Spectroscopic evidence of inhomogeneous distribution of Nd in YVO4, YPO4 and YAsO4 crystals

Nd³⁺ : YVO₄ is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd³⁺ in three zircon type crystals YMO₄ (M=V, As, P). In particular, Nd³⁺ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO₄, single crystals containing 7 ± 1 × 10¹⁸ Nd³⁺ ions/cm³, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd³⁺ ions. Nd³⁺ ions are found to be inhomogeneously distributed in tetragonal D_2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd³⁺ ions are gathered in Nd³⁺–Nd³⁺ pairs for 7.2 ± 0.2 × 10¹⁹ Nd³⁺ ions/cm³.     

钛酸钾晶须-玻璃纤维/苯并噁嗪混杂复合材料的摩擦磨损性能

利用六钛酸钾晶须（K₂O·6TiO₂）对苯并噁嗪（BOZ）树脂及玻璃纤维/苯并噁嗪（GF/BOZ）复合材料的摩擦磨损性能进行改性,分析了K₂O·6TiO₂/BOZ复合材料以及K₂O·6TiO₂-GF/BOZ混杂复合材料的摩擦磨损性能以及改性机理。结果表明:因K₂O·6TiO₂的加入,K₂O·6TiO₂/BOZ复合材料以及K₂O·6TiO₂-GF/BOZ混杂复合材料的摩擦系数和比磨损率较纯BOZ树脂和GF/BOZ复合材料的明显降低。K₂O·6TiO₂显著减轻了BOZ树脂和GF/BOZ复合材料的摩擦粘着状况,使摩擦系数降低,同时磨粒磨损情况也大为减轻。GF/BOZ复合材料在摩擦过程中摩擦应力通过率先破坏GF和BOZ树脂的界面,进而诱发破坏GF束内、GF束间和层间BOZ树脂,使得GF/BOZ复合材料的摩擦系数比BOZ树脂降低,但比磨损率较BOZ树脂升高,而K₂O·6TiO₂的加入,使K₂O·6TiO₂-GF/BOZ混杂复合材料的比磨损率有效降低。BOZ树脂、GF/BOZ、K₂O·6TiO₂-GF/BOZ 3种材料的摩擦系数和比磨损率分别为0.34和0.66×10-6 mm3·（N·m）-1,0.19和1.2×10-6 mm3·（N·m）-1,0.09和0.69×10-6 mm3·（N·m）-1。      

纳米晶体钛基掺钽TiO2薄膜的摩擦磨损性能

采用室温直流反应磁控溅射技术在纳米晶体钛表面制备掺钽TiO2薄膜,研究了掺Ta量对纳米晶体钛基TiO2薄膜摩擦磨损性能的影响。结果表明：在室温模拟人体体液条件下,掺钽TiO2薄膜与不锈钢淬火钢球（Φ4mm）对摩的磨损率为10^-6-10^-5mm^3·m^-1 N^-1级;随着Ta含量的增加,薄膜的摩擦系数和磨损率呈先...     

Abrasive wear behaviour of polymeric materials

In this study the abrasive wear behaviour of aliphatic polyketone (APK), polyoxymethylene (POM), ultrahigh molecular weight polyethylene (UHMWPE), polyamide 66 (PA66), and 30% glass fibre reinforced polyphenylenesulfide (PPS + 30%GFR) engineering polymers at room temperature were studied. Pin-on disc arrangement wear tests were carried out at 1 m/s test speed and load value of 10 N. Tests were carried out for 50, 100, 150 and 200 m sliding distances. Emery paper grid varying from 150 to 1200 grade were used as an abrasive disc surface. After each test the mass loss of the pin was recorded. Finally the specific wear rates were deduced from wear volume of the pin for test duration distances of 50, 100, 150 and 200 m. The results showed that the highest wear rate is for POM with a value of 8.5 × 10⁻⁴ mm³/N m and the lowest wear rate is for UHMWPE with a value of 3.36 × 10⁻⁵ mm³/N m. Furthermore, for all materials the wear rate increases linearly with increasing wear duration distance.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.     

