Laser Surface Hardening of 9CrSi Steel

The effects of laser hardening parameters such as beam power,beam diameter and scanning rate on microstructure and mardness of 9CrSi steel were investigated.The microstructure of the surface layer of 9CiSi steel was changed from pearlite to martensite,retained austenite and carbide by laser hardening .The depth of the hardened layer increased with increasing laser energy density and the surface hardeness increased by 3-5times as high as the untreated steel.The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer.The wear mode at low speed was abrasive,while the wear mode at high speed was adhesive.     

45 钢表面激光相变硬化改性组织及耐蚀性能

目的为了改善45钢表面状态,提高其表面性能,采用CO2激光器对其表面进行激光相变硬化处理。方法利用带有能谱的扫描电子显微镜(SEM/EDS)、盐雾试验机等,对激光相变硬化层组织及耐蚀性能进行了观察和分析。结果激光相变硬化层由熔化区、相变硬化区和热影响区三部分组成,其组织依次为:混合马氏体+未溶碳化物、针状马氏体、残余奥氏体。随扫描速度增加,耐蚀性先变好而后变差。结论激光相变硬化处理可改善45钢的表面性能,显著提高其耐蚀性能。     

40Cr激光熔凝硬化组织形态及硬度研究

利用CO2轴流激光加工机对40Cr钢表面进行激光熔凝硬化处理。利用扫描电子显微镜、金相显微镜和显微硬度计研究了不同工艺下熔凝硬化层及基体的显微组织和硬度分布特征。实验表明：熔凝硬化层由熔化区、相变硬化区和热影响区组成;由表及里组织分别为极细隐晶马氏体＋少量残余奥氏体、隐晶马氏体＋碳化物＋残余奥氏体、马氏体＋回火屈氏体＋铁素体。硬化层最高硬度约是基体的3倍;随着扫描速度的增加表层硬度先增加后减小,当扫描速度为2.5m·min^-1时,表层硬度最大,为1097.9HK。     

激光扫描速度对40Ct钢激光表面合金化层组织性能的影响

为了改善金属拉拔卷筒40Cr铜的性能,采用Mo制成合金粉末,用CO2激光对卷筒表面进行激光合金化处理。研究激光合金化的工艺参数,对不同扫描速度下合金化层的质量进行比较并对其组织进行分析。结果表明：激光合金化工艺参数为：功率P=2．0kW,焦距f=315mm,搭接率为40％,扫描速度V=6mm／s,获得的合金化层具有良好的组织和性能,没有裂纹产生,未发现不熔物,组织较均匀。     

Surface Hardening of Carbon Steel Using High Powered YAG Laser

A high powered YAG laser with kaleidoscope for surface modification was applied to the surface hardening of carbon steels containing 0. 18-0.54 wt% C without the absorbents, and the relationships between laser processing and surface hardening were investigated by hardness and microstructure. The structure of the hardened zone underwent complete martensitic transformation in all of the carbon steels tested, and its hardness increased with greater carbon content. Under identical irradiated conditions, the hardened zone expanded with increasing carbon content. A hardened zone extending from the surface to a depth of 1.0 mm was obtained at a laser power of 1.0 kW and a scanning speed of 1 mm/sec. It was found that in the surface hardening of carbon steels, a high powered YAG laser can be used to control the hardened zone by selecting the appropriate irradiation conditions, however, the hardened zone was affected by the assistant gas and the flow rate.     

基于响应面法的H13模具钢激光增材再制造工艺优化

本研究采用中心复合响应面法对H13模具钢的激光增材再制造工艺参数进行优化,将激光功率(A),扫描速度(B)和送粉量(C)等激光再制造工艺参数作为优化变量,修复层宽度(W)、高度(H)和显微硬度(HAR)等成形特征作为响应值,通过方差分析构建了工艺参数与修复层成形特征值之间的回归预测模型。通过建立摄动图与三维响应面图分析了工艺参数之间的交互作用对修复层成形特征的影响规律。结果表明,修复层的宽度和高度均随激光功率的增加而增加,随扫描速度的增加而减少。提高送粉量有助于提高修复层高度,但是不利于修复层宽度的增加。同时提高扫描速度和激光功率情况下容易获得较高的硬度值。最后,H13模具钢的最佳激光增材再制造工艺参数确定为:激光功率为2.8 kW,扫描速度为4 mm/s,送粉量为16 g/min。     

激光相变硬化提高旋转接头的耐磨性

为了提高35CrMo旋转接头的耐磨性,采用正交试验法研究了35CrMo旋转接头激光相变硬化适合的工艺方法和参数,获得的优化工艺参数为:激光功率P=1 500 W,光斑直径D=3.5 mm,扫描速度V=20 mm/s.结果表明:激光相变硬化层的平均硬度达786 HV1 N,比渗氮淬火提高了约30%,耐磨性提高了约1倍,表面残余应力大部分为压应力,能满足旋转接头工作要求,为改进旋转接头的表面处理方法提供了依据.     

