Residual Thermal Stresses of Laser Cladding of Intermetallic-Ceramic Composite Coatings

The stresses in laser cladding of Ni3Al-WC composite coating co and in heat affect zone (HAZ) σh have been induced based on considering the influences of laser processing parameters power P and beam traverse speed v.According to the calculated results, certain limits of P and v are necessary in order to obtain crack free coatings. It agrees well with the experimental results.

Ceramic-Metal Composite Coating by Laser Cladding

Four kinds of ceramics (silicon carbide, boron carbide, aluminum oxide and tungsten carbide) were added into Ni base self-fluxing alloy as reinforcing materials in order to obtain metalceramic composite coating by means of laser cladding. A lot of experiments have been carried out to test the processability of the four kinds of ceramics with different sizes and contents. The microstructures of sintered tungsten carbide (S-WC) and cast tungsten carbide (C-WC) reinforced Ni base alloy coatings were analysed, the distortion regulation of laser clad specimens was revealed. The wear resistance of the composite coating has been tested.

Coarse WC Particles Ceramic-Metal Composite Coating by Laser Cladding

The coarse WC particles ceramic-metal com- posite coatings with WC density of 67 wt-% and thickness of 1.0-1.2 mm have been cladded on 20Ni4Mo steel surface by a 2 kW CO_2 laser.The sintered WC particles with the size of 600-1000 μm are chosen as the main strengthening phase, Ni-base self-flux alloy as the binder in the compo- site coatings.The microstructure and microhardness of both WC particles and binder are analysed.The rigid ball indention with acoustic emission technique is used to evaluate the brittleness of the coating.Finally,the abrasive wear resistance of the coating is tested.Besides,the coatings with the same ratio and size of WC parti- cles in low carbon steel tube rod were cladded on 20Ni4Mo steel by atomic hydrogen welding tech- nique and analysed by the same way,their results are compared.

Cyclic oxidation behavior of NiCoCrAlY/YSZ@Ni composite coatings fabricated by laser cladding

Composite coating on GH4169 alloy is prepared by laser cladding yttria-stabilized zirconia(YSZ)@Ni core-shell powdersmixed with NiCoCrAlY alloy powders.The cyclic oxidation behavior of the coatings,especially the growth process of theoxide layer,is investigated based on experimental research and first-principle calculations.The results indicate that theoxidation resistance of coated GH4169 alloy is beer than that of uncoated GH4169 alloy.The coating has three layers:acellular dendrite outer layer,a planar YSZ interlayer,and an inner layer composed of Cr2O3 formed during laser clading.After oxidation at 1000 and 1050℃,as the oxidation time increases,the cellular dendrite outer layer becomes thicker,andthe planar yttria-stabilized zirconia interlayer becomes thinner.Between the planar interlayer and Cr2O3 inner layer,and Al2O3 layer formed.Notably,cracks formed in the intcrface of Al2O3/Cr2O3 owing to thcir weak interface strength,whichled to the failure of the composite coating.

Characterization of gradient Ni-Fe/SiC composite coating on mild steel by thermal spraying in combination with laser cladding

Metal matrix composite coating Ni-Fe/SiC was prepared on an iron-based substrate bythermal spraying combined with laser cladding,using SiC particulates as the reinforcing agent.The micro-structures of the coatings formed at different thermal spraying and laser cladding conditions were character-ized by means of X-ray diffraction and electron probe microanalysis.The thermal oxidation properties of themixed powders composed of different content of SiC particulates and relevant Ni-based alloy as the balancewere examined using differential scanning calorimetry.The hardness profile of the thermal sprayed and lasercladding coatings was investigated as well.It was found that SiO2particulates were generated and dissolvedand dispersed during the melting and solidification of the laser cladding process,which was ascribed to theoxidation of the dispersed SiC particulates.The micro-hardness depth profile of the target laser claddingcomposite coating was characterized by gradient distribution,which could be related to the gradient distribu-tion of the hard SiC and SiO2particulates in the dendrites and interdendrites of the cladding layer.Both SiCand SiO2particulates contributed to greatly increasing the microhardness and mechanical properties of the ti-tled laser cladding composite coatings.

