Segregation of niobium in laser cladding Inconel 718 superalloy

Inconel 718 superalloy is widely used in the aerospace and turbine industry. Segregation of niobium appears in the laser cladding Inconel 718 superalloy and consequently influences the phase transformation during the rapid solidification. In order to control the microstructure and improve the mechanical properties of the deposited coating, the the influence of solidification conditions on the segregation of niobium and the resultant formation of Nb-rich Laves phase was studied using the microstructure observation and EDS analysis. The results show that the cooling rate has considerable influence on the microstructure of the deposited coating. High cooling rate is beneficial for suppressing the segregation of Nb and reducing the formation of Laves phase, which is believed to be detrimental to the performance of the Inconel 718 alloy.

Study of Cracking Mechanism and Wear Resistance in Laser Cladding Coating of Ni-based Alloy

Nickel-based alloy coatings were widely used for the remanufacturing of dies and moulds by laser cladding,but the crack sensitivity would be increase due to the higher strength and hardness,which reduced the wear resistance of Ni-based alloys.In this paper,Ni-based coatings with the addition of a plastic phase(an austenitic stainless net)were prepared using laser cladding technology,and the CeO_(2)was added in cladding layers.The cracking mechanism,microhardness,microstructure,phase composition,and wear properties were investigated.The relationship between thermal stress and the elastic and plastic fracture had been developed from the standpoint of fracture mechan-ics and thermal elastic fracture mechanics.The fracture criterion of the nickel-based coating was obtained,and the study has shown that the crack sensitivity could be reduced by decreasing the thermal expansion coefficientΔα.Thus,a new method was proposed,which the stainless steel nets were prefabricated on the substrate.It was found that the number of cracks reduced significantly with the addition of stainless steel net.When the stainless steel net with 14 mesh was added in Ni-based coatings,the average microhardness of nickel composite coating was 565 HV_(0.2),which was 2.6 times higher than that of the 45 steel substrate.Although the rare earth oxide 4 wt.%CeO_(2)and stainless steel net were added in the Ni-based coating reducing the microhardness(the average microhardness is 425 HV_(0.2)),the wear resistance of it improved substantially.The wear volume of Ni-based composite coating was 0.56×10^(−5) mm^(3)·N^(−1)·m^(−1),which was 85.1%lower than that of 45 steel.The experiment results have shown that the Nickel-based composite coating is equipped with low crack sensitivity and high abrasive resistance with austenitic stainless net and the rare earth oxide 4 wt.%CeO2.This research offers an efficient solution to produce components with low crack susceptibility and high wear-resistance coatings fabricated by laser cladding.

Microstructure Evolution and Cracking Control of 316L Stainless Steel Manufactured by Multi-layer Laser Cladding

Multi-layer laser cladding manufacturing is a newly developed rapid manufacturing technology. It is a powerful tool for direct fabrication of three-dimensional fully dense metal components and part repairing. In this paper, the microstructure evolution and properties of 316L stainless steel deposited with this technology was investigated, compact components with properties similar to the as-cast and wrought annealed material was obtained. Cracking was eliminated by introducing of supersonic vibration and application of parameter adjustment technologies.

Effect of Y_2O_3 on Cracking Susceptibility of Laser-Clad Ti-Based Composites Coatings

Ti-based composite coatings reinforced by in situ synthesized TiB and TiC were deposited on Ti6AlaV substrates by laser cladding. The effects of Y2O3 on the microstructure and cracking susceptibility of the coatings were investigated in details. It is shown that a small amount of Y2O3 addition can significantly refine the microstructure of the coatings by hastening spheroidization of the primary phase structure. The maximum refinement in microstructure was obtained with the optimum （2 wt%） addition of Y2O3. Moreover, it can increase the volume fraction of TiC and reduce the residual stress of the coatings due to the decrease in lattice distortion of the α（Ti） matrix. All of these factors lead to the reduction in cracking susceptibility of the coatings containing Y2O3 on the premise that the hardness of the coatings is improved. The fracture toughness of the coatings without and with Y2O3 （2 wt%） is 8.32 and 17.36 MPa.m1/2, respectively. Scanning electron microscope examination reveals a transition of the fractured surfaces from cleavage fracture to quasi-cleavage fracture resulting from the Y2O3 addition.

