Effects of WC-Co reinforced Ni-based alloy by laser melting deposition: Wear resistance and corrosion resistance

WC-Co reinforced C276 alloy composite coatings are fabricated on Q235 steel by laser melting deposition.The microstructure,hardness,wear performance,and electrochemical corrosion behavior of composite coating are studied.The results show that WC-Co particles are mostly uniformly distributed in the coating and provide favorable conditions for heterogeneous nucleation.The microstructure of C276/WC-Co composite coatings is composed of γ-Ni solid solution dendrites and MoNi solid solution eutectics.The WC-Co particles can effectively improve the hardness and wear resistance of C276 alloy.The average hardness of the composite coating containing 10-wt% WC-Co(447 HV_(0.2)) are 1.26 times higher than that of the C276 alloy(356 HV_(0.2)).The wear rate of composite coating containing 10-wt% WC-Co(6.95 ×10^(-3) mg/m) is just 3.5% of that of C276 coating(196.23 × 10^(-3) mg/m).However,comparing with Hastelloy C276,the corrosion resistance of C276/WC-Co composite coating decreases.

Simulation and Analysis of Electromagnetic Force in Laser Melting Deposition by Electromagnetic Impact

Magnetic field was introduced in laser melting deposition to reduce the pores in workpieces.Finite 3-D model of the coil-deposition layer-substrate was established.Simulation results show that the electromagnetic force in deposition layer mainly concentrates in the projection area of the coil.Axial electromagnetic force shows repulsion in one cycle.The experimental results indicate that the magnetic field is beneficial for grain refinement,microhardness increasement and decline of quantities and average sizes of pores.

Influence of Electroshocking Treatment on Microstructure and Mechanical Properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Thin-Wall Specimen Manufactured by Laser Melting Deposition

In order to improve the properties of titanium alloys manufactured by laser melting deposition(LMD),the electroshocking treatment(EST)was proposed in this work.The effects of EST on microstructure and mechanical properties of LMD Ti-6.5Al-3.5Mo-1.5Zr-0.3Si were investigated.The results showed that the width of the heat affected band decreased and disappeared under the thermal and athermal effects of EST,resulting in the uniform microstructure.In the microstructure,theαlaths became coarser gradually,and the quantity ofα/βinterface was reduced.The reduction of the quantity ofα/βinterface leads to make less resistant to dislocation,resulting in the reduction in hardness and strength.The discontinuous grain boundaryαphase and nucleationαcolony near grain boundary inhibited the crack propagation and improved the ductility.Summary,EST can manipulate the microstructure and improve the mechanical properties of LMD titanium alloys.

High-cycle fatigue crack initiation and propagation in laser melting deposited TC18 titanium alloy

This article examines fatigue crack nucleation and propagation in laser deposited TC18 titanium alloy. The Widmanstatten structure was obtained by double-annealing treatment,. High-cycle fatigue （HCF） tests were conducted at room temperature with the stress ratio of 0.1 and the notch concentration factor Kt = 1. Fatigue cracks initiated preferentially at micropores, which had great effect on the HCF properties. The effect decreased with the decrease of pore size and the increase of distance from the pore location to the specimen surface. The crack initiation region was characterized by the cleavage facets of a lamella and the tearing of β matrix. The soft a precipitated-free zone formed along grain boundaries accelerated the crack propagation. Subsurface observation indicated that the crack preferred to propagate along the grain boundary α or border of a lamella or vertical to a lamella.

