特定强度分布脉冲激光表面强化实验

激光硬化层均匀性受光束空间强度分布和作用时间的影响.采用二元光学变换技术得到光束中心线强度比值为1:2:3、3:2:1和1:1:1的5×5点阵光斑,研究这三种强度分布光斑对Q235钢脉冲激光硬化后表面形貌、硬化层形状、硬度及耐磨性的影响.结果表明,激光光斑的空间强度分布对Q235钢硬化层均匀性影响很大,1:2:3强度分布光斑作用下的材料表面形貌、硬化层均匀性、硬度均匀度均优于1:1:1强度分布光斑.     

激光冲击对热作模具钢残余应力场的影响规律研究

研究了激光脉冲能量、激光光斑直径等工艺参数对激光冲击H13热作模具钢表面及深度方向的残余应力大小和分布的影响,系统研究了激光冲击对H13热作模具钢的表面强化机理。结果表明,随激光脉冲能量和光斑直径的增加,沿X轴方向的表面残余压应力增加,但增加幅值逐渐减小,最大残余压应力可达700 MPa;深度方向的残余压应力也会增加,增幅也是逐渐变小。研究发现,激光冲击H13热作模具钢对沿X轴方向表面残余应力的影响范围与激光脉冲能量和激光光斑尺寸等参数无关。数值分析结果和实际结果吻合度很好,为H13热作模具钢性能的提高和改善提供了新方法。     

无保护层激光冲击强化的热效应研究

目的 深入理解无保护层激光冲击强化(LSPwC)的物理过程。方法 对轧制TA2纯钛板材进行LSPwC处理,通过激光扫描显微镜、X射线应力仪分析试样的表面形貌和残余应力分布,使用透射电子显微镜分析LSPwC后试样表层的微观组织特征。使用Abaqus软件建立LSPwC过程的热力耦合仿真模型,分析试样温度和应力演变规律。结果 当激光脉冲能量为30 mJ、光斑直径为0.4 mm时,经LSPwC处理后TA2试样表面形成了厚度约为50μm的残余拉应力层,其最大残余压应力达到560 MPa,出现在距表面100μm的次表层;经LSPwC处理后TA2试样表面产生了超细马氏体晶,距表面100μm的微观组织表现为高密度位错缠结。随着激光脉冲能量和光斑直径的增大,激光热效应的持续时间增长、热影响深度增大,经LSPwC处理后TA2试样的残余压应力层深度增大。在LSPwC过程中,距表面10.2μm以内深度层的冷却速度超过10⁶℃/s,但冷却速度随着脉冲能量和光斑直径的增大而减小。结论 在LSPwC过程中,激光热效应和激光诱导冲击波作用,导致试样表层迅速升温,并发生塑性变形,然后快速降温,形成...     

激光冲击处理对AZ31B镁合金表面质量的影响

为了研究激光冲击处理对AZ31B镁合金表面质量的影响,采用波长1 064 nm、脉冲宽度15 ns、脉冲能量10 J、光斑直径3mm的钕玻璃脉冲激光器,对轧制态AZ31B镁合金薄板试样表面进行激光冲击处理。试验结果表明:单次冲击所形成的凹坑深度达到39.122μm;由于激光能量分布不均匀,导致AZ31B镁合金表面粗糙度值增大。     

