激光应用 激光工业应用

TG156．99 2005042607 激光重熔等离子喷涂自润滑复合涂层研究=Study of plasma spray and laser remelting self-lubricating composite coatings[刊,中]／应丽霞(哈尔滨工业大学机电工程学院, 黑龙江,哈尔滨(150001)),王黎钦…／／光电子·激光,- 2005,16(1),-105-109 为获得高副接触情况下具有抗疫劳的自润滑涂层,采用包覆的Ni包TiB2和Ni包石墨超细微粉,在9Cr18不锈钢表面,利用激光重熔等离子喷涂方法制备金属陶瓷自润滑复合涂层。研究了涂层制备的工艺方法、组织特征、界     

镍基非晶复合涂层激光制备及其纳米压痕测试

采用大功率半导体激光熔覆和重熔的工艺在低碳钢表面制备Ni-Fe-B-Si-Nb合金非晶复合涂层,并对所得涂层进行了纳米压痕性能测试。研究结果表明,当激光熔覆时激光功率为0.8kW,熔覆速度为0.36m/min,送粉速度为12g/min,重熔时激光功率为3.5kW,熔覆速度为8m/min,在低碳钢表面成功制备了Ni40.8Fe27.2B18Si10Nb4非晶复合涂层,涂层主要由非晶相和NbC颗粒相组成。纳米压痕测试结果表明经激光重熔后所得非晶复合涂层的显微硬度和弹性模量远远大于未重熔的熔覆层,并且也大于同成分大块非晶。     

掺杂相对ZrB2陶瓷涂层抗激光烧蚀性能的影响

耐高温陶瓷作为高熔点材料,具有优异的高温抗烧蚀性能,有可能满足未来抗激光防护的需求。为摸清ZrB₂陶瓷涂层抗激光防护性能,采用高功率固体激光器作为测试光源,搭建了激光烧蚀实验平台和激光耦合特性测量系统,重点对ZrB₂陶瓷涂层开展了激光烧蚀实验和涂层反射率测试。实验研究了不同激光参数条件下ZrB₂涂层抗激光烧蚀性能,以及掺杂相(SiC、MoSi2)的影响。结果表明,相比于未掺杂ZrB₂涂层,掺杂后ZrB₂涂层抗激光烧蚀能力明显下降。分析认为掺杂相可提高ZrB₂涂层抗氧化性能,但不利于发挥氧化生成物ZrO2的高反射和隔热作用,致使抗激光损伤阈值降低。激光损伤前后涂层反射率的测试结果,也证实了ZrO2的高反射率是增强ZrB₂涂层抗激光损伤阈值的关键。同时,利用有限元软件建立了连续激光烧蚀下ZrB₂陶瓷涂层温度计算模型,并以基底发生熔化为判据,仿真得到了陶瓷涂层典型的抗激光烧蚀阈值参数。     

曲面对层板/热障涂层耦合结构冷却特性的影响

先进的双层壁化叶片表面喷涂热障涂层是提升未来航空发动机热效率的关键技术之一。本文利用数值模拟探讨了壁面曲率对涂敷热障涂层的双层层板冷却结构体系中各热防护措施(包括：气膜冷却、内部近壁换热及表面涂层隔热)的影响,并在不同热障涂层厚度和冷/热气流吹风比下,开展了金属表面综合冷却效率(?)和TBC热防护效率(τ)对壁面曲率的敏感性分析。结果表明：曲面对气膜效率和热障涂层热防护作用影响较大,但几乎不会影响内部传热。凸面模型具有最高的气膜效率,而在凹面模型中使用热障涂层会产生最大的?增量。整体来看,凸面具有最高的?和τ,凹面下这两种效率均最低。吹风比增加会显著降低?和τ对曲面的敏感性。热障涂层厚度增加会削弱?对曲面的敏感性,但会增强τ对曲面的敏感性。     

火焰喷涂重熔Ni基WC复合涂层的耐磨性能试验研究

利用火焰喷涂重熔方法制备了Ni基WC复合涂层，并进行了耐磨性能试验研究.通过扫描电子显微镜观察涂层磨损后的表面形貌，分析了WC体积分数、颗粒分布均匀性、包裹粉颗粒尺寸对涂层耐磨性的影响.结果表明:涂层硬度和耐磨性随着WC体积分数增加而提高，当WC体积分数过高时，降低了涂层致密性，其硬度和耐磨性反而有所下降；聚乙二醇(PEG)400+PEG2000+无水乙醇混粉方式的WC颗粒分布最均匀，降低了涂层磨损量；加入相同体积分数的亚微米级WC所制备的涂层耐磨性较微米级WC所制备的涂层耐磨性好. 关键词： 火焰喷涂 显微组织 颗粒尺寸 耐磨性能     

