硅钢表面激光熔覆高硅涂层对性能的影响

用Nd:YAG脉冲激光在低硅钢表面制备激光熔覆高硅涂层,研究了激光熔覆高硅涂层样品的组织和磁性能.结果表明,制备出的激光熔覆高硅涂层组织致密、无气孔和裂纹,且与基体有良好的冶金结合.经激光熔覆后硅钢表面存在熔覆区、界面结合区和热影响区.熔覆区的显微组织不均匀,随着与结合界面距离的增加,由柱状晶变为树枝晶,最终过渡到表层的细小树枝晶组织.熔覆层与基体之间的结合界面为平面晶组织,热影响区为马氏体组织.熔覆涂层的显微硬度远高于低硅钢基体,其主要原因是涂层具有较高的Si含量,涂层中的α-Fe和γ-Fe双相组织也导致了硬度的提高.激光熔覆高硅涂层硅钢样品经扩散退火后具有室温铁磁性,Si含量的提高使其室温直流磁性能优于原始低硅钢.     

基于工业合金激光熔覆制备Fe基非晶涂层

以FeCoCrMoCBY块体合金为熔覆材料,采用激光熔覆在低碳钢表面制备非晶涂层,探讨不同激光功率对涂层成形及组织的影响,通过显微硬度仪、电化学工作站测试涂层显微硬度及耐腐蚀性能。研究结果表明,其他参数不变,激光功率为17.6~20.8 W时,涂层成形良好,与基材呈典型冶金结合。随激光功率增加,涂层稀释率升高,裂纹倾向增大,非晶化程度降低。激光功率为17.6 W时,涂层主要由非晶组成,稀释率低于24.2%,结构致密,包括热影响区、熔合区和熔覆区;涂层平均显微硬度为1 330HV,约高于基材9倍,在3.5%NaCl溶液中的耐腐蚀性能明显优于316L不锈钢。     

钛合金表面激光熔覆Co-WC复合涂层的组织及力学性能

在钛合金TC4(Ti-6Al-4V)表面利用激光熔覆Co-WC复合涂层,利用扫描电镜(SEM)、能谱分析仪(EDS)和硬度计研究涂层的微观组织及力学性能。结果表明,Co+15%WC、Co+30%WC及Co+45%WC试样熔覆层与基体都实现了冶金结合,表层激光熔覆层涂层内组织均匀致密,没有气孔、裂纹等缺陷。而Co+60%WC试样虽然熔覆层与基体界面也为冶金结合,但是熔覆层内发生了开裂。激光熔覆Co-WC复合熔覆层的宏观洛氏硬度较TC4基体提升了2~3倍,合金粉末中WC的含量比例越高,熔覆涂层试样的宏观洛氏硬度的提升越明显。4种熔覆试样从基体到熔覆层表面,其显微硬度都是逐渐升高的趋势,熔覆层表面显微硬度达到TC4基体的显微硬度的近3倍。在Co基合金粉末中添加WC的最大含量为45%,高于45%之后,熔覆层显微硬度值下降。     

激光熔覆镍包石墨和石墨烯复合涂层组织和性能分析

采用激光熔覆技术在40CrNi2Si2MoV钢基体表面分别制备镍包石墨和石墨烯复合涂层,测试分析了涂层的物相、微观组织、显微硬度以及摩擦磨损性能。结果表明:激光熔覆涂层主要由γ-Ni、Ni_3B、M_(23)C_6和M_7C_3相组成,均为树枝晶和共晶组织;从熔覆层表面到基体的显微硬度呈现出四个台阶,硬度最高值出现在亚表层;两种涂层均具有较好的减摩性能和耐磨性能。     

激光熔覆Al65Cu2OCr15准晶态合金的相选择问题

研究了在45#钢基体表面激光熔覆Al65Cu20Cr15准晶态合金过程中，工艺参数激光功率（P）和扫描速度（v)对激光熔覆涂层相结构的影响。结果表明，激光功率和扫描速度的变化使基体材料对熔覆涂层的稀释率发生改变，随着激光熔覆稀释率的增加，熔覆层的相结构依次为λ＋I，I＋β，β，β＋d，d Fe，激光熔覆涂层相结构的差异使涂层具有不同的显微硬度，参数δ（P／v)决定激光熔覆过程的稀释度，从而直接影响激光熔覆准晶涂层的相结构，涂层的表面显微硬度也因涂层相结构的不同而有所差异。     

