铜表面激光熔覆镍基合金的显微组织与硬度

用超音速火焰喷涂方法在铜基体表面预置一层镍基合金涂层后,再用高功率密度的激光进行熔覆;用OM、SEM、XRD、显微硬度计对熔覆层进行了表征.结果表明:熔覆层组织致密、无裂纹,气孔、夹杂等缺陷明显减少;在熔覆层底部形成了高熔点、高密度钨相带,其显微硬度明显升高;熔覆层与基体的界面处有铜、镍互渗的冶金结合层形成,其厚度约为13μm;熔覆层的显微硬度是铜基体硬度的8倍以上.     

激光熔覆成形试验研究及结果分析

进行了以Ni基合金粉末、316L不锈钢合金粉末为熔覆材料的激光熔覆成形试验,得到了组织致密无缺陷的金属零件;针对激光熔覆中的裂纹问题,进行了Ni基合金粉末单道、多道和梯度材料熔覆过程的裂纹试验,分析了材料成分对裂纹产生的影响;进行了超声振动下的激光熔覆试验研究,初步结果表明,在熔覆过程中引入超声振动不仅可细化熔覆层的组织,还可有效提高熔覆层的硬度.     

激光功率对熔覆Ni基涂层性能的影响

为提高45号钢表面硬度和耐磨性,可以在45号钢的表面采用激光熔覆技术熔覆合金涂层提高其表面性能。镍基合金熔覆层硬度高、耐磨、抗腐蚀、抗弯曲、可以在极端环境下具有稳定的性能,但在激光熔覆层中易产生裂纹。为改善45钢表面性能,在相同的扫描速率下采用不同功率在其表面激光熔覆制备了Ni基(Ni60)复合涂层,对不同激光功率熔覆层的性能检测使用金相显微镜、显微硬度仪、扫描电镜。结果表明:随着激光功率的增加,表面粗糙度变大,熔覆层的宽度、高度、基材的熔化深度都有一定程度的增大,裂纹出现趋势减小。在45号钢上熔覆Ni60合金粉末可以提高基材表面显微硬度,熔覆层显微硬度高出基材显微硬度约700HV,激光熔覆技术在一定范围内可以实现对基材的表面硬化。     

激光熔覆制备Fe基合金涂层的微观结构与力学性能*

采用激光熔覆在25Cr2Ni4MoV钢基材表面制备铁基合金涂层,研究激光熔覆涂层的微观组织、显微硬度、抗剪强度、摩擦磨损性能。结果表明：激光熔覆Fe基合金涂层与25Cr2Ni4MoV钢基材界面形成了良好的冶金结合;激光熔覆层为典型的树枝晶形貌,由浅灰色及深灰色2种不同物相相间组成;激光熔覆区的显微硬度显著高于基体区和熔合区,平均剪切强度达280.83 MPa;激光熔覆Fe基合金涂层的平均干摩擦因数、磨痕轮廓深度及平均磨损体积较25Cr2Ni4MoV钢基材分别下降了约25%、45%及50%;激光熔覆所制备的Fe基合金涂层的耐磨性能远高于25Cr2Ni4MoV钢基体,该型涂层对基体有着良好保护作用。     

镍合金激光熔覆层的组织结构分析

研究了镍-铬-硼-硅合金激光熔覆涂层的组织与相结构;测试了熔覆层的显微硬度,分析了激光熔覆层中的择尤取向问题,探讨了激光功率、熔覆道次对组织的影响。结果表明：激光熔覆层显微硬度值为400-500HV;熔覆层组织由枝状晶与等轴晶组成,其主要相结构是γ-Ni;不同激光功率下熔覆层存在不同程度的择尤取向,单层多道激光熔覆使择尤取向有所减弱。     

激光涂层及多冲后的组织结构变化

采用激光熔覆、等离子喷焊、火焰堆焊三种工艺制备抗多冲接触涂层。显微分析表明:激光熔覆层组织致密,晶粒细小,与基体结合牢固,对基体热影响小,稀释率最低;消除裂纹、孔隙、夹杂物等缺陷的覆层成品率最高;激光熔层在其屈服强度20%的多冲载荷下,表层组织混乱,晶粒出现扭曲变形;Co基合金覆层X射线衍射谱相位和峰值强度发生了较大变化;Ni基合金覆层衍射谱没有变化;Fe基合金覆层衍射谱有较小变化。X射线衍射表明,三种涂层下部在多冲前后的衍射谱均无变化。多冲表面有较强的“接触面表面效应”,激光涂层具备良好的表面抗多冲性能。     

