铁基抗高温磨损激光熔覆涂层强韧设计和研究II:Fe-Cr-C-W-Ni激光熔覆层的微观组织及性能

本文以对热工模具进行失效分析的基础上，利用激光熔覆技术，在５ＣｒＭｎＭｏ基础上设计并制备强韧兼备的抗高温磨损涂层。

YAG激光诱导放电复合毛化坑形貌研究

从机理上讨论了激光诱导放电采用阴极性放电可改善放电坑形貌，并从实验上得出放电坑直径在不同放电介质下随放电脉宽的变化关系。当工件表面涂层为聚四氟乙烯时，研究了放电坑由单坑变为多坑形貌的原因是电脉冲后期通道中电子供给不足，电弧由聚集型过渡到扩散型，导致阳极斑点不稳定。

MATLAB在Cr涂层微裂纹组态分析中的应用

镀Cr身管在使用时普遍存在涂层剥落问题.本文结合我国某新型号机枪枪管的研制工艺,对涂层微裂纹组态、控制因素及其与破坏模式的关系进行研究.鉴于微裂纹的纳米级宽度,本文通过特殊的金相制样方法将其扩宽,从而得到反映微裂纹组态的低倍照片.应用MATLAB对微裂纹特征进行统计分析,得出微裂纹密度、长度等特征参数与涂层失效模式间的对应关系,同时证实基体激光离散预处理对微裂纹组态有控制作用.

钢基身管内镀铬层下的激光淬火基体界面腐蚀与铬层剥落

钢基身管镀铬层在高温腐蚀性气体中服役,采用YAG激光器对身管内表面作螺旋线状离散淬火预处理后再电镀铬的复合工艺,形成了基体界面呈激光淬火区/激光未处理区周期性变化的铬层/基体结构.对该身管进行高温腐蚀介质为火药气体的靶场实验.对实验后的基体界面腐蚀形貌与铬层剥落的关系研究表明:次界面裂纹的形成是基体界面高温气体腐蚀的根本原因,基体界面腐蚀的结果是形成基体烧蚀坑,烧蚀坑上的铬层以断裂形式剥落.激光淬火预处理钢基体通过抑制次界面裂纹的形成避免了基体界面高温气体腐蚀损伤,提高了铬层的抗剥落能力.

Measurement Of Fracture Toughness And Interfacial Shear Strength Of Hard And Brittle Cr Coating On Ductile Steel Substrate

The fracture toughness and interfacial adhesion properties of a coating on its substrate are considered to be crucial intrinsic parameters determining performance and reliability of coating-substrate system. In this work, the fracture toughness and interfacial shear strength of a hard and brittle Cr coating on a normal medium carbon steel substrate were investigated by means of a tensile test. The normal medium carbon steel substrate electroplated with a hard and brittle Cr coating was quasi-statically stretched to induce an array of parallel cracks in the coating. An optical microscope was used to observe the cracking of the coating and the interfacial decohesion between the coating and the substrate during the loading. It was found that the cracking of the coating initiated at critical strain, and then the number of the cracks of the coating per unit axial distance increased with the increase in the tensile strain. At another critical strain, the number of the cracks of the coating became saturated, i.e. the number of cracks per unit axial distance became a constant after this critical strain. Based on the experiment result, the fracture toughness of the brittle coating can be determined using a mechanical model. Interestingly, even when the whole specimen fractured completely under an extreme strain of the substrate, the interfacial decohesion or buckling of the coating on its substrate was completely absent. The test result is different from that appeared in the literature though the identical test method and the brittle coating/ductile metal substrate system are taken. It was found that this difference can be attributed to an important mechanism that the Cr coating on the steel substrate has a good adhesion, and the ultimate interfacial shear strength between the Cr coating and the steel substrate has exceeded the maximum shear flow strength level of the steel substrate. This result also indicates that the maximum shear flow strength level of the ductile steel substrate can be only taken as a lower bound estimate on the ultimate shear strength of the interface. This estimation of the ultimate interfacial shear strength is consistent with the theoretical analysis and prediction presented in the literature.

