Effect of spark plasma sintering and reinforcements on the formation of ultra-fine and nanograins in AA2024-TiB2-Y hybrid composites

This study reports the influence of sintering mechanism and reinforcement materials on the formation of ultra-fine and nanograins in Al-TiB₂-Y nanohybrid composites. The mechanical properties of the composites and their corresponding micro and nanostructures are correlated. The experimental and characterization results revealed that despite the addition of TiB₂, the hard and brittle Al₃Ti phase formation in the composites was suppressed and hence, their ductility was retained. It was found that yttrium content of 0.3 ?wt% was the optimum amount which created advantageous spark plasma sintering conditions, and the addition of 0.3 ?wt% promoted the formation of bi-modal size grains (ultra-fine and nano) along with micro grains, Ω and other nano precipitates, resulting in a significant enhancement in the composite properties. The formation of ultra-fine and nanograins may be attributed to the combined effect of melting and rapid solidification at necking zones due to Joule's heating and thermo-mechanical fatigue. Among all the sintered composites, the highest hardness (137 HV), ultimate tensile strength (UTS) (496 ?MPa), yield strength (YS) (438 ?MPa) with 15.7% elongation were obtained in the sintered sample reinforced with 1.0 ?wt% TiB₂ and 0.3 ?wt% yttrium.     

电沉积Ni—P—Si3N4复合镀层的摩擦学特性

通过摩擦磨损试验、Ｘ射线衍射分析和电子探针分析等，研究电沉积Ｎｉ－Ｐ－Ｓｉ３Ｎ４复合镀层的摩擦磨损机理及其与结构和力学特性的关系。结果表明，在干摩擦条件下，复合镀层中的Ｓｉ３Ｎ４微粒能有效降低摩擦副之间的粘着脱落和犁沟效应；在油润滑条件下，复合镀层中Ｓｉ３Ｎ４微粒起到支承载荷作用，同时有利于边界润滑膜的形成，避免粘着磨损，复合镀层中Ｓｉ３Ｎ４微粒共析量的增加是提高复合镀层耐磨性的重要因素。     

High-throughput synthesis of oxidation-resistant Nb–Si based alloy thin film by magnetron co-sputtering

A high-throughput method was applied to study oxidation behavior of Nb–Si based alloy using composition spread alloy film as combinatorial libraries. An extended range of composition gradients of Nb–Si based alloy film was deposited by (multi)magnetron co-sputtering. The as-deposited film was composed of amorphous phase. Cr₂Nb, Nb₅Si₃ and Nb_ss could be detected after annealing treatment. After oxidation at 1250 ?°C for 10 ?min and 20 ?min, the film composition space was divided into three regions of the distinct oxide scales. The compositions for establishment of the different oxides on Nb–Si based alloy was defined efficiently across the entire composition space by the combinatorial libraries.     

Formation mechanism of interfacial microstructures and mechanical properties of Ti2AlNb/Ni-based superalloy joints brazed with NiCrFeSiB filler metal

Dissimilar brazing of Ti₂AlNb-based alloy and Ni-based wrought superalloy (GH536) was studied using NiCrFeSiB filler metal. The Ti₂AlNb/GH536 joints were analyzed by scanning electron microscope (SEM) equipped with an electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The formation mechanism of interfacial microstructure and mechanical properties of Ti₂AlNb/GH536 joints were studied. The results indicated that Ti₂Ni(Al,Nb), AlNi₂Ti and TiB₂ reaction layers were formed in the joint adjacent to Ti₂AlNb base metal. These layers resulted in high micro-hardness and the weak link of the joint. γ solid solution was formed through isothermal solidification and β₁-Ni₃Si phase precipitated in the γ solid solution during cooling process. Ni₃B, β₁-Ni₃Si and CrB phases appeared in the centre of the joint. Blocky and needle-like borides formed within the diffusion affected zone of GH536 base alloy. The maximum tensile strength of Ti₂AlNb/GH536 joints reached 425 ?MPa ?at room temperature and the strength value of 373 ?MPa was maintained at 923 ?K.     