TC4表面WC/Ni-MoS_(2)钛基复合涂层组织与摩擦学性能

拟在TC4表面合成Ti-S系自润滑耐磨熔覆层,并探究WC添加对涂层组织与摩擦学性能的影响,设计了TC4+Ni-MoS_(2)+xWC(x=5%、10%和15%)钛基材料体系,通过同轴送粉激光熔覆技术完成了涂层制备。研究表明,增加WC含量不利于改善涂层成形质量,但WC添加量变化并未影响涂层析出相种类,三种涂层均包括TiC、Ti_(2)Ni、Ti_(2)S和β-Ti基体;随着WC含量增大,TiC分布数量增多,粒径增大,生长形态由类球状逐渐演变为花瓣状;润滑相MoS_(2)未能在涂层中得到保留,其完全溶解后在钛基熔池体系下合成了与润滑相TiS等形态相似的条状相Ti_(2)S。三种WC含量的涂层显微硬度和耐磨性能均高于TC4基材,磨损机理均为磨粒磨损,但减摩性能均不低于TC4基材,说明原位Ti_(2)S相不具备自润滑功能;WC含量增加虽然有利于增大涂层的显微硬度和耐磨性能,但引起了涂层磨损面质量下降,摩擦系数波幅增大。

Residual stress distribution in different depths of TiNi/Ti_2Ni-based laser clad coating prepared at different environmental temperatures

This study aimed to effectively reduce the cracking susceptibility of the laser clad coating by enhancing the environmental temperature during laser cladding,and reveal the residual stress distribution in different depths of the coating.The TiNi/Ti2Ni-based coatings were prepared on Ti6Al4V by laser cladding at different environmental temperatures of25,400,600and800°C.The changes in residual stress along the depth of the coatings were investigated in detail by the nanoindentation method.Results showed that the average residual stress of2.90GPa in the coating prepared at25°C was largest.With the increase in environmental temperature,the average residual stress was reduced to1.34GPa(400°C),0.70GPa(600°C)and0GPa(800°C).For all the coatings,the residual stress was increased with increasing the distance from the coating surface.Enhancing the environmental temperature can effectively reduce the cracking susceptibility of the coatings.

激光熔覆NiCrBSi合金涂层的裂纹形成机理

从微观组织研究了激光熔覆NiCrBSi镍基涂层的裂纹形成机理,分析了涂层显微组织、裂纹形貌和断口成分.结果显示:Ni60涂层具有高裂纹敏感性,即使涂层与基体热膨胀系数差异较小,涂层也容易开裂.原因是:①Ni60涂层包含大量的粗大硬质初生相和硬质共晶组织以及较少的韧性相,具有高的脆硬性;②断口聚集含Ca、S、Si等元素的熔渣;③粗大的硬质相妨碍了液体金属的自由流动,造成金属基体的不连续性;④粗大硬质相晶界处的液膜易在拉应力作用下破裂,形成缩孔或微裂纹,从而成为裂纹源.此外,裂纹在顶端起裂并向下扩展,裂纹多沿粗大硬质相晶界扩展,具有典型的凝固裂纹特征.

Stellite-6+VC混合粉末激光熔覆性能的研究

小功率脉冲激光下飞机叶片的强化是现在急需解决的问题,本试验通过采用光纤传输300 W Nd:YAG脉冲激光熔覆系统,在低碳钢(SM400B)上熔覆Co基合金(Stellite-6)和碳化钒(VC)混合粉末(VC的质量分数变化范围为0~100%),并对熔覆层的性能进行了研究,从而探究小功率脉冲激光下飞机叶片强化的工艺。试验结果表明,随着VC质量分数的增加,熔覆层组织由亚共晶组织转变为过共晶组织。当VC质量分数小于80%时,熔覆层硬度、裂纹敏感性及耐磨性能随VC增加而增加;当VC质量分数大于80%时,由于母材的稀释作用,熔覆层硬度、裂纹敏感性及耐磨性能随VC增加而降低。试验表明,使用Co基合金(Stellite-6)和碳化钒(VC)混合粉末可以形成耐磨性好、硬度高,裂纹敏感性低的熔覆层,对飞机叶片产生较好的强化效果。

Mo元素对NiCrBSi合金激光熔覆层开裂敏感性的影响

采用CO2固体激光器,在45CrNi钢表面制备了添加成分(质量分数,%)为0,2.5,5.0,7.5,10.0Mo的NiCrBSi合金熔覆层,研究了Mo元素对熔覆层开裂敏感性的影响,并从线膨胀系数和熔覆层凝固组织特性两方面对其影响进行了分析.结果表明,NiCrBSi合金对裂纹很敏感,熔覆层表面出现大量横向宏观裂纹,NiCrBSi合金中添加质量分数5.0%Mo,可改善凝固组织中硬质相的成分和形态,降低熔覆层的线膨胀系数,二者综合作用,降低了熔覆层的开裂敏感性.