Microstructure and mechanical properties of laser melting deposited Ti_2Ni_3Si/NiTi Laves alloys

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions of Ni-39Ti-11Si and Ni-42Ti-8Si (%, mole fraction, the same below), respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-11Si alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy designed using cluster-plus-glue-atom model for laser additive manufacturing

A novel Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy was designed using the cluster formula approach(cluster-plus-glue-atom model)and prepared by laser melting deposition(LMD).Its composition formula 12[Al-Ti_(12)](AlTi_(2))+5[Al_(0.8)Si_(0.2)-Ti_(12)Zr_(2)](V_(0.8)Mo_(0.2)Nb_(1)Ti)features an enhancedβ-Ti via co-alloying of Zr,V,Mo,Nb and Si.The experimental results show that the cluster formula ofαandβphases in the novel alloy are respectivelyα-[Al-Ti_(11.5)Zr_(0.5)](Al_(1)Ti_(2))andβ-[Al_(0.8)Si_(0.2)-Ti_(13.2)Zr_(0.8)](V_(1)Mo_(0.4)Nb_(1.6)),both containing Zr elements.The fitted composition via the α andβphase cluster formulas has little difference with the actual alloy composition,suggesting that the validity of cluster-plus-glue-atom model in the alloy composition design.After hot isostatic pressing(HIP),both the Ti-6Al-4V and the novel alloy by LMD are characterized by prior-βcolumnar grains,while the typical<100>texture disappears.Compared with Ti-6Al-4V,Ti-5.55Al-6.70Zr-1.50V-0.70Mo-3.41Nb-0.21Si alloy exhibits a combination of higher strength(1,056 MPa)and higher ductility(14%)at room temperature and higher strength(580 MPa)at 550℃ after HIP,and can potentially serves as LMD materials.

激光增材制造钛合金微观组织和力学性能研究进展

激光选区熔化(SLM)技术与激光熔化沉积(LMD)技术在航空航天、生物医疗等领域的应用具有巨大潜力,但由于成形的Ti6Al4V合金构件存在较差的表面质量、较大的残余应力以及内部孔洞等问题,影响了构件的力学性能,从而制约了其大规模的应用。针对这一现状,首先概述了激光选区熔化技术与激光熔化沉积技术的制造原理,比较了2种增材制造技术的成形参数及其特点,并分析了2种不同成形技术的自身优势以及适用场合。其次,从2种增材制造技术成形钛合金的工艺参数入手,综述了激光功率、扫描速度、激光扫描间距、铺粉厚度、粉床温度等参数对SLM工艺成形钛合金的影响,以及激光功率、扫描速度、送粉速率等参数对LMD工艺成形钛合金的影响。发现成形工艺参数直接影响了粉末熔化程度、熔合质量和成形显微结构,从而影响成形件的组织与力学性能。此外,综述了不同的扫描策略对两种增材制造技术成形钛合金的表面质量与力学性能的影响,可以发现在不同扫描策略下同一试样表面的不同区域表面质量、残余应力以及抗拉强度存在较大差异,同一扫描策略下试样的不同表面之间也存在各向异性。最后,探讨了不同热处理工艺对钛合金微观组织和力学性能的影响,通过合适的热处理能够降低成形构件应力,并调控组织相变和性能。

激光熔化沉积Al-Mg-Sc-Zr合金单熔道成形质量预测

本研究探讨了激光熔化沉积(LMD)工艺参数对Al-Mg-Sc-Zr合金单熔道成形质量的影响,并采用BP神经网络模型和改进的PSO-BP神经网络模型预测了不同工艺参数下的成形孔隙率。结果表明:Al-Mg-Sc-Zr合金的LMD单熔道成形孔隙率,随着激光线能量密度的增加呈现先上升后下降再上升的趋势,在175 J/mm^(2)时孔隙率达到最小值,仅为1.38%。在相同的送粉工艺参数下,LMD成形熔道宽度和熔道深度均与激光功率呈现出正相关性,而熔道高度和熔道深度均与扫描速率呈现出负相关性。相较于BP神经网络模型,改进的PSO-BP神经网络模型的平均绝对误差降低了29.69%,平均相对误差降低了19.42%,均方误差降低了19.02%,相关系数提升了63.44%。

