激光能量密度对Al2O3颗粒增强Ni60A激光熔覆涂层组织及性能的影响

目的 实现钛合金表面强化和正向改性,扩大钛合金应用范围。方法 采用预置粉末法在钛合金表面制备Ni60A-Al₂O₃激光熔覆层,通过改变激光功率,进而研究激光能量密度对Ni60A-Al₂O₃熔覆层横截面形貌、微观组织、元素分布、显微硬度以及耐磨性和耐腐蚀性的影响规律。结果 激光能量密度对熔覆层的平整性、成形性有着直接影响。不同激光能量密度下的熔覆层微观组织相似,但在125 J/mm²下,熔覆层形成的陶瓷增强相分布更均匀,且杂质相衍射峰面积较小,元素分布更均匀。此时,熔覆层的力学性能也最好,平均显微硬度值为1132.7HV0.2,较基体硬度提升约3.3倍,摩擦系数最小,且波动较平稳,磨损率也最低,具有较好的减摩性和耐磨性。125J/mm²下熔覆层形成的陶瓷增强相TiC、TiB₂既能作为不良导体降低电化学腐蚀速率,又由于分布均匀而避免应力集中引发裂纹,较其他激光能量密度下的熔覆层具有较好的耐腐蚀性。结论 利用控制变量法探究激光能量密度对Ni...     

激光功率与扫描速度对选区激光熔化钴铬合金组织性能的影响

目的 明确选区激光熔化钴铬合金中激光线能量密度、激光功率和激光扫描速度对成形件组织、性能的影响,探究优化工艺参数的方法。方法 基于ANSYS有限元软件模拟选区激光熔化过程中熔池尺寸的基础上,通过金相显微镜分析了熔池尺寸和显微组织,电子背散射衍射分析了晶粒尺寸,使用力学试验机和洛氏硬度计研究了试样的力学性能。结果 随着线能量密度降低,成形件的熔池尺寸、晶粒大小、冷却速度和力学性能降低。但在激光线线能量密度为0.242 J/mm的条件下,扫描速度为1 200 mm/s时成形试样的致密度为98.7%,抗拉强度为867 MPa,延伸率为6.5%,其力学性能均高于扫描速度为950 mm/s时成形的试样,与线能量密度更高的0.263 J/mm成形条件下250 W+950 mm/s的成形试样力学性能相近。结论 激光线能量密度是影响选区激光熔化钴铬合金熔池尺寸和组织性能的关键因素,但熔池尺寸与激光线能量密度没有线性关系。相同的线能量密度下,增加激光扫描速度,有利于获得大的熔池尺寸和冷却速度,提高成形件的致密度和降低晶粒尺寸,最终使成形件力学性能提高。     

不同选择激光熔化工艺参数下Al-4.77Mn-1.37Mg-0.67Sc-0.25Zr合金的拉伸性能及显微组织（英文）

采用选择激光熔化(SLM)技术在不同工艺参数下制备Al-4.77Mn-1.37Mg-0.67Sc-0.25Zr合金(质量分数,%),通过拉伸试验和显微观察研究合金的组织和力学性能。结果表明：当能量密度为104～143 J/mm³时,力学性能保持相对稳定;屈服强度为335～338 MPa,抗拉强度为397～400 MPa,伸长率均在11%以上。在此能量密度区间内,SLM合金缺陷和粗大金属间化合物较少,与此同时,有大量细小的Al Fe Mn Sc Zr相析出。当能量密度超过152 J/mm³时,可以观察到一些孔洞和裂纹,且伸长率急剧下降。定量计算结果表明,该合金固溶强化、晶界强化和析出强化占比分别为44%、41%和15%。     

不锈钢表面激光熔覆镍基合金涂层的数值模拟与试验

为改善不锈钢表面熔覆质量,探究能量密度对不锈钢表面激光熔覆镍基合金涂层质量的影响,利用Visual-Environment数值模拟软件,基于高斯体热源模型,通过改变激光功率获得不同的能量密度输入,对304不锈钢表面激光熔覆Ni35合金涂层的过程进行了数值模拟分析,并采用相应能量密度对应的激光功率进行试验验证。模拟结果表明,激光功率为900 W,扫描速度为6 mm/s,光斑半径为1 mm时,对应的激光能量密度为75 J/mm²,所得温度分布云图峰值温度2459.55℃,在较合理的温度范围内(2400～2600℃)。试验验证结果显示,该工艺参数下熔覆层宏观形貌较好且微观组织致密,基体与涂层间形成了良好的冶金结合。     

