应用激光技术修复碱过滤器轴的工艺与性能研究

介绍了运用激光技术对失效的MB40密闭加压过滤器轴进行功能性修复的工艺方法。先采用自熔性好的合金激光熔覆恢复尺寸，再用激光合金化强化表层。并对修复层的显微组织、耐磨性、耐蚀性等进行对比分析，为厚层功能性修复提供了工艺方法和理论依据。实验结果表明，激光熔覆加合金化的方法是轴件修复的有效途径之一，适用于修复磨损厚度较大的轴件。     

盐刮刀激光熔覆表面强化工艺开发及应用

针对双级推料式离心机盐刮刀磨损快、进口刮刀备件费用高的难题,通过对比优选与试验研发出盐刮刀激光熔覆表面强化工艺——采用316L奥氏体不锈钢加工制作刮刀,并在表面同轴送粉激光熔覆球状WC。实践证明经熔覆处理的盐刮刀使用寿命超过原厂进口备件。     

齿轮模具——激光表面强化工艺与装备技术进展

齿轮模具激光表面强化技术是指在数控环境下，利用高能量密度的激光束和涂料或熔覆材料对齿轮或模具表面进行处理，改变其表层的组织或成分，实现表面相变强化或增强性修复的技术。     

激光熔覆Ni包WC复合涂层的组织、耐磨和耐蚀性分析及应用

对45钢基体进行激光熔覆Ni包WC金属陶瓷涂层强化处理,通过X射线衍射(XRD)、扫描电子显微镜-能谱分析(SEM-EDX)和透射电子显微镜(TEM),研究了激光熔履Ni包WC涂层的显微组织和物相组成,并采用摩擦磨损试验和电化学测试系统研究了Ni包WC涂层的摩擦磨损性能和耐蚀性能.结果表明,在激光熔覆Ni包WC金属陶瓷...     

大型颚式破碎机偏心轴激光熔覆再制造技术研究

为了实现对大型颚式破碎机偏心轴的激光熔覆再制造修复，采用激光熔覆技术在偏心轴材料40CrMnMo试验轴段上制备铁基熔覆层。通过正交试验选择最佳的工艺参数，研究了最佳工艺参数下的熔覆层组织性能，利用金相显微镜、显微硬度计对熔覆层的金相组织、显微硬度进行了研究，最后成功对偏心轴进行了激光熔覆再制造修复，恢复了尺寸公差，并提高了表面使用性能。经激光熔覆再制造后零件在使用性能和产品质量上都能达到甚至超越新品的水平，但成本仅为新品的三分之一，给客户带来较大的经济效益，为水泥行业的再制造发展提供一种新的先进技术，为循环经济的可持续发展提供动力。     

船舶海水管路激光熔覆涂层研究进展

首先分析了海水管路腐蚀失效原因；其次，从激光熔覆耐蚀金属涂层的性能、熔覆金属涂层的工艺以及复杂工件内部熔覆涂层的现状3个方面进行综述；最后，总结并为海水管路激光熔覆涂层的研究和发展指出了方向。     

汽车用AZ91镁合金的表面激光改性研究

为了解决压铸AZ91镁合金耐蚀和耐磨性能较差的问题,采用激光熔覆的方法在汽车用压铸AZ91镁合金表面制备了激光熔覆层,研究了激光功率和激光扫描速度对熔覆层成型、截面和表面形貌、物相组成、耐蚀和耐磨性能的影响。结果表明,过小/过大激光功率或者过大扫描速度会使得熔覆层中产生气孔、熔坑等缺陷;不同激光功率和扫描速度下,熔覆层与AZ91镁合金基体结合良好,AZ91镁合金表面激光熔覆层都主要由α-Mg、Mg₁₇Al₁₂、AlCu₄、Al₄MgY和MgAl相组成;随着激光功率增加,熔覆层表面晶界间距离和晶粒尺寸增大,熔覆层平均维氏硬度会逐渐减小;随着激光扫描速度增加,熔覆层厚度和熔覆层晶粒尺寸逐渐减小。激光熔覆层的耐蚀性和耐磨性都优于AZ91镁合金基体,Al-Cu/Y₂O₃熔覆层适宜的激光熔覆工艺为：激光功率1100 W、扫描速度500 mm/min,此时激光熔覆层与基体结合良好,熔覆层致密、晶粒细小、硬度较高,具有良好的耐蚀性和耐磨性。     

