Structural and mechanical properties of nano-crystal TiN coatings

The structural and mechanical properties of TiN coatings prepared by ion beam assisted deposition (IBAD) were studied. The coatings have a polycrystal structure with grain size of ≈10nm or less. The hardness of the coatings increases with increasing grain size of TiN crystallites. The coating with grain size of 10.3 nm even has a superhardness of 44.7 GPa. The relationship between the hardness and the grain size in the nano-crystalline coatings was discussed on the basis of grain-boundary triple junctions.

     

Structural and mechanical properties of nano-crystal TiN coatings

The structural and mechanical properties of TiN coatings prepared by ion beam assisted deposition (IBAD) were studied. The coatings have a polycrystal structure with grain size of ～10 nm or less. The hardness of the coatings increases with increasing grain size of TiN crystallites. The coating with grain size of 10.3 nm even has a superhardness of 44.7GPa. The relationship between the hardness and the grain size in the nano-crystalline coatings was discussed on the basis of grain-boundary triple junctions.     

不锈钢表面激光熔覆层与喷焊层耐磨性对比研究

本文研究在１Ｃｒ１８Ｎｉ９Ｔｉ基体上采用激光熔覆和离子喷焊二种工艺形成的涂层对耐磨性的影响。使用５ｋＷ横流ＣＯ２激光器对预置在基体上的Ｃｏ基自熔合金粉末进行单道或多道扫描，得到的熔层与等离子焊层对比结果是：激光熔层缺陷率低，成品率高，其结构致密均匀，晶粒细小，成分稀释率更小，对基体热影响小，熔层硬度与强韧性更高。性能试验证明：激光熔层具有更高的抗擦伤磨损和抗冲击滑动高温磨损性能，耐磨性提高了一倍左右。     

45°高反膜中节瘤缺陷的电场增强效应及损伤特性

研究设计和制备了中心波长为1064 nm的45°多层膜反射镜,通过数值仿真结合实验,对薄膜中节瘤缺陷引起的电场增强效应及其对薄膜抗激光损伤性能的影响进行了研究。结果表明:当1064 nm激光从右至左45°斜入射时,电场增强效应主要出现在节瘤缺陷的表层及其左侧轮廓中部,电场增强效应随节瘤缺陷尺寸增大而增强。实验上,在清洁的基板表面喷布单分散SiO2微球作为人工节瘤种子,采用电子束蒸发制备法完成多层全反膜的制备,采用R-on-1方式对薄膜样品进行激光损伤测试。结果表明,薄膜的损伤阈值随着节瘤缺陷尺寸增加而减小。通过综合分析电场增强效应、薄膜损伤测试结果及损伤形貌特征得出,薄膜损伤阈值降低是由于节瘤缺陷和薄膜中微缺陷共同作用的结果。     

Effect of pulsed laser parameters on in-situ TiC synthesis in laser surface treatment

Commercial titanium sheets pre-coated with 300-μm thick graphite layer were treated by employing a pulsed Nd:YAG laser in order to enhance surface properties such as wear and erosion resistance. Laser in-situ alloying method produced a composite layer by melting the titanium substrate and dissolution of graphite in the melt pool. Correlations between pulsed laser parameters, microstructure and microhardness of the synthesized composite coatings were investigated. Effects of pulse duration and overlapping factor on the microstructure and hardness of the alloyed layer were deduced from Vickers micro-indentation tests, XRD, SEM and metallographic analyses of cross sections of the generated layer. Results show that the composite cladding layer was constituted with TiC intermetallic phase between the titanium matrix in particle and dendrite forms. The dendritic morphology of composite layer was changed to cellular grain structure by increasing laser pulse duration and irradiated energy. High values of the measured hardness indicate that deposited titanium carbide increases in the conditions with more pulse duration and low process speed. This occurs due to more dissolution of carbon into liquid Ti by heat input increasing and positive influence of the Marangoni flow in the melted zone.     

