金属的凝固和凝固系数

本文根据耗散结构理论所建立的凝固模型,推导出的过冷度方程,指出金属的凝固与结晶凝固系数β是密切相联系的。其中结晶凝固系数为并且讨论了ρ值在不同情况下的物理意义以及β值在金属凝固中的作用。     

A Study of Laser Melting and Rapid Solidification of an NbAl3 Alloy

The present study examines the laser rapid solidification of NbAl₃ alloy. The heat transfer process that occurs during heating, melting and solidification is studied theoretically, and the computed cooling rate corresponding to laser pulse is used to control the solidification process. Cross-sections of the solidified zones are examined using an SEM technique. Laser melting is carried out under different pressures of oxygen. The laser melting is shown to improve the ductility of the substrate through the change of dual phase structure of NbAl₃ to a three phase structure.     

Excellent Mechanical Properties and Energy Absorption of Hexagonal-Body-Centered Lattice Structure Fabricated by Selective Laser Melting

Inspired by the crystal lattice characteristics of hexagonal-close-packed and body-centered-cubic metals, a novel hexagonal-body-centered (HBC) lattice structure is constructed for energy absorption. HBC lattice structures with three different c/a ratios are prepared by selective laser melting (SLM) using 316 L stainless steel powder. The geometric features and energy absorption performance of the fabricated HBC lattice structures with different c/a ratios are studied by scanning electron microscopy and quasistatic compression tests, respectively. The results show that the HBC lattice structure prepared by SLM not only exhibits good formability, but also demonstrates excellent mechanical properties and energy absorption capacity. The c/a ratio significantly affects the mechanical properties and energy absorption performance of HBC lattice structures. The Young's modulus, yield strength, and energy absorption increase as the c/a ratio decreases. Compared with other lattice structures, the HBC lattice structure exhibits better energy absorption at the same relative density, thus indicating the usefulness of the HBC lattice structure as a lightweight energy-absorbing structure.     

选区激光熔化成形的316L不锈钢点阵夹层结构的力学性能和能量吸收性能研究

目的 以选区激光熔化（SLM）成形的316L不锈钢点阵夹层结构为研究对象,研究单一、混合芯层对点阵夹层结构力学性能和能量吸收性能的影响,为轻质高强耐撞点阵夹层结构提供设计依据。方法 通过SLM成形技术,以316L不锈钢粉末为原材料,制备点阵夹层结构,利用扫描电镜对SLM成形的点阵夹层结构几何结构特征进行观察,利用准静态压缩实验对点阵夹层结构的力学性能和能量吸收性能进行研究。结果 在选定的SLM成形工艺参数下,SLM成形的点阵夹层结构芯层的连接杆表面存在一定的粗糙度且斜向连接杆的表面粗糙度比竖直连接杆的表面粗糙度大。在SLM成形的点阵夹层结构中,混合点阵夹层结构BFB和FBF的弹性模量分别为2 525.7 MPa和2 493.8 MPa,屈服强度分别为36.3 MPa和38.3 MPa,能量吸收分别为16 J和17.2 J,比吸能分别为1.21 J/g和1.36 J/g,其弹性模量、屈服强度、能量吸收和比吸能均优于单一BCCZ点阵夹层结构的。在准静态压缩过程中,BFB和FBF这2种混合点阵结构芯层的变形模式不同于单一BCCZ点阵结构芯层的。结论 与单一点阵夹层结构相比,2层BCCZ布置在...     

One Method of Determination of the Effective Absorption Coefficient in Pulsed Laser Irradiation of Metals

An experimentaltheoretical method of determination of the absorption coefficients in laser treatment of metals has been proposed based on the solution of the boundaryvalue axisymmetric problem of heat conduction for a halfspace and metallographic measurements of the dimensions of the thermalhardening zone.     

