化学镀碳纤维增强羟基磷灰石复合材料的性能

通过化学镀方法,在碳纤维表面分别镀上Ni和Cu+Ni镀层,以这种表面改性碳纤维与羟基磷灰石陶瓷复合,制备表面改性碳纤维增韧增强羟基磷灰石复合材料,研究各种碳纤维的含量对复合材料的抗弯强度、断裂韧度、尺寸变化率和孔隙率的影响。结果表明,表面改性碳纤维可以显著提高材料的性能,尤其是铜镍复合镀碳纤维的效果更好,其断裂韧度可达基体断裂韧度的2.5倍,抗弯强度可达基体抗弯强度的3.4倍,增韧增强后的复合材料的尺寸和孔隙率变化不大。     

TiCp/3Al2O32SiO2复合材料的强韧化与低温冷处理

研究了TiC粒径与TiCp/3Al2O32SiO2基复合材料的横向断裂强度和断裂韧度之间的关系,探讨了低温冷处理对复合材料性能的影响.研究结果表明,添加适宜粒径的TiC颗粒能够提高3Al2O32SiO2材料的横向断裂强度和断裂韧度,TiC颗粒增韧的粒径范围为14～26μm;增强的粒径范围为＜14μm.低温冷处理不仅可以进一步提高复合材料的强度和韧性,而且可以改变增韧的粒径范围,使增韧和增强的粒径范围部分重合,这为正确进行材料的强韧化设计和合理制定强韧化工艺提供了依据.     

熔石英基复合材料性能的研究

用热压烧结方法制得碳纤维与氮化硅颗粒复合补强增韧熔石英基复合材料,其熔石英基体保持非晶态,只有少量鳞石英析出。材料的抗弯强度达到１１３．７ＭＰａ,断裂韧性为１．５３ＭＰａ．ｍ＾１／２,补强增韧效果明显。     

加压烧结工艺对碳纤维增强TiC复合材料力学性能的影响

采用真空加压烧结工艺制备了 2 0 % (体积分数 )短碳纤维增强TiC复合材料 (Cf/TiC) ,研究了加压烧结温度、烧结时间和烧结压力对力学性能的影响。烧结温度由 190 0℃提高到 2 10 0℃ ,复合材料的横向断裂强度和断裂韧度分别由 387MPa和 4 14MPa·m1/2 提高到 5 93MPa和 6 87MPa·m1/2 ,当烧结温度再提高到2 2 0 0℃ ,强度和韧性反而有所下降。加压压力由 2 0MPa提高到 35MPa时 ,横向断裂强度和断裂韧度分别由5 5 7MPa、6 41MPa·m1/2 提高到 6 0 2MPa和 6 92Mpa·m1/2 。当保温时间由 0 5h提高到 2h时 ,复合材料的横向断裂强度和断裂韧度分别由 5 6 8MPa、6 5 3MPa·m1/2 提高到 5 93MPa和 6 87MPa·m1/2 。Cf/TiC复合材料合适的烧结工艺是在 2 10 0℃、30MPa下烧结 1h ,所制备的材料的相对密度为 97 6 % ,弹性模量为 416GPa ,横向断裂强度为 5 93MPa ,断裂韧度为 6 87MPa·m     

SiC和Ti(C,N)颗粒弥散陶瓷材料的力学性能与微观结构

采用热压工艺制得SiC和Ti(C,N)双相弥散Al2O3基陶瓷复合材料，该材料具有较高的抗弯强度、断裂韧度和硬度。研究表明：只有在合适的热压工艺和组分条件下才能获得良好的微观结构与力学性能。该陶瓷复合材料的增韧机制主要是裂纹桥联、裂统偏转和颗粒拔出。此外，大量孪晶和位错的存在在对材料的增韧补强也有所贡献。     