直接激光沉积Fe-Cr-Ni梯度合金钢的组织与性能

采用直接激光沉积技术制备了具有外强内韧组织性能的12CrNi2Y-50Cr6Ni2Y-70Cr8Ni2Y梯度合金钢试样,利用光学显微镜、扫描电镜、透射电镜、硬度计、摩擦试验机等分析手段,对直接激光沉积的梯度合金钢试样的组织结构、界面结合性、硬度梯度分布及耐磨性等进行了研究。结果表明,在优化的激光沉积参数下,成功制备出了无裂纹夹杂缺陷、梯度过渡界面处呈现冶金结合的12CrNi2Y-50Cr6Ni2Y-70Cr8Ni2Y梯度合金钢试样。梯度合金钢的组织呈现出由粒状贝氏体+板条贝氏体+少量马氏体→板条贝氏体+板条马氏体→板条马氏体+片状马氏体的变化趋势,对应硬度呈356 HV0.2→551 HV0.2→712 HV0.2梯度分布,体积磨损率呈现2.01×10^-4 mm³·N^-1·m^-1→1.33×10^-4 mm³·N^-1·m^-1→0.71×10^-4 mm³·N^-1<...     

表面张力对激光焊接熔池及匙孔的影响

基于FLUENT19.0软件,建立了激光焊接热-流耦合模型,对比分析了不同表面张力温度系数(为负值)对熔池流场的影响.结果表明,随着表面张力温度系数的减小,熔池后方顺时针漩涡的流动趋势逐渐减弱,甚至消失,而且焊接飞溅的数量增多.纵截面熔池长度逐渐增加,纵截面熔池流体最大流动速度逐渐增大,熔池横截面的面积逐渐减小.当表面张力温度系数为-2.5×10^-4 N/(m·K)时,熔池长度平均值为3.28 mm、熔池流体最大流动速度的平均值为2.89 m/s、熔池横截面面积的平均值为4.52 mm²;当表面张力温度系数为-3.5×10^-4 N/(m·K)时,熔池长度平均值为3.73 mm、熔池流体最大流动速度的平均值为3.53 m/s、熔池横截面面积的平均值为4.03 mm²;当表面张力温度系数为-4.9×10^-4 N/(m·K)时,熔池长度平均值为4.14 mm、熔池流体最大流动速度的平均值为4.09 m/s、熔池横截面面积的平均值为3.28 mm².     

激光熔化沉积制备2A50锻造铝合金组织性能*

工艺参数的协同调控决定了沉积工件的组织与性能,在锻造铝合金零件激光增材修复工程应用方面具有重要研究价值。 采用 OM、SEM、XRD 等试验方法,研究能量密度对激光沉积成形 2A50 铝合金构件组织与性能的影响规律。结果表明：当能量密度低于 200 J / mm²时,成形效果较差且产生粉末球化、未熔合等凝固缺陷;随着能量密度的提高,沉积试样底部和顶部一次枝晶间距均明显缩短、平均硬度由 85.7 HV 提高至 92.1 HV;过高的能量密度输入会导致熔池内部分低熔点合金元素蒸发形成气孔缺陷、同时削弱了合金元素的固溶强化效果。在优化的能量密度(333 J / mm² )条件下,激光沉积成形 2A50 锻造铝合金构件获得了较优的综合力学性能,其屈服强度、抗拉强度和延伸率分别为 85 MPa、207 MPa 和 14%。为航空重大装备关键零部件的激光增材修复探索出一条行之有效的技术途径。     

