Hybrid effect,mechanical properties and enhancement mechanism of oil-well cement stone with multiscale silicon carbide whisker

Cement-based materials typically have a relatively high compressive strength and a relatively low tensile strength. In this paper, multiscale silicon carbide whiskers (SW) were used to improve mechanical properties of oil-well cement stone. The structure and properties of whisker cement stone were analyzed via mechanical testing and cement sheath integrity. The results demonstrated that multiscale SW mixing showed a positive hybrid effect and could effectively improve the compressive strength, the flexural strength, and the splitting tensile strength of oil-well cement stone by 8.96%, 137.44% and 27.96%. The modulus and porosity of the whisker cement stone significantly reduced. The filling effect, whisker pinning, the pullout, and the whisker bridging were regarded as effective mechanisms for the addition of SW when improving the mechanical properties and microstructures of oil-well cement stone.     

Hot Isostatically Pressed Alumina-Silicon Carbide-Whisker Composites

Alumina-silicon carbide-whisker composites were hot isostatically pressed at 1550°C and 200 MPa for 1 h. The silicon carbide whiskers were treated in different acid and gas environments before they were pressed. All samples exhibited linear elastic behavior with no ductility tendency. Improved strength and fracture toughness were obtained compared with unreinforced alumina. Mechanisms for the improved mechanical properties are discussed. These include grain growth control, whisker encapsulation of defects, and related stress relief at the defect.     

Particulate composites from coated powders

A method is described for coating SiC whiskers with a thick layer of alumina to form homogeneous alumina matrix/silicon carbide whisker particulate composites. The method uses controlled heterogeneous precipitation in a relatively concentrated suspension of whiskers. The suspension-coated whiskers can be converted to a free-flowing powder after calcination. The processing parameters and the results of consolidation of the composite powder are reported. Nearly fully dense composites, containing over 40 vol.% whiskers, could be prepared.     

Combination of direct ink writing and reaction bonded for rapid fabrication of SiCw/SiC composites

Silicon carbide ceramic matrix composites are widely used in aerospace field due to their advantages of high temperature resistance, high strength and corrosion resistance. However, its application is greatly limited because of the difficulty in preparing complex shape structures by traditional machining methods. Here, a new strategy for preparing SiC_w/SiC complex structure by combining direct ink writing with reaction bonding is proposed. A water-based slurry consisting of silicon carbide, carbon powder and silicon carbide whisker was developed. The influence laws of C content and SiC_w content in slurry on sintering properties of direct-written samples were studied. The reaction bonding mechanism and whisker reinforcing and toughening mechanism were analyzed by means of microstructure and phase composition. The results show that the slurry exhibits shear thinning behavior with stress yield point, and its flow behavior and plasticity meet the requirements of direct writing. When the carbon content is 6.4 wt%, the maximum flexural strength is 239.3 MPa. When 15 wt% SiC_w was added, the flexural strength of the composite reached 301.6 MPa, and when 20 wt% SiC_w was added, the fracture toughness of the composite reached 4.02 MPa m^1/2, which was increased by 26% and 18% compared with single-phase SiC, respectively. The reinforcing and toughening mechanisms of the whiskers mainly include whisker pullout, crack deflection and whisker bridging. After direct ink writing and reaction bonded, the whole process shows good near net forming ability. 3D printed SiC_w/SiC composites have great application prospects in aerospace field.     

PA66/PP/晶须硅复合材料的制备与性能

通过双螺杆挤出机采用熔融共混的方法制备了尼龙(PA)66/聚丙烯(PP)/晶须硅复合材料.研究了偶联剂的种类以及晶须硅的用量对复合材料体系力学性能、微观形态和热性能的影响.结果表明,采用硅烷偶联剂KH560处理的晶须硅具有较好的分散性.晶须硅能够显著提高PA66/PP合金的拉伸和弯曲强度,对复合材料的韧性也有一定的改善...     

