Investigations of TaB2 on oxidation-inhibition property and mechanism of Si-based coatings in aerobic environment with broad temperature region for carbon materials

To investigate the formation mechanism of the dendrites glass-ceramics and the effect of TaB₂ modifier on the oxidation-inhibition ability of Si-based coatings in aerobic environment with broad temperature region for carbon materials, the Si-based coatings modified with different TaB₂ content were fabricated by the liquid phase sintering method. The fabricated coatings and its corresponding composite powders were investigated in dynamic TG aerobic environments up to 1500 ℃. The initial oxidation temperatures of Si-based coatings modified with TaB₂ powders are almost completely suppressed to 800 ℃. With the increase of TaB₂ phase content, the relative oxygen permeability of the Si-based coatings is significantly reduced, which can be interpreted as the generation of liquid boride, silicide and Ta-Si-B-O compound glass ceramics those can improve the stability of the coating. The formation mechanism of the dendrites glass-ceramics was illustrated.     

基于改进飞蛾扑火优化算法的MIMO雷达相位编码信号集设计

提出一种MIMO雷达相位编码信号集设计方法，该方法对飞蛾扑火优化算法进行改进，利用改进的飞蛾扑火算法优化相位编码信号集，提高其正交性.在改进方法中，增加对火焰的更新过程，使火焰不仅能够保存最优飞蛾位置还具有搜索最优解的功能.优化过程以自相关函数旁瓣峰值和、互相关函数峰值和，以及自相关函数旁瓣能量、互相关函数能量作为算法适应度函数.仿真实验结果表明，改进方法明显提高了飞蛾扑火优化算法的收敛速度和收敛精度，且优化得到的信号集具有较低的自相关旁瓣值和互相关值.     

Fabrication of high-purity HfSi2 powder via molten salt-assisted magnesium thermal reduction

In this work, high-purity HfSi₂ powders were successfully fabricated via a molten salt-assisted magnesium thermal reduction method using HfO₂ and Si as raw materials. The effects of reaction temperature and time on the formation of HfSi₂ were systemically investigated. The morphological and phase composition of as-prepared HfSi₂ powders were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen/oxygen determinator. The results indicated that as-obtained HfSi₂ powders possess the orthorhombic structure with approximately 6.4 μm in size and the oxygen content as low as 0.20%. This work can provide a novel route to fabricate the high-purity transition metal silicides powders.     

DP980高强钢连续退火后的组织与性能

研究了不同工艺参数对980 MPa级连续退火双相钢组织及力学性能的影响,利用光学显微镜、透射电镜(TEM)以及拉伸试验对双相钢的微观组织和力学性能进行测试及分析。结果表明:DP980钢的退火组织主要由铁素体、马氏体岛和少量的贝氏体组成,马氏体岛附近的位错密度较高。随着均热温度的升高,DP980钢的抗拉强度呈现先降低后升高的趋势,屈服强度与抗拉强度的趋势一致,伸长率先升高后降低。随着过时效温度的升高,DP980钢的抗拉强度和屈服强度降低,降低幅度较小,伸长率上升,但变化不明显,说明通过调整过时效温度来调控其力学性能的作用较小。     

相场法模拟GaAs衬底上InGaAs异质结表面形貌

本工作采用相场法模拟GaAs衬底上生长的In_(0.3)Ga_(0.7)As多层异质结构薄膜表面。通过引入多序参量,使用半隐性傅里叶谱方法求解Cahn-Hilliard方程可以求得带缓冲层结构的薄膜表面形貌。计算结果模拟了薄膜生长过程,研究显示,使用In0.15-Ga0.85As缓冲层,厚度从1nm增加到4nm,薄膜表面临界波长从34nm提升到80nm。随着缓冲层的厚度从1nm增加到10nm,使用正弦波表面的模拟结果显示,薄膜表面粗糙度从2.87nm下降到0.43nm,随机叠加波表面的模拟结果也类似,表面粗糙度从1.21nm下降到0.18nm。热力学分析和应变分布分析可以解释缓冲层对薄膜表面形貌演化的作用。该模拟计算方式对设计缓冲层结构有很大的帮助,模拟计算的结果可以与实验相比对。     

Room temperature response and enhanced hydrogen sensing in size selected Pd-C core-shell nanoparticles: Role of carbon shell and Pd-C interface

In the present work, the effect of carbon shell around size selected palladium (Pd) nanoparticles on hydrogen (H₂) sensing has been studied by investigating the sensing response of Pd-C core-shell nanoparticles having a fixed core size and different shell thickness. The H₂ sensing response of sensors based on Pd and Pd-C nanoparticles deposited on SiO₂ and graphene substrate has been measured over a temperature range of 25 °C–150 °C. It is observed that Pd-C nanoparticle sensor shows higher sensitivity with increase in shell thickness and faster response/recovery in comparison to that of Pd nanoparticle samples. Pd-C nanoparticles show room temperature H₂ sensitivity in contrast to Pd nanoparticles which respond only at higher temperatures. Role of carbon shell is also understood by investigating H₂ sensing properties of Pd and Pd-C nanoparticles on graphene substrates. These results show that higher catalytic activity and electronic interaction at Pd-C interface, a complete coverage and protection of Pd surface by carbon and presence of structural defects in nanoparticle core are important for room temperature and higher sensing response.     

Strength and strain-hardening enhancement by generating hard delta-ferrite in twinning-induced plasticity steel

ABSTRACT

A dual-phase (12?vol.% delta-ferrite?+?78?vol.% austenite) high manganese twinning-induced plasticity (TWIP) steel was produced by hot rolled and annealing treatment. In comparison with the fully austenitic TWIP steel, both the yield and ultimate tensile strength of the dual-phase TWIP steel reinforced by hard delta-ferrite are significantly increased. It was found that the delta-ferrite in dual-phase steel exhibits a high hardness owing to the formed DO₃ structured intermetallic phase within ferrite. The presence of delta-ferrite dramatically improves the strain-hardening ability of TWIP steel. This is principally attributed to the effects of strain partitioning between hard delta-ferrite and softer austenite on the kinetics of deformation twinning and/or additional geometrical necessary dislocation (GND) during the deformation process.     

超亲水毛细芯环路热管启动及热性能分析

为解决电子设备高热通量下的散热问题，采用H₂O₂氧化法对烧结毛细芯进行了超亲水改性，研究了毛细芯表面润湿性对吸液性能的影响。并将改性后的超亲水毛细芯应用到环路热管内，研究了倾斜角度及加热功率对超亲水毛细芯环路热管的换热特性的影响。实验结果表明：超亲水毛细芯的吸液速度增加，吸液时间较亲水毛细芯减小了3.52ms；与普通亲水毛细芯环路热管相比，在加热功率Q=200W时，超亲水毛细芯环路热管蒸发器中心温度降低了约6.0℃，在Q=20W时启动时间与温度分别降低了33s与2.5℃。同时发现超亲水毛细芯环路热管在正重力状态时的运行温度更低，热阻较小，最低热阻仅为0.084℃/W。