17-4PH沉淀硬化不锈钢表面强化技术

本文综述了当前17-4PH表面强化技术的研究进展,着重分析了稀土等离子渗氮技术、激光熔覆技术以及激光合金化技术的优势及面临的问题。等离子渗氮过程中加入一定量稀土之后,能通过加快界面反应、吸附扩散反应的进行,渗氮效率提升,且能改善基体表面的硬度以其耐磨性,激光表面强化技术已在各方面展现出其应用优势,但其强化材料基本仍为喷涂材料,其熔点、凝固温度、硬度与韧性均不适合于激光表面强化技术。稀土对渗氮的作用机理以及激光表层强化材料将是今后研究的重点。     

激光熔覆技术的研究与应用

激光熔覆技术在金属3D打印技术中得到了广泛的应用,其中最典型的就是航空发动机叶片采用3D打印技术一次成型。将激光熔覆技术应用在第四代冷却机上,可以实现传统铸造工艺达不到的尺寸精度,强化耐热钢工件以及实现工件的快速修复再利用,可大幅提高工件的使用寿命。     

挤压造粒机螺杆元件表面激光熔覆工艺研究

本文采用激光熔覆工艺在38ClMoAl基体上熔覆5～6 mm两种Cr18系列新型熔覆材料，分析熔覆金属的组织形貌，并测定其耐磨性和硬度变化；通过对比修复螺杆原件前后内孔花键尺寸，判定激光熔覆工艺修复过程中的变形量大小。研究结果表明，熔覆金属与基体结合良好，主要是以枝晶状马氏体为主，枝晶间弥散分布着硬质碳化物；在熔覆层与基体之间其形成细小的热影响区，熔池液体沿垂直于界面的最大散热方向快速生长，形成了明显的向上生长的胞状晶、树枝晶。1#熔覆金属硬度平均在50～52 HRC,2#熔覆金属的硬度平均在54～57 HRC之间；通过磨损对比可知，两种熔覆金属磨损失重分别是是45#淬火钢的68%和36%。检测对比螺杆元件修复前后的尺寸，采用激光修复后的零件尺寸变形量平均在0.12 mm以内，符合修复要求。     

Measurements of the melting point of graphite and the properties of liquid carbon (a review for 1963-2003)

Scientific literature on the melting temperature of graphite and its properties in melting is reviewed, beginning with the study by Bundy in 1963 and proceeding up to 2003. Data obtained by Pirani in 1930 that has been quoted in some recent publications is also considered. Successive experimental data and theoretical predictions on the melting point of carbon are summarized. The history of carbon studies, starting in 1963, is given, covering both laser and electrical heating of the graphite. The main divergence in the experimental results is in the value of the true melting temperature of graphite in the range of 4000 or 5000 K.The paper first describes laser heating. Pulsed laser heating of graphite usually shows the absence of a melting temperature plateau in the heating of a low-density graphite specimen (only a deflection point is observed on the increasing signal of the pyrometer). Carbon vapour, as a result of graphite sublimation, usually plays a leading role in the temperature measurements near the melting point under slow heating.The volume electrical heating of graphite is then discussed. Several electrical pulse investigations are listed: measurements of different properties; heating of low density graphite; and very slow pulse heating up to steady-state by alternating current. A separate section shows the data on spectral emissivity investigations, which are required in graphite temperature measurements.Reliable experimental data for the graphite melting point are presented: enthalpy of solid state under melting (10.5 kJ/g); enthalpy of liquid state under melting (20.5 kJ/g); heat of graphite melting (10 kJ/g); liquid-carbon resistivity (730 μΩ cm) near the melting point at a density of 1.8 g/cm³ under high pressures (several GPa); estimation of expansion (70%) during melting at 100 MPa pressure; and melting temperature T_m = 4800 ± 100 K at a pressure 10-100 MPa. Most of these data are obtained by electrical fast heating (1-5 μs), that are supported by the data of carefully executed laser-pulse heating.     