激光体能量密度对选区激光熔化成形的有限元分析EI北大核心CSCD

建立Ti-6Al-4V合金三维有限元模型,探究低功率密度下不同的激光体能量密度对选区激光熔化多层沉积成形过程热行为及热应力演变的影响。本模拟采用热−结构间接耦合的方式计算应力场,利用Sqarse/PCG自动求解器增加其收敛性。结果表明:随着低功率密度下激光体能量能量密度从37.04 J/mm^(3)增加至74.07 J/mm^(3),温度分布具有相似的变化趋势,熔池深度及宽度先增大后趋于平稳,实验熔宽与模拟结果基本一致。随着激光体能量密度的增加,整体残余应力呈减小趋势,降幅6.30%。表面应力呈“条带状”周期性分布,应力集中处于扫描轨道的搭接区域,基板层边缘处应力较大。通过对比模拟与实验层间残余应力结果,可见随着体能量密度的增加两者具有相同的变化趋势,最大偏差6.28%。在能量密度为37.04~74.07 J/mm^(3)范围内,经线性拟合后,模拟/实验层间残余应力与硬度值呈反比关系。     

带热障涂层镍基单晶高温合金的激光制孔研究

采用毫秒激光和皮秒激光在带热障涂层的镍基单晶合金上加工了气膜孔,对比研究了长脉冲与超短脉冲加工对热障涂层及金属基体孔壁形貌的影响。实验发现,波长1064 nm的毫秒激光在试样表面产生的能量密度直接影响到陶瓷层的加工。以2866 J/cm2的能量密度从陶瓷面加工,陶瓷面的熔化所需要的热积累时间长,热量会传导至高温金属,产生类似熔池的热影响;而从金属面加工则由于陶瓷是最后加工的材料,有足够的热积累时间熔化陶瓷涂层,从而直接打通小孔。当毫秒激光的能量密度提高至6369 J/cm2时,热量在涂层中的积累速度加快,陶瓷材料能够快速熔化,从而避免了金属基体先于陶瓷熔化的现象,同时,加工过程中熔化后的陶瓷会经过孔通道,从而出现附着在孔壁上的现象。采用皮秒激光加工陶瓷涂层仅需要能量密度达到32 J/cm2,皮秒激光旋切制孔是将小孔圆周上的材料全部剥蚀掉,直至孔打通,而孔内的材料会从孔中掉出。皮秒激光加工中产生的等离子体冲击力会引起涂层的开裂,由于热障涂层制备方法不同引起涂层中的裂纹方向有所不同,等离子喷涂制备的涂层为层状结构,裂纹易沿平行于表面方向生长,而EB-PVD制备的涂层为柱状晶结构,裂纹多出现在柱状晶的间隙。     

激光功率对Al2O3-ZrO2共晶陶瓷成形质量的影响

采用激光近净成形系统成形了Al2O3-Zr O2(Y2O3)共晶陶瓷,研究了激光功率对成形形貌以及陶瓷内部裂纹、气孔的影响规律,利用X射线衍射仪和扫描电镜对样件进行相成分分析和微观组织观察。研究表明,相对较高的激光功率可以得到裂纹以及气孔较少的陶瓷样件;陶瓷样件具有紧凑排列的胞状共晶组织,亚微米级t-Zr O2(Y2O3)纤维均匀分布在胞状共晶组织内部。由于激光近净成形加工具有层层堆积的特点,微观组织呈现出垂直于沉积方向的周期性带状组织。     

High quality welding of stainless steel with 10 kW high power fibre laser

Abstract

The objectives of this research are to investigate penetration characteristics, to clarify welding phenomena and to develop high quality welding procedures in bead on plate welding of type 304 austenitic stainless steel plates with a 10 kW fibre laser beam. The penetration depth reached 18 mm at the maximum at 5 mm s^?1. At 50 mm s^?1 or lower welding speeds, however, porosity was generated at any fibre laser spot diameter. On the other hand, at 100 mm s^?1 or higher welding speeds, underfilling and humping weld beads were formed under the conventionally and tightly focused conditions respectively. The generation of spatters was influenced mainly by a strong shear force of a laser induced plume and was greatly reduced by controlling direction of the plume blowing out of a keyhole inlet. The humping formation was dependent upon several dynamic or static factors, such as melt volume above the surface, strong melt flow to the rear molten pool on the top surface, solidification rate and narrow molten pool width and corresponding high surface tension. Its suppression was effective by producing a wider weld bead width under the defocused laser beam conditions or reduction of melt volume out of keyhole inlet under the full penetration welding conditions. Concerning porosity, X-ray transmission in situ observation images demonstrated that pores were formed not only from the tip of the keyhole but also at the middle part because of high power density. The keyhole behaviour was stabilised using a nitrogen shielding gas, resulting in porosity prevention. Consequently, to produce high quality welds in 10 kW high power fibre laser welding, the reduction procedures of welding defects were required on the basis of understanding their formation mechanism, and 10 kW fibre laser power could produce sound deeply penetrated welds of 18 mm depth in a nitrogen shielding gas.     

