纳米Nb粉对等离子弧喷焊铁基合金组织与耐磨性的影响

采用等离子弧喷焊技术在Q235表面制备未添加与分别添加1wt%, 3wt%和5wt%纳米Nb粉的铁基合金喷焊层。通过X射线衍射仪(XRD)、金相显微镜(OM)、扫描电镜(SEM)和能谱仪(EDS)对喷焊层的相组成、显微组织、微区成分及磨损形貌进行分析;利用维氏硬度仪和销盘磨损仪检测喷焊层截面硬度和表面耐磨性。结果表明,铁基喷焊层主要由α-Fe, γ-Fe和Cr7C3组成,添加纳米Nb粉后原位生成NbC相,且随Nb含量增至5wt%,出现了Cr23C6相。纳米Nb粉的加入使喷焊层组织中未转变的奥氏体增多,组织形貌由近等轴晶转变为树枝晶,并且添加5wt%纳米Nb粉的喷焊层组织发生明显细化。添加纳米Nb粉使喷焊层的硬度明显提高,其中添加1wt%和3wt%纳米Nb粉的喷焊层硬度均可达约766 HV0.3。纳米Nb粉的加入同时提高了喷焊层的耐磨性,磨损机制由黏着磨损变为磨粒磨损。     

激光重熔高速电弧喷涂FeNiCrAl涂层的工艺优化

以外观形貌、孔隙率和显微硬度为评价指标,利用正交试验并结合极差分析法考察了激光功率、扫描速率和搭接步距这3个激光重熔工艺参数对高速电弧喷涂FeNiCrAl涂层重熔层的影响,得到优化工艺参数为:激光功率1 700 W,扫描速率10mm/s,搭接步距2.1 mm。结果表明,影响激光重熔最主要的参数是激光功率,随着激光功率的增大,重熔层的孔隙率先增大后减小,显微硬度显著增加。优化后所制重熔层的孔隙率为0.9%,显微硬度567.03 HV_(0.1),比喷涂层的显微硬度提高38.5%。重熔后,喷涂层的层状堆叠结构消失,产生了树枝晶和枝晶间组织。     

等离子喷涂Ni包WC陶瓷涂层激光重熔研究

利用X射线衍射、金相显微镜及显微硬度计研究了等离子喷涂Ni包WC陶瓷涂层激光重熔后的组织结构和硬度变化特征。结果表明:利用激光重熔Ni包WC陶瓷涂层,能够有效提高涂层的致密度,减少孔隙率,XRD显示WC相在激光重熔后分解为W2C相,而显微硬度稍有提高。     

车轴钢表面激光熔覆铁基合金涂层研究

通过激光熔覆技术在车轴表面熔覆一层高强度铁基合金形成复合涂层,研究了复合涂层制备过程中,激光功率、扫描速度、送粉量三个参数对熔覆涂层质量的影响,并且通过正交实验法得到最佳制备工艺。测试结果表明,在此工艺下制备的铁基合金涂层的硬度约为890 HV,是原有基体材料EA4T钢(280 HV)的3倍多。对磨实验中,铁基熔覆涂层损失量较小,约为0.1 g,远小于对磨金属的损失量。铁基合金涂层的硬度和耐磨性相较于基材都得到较大提高。     

激光重熔等离子喷涂NiCr-Cr3C2涂层微观结构和性能研究

利用扫描电镜(SEM)、能谱仪(EDS)、显微硬度计及金相分析软件,对等离子喷涂NiCr-Cr3C2涂层激光重熔前后的显微组织结构、硬度和孔隙率变化进行研究,并探讨不同扫描速度对激光重熔效果的影响.结果表明:利用激光重熔NiCr-Cr3C2陶瓷涂层,能够有效提高涂层的硬度和致密度,减少孔隙率;研究条件下1.5m/min的扫描速度时激光重熔效果最好.     

激光重熔NiCrAlY涂层研究

采用空气等离子喷涂技术(APS)将NiCrAlY粉末作为粘结层材料喷涂在IN718镍基合金上,再用5 kW CO2连续激光器对其进行激光重熔处理,利用扫描电镜(SEM)、能谱分析(EDX)和X射线衍射(XRD)等手段对等离子喷涂层和激光重熔层的微观组织与成分进行了比较分析.结果表明:应用优化激光重熔工艺进行重熔后,涂层...     

激光重熔纳米晶镍镀层的研究

介绍了喷射电镀的基本原理,采用自行设计制造的喷射电镀设备制备纳米晶镍镀层,并对镀层进行激光重熔处理.重点研究了在直流电源和脉冲电源作用下,电流密度对镀层金属的微观结构的影响,以及采用激光重熔处理对直流纳米晶镍镀层形貌的影响;考察了金属基体、喷射电镀层以及激光重熔后的镀层的显微硬度的变化.研究结果表明:与基体金属相比,喷射电镀层的显微硬度有明显提高;经过激光重熔处理后镀层的显微硬度得到进一步提高.     