形状记忆晶相强韧化Ti基非晶复合材料的组织和力学性能

设计了具有形状记忆效应和较强非晶形成能力的(Ti50Ni50-yMy)100-xCux合金,采用悬浮熔炼-水冷铜模吸铸法,通过组元调控制备具有组织连续梯度的形状记忆合金/非晶基复合材料,并研究其组织和力学行为。结果表明:B2-Ti(Ni,Cu)过冷奥氏体相和B19'-Ti(Ni,Cu)热诱发马氏体相析出在铸态非晶基体上,加载断裂应力诱发马氏体相变,马氏体衍射峰比铸态增强且马氏体择优取向。凝固过程的温度梯度决定了复合材料的组织梯度,由表及里,主要为非晶相、马氏体相和奥氏体树枝晶相。加载时形变诱导相变对非晶基体同时增强增韧,复合材料的综合力学性能优异,以连续屈服和强烈的加工硬化为主要特征,(Ti0.5Ni0.48Co0.02)80Cu20断裂强度高达2464 MPa,塑性应变达到13.6%。复合材料断裂表面存在大量密集均匀的脉络纹,析出相周围形成的多重剪切带和玻璃基体上剪切带,扩展方向分别与加载方向呈90°和45°角。     

无压烧结制备透辉石增韧补强氧化铝基结构陶瓷材料

采用温度梯度无压烧结工艺制备了透辉石增韧补强Al2O3基结构陶瓷材料,探讨了其烧结致密化特性,对无压烧结后材料的硬度、断裂韧度和抗弯强度进行了测试和分析;分析了复合材料力学性能随透辉石含量变化的关系;探讨了复合材料断面断裂方式的变化对其力学性能的影响.与纯Al2O3相比,透辉石/ Al2O3复合材料的力学性能得到明显提高,其中AD3[97% Al2O3 + 3%(体积分数)透辉石]综合力学性能较好,其硬度、抗弯强度和断裂韧度分别为15.57 GPa、417 MPa和5.2 MPa·m1/2.力学性能提高的主要原因是添加相与Al2O3基体之间界面反应的发生以及透辉石对复合材料的晶粒细化效应.     

表面改性纳米SiO2对铜基摩擦材料摩擦学性能的影响

为提高铜基粉末冶金摩擦材料的综合性能,采用粉末冶金法分别制备了Cu和Ni包覆的纳米SiO2(n-SiO2)颗粒增强的铜基摩擦材料.通过惯性试验,考核了摩擦材料的摩擦磨损和耐热性能;采用扫描电子显微镜(SEM)、显微硬度计研究了材料的显微组织、基体硬度和磨损机理.结果表明:表面改性n-SiO2可细化铜基摩擦材料的基体组织,显著提高铜基体的硬度;添加Cu/n-SiO2和Ni/n-SiO2的摩擦材料的耐磨性能比添加未表面改性n-SiO2的摩擦材料分别提高3.95倍和7.46倍;n-SiO2颗粒增强铜基摩擦材料的主要磨损机理为犁沟式磨料磨损.     

MgO/HA复合材料的强韧化与冷处理

以多种不同粒径的MgO颗粒为第二相,以HA为基体,采用无压烧结法制备MgO/HA复合材料;研究MgO粒径与MgO/HA复合材料的抗弯强度和断裂韧性之间的关系,探讨冷处理对复合材料性能的影响。结果表明:添加适宜粒径的MgO颗粒能够提高HA复合材料的抗弯强度和断裂韧性,其断裂韧性可达基体断裂韧性的1.5倍,抗弯强度可达基体抗弯强度的1.29倍,MgO颗粒增韧的粒径范围为15～35μm,增强的粒径范围为<25μm。冷处理可以进一步提高复合材料的强度和韧性,而且可以改变增韧和增强的MgO粒径范围,使增强与增韧粒径的重叠范围变宽。     

热压原位合成（Cu-Mo）／Mo5Si3复合材料

为改善Mo5Si3的室温脆性,以Mo、Cu、Si粉体为原料,通过热压反应烧结原位合成制备了(Cu-Mo)/Mo5Si3复合材料。其微观组织由Mo5Si3和少量Mo形成的相和Cu基固溶体相两相组成,且各相分布均匀、组织致密。随着Cu含量(质量分数)的增加,Mo5Si3的体积分数减少,材料的硬度下降,而相对密度、抗弯强度和断裂韧度提高。Cu和Mo的协同增韧,加之Mo5Si3的高强度和高硬度使(Cu-Mo)/Mo5Si3复合材料具有良好的强韧性配合。     