不同功率下激光重熔对Mg-Zn-Y-Zr合金性能的影响研究

由于镁合金耐磨及硬度性能较差,应用激光重熔技术进行表面改性就显得尤为必要,其中激光功率因素所产生的影响十分显著。为了探究激光重熔中功率因素对稀土镁合金的微观组织结构,硬度以及摩擦磨损性能的影响。通过使用3kW的DILAS半导体激光器对Mg-1.85Y-7.91Zn-0.75Zr(质量分数,%)合金进行不同功率下的激光重熔实验。采用光学显微镜(OM),电子扫描显微镜(SEM),X射线衍射仪(XRD)和能谱仪(EDS)观察所制得试样的组织,形貌,相成分及分布;使用显微硬度计测量维氏硬度;使用摩擦磨损试验机测试样品的摩擦磨损性能,从而得出不同激光功率对组织,性能的影响。研究表明,经过重熔处理的合金宏观凝固组织明显细化,且随着功率升高,晶粒变大,第二相分布愈加弥散。由于细晶强化,固溶强化以及弥散强化的影响导致了硬度和耐磨性提高,其中800,1000,1200,2000W激光功率作用下重熔细晶区的维氏硬度平均值分别为90.97,93.47,94.20,95.53HV,而粗晶基材区的维氏硬度平均值仅为63.90HV,2000W功率作用下的硬度照比基材提升了49.50%。随着功率的升高,耐磨性越高且逐渐从以黏着磨损为主过渡到以磨粒磨损为主。可见,激光重熔技术可以明显强化该稀土镁合金,激光功率的增大可以显著增加该合金的硬度以及抗摩擦磨损性能。     

石墨改性环氧树脂抗强激光辐照性能

 在激光硬杀伤防护体系研究中,制备了鳞片石墨改性环氧树脂涂层,分析了它与辐照激光能量耦合作用规律,研究了其热烧蚀性能、隔热性能等抗激光辐照性能,并对不同参数激光辐照后该材料的损伤形貌进行宏观、微观分析,确定了损伤阈值与损伤形式。实验结果表明：石墨改性环氧树脂具有优良的抗强激光辐照性能,连续激光辐照下功率密度损伤阈值高于2 kW/cm²;高温下与激光能量耦合系数仅为10%左右,稳定热烧蚀率低至μg/J量级;具备优良的纵向隔热性能,高温下热导率在10 W·K^-1·m^-1以下;低功率密度激光辐照下损伤形式为轻微氧化,高功率密度激光辐照下则以汽化烧蚀为主;材料制备工艺简单,成本低廉,与被加固材料界面结合良好。     

基于等离子喷涂的反射型激光防护涂层研究

本文首先介绍了激光武器在未来战争中的突出地位和发展现状,阐明了高能激光束与目标材料相互作用时的热效应毁伤机理;总结了基于等离子喷涂的反射型激光防护涂层的研究进展,包括等离子喷涂金属涂层和陶瓷涂层的研究进展、以及各自的技术特点和防护效果,为高能激光防护领域的研究提供了借鉴。研究结果表明,控制金属涂层在激光辐照过程中的氧化现象能有效地提高涂层的激光防护性能,同时具有优异反射性能的新型陶瓷涂层在高能激光防护领域中有较好的发展前景。     

强流脉冲电子束辐照对NiCoCrAlY涂层结构和性能的影响

 采用低气压等离子体喷涂在DZ4镍基高温合金表面沉积NiCoCrAlY 涂层,并利用强流脉冲电子束（HCPEB）对其进行辐照处理。对HCPEB辐照处理前后的涂层的结构和性能分析得出,经HCPEB辐照处理后,疏松的涂层表面重熔,变得致密平整,产生微区光滑、熔坑和裂纹。X射线衍射分析表明,电子束辐照后涂层中的γ′相增多,涂层没有产生明显的残余微观内应力。900 ℃静态空气等温氧化试验结果显示,HCPEB辐照处理后,涂层的抗氧化性能明显提高。原因在于电子束辐照处理的涂层氧化后表面形成了更加完整的Al2O3保护层,同时γ′相的增加也有利于其耐氧化性能的提高。     

板料激光成型技术的实验研究

激光成型是一种利用激光作为热源的热应力无模成型新技术。介绍了板料激光成型技术的工艺过程及影响激光成型的主要因素 ,通过实验研究了激光能量因素、板料的材料性能及几何参数对板料弯曲角度的影响     

Laser surface remelting of plasma sprayed nanostructured Al2O3-13wt%TiO2 coatings on titanium alloy

