基于Bayes方法的Al-Mg-Mn合金断裂韧度研究

基于Bayes方法研究了Al-5.2Mg-0.7Mn-0.20Sc-0.1Zr合金的平面应变断裂韧度。结果表明,Al-5.2Mg-0.7Mn-0.20Sc-0.1Zr合金热轧板在L-T和T-L取向KIC值分别为32.66和32.03 MPa·m1/2,平面应变断裂韧度各向异性差别较小。     

转速对2524铝合金搅拌摩擦点焊组织与性能的影响

对2524铝合金薄板进行搭接搅拌摩擦点焊试验, 研究了搅拌头转速对其组织与性能的影响。结果表明, 随转速增加, 焊点外侧飞边越加严重, 组织畸变程度增加, 焊核区宽度增大, 有效连接宽度先增大后减小。母材区硬度最大, 热影响区硬度最低;在焊核区内, 显微硬度随转速增加而增大, 当转速为1 100 r/min时达到最大133.9HV, 而热影响区在300 r/min时硬度最大。在单向拉伸试验中, 接头剪切强度随转速增加先增大后减小, 在700 r/min时达到最大值3 510 N;接头呈现出两种断裂模式: 即低转速下平行于两板面断裂和高转速下沿倾斜方向断裂;断口呈现明显的剪切韧窝形态, 韧窝小而浅, 焊接接头为韧性断裂。     

机制砂混凝土耐磨性的主要影响因素分析及多因素计算模型

本文研究了砂类型、砂率、石粉含量和抗压强度对机制砂混凝土耐磨性的影响,建立了磨损量的多因素计算模型。结果表明:由于含石粉及具有更高的粗糙度和坚固性,石灰岩与辉绿岩机制砂制备的C30、C40混凝土耐磨性比河砂混凝土提高20%以上;在0.40~0.44范围内选取较低的砂率可获得较优的耐磨性;利用石粉含量为5%~11%(质量分数)的机制砂制备混凝土,石粉含量为9%时可获得最佳的混凝土耐磨性,微观分析表明此时混凝土密实度最佳;通过灰色系统理论确定了耐磨性影响因素的影响程度排序为:砂率R₃>压碎值R₂>粗糙度R₁>抗压强度R₅>石粉含量R₄>0.6;对比验证表明提出的混凝土磨损量多因素计算模型具有较高的预测精度和良好的适用性。     

铸态Mg-xSn-1Mn合金的显微组织和阻尼性能

采用光学显微镜(OM)、维氏硬度计、热动态分析仪、X射线衍射(XRD)、多功能内耗仪等,研究了Sn含量对Mg-xSn-1Mn合金显微组织、阻尼性能和力学性能的影响。结果表明:当Sn含量从2%增加到8%时,Mg-xSn-1Mn合金的枝晶间隙呈现细化的趋势,硬度从43.84 HV0.1增加至54.00 HV0.1,呈单调增加的趋势。应变无关阻尼随着Sn含量的增加呈现先增后减的趋势,在Sn含量为4%时达到最大,应变相关阻尼则随着Sn含量的增加呈现逐渐减小的趋势。在低温阶段,相同Sn含量的合金的阻尼随着频率的增大呈现增加的趋势;但在高温下,阻尼值在低频时的上升速率比高频时快,并随着温度的升高,低频阻尼和高频阻尼趋向于相等。当Sn含量不同时,随着温度的升高,Sn含量较高的合金的阻尼值上升速率变快。     

Optimised phase compositions and improved microwave dielectric properties based on calcium tin silicates

The Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) low-permittivity microwave dielectric ceramics were prepared through solid-state reaction at 1350–1450 °C for 5 h. The relations between microwave dielectric properties and phase compositions for non-stoichiometric Ca_(1+2y)Sn_(1-x)Si_(1+y)O_(5-2x+4y) ceramics have been investigated. A single CaSnSiO₅ phase with abnormally positive temperature coefficient of resonant frequency (τ_f = + 62.5 ppm/°C) was synthesised at 1450 °C. This composition was an effective τ_f compensator of CaSiO₃ and Ca₃SnSi₂O₉ phases with typically negative τ_f value. The CaSiO₃ second phase was related to the Sn deficiency in the CaSn_(1-x)SiO_(5-2x) (0 < x < 1.0) composition, whereas the Ca₃SnSi₂O₉ second phase was obtained by controlling the Ca:Sn:Si ratios on the basis of the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (0 < y < 1.0) composition. A promising low-permittivity millimetre-wave ceramic with most excellent microwave dielectric properties (ε_r = 10.2, Q×f = 81,000 GHz and τ_f = −4.8 ppm/°C) was produced from the Ca_(1+2y)SnSi_(1+y)O_(5+4y) (y = 0.4) ceramic.     