损伤轴面激光熔覆修复残余应力测量及分析

残余应力直接影响激光熔覆修复机械零件的结构强度和安全性能,为了掌握损伤轴面激光熔覆修复后的残余应力分布情况,以40Cr钢零件轴为基材,Ni60自熔合金粉末为熔覆材料,采用脉冲激光熔覆工艺制备零件轴表面修复试件,利用盲孔法对零件轴修复试件进行残余应力分布特性分析。结果表明,在轴面激光熔覆的镍基合金修复层中产生了不可忽略的残余拉应力,高应力区位于熔覆层始末两道上;轴线方向检测点上X方向残余应力呈"M"形分布,Y方向残余应力呈"Λ"形分布,σx值较高,接近基材屈服强度的45. 9%,而圆周方向检测点的X方向和Y方向残余应力相对稳定,最大拉应力约为200 MPa;激光扫描路径对轴面熔覆层的残余应力值的影响大、分布形状的影响小,螺旋路径熔覆产生的残余应力值较低,更适合圆周面修复,但熔覆层始末两道边沿处的残余应力比中间部位高,有必要采取适当措施进行消应力处理,以获得优良的修复效果。     

镍基自熔合金激光熔覆层和喷焊层的组织与性能对比

对Ni60镍基自熔合金激光熔覆层和喷焊层的表面形貌、显微组织、硬度和耐腐蚀性能等进行了对比分析。结果表明:激光熔覆层的表面成型性比喷焊层的好;大部分激光熔覆层组织处于非平衡、亚结晶状态,且具有强、韧两相微观结构特征;喷焊层组织中富含碳化物等硬质相;激光熔覆层和喷焊层与基体均能形成冶金结合;喷焊层的平均硬度比激光熔覆层的高,但其分布并不均匀;激光熔覆层的耐腐蚀性能优于喷焊层的。     

Y2O3对45钢表面激光熔覆镍基合金的影响

研究了Y2O3对镍基合金激光熔覆层显微组织、相结构以及性能的影响。结果表明加入Y2O3的镍基激光熔覆层显微组织细小均匀，且不出现微裂纹。熔覆层形成的物相有Fe-C，Fe-B和NiCrFe等。与纯镍基熔覆层相比，加入Y2O3的镍基熔覆层显微硬度有较大提高，其耐磨性能比淬火和软氮化后明显提高；加稀土的激光合金化比不加稀土的激光合金化的耐磨性要有所提高。     

球墨铸铁的激光熔覆研究

常温下采用激光熔覆工艺修复球墨铸铁工件,存在熔覆层裂纹的问题。采用镍基合金能够改善裂纹情况,但基材界面裂纹问题依旧无法得到解决。因此,采用预热+后热的热处理工艺,消除了激光熔覆的裂纹问题,获得良好的熔覆层,恢复了球墨铸铁工件原有尺寸,提高了表面的综合性能,延长工件的使用寿命。     

激光熔覆工艺参数对铁基双层涂层组织和残余应力的影响

针对激光熔覆过程中剧烈的温度场变化伴随着应力、应变演化,进而导致零件具有高裂纹敏感性的问题,对不同激光扫描路径及工艺参数下残余应力演变规律进行研究。采用激光熔覆在Q345钢上制备了Fe基双层多道涂层,并以X射线衍射法结合电化学腐蚀剥层法测量沿涂层深度方向的残余应力分布,探究激光扫描路径、功率以及扫描速度对涂层显微组织和应力分布的影响。结果表明：涂层表面和内部为残余压应力,在涂层基体熔合线处残余应力发生突变,热影响区表现为残余拉应力;激光熔覆工艺对涂层残余应力的大小和分布规律有显著影响,当激光扫描路径为轮廓偏置式、激光功率为1.8 kW、扫描速度为0.02 m/s时,涂层具有最优的残余应力分布和成形质量;残余应力的产生主要与激光束对熔池的冲击作用以及熔覆层的非平衡凝固特性有关。     