Rapid Directional Solidification with Ultra-High Temperature Gradient and Cellular Spacing Selection of Cu-Mn Alloy

The detailed laser surface remelting experiments of Cu-31.4 wt pct Mn and Cu-26.6 wt pct Mn alloys on a 5kW CO2 laser were carried out to study the effects of processing parameters (scanning velocity, output power of laser) on the growth direction of microstructure in the molten pool and cellular spacing selection under the condition of ultra-high temperature gradient and rapid directional solidification. The experimental results show that the growth direction of microstructure is strongly affected by laser processing parameters. The ultra-high temperature gradient directional solidification can be realized on the surface of samples during laser surface remelting by controlling laser processing parameters, the temperature gradient and growth velocity can reach 10^6K/m and 24.1mm/s, respectively, and the solidification microstructure in the center of the molten pool grows along the laser beam scanning direction. There exists a distribution range of cellular spacings under the laser rapid solidification conditions, and the average spacing decreases with increasing of growth rate. The maximum,λmax, minimum, λmin, and average primary spacing,-↑λ, as functions of growth rate, Vb, can be given by, λmax=12.54Vb^-0.61,λmin=4.47Vb^-0.52, -↑λ=9.09Vb^-0.62, respectively. The experimental results are compared with the current Hunt-Lu model for rapid cellular/dendritic growth, and a good agreement is found.     

激光扫描速度对40Cr钢表面组织结构的影响

对调质态的４０Ｃｒ钢试样用ＣＯ２连续波输出激光速进行相变硬化处理，用穆斯堡尔谱学方法研究了激光扫描速度对试样表面层组织结构的影响，结果表明，４０Ｃｒ钢激光硬化层的组织为马氏体，残余奥氏体和少量未溶碳化物。随激光扫描速度增大，试样中的马氏体和未溶碳化物的含量不断增加，残余奥氏体含量则连续下降。     

激光冲击1Cr17铁素体不锈钢的组织与性能

针对1Cr17铁素体不锈钢冲击制品硬度随冲击载荷变化增加的情况,进行了一定的实验研究,分析了1Cr17铁素体不锈钢在激光冲击下的组织变化机理,结果表明,随着激光功率增加,1Cr17的加工硬化效应相应提高,得到的硬度越高;在激光冲击后,铁索体的组织主要以调幅分解为主,激光功率增加,调幅分解加剧,形成的格子布形态粗化,并最终在激光功率42J的冲击过程中导致相变产生,生成类马氏体组织。     

Excimer Laser Micromachining of CMSX2 and TA6V Alloys

Excimer laser may be used in the micromachining of various materials, especially in cases where surface finishing by a conventional machining method is difficult. In this study, the process was applied onto two high performance alloys: CMSX2 and TA6V, widely used in the aircraft industry. An attempt was made to determine the relationship between the laser parameters (fluence, frequency, pulse number) and the shape of the formed craters, the proportion of the ablated material and the laser hardening effects. Energy density of 2.5 kJ.cm^-2 was found to be the critical value above which the amount of material ablated and resolidified tend to a constant rate, while the depth attained was influenced only by the other laser parameters (frequency and number of pulses). For the highest energy density applied (10.2 kJ.cm^-2) the formed craters were cone-shaped, in the case of CMSX2, and rectangular, in the case of rolled TA6V. In fact, a prior rolling procedure of TA6V had a great influence on the ablation mechanism. Shock waves occurred hardening affect only the region of CMSX2 sub-surface.     

TC4零件激光快速修复加工参数带的选择

通过研究激光加工参数,包括激光功率、光束扫描速度以及送粉率对热输入效率η和熔覆层形状系数ζ的影响规律,并结合激光快速修复过程对热输入效率和熔覆层形状系数的要求,建立了TC4激光快速修复的加工参数带。采用文章所确定的加工参数带中的参数,有利于减小激光快速修复件的变形,得到的修复件无熔合不良缺陷。     

Numerical simulation of transient and residual stresses caused by laser hardening of slender elements

A mathematical and numerical model of progressive laser hardening with regard to influence of thermal field and phase transformation under transient and residual axial stresses field is presented. The thermal field was determined on the basis of the diffusion-convection equation which was solved by a suitable superposition of Greens function. TIT diagrams were chosen as a basis for describing phase transformations during the heating and cooling process. The stresses were determined on the base of model of plastic flow with isotropic hardening. The changes in thermomechanical parameters of material as a function of phase contents and thermal field were considered in the stress calculations.     

