Fibre laser micro-cladding of Co-based alloys on stainless steel

Laser micro-cladding by powder injection has been used to produce Co-based alloy clad strips with geometrical characteristics in the micrometer range (width: 45 µm, height: 15 µm). A new experimental set-up based on the use of a single mode fibre laser and a powder microfeeder was used to produce such coatings. A systematic study on the influence of several processing parameters (laser power, processing speed, mean precursor particle size) on the geometric features of the clad strips was carried out. Moreover Young's modulus and hardness measurements of the micro-clad strips allow affirming that these micro-cladding coatings maintain the mechanical properties typical from this hardfacing alloy.Reparation of defective microparts, surface functionalisation of small areas, or rapid fabrication of prototypes are areas of application of this rapid one step microcoating technique.     

激光热处理发展现状

报导了国内、外激光热处理设备、工艺、理论研究的概况；并重点概述了激光热处理工业应用和产业化发展的现状及市场动态。     

Unique corrosion and wear resistant identification tags via LISI™ laser marking

A method of marking metal items with unique corrosion and wear resistant identification tags has been developed at the Center for Laser Applications (CLA) at the University of Tennessee Space Institute (UTSI). The method, coined LISI™ laser marking, uses a laser beam to melt a pre-placed powder mix of alloying compounds into the surface of the part in a desired pattern. The formulation of the powder mix is designed to enhance the surface properties of the laser processed areas and protect the identification tags from the specific corrosion and aggressive wear during transportation, operation and overhaul. The specific marking preparation steps, typical processing conditions and a representative set of results are presented for LISI™ laser marking of AISI 4340 steel with Cr-CrB₂, and 2024 aluminum with WC. Results include transverse cross-sectional views and hardness measurements of the marked material, and data on the concentration of alloying compounds within the laser melted layer. The corrosion and wear resistance of LISI™ data matrix marks was also investigated.     

Laser surface coating of Fe-Cr-Mo-Y-B-C bulk metallic glass composition on AISI 4140 steel

Fe-based bulk metallic glasses exhibit very high hardness, elastic modulus/limit and wear/corrosion resistance. In the present investigation, an attempt has been made to develop an amorphous coating with Fe₄₈Cr₁₅Mo₁₄Y₂C₁₅B₆ bulk metallic glass on AISI 4140 substrate by laser surface processing. Following coating, the microstructure and phase aggregate were analyzed by scanning electron microscope and X-ray diffraction, respectively. Microhardness and wear resistance were assessed using Vickers microhardness tester and ball-on-plate wear testing machine, respectively. The coating thickness varied directly with incident laser power and interaction time. Despite trials with wide range of process parameters, the present experiments were unable to retain complete amorphous surface microstructure after laser surface coating. Numerical prediction of the thermal profile and related parameters suggest that the cooling rate and thermal gradient experienced by the coated zone were fairly high. Yet failure to retain amorphous/glassy microstructure of an otherwise bulk metallic glassy alloy suggests that compositional changes (solute redistribution) within the coated zone and across the coating-substrate interface are responsible for nucleation and growth of crystalline phases from the melt. However, correlation between coating parameters and surface microstructure and properties allowed determination of the optimum conditions that ensured fine grained uniform microstructure with a significant improvement in hardness and wear resistance.     

机械合金化制备Fe-Cr-Mn-N奥氏体不锈钢厚熔覆涂层的研究

本实验采用机械合金化方法制备了Fe₇₆Cr₁₂Mn₁₂N合金粉末,研究其机械合金化过程,并对机械合金化的机制进行探讨。研究表明,棒磨4小时时粉末就可以完全合金化,并且随着棒磨时间增加,衍射峰逐渐宽化,衍射强度逐渐降低。粉末颗粒形貌也逐渐类球形化。机械合金化得到的非球形固溶体粉末也可用于激光熔化沉积(LMD)增材制造技术,解决了LMD对球形粉末的局限性,机械合金化粉末通过LMD技术得到的厚熔覆涂层具有较好的耐蚀性,其物相结构是BCC+FCC的双相结构,同时在打印过程中有Cr₂N生成,维氏硬度最高达到456.3HV。     

亚微米陶瓷颗粒补强合金化涂层的研究

以亚微米级TiC和CrxCy合金混合粉末为原料,采用激光合金化技术在球铁表面制备出耐磨、耐腐蚀、耐高温的合金化层.利用XRD、SEM、EDS等分析了激光合金化层的相组成及微观组织,并测试了激光合金化的显微硬度,在室温干摩擦条件下测试了涂层的耐磨性.结果表明,合金化涂层致密,硬度(HV)达930(测试载荷2 000 N),干摩擦条件下材料磨损量是基材球墨铸铁的1/16,合金化涂层的耐磨性有一定的提高.     

