热处理对Ti_(35)Zr_(30)Be_(27.5)Cu_(7.5)非晶合金压缩性能的影响

利用铜模铸造法获得了直径为2 mm的Ti35Zr30Be27.5Cu7.5块体非晶合金。采用X射线衍射(XRD)、扫描电镜(SEM)、差氏扫描量热仪(DSC)及压缩试验等方法研究了非晶合金的相结构、显微组织和热稳定性,以及热处理对其压缩强度及塑性的影响。结果表明:在553和583 K温度下分别保温5 h后,实验合金仍保持为非晶态;在613 K保温1 h后,有晶化相出现。Ti35Zr30Be27.5 Cu7.5非晶合金在583 K下保温1 h后其塑性变形量达到了6.57%,较热处理前提高了1倍,且保持了热处理前的强度,屈服强度和抗压强度分别为1921 MPa,2169 MPa。随着热处理温度的提高,非晶相含量减少,合金断裂强度、塑性变形量随之降低;同时合金断裂方式由韧性断裂转变为脆性断裂。     

微量元素P、B对GH4169合金组织与蠕变性能的影响

通过对等温锻造合金进行直接时效、蠕变性能测试和组织形貌观察,研究了微量元素P、B对GH4169合金组织结构及蠕变行为的影响.结果表明:添加微量P、B可促使粒状δ相在合金中析出,且沿晶界不连续析出的δ相可抑制晶界滑移,提高合金的蠕变抗力;在试验温度和应力范围内,测定出GH4169G合金具有较高的蠕变激活能Q=594.7 ...     

一种基于HEED的簇首多跳融合路由算法

无线传感器网络节点的能量有限,如何高效使用能量以延长网络寿命成为研究热点之一。针对HEED协议中簇首与基站直接通信能量消耗过大的问题,根据能耗模型与网络模型,提出一种基于HEED的簇首多跳融合路由算法,并用MATLAB在随机分布的传感器网络区域内进行算法的有效性仿真研究。仿真结果表明,新算法相对于HEED算法有效地延长了网络的生命周期。     

一种DSP内嵌DARAM的电路设计与ADvanceMS仿真验证

介绍了一种DSP芯片内嵌DARAM的电路结构,详细分析了接口电路中各个模块的功能,包括地址译码电路,字线译码电路,位线选择电路及控制电路四部分内容。着重介绍了控制电路的原理,及如何实现一个周期"双存取"的功能。利用数模混合仿真工具ADvance MS对整体电路进行仿真,结果证明DARAM可以在一个时钟周期内完成一次读和一次写操作,实现预期的功能,为DSP设计乃至SOC的设计工作提供了参考。     

三阶一位量化CIFB结构∑-△ADC调制器设计

提出了一种基于Maltab SIMULINK的Sigma-Delta调制器的设计与仿真方法,采用单环三阶CIFB结构、一位量化器位数和256倍过采样率,设计中对噪声传输函数的零极点和系统反馈系数进行了优化,缩小了模拟电路的设计难度,提升了系统稳定性.在考虑积分器的有限直流增益、饱和电压、压摆率和增益带宽等非理想因素情况下进行建模,得到了SNDR和ENOB分别为123 dB,20.14 bits,仿真结果表明,该结构可在低量化位数的情况下,得到较高的精度和较好的稳定性,可在高层次上指导调制器晶体管级电路设计.     

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.     

双目摄像机标定与特征点匹配方法的研究

传统标定方法具有实验环境要求高、结果精确度低、鲁棒性差等显著缺点,为此提出一种基于软件编程的主动视觉标定方法。通过建立摄像机针孔成像线性模型,考虑畸变影响的非线性模型矫正,推导出双目摄像机标定参数,并应用软件编程实现摄相机标定,获得精度高、鲁棒性较好的结果。同时,针对当前已有的图像匹配算法,对图像尺度变化适应性较差等问题,以Harris算子为基础,通过增加图像变换尺度参数,得到具有尺度不变性的改进算法。基于软件编程实现特征点坐标提取与匹配,结果显示改进后算法耗时变短、计算结果精度和鲁棒性均有所提高,为深入研究双目摄像机障碍物识别与路径规划奠定了基础。     