不同沉积参量下ZrO2薄膜的微结构和激光损伤阈值

ZrO2采用X射线衍射(XRD)技术分析了不同充氧条件和沉积温度对ZrO2溥膜组成结构的影响,并对不同工艺下制备的薄膜的表面粗糙度和激光损伤阈值进行了测量。结果发现随着氧压的升高,ZrO2溥膜将由单斜相多晶态逐渐转变为非晶态结构,而随着基片温度的增加,溥膜将由非晶态逐渐转变为单斜相多晶态。同时发现随着氧压升高晶粒尺寸减小,而随着沉积温度增加,晶粒尺寸增大。氧压增加时工艺对表面粗糙度有一定程度的改善,而沉积温度升高,工艺对表面粗糙度的改善不明显。晶粒尺寸大小变化与表面粗糙度变化存在对应关系。激光损伤测量表明,氧压条件和沉积温度对ZrO2薄膜的抗激光损伤能力有着较大影响。     

Structural changes in tin oxide thin film with laser exposure

The effects of laser irradiation on the surface, structure and optical properties of SnO thin films deposited on glass substrates using electron beam evaporation, are investigated. The thin film samples are irradiated using fundamental beam at 1064 nm from Q-switched Nd:YAG pulsed laser with different power densities. Structural morphology of the film is investigated using XRD patterns and AFM image. Both XRD pattern and AFM image show increase in grain size of the film with increasing laser power density. Other optical phenomena, photoluminescence emission, transmission, refractive index determination and optical band gaps calculations are also carried out at various laser power densities. Results from all these investigations reveal expansion in grain size of the crystalline SnO thin film with increasing laser power density.     

Size and Interface Control of Novel Nanocrystalline Materials Using Pulsed Laser Deposition

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline materials with an accurate grain size and interface control. Using this method, the grain size in the case of Cu thin films was controlled by introducing a few monolayers of insoluble elements having high surface energy such as W, which increases interfacial energy and provides more nucleation sites. The grain size is determined by the thickness of Cu layer and the substrate temperature at which it transforms into islands (nanocrystalline grains) of fairly uniform size which we desgnate as self-assembling approach. Using this approach, the grain size was reduced from 160nm (Cu or Si (100) substrate) to 70–80nm for a simple W layer (Cu/W/Si (100)) to 4nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness of these films was evaluated using a nanoindentation technique, a significant increase in hardness from 2.0GPa for coarse-grained 180nm to 12.5GPa for 7nm films was observed. However, there is decrease in hardness below 7nm for copper nanocrystals. The increase in hardness with the decrease in grain size can be rationalized by Hall–Petch model. However, the decrease in slope and eventually the decrease in hardness below a certain grain size can be explained by a new model based upon grain-boundary deformation (sliding). We also used a similar materials processing approach to produce quantum dots in semiconductor heterostructures consisting of Ge and ZnO dots or nanocrystals in AlN or Al₂O₃ matrix. The latter composites exhibit novel optoelectronic properties with quantum confinement of phonons, electrons, holes and excitons. Similarly, we incorporated metal nanocrystals in ceramics to produce improved mechanical and optical properties.     

Tailored internal coating of components by PLD and pulsed laser evaporation

An advanced PLD technique combining laser ablation and laser induced thermal evaporation was introduced to deposit thin films onto the inner surfaces of components.Beside the well known film properties of the classical PLD, like high reproducibility, smooth surface and high thickness precision, this novel combination of laser ablation and evaporation is characterized by improved or extended properties in terms of microstructure, deposition rate and possible layer thickness. The extension of the conventional PLD process allows for the co-deposition of dense, amorphous films as well as columnar grown or even porous films with thicknesses up to several tens of micrometers.In a first successful application of the novel process, tailored thermal barrier coatings (TBCs) for combustion chambers were realized. A remarkable result was that these coatings sustained very large strains of about 5% without notable delaminations. Under hot gas testing in model combustion chambers, the PLD-TBCs showed very promising behavior with excellent adhesion.Super hard, amorphous carbon films (DLC) deposited onto the inner surfaces of small components by this PLD technique are characterized by a Youngs modulus of about 400–500 GPa and a low friction coefficient of about 0.1. Due to its layered structure, with graded material density and hardness, this DLC exhibits relatively low internal compressive stresses of about -1...-2 GPa. PACS 81.15.Fg; 68.55-a; 46.50+a     