Highly <Emphasis Type="Italic">C</Emphasis>-axis oriented LiNbO<Subscript>3</Subscript> thin film on amorphous SiO<Subscript>2</Subscript> buffer layer and its growth mechanism

LiNbO3 waveguiding films with highly C-axis orieatation and superior crystallographic quality have been deposited on the amorphous SiO2 buffer layer of Si wafer by pulsed laser deposition (PLD) technique. X-ray diffraction,high-resolution electron transmission microscopy and atomic force microscopy were applied to characterizing the quality and orientaion of LiNbO3 thin film, and the optimized depositioa coaditioas have been determined for C-axis oriented growth. LiNbO3 thin films on amorphous SiO2 buffer layer were composed of intimate arrangements of quadrangular single crystal domain (150 nm x 150 nm) with C-axis orientatioa, and displayed sharp interface structures. The measurements of prism coupling technique indicate that the laser can be coupled into the LiNbO3 film and TE and TM waveguiding modes were detected. In addition, the possible mechanism of oriented growth on amorphous buffer layer and “film-substrate effects“ were discussed briefly, which suggests that its growth mechanism is likely analogous to the Voimer model with characteristics of three-dimensional islands nucleation on the smooth crystal surface.     

Correlation between structure and hardness of magnetron sputtering deposited CNx films

Carbon nitride films are deposited on Si (001) substrates by reactive dc magnetron sputtering graphite in a pure N2 discharge. The structure of carbon nitride films has been probed using Fourier transformation infrared, near edge X-ray absorption fine structure (NEXAFS) and high resolution electron microscopy (HREM), and the hardness has been evaluated in nanoin-dentation experiments. FTIR spectra show that N atoms are bound to sp1, sp2, and sp3 hybridized C atoms. C1s NEXAFS spectra show that the intensity of π* resonance is the lowest for the film grown at substrate temperature TS = 350℃, with a turbostratic-like structure and high hardness, while it is the highest for the film grown at TS = 100℃, with an amorphous structure and low hardness. The correlation between the structure and hardness of carbon nitride films has been discussed.     

Effects of Cr and Mo elements on the microstructures and compressive properties of the in situ (TiC_xN_y–TiB_2)/Ni cermets

In-situ(TiC_xN_y–TiB_2)/Ni cermets with 70 wt%TiC_xN_y–TiB_2 were successfully fabricated by combustion synthesis and hot pressing sintering in Ni-Ti-B_4C-BN powder systems.The microstructures,density,compressive properties,and hardness of the TiC_xN_y–TiB_2/Ni cermets with the addition of 0–8 wt%Cr/Mo to the Ni-Ti-B_4C-BN powder systems were compared and analysed.The results showed that the ceramic particles distributed uniformly in the cermets,and the size of the ceramic particles reduced with the Cr/Mo addition.Both Cr and Mo addition can improve the hardness,compressive properties,and fracture strains of the cermets.The hardness,compressive strength,and fracture strain of the(TiC_xN_y–TiB_2)/(Ni+Cr)cermets increased from 1561 HV,2.94 GPa,and 2.9%to 1864 HV,3.65 GPa,and 3.4%,respectively when the Cr content increased to 5 wt%.The hardness and compressive strength of the(TiC_xN_y–TiB_2)/(Ni+Mo)cermets increased from 1561 HV and 2.94 GPa to 1902 HV and 3.43 GPa,respectively when the Mo content increased to 8 wt%.The cermets with Cr had better compressive properties than the cermets with Mo.     

Anti-allergic effects of ethanol extracts from brown seaweeds

Ethanol extracts of brown seaweeds from Pakistan and China were isolated and compared for their antiallergenic activities. They included Sargassum tennerimum (ST) and Sargassum cervicorne (SC) from Pakistan, and Sargassum graminifolium turn (SG), Sargassum thunbergii (STH), and Laminaria japonica (LJ) from China. The ethanol extracts of these brown seaweeds were optimized at 85% (v/v) ethanol for the maximum yield of phlorotannin, an inhibitor against hyaluronidase. Total phlorotannins contained in the crude extracts were measured as 1.71% (SG), 0.74% (STH), 0.97% (LJ), 3.30% (SC), and 5.06% (ST). The 50% inhibitory concentrations (IC₅₀) of Pakistani SC and ST were 109.5 and 21 μg/ml, respectively, lower than those of Chinese SG, STH, and LJ (134, 269, and 148 μg/ml, respectively). An antiallergic drug, disodium cromoglycate (DSCG), had an IC₅₀=39 μg/ml, and a natural inhibitor of hyaluronidase, catechin, had an IC₅₀=20 μg/ml. The IC₅₀ of ST extract was found similar to that of catechin (21 vs 20 μg/ml) and lower than that of DSCG (21 vs 39 μg/ml). This suggests that ST is a potent inhibitor of hyaluronidase, indicating a promising future development of natural antiallergic medicines or functional foods.     