激光熔丝增材制造监测与控制系统研究现状

激光熔丝增材制造作为一种定向能量沉积技术,具有很好的发展前景。文中对国内外激光熔丝增材制造监测与控制系统进行归纳概述。现阶段,国内外激光熔丝增材制造常见的监测系统包括结构光扫描系统、红外测温成像系统等,实时监测沉积层高度、熔池状态;常见的控制系统为以闭环控制策略为主的在线反馈送丝速率控制系统、在线反馈激光功率控制系统等,在线监测系统与控制系统协同作用,能够显著优化增材制造工艺、提高成形质量。介绍了包括三维超声波扫描技术、电磁振动监测技术在内的新兴激光熔丝增材制造监测技术。结合激光熔丝增材制造技术的工艺难题对下一代监测与控制系统进行展望。国内外对沉积层高度和宽度、熔池尺寸和温度等监测对象已有较为充分的研究和试验验证,但在沉积过程中,由于激光的高能量密度会造成高温度梯度,因此对沉积过程在线高精度、高质量监测与控制技术的研究变得至关重要。 创新点： 激光熔丝增材制造成形精度要求高,同时国内外对该技术的相关工艺、成形原位控制的研究处于起步阶段,对沉积层、熔池偏差的实时监测与控制进行深入研究具有重要意义。     

激光熔覆熔池动态演化及缺陷工艺调控研究进展

激光熔覆是一种高能束增材修复技术,具有热影响区小、组织性能可控性强、材料选择范围广等系列优势,目前已广泛应用于能源动力等领域关键金属构件的增材制造成形与受损零部件的修复再制造中。激光熔覆是以“激光”为热源的能量沉积技术,包括高能激光束冲击、表面熔池熔化快凝及熔覆表面层形成等多种物理、化学过程,其中熔池内金属热流体动力演化行为与熔覆层缺陷及表层组织性能调控密切相关。金属熔池具有“急热骤冷”的凝固特征,其内部对流、传热和传质等行为决定了熔覆层中温度及应力分布状态,是诱导熔覆层内气孔、裂纹等组织内部缺陷形成的关键因素。从激光熔覆过程中熔池内部对流、传热与传质的动态物理特性出发,论述了激光热源的理论模型设计、动态熔池中“流场+温度场+应力场”的多物理场数值模拟等方面的相关研究。在此基础上,分析了激光熔覆层典型缺陷-裂纹和气孔的形成机理及特征,总结了“材料-工艺-熔凝行为-涂层缺陷”的内在关联机制。同时,针对单一工艺方式调控熔池内熔凝过程的局限性,概述了多种复合能量场调控技术对熔覆层内部缺陷的作用机制与调控效果。最后,总结了当前激光熔覆层缺陷动态形成过程中存在的问题,并对其发展趋势进行了展望。     

Selective laser melting of aluminium components

Previous work has shown that the processing of aluminium alloys by selective laser melting (SLM) is difficult, with reasonable components only being produced with high laser powers (minimum 150 W) and slow laser scanning speeds. The high laser power is a significant problem as it is higher than that used in many SLM machines. Also, the combination of high power and low speed creates a large melt pool that is difficult to control, leading to balling of the melt and possible damage to the powder distribution system. Even when processing is carried out successfully, the high power and slow scan speed significantly increase build time and the manufacturing costs.This paper considers the changes that can be made to the SLM process so as to reduce the laser power required and increase the laser scanning rates, while still producing components with a high relative density. It also considers why aluminium and its alloys are much more difficult to process than stainless steels and commercially pure titanium. Two MCP Realizer machines were used to process 6061 and AlSi12 alloys, one processing at 50 W and the other 100 W laser power. Even with an optimum combination of process parameters a maximum relative density of only 89.5% was possible (achieved with 100 W). The major confounding factor for processing aluminium and its alloys was found to be oxidation due to the presence of oxygen within the build chamber. This formed thin oxide films on both the solid and molten materials. It was observed that the oxide on the top of the melt pool vaporised under the laser creating a fume of oxide particles, while melt pool stirring, probably due to Marangoni forces, tended to break the oxide at the base of the melt pool allowing fusion to the underlying tracks. However, the oxides at the sides of the melt pool remained intact creating regions of weakness and porosity, as the melt pool failed to wet the surrounding material. Therefore, if 100% dense aluminium components are to be produced by SLM, using low laser powers, methods need to be developed that can either disrupt these oxide films or avoid their formation.     

