.这说明一定数量的添加剂可以促进棒晶的生长和发育.原位形成的棒晶,使材料起到了自增韧的效果,大幅度提高了复合材料的力学性能。     

Al_6Si_2O_(13)晶须和TiC颗粒复合强化多孔Al_2TiO_5基复合材料

以γ-AlOOH和TiO_2为原料,添加不同质量分数SiC晶须(SiCw),采用无压反应烧结法制备多孔(Al_6Si_2O_(13)+TiC)/Al_2TiO_5复合材料,分析了SiCw质量分数对(Al_6Si_2O_(13)+TiC)/Al_2TiO_5复合材料孔隙率和抗压强度的影响,讨论了SiCw的强化机制。结果表明:不添加SiCw时,产物主要为Al_2TiO_5和少量Al_2O_3,还有少量未反应的TiO_2;加入SiCw之后,还形成了Al_6Si_2O_(13)和TiC相,TiC和Al_6Si_2O_(13)分别以规则颗粒状和晶须形态存在于Al_2TiO_5基体中。TiC颗粒与Al_6Si_2O_(13)晶须通过细化显微组织、裂纹偏转和晶须桥连机制,起到协同强化作用。SiCw的添加使孔隙率和抗压强度同时大幅度提高,随着SiCw质量分数的增加,(Al_6Si_2O_(13)+TiC)/Al_2TiO_5复合材料孔隙率降低,抗压强度提高的速率减小,当SiCw的质量分数为7.2%时,抗压强度最高,达到301.81 MPa。     

新型复相陶瓷刀具材料的研制及切削可靠性研究

研制成功了国内外尚属空白的新型陶瓷刀具材料——碳化硅晶须(SiCw)增韧和碳化硅颗粒(SiCp)弥散补强Al_2O_3陶瓷刀具材料JX-2系列,其硬度为93.5～94.8HAA,抗弯强度为650～750MPa,断裂韧性为7.5～8.5MPa·m~(1/2),并且具有导热性好和成本低等优点。 对原料组分和热压烧结工艺进行了优化设计;证实了晶须和颗粒具有增韧补强的协同作用,根据能量耗散理论,建立了晶须桥联、拔出、裂纹偏转和微裂纹增韧的理论模型;详细研究了该陶瓷刀具材料的界面力学行为及其与材料力学性能的关系,研究了材料的界面作用机理;建立了Al_2O_3/SiCw/SiCp系陶瓷刀具材料界面结合强度L_f和断裂韧性K_(IC)的关系模型,据此可以实现复合陶瓷刀具材料的组分优化设计,缩短复合材料的研制时间。 深入研究了新型复相陶瓷刀具材料的切削性能及其磨损破损机理,并对刀具热磨损和热破损的机理进行了强激光热模拟;研究了该刀具材料力学性能、界面结合强度和刀具破损寿命的随机性,它们的分布规律均较好地服从威布尔分布,首次提出了用界面结合强度评价JX-2陶瓷刀具破损可靠性的新方法。     

SiCw/MB15镁基复合材料超塑性

对SiCw/MB15镁基复合材料的超塑性变形行为进行了研究.结果表明:SiCw/MB15镁基复合材料在340℃,应变速率为1.66×10-2s-1变形条件下,断裂延伸率达到200%,应变速率敏感性指数m为0.35;超塑性变形后基体中出现了许多空洞和近似平行于断口的细小裂纹;晶须在基体中随机排布,失去了变形前轴向平行于挤压方向的特点,说明基体晶粒在变形中发生了滑动.     

Microstructure and mechanical properties of barium aluminosilicate glass-ceramic matrix composites reinforced with SiC whiskers

BAS glass-ceramic composites reinforced with different volume fractions (0, 10, 20, 30, 40 vol%) of SiC whiskers were successfully fabricated by a hot-pressing method. The microstructure, whisker/matrix interface structure, phase constitution and mechanical properties of the composites have been systematically studied by means of SEM, TEM, XRD techniques as well as three-point bending tests. It was demonstrated that the incorporation of SiC whiskers could significantly increase the flexural strength and fracture toughness of BAS glass-ceramic matrixes. The celsian seeds can effectively promote the hexacelsian-to-celsian transformation in BaAl₂Si₂O₈. The active Al₂O₃ added to the BAS matrix obviously reduced the amount of SiO₂ in the matrix and formed needle-like mullite. The high temperature strengths of the composites were also investigated.     

CVD SiC fiber-reinforced barium aluminosilicate glass—ceramic matrix composites

Unidirectional CVD SiC (SCS-6) monofilament reinforced BaOAl₂O₃2SiO₂(BAS) glass—ceramic matrix composites have been fabricated by a tape lay-up method followed by hot pressing. The glass matrix flows around fibers during hot pressing resulting in nearly fully dense (95–98%) composites. Strong and tough composites having first matrix cracking stress of 250–300 MPa and ultimate flexural strength as high as 900 MPa have been obtained. Composite fracture surfaces showed fiber pullout with no chemical reaction at the fiber/matrix interface. From fiber push out, the fiber/matrix interfacial debond strength and the sliding frictional stress were determined to be 5.9 ± 1.2 MPa and 4.8 ± 0.9 MPa, respectively. The fracture surface of an uncoated SiC (SCS-0)/BAS composite also showed fiber/matrix debonding, fiber pullout, and crack deflection around the fibers implying that the SiC fibers may need no surface coating for reinforcement of the BAS glass-ceramic. Applicability of micromechanical models in predicting the first matrix cracking stress and the ultimate strength of these composites has also been examined.     