激光熔覆加工头聚焦性能及成形工艺研究进展

激光熔覆作为一种十分有前途的制造技术,已在工业中广泛用于部件修复、表面改性以及增材制造等领域。在激光熔覆系统中,激光熔覆加工头是其关键核心部件,可以在基材表面实现激光束、熔覆材料和熔池之间的精准耦合并形成连续熔覆层。激光熔覆加工头内置有光学镜组,主要用于激光束的传输、变换和聚焦,可以根据不同的加工需求对光束进行处理。主要从分析激光熔覆加工头聚焦性能对熔覆成形工艺影响的角度出发,综述了加工头的设计及其成形工艺的发展,具体包括光斑尺寸、光斑形状、光斑能量分布、激光功率、光源特性等对材料沉积速度、材料利用效率、熔覆层质量等的影响。首先按照激光熔覆的材料类型和材料与激光束的耦合形式,对激光熔覆光料耦合方式及加工头进行了简要概述,并对成形工艺造成的影响进行了总结。其次分别讨论了连续高斯光束和平顶光束以及脉冲激光的聚焦性能对熔覆层的影响,同时概述了3种不同形状光斑（圆形、矩形、环形）的能量分布特性和光斑尺寸对成形工艺的影响;接着研究了激光能量密度对熔覆层质量的影响;基于超高速激光熔覆技术分析提出透镜长焦深聚焦特性能够大幅提升激光熔覆的加工效率。最后展望了激光熔覆加工头聚焦性能在成形工艺上的发展趋势...     

OFHC铜高应变率激光冲击微坑的尺寸效应(英文)

采用高温无氧铜材料,实验研究激光冲击压力作用下铜材料表面微坑的几何特征以及尺寸效应作用规律。通过控制热处理温度与保温时间,在厚度截面方向获得多种不同晶粒粒径的试样,结合2种不同光斑大小的实验,研究激光冲击表面高应变率塑性变形的大小效应作用特征。实验结果表明:在相同激光能量条件下,大光斑冲击产生的微坑深度较大。晶粒粒径对微坑深度有较大的影响,小晶粒条件下,产生的坑深较小;大晶粒条件下,光斑大小与晶粒粒径对于坑深的影响较为显著。     

激光冲击强化对TC17表面形貌及残余应力场影响的有限元数值模拟研究

激光冲击强化是一种新型表面改性技术,能够在金属部件表面引入残余压应力提高其疲劳、耐磨和腐蚀性能。研究了不同能量脉冲激光(3,5和7 J)冲击强化对TC17钛合金材料表面形貌和最大塑性变形的影响并通过有限元数值模拟激光冲击强化过程。运用白光干涉仪表征试样表面三维形貌和表面塑性应变,采用有限元数值模拟验证表面塑性应变并研究表面和深度方向残余应力场分布规律。结果表明:实验法和有限元法测定试样表面塑性应变深度具有较高的一致性,3、5和7 J冲击下的最大残余应力分别为136.7、407.6和637.3 MPa,塑性影响层深度从约400μm增加到约1050μm。因此,增加激光冲击能量有益于提高残余应力场的大小和深度。     

轮齿激光冲击诱导残余应力的数值模拟

采用波长为1064 nm,脉冲宽度为23 ns,光斑半径为5 mm,单次脉冲能量为40 J的激光对渐开线直齿圆柱轮齿齿面进行了激光冲击强化处理,并借助ANSYS/LS-DYNA软件模拟了残余应力场的形成过程;随后运用有限元方法研究了激光脉冲参数对轮齿根部残余应力的影响。结果表明,激光冲击强化后,在轮齿表面及深度方向上通过数值模拟获得的残余应力与实验测量值得到了较好的吻合;对轮齿齿根进行激光冲击强化时,选用脉宽为25 ns、高斯波形的激光加载能够获得较理想的残余应力分布;同时激光冲击强化对圆角半径较小的齿根效果更明显。     