Microstructure and mechanical properties of functionally graded TiCp/Ti6Al4V composite fabricated by laser melting deposition

Crack-free functionally graded TiC particle (TiC_p) reinforced Ti6Al4V (TiC_p/Ti6Al4V) composite was manufactured by laser melting deposition (LMD) technology with TiC volume fraction changing gradually from 0% to 50%. This research focuses on the relationship between the microstructure and mechanical properties (microhardness and tensile properties) of TiC_p/Ti6Al4V composites under different TiC volume fractions. Besides the unmelted TiC particles, the granular and chain shaped eutectic TiC phases are observed in the composite with 5 vol% TiC due to the melting and dissolution of TiC particles into matrix. The granular and dendritic primary TiC phases are obtained in the composite with 10 vol% TiC, while the chain shaped eutectic TiC phases can scarcely be seen. The main reinforcement phases are primary TiC phases when the TiC volume fraction exceeds 15%. (i) The quantity of unmelted TiC particles, (ii) the quantity and size of primary TiC phases and (iii) the porosity of composite increase gradually when the TiC volume fraction increases. The interfaces exhibit good bonding between consecutive layers. The microhardness of the functionally graded TiC_p/Ti6Al4V composite increases gradually with TiC volume fraction increasing. It is attributed to the C element in solid solution and the appearance of eutectic and primary TiC phases. The microhardness at the top layer with 50 vol% TiC is improved by nearly 94% compared with that at the Ti6Al4V side. The tensile strength of TiC_p/Ti6Al4V composite with 5 vol% TiC is enhanced by nearly 12.3% compared with that of the Ti6Al4V matrix alloy. However, both the tensile strength and elongation of composite decrease gradually when the TiC volume fraction exceeds 5%. The reason is that the quantity of brittle unmelted TiC particles and the quantity and size of dendritic TiC phases increase with TiC volume fraction increasing. The fracture mechanism of the TiC_p/Ti6Al4V composite is quasi-cleavage fracture.     

The internal stress state in lamellar PST-crystals of the intermetallic alloy TiAl after compressive deformation

The microstructure of γ-based TiAl alloys often exhibits grains with an internal lamellar structure consisting of alternating γ-TiAl and α₂-Ti₃Al lamellae. Even in undeformed material, internal coherency stresses, due to the lattice misfit between the two phases and the tetragonality of the γ-phase are present. The goal of this work was to investigate the evolution of internal strains induced by compressive deformation of PST-specimens of the alloy TiAl at room temperature and at 800°C. The results of X-ray measurements of different peak profiles, performed with a special high-resolution double-crystal diffractometer are reported, which revealed the dependence of the deformation-induced internal strains on the orientation of the lamellar boundaries with respect to the axis of deformation.     

P doped CoMoO4/RGO as an efficient hybrid catalyst for hydrogen evolution

Transition metal oxides, as newly earth-abundant and low-cost catalysts, have been regarded as promising materials for electrocatalytic oxygen evolution. However, they are rarely used as an electrocatalyst in hydrogen evolution reaction (HER) due to the poor HER activity. Herein, we present a facile two-step method to synthesize P doped CoMoO₄/RGO (P-CoMoO₄/RGO) with different atomic ratios of Co²⁺/Co³⁺ through a simple phosphorization strategy by changing the mass of NaH₂PO₂. The effective P-doping into CoMoO₄/RGO can modify the electronic properties and modulate the atomic ratio of Co²⁺/Co³⁺, which promotes the electron transfer and creates more activity sites. Therefore, the optimized P-CoMoO₄/RGO with a relatively larger atomic ratio of Co²⁺/Co³⁺ shows superior HER performances in alkaline media, which affords a current density of 10 mA cm⁻² at a small overpotential of 90 mV and a low Tafel slope of 62 mV dec⁻¹ along with having satisfactory long-term stability. This work provides a valuable route to enhance the HER activity of transition metal oxides.