WC基热喷涂金属陶瓷涂层的激光改性研究

本工作研究了CO2激光重熔处理对超音速火焰喷涂WC--Co和WC--NiCr涂层的组织结构和摩擦学行为的影响。结果表明：选定优化参数下,激光重熔可降低涂层气孔率,提高涂层显微硬度,涂层与基材之间实现冶金结合;干摩擦条件下,涂层经过激光重熔处理耐磨性能显著提高;但润滑条件下劣于未经重熔处理涂层,这可能与未重熔涂层含有较多的气孔,可存储润滑油较好地发挥润滑效果有关。     

Laser hardening of aluminum bronzes

The susceptibility of two-phase aluminum bronzes to harden by quenching is well known. This work deals with the features of hardening from liquid or solid phases of several bronzes with 9-11% Al under the action of CO₂ continuous wave laser beam with a power of 1300 W coupled with a table in x-y-z coordinates digitally controlled. In order to determine the hardening conditions, the influence of the processing parameters on the geometry of the hardened layer and surface hardness was analyzed. By the microstructural analysis of the hardened layer, the hardening degree measured by the microhardness meter and structural changes were correlated. The microhardness profile on the depth of the heat-affected zone was traced. The range of the analyzed bronzes points out the influence of the initial condition and of the Ni, Fe, and Mn alloy elements contents on the microstructure, size, and hardness of the hardened layer. The effect of subsequent tempering was investigated.     

The influences of processing parameters on forming characterizations during laser rapid forming

Laser rapid forming experiments were carried out with 316L stainless steel and nickel-base alloy to investigate the influences of the processing parameters on forming characterizations systematically. It is found that the height of a single cladding layer was very important for fabrication accuracy and forming stability of components of laser rapid forming because it was affected by almost all processing parameters and was quite difficult to precisely control. For the system with lateral powder feeding pattern, the powder injection point was the most important factor to the height control of single layer. The variation of the width of single clad, which was mainly affected by laser power, spot diameter and scanning velocity, was similar to that in laser surface melting. The surface quality was another important characterization for laser rapid forming and was remarkably affected by oxidation and the powder adhesion. In order to improve the surface quality, the flow flux of shielding gas should be 10 l min⁻¹ and the powder stream cannot be injected to the tail part of the melt pool. Based on the investigation, some metal components were fabricated.     

高速重复扫描激光塑料焊接工艺研究

目的 提高PA66塑料的焊缝剪切强度,达到实际生产要求.方法 采用高速扫描振镜对PA66塑料进行扫描激光焊接,分析重复焊接次数对塑料焊缝外观及剪切强度的影响,并且对焊缝截面进行测试,分析工艺参数对焊缝截面的影响规律.通过对工艺参数(激光平均功率、重复焊接次数、焊接速度、离焦量)进行四因素四水平正交实验,得到焊缝剪切强度...     

选区激光熔化工艺参数对Ti-6Al-4V成形质量的影响

选区激光熔化是一种利用高能束选择性熔化金属粉末进而直接制造复杂几何形状产品的增材制造技术。采用选区激光熔化成形Ti-6Al-4V样品,分析影响选区激光熔化成形质量的主要因素,采用体式显微镜、金相显微镜、扫描电子显微镜(SEM)、显微硬度计系统研究了不同工艺参数对Ti-6Al-4V合金选区激光熔化成形样品的表面形貌、致密度、组织、显微硬度的影响规律。研究得出Ti-6Al-4V合金选区激光熔化成形的优选工艺参数为:扫描功率450W,扫描速度2 500mm/s,扫描间距0.07mm,该工艺参数下打印出的样品具有较为优良的成形质量,致密度高达97.8%,显微硬度平均值为446HV。     

热锻模型面激光熔覆耐热耐磨覆层的试验研究

为了制备符合锻模使用性能要求的模膛型面耐热耐磨层,进行了在指定的W6Mo5Cr4V2基体上激光熔覆金属陶瓷Ni60／Ni-Cr-Cr2C2的试验研究。主要研究熔覆材料的成分构成,熔覆时的激光参数及所制备的熔覆层的物相、组织形貌及显微硬度分布。试验结果说明采用50％：50％的Ni60粉和Ni-Cr-Cr3C2粉做覆层材料,采用激光功率1．7Kw,扫描速度4mm／s,光斑直径为3mm,预涂厚度为0．6mm的激光熔覆工艺,可以得到组织细化硬度较高的激光覆层。说明激光熔覆金属陶瓷是制备热锻模膛表面强化层的一种有前途的方法。     

Characteristics of Laser Reflow Bumping of Sn3.5Ag and Sn3.5Ag0.5Cu Lead-Free Solder Balls

ead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX （scanning electron microscopy/energy dispersive X-ray spectrometer） was used to analyze the formation of intermetallic compounds （IMCs） at interface region. A finite element modeling on the temperature gradient and distribution at the interface of solder bump during laser reflow process was conducted to elucidate the mechanism of the IMCs growth direction. The results show that the parameters window for laser reflow bumping of Sn3.5Ag0.5Cu was wider than that of Sn3.5Ag. The shear strength of Sn3.5Ag0.5Cu solder bump was comparable to that of Sn3.5Ag solder bump, and was not affected obviously by laser power and irradiation time when appropriate parameters were used. Both laser power and heating time had a significant effect on the formation of IMCs. A continuous AuSn4 intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and Au/Ni/Cu metallization layer when the laser power is small. The formation of needle-like AuSn4 was due to temperature gradient at the interface, and the direction of temperature gradient was the preferred growth direction of AuSn4. With increasing the laser power and heating time, the needle-like AuSn4 IMCs dissolved into the bulk solder, and precipitated out once again during solidification along the grain boundary of the solder bump.