基于一种改进逐点比较插补法的激光打标机控制加工算法

在激光打标系统中,逐点比较插补法是一种普遍使用的算法。这种算法在控制激光运动轨迹和对图像轨迹的拟合过程中,起到极其重要的作用。由于逐点比较插补法具有运算直观,脉冲输出均匀,调节方便等特点,所以是一种较为适合打标机系统应用的插补算法。但是传统的逐点比较插补算法存在精度低和速度慢等问题。为了改善该算法的性能,对传统逐点比较插补算法进行了改进,并进行了计算和模拟仿真。结果表明改进比较插补算法在精度和速度上都有明显提高。     

Nickel foam-supported Fe,Ni-Polyporphyrin microparticles: Efficient bifunctional catalysts for overall water splitting in alkaline media

Developing highly active, stable and sustainable electrocatalysts for overall water splitting is of great importance to generate renewable H₂ for fuel cells. Herein, we report the synthesis of electrocatalytically active, nickel foam-supported, spherical core-shell Fe-poly(tetraphenylporphyrin)/Ni-poly(tetraphenylporphyrin) microparticles (FeTPP@NiTPP/NF). We also show that FeTPP@NiTPP/NF exhibits efficient bifunctional electrocatalytic properties toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Electrochemical tests in KOH solution (1 M) reveal that FeTPP@NiTPP/NF electrocatalyzes the OER with 100 mA cm⁻² at an overpotential of 302 mV and the HER with 10 mA cm⁻² at an overpotential of 170 mV. Notably also, its catalytic performance for OER is better than that of RuO₂, the benchmark OER catalyst. Although its catalytic activity for HER is slightly lower than that of Pt/C (the benchmark HER electrocatalyst), it shows greater stability than the latter during the reaction. The material also exhibits electrocatalytic activity for overall water splitting reaction at a current density of 10 mA cm⁻² with a cell voltage of 1.58 V, along with a good recovery property. Additionally, the work demonstrates a new synthetic strategy to an efficient, noble metal-free-coordinated covalent organic framework (COF)-based, bifunctional electrocatalyst for water splitting.     

带有方形肋及双倾斜肋片的细通道内流动、传热和熵产分析

为了探究带有方形肋及双倾斜肋片细通道的流动换热及熵产特性，设计了2种带有方形肋及双倾斜肋片的组合细通道(MCDS-L, MCDS-R)，然后采用数值模拟的方法分析其流动特性、传热特性和熵产特性，并将其分析结果同2种方形肋细通道(MCS-L, MCS-R)和一种双倾斜肋片细通道(MCD)进行对比。结果表明，在所研究的雷诺数范围内，组合通道的摩擦阻力系数基本一致且均高于其他3组通道(MCS-L, MCS-R, MCD) 。此外，组合通道的努塞尔数均高于其他3组通道，而熵产增大数均低于其他3组通道。其中，MCDS-L通道的努塞尔数最大，熵产增大数最低。表明MCDS-L通道的换热效果最佳，能量的综合利用程度最高。研究成果为微细通道热沉的设计提供参考。     

Highly textured and strongly anisotropic TiB2 ceramics prepared using magnetic field alignment (9T)

Highly textured TiB₂ ceramics were prepared by slip casting an aqueous suspension in a magnetic field of 9 T, followed by sintering using Field Assisted Sintering Technology (FAST). Particle size refinement by ball milling improved both the degree of texturing and densification of the material (RD > 98 %). The sintered material exhibited a Lotgering orientation factor of 0.90, with the c-axis of TiB₂ oriented parallel to the magnetic field and FAST pressing direction. The texturing effect induced by the uniaxial pressing was negligible. The textured TiB₂ material exhibited a significant anisotropy in mechanical properties; the values of hardness and indentation elastic modulus measured along directions transverse to the c-axis of TiB₂ were 37 % and 13 % higher than the ones measured along the c-axis direction. Moreover, the specific wear rate of a surface of textured TiB₂ parallel to the field was one order of magnitude lower than a surface perpendicular to the field.