Fabrication,characterization and mechanical properties of SiC-whisker-reinforced Y-TZP composites

The microstructure and mechanical properties of hot-pressed yttria-stablized tetragonal zirconia polycrystals (Y-TZP) reinforced with up to 30 vol % SiC whiskers were investigated. The homogeneously dispersed and fully dense SiC whisker/Y-TZP composites were fabricated by wet-mixing the constitutents and uniaxially hot-pressing the resulting powder. The grain size of the matrix depended on the whisker volume fraction and the hot-pressing temperature. The significant increase of fracture toughness of about MPa m^1/2 at 10 Vol % SiC and a small increase in strength were achieved by uniformly dispersing the whiskers in the Y-TZP matrix. Fracture surfaces revealed evidence of toughening by the mechanisms of crack deflection, pullout, and crack bridging by the whiskers and also a phase transformation of ZrO₂. The observed increase in the fracture toughness of Y-TZP due to the addition of SiC whiskers was correlated with existing models of toughening mechanisms. Good agreement was achieved between the theoretical predictions and the experimental toughness values, obtained from the Y-TZP/SiC_w composites.     

增强体含量对SiC_W/SiC层状陶瓷复合材料强韧性的影响

采用流延-化学气相渗透(TC-CVI)工艺制备SiC晶须(SiC_W)/SiC层状陶瓷复合材料,研究了SiC_W含量对层状陶瓷复合材料力学性能和微观结构的影响,探讨了SiC_W/SiC层状陶瓷复合材料的强韧化机制。结果表明:TC-CVI工艺能够有效提高复合材料中晶须含量(40vol%),减少制备过程对晶须损伤,所制备的SiC_W/SiC层状陶瓷复合材料具有合适的层内及层间界面结合强度。随着SiC_W含量增加,层状陶瓷复合材料的密度和力学性能均有明显提高。含40vol%晶须的SiC_W/SiC层状陶瓷复合材料的密度、弯曲强度和断裂韧性均比含25vol%晶须的分别提高了8.4%、30.8%和26.7%。断口形貌中能够观察到层间及层内的裂纹偏转,层内的裂纹桥接和晶须拔出等,这些为主要的增韧机制。高含量SiC_W及合适的层间和层内界面结合强度,对提高SiC_W/SiC层状陶瓷复合材料强韧性有明显作用。     

Microstructure and mechanical properties of BAS/SiC composites sintered by spark plasma sintering

High-density BAS/SiC composites were obtained from β-SiC starting powder by the spark plasma sintering technique. Various physical properties of the BAS/SiC composites were investigated in detail, such as densification, phase analysis, microstructures and mechanical properties. The results demonstrated that the relative density of the BAS/SiC composites reached over 99.4% at 1900 °C. The SiC grains were uniformly distributed in the continuous BAS matrix which is probably because of complete infiltration of the SiC particles in BAS liquid-phase formed during sintering. The pull-out of SiC particles, crack deflection and bridging were observed as the major toughening mechanism. The flexural strength and fracture toughness of the BAS/SiC composites sintered at 1900 °C were up to 560 MPa and 7.0 MPa·m^1/2, respectively.     

Preparation and Characterization of BAS Reinforced with SiC Platelets

1. IntroductionOne of the primary objects of NASA high temperature engine materials program (HITEMP) is thedevelopment of ceramic-matrix composites for employmellt in the hot section components of advancedaeropropulsion systems of future. Glass and glasscertalcs having typically low elajstic modulus allowtrue reinforcement with high modulus ceramic materials such as short fibers, whiskers, platelets. Therefore,parts of the effort including the development of glassceramic matrix composites …     

碳化硅晶须补强氧化铝复合材料的制备及其力学性能

本论文利用商用γ-Al₂O₃粉体和上海硅酸盐所制备的碳化硅晶须,通过热压工艺来制备碳化硅晶须补强氧化铝复合材料．当晶须含量为30vol％时,室温下复合材料的抗弯强度为812±38MPa,断裂韧性为8．8±0．1MPa·m^1／2;在1200℃、Ar气氛下,分别为560±61MPa和6．1±0．4MPam^1／2．在氮气氛下,由于晶须的损伤易导致材料的力学性能下降．添加剂可降低复合材料的烧结温度,但不利于其力学性能．显微结构观察发现,不同温度下,AS复合材料的增韧机理有变化．     

An aluminum borate whisker-reinforced aluminum matrix composite with high plasticity

A pure aluminum matrix composite reinforced by ZnAl₂O₄-coated Al₁₈B₄O₃₃ whiskers was fabricated by a squeeze casting technique. The effect of ZnAl₂O₄ coating content on the wettability between whiskers and matrix, the ultimate tensile strength and elongation to fracture of the composite were investigated. The results show that the interface wettability and the ultimate tensile strength increase with increasing the coating content. The coating content remarkably affects the elongation to fracture of composites. When the mass ratio of ZnO and ABOw is 1:30, the elongation to fracture of the composite can reach 7.9% at room temperature.     

热挤压对SiCW/Al复合材料塑性的影响

对ＳｉＣｗ／Ａｌ复合材料进行了热挤压，并用ＳＥＭ对拉利断口进行了观察和分析。研究结果表明，抗挤压能够明显地提高ＳｉＣｗ／Ａｌ复合材料的塑性。热挤压导致复合材料塑性提高的原因是由于热挤压变形造成基体塑性的提高，以及晶须的折断和沿挤压方向定向排列的结果。