铁素体不锈钢激光熔覆层组织和性能研究

采用无碳合金粉末和低碳合金粉末对铁素体不锈钢进行激光表面熔覆处理,借助光学显微镜(Optical microscope,OM)、扫描电子显微镜(Scanning electron microscopy,SEM)、能谱分析仪(Energy dispersive spectrometry,EDS)、X射线衍射仪(X-ray diffractometry,XRD)、显微硬度仪、摩擦磨损试验仪、电化学工作站对熔覆层显微组织、化学成分、硬度、耐磨性和耐蚀性进行评价。结果表明,两种激光熔覆层均无裂纹、气孔等宏观缺陷,显微组织主要由等轴晶、包状晶、树枝晶和枝间共晶组成。无碳熔覆层与低碳熔覆层均含有α-Fe、Fe-Cr合金相、Cr单质相以及Cr_(9.1)Si_(0.9)、Fe_(9.7)Mo_(0.3)、Fe_(10.8)Ni、Fe_(19)Mn等金属间化合物。此外,低碳熔覆层还产生了间隙化合物Cr_7C_3以及马氏体相C_(0.055)Fe_(1.945)。低碳熔覆层硬度为750 HV0.5,显著高于母材硬度250 HV0.5;无碳熔覆层硬度为650 HV0.5,其热影响区发生软化。激光熔覆层相对于母材具有更为稳定的摩擦特性以及优异的耐磨性和耐蚀性,其中低碳熔覆层耐磨性和耐蚀性均优于无碳熔覆层。     

Eddy-current testing of the hardness,wear resistance,and thickness of coatings prepared by gas-powder laser cladding

The possibility of applying the eddy-current method to estimate the composition, hardness, abrasive wear-resistance, and wear resistance under sliding friction conditions of chromium-nickel and chromium-nickel-cobalt coatings prepared by gas-powder laser cladding was studied. Variations in the readings of an eddy-current instrument along the depth of the surface cladding layer and with changing thickness of coatings, which are due to the distribution of structural components in coatings and large differences between the electromagnetic characteristics of cladding layers and the ferromagnetic steel base of specimens, were determined. A technique of the eddy-current testing of the thickness of Cr-Ni and Cr-Ni-Co cladding coatings on a ferromagnetic steel base is proposed. It allows one to estimate the quality of the strengthening laser cladding and subsequent grinding, monitor the state of coatings under service conditions, and forecast the residual life of cladding elements subjected to intense wear.     

机械冲击对高硬激光熔覆层力学性能与微观组织的影响

为减少高硬合金激光熔覆层缺陷,提出了一种将机械冲击作用于激光熔覆过程的工艺方法,在45钢轴表面制备了Ni基、Fe基和Co基三种高硬合金熔覆层,对比分析了机械冲击对熔覆层力学性能和微观组织的影响。研究结果表明：加载机械冲击可改善熔覆层表面熔覆质量,抑制裂纹的萌生;机械冲击对不同材料的熔覆层力学性能影响不同,Ni65WC试样的可承受最大载荷提高了26.2%,但断裂总伸长量却减小了约37%,Fe90试样的可承受最大载荷提高了21.3%,而且断裂总伸长量亦增大约21%,Sti6+3%WC试样的可承受最大载荷提高了9.04%,其断裂总伸长量无明显变化;机械冲击使微观组织明显细化,显微硬度提高。     

激光熔覆Ni/TiC复合涂层组织与性能

采用激光熔覆技术在45钢样品表面制备了Ni/TiC复合涂层,利用光学显微镜、SEM,EDS,XRD、显微镜硬度计及摩擦磨损试验机等检测设备研究了Ni/TiC复合涂层的组织和性能。试验结果表明：Ni/TiC复合涂层没有出现裂纹、孔洞等缺陷,涂层与基体之间具有良好的冶金结合,涂层显微硬度沿层深皆呈明显的阶梯状分布,最外表面的熔覆层硬度最高,约为800 HV;熔覆试样的比磨损率比基体试样的比磨损率下降了86.5％,表明Ni/TiC复合涂层具有较好的耐磨性能。     