Hybrid laser processes for thick silver coating fabrication on AlN substrate

Aluminum nitride (AlN) are particularly suitable as integrated circuits (ICs) substrates due to its high thermal conductivity and excellent electricity insulation. However, its poor weldability with metals limits its usage. Recent research on surface metallization of AlN provides possible solutions to tackle this defect. Nevertheless, these solutions show some shortages such as complicated processes or insufficient electrical conductivity. In this paper, we report a method that consists of laser induced surface metallization and laser sintering of silver (Ag) coatings. A nanosecond laser was applied to induce a 10 μm thick aluminum (Al) layer from the AlN substrate. Afterwards, laser sintering of Ag layers was implemented, which could enhance the conductivity and the bonding performance between layers. With optimized laser parameters applied, both the electrical conductivity and the bonding tests demonstrated excellent physical properties. Finally, simulation and EDS analysis illustrated the melting evolution and confirmed a metallurgical combination of Al and Ag, thus enhancing bonding strength. Thanks to the small size of focused laser spot, electrical circuits width could be greatly narrowed if these findings were applied; hence highly dense ICs on AlN substrate become potentially available.     

Numerical simulation on evolution process of molten pool and solidification characteristics of melt track in selective laser melting of ceramic powder

A three-dimensional high-fidelity physical model for selective laser melting (SLM) of ceramic powder was created based on computational fluid dynamics (CFD) to examine the physical mechanism of molten pool and solidified tracks at mesoscopic scale. The discrete element method (DEM) was used to generate a randomly packed powder bed, and the volume-of-fluid method (VOF) was applied to dynamically monitor the free surface of the molten pool. The formation mechanism and evolution characteristics of the molten pool were found and analyzed, and the effects of laser power on the typical characteristics of solidified ceramic tracks of SLM were investigated. The molten pool was eventually solidified into a concave geometric shape track by surface tension. The laser power played a significant impact on the shaping quality of solidified ceramic track. When the laser power was too low, the melt track suffers from severe porosity and distortion defects, which can be effectively solved with increasing laser power. The simulation results were validated via single track selective laser melting of TiC ceramic powder.     

色粉对聚丙烯复合材料激光打标的影响

为研究配色聚丙烯(PP)复合材料中色粉对激光打标效果的影响,以PP为基体,云母、抗氧剂等为添加成分,以酞青蓝、酞青绿、炭黑和钛白粉为色粉成分,通过熔融共混、注塑成型制备了PP复合材料样板。通过激光打标制备了复合材料标记板,采用色差仪评价了标记板激光打标前后明暗度的变化和打标前后色差的变化。研究了酞青蓝、酞青绿、炭黑和钛白粉含量对激光打标效果的影响。结果表明,酞青蓝、酞青绿和钛白粉均对激光打标具有两面性,少量添加可减弱激光打标效果,含量提高后可通过自身颜色与样板颜色的差异减弱对激光打标效果的影响;炭黑含量越高,打标效果越差。     

Simulation of the ignition of organic explosives by a laser pulse in the weak absorption region

Numerical simulation of the ignition of RDX, HMX, and TATB by a nanosecond laser pulse was performed. The heat-conduction equation was solved in cylindrical coordinates with allowance for the multiple reflection of the light beam, a zero-order exothermic reaction, and melting. Despite the small temperature gradient due to the smallness of the radiation absorption coefficient, violation of thermal equilibrium due to Arrhenius nonlinearity leads to ignition of energetic materials from the surface. The critical energy density for ignition of PETN, RDX, HMX, and TATB by a nanosecond laser pulse was determined. Calculations have shown that with identical absorption and reflection coefficients, PETN is the most sensitive and TATB is the most heat-resistant.     