等离子熔覆技术在高压电器耐磨缸体中的应用

根据高压电器设备的工况环境,设计了一种铁基合金粉末,其成分为:Cr 18%,Si 2.0%,B 3.0%,Ni 5%,C 2.0%,Nb 0.6%,Fe余量。采用等离子熔覆技术在16Mn钢表面制得铁基合金熔覆层。采用光学显微镜(OM)、扫描电镜(SEM)、电子探针(EMPA)和X射线衍射仪(XRD)分析了等离子熔覆层的组织结构和成分,并进行了摩擦磨损试验。结果表明,所得等离子熔覆合金层非常致密,主要由γ-(Fe,Ni)、((Fe,Cr)_7(C,B)_3和Fe_3Ni_2相组成,具备良好的耐磨性。     

不同等离子熔覆铁基合金涂层在阀门密封面上的应用

在阀门密封面上用等离子熔覆技术制备了Fe45、Fe313和Fe316三种铁基合金涂层.利用光学显微镜、扫描电镜、能谱仪和X射线衍射仪表征了熔覆层的显微组织和物相组成.采用维氏硬度计测试了熔覆层的显微硬度,并使用电化学工作站和全浸腐蚀试验测试了它们的耐蚀性.结果表明,Fe45熔覆层呈现均匀的等轴晶组织,Fe313和Fe316熔覆层在与基体接触的区域形成了细晶粒区,而在熔覆层的中部出现了柱状晶组织.3种熔覆层的主要硬质相均为M7C3型碳化物,其中存在固溶相(Fe,Cr).3种熔覆层的显微硬度都高于基体,Fe45、Fe313和Fe316熔覆层的平均显微硬度为629.76、550.51和408.91 HV.Fe316熔覆层的耐蚀性最佳,Fe45熔覆层的耐蚀性最差.     

激光重熔处理等离子喷涂陶瓷涂层的研究现状及展望

本文介绍了激光重熔等离子喷涂陶瓷涂层的研究进展,并对其进行了展望。激光重熔使等离子喷涂涂层致密性提高,涂层与基体的结合方式由机械结合为主改为冶金结合为主,层状组织变化为柱状组织;激光重熔使等离子喷涂涂层的热疲劳抗力、耐蚀性、耐磨性、抗高温氧化性等性能提高。指出了激光重熔等离子喷涂陶瓷涂层目前存在的问题,探讨了激光重熔等离子喷涂陶瓷涂层易产生裂纹,甚至发生涂层剥落等问题的原因,提出了激光重熔技术的研究方向。     

Online monitoring of laser remelting of plasma sprayed coatings to study the effect of cooling rate on residual stress and mechanical properties

This investigation deals with laser remelting of plasma sprayed alumina and chromia coatings. The time-temperature history of the laser remelted zone was recorded using an infrared pyrometer during the remelting operation. Cooling rates, under varying scanning speed, were determined from the time temperature curve. Surface morphology, microstructure, and phases of the laser treated and as-sprayed coatings were characterized using scanning electron microscopy, optical microscopy, X-ray diffraction, respectively. X-ray diffraction was also employed to measure the surface residual stress of the coatings. Inherent features of plasma sprayed coatings like porosity and inter-lamellar boundary were obliterated upon laser remelting. A columnar grain growth perpendicular to the laser scanning direction was observed. The range of roughness of the as-sprayed coatings reduced from 6 to 8?µm to 1–2?µm in the remelted layers. For both coatings, more than 90% reduction in porosity was found upon laser remelting. Surface residual stress of the as-sprayed alumina and chromia coatings was found to be tensile and compressive, respectively. Within the limits of the testing condition the tensile residual stress of the remelted layers increased by up to around 500% in the alumina coatings. In the chromia coating a decrease of compressive stress by up to around 80% was recorded. In the remelted layer the tensile nature of the stress showed a tendency to increase with an increase in the cooling rate. However, the state of stress of the as-sprayed layer, i.e., tensile or compressive, was retained in the remelted layer. The residual stress was found to decrease in the remelted layer with an increase in the degree of overlap of the remelted tracks.     

Characterization of Laser Remelted Plasma-Sprayed Mo Coating on AISI 1020 Steel

Plasma-sprayed molybdenum (Mo) coating was deposited on an AISI 1020 steel substrate. Laser remelting was used to eliminate the open pores and microcracks of the plasma-sprayed molybdenum coating. The quantitative investigation of porosity was carried out with the help of Biovis image analysis software. The microhardness was measured using a Vickers indenter. The influence of laser remelting on the wear volume loss of plasma-sprayed Mo was estimated by using a pin-on-disc wear test rig. The worn surface was characterized by scanning electron microscopy. The experimental results demonstrate that the porosity of the coating was decreased and microhardness was improved by laser remelting. The laser remelted plasma-sprayed Mo coating exhibits better wear resistance compared to the untreated plasma-sprayed Mo coating. It is concluded that laser remelting is a potential treatment for the plasma-sprayed coating. In this study, the laser remelted plasma-sprayed Mo coating exhibited of lowest porosity, higher hardness and better wear resistance.     