Different Approaches to the Investigation and Testing of the Ni-Based Self-Fluxing Alloy Coatings—A Review. Part 2: Microstructure,Adhesive Strength,Cracking Behavior,and Residual Stresses Investigations

After presenting general facts about Ni-based self-fluxing alloy coatings and describing the wear and corrosion studies in Part 1, Part 2 of the article deals with the review and systematization of the investigations on behavior of these coatings exposed to external mechanical loading (cracking behavior, adhesive strength, fatigue), residual stresses, and microstructure (particle state, phases, porosity, dilution, dissolution) considering the period from 2000 to 2013. The following deposition technologies are included: flame spraying, high-velocity oxy/air fuel spraying, detonation gun spraying, electric arc spraying, plasma spraying, plasma-transferred arc welding, and laser cladding. In addition to the review of investigations on microstructure and effects of external loading and residual stresses, reference is also given to papers describing the application of the Ni-based self-fluxing coatings, as well as to those in which these coatings were used as a reference material or an addition to obtain a composite coating.     

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。     

WC颗粒增强镍基涂层改善制动盘组织与磨损性能

为提高汽车制动盘耐磨和高温氧化性能,延长其使用寿命,采用激光熔覆技术在中碳钢表面制备了以WC颗粒为增强相的Ni基复合涂层.借助SEM和XRD等表征手段对制动盘表面涂层进行了组织和物相分析,利用维氏硬度计测试了制动盘表面涂层截面显微硬度分布,通过摩擦磨损实验研究了制动盘表面涂层的磨损性能.研究表明,制动盘表面涂层主要由γ-（Ni,Fe）固溶体、均匀分布WC颗粒和碳化物抗磨损相组成.涂层平均显微硬度HV0.2670,显微硬度值波动较小较为平稳,证明涂层组织比较均匀.在多种强化效果共同作用下,制动盘表面涂层的磨损量与基材相比明显减小,仅为基材的20％,抗磨损性能显著提高.     

激光熔覆Inconel718合金涂层与基体界面的组织及力学性能

研究了激光熔覆Inconel718合金涂层与基体界面的微观组织及力学性能,结果表明：由于强化相的溶解,热影响区的硬度及强度降低,典型激光熔覆工艺条件下,扫描速度越快,热影响区越窄;熔覆层底部无平面晶组织,熔合区结合致密,化学成分一致,组织过渡平滑,熔覆层内部为枝晶组织,晶间有较多的Laves相,硬度较热影响区高;时效热处理后,热影响区及熔覆层的强度接近原始基材,界面区域力学性能过渡的平滑性改善。     

Finite element modeling of heat transfer in single and multilayered deposits of Ni-WC produced by the laser-based powder deposition process

The localized high-energy input and high-cooling rate inherent in the laser-based powder deposition (LBPD) process yield deposits with superior mechanical and metallurgical properties. However, these characteristics induce thermal stresses within the deposited material that subsequently lead to cracks. This tendency is predominant in the LBPD of metal–ceramic composite materials such as nickel (Ni) and tungsten carbide (WC). In this study, the thermal behavior of single and multilayered compositionally graded Ni-WC composite material during LBPD is studied using an experimentally verified three-dimensional finite element model. The model incorporates both directional- and temperature-dependent material properties. The effect of the mass fraction of the reinforcement, laser power, scanning speed, powder flow rate, and preheating temperature on temperature, temperature gradient, cooling rate, and molten pool evolution are investigated. The distribution and dissolution of WC in Ni-WC deposits are analyzed in the light of the scanning electron microscope, energy-dispersive spectroscopy, and microhardness distribution. The dissolution of WC in the molten Ni varies based on the mass fractions of the Ni and WC and the prevailing thermal conditions such as molten pool temperature and cooling rate. Experimental and numerical results confirm that the desired composition gradient can be achieved in a multilayered Ni-WC composite material deposit by adjusting the laser power. The developed heat transfer analysis may be used to select the suitable process variables needed to achieve the desired properties in the LBPD of single and multilayered Ni-WC composite material.