C.V.D. Coating of Alumina Reinforcing Particles to Improve the Wear Resistance of H.S.S. Based Composites

C.V.D. coating of the reinforcing ceramic particles used in particulate metal matrix composites allows the control of reactivity at the particle/matrix interface. Wear resistant high speed steel-based composites containing uncoated A1₂0₃, uncoated TiC and C.V.D. coated A1₂0₃ were liquid phase sintered, then characterized using “pin-on-disc” wear testing. TiC or TiN C.V.D. coatings of A1₂0₃ were tested to determine die increase in reactivity of the particles with the liquid phases formed during sintering. This resulted in a porosity decrease at the particle/matrix interface in addition to a better ceramic/metal cohesion due to improved wettability. Reactivity and wettability were studied using differential thermal analysis, electron microprobe analysis, transmission electron microscopy, and image analysis. Results from pin-on-disc wear testing illustrated the role of the C.V.D. coating on the wear behavior of the studied materials. Lower wear rates were obtained with the composites containing TiC or TiN-coated Al₂0₃. These results showed that there is a relation between wettability of ceramic particles by the metallic phases and wear resistance of the composites.     

电子束重熔对机械合金化法制备TiC/Ti复合涂层组织及摩擦性能的影响

对机械合金化（MA）法制备的TiC/Ti复合涂层进行电子束重熔处理,分析了经过不同电子束扫描速度的重熔工艺后TiC/Ti复合涂层组织和耐磨性能的变化规律。结果表明,当扫描速度为5~15 mm/s时,重熔处理消除了MA法制备的TiC/Ti复合涂层中的孔隙和裂纹,使其硬度与耐磨性能显著提高;但扫描速度过快（20 mm/s）时,TiC/Ti复合涂层内部出现重熔导致的孔洞缺陷。随着扫描速度由5 mm/s增加至15 mm/s,重熔后TiC/Ti复合涂层中的TiC相由粗大树枝状晶体逐渐转变为弥散分布的短棒和颗粒状晶体,弥散强化作用和固溶强化作用逐渐增强,TiC/Ti复合涂层的硬度由重熔前HV 554逐渐提高至HV 783,磨损速率由5.93×10-4 mm3（N·m）-1逐渐下降至1.75×10-4 mm3（N·m）-1,扫描速度为15 mm/s重熔后TiC/Ti复合涂层的性能最佳。      

Improved tribological properties of sputtered MoS2 films through N implantation

The effect of N⁺ implantation on the microstructural and tribological properties of r.f.-sputtered MoS₂ films was studied. The cross-section scanning electron micrographs show that, after N⁺ implantation, the loose column structure of the sputtered MoS₂ films increases in density. A decrease in film thickness of about 50% is also observed. The results of X-ray diffraction analysis show that N⁺ bombardment enhances the (100) edge plane orientation of the MoS₂ crystal in the film. The scratch test indicates an improved film-substrate adherence. The tribological test results indicate that N⁺ implantation yields a distinct enhancement in the wear life of the sputtered MoS₂ films. Compared with the as-deposited MoS₂ film, the wear life of the sputtered MoS₂ films implanted with 150 keV N⁺ at 1 × 10¹⁶ N⁺ cm⁻² shows a threefold increase in a relative humidity of 60%–70% and a twofold increase in a vacuum of 5 × 10⁻³ Pa. However, N⁺ implantation inreases the friction coefficient. The lubrication model of the N⁺-modified film is given.     