Microstructural evolution and abrasive resistance of WC7Co ceramic particle-reinforced Ti6Al4V composite coating prepared by pulse laser cladding

WC7Co/Ti6Al4V composite coatings are deposited on the pure Ti substrate by pulse laser cladding(LC).During the laser melting process,the decomposition of WC7Co particles will lead to the evolution of microstructure and phases,which is directly related to the wear resistance and mechanism of composite coating.The microstructural evolution,phase compositions and interface reaction of WC7Co/Ti6Al4V composite coating were examined by scanning electron microscopy,energydispersive spectrum and X-ray diffraction(XRD).The hardness of different structures and abrasive resistance of composite coating were measured.The results show that the typical microstructure of LC WC7Co/Ti6Al4V composite coating can be classified into dissolved WC7Co composite structure and un-dissolved WC7Co structure.According to XRD results,there are Ti solid solution,W,TiC,VC,Co3W3C and secondary W2C in composite coating.The eutectic structure formed by the dissolved WC7Co particles consisted of W,W2C,TiC and P-Ti solid solution.The mean hardness of different structures exhibits a significant gradient distribution in composite coating.A reaction layer composed of TiC,W and W2C is also generated onto the interface between un-dissolved WC7Co particles and Ti6Al4V alloy matrix.The abrasive mechanisms of WC7Co/Ti6Al4V composite coating are mainly adhesive wear and oxidation wear during the dry sliding process.

激光熔覆WC/316L复合涂层结构及磨损性能

为改善激光熔覆过程中WC增强金属基复合涂层分解与分布不均匀的问题,采用激光熔覆技术制备了50%WC含量的WC/316L复合涂层,分别采用扫描电子显微镜(SEM)、显微维氏硬度计、摩擦磨损试验机表征了熔敷层的组织形貌、硬度与摩擦磨损性能。结果显示,低热输入量可以防止WC颗粒下沉,提升熔覆层厚度方向上的WC颗粒分布均匀性;但WC的平面分布均匀性较差,同时低热输入导致WC颗粒结合较弱,易发生脱落;熔覆过程中,粉末中15%的WC发生分解。研究表明,通过降低激光热输入量,可以制备WC厚度方向较为均匀的复合涂层,提升熔覆层耐磨性,但是需要优化WC平面分布均匀性与WC颗粒结合性能。

激光熔覆陶瓷颗粒增强金属基复合材料研究进展

陶瓷增强金属基复合材料(MMCs)因其优异的耐磨性、韧性、高温蠕变性能和疲劳强度,广泛应用于生物医学、航空航天、电子等高端工程行业。激光熔覆是在基体表面利用激光束使陶瓷及其他特殊粉末与基体表层融化,并自激冷却形成冶金结合涂层的环保新技术,具有沉积效率高、厚度可控、热变形小、冷却快、稀释率小以及冶金结合等优点。介绍了激光熔覆陶瓷颗粒的形成方式对MMCs性能的影响,讨论了激光熔覆辅助能场及高速激光熔覆技术对MMCs的界面强化效应,并分析了陶瓷颗粒的强化机制和激光辅助能场的作用机制。最后,对目前激光熔覆陶瓷颗粒增强基金属复合材料研究的发展进行了展望。

TC4表面激光熔覆硬质涂层的制备与分析

为解决TC4钛合金硬度低、耐磨性差等缺点,利用激光熔覆技术,采用4 kW大功率Laser4000半导体激光器,在TC4表面制备了以HfC、TaC和ZrC等比例三元陶瓷相(比例分别为0%、5%、10%、15%)为增强相的钛基硬质涂层。熔覆结束后对熔覆件进行切割、打磨、抛光和腐蚀制备金相试样,利用电子显微镜(EM)、扫描电镜(SEM)、EDS能谱仪、X射线衍射仪(XRD)等试验手段对不同材料组分的熔覆涂层进行了宏观形貌、微观组织和性能的对比分析;利用TH120A里氏硬度计测熔覆层的宏观硬度值,利用Qness型号维氏显微硬度计分析熔覆试样截面微观硬度变化规律。研究结果表明:三元陶瓷相的添加,使熔覆层与基材形成了良好的冶金结合,并且基材与熔覆层有着明显的平滑的分界线;熔覆层主要由α+β针状马氏体基体及析出的棒状和块状α相组成,其中添加质量分数为15%的三元陶瓷增强相的涂层熔覆层由块状晶组成,且晶粒最为粗大,添加质量分数为5%和10%的三元陶瓷增强相的涂层,棒状和块状的α相尺寸明显变小,晶粒明显被细化,组织更加均匀致密;熔覆层柱状和块状α相的主要成分为Ti以及微量的Al、Zr、Hf和V元素,涂层的针状马氏体中含有较高的Al、Zr、Ta和V元素,在晶间的黑色β相中含有微量的Zr和Ta元素。测试发现,Hf、Ta元素通常存在于不同的物相中;激光熔覆后的试件的硬度都有所提高,当三元陶瓷添加量的质量分数为10%时,熔覆层晶粒最为细小,分布均匀,硬度最高,达到715 HV,是TC4基材的2.31倍。