钛合金表面激光熔覆Ni基梯度涂层的研究

为了改善Ti6Al4V钛合金表面耐磨性能和抗高温氧化性能,采用CO2激光在Ti6Al4V钛合金表面进行激光熔覆Ni基梯度涂层试验.利用扫描电镜和显微硬度计等手段分析了熔覆层组织,测试了基体和熔覆层的显微硬度.结果表明,采用适当的工艺参数,可以在钛合金表面获得连续、均匀、无裂纹和气孔的熔覆层.熔覆层组织由树枝晶和晶间共晶组织构成,并与基体形成牢固的冶金结合.由基体到表面,显微硬度过渡平稳,呈明显梯度渐变特征.     

激光熔覆微-纳米碳化钨复合涂层结构与性能研究

以微米和纳米级晶粒Co包碳化钨为增强相,自熔合金粉末Ni60B为粘结剂,采用激光熔覆的方法在45钢表面制备出微-纳米碳化钨增强Ni基合金复合涂层.采用扫描电镜、X射线衍射等手段对粉末和涂层的相结构、显微组织等进行了分析观察,采用显微硬度计分析了涂层表面硬度随成分的变化规律和截面硬度的分布曲线.结果表明,纳米碳化钨粉末的添加有助于改善涂层的熔覆性能和提高涂层的表面硬度.     

45钢表面Ni基激光熔覆层的耐蚀性能

为改善45钢表面的力学性能和耐蚀性,在相同功率下采用不同扫描速率在其表面激光熔覆制备了Ni基(Ni35A)复合涂层。利用金相显微镜、X射线衍射仪、显微硬度计和电化学腐蚀测试系统对熔覆试样进行组织形貌、相组成、显微硬度和耐蚀性能分析。结果表明:熔覆试样由熔覆层、结合区和基体3部分组成;熔覆层组织细密并与基体冶金结合,扫描速率过大时易形成裂纹;熔覆层主要由FeNi3和Ni3B相组成,不同速率所得熔覆层显微硬度均超过400 HV;扫描速率为500 mm/min时熔覆试样自腐蚀电位提高了40 mV。     

TC4钛合金表面激光熔覆NiCrCoAlY-Cr3C2复合涂层的摩擦和高温抗氧化性能

为了提高TC4 钛合金表面摩擦磨损和高温抗氧化性能,以 NiCrCoAlY+20%(质量分数)Cr3 C2 混合粉末作为熔覆粉末,采用激光熔覆技术在TC4 钛合金表面制备NiCrCoAlY-Cr3 C2 复合涂层,利用OM,SEM,XRD,EDS等分析涂层的显微组织和物相组成;采用 HXD-1 000TB 显微硬度计测量涂层显微硬度;采用 MMG-500 三体磨损试验机与 WS-G1 50 智能马弗炉对涂层和基体进行摩擦磨损及高温抗氧化实验.结果表明:利用激光熔覆技术在 TC4 钛合金表面可以制备形貌良好、无裂纹和气孔等缺陷的复合涂层.熔覆区显微组织结构致密,多为针状晶和树枝晶;结合区的显微组织主要由平面晶、胞状晶和树枝晶组成,生成了多种可提高耐磨性和高温抗氧化性的碳化物、氧化物和金属间化合物.复合涂层的最高显微硬度为 1344HV,约为钛合金基体 350HV的 3.8 倍;复合涂层的摩擦因数为0.2～0.3,较钛合金基体的摩擦因数0.6～0.7 明显下降;相同条件下复合涂层的磨损失重为0.00060 g,是钛合金基体磨损失重 0.06508 g 的0.9%;恒温 850 ℃氧化 100 h后复合涂层氧化增重为 6.01 mg·cm－2 ,约为钛合金基体氧化增重 25.10 mg·cm－2的24%.激光熔覆技术有效改善了TC4 钛合金表面的摩擦磨损和高温抗氧化性能.     

