固溶温度对VAR制备传感器用Ti-6Ni-3Mo-1Sn合金组织和力学性能的影响

对真空自耗电极电弧熔炼制备的传感器用Ti-6Ni-3Mo-1Sn合金进行热处理,先经过不同温度的固溶处理在经过500℃时效处理4 h,通过实验测试手段研究固溶温度对固溶态和时效态合金组织和力学性能的影响。研究结果表明:固溶温度700℃时,在固溶态合金晶粒中产生了大量初生α相。随着固溶温度增加,形成了更大的β晶粒。以更高温度处理后固溶态合金获得更大拉伸强度以及屈服强度,而伸长率表现为先升高再减小。经过时效处理的时效态合金晶粒中产生了许多弥散态的细小α相。以700℃固溶处理后,形成了初生α相,在残余β相内产生更多β稳定元素。随着固溶温度增加,时效态Ti-6Ni-3Mo-1Sn合金的拉伸强度,屈服强度及伸长率均表现出先增加后减小,最大值发生在固溶温度700℃时,分别为1268,1192 MPa, 5.62%。在低于700℃固溶时效处理后的试样断口区域形成许多尺寸差异较大微孔,呈现脆性断裂特点。     

Effects of grain boundary diffusion of PrCu alloy on microstructure and coercivity of hot deformed(Nd,Ce)-Fe-B magnets

The technology of using high abundance rare earth element Ce in permanent magnets has attracted many concerns.In this work,the magnetic properties and microstructures of hot deformed(Nd_(1-x)Ce_x)_(13.8)Fe_(76.1)Co_4 Ga_(0.5)B_(5.6) magnets and a selective magnet treated with PrCu grain boundary diffusion process(GBDP) were investigated systematically.It is found that Ce is beneficial to improving the plastic deformation ability of NdFeB magnets.The strongest c-axis orientation is achieved in the HD magnets with Ce concentration of x=0.3,resulting in good comprehensive magnetic properties of B_r=13.00 kGs,H_(cj)=10.12 kOe,(BH)_(max)=38.42 MGOe.Based on that,the GBDP was implemented on the magnets with the best orientation using Pr_(68)Cu_(32) ribbons and the magnetic properties of B_r=12.87 kGs,H_(cj)=15.65 kOe,(BH)_(max)=37.48 MGOe were obtained.The results of composition distribution and Curie temperature test of the GBDPed magnets illustrate that Pr diffuses into the(Nd,Ce)_2(Fe,Co)_(14)B grains to substitute Ce,which not only improves the Curie temperature of the grains,but also enhances the magnetic performance of the magnets.Through GBDP,the thermal stability of magnets has also been improved.     

功能化氧化石墨烯/壳聚糖纳米复合材料的制备及力学性能研究

以壳聚糖为基体、氧化石墨烯为活性增强相,采用溶液复合的方法制备了氧化石墨烯/壳聚糖纳米复合材料。为使氧化石墨烯均匀地分散在壳聚糖溶液中,对氧化石墨烯的表面进行了功能化处理。通过TEM、SEM、XRD、TGA和力学实验对氧化石墨烯的分散性,复合材料的结晶性能、热性能和力学性能进行了分析。研究结果表明,表面处理后的氧化石墨烯均匀分散于壳聚糖溶液中,未出现絮凝和团聚现象,复合材料中氧化石墨烯也以层片堆叠的方式存在。复合材料中壳聚糖基体的结晶峰位置和结晶度不随氧化石墨烯的加入而改变。复合材料的杨氏模量随着氧化石墨烯含量的增加而提高,断裂伸长率随氧化石墨烯含量增加而降低;当氧化石墨烯含量达到5%(质量分数)后,材料由韧性变为脆性,强度降低。复合材料的热稳定性随着氧化石墨烯含量的增加而提高。     

HFC-32制冷剂饱和液体热力性能参数计算模型

制冷剂简单有效的热力性能参数计算模型对制冷循环的仿真是十分必要的.提出了HFC-32制冷剂饱和液体的蒸汽压和密度关联式计算模型;在HFC-32的GMA液体状态方程基础上,利用Helmholtz偏离函数和Maxwell关系式推导出了HFC-32饱和液体的焓、熵和比热容的计算模型;上述各模型均不存在迭代,保证了模型的计算精度和稳定性.将建立的各模型在饱和液体(275 ～ 335K,0.862～4.095MPa)范围内与REFPROP7计算值进行对比,结果表明,所有热力性能参数计算模型的相对平均误差不超过0.776％,最大误差小于4.464％,证明了所建立模型的可靠性.     

