不锈钢粉末的选择性激光熔化快速成形工艺研究

为了揭示选择性激光熔化快速成形过程中工艺对成形金属零件的影响规律,以不锈钢粉末为对象展开研究。首先,进行了单道扫描实验,结果表明水雾化制备的不锈钢粉末的单道扫描线不连续,球化现象严重,分析了其原因;然后,采用不同的成形工艺,成形出了金属块体,结果表明成形件的致密度与激光能量密度满足指数关系ρ=ρm-Aexp(-Ψ/K);最后,对选择性激光熔化成形件内部的显微组织进行了扫描电镜与光学显微分析,结果表明该组织极细小且不均匀,具有柱状和蜂窝状结构,熔化界面处的温度梯度最大,其组织变化最为剧烈。     

Research on Process and Microstructure Formation of W-Ni-Fe Alloy Fabricated by Selective Laser Melting

W-Ni-Fe alloys are important materials for many practical applications; however, at present, they are usually fabricated by conventional powder metallurgy techniques, which is difficult in fabrication with complex shapes. In this work, a selective laser melting (SLM) processing method was developed for fabricating W-Ni-Fe alloys parts. A process map was obtained for selection of proper laser parameters by optimizing processing conditions. Microstructures of laser fabricated samples in different laser energy inputs were investigated. There are two coexisting forming mechanisms in the SLM process: (i) liquid phase sintering (LPS) with full melting of Ni and Fe powders but non-melting of W powders and (ii) melting/solidification with full melting of W powders. Moreover, with increasing laser energy, a transition trend of forming mechanism from LPS to full melting/solidification can be observed.     

食盐中碘含量的分析测定

本介绍了碘含量的测定技术，重点阐述了滴定法、色谱法、光度法、电化学分析法、原子吸收光谱法的测定原理、方法及其优缺点。     

光流法在掺气水流流场测量中的应用进展

水利设施中掺气水流运动速度估计一直是水气两相流领域重点研究的课题,由于掺气水流中气泡复杂的演变机制和剧烈的湍动瞬变,导致现有的测量技术难以准确的表征水流流场情况。基于光流法的流场可视化技术因其独特的优势而成为图像识别领域重点研究的方向。光流法能够根据像素亮度计算出细观气泡运动的高分辨率光流场,弥补了传统的基于粒子图像测速技术的不足。为了全面反映国内外研究人员应用光流技术对掺气水流流场可视化估计的进展,本文从经典光流法的原理出发,综述了目前用于掺气水流中的几种光流技术及其特点,然后总结了光流技术在处理掺气水流这种复杂场景时采用的关键技术和参数选择情况。最后,探讨了光流技术在掺气水流应用中所面临的挑战和前沿问题,并对其未来的发展做出展望。     

Microstructure,grain orientation,and properties of ITO ceramics sintered with various heating rates

In this study, the microstructure, grain orientation, electrical resistivity, nanohardness, and fracture strength were systematically investigated in ITO ceramics sintered with different heating rates. It was found that ITO ceramics sintered at 1600°C consist of main phase (In₂O₃) and secondary phase (In₂SnO₅) and the distributions of coarse grains with high indium content and fine grains with high tin content are interval. The higher heating rate was found to refine the grain size and increase the {1000} textured secondary phase. The increase in electrical resistivity of ITO ceramics was due to the decrease in oxygen vacancies caused by the reducing oxide decomposition. Moreover, the nanohardness of fine grains was found to be higher than that of coarse grains due to the reinforcement effect of Sn element. Besides, the increase of heating rate is beneficial to enhance the fracture strength due to the higher resistance of grain boundary to fracture propagation and the predominantly intergranular fracture.     

Effect of heat treatment on the dispersion and sintering behaviour of tin doped indium oxide powders

Due to the importance of structural uniformity of ITO targets on the properties of ITO films, the untreated and heat treated tin doped indium oxide powders were used to study the effects of four different dispersants on the dispersion behaviour of nanosized ITO powders. The optimum dispersant is NH₄PAA and its optimum amount is 1.00?wt% when the pH value is 9.0. In addition, the effect of the treatment temperature of nanosized ITO powders on the dispersion and sintering behaviour was also studied by SEM, TEM and XRD. The solid loading of ITO slurries and the relative density of the sintered bodies prepared with ITO powders treated at 900?°C could reach 40?vol% (untreated, 25?vol%) and 98.53% (untreated, 95.04%), respectively. The results indicate that the heat treatment of powders at 900?°C allowed obtaining powders from which ITO aqueous suspensions with high solid loading could be prepared and dense bodies after sintering. In another word, the appropriate heat treatment process for tin doped indium oxide powders could reduce the sintering temperature by 50?℃ and refine the grain size.     

High Cycle Fatigue Property of Al–Mg–Sc–Zr Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of high-strength Al–Mg–Sc–Zr alloy possesses great potential application in the aerospace industry. However, fatigue performance has become a very important issue in the safety and durability design of engineering structures. Herein, the high cycle fatigue property of LPBF-fabricated Al–Mg–Sc–Zr alloy and its correlation with defects, microstructure, and precipitated phases are studied. The LPBF-manufactured Al–Mg–Sc–Zr alloy appears heterogeneous structure composed of equiaxed grains at the molten pool boundary and columnar grains at the inner of the molten pool. After aging treatment (325 °C/4 h), the nanosized Al₃Sc intragranular particles and Mn-rich intergranular particles are precipitated, leading to more difficult movement of dislocations that favors the fatigue strength. The ultimate tensile strength of the samples after aging treatment is 507.05 MPa and corresponding 10⁷ cycle fatigue strength (R = −1) is 106 MPa. The fracture morphology of the fatigue specimens shows that the fatigue cracks start from the surface defects with strong stress concentration, especially the lack of fusions, and then expand through the surplus part.     

Effect of Pr2O3 on the microstructure and hydrogen evolution property of nickel sulphur coatings electrodeposited on the nickel foam substrate

This paper studies the effect of the Pr₂O₃ addition on the hydrogen evolution property and microstructures of the Ni-S coating electrodes. The coating electrodes with and without Pr₂O₃ have been prepared through electrodeposition using a modified Watts bath. Results indicated that Ni-S coating with Pr₂O₃ shows a much better electrocatalytic activity than that without Pr₂O₃. XRD and SEM results indicated that the high electrocatalytic activity for the Ni-S coating with Pr₂O₃ addition is due to the larger surface area and amorphous microstructure.