Effect of cooling rate on residual stress and mechanical properties of laser remelted ceramic coating

Mild steel substrates were coated with commercially available alumina and chromia powders using the powder flame spraying process. The top layers of the flame sprayed coatings were remelted using a 2?kW fiber laser. Thermo-cycles of the laser remelting process were monitored on-line using an infrared pyrometer. Cooling rates were varied using different laser scanning speeds. Surface morphology, microstructure and phases of the laser treated and as-sprayed coatings were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and X-ray tomography. Surface residual stress of the as-sprayed and laser treated coatings was measured using X-ray diffraction. The inherent defects like porosity and inter-lamellar boundary diminish to a great extent upon laser remelting. Surface residual stress of the remelted coatings tends to increase with increase in cooling rate. Surface crack density of the laser treated coating was reduced appreciably when coatings were preheated prior to laser remelting.     

Ultrasonic cavitation erosion of as-sprayed and laser-remelted yttria stabilized zirconia coatings

Cavitation erosion resistance of 8 wt.% yttria stabilized zirconia has been investigated in specimens prepared by atmospheric plasma spraying and laser remelting post treatment. The results indicate that as-sprayed coatings involve defects such as primary cavities and initial micro cracks inside a particle and among the interfaces of particles. When the specimens are subjected to cavitation erosion, the micro cracks initiate and coalesce along with chip removals. Laser remelting produces a dense glazed layer with some cracks though the coatings. With the increasing of erosion time, large pieces are delaminated from coating-substrate interface leading to a significant mass loss. However, the resistance of laser remelted coatings to cavitation erosion is significantly improved when they are impregnated with epoxy by vacuum castable mounting. The relationship between cracks formed inside the laser remelted YSZ coatings and their damage mechanism under cavitation is discussed.     

Research of laser remelting on the thermal-mechanical behaviors and heat treatment of yttria-stabilized zirconia coatings

In this study, the thermal and mechanical behaviors were investigated by simulating laser remelting of atmospheric plasma-sprayed yttria-stabilized zirconia coatings, and the molten depth and regions of stress concentration were compared between simulation and experiment. The heat  treatment process of the remelted coating was also simulated. The crack formation mechanism in the YSZ coating remelted by laser and the heat-treatment effect on residual stress were investigated. Results showed that the simulated results were consistent with the experimental measurements, and the residual thermal stress was the main cause of cracks formation. The coating remelted by a laser power of 1500 W and a scanning rate of 9 mm/s possessed less residual concentrated stress and segmented cracks. Heat treatment released concentrated stress, which was still accurate for the ceramic coating. If the coatings were slowly heated to demonstrate heat treatment after laser remelting, the cracks in the remelted layer decreased correspondingly.     

Microstructure and wear resistance of in-situ synthesized Ti(C,N) ceramic reinforced Fe-based coating by laser cladding

In order to enhance the wear resistance of Fe-based cladding layer, TiN, Ti and graphite were added into Fe313 powder and in-situ formation of Ti(C, N) ceramic reinforcement phase was carried out by laser cladding. Firstly, thermodynamic calculations were used to determine the feasibility and favorability of a chemical reaction. Then, the reaction mechanism was investigated by adding five groups of different contents and carrying out EDS and phase analysis. We report that large TiN particles do not completely decompose and in-situ synthesized TiC phase forms around large TiN particles. However, small TiN particles are completely decomposed and directly formed the Ti(C, N) phase. Finally, through the friction and wear tests, it has been observed that the friction coefficient of a sample, with three powders added, was 0.559 times smaller than the substrate and 0.725 times smaller than the initial powder, and the wear volume of the same sample was 0.365 times smaller than the substrate and 0.799 times smaller than the initial powder. Therefore, it can be concluded that the in-situ synthesis of Ti(C, N) ceramic reinforced Fe-based coatings by laser cladding greatly improves the wear resistance of the Fe313 layer.     

3Cr2W8V模具钢表面激光相变淬火的显微组织及耐磨性能研究

采用高功率CO2激光束对3Cr2W8V模具钢表面进行相变淬火,研究了相变强化层的显微组织与耐磨性能。结果表明：激光表面强化处理后的显微组织由品粒细小的码氏体和残余奥氏体组成,显微硬度比处理前提高了1．5倍,耐磨性能提高了1倍,同时变形小,可用于模具的表面处理。