Surface modification of pure titanium by pulsed electron beam

The microstructure, hardness and corrosion resistance of commercially pure Ti treated by low energy high current pulsed electron beam (LEHCPEB) have been investigated. The thin near-surface melted layer rapidly solidified into β and subsequently transformed into ultrafine α′ martensite. This has led to a drastic improvement of the corrosion properties and a significant increase (more than 60%) in hardness of the top surface.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

Research of rapid and direct thick coatings deposition by hybrid plasma-laser

In this paper, a new technology of direct and rapid thick coatings fabrication with hybrid plasma-laser deposition manufacturing (PLDM) technology is advanced which is also suitable for functional prototyping and tooling applications. It emphasizes on the influence of laser to the microstructure of coatings and physical properties of surface layers. Unlike the direct rapid plasma deposition manufacturing (PDM), in hybrid plasma-laser deposition manufacturing, the laser beam enters into plasma arc beam and focuses on the molten pool as assisting heat energy. A 280 W pulsed Nd:YAG (yttrium-aluminum garnet) laser machine is used to inspect the effect. The experimental results show that the laser beam could improve the surface state; the elements distribution of coatings deposited by PLDM was even; the physical properties of surface coatings fabricated with PLDM were better than that deposited by PDM.     

Laser glazing of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaalumminate (LMA) is an important candidate for thermal barrier coatings due to its thermal stability and low thermal conductivity. On the other hand, laser glazing method can potentially make thermal barrier coatings impermeable, resistant to corrosion on the surface and porous at bulk. LMA powder was synthesized at 1600 °C by solid-state reaction, pressed into tablet and laser glazed with a 5-kW continuous wave CO₂ laser. Dendritic structures were observed on the surface of the laser-glazed specimen. The thicker the tablet, the easier the sample cracks. Cracking during laser glazing is attributed to the low thermal expansion coefficient and large thickness of the sample.     

Effect of laser parameters on properties of surface-alloyed Al substrate with Ni

Experimental investigations were carried out to examine the influence of the spot size and peak-power density of a pulsed Nd:YAG laser on the depth of the alloyed layer, the microstructure and the hardness in laser surface alloying of Al with Ni. It was found that the effect of both the peak-power density and the amount of energy absorbed from the laser beam on the depth of the alloyed layer and hardness must be considered simultaneously. In this work, the hardness of the alloyed layer was found to be 10–15 times the value for base Al.     

Numerical study on the thermo-stress of ZrO2 thermal and barrier coatings by high-intensity pulsed ion beam irradiation

This paper studies numerically the thermo-mechanical effects of ZrO2 thermal barrier coatings (TBCs) irradiated by a high-intensity pulsed ion beam in consideration of the surface structure.Taking the deposited energy of ion beams in TBCs as the source term in the thermal conduction equation,the distribution of temperature in TBCs was simulated.Then,based on the distribution,the evolution of thermal stress was calculated by the finite element method.The results show that tensile radial stress formed at the valley of TBC surfaces after irradiation by HIPIB.Therefore,if cracks happen,they must be at valleys instead of peaks.As for the stress waves,no matter whether through peak or valley position,tensile and compressive stresses are present alternately inside TBCs along the depth direction,and the strength of stress decreases with time.     