Mechanical behavior of rapidly solidified Al-Al2Cu and Al-Al3Ni composites

The eutectic alloys Al-Al₂Cu and Al-Al₃Ni have been unidirectionally solidified at rates from 1.05 to 6.80 in, per min by a semicontinuous casting technique, and then tested in tension at room temperature. In both alloys the flow stress and ultimate tensile strength increased with increasing solidification rate, except for the highest solidification rate. The increases in matrix work-hardening rate with solidification rate were too great to be accounted for by dislocation pileup mechanisms, but were found to correlate with elastic constraint effects of the matrix aluminum phase by the reinforcing phases. In the Al-Al₂Cu eutectic the strength of the Al₂Cu platelets increased as the platelet width decreased with increasing growth rate. Misalignment of the composite caused by either a cellular or a macroscopically concave solid-liquid interface resulted in a decrease in the ultimate strength, especially in the rod-like Al-Al₃Ni alloy. This has been related to the fracture behavior of the composites. The very low fracture toughness of the lamellar Al-Al₂Cu eutectic is consistent with models of composite materials, and seriously limits the alloy’s usefulness for engineering applications.     

添加W/Cr和WC/Cr3C2对铁基金刚石锯片性能的影响

以Fe-30%Cu(质量分数)合金粉末、单质Sn粉和Cu粉的混合粉末为基体,分别用W/Cr/Ni混合粉末和WC/Cr3C2/Ni混合粉末作为添加剂,制备金刚石锯片胎体材料,并利用加压烧结方法制备金刚石锯片。分析胎体材料的致密度、组织结构和力学性能以及金刚石锯片的切割性能。结果表明:胎体中添加Ni-W/Cr或Ni-WC/Cr3C2后,硬度、冲击韧性和抗弯强度最大增幅分别达到19.2%、11.7%和6.9%,致密度由96.50%降至93.1%～94.8%;胎体材料中添加2.44%W和2.44%Cr(体积分数)的金刚石锯片具有最优的干切性能,磨耗比和切割速率分别达到105.3 m/mm和1.66 m/min;添加4.36%WC和0.67%Cr3C2(体积分数)的金刚石锯片具有最优的湿切性能,磨耗比和切割速度分别达到109.6 m/mm和2.17 m/min。     

Characteristics of hot-pressed fiber-reinforced ceramics with SiC matrix

Silicon carbide ceramics’ matrix composites with SiC or C filaments were fabricated through hot pressing, and the effects of the filament pullout on their fracture toughness were experimentally investigated. The C-rich coating layers on the SiC filaments were found to have a significant effect on the frictional stress at the filament/matrix interfaces, through assising the filamet pullout from the matrix. Although the coating layers were apt to burn out in the sintering process of SiC matrix compposites, a small addition of carbon to the raw materials was found to be effective for the retention of the layers on the fibers, thus increasing the fracture toughness of the composites. The fracture toughness of the C filament/SiC matrix composite increased with temperature due to the larger interfacial frictional stress at higher temperatures, because of the higher thermal expansion of the filament in the radial direction than that of the matrix.     

Strength degradation of SiC fiber during manufacture of titanium matrix composites by plasma spraying and hot pressing

Titanium matrix composites (TMCs) reinforced with Sigma 1140+ SiC fiber have been manufactured by a combination of low pressure plasma spraying (LPPS spray/wind) and simultaneous fiber winding, followed by vacuum hot pressing (VHP). Fiber damage during TMC manufacture has been evaluated by measuring fiber tensile strength after fiber extraction from the TMCs at various processing stages, followed by fitting of these data to a Weibull distribution function. The LPPS spray/wind processing caused a decrease in mean fiber strength and Weibull modulus in comparison with as-received fibers. A number of fiber surface flaws, primarily in the outer C layer of the fiber, formed as a result of mechanical impact of poorly melted particles from the plasma spray. Coarse feedstock powders promoted an increase in the population of fiber surface flaws, leading to significant reduction in fiber strength. The VHP consolidation promoted further development of fiber surface flaws by fiber bending and stress localization because of nonuniform matrix shrinkage, resulting in further degradation in fiber strength. In the extreme case of fibers touching, the stress concentration on the fibers was sufficient to cause fiber cracking. Fractographic studies revealed that low strength fibers failed by surface flaw induced failure and contained a large fracture mirror zone. Compared with the more widely investigated foil-fiber-foil route to manufacture TMCs, LPPS/VHP resulted in less degradation in fiber strength for Sigma 1140+ fiber. Preliminary results for Textron SCS-6 fiber indicated a much greater tolerance to LPPS/VHP damage.     

