Microstructure and mechanical properties of titanium components fabricated by a new powder injection molding technique

A powder injection molding (PIM) binder system has been developed for reactive metals such as titanium that employs an aromatic compound as the primary component to facilitate easy binder removal and mitigate problems with carbon contamination. In the study presented here, we examined the densification behavior, microstructure, and mechanical properties of titanium specimens formed by this process using naphthalene as the principle binder constituent. In general, it was found that tensile strengths could be achieved comparable to wrought titanium in the PIM-formed specimens, but that maximum elongation was less than expected. Chemical and microstructural analyses indicate that this process does not add oxygen to the material,suggesting that the use of higher purity powder and further process optimization should lead to significant improvements in ductility.     

Carbon fibres: structure and mechanical properties

The microstructure of six types of acrylic-based and hydrated cellulose-based carbon fibres of strengths from 1650 to 6120 MPa and elastic moduli from 97 to 228 GPa were studied by scanning electron microscopy (SEM). A ‘microcomposite’ structure of carbon fibres studied consisting of quasi-amorphous (‘matrix’) and orientated fibrillar carbon was revealed. This led to a new model of the fibre structure. The analysis of results of testing different carbon fibres defines the elastic modulus of ‘matrix’ carbon, and shows plastic drawing of fibrils. The model describes the properties of fibres and predicts ways to improve the fibre properties.     

Microstructure and mechanical properties of Al-Mg-Si alloy fabricated by a short process based on sub-rapid solidification

Al-Mg-Si(AA6xxx) series alloys have been used widely in automotive industry for lightweight purpose.This work focuses on developing a short process for manufacturing Al-0.5Mg-1.3Si(wt.%) alloy sheets with good mechanical properties. Hereinto, a preparation route without homogenization was proposed on the basis of sub-rapid solidification(SRS) technique. The sample under SRS has fine microstructure and higher average partition coefficients of solute atoms, leading to weaker microsegregation owing to the higher cooling rate(160℃/s) than conventional solidification(CS, 30℃/s). Besides, Mg atoms tend to be trapped in Al matrix under SRS, inducing suppression of Mg_2Si, and promoting generation of Al Fe Si phase.After being solution heat treated(T4 state), samples following the SRS route have lower yield strength compared with that by CS route, indicating better formability in SRS sample. After undergoing pre-strain and artificial aging(T6 state), the SRS samples have comparable yield strength to CS samples, satisfying the service requirements. This work provides technological support to industrially manufacture high performance AA6xxx series alloys with competitive advantage by a novel, short and low-cost process,and open a door for the further development of twin-roll casting based on SRS technique in industries.     

Review Processing and mechanical properties of fine-grained magnesium alloys

Magnesium alloys are promising light structural materials. The present paper focuses on fine-grained magnesium-based materials. Grain refinement is attained by hot working without additional treatments. Also, a very small grain size of less than 1 m is obtained by equal channel angular extrusion. A good combination of high strength and high ductility at room temperature is attained by grain refinement. Furthermore, fine-grained magnesium-based materials exhibit superplastic behavior at high stain rates (10^–1 s^–1) or low temperatures (473 K). These point out the importance of grain refinement to process magnesium-based materials with excellent mechanical properties.     

Effect of fine-grained structure on the mechanical properties of superalloys K3 and K4169

The fine-grained structures of superalloys K3 and K4169 were achieved by the addition of refiners. Test bars for the determination of mechanical properties were cast under the chosen conditions to study the tensile properties at room and intermediate temperatures, and the stress rupture properties at intermediate temperatures. Results show that for alloy K3, the yield and tensile strengths of the fine-grained samples are superior to those of the conventional ones at room and intermediate temperatures, but there is little difference in tensile plasticity. The stress rupture life of the fine-grained sample is much longer than that of the conventional at 750°C, whereas it has no remarkable change at 800°C. For alloy K4169, the yield and tensile strengths of fine-grained samples are still superior to those of the conventional ones at room temperature and 760°C. In addition, the stress rupture life of the fine-grained sample is 1.1 times longer than that of the conventional one at 760°C. However, the permanent plasticity almost remains the same. The fracture of the samples was examined by scanning electron microscopy (SEM) and the fracture mechanisms were investigated.     

Evaluation of mechanical properties of high-temperature superconducting bulks fabricated by a melt-processing

High-temperature superconducting bulks with highly oriented crystallographic structures are expected to be applied for high field quasi-permanent magnets, current leads and so on. However, the bulks sometimes fracture due to the thermal stress on the cooling process or the electromagnetic force during the magnetization. Thus, it has been recognized that improvement and understanding of the mechanical properties of bulks are indispensable for practical application. In this review, we summarize the present status of evaluation process of the mechanical properties for various bulks. The Young’s modulus, Poisson’s ratio, fracture strength, fracture toughness and hardness are evaluated by tensile, bending, compression and hardness tests. The mechanical properties are anisotropic, mainly due to the crystallographic structure and pre-existing micro-cracks associated with it. Data obtained are summarized and the influential parameters associated with the microstructure and testing condition for the mechanical properties are explained.     