Plasma sprayed nanostructured coatings were successfully fabricated on a titanium alloy (Ti-6Al-4V) substrate using the as-prepared nanostructured Al₂O₃-13wt%TiO₂ feedstock. A CO₂ laser was used to remelt the plasma sprayed coatings. The effects of laser remelting on the phase constituents, microstructure and properties of the ceramic coatings were investigated. The laser remelted coatings (LRmC) possessed a much denser and more homogenous structure and excellent metallurgical bonding to the substrate. The average porosity of the LRmC was reduced to 0.9%, compared with 6.2% of the as-sprayed coatings. The net-like structure in the as-prepared feedstock remained in the coatings before and after laser remelting. The metastable γ-Al₂O₃ phase in the as-sprayed coatings transformed to stable α-Al₂O₃ during laser remelting. The LRmC could remain nanostructure. The microhardness of the coatings was enhanced to 1000-1400 HV_0.3 after laser remelting, which was much higher than that of the plasma sprayed coatings and 2-3 times higher that of the substrate. Significant decreases in surface roughness were also found in the LRmC.     

Influences of laser remelting on microstructure of nanostructured Al2O3-13 wt.% TiO2 coatings fabricated by plasma spraying

The effects of laser remelting on microstructure of nanostructured Al₂O₃-13 wt.% TiO₂ ceramic coatings prepared by plasma spraying with agglomerated powders were studied. The microstructure of the feedstock, as-sprayed and laser-remelted coatings were investigated by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). The results indicate that the plasma-sprayed ceramic coating consists of both fully melted regions and partially melted regions. The totally ceramic coating, especially the fully melted regions, has a typical plasma-sprayed lamellar-like structure as the conventional coating, and has some pores. According to the difference of microstructures, the partially melted regions can be divided into liquid-phase sintered regions (a three-dimensional net or skeleton-like structure: Al₂O₃-rich submicron particles embedded in the TiO₂-rich matrix) and solid-phase sintered regions (remained nanoparticles). The lamellar defect of the as-sprayed coating is erased, and the compactness of the coating is improved significantly after laser remelting. The laser-remelted region composed of fine equiaxed grains, which are different from the conventional column-like crystals along the direction of the heat current. Due to the rapid solidification of laser remelting process, there are still some nanoparticles in the remelted region because of an insufficient time for grains growth.     

Finite element simulation of stress distribution and development in 8YSZ and double-ceramic-layer La2Zr2O7/8YSZ thermal barrier coatings during thermal shock

In this paper, the thermal stress of the double-ceramic-layer (DCL) La₂Zr₂O₇/8YSZ thermal barrier coatings (TBCs) fabricated by atmospheric plasma spraying (APS) during thermal shock has been calculated. The residual stress of the coating after being sprayed has been regarded as the initial condition of the first thermal cycle. The characteristic of the stress development during the thermal cycle has been discussed, and the influence of the defects on the failure mode during the thermal cycle has also been discussed systematically. Finite element simulation results show that there exist higher radial thermal shock stresses on the ceramic layer surface of these two coatings. There also exist higher thermal stress gradient at the interface between the ceramic layer and the metallic layer. Higher thermal stress in 8YSZ/NiCoCrAlY coating lead to the decrease of thermal shock property as compared to that of LZ/8YSZ/NiCoCrAlY coating. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coating and can also reduce the thermal stress. Considering from the aspects of thermal insulation ability and the thermal shock resistance ability, DCL type LZ/8YSZ TBCs is a more promising coating material compared with the single-ceramic-layer (SCL) type 8YSZ TBCs for the application.     

Effect of λ/2 SiO_2 overcoat on the laser damage of HfO_2/SiO_2 high-reflector coatings

The effect of λ/2 SiO2 overcoat on the laser damage characteristics of HfO2/SiO2 high-reflector (HR) coatings is investigated with 1-on-l and N-on-1 laser damage test methods. The laser damage surface of 1-on-l is analyzed by a step analyzer. The surface morphologies show that laser damage makes the coating damaged area protrudent and rough for HR coating without λ/2 silica overcoat, but concave and smooth for HR coating with A/2 silica overcoat. The result of 10-on-l multi-pulse irradiation on the same point of the coating shows that there is an energy density stage on the damage curve. If the laser energy density is within the range of the stage, HfO2/SiO2 HR coatings with λ/2 silica overcoat will not be damaged more than 2 times for multi-shots, and the surface damages are very slight so that there is no impact on the coating performance. Another interesting result is that the energy density stage extends from the damage threshold to the point of about 3 times of threshold, which is similar to the     

Microscopic observation of laser glazed yttria-stabilized zirconia coatings

Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2-9 μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases.     