面向涂层裂纹的激光熔覆预测模型研究

针对激光熔覆关键工艺参数与制备涂层之间因存在复杂非线性映射关系而产生的裂纹缺陷问题,通过将遗传算法与BP神经网络结合起来构建工艺参数与涂层裂纹密度之间的网络模型,利用MATLAB软件对建立的网络模型进行训练、拟合预测。结果表明,遗传算法对BP神经网络优化后的模型中预测误差最小为3.06%,平均误差控制在11.57%以内,均方误差为0.0008,模型预测精度高,性能稳定。验证了理论模型与实际试验相结合的可行性,减少了涂层裂纹工艺研究所需的大量重复性试验,为制备无裂纹镍基熔覆层具有重要意义。

TiC-NiCrBSi复合材料的激光熔覆成形性分析

在一定的熔覆工艺下获得完整无缺陷的熔覆层,直接决定激光熔覆陶瓷-金属复合材料(MMC)的实际应用.利用CO2激光器在低碳钢表面制备"TiC-NiCrBSi"陶瓷-金属熔覆层,通过调整粉末配方改善熔覆层的表面成形和组织均匀性,通过分析气孔和裂纹的产生原因,采取对应措施获得了无缺陷熔覆层.结果表明,TiC质量分数可增加到40%,加入适量钼铁可改善表面成形以及TiC在组织中的分布均匀性;激光熔覆层中的裂纹为冷裂纹,镍基合金中加入TiC可因其变质剂作用而抑制裂纹的产生,但钼铁加入量过大则会促使产生裂纹.熔覆层中的气孔因使用有机粘结剂而产生,降低激光扫描速率或采用无机粘结剂可消除气孔.

钨极氩弧焊与激光熔覆修复的K403镍基高温合金导向器叶片组织与性能

K403镍基高温合金具有优异的室温和高温综合性能,广泛用于航空发动机涡轮叶片及导向器的制造。针对涡轮叶片长期服役于复杂工况产生的裂纹缺陷等问题,本工作先对钨极氩弧(tungsten inert gas,TIG)焊和激光熔覆两种工艺修复后的组织与拉伸性能展开对比分析,而后使用激光熔覆工艺修复叶片,并进行无损检测。利用OM、SEM观察微观组织、断口形貌,利用EDS进行相的成分分析。结果表明:TIG焊修复工艺在修复界面区附近易产生微裂纹缺陷,主要碳化物相和低熔点共晶组织引起;激光熔覆工艺修复区域的晶粒与组织更加均匀,微裂纹缺陷更易得到控制;激光熔覆工艺修复的试样综合力学性能明显高于TIG焊修复工艺的试样,且激光熔覆工艺具有较好的工艺稳定性,TIG焊修复工艺的室温拉伸强度为K403母材强度的69.22%,激光熔覆修复工艺室温抗拉强度达到了母材的87.44%,断口形貌显示修复区域的室温拉伸断口呈现出混合断裂特征,高温拉伸断口呈现出沿晶断裂的特征。修复区域的微裂纹、局部液相不足缺陷和碳化物是拉伸断裂的主要原因。激光熔覆修复工艺具有热源集中、热影响区小的优势,能够有效抑制修复区缺陷并细化微观组织,在叶片修复方面具有更大优势。使用激光熔覆修复工艺完成了叶片试车过程产生的边缘板裂纹损伤修复,经过荧光检测及煤油-白垩检测,满足相关使用要求。

激光重熔功率对镍基高温合金熔覆层组织性能的影响

为了解决镍基高温合金涂层“强度有余,韧性不足”的问题,采用激光重熔工艺处理激光熔覆Inconel718合金涂层,研究重熔功率对涂层表面形貌、物相组成、显微组织和拉伸性能的影响。结果表明:重熔后的熔覆层表面粉末附着减少,表面形貌得到明显改善;激光重熔后熔覆层的组织仍是由γ-(Ni,Fe,Cr)和γ″-Ni_(3)Fe双相组成,随着激光重熔功率的增大,组织中γ″-Ni_(3)Fe相的体积分数先增加后减少,且涂层顶部和中部组织的晶粒尺寸先减小后增大;经重熔后涂层的拉伸强度和屈服强度略有降低,但伸长率获得显著提升,重熔功率为1200、1350和1500 W时分别提高了47.4%、52.6%和48.7%;重熔功率为1350 W时试样断口中韧窝分布均匀,此功率重熔处理的涂层韧性最好。激光重熔工艺可以有效地提高熔覆层的力学性能。