离子推力器溅射沉积物防剥离放电室的设计及激光选区熔化增材制造研究

为了抑制离子推力器寿命末期由溅射沉积导致的放电室膜层剥落物脱落,首先采用理论研究和试验的方法开展了剥落物抑制放电室的设计,基于零件结构和增材制造特点开展了零件工艺性分析并提出解决方案,实现了放电室增材制造,开展了离子推力器放电室溅射物防脱落性能测试。结果表明:放电室内表面设计纹理化结构排布形式为正六边形,凸起部分外接圆直径0.5 mm,间距0.25 mm,高度0.5 mm时可降低溅射沉积物脱落概率及碎屑尺寸,通过分层旋转扫描,选择激光功率425 W,扫描速度1200 mm/s工艺参数可实现大尺寸薄壁、具有复杂微小特征钛合金回转体制造,通过结构拓扑,镂空点阵结构、工艺参数和空间摆放位置优化,成型零件壁厚一致性偏差小于0.10 mm。放电室优化前后推力器性能稳定,各工作点关键参数相对误差小于4%。本文的研究为离子推力器放电室溅射沉积物脱落抑制方法和复杂结构的激光选区熔化增材制造成型提供了工程应用方案。

激光熔化沉积Al_(x)CoCrFeNi系高熵合金的组织与性能

本工作通过激光熔化沉积技术制备了Al_(x)CoCrFeNi(x=0,0.3,0.5)系高熵合金,并研究了Al的添加对激光熔化沉积CoCrFeNi合金的物相结构、组织形貌及性能的影响规律。研究结果表明:Al_(0)与Al_(0.3)高熵合金的微观结构为单相FCC结构固溶体,而Al_(0.5)高熵合金的微观结构为在FCC相基底的晶界/枝晶界处析出富集Al、Ni原子的B2相。合金样品的拉伸力学性能表明:Al_(0.5)CoCrFeNi高熵合金的屈服强度达到了原合金的2.66倍(140~372 MPa),抗拉强度达到约716 MPa,延伸率约为40%;电化学极化曲线分析表明,Al_(x)CoCrFeNi系高熵合金在1 mol/L的H_(2)SO_(4)溶液中均具有显著的稳定钝化区,Al添加引起的致钝电流和维钝电流随着Al含量的增加呈现先减小后增大的趋势。

激光熔化沉积30CrNi2MoVA温度场数值模拟研究

30CrNi2MoVA钢被广泛用于军工炮管制备,由于工作环境恶劣,其零件表面易出现磨损、裂纹等损伤,常采用激光熔化沉积技术(laser melting deposition,LMD)完成表面修复工作。LMD过程中的热行为决定了材料组织演变从而影响零件的表面质量及力学性能。基于ABAQUS搭建LMD过程30CrNi2MoVA钢的温度场有限元模型。研究LMD过程中温度场的分布以及加工工艺参数对温度场的影响,分析了薄壁件沉积过程中的热历史及传热特征,并设计了相关实验验证模型的适用性。结果表明:LMD温度场沿扫描方向呈对称分布,激光功率每增大100 W,熔池最高温度增加约40℃,扫描速度则相反。随着沉积层数上升,热积累效应增大,熔池峰值温度升高,冷却速度降低。

退火温度对激光熔化沉积TC31高温钛合金组织与性能的影响

为改善激光熔化沉积TC31高温钛合金力学性能,本文通过光学显微镜、SEM、TEM和力学性能测试的方法研究了退火温度对合金中组织演化行为的影响,及其与合金室温和650℃高温力学性能的关系。结果表明:组织中初生α相含量随着退火温度升高而降低,其溶解主要发生在950℃以上,980℃退火后含量仅为29%。当退火温度超过930℃时,初生α相片层宽度明显增加。随着退火温度升高,α/β界面处析出的(Ti,Zr)6Si3相尺寸增加,且进入α相片层内部。合金在800~1000℃退火时,合金室温拉伸屈服强度随退火温度升高趋于降低。受相界面析出的硅化物聚合长大及α相片层尺寸增加等因素影响,合金高温屈服强度随退火温度升高先降低后增加。合金经过1000℃退火后,呈现良好的高温性能,其650℃下抗拉强度达657 MPa、屈服强度约为466 MPa、延伸率27%。