炭布/树脂复合摩擦材料的湿式摩擦学性能

基于炭布优异的摩擦磨损性能、 自润滑性能以及低密度等特点, 将其应用于湿式摩擦材料中, 以适应高转速、 大压力或润滑不充分等极端工况。分别以1 K、 3 K和6 K碳布为增强体, 制备出三种炭布/树脂复合摩擦材料, 研究了其湿式摩擦学性能。结果表明: 随着纤维束内单丝数量的增加, 摩擦材料的瞬时制动稳定性降低, 动摩擦系数减小, 但是耐磨性能提高。所有摩擦材料的磨损率小于1.10×10^-5 mm³/J, 表现出较好的耐磨性能, 并且对偶材料的磨损率很小, 仅为0.40×10^-5 mm³/J。磨损主要表现为纤维断裂、 拔出及树脂脱粘等形式, 但是在磨损表面没有形成大尺寸磨屑和明显的"第三体"磨粒, 导致摩擦材料和对偶材料的磨损率较小。     

微量W元素的添加对CoCrFeNiMnAl高熵合金的组织与性能的影响EI北大核心CSCD

高熵合金(HEAs)表现出比传统合金更为优异的耐磨耐蚀性能,逐渐成为金属材料领域的研究热点。采用金属热还原法制备不同W含量的CoCrFeNiMnAlW_(x)(x=0.12,0.15,0.19)高熵合金,研究微量W元素的添加对CoCrFeNiMnAlW_(x)高熵合金的相结构、微观组织与性能的影响。采用XRD,SEM和EDS等技术表征该合金的相结构、显微组织及元素分布,利用材料表面性能测试仪和电化学工作站测定该合金的摩擦磨损性能和电化学腐蚀性能。结果表明:不同W含量高熵合金均由两种不同晶格常数的BCC相组成,随着W含量的增加,BCC1相微观相貌并没有明显的变化,但是BCC2相的微观形貌和元素分布随W含量的变化而明显变化,而耐磨损性能和耐腐蚀性能均有一定程度的提高,CoCrFeNiMnAlW_(0.19)合金的摩擦因数和磨损率分别为0.684和1.06×10^(-5)mm^(3)/(N·m),磨损机制由黏着磨损转变为黏着磨损和磨粒磨损相结合,最后再转变为摩擦磨损;在3.5%NaCl溶液中的腐蚀电流密度从6.08×10^(-6)A/cm^(2)减小到1.72×10^(-6)A/cm^(2),腐蚀速率也逐渐减小。     

45钢离子氮碳氧三元共渗与QPQ处理对比研究EI北大核心CSCD

盐浴复合(QPQ)技术为公认的能同时提高金属材料耐腐蚀性和耐磨性的表面改性技术,但其推广使用受到环保制约。为开发绿色高效表面改性技术,探索了离子氮碳氧三元共渗(PNCO)技术,并与QPQ技术改性效果进行了对比研究。选择45钢为原材料,分别采用PNCO技术和QPQ技术进行表面改性。利用光学显微镜及扫描电子显微镜、XRD、显微硬度计、摩擦磨损试验机、浸泡腐蚀实验对两种表面处理试样的截面显微组织、物相、表面及截面硬度、耐磨性和耐腐蚀性进行测试和分析。结果表明,在510℃×4 h工艺条件下,PNCO处理获得的化合物层厚度为20.14μm,有效硬化层厚度为59μm,截面最高硬度为760HV_(0.05),磨损率为1.39×10^(-3)g·N^(-1)·m^(-1),腐蚀失重率为0.39%。XRD结果分析表明,PNCO处理后渗层形成了Fe_(x)N化合物和以Fe_(3)O_(4)为主的氧化物相。PNCO和QPQ对比研究发现,两者表层硬度、耐磨性及耐腐蚀性均相近。本研究为绿色高效表面改性技术提供了可行的研究方向。     

Information geometry in functional spaces of classical and quantum finite statistical systems

Statistical states and bounded random variables (observables) of finite physical systems can be represented in real Banach spaces L_s¹ and L_s^∞, respectively. Since both norms are Krein-weak, the solution of the estimation problem in these spaces is not necessarily unique. The latter property occurs on the Hilbert-Schmidt space L_s² which is connected with the Onicescu information energy and the method of least squares. The square information is only an approximation of the “true” logarithmic Shannon information which induces a “logarithmic” asymmetric geometry by means of the concept of relative information (gain of information). This geometry was known in the classical case as the asymmetric Pythagorean geometry (Chentsov [10]) and is approximated by the Riemannian geometry of Fisher's information (Kullback and Leibler [45]). This paper shows that a similar geometric construction is also possible in the quantum case. The fundamental formulae of the quantum case are given (they differ in some details from the classical ones), and possible physical applications are shortly sketched.     