熔覆电流对Inconel 625涂层组织与性能的影响

为了提高合金钢表面熔覆镍基合金涂层的质量,研究工艺参数对镍基合金涂层性能的影响,采用等离子熔覆技术制备Inconel 625涂层,利用金相显微镜、XRD观察并测试涂层的显微组织形貌与物相组成,采用电化学方法、显微硬度测试以及摩擦磨损试验研究了熔覆电流对涂层耐蚀性能和耐磨性能的影响规律。结果表明：熔覆电流改变了Inconel 625涂层的组织形貌和γ-Ni相不同晶面的择优倾向,当熔覆电流为80 A时获得组织细小、结构致密、(111)晶面择优生长的镍基合金涂层;与熔覆电流分别为60,70,90 A条件下制备的涂层相比,该涂层的腐蚀倾向最小,腐蚀速率最低,钝化区间最大,耐蚀性能优异;Inconel 625涂层的显微硬度值显著大于基体,当熔覆电流为80 A时涂层的显微硬度值最大,约为基体的1.89倍,耐磨性能最佳。     

Adaptable and Reprogrammable Surfaces

Establishing control over chemical reactions on interfaces is a key challenge in contemporary surface and materials science, in particular when introducing well‐defined functionalities in a reversible fashion. Reprogrammable, adaptable and functional interfaces require sophisticated chemistries to precisely equip them with specific functionalities having tailored properties. In the last decade, reversible chemistries—both covalent and noncovalent—have paved the way to precision functionalize 2 or 3D structures that provide both spatial and temporal control. A critical literature assessment reveals that methodologies for writing and erasing substrates exist, yet are still far from reaching their full potential. It is thus critical to assess the current status and to identify avenues to overcome the existing limitations. Herein, the current state‐of‐the‐art in the field of reversible chemistry on surfaces is surveyed, while concomitantly identifying the challenges—not only synthetic but also in current surface characterization methods. The potential within reversible chemistry on surfaces to function as true writeable memories devices is identified, and the latest developments in readout technologies are discussed. Finally, we explore how spatial and temporal control over reversible, light‐induced chemistries has the potential to drive the future of functional interface design, especially when combined with powerful laser lithographic applications.     

Atomic-scale visualization of oxide thin-film surfaces

The interfaces of complex oxide heterostructures exhibit intriguing phenomena not observed in their constituent materials. The oxide thin-film growth of such heterostructures has been successfully controlled with unit-cell precision; however, atomic-scale understandings of oxide thin-film surfaces and interfaces have remained insufficient. We examined, with atomic precision, the surface and electronic structures of oxide thin films and their growth processes using low-temperature scanning tunneling microscopy. Our results reveal that oxide thin-film surface structures are complicated in contrast to the general perception and that atomically ordered surfaces can be achieved with careful attention to the surface preparation. Such atomically ordered oxide thin-film surfaces offer great opportunities not only for investigating the microscopic origins of interfacial phenomena but also for exploring new surface phenomena and for studying the electronic states of complex oxides that are inaccessible using bulk samples.     

Contact angle measurement on micropatterned surface using sessile drop shape fit profile detection

Abstract

Micro-nano patterned surfaces have significant applications in various fields as they behave differently under the effect of catalysts, magnetic energy, electronic emission/absorption, optics and biological cells. Engineering these topologies demands a better understanding of the contact angle. The current contact angle measurement techniques assume the drop to be a perfect sphere, neglect gravitational and molecular dispersion effects; thereby leading to inaccuracies. This is because the micro-machined surfaces exhibit sub-micrometre scale porosity and pattern dimensions are comparable to the droplet size, resulting in composite interfaces at micro-nano scale. In this paper, the authors assessed the adaptability of conventional measurement techniques for textured surfaces and developed an algorithm that is based on curve fitting over sessile drop after edge detection. The algorithm performs edge detection, contact point identification and curve fitting and corrects uneven surfaces and was tested on micro-patterned surfaces fabricated over three different materials: polydimethylsiloxane, polystyrene and acrylic using laser.     

Differential laser absorption and thermal emission for remote identification of opaque surface coatings

We experimentally and theoretically studied the phenomenon of thermal emission from nonvolatile liquid surface coatings following heating with a pulsed CO(2) laser. The effects of thermal diffusion across the liquid-air and liquid-substrate interfaces as well as the full absorption spectrum of the liquid are addressed theoretically. The differential temporal and intensity characteristics of the thermal emission signal from the heated surface coating, resulting from the differential heat deposition profile for on- and off-resonance excitation, are shown to be useful for the purposes of identifying different surface contaminants. The application of this technique to standoff thermal imaging of contaminated surfaces is discussed.     