氮化硅陶瓷的摩擦磨损特性

采用无压烧结和反应烧结两种方法制备氮化硅陶瓷，利用拴盘式摩擦实验机考察了氮化硅与ＧＣｒ１５球对磨的摩擦损特性，结果表明，虽然氮化硅具有较高的摩擦系数，但磨损率较低，特别是在水和油等介质存在的条件下，氮化硅具有低摩擦和磨损的特性。     

The evolution of microstructure and mechanical properties during high-speed direct-chill casting in different Al-Mg2Si in situ composites

The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al-Mg₂Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al-Mg₂Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg₂Si particles (from 28 to 12 μm), the spacing of eutectic Mg₂Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg₂Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg₂Si phase and the grains in the Al-Mg₂Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al-Mg₂Si composites and AA6061 alloy billets.     

Interface bond mechanisms of ceramic-cemented carbide compact insert

Conclusion Ceramic-cemented carbide compact inserts have been developed by hot-pressing sintering techniques, the upper part of the compact insert is of Al₂O₃ + TiB₂ ceramic material, while the base part of the compact insert is of WC + Co cemented carbide. The compact insert makes full use of the advantages of the high hardness of ceramic materials and the high strength of cemented carbide, and its mechanical properties are just between that of Al₂O₃ + TiB₂ and WC + Co. SEM, XRD and electron microprobe analysis showed that element diffusion and formation of new phases are the main causes for the bond of Al₂O₃ + TiB₂ with WC + Co in the interface.     

水镁石润滑剂的研制及其润滑性能的研究

研制一种润滑性能较好的水基粘土润滑剂.在MMW-5G摩擦试验机上比较13种粘土材料的干粉摩擦性能,发现水镁石的润滑效果最好,以水镁石为基料,配置成环保水基润滑剂,然后以四球为摩擦副,比较含不同量的聚丙烯酰胺(PAM)、硼酸的该润滑剂的摩擦系数,得到最优配比下PAM、硼酸的浓度分别为1%和5%,摩擦系数相对于空磨降低了85%.关于PAM含量、硼酸含量、粘土种类的三因素三水平的正交试验(L9(34)),验证了单因素的最优配比.参考最优配比,研究不同粘土材料的摩擦性能、该润滑剂在不同载荷、转速下摩擦性能的变化.结果表明:同其他粘土材料相比,该润滑剂的润滑效果较好;随着载荷的增加摩擦系数先减小后增大;随着转速的增加摩擦系数逐渐减小.     

天然海水润滑下不锈钢316L与PEEK450CA30的摩擦磨损性能

为了寻找适合于低速大扭矩水液压马达配对副的材料,采用MMU-5G屏显式高温材料端面摩擦磨损试验机考察不同转速、不同载荷下,摩擦副316L-PEEK450CA30在海水中的摩擦磨损性能,并借助OLYMPUS-SZX体式显微镜对试样的磨损表面进行形貌观察。结果表明:在转速和载荷比较低的情况下,摩擦副316L-PEEK450CA30的摩擦系数较小,磨损性能较好;当转速或载荷增大时,摩擦副的摩擦系数和接触面的磨损情况会急剧增大。在转速300r/min、载荷100N和转速100r/min、载荷300N的情况下,摩擦副316L-PEEK450CA30还会发生轻微的黏着磨损。最后得出,当转速为100r/mim、载荷为100N时,对偶副间的摩擦系数最小,耐磨损程度最好,适合作为低速大扭矩水液压马达的对偶副材料。     

医用不锈钢表面TiN薄膜的组织结构和力学性能研究

为改善医用不锈钢的耐磨性,采用反应磁控溅射在304不锈钢表面沉积了TiN薄膜,研究了Ti过渡层沉积时间对TiN薄膜微观结构和力学性能的影响。通过Ｘ射线衍射仪、扫描电子显微镜、纳米压痕仪、FST1000型薄膜应力测试仪、HSR-2M摩擦磨损试验机和WS-2005型涂层附着力自动划痕仪对样品进行微观组织表征和力学性能测试。结果表明,当Ti过渡层沉积时间为20 min,Ti过渡层厚度为340 nm时,TiN薄膜结晶性最强,硬度和弹性模量达到最大值,分别为21.6 GPa和327.5 GPa,平均摩擦因数达到最小值0.45,临界载荷达到最大值24.7 N,TiN薄膜的力学性能、摩擦性能以及与基体的结合力达到最优。进一步延长Ti过渡层的沉积时间,TiN薄膜的柱状晶组织粗化、力学性能、摩擦性能以及与基体的结合力均降低。     