超高速激光熔化扫描速度对Al-Mg-Sc高强铝合金性能的影响

为了明确超高速激光熔化沉积Al-Mg-Sc高强铝合金的沉积态组织及力学性能特征,以7075铝合金为基体,采用自主开发的LDF3000-40型激光熔化沉积设备制备Al-Mg-Sc高强铝合金,探究激光扫描速度对材料微观组织与室温拉伸性能的影响。结果表明:超高速激光熔化沉积样品均无明显裂纹,但含有少量小尺寸气孔。沉积态组织由细小的α-Al等轴晶及弥散分布的Al_(3)(Sc,Zr)颗粒构成。利用数值模拟进一步研究扫描速度对力学性能的影响,发现在0.1~1 m/s范围内,较高的激光扫描速度能减少粉末材料的堆积,降低沉积层表面的孔隙率,因此可以提高力学性能。沉积态样品最大抗拉强度为303 MPa,断裂伸长率为22.5%。

激光熔化沉积H13钢微观组织及力学性能研究

激光熔化沉积技术在模具修复行业有着巨大应用前景,而沉积部件的微观组织和力学性能随激光参数变化的规律对模具修复工艺窗口的选择具有重要意义。采用激光熔化沉积技术制备了H13钢,研究了不同激光功率和扫描速度下H13钢沉积层微观组织演变及其对力学性能的影响。结果表明,激光功率一定时,随着扫描速度由400 mm/min增加到600 mm/min,马氏体尺寸细化,含量增加,沉积层的硬度提高约3%、塑性降低约1%,而强度先增加后减少;缺陷增多导致其与基体的结合强度下降约20%。扫描速度一定时,随着激光功率由1800 W增加到2200 W,马氏体尺寸增大、含量减少,沉积层硬度降低约5%,强度和塑性分别提高约34%和2%;同时缺陷减少使得结合强度提高约58%。

激光熔化沉积钛合金-高熵合金梯度材料组织演变研究

目的研究钛合金-高熵合金梯度材料不同位置沉积层的微观组织形貌及力学性能演变规律。方法采用激光熔化沉积的工艺制备了钛合金-高熵合金梯度材料,并建立了有限元仿真模型来辅助分析。研究对象为TA15基板上单道多层的梯度沉积层,在设计梯度材料成分时,相邻梯度的材料比例变化量为10%(质量分数),TA15钛合金的质量分数由100%逐渐降低至0%,AlNbTiVZr的质量分数逐渐增大。基于实验对有限元模型进行了一定程度的简化处理,通过热物性参数计算软件和经验公式获取了梯度成分材料的热物性参数,进行了单层单道激光熔化沉积实验以完成热源校核,在与实验相同的工艺参数下计算了温度场并进行了分析。结果在一层一冷的冷却策略下,多层沉积仍存在一定的热累积现象,沉积15层后,沉积层中部的温度峰值基本保持在2489℃,根据循环曲线,沉积层中部的重熔范围超过1/2。结论随着高熵合金含量的增加,组织由细小等轴晶、胞状晶和柱状晶转变为多边形晶粒,V、Nb等β稳定元素的增加和Al等α稳定元素的减少抑制了组织中针状α相的形成,V、Nb等元素在晶界产生了明显偏析现象并逐渐增多,抑制了晶粒生长且增强了细晶强化作用,显微硬度随之增大。

Unsteady state precipitation of M_(23)C_(6)carbides during thermal cycling in reduced activation steel manufactured by laser melting deposition

The temperature field distribution and thermal history of Fe-9Cr2WVTa reduced activation steel prepared by laser melting deposition(LMD)have been calculated with Gaussian and Ring laser beams,and the nucleation and growth behaviors of M_(23)C_(6)precipitates in the 1st,7th and 19th layers have been calculated using the modified classical nucleation theory and Svoboda Fischer Fratzl Kozeschnik model.The energy distribution shows W-shape with Ring laser beam while it shows V-shape with Gaussian laser beam,which results in the more uniform M_(23)C_(6)size in the same layer with Ring laser beam.Precipitates in the bottom(i.e.,the 1st layer)have the minimum size and the size increases with the layer number with Gaussian and Ring laser beams.The temperature history,the instantaneous nucleation rate and the size evolution of M_(23)C_(6)have been systematically discussed.The results indicate that the nucleation,growth and re-dissolution of precipitates in reduced activation steel depend on the amount of energy absorbed in the thermal cycle during LMD.The continuous accumulation of energy during the thermal cycle leads to larger M_(23)C_(6)at the top area.The unsteady state precipitation dynamics of M_(23)C_(6)carbides during thermal cycling are consistent with the simulation results.