SiC晶须增强Al2O3—TiC复相陶瓷的研究

运用品须补强和粒子弥散双重手段,对氧化铝材料的性能进行改进。比较了Al_2O_3-TiC(AT),Al_2O_3/SiC_w(As),Al_2O_3-TiC/SiC_w(ATS)材料的力学性能,证实ATS材料有明显的迭加增强增韧效果,并具有良好的高温力学性能。抗氧化实验证实,将SiC晶须加入AT中以后,材料的抗氧化性能有明显改进。从热膨胀失配角度分析和SEM显微结构观察证实,ATS材料的主要增韧机理是界面解离和裂纹偏转。     

In Situ Observations of Toughening Processes in Alumina Reinforced with Silicon Carbide Whiskers

An in situ study is made of crack interfaces in composites of alumina reinforced with silicon carbide whiskers. Both qualitative observations of the whisker-bridging micro-mechanisms and quantitative measurements of the crack profile are made to assess the specific role of the whiskers on the toughness curve ( T -curve or R -curve). At small crackwall separations the whiskers act as elastic restraints to the point of rupture. In some cases the whiskers remain in frictional contact with the alumina matrix over large pullout distances (more than 1 μm) corresponding to a bridging zone approaching 1 mm. The results are discussed in relation to existing models of whisker reinforcement and published long-crack T -curve data.     

Influence of Al2O3 whisker concentration on flexural strength of Al2O3(w)–ZrO2 (TZ-3Y) composite

On investigating the possibility of using alumina whisker reinforced 3 mol% Yttria stabilized Tetragonal Zirconia (TZ-3Y) composite for bioceramic applications, presented here is the influence of varying whisker concentration (2, 5, 10, 15 and 20 wt%) on flexural strength of the composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina during sintering. It was found that with addition of alumina whiskers, strength was increased and reached a maximum value of 1212±60 MPa and 1325±65 MPa, in pure and 1 wt% CTAB added samples respectively, at a concentration of 10 wt% Al₂O₃ whiskers. The strength values of the synthesized composite can compete well with commercially available materials for dental applications.     

轮胎半焦制备碳化硅晶须的研究

以轮胎半焦和石英砂为原料,采用碳热还原法制备出碳化硅晶须.利用X射线衍射仪(XRD)和扫描电镜(SEM)对制得的产物进行物相组成和形貌分析,探究反应温度(1300～1500℃)、反应时间(120～300 min)、升温程序以及半焦粒度对合成碳化硅晶须的影响规律.结果表明:温度控制在1350℃左右,且采用先升至1500℃...     

晶须/滑石粉共改性车用聚丙烯复合材料性能研究

以滑石粉和晶须为填料,制备了晶须和滑石粉共改性聚丙烯复合材料,并研究了该复合材料的力学性能。结果表明:当滑石粉与晶须质量百分比为12∶8时,复合材料的拉伸屈服强度、弯曲强度、弯曲模量、冲击强度和熔体流动速率等综合性能最佳。     

Mechanical properties and microstructure of oil-well cement stone enhanced with submicron SiC whiskers

In order to improve the intrinsically brittle nature of the oil-well cement stone, a new type of submicron-fibrous whisker, referred to as the silicon carbide whisker (SiC whisker) was added into cement paste. The cement-based composites were prepared with the various amounts of submicron SiC whiskers. The composites were analyzed via scanning electron microscopy (SEM), mechanical testing, X-ray diffraction (XRD), infrared spectrum analysis (FTIR), and thermal stability analysis in order to understand the enhanced effect that the submicron SiC whiskers had on the applied properties and mechanisms of oil-well cement stone. The compressive strength, the tensile strength, and the flexural strength of the sample with 1% of additional submicron SiC whiskers increased by 9%, 104%, and 26%. The ultimate strain was more than 5%, which increased 194%. The elasticity modulus was 4648.4MPa, which decreased 31.1% after 28 curing days. These improved the mechanical properties of the cement-based composites primarily because of the microscopic mechanism of reinforcement via the submicron SiC whisker, including the bridging effect, the crack deflection, and the pull-out effect.