Wear resistance of reactive plasma sprayed and laser remelted TiB2-TiC0.3N0.7 based composite coatings against medium carbon steel

Wear resistance of reactive plasma sprayed TiB₂-TiC_0.3N_0.7 based composite coatings and the as-sprayed coating with laser surface treatment was investigated using plate-on-plate tests. Wear tests were performed at different normal loads and sliding speeds under dry sliding conditions in air. The surface morphologies of counterparts against as-sprayed and laser remelted coatings were investigated. The microstructure and chemical composition of wear debris and coatings were studied using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The results show that the wear resistance of the laser remelted coating is improved significantly due to their increased microhardness and reduced flaws. The primary wear mechanism of the remelted coating is oxidation wear and its minor wear mechanisms are grain abrasion and fatigue failure during the course of wear test. In contrast, the primary wear mechanism of the as-sprayed coating is grain abrasion at the low sliding speed (370 rpm) and fatigue failure at the high sliding speed (549 rpm). The oxidation wear mechanism is a minor contributor for the as-sprayed coating.     

The resistance to wear and corrosion of laser-cladding Al2O3 ceramic coating on Mg alloy

The paper presents a study on the preparation of Al₂O₃ ceramic coating on AZ91HP Mg alloy by laser remelting plasma-sprayed coating. It was found that after laser remelting, the coating exhibited obvious layer-like characteristics due to influence of temperature distribution, thermophysical parameters and layer thickness. According to the microstructural difference, the coating can be divided into the melted zone with the α-Al₂O₃ column-like crystal, the sintered zone with flock-like structure, the residual plasma-sprayed zone with loosened structure. Because of the dense column-like crystal, the hardness, wear and corrosion resistance of the laser remelted coating are much higher than those of the plasma-sprayed coating and as-received Mg alloy.     

Influence of laser remelting on the microstructure and phases constitution of plasma sprayed hydroxyapatite coatings

In this paper, the plasma sprayed coatings were treated by laser remelting. The morphologies, elements analysis and phases of both sprayed and remelted coatings were studied by means of electron probe microanalysis (EPMA), X-ray diffraction (XRD) and so on. The results show that the structure of the sprayed coatings is coarse, the amorphization of HA is tremendous, and the bonding state between the coating and the substrate is mechanical combination. After the sprayed coatings were treated by laser remelting in a proper conditions, the properties of the coatings are improved greatly. The microstructure of remelted coatings is columnar and cellular dendritic crystal which is homogeneous and compact, and the coating consists of HA, -TCP and CaO phases, the Ca/P ratio of transition layer is close to 1.67, but the Ca/P ratio of surface layer is higher than that of HA because of the loss of P.     

HfO2／SiO2高反射膜的缺陷及其激光损伤

用原子力、Normaski和扫描电子显微镜等分析仪器,对高损伤阈值薄膜常采用HfO2/SiO2薄膜进行了表面显微图象研究,分析了薄膜常见的表面缺陷,如节瘤,孔洞和划痕等。薄膜表面缺陷的激光损伤实验表明,不同缺陷的抗激光损伤能力不大相同。节瘤缺陷最低,约为15J/cm^2,薄膜的损伤阈值主要由其决定,孔洞的激光损伤能力与节瘤相比较高,约为节瘤的2－3倍。节瘤缺陷在低能量密度的激光损伤所形成的孔洞,与镀制过程中形成的孔洞形貌相似,激光再损伤能力也相似。低能量密度的激光把瘤缺陷变为孔洞缺陷是激光预处理提高薄膜损伤阈值的原因之一。     

Weathering performance of the polyurethane nanocomposite coatings containing silane treated TiO2 nanoparticles

Nano-filled polyurethane coatings were prepared by incorporation of various amounts of untreated and amino propyltrimethoxy silane (APS) treated TiO₂ nanoparticles. TEM and AFM techniques were employed to evaluate dispersion of nanoparticles and surface morphology of the coating, respectively. TEM observations revealed that the APS treated nanoparticles have a better dispersion and smaller agglomeration, compared with their untreated counterparts. AFM images revealed that, surface roughness of the coatings increased with increasing of nanoparticles content, however, at equal level of loadings; coatings containing untreated nanoparticles showed a higher surface roughness.Colour changes (colour coordinates data measurements), mechanical properties and surface morphology of the PU nanocomposite coatings, before and after being exposed to a QUV chamber for 1000 h were studied using various techniques. The results revealed that addition of 0.5 to 1.0 wt.% APS treated TiO₂ nanoparticles reduces photocatalytic activity, and improves the weathering performance PU nanocomposite coatings. Tensile strength measurements showed significant improvement of mechanical properties of PU coatings containing modified TiO₂ nanoparticles. Results also revealed that the colour measurement is a useful technique and non destructive method for evaluation of coating's performance against weathering conditions. The experimental results showed a good correlation between different techniques findings.