激光冲击强化对回转支承用钢42CrMo表面性能的影响

目的研究激光冲击强化对回转支承用钢42CrMo表面形貌、表面硬度、微观组织和残余应力的影响,为后续研究激光冲击强化技术在回转支承上的应用提供指导和依据。方法采用高功率短脉冲的强激光束对回转支承用钢42CrMo试样进行激光冲击处理,然后用共聚焦显微镜进行表面形貌观察,用维氏硬度计测量冲击前后试样的表面硬度,用扫描电子显微镜观察截面微观组织结构,最后运用ABAQUS模拟激光冲击后的残余应力场。结果光斑直径为3 mm,脉冲宽度为8 ns,激光能量为2、3、4、5 J的情况下,激光冲击后产生的微凹坑最大深度分别为2.17、3.54、4.67、6.07μm,材料表面最高硬度较基体分别提高了10.10%、12.58%、13.58%、17.38%,材料表面的最大残余压应力分别为-210、-384、-495、-508 MPa。观察微观组织发现,激光冲击后塑性变形区的板条马氏体长度和宽度较基体材料更小,且分布更加均匀。结论激光冲击强化回转支承用钢42CrMo后,会在材料表面产生微米级的凹坑,并在材料表面和一定深度方向上产生残余压应力。在一定参数范围内,凹坑最大深度、材料表面硬度和最大残余压应力均随激光能量的增大而增大。回转支承用钢42CrMo的激光冲击强化机理是板条状回火马氏体的细化。     

激光冲击强化TC17钛合金室温和高温拉伸性能研究

目的分析激光冲击强化对钛合金室温和高温拉伸性能的影响。方法用YAG纳秒脉冲激光器对TC17钛合金板状拉伸试样表面进行双面激光冲击强化,脉冲能量为25 J,脉冲宽度为15 ns,光斑尺寸为4.2 mm×4.2 mm,搭接率为10%,强化1次。通过室温及400℃下拉伸试验,获得强化前后试样的抗拉强度、屈服强度和断裂伸长率,利用X射线衍射法测试拉伸前后试样表面的残余应力,并在扫描电镜下观察拉伸试样断口微观形貌。结果室温拉伸试验时,激光冲击强化对TC17钛合金的室温抗拉强度和伸长率几乎无影响,但强化后的室温屈服强度下降约6.1%,有/无强化试样均没有明显的屈服点,距离强化试样断裂位置10 mm的表面残余压应力较拉伸前下降约12%。400℃拉伸试验时,激光冲击对TC17钛合金的高温抗拉强度和屈服强度均影响较小,有/无强化试样均出现明显的屈服点,距离强化试样断裂位置10 mm的表面残余压应力较拉伸前下降约44%。结论激光冲击强化在TC17钛合金表面引入显著的残余压应力分布,对屈服强度具有一定程度的影响。强化后试样的屈服强度与拉伸过程中残余压应力松弛速率有关,室温拉伸过程的残余应力松弛较高温拉伸过程慢,试样内部的平衡拉应力区更容易先发生屈服。这是造成室温拉伸屈服强度小幅降低的主要原因。     

Predictive modeling and experimental results for laser hardening of AISI 1536 steel with complex geometric features by a high power diode laser

This paper presents predictive modeling and experimental results on laser hardening of AISI 1536 steel shafts with a complex geometric feature. A three-dimensional thermal model is used to predict the workpiece temperature distribution, which is coupled to a two-dimensional kinetic model to predict the resultant hardness and phase distribution. Surface temperature measurements are performed to validate the thermal model, while the kinetic model is validated through furnace hardening and laser hardening experiments. A 2.5-mm case depth is achieved on simple geometry parts, while a 1.5-mm case depth is obtained on parts with a groove of 2.0-mm radius. The case hardness values and distributions show good agreement with predicted results and are found to be uniform throughout, with the values between 55 and 57 in Rockwell C.     

激光-MAG复合焊等离子体辐射分析

对于MAG焊、激光-MAG复合焊的等离子体辐射,采用中空探针,使特定点的辐射通过探针对其等离子辐射进行空间分布采集,对比分析激光复合前后等离子体辐射光谱的分布规律,并结合高速摄像,为激光-MAG复合焊的耦合机理研究和工程应用提供理论基础.结果表明,激光复合后,在电弧中心形成一个辐射明显增大的区域,区域外侧存在一个辐射降低区域;在电弧前侧激光复合作用位置,会形成一个以铁辐射谱线为主的"电离通道".激光复合后,电离通道的存在为电弧的稳定提供了基础;在中心区形成了能量集中的辐射通道,改变了电弧中能量的分布,使能量更集中于中心区域,获得比传统MAG焊更大的熔深.     