单道多层LMD成形过程沉积尺寸波动分析与预测

激光熔化沉积技术(LMD)可快速制造高性能的复杂结构零件,但是在零件成形过程中存在沉积尺寸不稳定的工艺现象。面向激光熔化单道多层沉积过程,开展实验研究分析了关键工艺参数对沉积尺寸的影响规律。结果表明:同一沉积层内的沉积尺寸整体趋于稳定;由于热累积效应等因素,在接近基板的区域内的不同层间的沉积尺寸整体波动较大,而在堆积到一定层数后尺寸波动减小;进一步分析了不同沉积区域内激光功率和扫描速度与沉积宽度及高度之间的关系,并建立了基于工艺参数的多层沉积尺寸预测模型,模型预测误差在5%以内。该研究为后续激光熔化沉积过程的尺寸稳定控制及工艺参数优化提供了依据。

航天高强不锈钢LMD成形缺陷分析及控制

为明晰航天高强不锈钢激光熔化沉积成形过程基础科学问题,推动其在航天液体火箭发动机领域的应用进程,针对航天高强不锈钢LMD成形过程中常见表面焊瘤、气孔、熔合不良等缺陷的形貌特征及产生机理进行深入分析,并提出对应的控制措施:通过优化边框扫描速度促进熔覆道的流动变形,极大减少了成形件侧表面及倾斜面的焊瘤缺陷;使用PREP方法制备粉末材料替代当前GA法制备的粉末材料,成形试件孔隙率降低至0.1%以下,气孔缺陷基本消除;采用提升“层间重熔能力”和减小相邻熔覆道间“沟壑”高度的方法,消除了成形件内部熔合不良缺陷。

激光熔化沉积制造翅片热管管壳

为了提高核电热管的散热效率,采用激光熔化沉积技术在316热管的冷凝段管壳上制造了316散热翅片。用扫描电镜(SEM)观察了热管及翅片的显微组织,用能谱仪(EDS)进行元素分析,并测试了显微硬度和散热性。结果表明,激光熔化沉积的316翅片外形精度符合要求;翅片的平均硬度为280.92 HV0.5,比不锈钢管的平均硬度(209.9HV0.5)高33.8%,且硬度均匀性好;翅片热管的低温效率提高了16.7%,高温散热效率提高了32.9%。翅片晶粒主要有2种结构:等轴晶粒,柱状或枝晶状晶粒;翅片硬度提高的主要原因是细晶强化和位错强化;基材与翅片之间、翅片每层之间结合良好,精度高,是热交换量增大的保证。

激光熔化沉积稀释率对重熔行为与致密度的影响

由于激光熔化沉积(Laser melting deposition,LMD)制造的零件存在气孔、熔合不良、微裂纹、杂质等固有缺陷,其疲劳力学性能一般低于传统工艺制造的零件。为了减少LMD零件中的缺陷,研究激光熔化沉积过程中缺陷形成与控制机理是十分必要的。本研究利用三维有限元模拟结合显微观察法分析阐明了激光熔化沉积过程中单道稀释率对重熔行为与沉积零件致密度的影响。首先测量了不同工艺参数下LMD零件的致密度,建立了单道沉积面能量密度与零件致密度的拟合曲线;然后研究了工艺参数对单道沉积几何特征的影响规律,以及单道沉积稀释率对零件沉积过程中重熔行为的影响;最后建立了单道沉积稀释率与零件致密度的拟合曲线,并发现其拟合度更高。本研究对激光熔化沉积过程中零件致密度控制具有一定的指导意义。