镁表面铝熔覆层微观组织的观察

为改善镁合金表面的耐腐蚀性能,以铝粉作为激光熔覆材料,在镁表面进行激光熔覆,得到了无气孔、无裂纹且与基体能够良好结合的熔覆层结构.研究了激光工艺参数对该熔覆层的微观组织的影响.     

Laser cladding of Ni/Cu/Al functionally graded coating on magnesium substrate

Laser cladding of graded multi-layer Ni/Cu/Al coatings on magnesium substrates was performed with the aim of improving the inherently low corrosion and wear resistance of magnesium. The quality of the coating was found to be good: the interfaces between the different layers are generally free from any major solidification defects such as porosity and cracks. Despite the fact that considerable mixing had occurred in the Al layer, the top Ni layer was free from Al and Mg. The top Ni layer comprises a single solid solution (Ni) phase; its corrosion and wear resistance was found to be excellent. The wear properties of the coating were explained in terms of stacking fault energy and the ratio of hardness to elastic modulus.     

高铬铸铁中铌的研究综述

论述了高铬铸铁的发展和应用情况,介绍了铌在高铬铸铁中的形态和对组织的作用,以及含铌高铬铸铁的性能特点,在耐磨领域、堆焊领域和冷轧辊领域的应用情况;综述了国内外这些方面的研究成果。     

Microstructure and tribological properties of Cuss-toughened Cr–Cu–Si metal silicide alloys

Wear resistant Cr–Cu–Si metal silicide alloys with different Cu contents were fabricated by the laser melting process. The Cr–Cu–Si alloys have a similar microstructure consisting of the Cr₅Si₃/CrSi dual-phase primary dendrites and the interdendritic Cu-based solid solution (Cu_ss). The Cu content has no effect on the phase constitutions of the alloys. The Cr₅Si₃/CrSi dendrite volume fraction and hardness of the Cr–Cu–Si alloys decrease with the increasing Cu content. Wear test results indicate that all the Cu_ss-toughened metal silicide alloys have excellent wear resistance and low coefficient of friction. Wear resistance increases and friction coefficient decreases with the decreasing Cu content.     

Effect of laser surface treatment on corrosion and wear resistance of ACM720 Mg alloy

A creep resistant Mg alloy ACM720 was subjected to laser surface treatment using Nd:YAG laser equipped with a fiber optics beam delivery system in argon atmosphere. This treatment was found to be beneficial for the corrosion and wear resistance of the alloy. Long-term linear polarization resistance and Electrochemical Impedance Spectroscopy measurements confirmed that the polarization resistance values of laser surface treated alloy were twice as high as that for the untreated alloy. The improved corrosion resistance was attributed to the absence of the second phase Al₂Ca at the grain boundary, microstructural refinement and extended solid solubility, particularly of Al, in α-Mg matrix owing to rapid solidification. The laser treatment also increased surface hardness two times and reduced the wear rate considerably due to grain refinement and solid solution strengthening.     

Laser cladding of high-entropy alloy on H13 steel

High-entropy alloy layer up to 150 lm in thickness was formed on H13 substrate with a metallurgical bonding at the coating/substrate interface. Simple solid solution phases were formed in the coating layer with a typical microstructure composed of both dendrite and interdendrite. The microstructure at the top of the cladding zone consists of equiaxed grains while that at the bottom consists of columnar grains. The coating layer exhibits great enhancement in microhardness and wear resistance compared with the H13 substrate.     

Laser surface modification using Inconel 617 machining swarf as coating material

A single-stage, blown powder laser cladding process is used to deposit a protective layer of Ni-based alloy Inconel 617 on mild steel substrates. A Design of Experiments methodology is used to analyse the effects of the major laser cladding processing parameters on the deposited layer characteristics. Layer thickness, microstructure, dilution, elemental composition and corrosion resistance are analysed and correlated with the processing parameters and the overall effectiveness of the protective coating assessed. The work is different in that the protective material, usually in the form of costly powder, is in this case virtually cost-free and simply recycled from machining waste without any costly atomisation or similar process. The results show a number of significant relationships between the processing parameters and the effectiveness of the protective coating. The layer thickness and hardness were found to increase with the mass feed rate and decrease with an increase in laser power. A mainly columnar dendritic microstructure was observed in the clads. There was no evidence of significant bonding defects, trapped unmelted particles or porosity under most conditions. In all samples, the coatings displayed significant higher corrosion resistance than the mild steel sample.     