A Comparative Study of High-Power Diode Laser and CO2 Laser Surface Hardening of AISI 1045 Steel

The study investigates laser surface hardening in the AISI 1045 steel using two different types of industrial laser: a high-power diode laser (HPDL) and a CO₂ laser, respectively. The effect of process parameters such as beam power, travel speed on structure, case depth, and microhardness was examined. In most cases, a heat-affected zone (HAZ) formed below the surface; a substantial increase in surface hardness was achieved. In addition, big differences were found between the hardened specimens after HPDL surface hardening and CO₂ laser surface hardening. For HPDL, depths of the HAZ were almost equal in total HAZ o, without surface melting. For CO₂ laser, the depths changed a lot in the HAZ, with surface melting in the center. To better understand the difference of laser hardening results when use these two types of laser, numerical (ANSYS) analysis of the heat conduction involved in the process was also studied. For HPDL method, a rectangular beam spot and uniform energy distribution across the spot were assumed, while for CO₂ laser, a circular beam spot and Gaussian energy distribution were assumed. The results showed that the energy distribution variety altered the thermal cycles of the HAZ dramatically. The rectangular HPDL laser beam spot with uniform energy distribution is much more feasible for laser surface hardening.     

Thermal analysis of laser surface transformation hardening—optimization of process parameters

This paper deals with the optimization of process parameters for maximum productivity (given by the product of scanning velocity and cross feed) in laser transformation hardening. The process parameters considered are laser beam power, P; laser beam diameter, D_b; and the heat intensity distribution, namely, normal, bimodal, or uniform. A thermal analysis of the laser surface transformation hardening of gears was conducted (based on Jaeger’s classical moving heat source method) by considering the laser beam as a moving plane (disc) heat source to establish the temperature rise distribution in the workpiece (gear) of finite width. In a recent investigation [Int. J. Heat Mass Transfer 44 (2001) 2845], the authors considered the case of a heat source with a pseudo-Gaussian (or normal) distribution of heat intensity. The analytical results were compared with the experimental results published in the literature. In laser heat treatment of steel, it is generally considered preferable to use a wider heat intensity distribution, such as uniform or bimodal, for it enables more uniform case hardening depth. In this paper, this model is extended to cover bimodal and uniform distributions and compared with the normal distribution. Scanning velocities for no surface melting and for a case hardening depth of 0.1 mm were determined for surface transformation hardening of AISI 1036 (EN 8) steel for a range of laser beam powers, P, laser beam diameters, D_b, and various heat intensity distributions. Since diffusion during the heat treatment (surface transformation hardening) process is a time dependent phenomenon, based on the literature review, an interaction time of 15 ms was taken as a basis. It is hoped that laser industry with adequate facilities available can validate the thermal analysis and subsequent optimization presented in this paper.     

Laser transformation hardening on rod-shaped carbon steel by Gaussian beam

Laser transformation hardening(LTH) is one of the laser surface modification processes. The surface hardening of rod-shaped carbon steel (SM45C) was performed by lathe-based laser composite processor with Gaussian-beam optical head. The LTH characteristics by dominant processes, longitudinal and depth directional hardness distributions and behaviors of phase transformation in hardened zones were examined. Especially, two concepts of circumferential speed and theoretical overlap rate were applied. When laser power increased or circumferential speed decreased, the surface hardening depth gradually increases due to the increased heat input. Moreover, the longitudinal hardness distribution particularly shows periodicity of repetitive increase and decrease, which results from tempering effect by overlap. Finally, the feasibility of laser transformation hardening is verified by using the beam with Gaussian intensity distribution.     