An Accurate Value for the Absorption Coefficient of Silicon at 633 nm

High-accuracy transmission measurements at an optical wavelength of 633 nm and mechanical measurements of the thickness of a 13-µm thick silicon-crystal film have been used to calculate the absorption and extinction coefficients of silicon at 633 nm. The results are 3105±62 cm⁻¹ and 0.01564±0.00031, respectively. These results are about 15% less than current handbook data for the same quantities, but are in good agreement with a recent fit to one set of data described in the literature.     

新能源汽车空调鼓风机气动噪声特性分析及优化

由于缺少发动机噪声的覆盖,新能源汽车空调鼓风机产生的气动噪声成为影响乘车舒适性的重要噪声源,主要针对某新能源汽车空调鼓风机系统进行气动噪声特性分析和优化,以适应更加严苛的噪声控制要求。采用ANSYS数值模拟软件和半消声实验室,通过对原始叶轮模型流场和声场的研究分析复杂的轮毂、叶片、气流和结构部件周期性相互作用产生的气动噪声特性,并开展轮毂型线和叶顶弧度对气动噪声的影响研究,其中轮毂型线模型最大可以分别降低43 阶次叶频噪声和总声压级5.0 dB和4.2 dB,叶顶弧度模型最大可以分别降低43 阶次叶频噪声和总声压级4.0 dB和2.7 dB。研究结果对优化新能源汽车空调鼓风机在受限空间内气动噪声控制具有一定的参考意义。     

Fabrication of Metallic Fibers with High Melting Point and Poor Workability by Unidirectional Solidification

Innovative method acceptable for production of Iridium (Ir) and Ruthenium (Ru) metal fibers with high melting point and poor workability is developed using an alloy‐micro‐pulling‐down (A‐μ‐PD) method and ceramic crucibles with sufficient mechanical and thermal shock resistance. As‐grown (as‐solidified) Ir and Ru fibers are approximately 1 mm in diameter and their lengths exceed 15 and 0.3 m, respectively. Both Ir and Ru fibers are composed of number of elongated grains oriented along a growth direction, which is attributable to the unidirectional solidification. The flexibility and oxidation resistance of the Ir fiber grown by the A‐μ‐PD method is considerably improved as compared to a commercial Ir wire made by wire‐drawing process.

     

激光熔化沉积铝合金显微组织及力学性能

目的 提高激光熔化沉积铝合金的成形质量。方法 以颗粒度45~105 μm的AlSi10Mg粉末为材料,4045铝合金为基板,利用激光熔化沉积设备在充氩舱内进行铝合金成形试验。测试试样的硬度和拉伸性能,并通过扫描电子显微镜和光学显微镜进行显微组织形貌分析。结果 在沉积方向上,试样显微组织呈现周期性条带状纹路,搭接区域呈现出比较明显的弧形特征;含有大量的细密树枝晶。该合金相成分主要包括:Al相、共晶Si相及少量的Mg2Si强化相。沿扫描方向,试样平均硬度值约为130HV;沿沉积方向,试样平均硬度值约为100HV;沉积态试样的屈服强度约为185.75 MPa,伸长率约为15.21%;沉积态试样拉伸性能明显优于压铸试样;该铝合金的失效形式为韧性断裂。结论 AlSi10Mg在激光熔化沉积时具有良好的成形能力,沉积态的组织强度高于铸态组织强度。     

Reflectionless Absorption of Electromagnetic Radiation in Its Incidence on the Two‐Layer System Dielectric–Metal at an Angle

A study is made of the conditions of occurrence of the total reflectionless absorption of electromagnetic radiation in its incidence, at an angle, on a layer of an absorbing dielectric applied to a metal substrate. The equations of the relationship between the selective values of the angle of incidence of the wave and the thickness of the coating layer and its dielectric properties for which we have the effect of total absorption of the incident wave with a different type of its polarization are obtained. The possibility of experimental observation of the indicated effect is considered.     