一种改进的基于三角形折叠和包络的网格简化

我们提出了一种带属性的三角形网格简化方法,该方法利用包络和二次误差矩阵来共同控制简化：利用包络控制网格简化的全局误差,保证简化的整体效果;利用二次误差矩阵对网格简化的局部误差进行控制,以保持模型的局部特征和细节。算法中还加入了颜色、纹理方面的参数,以保持模型的颜色和纹理特征。     

Mg:Er:LiNbO3晶体的激光性能和550nm寿命特性研究

本文采用Czchrzlski技术生长出优质的Mg:Er:LiNbO3[(X=2%, 4%, 6%, 8%, y=% （mol%）)]晶体,测试Mg:Er:LiNbO3晶体的光损伤阈值,红外光谱和紫外—可见吸收光谱,Mg2+浓度增加抗光损伤能力增加,其中Mg(6mol%):Er:LiNbO3和Mg(8mol%):Er:LiNbO3晶体抗光损伤阈值比LiNbO3晶体提高二个数量级以上。它们的红外光谱OH-吸收峰移到3535cm-1附近。Mg:Er:LiNbO3晶体中随着Mg2+浓度增加吸收边紫移程度增大。研究Mg:Er:LiNbO3晶体抗光损伤阈值增强机理,OH-吸收峰移动机理和吸收边移动机理。采用0.523μm激光进行泵浦获得高的利用率。在波长510—580nm范围内得到Mg:Er:LiNbO3晶体稳态发射谱。掺进4mol%的MgO是Mg:Er:LiNbO3晶体寿命最长的晶体。     

基于图形硬件的快速RCS估算

为了对复杂目标模型进行快速估算,在介绍复杂目标的RCS计算系统emX及其所采用的物理光学方法、几何光学寻迹方法和物理绕射方法的基础上,结合图形硬件对估算进行了加速,实现了对于复杂目标模型的一次反射,多次散射和边缘绕射相结合的快速RCS计算算法。最后对实验数据进行了对比和分析,结果证明,该方法是一种有效的RCS快速估算方法。     

Synthesis of pewter alloy from tin–copper–antimony powder mixtures by microwave and conventional sintering

Abstract

Two compositions of pewter alloy were sintered using both microwave and conventional vacuum sintering, and the effects of sintering time, temperature and weight percentage of copper and antimony on the mechanical and structural properties were examined for both sintering methods. Microwave sintered samples had finer microstructures, higher densities, higher hardness and tensile strength compared to the conventionally sintered samples and traditionally cast pewter. By increasing the copper and antimony contents, higher hardness was achieved. Better mechanical properties were found after microwave sintering after shorter sintering times compared with conventional sintering, but longer sintering times resulted in better diffusion for both sintering methods. The microwave sintered samples in general were capable of achieving similar amounts of diffusion to those conventionally sintered for the same time. But the total sintering process is much faster in microwave heating than in conventional heating due to the rapid heating effect.     

Crystallisation process of Al80Fe10Ti10 amorphous phase

Abstract

In the present study, crystallisation behaviours of the Al₈₀Fe₁₀Ti₁₀ amorphous phase (prepared by mechanical alloying) has been investigated using X-ray diffraction and differential thermal analysis techniques. It was found that Al₈₀Fe₁₀Ti₁₀ amorphous phase exhibits one-stage crystallisation on heating [amorphous to Al₁₃Fe₄, Al(Fe,Ti) and Al₅Fe₂ intermetallic phases]. The activation energies for crystallisation of Al₈₀Fe₁₀Ti₁₀ amorphous phase were determined as 326, 322, 351 and 301 kJ mol^?1 by means of the Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman and Afify equations respectively. Kinetic parameters such as Avarmi exponent or reaction order n and frequency factor K_o were also discussed. The reaction orders obtained for the crystallisation was ～2·03, suggesting that a diffusion controlled crystallisation process with a decreasing nucleation rate was the crystallisation mechanism. The deduced K_o value for crystallisation peak was calculated to be 6·75×10¹⁰ s^?1.     

Process window for electron beam melting of Ti-6Al-4V

Selective electron beam melting (EBM) is a powder-bed based additive manufacturing technique for the fabrication of dense metallic parts. As a free-form deposition process EBM offers a high degree of freedom in design and a highly efficient utilization of material. For a widespread industrial application the achievable build rate is a critical factor. In this paper the process window for Ti-6Al-4V is explored by varying beam current and scan speed in a wide range. The EBM specimens were characterized by their density, porosity size and distribution, chemical composition, microstructure, hardness and tensile strength. Key findings include: (1) the minimum line energy necessary to achieve full density, (2) parameter sets for increased build rates at full density, and (3) formation of α'-martensite at high scan rates.