Automatic extraction and visualization of spatial position data for bulk porosities in laser weldments with complex structures

The left and right-turning scheme of weldments was adopted to detect small porosities in laser weldments with complex structures. Detection images were obtained in this study. An algorithm that determines the optimal structure elements for morphology simulation was provided to achieve fidelity segmentation of small porosities. Mathematical models for the defect depth and deviation of bulk porosities were established based on the geometric features of laser weldments. Thus, the features of spatial distribution of small porosities were determined. To improve detection efficiency, the automatic extraction of spatial position data for bulk porosities was divided into two parts: automatic extraction of projection distance, which is important for the determination of weld porosity depth and deviation, and automatic extraction of porosity size. The porosity distribution in the longitudinal direction was obtained by automatic searching, and the features of the spatial distribution of weld porosities were procured. A 3D model of laser weldments was established to visualize the spatial distribution of porosities. Extracted data were inputted to the model, and the spatial positions of bulk porosities were visualized.     

40CrNiMoA钢激光相变硬化技术

研究了40CrNiMoA钢激光淬火工艺参数与硬化层深度及硬度之间的相互关系，以及淬硬层微观结构特征。结果表明，随着光斑扫描速度的提高，硬化层深度降低，表面硬度存在一个极大值；随着激光功率的升高，硬化层深度增加，表面硬度也存在一个极大值，激光淬火硬化层依其组织特征，分为完全淬硬区，过渡区及高温回火区。     

激光表面淬火对铬钼铸铁组织和硬度的影响

采用TH-3DC3000型激光加工系统对铬钼铸铁进行了激光表面淬火处理,研究了不同激光功率和扫描速度对铬钼铸铁显微组织、表面硬度及硬化层深度的影响。结果表明,经激光表面淬火后,铬钼铸铁的组织由硬化区、过渡区和基体3个区域组成,硬化区组织为隐晶马氏体、残留奥氏体和球状石墨,过渡区组织为隐晶马氏体、珠光体和球状石墨,基体组织为铁素体、珠光体和球状石墨。在激光表面淬火未对试件产生过热影响时,激光功率的增大和扫描速度的降低均会提升铬钼铸铁的表面硬度和硬化层深度。在5 mm×20 mm的矩形激光光斑下,确定最优的参数组合为激光功率2300 W、扫描速度0.003 m/s,采用该参数组合对铬钼铸铁进行激光淬火处理时,表面硬度为760 HV0.3,硬化层平均硬度为724 HV0.3,硬化层深度可达1.4 mm以上。     

齿轮激光淬火硬化层数值模拟

建立了采用轴向扫描工艺对渐开线齿轮进行激光淬火时的三维温度场数值模型,采用ANSYS软件模拟激光束扫描过程中齿面及轮齿横截面的温度分布。结果表明,激光淬硬层深度模拟结果与试验结果相吻合,可以通过该温度场模型对各种模数和齿数的齿轮激光淬火过程进行模拟,快速得到与实际相近的硬化层深度分布曲线。建立该数值模型的一些思路和方法也适用于各种曲面类零件激光淬火的数值模拟。     

高铬铸钢激光熔凝组织与性能研究

为提高锅炉燃烧器喷嘴的表面性能,采用5kW横流CO2激光加工系统对高铬铸钢表面进行熔凝处理,并进行显微组织分析和硬度测试.研究结果表明:铸态高铬铸钢晶粒较粗大、组织不均匀,原始组织以奥氏体为基体,还存在大量网状断续共晶碳化物、莱氏体.经激光凝熔后,显微组织明显细化,其试样剖面组织分为激光熔凝区(细小奥氏体 少量细小未熔碳化物)、激光相变区(奥氏体 少量晶界碳化物)、过渡区和母材4个区域.熔凝区和相变硬化区的淬硬深度依工艺参数不同.可达0.2～0.3mm.由于形成了奥氏体组织,高铬铸钢表面硬度增加不明显,硬度最大值出现在相变硬化区.