Synchrotron-Based X-ray Microtomography Characterization of the Effect of Processing Variables on Porosity Formation in Laser Power-Bed Additive Manufacturing of Ti-6Al-4V

The porosity observed in additively manufactured (AM) parts is a potential concern for components intended to undergo high-cycle fatigue without post-processing to remove such defects. The morphology of pores can help identify their cause: irregularly shaped lack of fusion or key-holing pores can usually be linked to incorrect processing parameters, while spherical pores suggest trapped gas. Synchrotron-based x-ray microtomography was performed on laser powder-bed AM Ti-6Al-4V samples over a range of processing conditions to investigate the effects of processing parameters on porosity. The process mapping technique was used to control melt pool size. Tomography was also performed on the powder to measure porosity within the powder that may transfer to the parts. As observed previously in experiments with electron beam powder-bed fabrication, significant variations in porosity were found as a function of the processing parameters. A clear connection between processing parameters and resulting porosity formation mechanism was observed in that inadequate melt pool overlap resulted in lack-of-fusion pores whereas excess power density produced keyhole pores.     

Observation of keyhole-mode laser melting in laser powder-bed fusion additive manufacturing

Laser powder-bed fusion additive manufacturing of metals employs high-power focused laser beams. Typically, the depth of the molten pool is controlled by conduction of heat in the underlying solid material. But, under certain conditions, the mechanism of melting can change from conduction to so-called “keyhole-mode” laser melting. In this mode, the depth of the molten pool is controlled by evaporation of the metal. Keyhole-mode laser melting results in melt pool depths that can be much deeper than observed in conduction mode. In addition, the collapse of the vapor cavity that is formed by the evaporation of the metal can result in a trail of voids in the wake of the laser beam. In this paper, the experimental observation of keyhole-mode laser melting in a laser powder-bed fusion additive manufacturing setting for 316L stainless steel is presented. The conditions required to transition from conduction controlled melting to keyhole-mode melting are identified.     

激光增材制造过程中激光与粉末的相互作用研究现状

激光增材制造是通过激光加热熔化粉末或丝材并逐层叠加而形成所需工件的一种增量制造技术。该技术涉及非常复杂的非平衡物理和化学冶金过程,在加工过程中易产生非平衡组织和晶粒取向。激光与粉末的相互作用过程是整个加工过程中最为重要的部分,系统总结激光与粉末的相互作用对于增进对激光增材制造技术的理解,进而提升工件性能具有重要的意义。按照送粉式与铺粉式激光增材制造两种加工方式,分析了激光能量的衰减、粉末颗粒温度的上升以及激光-粉末-熔池的相互作用,综述了激光与粉末相互作用的研究现状。     

Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by In Situ Laser Directed Energy DepositionEI北大核心CSCD

以Ni粉与Ti粉为原料,采用激光定向能量沉积(LDED)技术制备NiTi形状记忆合金。利用XRD、物相拟合、SEM、EDS和DSC等测试方法,对NiTi合金的显微组织、物相含量和物相转变进行分析,随后采用压缩圆柱样品进行形状记忆效应测试,并评估其形状记忆效应。激光能量密度较低时,NiTi合金中产生大量Ni_(4)Ti_(3)相沉淀,随着激光能量密度增加,Ni_(4)Ti_(3)相消失。激光能量密度为20.0 J/mm^(2)时,NiTi合金具有2878 MPa的压缩断裂强度与34.9%的压缩失效应变,且样品在循环20 cyc后具有88.2%形状记忆恢复率。