The design and selection of materials for a general purpose mechanical seal

The predominant requirements for mechanical seals for use on modern continuous process plants are reliability, safety and ease of fitting & maintenance. Many users do not have specific engineering skills to select specially designed seals for particular applications. Nor do they have the fitting skills on process plants to deal with complex mechanical seals which may have many individual components which require expert fitting on the plant itself. The need was therefore identified for a general purpose mechanical seal which was easy to select for a particular application, and was both safe and reliable in operation. This paper describes the design, testing, development and areas for application of the Flexibox FFET general purpose cartridge seal for standard metric and inch shafts and a wide range of process and industrial machines, handling liquids — as varied as water, oil, chemicals and slurries.     

天然高分子泡沫材料的复合结构与力学性能

通过扫描电子显微镜和光学显微镜研究了2 种天然高分子泡沫材料, 即玉米秆芯和高粱秆芯切面的泡孔形态结构及胞体堆砌模式。测试了材料在轴向和径向的压缩杨氏模量和压缩屈服强度等力学性能, 探讨了泡沫材料的压缩变形机制, 建立了天然泡沫材料的复合结构模型, 并分析了力学性能与复合结构的关系。研究结果表明, 这2 种天然泡沫均由一种近似六棱柱和少量圆形管状胞体构成, 它们在轴向的杨氏模量和屈服强度分别比径向的大4 倍以上。导管增强的复合结构是引起天然泡沫材料具有明显各向异性的重要原因, 其中厚壁导管的轴向杨氏模量约为不规则六棱柱胞体的105 倍。      

改进sol-gel技术BST薄膜的制备及性能研究

为了制备高性能BST薄膜,采用改进的溶胶 凝胶(sol gel)方法在Pt/Ti/SiO2/Si基片上制备出了不同结构、不同组成的BST薄膜;研究了BST薄膜的微观结构及其介电、铁电性能。XRD分析表明,当热处理温度为750℃时,得到完整钙钛矿结构的薄膜材料。SEM电镜显示,含种子层的Ⅱ、Ⅲ、Ⅳ3种不同类型的BST薄膜的结晶状况有很大改善。得到的BST20薄膜的介电峰温区覆盖常温段,介电常数为405,介电损耗为0.011,剩余极化强度为Pr=2.3μC·cm-2,矫顽场为Ec=45kV/cm。     

High-density carbon nanotube buckypapers with superior transport and mechanical properties

High-density buckypapers were obtained by using well-aligned carbon nanotube arrays. The density of the buckypapers was as high as 1.39 g cm(-3), which is close to the ultimate density of ideal buckypapers. Then we measured the transport and mechanical properties of the buckypapers. Our results demonstrated that its electrical and thermal conductivities could be almost linearly improved by increasing its density. In particular, its superior thermal conductivity is nearly twice that of common metals, which enables it a lightweight and more efficient heat-transfer materials. The Young's modulus of the buckypapers could reach a magnitude over 2 GPa, which is greatly improved compared with previous reported results. In view of this, our work provided a simple and convenient method to prepare high-density buckypapers with excellent transport and mechanical properties.     

The dynamic properties of SiCp/Al composites fabricated by spark plasma sintering with powders prepared by mechanical alloying process

The dynamic compressive properties of SiC particle reinforced pure Al matrix composites, fabricated by spark plasma sintering technique with mixture powders prepared by mechanical alloying process, were tested in this paper. Two different average SiC particle sizes of 12 μm and 45 μm were adopted, and the compressive tests of these composites at strain rates ranging from 800/s to 5200/s were conducted by split Hopkinson pressure bar. The damage mechanism of the SiC_p/Al composites was analyzed through the microstructural observations and high-precision density measurements. Results show that the dynamic properties and damage accumulation of these composites are significantly affected by the particle distribution, size, particle cracking, particle/matrix interface debonding and adiabatic heat softening. The composites containing smaller SiC particles exhibit higher flow stress, lower strain rate sensitivity, and less damage at high strain rate deformation.     

Microstructure and mechanical properties of Mg-Al-Zn alloy sheet fabricated by cold extrusion

Cold extrusion of AZ31 magnesium alloy sheets was studied in this paper. Microstructure and texture distributions of the as-extruded sheet were investigated by electron backscattered diffraction (EBSD) method. The grains were significantly refined and the average grain size was 1.6 μm. Dynamic recrystallization has taken place during the extrusion process, which resulted in the high frequency of high angle grain boundaries in the sheet. After the cold extrusion, a weak double-peak type basal texture was formed. The formation of the texture was ascribed to the non-basal <c + a> slips. Tensile tests revealed that mechanical properties were enhanced due to grain size refinement, but mechanical anisotropy was obvious. It is believed that mechanical anisotropy was related to the splitting of basal texture.     