激光熔覆原位合成反应机制的研究

通过激光熔覆技术,采用不同粒度BN和Ti粉为原料在Ti-3Al-2V钛合金表面原位合成Ti B/Ti N钛基复合涂层。采用扫描电子显微分析(SEM)、X射线衍射(XRD)和显微元素分布(EPMA)分析强化相的形貌、相组成和元素分布,探讨激光熔覆条件下Ti-BN体系原位合成反应机制。结果表明:采用不同粒度BN和Ti粉为原料制备Ti B/Ti N-Ti基复合涂层。粗BN为原料强化相原位反应机制主要由扩散机制和溶解-析出机制共同控制,BN为形核质点,促进Ti N的形核生长;细BN为原料强化相原位反应机制主要由溶解-析出机制控制。

金属基体激光熔覆陶瓷基复合涂层的裂纹成因及控制方法

参考了较多国内外有关文献,较为系统地分析了金属基体激光熔覆陶瓷基复合涂层裂纹的形成机理,总结出降低裂纹倾向的方法:选择合适的激光熔覆参数;激光熔覆时对金属基体进行预热或后热处理;采用添加中间过渡层或梯度涂层的方法;在金属基体激光熔覆陶瓷基复合材料中添加增韧、增塑元素。这些方法为控制金属基体激光熔覆陶瓷基复合涂层的裂纹形成提供了有益参考。

定向凝固镍基高温合金上激光熔覆Inconel738的裂纹敏感性研究

针对定向凝固镍基高温合金叶片的强化与修复需求,研究了在定向凝固镍基高温合金基体上激光熔覆In conel738的裂纹敏感性问题。在定向凝固镍基高温合金基体上激光熔覆Inconel738合金对裂纹非常敏感,所产生的裂纹为热裂纹,由定向凝固基体晶界处引发并穿过界面向熔覆层发展;多层熔覆过程中熔覆层间也会产生热裂纹,热裂纹沿晶界纵向扩展。定向凝固高温合金基体晶界处的低熔共晶成为主要的裂纹源。严格控制激光熔覆过程中的热输入量可以显著降低裂纹敏感性。选择适当的熔覆工艺方法和参数可以在定向凝固镍基合金基体上形成良好冶金结合且无裂纹的基本保持定向凝固特性的熔覆层组织。

激光熔覆NiCr/Cr_3C_2-Ag-BaF_2/CaF_2金属基高温自润滑耐磨覆层的组织结构及摩擦学性能

利用激光熔覆技术在不锈钢表面制备了NiCr/Cr3C2-Ag-BaF2/CaF2金属基高温自润滑耐磨覆层,用X射线衍射仪分析了复合粉末及其激光熔覆耐磨覆层的物相组成,用扫描电子显微镜分析了耐磨覆层横截面的显微组织结构特征。在干滑动磨损试验条件下测试了覆层的耐磨性能,并用扫描电子显微镜观察和分析了覆层的摩擦磨损机理。试验结果表明,激光熔覆NiCr/Cr3C2-Ag-BaF2/CaF2金属基高温自润滑耐磨覆层,从室温到500℃试验温度范围内表现出了良好的减摩抗磨效果,并且随着温度的升高覆层材料表现出了不同的摩擦磨损机理,从室温到200℃温度范围主要表现为粘着磨损和磨粒磨损共同作用,温度超过200℃后主要表现为塑性变形和轻微的粘着磨损。