激光纹理化调控材料表面疏水性能研究进展

超疏水表面由于具有减阻、抗污、防水等独特性能,广泛应用于日常生活、军事、工业等场景,材料表面的微纳结构及化学成分对其超疏水性能有着重要影响。激光纹理化技术由于具有加工分辨率高、加工方式灵活、可加工材料多等优势,可用于制备疏水性能精确可控的表面微纳结构,在制造超疏水表面方面有着广阔的应用前景。首先,介绍了激光纹理化的作用机理,综述了常用的激光纹理化方式,如激光直接写入法、激光干涉图案化法及激光诱导周期性结构法等,并介绍了激光参数对微纳结构的影响。根据表面微纳结构的形貌、周期及尺寸特点对激光纹理化制备的表面分层微纳结构进行了总结归纳,包括覆盖随机纳米结构或激光诱导周期性结构的微沟槽、微网格、微柱及微峰,重点介绍了分层微纳结构的制备方式及微纳结构对疏水性的影响。总结了提高分层微纳结构表面疏水性的后处理方式,包括环境老化、表面化学改性及热处理等,并介绍了后处理方式调控疏水性的作用机理。最后,对采用激光纹理化技术制备超疏水表面的应用前景进行了展望。     

Enhanced Optoelectronic Performance of a Passivated Nanowire‐Based Device: Key Information from Real‐Space Imaging Using 4D Electron Microscopy

Managing trap states and understanding their role in ultrafast charge‐carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)‐based devices. A key challenge is to selectively map such ultrafast dynamical processes on the surfaces of NWs, a capability so far out of reach of time‐resolved laser techniques. Selective mapping of surface dynamics in real space and time can only be achieved by applying four‐dimensional scanning ultrafast electron microscopy (4D S‐UEM). Charge carrier dynamics are spatially and temporally visualized on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT). The time‐resolved secondary electron images clearly demonstrate that carrier recombination on the NW surface is significantly slowed down after ODT treatment. This observation is fully supported by enhancement of the performance of the light emitting device. Direct observation of surface dynamics provides a profound understanding of the photophysical mechanisms on materials' surfaces and enables the formulation of effective surface trap state management strategies for the next generation of high‐performance NW‐based optoelectronic devices.     

Modeling of the rough-interface effect on a converging light beam propagating in a skin tissue phantom

Light distribution in a strong turbid medium such as skin tissue depends on both the bulk optical properties and the profiles of the interfaces where mismatch in the refractive index occurs. We present recent results of a numerical investigation on the light distribution inside a human skin tissue phantom for a converging laser beam with a wavelength near 1 mum and its dependence on the roughness of the interfaces and index mismatch. The skin tissue is modeled by a two-layer structure, and within each layer the tissue is considered macroscopically homogeneous. The two interfaces that separate the epidermis from the ambient medium and the dermis are considered randomly rough. With a recently developed method of Monte Carlo simulation capable of treating inhomogeneous boundary conditions, light distributions in various cases of interface roughness and index mismatch are obtained, and their relevance to the measurements of optical parameters of the skin tissue and laser surgery under the skin surface are discussed.     

Multimode laser Fizeau interferometer for measuring the surface of a thin transparent plate

A Fizeau interferometer utilizes a multimode laser as a light source for testing thin transparent plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between two surfaces is equal to twice a multiple of the laser's effective cavity length. For three parallel surfaces, we can either adjust their separations or select a laser such that only two of the three surfaces meet the requirement of twice a multiple of the laser's effective cavity length.     

Effect of laser surface texturing on Si3N4/TiC ceramic sliding against steel under dry friction

In efforts to investigate the influence of the surface texturing on the Si₃N₄/TiC ceramic, laser surface texturing (LST) was performed on the Si₃N₄/TiC ceramic by an Nd:YAG laser and different geometrical characteristics of regular-arranged micro-grooved textures were fabricated on the surfaces. The tribological properties of the textured and smooth samples were investigated by carrying out sliding wear tests against steel balls under dry condition using a ball-on-disk tribometer. Effect of surface texturing on the stress distribution was studied by finite element method (FEM). Results show that the textured surfaces exhibited lower friction coefficient and excellent anti-wear properties compared with smooth surfaces. The tribological characteristics depended greatly on the size and density of the micro-grooves, and the geometrical characteristics of the surface textures have a significant effect on the tribological behavior. Among the patterns investigated, the wavy-grooved samples exhibit the lowest friction coefficient and wear rate; and a large texture density may be the best for reduction of friction and wear of textured samples. While, the wear rate of balls sliding against textured surfaces is larger than that of balls sliding against smooth surfaces. FEM results show that surface texturing can improve the stress distribution of contact interfaces and reduce stress concentration.