VARI成型泡沫夹芯壁板结构界面性能

针对真空辅助成型工艺(VARI)制备的泡沫夹芯壁板面-芯界面粘接强度较低的问题, 提出铺放本体树脂胶膜和对芯材进行打孔两种解决方案。通过无损检测、三点弯曲力学性能测试、计算机模拟树脂充模流动以及微观界面结构观察, 探究两种方案的可行性及改善效果, 分析了胶膜的有无和厚度、打孔工艺参数对界面性能的影响。结果表明, 在不加入胶膜时界面强度最高, 胶膜厚度在0.5 mm时, 无损检测显示的界面缺陷最少, 胶膜厚度达到2 mm后界面质量下降; 合理设计芯材的打孔行、间距可以促进树脂充模流动, 形成质量好的连续界面, 同时还能提高结构刚度。     

Comparison of mechanical properties for equiaxed fine-grained and dendritic high-palladium alloys

Two Pd-Cu-Ga alloys and a Pd-Ga alloy were selected for study. Bars of each alloy were tested in tension for the as-cast and simulated porcelain-firing conditions, and values of mechanical properties were measured. Fracture surfaces and microstructures of axially sectioned fracture specimens were observed with the SEM. The two Pd-Cu-Ga alloys exhibited similar mechanical properties. The Pd-Ga alloy had lower strength and higher percentage elongation. Heat treatment simulating porcelain firing cycles decreased the strength of both Pd-Cu-Ga alloys and increased their ductility. However, this heat treatment did not significantly affect the mechanical properties of the Pd-Ga alloy. All three high-palladium alloys had the same modulus of elasticity. The amount of overall porosity was relatively minimal (< 1%) and not significantly different among the three alloys. However, porosity was a significant factor for UTS of one Pd-Cu-Ga alloy and the Pd-Ga alloy.     

Evaluation of the mechanical properties of multicomponent materials of stochastic structure

A new algorithm for simulating the mechanical behavior of a composite material of stochastic structure is proposed. The use of a model material, which is composed according to the parameters of the shape, size, and orientation distributions of the components in the real composite, as a standard medium is proposed. A procedure is proposed for determining the bounds of the interval of microvolume sizes in the model material which ensure that it is locally representative. The possibility of preliminarily estimating these bounds from the parameters of the distributions of geometric characteristics of the microvolumes, which does not require the solution of a sequence of inverse problems, is demonstrated. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (June 26, 1999)     

A novel high-entropy alloy with multi-scale precipitates and excellent mechanical properties fabricated by spark plasma sintering

Body-centered-cubic (BCC) high entropy alloys (HEAs) usually exhibit high strength but poor ductility. To overcome such strength-ductility trade-off, a novel (FeCr)₄₅(AlNi)₅₀Co₅ HEA was presented in this paper, which was designed and fabricated with mechanical alloying (MA) followed by spark plasma sintering (SPS), and has a heterogeneous microstructure with multi-scale precipitates. Electron microscopy characterization revealed that the sizes of the precipitates range from nano (<300 nm), sub-micron (300～800 nm) to micron (>1 μm). The bulk HEA exhibits excellent mechanical properties, of which the compressive yield strength, fracture strength, and plasticity at room temperature can reach 1508 MPa, 3106 MPa and 30.4 %, respectively, which are much higher than that of most HEAs prepared by Powder Metallurgy reported in the literatures, suggesting that the HEA developed is highly promising for engineering applications. The excellent mechanical properties of the bulk HEA can be attributed to that the multi-scale precipitates are fully coherent with the matrix, which could reduce the misfit strain at the interface, and relieve the stress concentration during deformation.     

Mechanical properties investigation of carbon/carbon composites fabricated by a fast densification process

Carbon/carbon (C/C) composites were prepared by thermal gradient chemical vapor infiltration with a fast densification rate. The fracture morphology and mechanical properties were examined by scanning electron microscopy and mechanical testing, respectively. The effects of preform type and heat treatment temperature (HTT) on the mechanical properties of C/C composites were analyzed. The results show that the average flexural strength drops from 47.8 MPa to 38.6 MPa as the HTT increases from 2100 °C to 2500 °C. C/C composites with felt as preform show brittle fracture and samples with needle-punched felt as reinforcement present obvious pseudoplastic property. The interlaminar shear strength of needle-punched felt reinforced composites is higher than that of sample with felt as preform by 44.26% owing to the needle-punched fiber in the thickness direction. The strength of interfacial bonding plays a key role to mechanical properties and failure behavior of C/C composites.     

The mechanical properties of Fe-Co heterogeneous alloys fabricated by powder metallurgy techniques

Fe-Co heterogeneous alloys fabricated by powder metallurgy techniques were hot rolled, cold rolled and then heat treated. These processes produced a type of fibre-reinforced composite which consisted of fibrous Fe and Fe-Co phases. The tensile strength of the alloys depended on the composition and degree of order of the Fe-Co phase. The rule of mixtures was applicable, provided that the dependence of strength in the Fe-Co phase on Co content was considered.