模具激光表面熔覆设备和技术的进展

概述了激光表面熔覆技术近年来发展的概况;激光熔覆工艺,激光表面熔覆技术装备,以及熔覆材料概况。文中介绍了轧辊激光堆焊层厚10mm以上（单面）的新要求,以及激光熔覆层高硬度（HRC60－65）的新要求。     

Characterization on laser clad nickel based alloy coating on pure copper

Nickel based alloy coating has been successfully deposited onto pure copper surface by laser cladding with coaxial powder feeding. Coating with thickness in the region of 1.5 mm can be obtained by depositing two layers of overlapping laser clad tracks. The microstructure observation from optical microscopy and scanning electron microscopy indicated that the coating was free of cracks and pores, and soundly bonded with the substrate. The X-ray diffraction analysis results showed that the coating was mainly composed of γ-(Ni, Cr, Mo, W) solid solution, some carbides and silicides. The average hardness of the coating was about HV_0.1 360, which was about 5 times that of the pure copper. The dry sliding wear tests showed the wear resistance of copper was significantly improved after laser clad nickel based alloy coating.     

Effect of power on microstructure and properties of laser cladding NiCrBSi composite coating

A laser clad NiCrBSi composite coating was fabricated on the surface of 42CrMo steel using 6?kW fibre laser. The morphology and composition of the composite coating formed under different powers were studied using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction spectroscopy. The microhardness and wear resistance were measured with a MICROMET-5103 digital microhardness tester and a MM-200 ring-block wear testing machine, respectively. The results showed that the cladding layer and the substrate have good metallurgical bonding. The microstructure nearing the fusion line is a columnar grain and that of the cladding layer is mainly a cellular grain. The main phases of the laser cladding layer are γ-Ni, (Fe,Ni), M₇C₃, M₂₃C₆ and CrB. The dilution rate of the laser cladding layer increased with the increase of laser power. The microhardness of the cladding layers decreased with the increase of laser power, and wear resistance of the cladding layer first increased and then decreased with the increase of laser power. When the laser power was 2000?W, the wear resistance of the composite coating was at its highest.     

Microstructure and anti-oxidation behavior of laser clad Ni-20Cr coating on molybdenum surface

A Ni-20Cr coating was deposited on a molybdenum substrate by laser cladding. The observation of the microstructure by SEM demonstrates that the coating is free of cracks and pores, and metallurgically bonded to the substrate. XRD and EDS analysis results show that some dilution occurs at the coating/substrate interface and that Mo combines with Ni-20Cr, to form a Ni-Cr-Mo alloy coating with slight oxidation. The oxidation behavior of the coating indicates that the laser clad Ni-20Cr coating can effectively prevent oxidation of molybdenum at 600 °C in air. The oxide scale formed on the coating surface by oxidation in air is composed of NiO, Cr₂O₃ and NiMoO₄.     

H90/钢反向凝固复合层的厚度变化规律

以08Al钢作为母带，H90黄铜作为复合材料，系统地研究了反向凝固复合工艺浸渍复合时间、铜液的温度以及钢带的预热温度和厚度对黄铜复合层厚度变化的影响规律。研究结果表明：随浸渍复合时间的增加，复合层的厚度变化经历了凝固生长、平衡相持和回熔3个阶段；铜液温度以及钢带预热温度和厚度变化不改变复合层厚度的变化规律，但对各阶段的持续时间和复合层的厚度有影响；钢带越厚以及铜液的温度和钢带的预热温度越低，复合层的厚度越厚。     

Sliding wear resistance of TiCp reinforced titanium composite coating produced by laser cladding

Titanium metal matrix composite coatings (MMC) are considered to be important candidates for high wear resistance applications. Laser cladding (LC) by coaxial powder feeding is an advanced coating manufacturing process, which involves laser processing fine powders into components directly from computer aided design (CAD) model.In this study, the LC process was employed to fabricate TiC particle reinforced Ti6Al4V MMC coatings on Ti6Al4V hot rolled samples.The experimental results show that during LC process, TiC particles are partially dissolved into melted Ti-base alloy and precipitated in the form of TiC dendrites during cooling.Dry sliding wear properties of these MMC layers have been compared with substrate materials wear. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show improved tribological properties connected with the TiC_p addition and the LC process parameters.     

Friction and wear of MoS2 films on laser textured steel surfaces

Incorporation of solid lubricant into micro-reservoirs produced by Laser Surface Texturing (LST) and its effect on the tribological properties of surfaces under dry friction is studied. The density of the dimple reservoirs and the height of the bulges around them are investigated in terms of the longevity of solid lubricant films burnished on LST steel surfaces. Friction tests were performed using a ball-on-flat device. Optimum density (40-50%) of the dimples is revealed. It is shown that the adhesion of solid lubricant in the space between the dimples is provided by mechanical engagement of particles in the rough surface and by smearing the solid lubricant around the dimples. Best results are obtained with the surfaces that were lapped to half of the height of bulges. Long wear life of burnished film on LST steel surfaces is apparently provided by preservation of thin MoS₂ film around the bulges and by supply of solid lubricant from the dimples to the surface.