• HIGHLIGHTS

• A submicron SiC whisker was used to enhance the oil-well cement

• The submicron SiC whisker could significantly increase the mechanical behaviors of the oil-well cement

• The reinforcing mechanism that the submicron SiC whisker had on the oil-well cement was discussed in detail.

• The influence that the submicron SiC whisker had on the integrity of the cement sheaths were evaluated

     

Mechanical Properties, Thermal Shock Resistance, and Thermal Stability of Zirconia-Toughened Alumina-10 vol% Silicon Carbide Whisker Ceramic Matrix Composite

Zirconia-toughened alumina (Al₂O₃–15 vol% Y-PSZ (3 mol% Y₂O₃)) reinforced with 10 vol% silicon carbide whiskers (ZTA-10SiC _w ) ceramic matrix composite has been characterized with respect to its room-temperature mechanical properties, thermal shock resistance, and thermal stability at temperatures above 1073 K. The current ceramic composite has a flexural strength of ∽550 to 610 MPa and a fracture toughness, K _IC , of ∽5.6 to 5.9 MPa·m^1/2 at room temperature. Increases in surface fracture toughness, ∽30%, of thermally shocked samples were observed because of thermal-stress-induced tetragonal-to-monoclinic phase transformation of tetragonal ZrO₂ grains dispersed in the matrix. The residual flexural strength of ZTA–10 SiC _w ceramic composite, after single thermal shock quenches from 1373–1573 to 373 K, was ∽10% higher than that of the unshocked material. The composite retained ∽80% of its original flexural strength after 10 thermal shock quenches from 1373–1573 to 373K. Surface degradation was observed after thermal shock and isothermal heat treatments as a result of SiC whisker oxidation and surface blistering and swelling due to the release of CO gas bubbles. The oxidation rate of SiC whiskers in ZTA-10SiC _w composite was found to increase with temperature, with calculated rates of ∽8.3×10⁻⁸ and ∽3.3×10⁻⁷ kg/(m²·s) at 1373 and 1573 K, respectively. It is concluded that this ZTA-10SiC _w composite is not suitable for high-temperature applications above 1300 K in oxidizing atmosphere because of severe surface degradation.     

Processing and Properties of Particulate Composites from Coated Powders

A method is described for sintering of highly loaded (≤20 vol%) alumina matrix/silicon carbide whisker or platelet composites to closed porosity. The method uses controlled heterogeneous precipitation in a suspension of whiskers or platelets. The suspension-coated particles are calcined to produce a free-flowing composite powder which can be hot-pressed or free-sintered to high density. The results of consolidation and mechanical property testing are reported.     

Silicon Carbide Whisker‐Reinforced Ceramic Tape for High‐Power Components

An attempt to enhance both mechanical strength and thermal conductivity of glass‐based tapes is described. Flexural strength of ~420 MPa and thermal conductivity of ~10.3 W/m/K have been achieved in fully densified tape comprising calcium aluminoborosilicate glass, aluminum nitride, and silicon carbide whiskers. Silicon carbide whiskers aligned parallel to the casting direction contributed significantly to the reinforcement of the microstructure with accompanying extensive densification over a broad temperature range. These results are compared with the more typical alumina filler substituted for the aluminum nitride.     

Longer‐lasting Al2O3‐SiCw‐TiC cutting tools obtained by spark plasma sintering

In this work, an electrically conductive powder mixture of alumina, silicon carbide whiskers, and titanium carbide has been used to obtain cutting tools with a standard SNGN geometry after machining spark plasma sintered disks with 150 mm in diameter and 10 mm height. The obtained cutting inserts from the sintered blanks were used in real conditions in order to make a wear study of this composition compared to the alumina‐silicon carbide whiskers inserts available in the market. In parallel, pin on disk wear studies were performed. Results are discussed in terms of the different properties and microstructural features of the different ceramic composites.     