激光熔覆纳米Al_2O_3等离子喷涂陶瓷涂层

采用X射线衍射仪、扫描电镜和显微硬度计研究了45#钢表面激光熔覆纳米Al2O3改性Al2O3+13%TiO2(质量分数)陶瓷涂层的相组成、微观结构和显微硬度,同时对涂层的磨损特性进行了考察。结果表明,激光重熔区亚稳相γ Al2O3转变成稳定相α Al2O3,熔覆层由粗颗粒α Al2O3和TiO2以及纳米α Al2O颗粒组成,在激光的作用下,等离子喷涂层的片层状结构得以消除;纳米Al2O3颗粒仍然保持在纳米尺度,填充在涂层的大颗粒之间,使涂层致密化程度得以提高,因此纳米Al2O3改性涂层的显微硬度较高,且其耐磨性能明显优于等离子喷涂层。

纳米颗粒增强NiCoCrAlY熔覆涂层的高温摩擦磨损行为(英文)

采用激光熔覆技术,在镍基高温合金表面制备相同含量的3种不同纳米颗粒增强的NiCoCrAlY涂层,考察它们在500℃空气氛围下的干摩擦磨损行为,并与未加纳米颗粒的涂层进行比较。结果表明:纳米颗粒增强涂层的高温摩擦磨损机制与未加纳米颗粒的涂层一致,均为强烈塑性变形引起的剥层磨损和氧化磨损;加入纳米颗粒后,涂层的摩擦因数增大且随滑行距离的增加呈减小趋势,涂层的磨损率仅为未加纳米颗粒涂层的34.0%～64.5%。在3种纳米颗粒中,纳米SiC颗粒对涂层高温耐磨性的改善最为显著。

激光熔覆铸造WC-Ni基合金中WC颗粒的烧损机理与评估

本文研究了激光熔覆金属陶瓷层中铸造WC颗粒的烧损方式和机理，证明激光熔覆过程中铸造WC颗粒主要以溶解扩散式的烧损为主，提出了评定WC颗粒烧损率的半定量公式为：

激光重熔纳米SiC复合陶瓷涂层组织和性能研究

研究了WC/Co-NiCrAl等离子复合陶瓷涂层、激光重熔等离子涂层、激光渗入纳米SiC涂层的组织结构、耐磨性能。结果证明 :在所定的工艺参数下 ,等离子喷涂层组织呈层片状 ,层间为机械结合界面 ;经激光重熔后 ,激光作用区涂层组织细化 ,孔隙率降低 ,耐磨性能是原等离子涂层的 1 3倍 ;渗入纳米SiC后 ,组织进一步细化 ,孔隙率进一步降低 ,SiC颗粒仍处于纳米尺度 ,分布在粗颗粒表面及粗颗粒之间 ,其耐磨性能是原等离子涂层的 2 .

激光熔覆陶瓷及其复合涂层的材料体系

分析了激光熔覆陶瓷及其复合涂层的国内外研究与发展现状 ,对激光熔覆耐磨涂层、耐蚀涂层、热障涂层、抗氧化涂层和生物材料涂层的材料体系。

纳米复合陶瓷涂层激光熔覆后的组织与耐磨性能

研究了45#钢表面激光熔覆纳米Al2O3复合陶瓷涂层的微观组织结构、显微硬度和磨损特性。结果表明,激光熔覆层由-Al2O3和TiO2以及Al2O3纳米颗粒组成,在激光的作用下,消除了原来等离子喷涂层的片层状组织;纳米颗粒仍然保持纳米尺度,填充在涂层的大颗粒之间,起着桥连的作用;同时涂层气孔率的降低使涂层致密化程度得以提高,纳米Al2O3涂层的显微硬度较高,且其耐磨性能明显优于等离子Al2O3+13%TiO2喷涂层。

激光熔覆陶瓷及其复合涂层的组织特征

综述了激光熔覆陶瓷及其复合涂层的组织特征与性能。分析了涂层区、结合区组织的形成机制及陶瓷 金属复合涂层中陶瓷相的溶解行为 。