Quantum Monte Carlo study of the CO interaction with a dimer model surface for Cr(110)

The chemisorption of CO on a Cr( 110) surface is investigated using the quantum Monte Carlo method in the diffusion Monte Carlo (DMC) variant and a model Cr2CO cluster. The present results are consistent with the earlier ab initio HF study with this model that showed the tilted/ near-parallel orientation as energetically favoured over the perpendicular arrangement. The DMC energy difference between the two orientations is larger (1.9 eV) than that computed in the previous study. The distribution and reorganization of electrons during CO adsorption on the model surface are analysed using the topological electron localization function method that yields electron populations, charge transfer and clear insight on the chemical bonding that occurs with CO adsorption and dissociation on the model surface.

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CWNd : YAG laser

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of gamma-FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni3Al gamma' phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility. (c) 2007 Elsevier B.V. All rights reserved.

YAG激光诱导放电通道伏安特性研究

研究了在空气、油膜和绝缘树脂薄膜这三种放电介质中的伏安特性,得出了在同一介质中,通道电极间电压不随其它初始条件改变而变化,只与放电介质对通道箍缩能力成正比,在本实验中薄膜的通道电压最高80.4V,空气中最低26.0V。通道中电流波形与放电介质有关,同样的高低压组合、相同放电脉宽下在空气和油膜中为矩形波,而在薄膜中为三角波,峰值电流变化不大。电流波形不随脉宽的改变而变化,当增大初始高压端或低压端输入时,电流随之增加,并且低压端输入对提高峰值电流更有效果。

铁基抗高温磨损激光熔覆涂层强韧设计和研究 Ⅱ:Fe-Cr-C-W-Ni激光熔覆层的微观组织及性能

利用ＯＭ、ＳＥＭ、ＴＥＭ研究了Ｆｅ－Ｃｒ－Ｃ－Ｗ－Ｎｉ激光熔覆涂层熔覆态及其高温时效态的微观组织结构。结果表明激光熔覆层组织细小，具有强韧两相组成（奥氏体和Ｍ_７Ｃ_３碳化物）的微观结构特征，高温时效处理组织中有Ｍ_（２３）Ｃ_６、Ｍ_６Ｃ、Ｍ_２Ｃ等新碳化物形成。显微硬度和冲击磨损实验证实了激光熔覆态和峰值时效态熔覆层均具有良好的力学性能。

YAG激光毛化技术进展

二十世纪八十年代，当比利时冶金研究中心(CRM)开发出CO_2激光毛化冷轧辊技术后，尝试用YAG激光进行轧辊毛化一直吸引着众多的研究者，这是因为YAG(1.06μm)激光波长比CO_2(10.6μm)激光波长短一个量级，材料对YAG激光有更高的吸收率，并用YAG激光可以聚焦到更小的光斑尺寸，同时使用电信号驱动的声光开关技术便于对毛化分布进行可设定控制。但是用传统声光调制的YAG激光虽然可以碇以很高的脉冲频率(>30kHz)，但单脉冲有量仅为10mJ左右，难以达到辊面毛化粗糙度的要求，因此人们认为YAG激光用于毛化的主要困难是脉冲能量太小。

Research on Q-Switched Nd : YAG laser engraving

IN this paper, the engraving process with Q-Switched Nd:YAG laser is investigated. High power density is the pre- requisition to vapor materials, and high repetition rate makes the engraving process highly efficient. An acousto- optic Q-Switch is applied in the cavity of CW 200 W Nd:YAG laser to achieve the high peak power density and the high pulse repetition rate. Different shape craters are formed in a patterned structure on the material surface when the laser beam irradiates on it by controlling power density, pulse repetition rate, pulse quantity and pulse interval. In addition, assisting oxygen gas is used for not only improving combustion to deepen the craters but also removing the plasma that generated on the top of craters. Off-focus length classified as negative and positive has a substantial effect on crater diameters. According to the message of rotating angle positions from material to be engraved and the information of graph pixels from computer, a special graph is imparted to the material by integrating the Q- Switched Nd:YAG laser with the computer graph manipulation and the numerically controlled worktable. The crater diameter depends on laser beam divergence and laser focal length. The crater diameter changes from 50 micrometers to 300 micrometers , and the maximum of crater depth reaches one millimeter.