理论研究半金属TiB2的电子结构和光学特性

为了系统地分析半金属TiB₂的能带结构及光学特性，采用密度泛函理论的第一性原理平面波赝势方法，计算分析了TiB₂的电子结构及光学特性。能带结构表明TiB₂具有直接带隙宽度为0.388 eV的半金属材料，在费米能级附近，态密度的价带主要由Ti的3p价电子和B的2p价电子起作用，导带由Ti的3d价电子起主要贡献。从获得的光学特性参数发现在光子能量为0.73 eV处，Ti的4s3p和B的2p电子发生共振，复介电函数的峰值主要出现在低能区，材料对紫外光的最大吸收系数为4.03×10⁵cm^-1。本研究得到的光学特性参数在光电子器件、微电子和紫外探测器等制作方面有着较好的参考作用。     

离心铸造高铅锡青铜合金摩擦磨损性能研究

采用离心铸造方法制备了高铅锡青铜(ZCu Pb22Sn1.5)合金,研究了载荷和摩擦速度对其摩擦磨损性能的影响及摩擦磨损机理.研究发现:在0.05 m/s摩擦速度下,随着载荷的增加,高铅锡青铜合金摩擦系数减小,磨损率增加,当载荷增加到120 N后,摩擦系数趋于稳定;在100 N载荷下,随着摩擦速度的增加,摩擦系数逐渐减小,磨损率增加,摩擦速度增加到0.10 m/s以后,摩擦系数迅速减小,到0.20 m/s以后摩擦系数趋于稳定;当继续增加载荷和摩擦速度时,由于铅润滑膜的破坏而增加了磨损率.在摩擦磨损过程中容易在摩擦表面形成软质铅润滑膜从而起到耐磨作用.     

湿滑状态下飞机轮胎与道面摩擦特性试验

湿滑道面会造成飞机制动性能下降,影响起降安全。本文通过搭建污染跑道摩擦特性测试装置,根据飞机在湿滑道面滑跑的实际情况,对飞机轮胎在不同水膜厚度、速度、载荷条件下运行的接触力、滑移距离进行研究,分析了湿滑条件下道面摩擦特性与影响因素间的关系。实验结果表明：水膜厚度对道面摩擦特性影响显著,水膜厚度为13mm时,轮胎与道面之间的接触应力变化明显,滑移距离大幅度增加。随着速度的增加,轮胎与道面之间的接触应力呈线性增加趋势,过高的速度会增加滑水风险。轮胎载荷的增加会减少湿滑道面上的滑移距离,在一定程度上提高飞机轮胎的载荷,能有效改善湿滑道面上的摩擦特性。     

硅片不同表面钝化工艺的稳定性研究

研究分析了热氧化钝化,用PECVD双面沉积SiNx:H膜钝化以及碘酒钝化三种表面钝化工艺的稳定性,通过WT-2000少子寿命测试仪对采用这三种钝化工艺的单晶硅片,多晶硅片以及物理提纯硅片在暗条件不同储存时间的少子寿命进行测量,分析得到三种表面钝化工艺的效果以及稳定性。研究结果表明:碘酒钝化效果好,用PECVD双面沉积SiNx:H膜钝化和热氧化钝化稳定性好。     

湿式离合器接合特性仿真与分析

为了研究湿式离合器的接合特性,考虑摩擦副表面温度、相对速度、粗糙度以及载荷对摩擦系数的共同影响,基于流体动力润滑理论、粗糙表面弹性接触理论、吸附热理论以及传热学理论建立了湿式离合器接合过程数学模型。分别讨论了接合压力、摩擦副表面粗糙度、摩擦材料渗透性对接合过程中油膜厚度、相对角速度以及传递转矩的影响规律。结果表明：增大接合压力,转矩响应、相对角速度减小速度以及油膜厚度减小速度都会加快,接合时间缩短,最小油膜厚度减小;减小摩擦副表面粗糙度,转矩响应减慢,但相对角速度减小速度和油膜厚度减小速度都会加快,接合时间缩短,最小油膜厚度减小;增大摩擦材料渗透性,转矩响应和相对角速度减小速度以及油膜厚度减小速度都会加快,接合时间缩短,但最小油膜厚度变化较小。     

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB2 + TiC by laser cladding

A Ni-based composite coating reinforced by in situ synthesized TiB₂ and TiC particles was fabricated on Ti6Al4V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The microstructure and the microhardness profile across the coating were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements (black blocky TiB₂, flower-like or equiaxial TiC, and fine acicular CrB) and the γ matrix. The hardness of TiB₂, TiC, and CrB reinforcements is much higher than that of the γ matrix. The dispersive distribution of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hardness is approximately Hv_0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.