Hard Alloy WC–24% Ni Obtained in the Solid Phase from Ultrafine WC,NiO, and C Powders. Part 2. Mechanical Properties

Mechanical properties of WC–24 mass% Ni alloy prepared by a combination in single stage of metal phase synthesis and compaction of an ultrafine mixture of WC–Ni powders by high-energy compaction and sintering are studied. Tungsten carbide, nickel oxide, and carbon are selected as the starting powders. After milling the initial powders the average particle size is 200-300 nm. Previously compacted briquettes of WC + NiO + C are heated, sintered, and pressed in the range 950-1300°C at vacuum of 0.133 Pa. Briquettes are also sintered in the liquid phase at 1350°C for comparison. Ultimate strength in bending, fracture toughness, ultimate strength in compression, and Vickers hardness are determined for specimens prepared at different temperatures. The dependence of mechanical properties on specimen consolidation temperature is studied. It is shown that these dependences for pressed specimens have a maximum at 1200-1250°C. The high level of properties (ultimate strength in bending 2500 MPa, ultimate strength in compression 3100 MPa, fracture toughness 19 MPa·m^1/2, and hardness 10.0 GPa) are achieved for a WC + Ni + C powder mixture to which carbon is added in the form of a liquid carbon-containing compound. Introduction into the mixture of commercial carbon grade P803 leads to low specimen mechanical properties. The effect on mechanical properties of porosity and pore size, and also grain boundary quality between particles is studied.     

纤维分散对C/C-SiC复合材料力学性能的影响

利用温压-原位反应法制备短炭纤维增强C/C-SiC复合材料,研究纤维分散对复合材料力学性能的影响.结果表明: 利用分散短炭纤维制备的C/C-SiC复合材料,其抗弯强度和抗压强度分别达到56.6MPa和89.3MPa.该材料纤维之间孔隙少,纤维与基体接合界面多,弯曲时有纤维拔出,为假塑性断裂行为.压缩时无纤维拔出,为脆性断裂行为.最后,利用LI V C提出的束丝数学模型证明了纤维分散有利于提高C/C-SiC复合材料的力学性能.     

原位转化碳纤维增韧氧化铝复合材料的制备工艺

以聚丙烯腈预氧化纤维为先驱纤维,使其在真空烧结过程中原位转化生成碳纤维来增韧氧化铝陶瓷材料.利用热重–差热分析和X射线衍射研究了聚丙烯腈预氧化纤维的相结构和化学结构以确定制备复合材料的升温烧结工艺,并探讨了加压方式和聚丙烯腈预氧化纤维含量对复合材料组织结构和性能的影响.研究发现聚丙烯腈预氧化纤维在差热曲线上444℃左右的放热峰和X射线衍射图谱中17左右的衍射峰是由预氧化阶段残留的未充分氧化的聚丙烯腈分子引起的;而1073℃左右的吸热峰和25.5左右的衍射峰说明预氧化纤维在加热烧结过程中已开始向碳纤维转变.热压烧结制备的复合材料的力学性能明显优于无压烧结.随着聚丙烯腈预氧化纤维含量的增加,复合材料的密度和显微硬度降低,而断裂韧性则先升高后降低,当聚丙烯腈预氧化纤维体积分数为20%时,复合材料的断裂韧性最大,达9.39MPa·m1/2,说明原位碳纤维的生成提高了复合材料的断裂韧性,其增韧机制主要为纤维拔出和脱黏.      

Fiber-Matrix interactions in brittle matrix composites

Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Metal-ceramic composites based on the Ti-B-Cu porosity system

A systematic study of the microstructure/fracture toughness/processing correlation of metal-ceramic composites in the Ti-B-Cu porosity system is presented. The composites are produced by the combustion synthesis process. Fracture surfaces indicate both ductile and brittle regions. The composites are made up of Ti as the only ductile phase and TiB, TiB₂, Ti₂Cu, and Ti₃Cu₄ as brittle phases. Density measurements and scanning electron microscopy (SEM) indicate that the samples contain distributed porosity. Ductile phase toughening is responsible for the increase in fracture toughness to a maximum value of 9.9 MPa(m)^1/2. Samples with large amounts of porosity do not benefit from this toughening process even though they containin situ formed whiskers. The fracture toughness of the composite is modeled by considering the additive influence of the ductile phase reinforcement (Ashby model) and the residual porosity (exponential model). Microstructural constants required for the model are evaluated from the comparison. A correlation between the mechanical properties and the combustion temperature is established. Formerly with the Department of Materials Science and Engineering, University of Cincinnati