混炼方式对螺旋纳米碳纤维增强天然橡胶复合材料力学性能的影响

采用干法和湿法两种混炼工艺制备了螺旋纳米碳纤维(HCNFs)/炭黑(CB)/天然橡胶(NR)复合材料,通过扫描电镜、拉伸试验机和应变扫描仪分别对所制备复合材料的界面形貌、力学性能和Payne效应进行了测试分析,考察了混炼方式对复合材料宏观力学性能及Payne效应的影响。结果表明,与纯CB填料相比,在干湿两种混炼方式下,添加适量的HCNFs(1～6份)能提高HCNFs/CB/NR复合材料的300%定伸应力、扯断伸长率、拉伸强度和硬度。与干法混炼相比,湿法混炼能明显增强HCNFs/CB/NR复合材料的Payne效应,并提升在HCNFs高添加量(2～6份)条件下的拉伸强度和扯断伸长率,这主要源于湿法混炼能够有效改善HCNFs在橡胶基质中的分散性。     

铝空气电池用6061和7075铝合金阳极电化学性能

研究了工业6061铝合金（6061）、航空7075铝合金（7075）和纯铝作为铝空气电池阳极材料的电化学性能，分析其作为阳极的可行性及适用环境。进行了阻抗、极化曲线和恒电流放电实验并进行了表面表征，计算了在40～120mA/cm²电流密度下连续恒流放电的阳极能量密度。用电子探针显微镜（EPMA）对电极表面形貌进行了研究，用波谱分析仪（WDS）进行表面分析。研究结果表明，合金元素在电池放电过程中会改变阳极的表面特性。6061中合金元素含量对电池阳极材料的性能产生了积极影响，使得合金的表面放电面积变大，放电均匀，更适合作为铝空气电池阳极材料。     

表面形态对铝合金表面注射结合性能的影响

通过对铝合金表面进行阳极氧化和偶联剂处理，提出了一种注塑工艺直接成形铝合金聚酰胺复合构件的方法。利用激光共焦扫描显微镜和傅里叶红外(FTIR)光谱仪对经处理过的铝合金表面结构和成分进行了分析，结果表明：铝合金表面粗糙度和偶联剂固化时形成的Si-O-Al、C-N等化学键对界面结合力有重要影响。讨论了阳极氧化工艺参数和偶联剂固化条件对铝合金表面形貌、成分和注塑复合构件力学性能的影响规律，借助扫描电子显微镜(SEM)分析了复合构件拉伸剪切的破坏机理。     

On processing of Ni-WC based functionally graded composite clads through microwave heating

Present study focuses on the development of four layered functionally graded clads (FGC) of Ni-WC based composite material on AISI 304 substrate through microwave heating route. Experimental trials were conducted inside a microwave applicator of domestic type at frequency range of 2.45?GHz. The optimal exposure time of 900?W microwave power was varied with compositional gradient and it was from 300 to 360?s. The mechanism of FGC formation through microwave heating was explained and developed FGC was subjected to mechanical and microstructure characterizations. The results of micro-structural analysis revealed that the FGC of ～1.8?mm thickness was produced and was free from any type of interfacial cracks and visible porosity. It was observed that WC particles were randomly dispersed in the nickel matrix. XRD study revealed the formation of inter-metallics, such as NiW₄, NiSi, and Cr₂₃C₆. Maximum value of microhardness was observed in the top FGC layer and was 880?±?30?HV.     

不同产地及成熟度牛油果及其油脂品质比较

分析不同产地及成熟度牛油果及其油脂理化性质,脂肪酸组成及反式脂肪酸组成。结果表明:牛油果作为水果,粗脂肪含量和粗蛋白质含量很高;不同产地及成熟度牛油果溶剂提取所得油脂理化性质和脂肪酸组成有一定的差异。研究可为进一步开发牛油果油和制定牛油果油标准提供参考。     

Effects of hydrogen content on powder metallurgy characteristic of titanium hydrides

The titanium dihydride (TiH₂) powder metallurgy has been attracted a lot of attention, but TiH₂ powder is difficult to press moulding. In this paper, the titanium hydride powder metallurgy including TiH₂ and unsaturated titanium hydrides (TiH_1.5) was investigated simultaneously compared with pure titanium metal powder metallurgy. The results indicates that the titanium hydride powder metallurgy is accompanied by the deoxidation self-purification effect during dehydrogenation process for both of TiH₂ and TiH_1.5, which have higher sintering density than pure titanium. There are the three stages relative to densification rate, namely the slow, rapid and full densification stages for all of three materials. The compressive yield strengths increase rapidly in the rapid densification stage and are unchangeable almost in the full densification stage after holding 2 h at 1300 °C. The titanium hydride powder metallurgy is helpful to obtain much better mechanical properties than the pure titanium metal powder metallurgy. Here the compressive yield strength of the as-sintered TiH₂ compact with the maximum hydrogen content is the best but has very small difference compared with that of the as-sintered TiH_1.5 compact after full sintering densification.     

Effect of thermomechanical processing on microstructure and mechanical properties of CoCrFeNiMn high entropy alloy

The CoCrFeNiMn high entropy alloy was produced by homogenization, cold rolling and recrystallization. The effects of thermomechanical processing on microstructures and tensile properties at different temperatures were investigated using X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and multi-functional testing machine. The results show that dendritic structures in cast alloy evolve into equiaxed grains after being recrystallized, with single face-centered cubic (FCC) phase detected. The most refined alloys, stemming from the highest rolling ratio (40%), exhibit the highest strength due to the grain boundary strengthening, while the variation of elongation with temperature shows a concave feature. For the coarse-grained alloys, both the ductility and work hardening ability decrease monotonically with increasing temperature. Serrated flow observed at intermediate temperatures is attributed to the effective pinning of dislocations, which manifests the occurrence of dynamic strain hardening and results in the deterioration in ductility. Besides, dimples on the fracture surfaces indicate the typical ductile rupture mode.     

Solidification of Be-free Ni-based dental alloy

A novel, Nb- and Si-rich and Be-free Ni-based alloy was cast by two methods of investment casting and continuous casting to study the microstructure evolution during solidification and its mechanical properties. The solidification of the alloy started with the primary crystallization of FCC-γ, followed by a binary eutectic reaction, with the formation of a heterogeneous constituent: FCC-γ+G-phase, which replaced the low-melting eutectic (FCC-γ+NiBe) in the Be-bearing alloys. AlNi₆Si₃ and γ′ formed during the terminal stages of solidification by investment casting, while the formation of AlNi₆Si₃ was suppressed by continuous casting. The Scheil solidification model agreed very well with the experimental results.     

A first-principles investigation on mechanical and metallic properties of titanium carbides under pressure

The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system.     

Fabrication of zirconia all-ceramic crown via DLP-based stereolithography

Zirconia ceramics have shown a wide applicable prospect in dental prosthetics because it possesses excellent mechanical performance and biocompatibility. The rheological behavior and curing properties of zirconia stereolithography slurry were studied, as well as the microstructure of the green, pyrolyzed, and sintered body. Variquat CC-42 NS was proved to be effective for zirconia powder dispersing in photocurable resin (SP-RC700). The curing characteristic of slurry showed that the depth of penetration tended to increase with the solid loading. Finally, the zirconia all-ceramic crowns were fabricated via DLP-based stereolithography printer. Results showed that the particles were evenly distributed in the cured resin matrix without obvious agglomeration, and the interlayered structure disappeared after binder burnout. The sample with a major crystalline phase of tetragonal zirconia and a porosity of 10(1)% were obtained after sintering at 1550°C.