新型丙烯聚合催化剂的性能与微观结构分析

采用激光粒度分布仪,扫描电子显微镜及差示扫描量热仪,分别对新型及原丙烯聚合催化剂及其聚合物的物性进行了分析,发现新型催化剂比原催化剂颗粒粒径分布窄且分布均匀,平均粒径小,比表面积大,颗粒形态良好。小试聚合实验结果表明：新型催化剂的催化效率高,氢调敏感,聚合物等规指数容易调节并可以控制,聚合物复制了催化剂的形态,且粒径分布较窄。同时,进行了丙烯－乙烯共聚实验,从聚合物熔点及乙烯含量的测定结果可以说明：新型催化剂共聚性能优良。     

聚四氟乙烯表面处理方法综述

从聚四氟乙烯的表面性能出发，研究其性能特点，进而介绍了化学处理、高温熔融、辐射接枝、等离子体、电解还原以及激光处理等聚四氟乙烯的各种表面处理方法。最后指出正是因为这些处理方法的不同，才为聚四氟乙烯的改性提供了更多的途径。     

Direct laser melting of Al2O3 ceramic paste for application in ceramic additive manufacturing

We develop the direct laser melting of ceramic paste technology for application in ceramic additive manufacturing (AM). The Al₂O₃ ceramic paste, which is a homogeneous mixture of DI-water and Al₂O₃ ceramic powders, was deposited on an Al₂O₃ substrate using free-forming extrusion (FFE), and subsequently melted by a CO₂ laser. To better control the laser melting process, the flow behavior of the laser-melted Al₂O₃ was investigated by evaluating the microstructure of the laser-melted Al₂O₃ single tracks. When the laser scanning speed increased from 1 to 3.5 mm/s at a fixed laser power, the permeation of the molten Al₂O₃ into the surrounding porous paste was reduced, resulting in the improvement of the surface uniformity of the laser-melted Al₂O₃ tracks. Through optimizing the laser scanning strategy, a fully-dense Al₂O₃ layer with smooth surface was achieved. The phase composition and density of the laser-melted Al₂O₃ layers were evaluated to study their properties. The thickness of the dense Al₂O₃ layer varied from ～90 μm to ～120 μm periodically due to the line-by-line scanning of the Gaussian laser beam. In addition, the relationship between the melting thickness and the laser scanning speed was also investigated to further improve the controllability of the laser melting process. This direct laser melting of ceramic paste technology is promising for applications in ceramic AM, such as 3D printing of ceramic components and high-temperature ceramic welding.     

Nylon 66 nanofibers prepared by CO2 laser supersonic drawing

Nylon 66 nanofibers were prepared by irradiating as‐spun nylon 66 fibers with radiation from a carbon dioxide (CO₂) laser while drawing them at supersonic velocities. A supersonic jet was generated by blowing air into a vacuum chamber through the fiber injection orifice. The fiber diameter depended on the drawing conditions used, such as laser power, chamber pressure, laser irradiation point, and fiber supply speed. A nanofiber obtained at a laser power of 20 W and a chamber pressure of 20 kPa had an average diameter of 0.337 μm and a draw ratio of 291,664, and the drawing speed in the CO₂ laser supersonic drawing was 486 m s^?1. The nanofibers showed two melting peaks at about 257 and 272°C. The lower melting peak is observed at the same temperature as that of the as‐spun fiber, whereas the higher melting peak is about 15°C higher than the lower one. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40015.     

Confined intra-molecular clustering in orientated polyethylene after annealing

Deuterated polyethylene tracer molecules with small amount of branches (12 C₂H₅- branches per 1000 backbone carbon atoms) were blended with a hydrogenated polyethylene matrix to form a homogenous mixture. The conformational evolution of the deuterated chains in a stretched semi-crystalline film was observed via online small angle neutron scattering measurements during annealing at high temperatures close to the melting point. Because the sample was annealed at a temperature closely below its melting point, the crystalline lamellae were only partially molten and the system could not fully relax. The global chain dimensions were preserved during annealing. Recrystallization of released polymeric chain segments allows for local phase separation thus driving the deuterated chain segments into the confining inter-lamellar amorphous layers giving rise to an interesting intra-molecular clustering effect of the long deuterated chain. This clustering is deduced from characteristic small angle neutron scattering patterns. The confined phase separation has its origin in primarily the small amount of the branches on the deuterated polymers which impede the crystallization of the deuterated chain segments.