激光熔覆增材制造研究

阐述了近年来激光熔覆技术的研究进展,系统地对比并总结了传统激光熔覆与超高速激光熔覆的工艺,还对比了2种工艺制备涂层的关键性能指标,并梳理金属合金粉末制备工艺及熔覆材料,总结了熔覆层裂纹抑制措施,指出目前激光熔覆存在的不足,展望了未来的发展方向。

激光熔覆铁基复合熔覆层的裂纹形成机理

激光熔覆是绿色再制造重点发展的工业技术。用高能密度的二氧化碳(CO_(2))激光束,在工件表面进行激光熔覆改性处理,形成成分和性能完全不同于母材的铁基复合熔覆层。激光熔覆层组织由马氏体α-Fe和细小弥散分布的碳氮化钛Ti(C,N)陶瓷颗粒组成。若激光熔覆工艺不当,会形成纵向或横向裂纹。熔合线附近的气孔和微空洞是复合熔覆层开裂的裂纹源,裂纹最初起裂于熔覆层与母材交界处,裂纹扩展为沿晶或穿晶断裂,属于脆性断裂。

ANSYS软件下的活塞头分析及激光熔覆改善性研究

使用ANSYS软件对船用6250柴油机活塞头的热应力进行分析,发现活塞头存在热应力集中的问题,并且存在不同程度的腐蚀。实验研究发现,采用激光熔覆技术,将镁钙系耐火材料应用在活塞头表层,在活塞头表层形成耐火耐腐蚀保护层,将使活塞头具有抗高温抗腐蚀的优势,极大减小了活塞头的龟裂现象。

Si对铸铁激光熔敷层抗裂性的影响

通过控制熔敷层内Si质量分数,进而控制奥氏体相与渗碳体相体积分数来抑制熔敷层裂纹的产生。在抗裂性最佳激光熔敷工艺参数基础上,首次系统地在不预热情况下研究了冶金元素Si对熔敷层奥氏体体积分数及表面裂纹率的影响,揭示了熔敷层开裂的微观机制。最终得到可显著降低熔敷层开裂敏感性的新激光熔敷材料。

镍基高温合金表面激光熔覆CoCrAlYSiHf_x涂层组织性能分析

选择激光熔覆技术在GH586镍基高温合金表面上制得了不同Hf含量的CoCrAlYSiHf涂层,并对涂层微观组织形态与涂层耐高温性能进行实验测试分析。研究结果表明:采用激光熔覆方法得到的涂层表面上形成了许多网状组织,在未添加Hf涂层的晶界部位产生了许多孔隙结构;在Hf含量0.1和0.3涂层内形成了更多的孔隙,同时沿晶区域产生了众多显微裂纹。在涂层的表面形成了许多具有致密结构的Cr2O3膜。涂层经过100h高温氧化处理依然由致密Cr2O3膜组成。未添加Hf涂层表面生成了约6μm厚的致密氧化膜,并且沿晶界处发生了一定成对内氧化。当Hf含量0.1和0.3涂层经过100 h高温氧化之后,其表面生成了厚度约12μm的氧化膜并含有较多孔隙。

涡轮叶片薄壁叶尖激光熔覆修复裂纹分析及控制

某型航空发动机高压涡轮工作叶片叶尖磨损后,采用激光熔覆技术进行修复,经X光探伤检查发现熔覆层与基体结合面上有纵向显微裂纹,其不合格率达到20%左右。通过基体材料成分分析、金相观察、扫描电镜、工业CT等手段分析裂纹产生原因,结果表明:裂纹为激光熔覆过程中应力过大产生的热裂纹,通过增加预热、调整激光出光模式等方式可有效降低裂纹故障率。控制措施实施后,继续跟踪检查24台叶片激光熔覆修复情况,其合格率达到99%以上。

线光斑激光熔覆Ni-Al金属间化合物工艺及组织研究

为了提高P92钢的耐高温氧化性能,采用线光斑在P92钢基体表面激光熔覆Ni-Al金属间化合物,对熔覆工艺参数进行了筛选,并对试样的组织形貌和成份进行了分析。结果表明,在筛选后的熔覆工艺下试样熔覆层未发现裂纹,无开裂倾向;P92钢基体熔化较少,基体中Fe元素扩散至顶部含量不到5%,熔覆层中主要物相为Ni3Al和NiAl,熔覆层顶部至基体部分的显微组织由等轴晶向树枝晶、柱状晶和平面晶转变。当激光功率1 800 W、扫描速度2 m/min、送粉速度为17 r/min、送粉气流量为8 L/min时,可以减少基体熔化和Fe元素扩散,从而对解决激光熔覆时Ni-Al金属间化合物熔覆层开裂、钢基体中Fe元素扩散问题提供了思路。