Temperature measurement during laser heating of thin films using a temperature-sensitive phosphor

A phosphor with temperature-dependent lifetime has been used to measure the temperature distribution produced by laser heating of a thin film surface. A gold thin film deposited on a quartz substrate is coated with 40 m film of the phosphor material. A cw argon ion laser (476 nm) beam is split into two beams, with the more intense beam focused to 15 m (1/e² radius) to heat the film through the quartz substrate. The weaker probe beam is chopped and focused tightly using a microscope objective to excite the phosphor from the other side. The spatial variation in lifetime, and hence the temperature distribution, is obtained by scanning the probe beam over the heated region. The temperature distribution measured for different film thickness's is compared with calculations using a finite element model. The calculated temperatures at the gold surface near the laser beam are higher than the experimentally measured values, and agree only when the heat-sinking effect of the phosphor material is taken into account. The results suggest that a phosphor layer thinner than a micron will be required (for 15 m laser spot size) so as not to perturb the temperature of the gold layer.     

Molecular structure and optical properties of PTFE-based nanocomposite polymer-metal coatings

The molecular organization of polytetrafluoroethylene (PTFE) thin coatings with incorporated Ag, Cu, and Mo nanoparticles that are deposited from an active gas component has been studied. Polyethylene terephtalate film coated by aluminium served as a substrate. The active gas component was produced by electron beam dispersion of original components in vacuum. The effect of metal particle size and its nature on the molecular structure of coatings have been investigated. Dichroism of thin nanocomposite coatings has been examined by polarized Fourier transform infrared spectroscopy using an attenuated total reflection unit. The morphology of the coatings has been analyzed by transmission (TEM), atomic-force (AFM), and scanning electron (SEM) microscopy. It is found that introduction of a metal (Ag or Cu) yields oriented layers at a lesser efficient thickness of a coating. The surface plasmon resonance of such structures was studied by measuring optical absorption of the coatings in the ultraviolet and visible ranges. The results show that the composite coatings containing Ag clusters are diameter less than 30 nm and absorb within the short-wave range from 400 to 550 nm.     

Surface modifications for mechanical applications

Chemical and high energy beam conversion coatings, as well as PVD thin films, are characterised to correlate microstructures and mechanical properties. In particular, thermochemical boriding and laser surface melting are considered to produce conversion coatings on iron alloys, and physical vapour techniques to deposit thin films of titanium nitride on iron. The mechanisms leading to selected microstructures and, consequently, to improved surface and interface properties are discussed.     

TC_4合金TiN激光表面合金化层的组织和硬度研究

通过采用CO_2激光对TC_4合金进行TiN表面合金化处理,探讨了激光功率对合金化层组织和硬度的影响。结果表明,激光合金化试样存在组织不同的三个区域,分别为TiN合金化层,基底熔凝层和淬火层。TiN合金化层由钛合金基体和TiN组成,其中TiN呈现颗粒和树枝晶两种形态。基底熔凝层为定向生长的柱状晶,基底淬火层为针状马氏体。TiN激光合金化层的硬度在700～1100HV之间,约为TC_4合金的2～4倍。     

磁场辅助激光熔覆制备Ni60CuMoW复合涂层

采用磁场辅助激光熔覆技术,在Q235钢表面制备了Ni60CuMoW复合涂层,借助SEM,EDS 和XRD 等表征手段对涂层进行了微观组织和物相分析,利用维氏硬度计测试了复合涂层截面的显微硬度分布,通过摩擦磨损实验和电化学测试系统研究了复合涂层的磨损性能和耐腐蚀性能。研究结果表明:涂层主要由-Ni,Cu）固溶体、硅化物和硼化物组成,Cr3Si晶粒细化且均匀致密;磁场辅助作用下,激光熔覆涂层平均显微硬度达到913HV0.5,为无磁场辅助涂层的1.5 倍,磨损失重仅为无磁场涂层的36%,自腐蚀电位上升了100 mV,腐蚀电流密度降低了70%,耐磨耐蚀性能得到了显著改善。