Investigation of the dependence of the contact resistance on the external gold layer in AuNiGeAu/n-GaAs

The contact resistance of an Au/Ni/Ge/Au metallization system on n-GaAs exhibits a drop in contact resistance from 13.3 × 10⁻⁶ ω cm² to 8.6 × 10⁻⁶ ω cm² when the external gold layer is varied from 800 Å to 6000 Å in thickness. Secondary ion mass spectroscopy indicates that the improvement in contact resistance is due to the gold's “regulating” the amount of NiAs formed, leading to an increase in the area fraction covered by the Ni₂GeAs. The result shows that the external gold layer deposited to improve bonding should be optimized in thickness. This role played by the external gold layer of the metal system in affecting the contact resistance has not been previously studied.     

高Cu铸造铝合金的摩擦磨损性能EI北大核心CSCD

采用压铸工艺制备Cu含量为5%~20%(质量分数,下同)的Al-Cu合金试样。在布氏硬度计上测定试样的硬度,利用球盘往复式磨损试验机进行3种载荷(1~5 N)的磨损实验,通过SEM和EDS分析不同Cu含量试样的磨损机理。结果表明:随着Cu含量从5%增加至20%,Al-Cu合金中θ相的体积分数由2.00%增加到25.80%,且θ相的尺寸逐渐增大;硬度从59HB增加到170HB。摩擦因数在0.4~0.85范围内变化;Al-Cu合金试样的比磨损率随Cu含量增加先急剧降低后趋于平缓,Cu含量达到15%以上合金试样比磨损率变化不大,最低比磨损率在4.1×10^(-4)mm 3·N^(-1)·m^(-1)左右;较低Cu含量试样的比磨损率随载荷变化显著,随着Cu含量增加比磨损率差别减小。Al-Cu合金的主要磨损机制为黏着磨损和磨粒磨损,低Cu含量试样以黏着磨损为主,高Cu含量试样以磨粒磨损为主;随着载荷的增加,低Cu含量试样黏着磨损程度增加,高Cu含量试样磨粒磨损程度增加。     

A uniaxial nonlinear viscoelastic constitutive model with damage for M30 gun propellant

The nonlinear viscoelastic mechanical response of a conventional tank gun propellant, M30, is modeled using a “modified superposition integral” that incorporates the effects of microstructural fracture damage. Specifically, a linear, time-dependent kernel is convolved with the first-time derivative of a power-law function of stress and a damage “softening” that accounts for damage evolution by a microcrack growth mechanism. The microcrack damage function is a master curve formed from shifted isothermal, compressive, uniaxial constant strain rate (0.01 s⁻¹ to 420 s⁻¹) data on solid, right-circular cylinders of M30 gun propellant. An attractive feature of the model is its ability to predict work-softening behavior under conditions of monotonically increasing deformation. Time-dependent predictions of stress versus time, failure stress versus failure time, and failure stress versus strain rate, quantitatively agree with experimental results from constant strain rate tests on the propellant. Theoretical predictions of time-dependent stresses for Heaviside and “ballistic-like” strain histories are also provided.     