Improved High-Temperature Strength of Silicon Nitride Toughened with Aligned Whisker Seeds

The effect of the amount of the sintering additives, i.e., yttria and alumina, on the microstructure and the high-temperature flexural strengths of silicon nitride with and without the aligned whisker seeds was examined. As the amount of the sintering additives was increased, both width and length of the grains were increased. The high-temperature strengths of silicon nitride with and without the aligned seeds were increased and decreased, respectively, according to the increase of the amount of the sintering additives. When both 4.8 wt% yttria and 2.2 wt% alumina were added to silicon nitride with the aligned whisker seeds, the experimental results indicated that it had three times the flexural strength as silicon nitride without the seeds at 1673 K. During the high-temperature flexure testing, observations did not indicate yielding present in the samples with the aligned whisker seeds, while it was present in samples without the whisker seeds. The reinforcing grains growing from the whisker seeds aligned perpendicular to the crack propagation direction acted as effective obstacles to the crack propagation and improved the fracture toughness.     

Two-Dimensional Whisker Percolation in Ceramic Matrix–Ceramic Whisker Composites

A computer model that treats ceramic-powder matrix–ceramic whisker composites as a percolative network of whiskers has been developed. The model calculates the critical fraction of whiskers at the percolation threshold for a two-dimensional random network of whiskers. The computed critical fraction was found to display an inverse dependence on whisker aspect ratio. In addition, the computed critical fraction (27 vol% for a whisker aspect ratio of 7) agreed well with the zero-shrinkage whisker fraction of 30 vol% in the densification of a colloid-pressed alumina–silicon carbide composite that exhibited a two-dimensional orientation of such whiskers.     

Aluminum‐borate‐whiskers‐reinforced bismaleimide composites. 1: preparation and properties

Aluminum‐borate‐whiskers‐reinforced bismaleimide (BMI/Al₁₈B₄O₃₃) composites were prepared, and the mechanical and thermal properties were investigated. Results show that the coupling agent used for surface treatment of whiskers has a great effect on the properties of these materials. Composites containing surface‐untreated whiskers, or silane‐compound‐KH 921‐treated whiskers, exhibited initially only a slight increase in the flexural strength when the whiskers weight content increased up to 5 wt%; thereafter, they showed a sharp decrease when the whiskers content was higher than 5 wt%. On the other hand, impact strength tests showed that the addition of the two kinds of whiskers decreased the impact strength of the composites. However, studies of the composite containing borate (BE4)‐treated whiskers showed that its flexural strength greatly increased with increasing whisker content. Moreover, the composite showed initially an increase in impact strength with a whisker content up to 10 wt%, then showing a slight decrease when the whisker content reached 15 wt%. Scanning electron microscopy observations revealed that the two coupling agents (KH 921 and BE4) employed in this work tend to change the fracture features of the composites from brittleness to that of ductile behaviour. Copyright © 2004 Society of Chemical Industry     

Thermal Conductivity/Diffusivity of Silicon Carbide Whisker Reinforced Mullite

The thermal conductivity and diffusivity of silicon carbide whisker reinforced mullite was shown to increase with whisker content. This effect was much greater for vapor-liquid-solid (VLS) whiskers than for rice-hull (RH) whiskers. This suggests that the thermal conductivity for the VLS whiskers was significantly higher than for the RH whiskers. Due to preferred orientation of the whiskers, thermal conductivity and diffusivity of the composite samples exhibited significant anisotropy.     

CaCO3晶须补强增韧不饱和聚酯树脂的研究

针对不饱和聚酯树脂（UPR）强度低、脆性大等缺陷,用添加碳酸钙晶须的方法对其进行改性,研究了碳酸钙晶须用量对树脂复合材料力学性能的影响。结果表明：当CaC03晶须的掺量为5％时,UPR／CaCO3晶须复合材料的拉伸强度、弯曲强度达到极大值39．2MPa、52．7MPa,比树脂基体分别提高了126％和73％;当CaCO3...