用激光熔融法制备稳定ZrO2快离子导体

利用连续ＣＯ２激光熔融法制备稳定ＺｒＯ２高 温快离子导体获得成功．Ｘ射线衍射分析表明激光熔 融后的样品为全立方相，电导率测试结果与国外学者用常规方法制备的同类快离子导体水平相当，温度为 １０００℃时电导率达到２×１０－２Ω·ｃｍ－１量级。     

Influence of a Jump in the Power of Laser Radiation on Its Measurement

Simulation and investigation of the effect of an isolated jump on realization of the unit of power of laser radiation and dissemination of the size of the unit are considered. Results are obtained by means of a newly developed algorithm that characterizes the behavior of the mean value of a signal and the standard deviation of a system as functions of the parameters of a jump in the power of laser radiation and the length and amplitude of the jump. If information concerning the time when a jump occurs is available, the proposed algorithm makes it possible to take into account how a jump affects the ultimate result of a measurement.     

选区激光熔化成型铝合金的研究现状及展望

随着航空航天、汽车轻量化的需求不断上升,经过结构优化的复杂金属构件采用增材制造技术一体成型必然是今后高端产品制造业的发展趋势.铝合金优异的综合性能与远低于钛合金原料的价格,使其在增材制造领域中极具应用和研究潜力.金属增材制造方法繁多,选区激光熔化技术(SLM)由于成型件表面质量优良、综合性能优异,在复杂结构与薄壁结构集成化的零件成型中具有显著优势,颇受科研和工业界关注.然而,由于铝合金粉末具有激光反射率高、热导率较大、流动性较差且易与氧气发生反应等特点,使得成型件极易产生球化、裂纹、孔隙、氧化夹杂等冶金缺陷,不能满足实际应用中的性能要求.其中,研究较为深入的AlSi10Mg、Al-12Si等铸造系铝合金并不能满足很多领域对强度的要求,高强合金在SLM成型过程中极易发生元素烧损、产生裂纹等不良现象.因此,明确各类缺陷的形成机理辅助调控SLM成型铝合金的工艺参数以减少缺陷产生,开发适用于SLM成型的新型铝合金粉末成为学者们的研究焦点.本文主要从Al-Si系铸造合金、高强铝合金以及铝基复合材料三个方面来介绍近年来SLM成型铝合金的研究进展.针对SLM成型的铝合金种类少、成型工艺条件不成熟、冶金缺陷难以控制以及零件性能与微观组织间的量化研究不系统的困境,提出可以引入材料基因工程(MGE)的理念,结合人工智能技术寻求成分-组织-工艺-性能之间的量化关系,开发适用于SLM成型特点的新型铝合金粉末,实现从应用需求出发反向设计材料成分与工艺的目的.     

真空感应熔炼和定向凝固制备多晶硅中铝的除杂

用真空感应熔炼和定向凝固法制备多晶硅,通过成分测定和理论计算研究了铝杂质的除杂机理。结果表明,在真空熔炼保温阶段(T≥1723 K),硅中的铝杂质明显蒸发;在随后的定向凝固过程中,铝杂质的分凝偏析是主要的,但仍有部分铝蒸发。建立了一个包括铝分凝和蒸发机制的新模型,模拟铝在硅中的分布曲线。模拟结果与铝在硅中的实际分布符合得很好。     

激光选区熔化成形装备的发展现状与趋势

激光选区熔化成形是最有前景的增材制造技术之一,近些年来激光选区熔化成形装备得到了迅猛发展。针对激光选区熔化成形尺寸偏小、成形精度偏低等问题,重点介绍了大尺寸、高精度激光选区熔化成形装备的发展现状,综述了使用长焦距f-θ场镜、振镜移动和多光束拼接成形等大尺寸成形方法以及采用短焦距f-θ场镜+低功率激光器和增减材复合制造等高精度成形方法,对各方法的原理和特点进行了阐述。最后,从装备研发、成形质量控制、软件开发、标准体系建立等方面对激光选区熔化成形技术的发展进行了展望。