莫来石与碳纤维协同填充的聚四氟乙烯基复合材料及其摩擦学性能

为了提高聚四氟乙烯（PTFE）的摩擦学性能,采用机械混匀、带温预压及烧结等工艺制备了莫来石和碳纤维填充的PTFE基复合材料,并通过FTIR、XRD、万能材料试验机、洛氏硬度计、DSC及热机械分析分别表征了PTFE基复合材料的显微结构、力学性能和热学性能;然后,使用MRH-3 型高速环块磨损试验机测定了复合材料的摩擦系数和磨损率,通过自制的硅油砂浆磨损装置测定了复合材料在不同温度下的耐砂浆磨损性能;最后,借助3D测量激光显微镜研究了复合材料摩擦面形貌,并分析了摩擦磨损机制。结果表明:莫来石和碳纤维在PTFE体系中起到填充增强作用,20wt%莫来石-10wt%碳纤维/PTFE复合材料的弹性模量由364 MPa增加至874 MPa;20wt%莫来石-10wt%碳纤维/PTFE复合材料的干摩擦系数较大,但其磨损率与纯PTFE相比降低了3个数量级以上,且此复合材料在水摩擦条件下仍能保持较好的摩擦系数和磨损率,摩擦系数为0.157,磨损率为7.40×10-6 mm3·N-1·m-1;此外,20wt%莫来石-10wt%碳纤维/PTFE复合材料在较高温度下仍能表现出良好的耐砂浆磨损性能。所得结论表明改性得到的PTFE 基复合材料的摩擦学性能显著提高,复合材料可用于有杆抽油井防偏磨。      

Computer simulation of martensitic textures

We consider a Ginzburg-Landau model free energy F(ε, e₁, e₂) for a (2D) martensitic transition, that provides a unified understanding of varied twin/tweed textures. Here F is a triple well potential in the rectangular strain (ε) order parameter and quadratic e₁², e₂² in the compressional and shear strains, respectively. Random compositional fluctuations η(r) (e.g. in an alloy) are gradient-coupled to ε, ˜ − ∑_rε(r)[(Δ_x² − Δ_y²)η(r)] in a “local-stress” model. We find that the compatibility condition (linking tensor components ε(r) and e₁(r), e₂(r)), together with local variations such as interfaces or η(r) fluctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective ε-ε interactions. We have carried out extensive relaxational computer simulations using the time-dependent Ginzburg-Landau (TDGL) equation that supports our analytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and Fe_xPd_{1 − x} alloys can be explained on the basis of our analysis and simulations.     

Scaling flow fields from the impact of thin plates

A dimensional analysis is performed to obtain velocity scaling relationships for the perforation of thin plates. The approach used is an extension of Dienes and Walsh's “late-stage equivalence” and Holsapple and Schmidt's “coupling parameter” concepts, used to simplify velocity scaling of impact phenomena. The coupling parameter C for plate perforation, is shown to have the form C=dU^μδ^ν for the perforation of thick plates and the form C=dU^μδ^ν f(t/d) for the perforation of thin plates (d is the projectile diameter, t is the plate thickness, U is the impact velocity and δ is the projectile density). It is shown that μ=1/2 for momentum scaling and μ=1 for energy scaling, however, from scaled hydrocode output it is found that, for aluminum impacting aluminum, the value of μ is equal to 0.83±0.03, which is neither energy nor momentum scaling. It is also shown that velocity scaling of thick plate perforation, using the same materials in the model and prototype and the same t/d, is not possible. An example of velocity scaling hydrocode output is given where the radial particle velocity wave profiles from the model calculation at U=55.6km/s and t/d=0.675 are similar to those from the prototype calculation with U=100km/s and t/d=1.08.     

氩弧重熔对20G钢渗硼层组织结构和耐磨性能的影响

为了降低渗硼层的脆性,提高其耐磨性,对20G钢渗硼层进行了氩弧重熔处理,研究了渗硼层重熔前后的形貌、相结构、显微硬度及耐磨性。结果表明：渗硼层由FeB和Fe2B两相组成,经氩弧重熔处理后FeB相消除,氩弧重熔渗硼层由Fe23（C,B）6和Fe2B相组成,包括氩弧重熔区和过渡区;氩弧重熔处理使渗硼层表层微观硬度降低,且使...