Microstructure and tribological properties of laser clad Ti2Ni3Si/NiTi intermetallic coatings

Wear resistant Ti₂Ni₃Si/NiTi full intermetallic composite coatings with a microstructure consisting of ternary metal silicide Ti₂Ni₃Si primary dendrites and interdendritic Ti₂Ni₃Si/NiTi eutectic were fabricated on a substrate of 0.2%C low carbon steel by the laser cladding process using Ti-Ni-Si alloy powders as the precursor materials. Microstructure of the coatings was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). Wear resistance of the laser clad Ti₂Ni₃Si/NiTi intermetallic coatings was evaluated under dry sliding wear test conditions at room temperature. Results indicate that the Ti₂Ni₃Si/NiTi intermetallic coatings have excellent abrasive and adhesive wear resistance under dry sliding wear test conditions because of the unique combination of high yield strength and toughness of the intermetallic compound NiTi and the high hardness, strong covalent dominant atomic bonds and possible strong hardness anomaly of the ternary metal silicide Ti₂Ni₃Si with MgZn₂ type Laves crystal structure.     

激光熔覆ZrB2-SiC增强Cu基复合涂层的微观结构与摩擦学性能

为了提高铜表面的强度和耐磨性,以复合粉末(Zr、Si、Ni包B4C、Cu)为原料,采用激光辅助原位合成技术,在纯铜基体表面制备了ZrB₂-SiC/Cu复合涂层。通过XRD、SEM和TEM分析了复合涂层的表面形貌、微观结构、相组成和界面结合,并测试了不同增强相含量熔覆层的硬度和摩擦学性能。结果表明：通过设计的原位化学反应成功在铜基体内合成了微米级针状ZrB₂和纳米级颗粒状SiC。增强相均与基体形成了清洁、无杂相的界面。2种不同维度与尺寸的增强体,通过多种强化机制,显著改善了复合涂层的力学性能;通过调整激光工艺参数可实现增强体尺寸的控制,随着增强相含量的提高,复合涂层的平均硬度和耐磨损性逐渐增加。当增强相含量为30%(质量分数,下同)时,复合涂层的平均硬度(HV0.2)为3028 MPa,约为纯铜的5.6倍。30%增强相涂层的载流磨损率与10%增强相的涂层相比,降低了约80%。较高含量增强相的复合涂层表现出优异的摩擦学性能。     

Microstructure and wear performance of gradient Ti/TiN metal matrix composite coating synthesized using a gas nitriding technology

Surface modification is an attractive method to enhance the surface hardness and wear resistance of titanium. In this paper, a continuous wave 2 kW Nd:YAG laser was used to synthesize Ti/TiN metal matrix composite coating on the surface of commercial pure titanium. The microstructure and the wear resistance of the synthesized metal matrix composite coating were investigated. The synthesized surface Ti/TiN metal matrix composite coating had a pronounced gradient microstructure through the melt depth. Good metallurgical bonding between the reinforcing phase of the metal matrix composite and the titanium matrix was observed. The hardness and wear resistance under block-on-ring dry sliding wear testing conditions of the synthesized Ti/TiN metal matrix composite coating were markedly enhanced.     

Microstructure and high-temperature wear behavior of laser clad Ni-Ti-Si ternary metal silicide coatings

Ni-Ti-Si ternary metal silicide coatings were fabricated on AISI 304 stainless steel by laser cladding process. The coatings consisted of Ni₁₆Ti₆Si₇ primary dendrite and interdendritic Fe-Ni-based solid solution γ and exhibited excellent abrasive and adhesive wear resistance under high temperature metallic dry sliding wear conditions. The excellent wear properties were attributed to the high hardness and covalent dominant atomic bond of the metal silicide Ni₁₆Ti₆Si₇. The dominant wear mechanism of the coating were delamination of the coating and material transfer from the mating surface.     

Microstructure development in laser forming of zirconium coatings on AZ91D magnesium alloy substrates

Zr-coatings were fabricated on AZ91D magnesium alloy substrates using laser forming by means of a blow powder technique. Multi-passes were required to form a pure Zr top coating layer on the AZ91D Mg substrate. The microstructure and phases of the coating were studied using XRD, EDS and SEM. The alloy element Al in AZ91 alloy was found to be important for the formation of a metallurgically bonded interface between the Zr coating and the matrix material. The coating can be classified as a three-layer structure with a pure Zr layer at the top surface. The development of the coating microstructure is explained with the aid of a schematic solidification scheme.     

化学复合镀层激光处理后基材组织与性能的研究

利用不同激光工艺参数对Ni-P-SiC化学复合镀层进行激光处理,运用扫描电镜、显微硬度计等对复合镀层基材的显微组织、硬度进行了综合分析,探讨了显微组织与硬度沿深度的变化规律.结果表明,当激光功率小于450 W,激光仅对镀层进行处理而对基材不产生影响;随着激光功率的加大,基材的显微组织及硬度发生了不同的变化.当激光功率大于450 W时,基材发生组织转变.500 W时基材表层组织为回火屈氏体 碳化物,显微硬度为350 HV0.1;当激光功率为550 W时基材表层组织为隐晶马氏体 碳化物,显微硬度为812 HV0.1,当激光功率为600 W时基材表层组织为针状马氏体 残留奥氏体,显微硬度为831 HV0.1.     

The corrosion behaviour of the aluminum alloy 7075/SiCp metal matrix composite prepared by spray deposition

Aluminum alloy 7075 and 7075/SiCp (MMC) were prepared by multi‐layer spray deposition method and the corrosion behaviour of them were studied by electrochemical measurements to study the effect of the addition of silicon carbide on the corrosion behaviour of the MMC. The electrochemical noise result shows that the amplitude of the potential noise of the composite is lower than that of the spray deposited 7075 alloy. The potentiodynamic polarization curves results show that both the cathodic oxygen reduction current density and the anodic dissolution current density of the 7075/SiCp MMC are less than those of the 7075 alloy. Thus, the addition of SiC particles increases the corrosion resistance of the MMC. This may be due to that the microstructure of the spray deposited MMC is compact and SiC particles are nonmetallic material, the addition of it minimizes the real corrosion area of the alloy.     

Phase constituents and mechanical properties of laser in-situ synthesized TiCN/TiN composite coating on Ti-6Al-4V

Laser in-situ synthesis technology at room temperature was applied to obtain TiCN/TiN composite coating. A pulsed Nd:YAG laser (wavelength 1064 nm) was used to melt the mixture of Ti and C powder. Pure nitrogen gas with a pressure of 0.4 MPa was introduced coaxially together with laser beam to the melting pool to react with Ti and C atoms and in-situ synthesize TiCN/TiN composite coating. The coating consists of TiC_0.3N_0.7, TiN and TiN_0.3, but the proportions of these three constituents vary with the laser power density. SEM results revealed that dendrites were oriented in accordance with the heat flow and a metallurgical bonding between the coating and the substrate was achieved. The in-situ synthesized TiCN/TiN composite coating, with a thickness of about 200 μm, increased the hardness and wear resistance compared to the bare Ti-6Al-4V substrate. A remarkable improvement of the average microhardness (3-4 times) and an enhancement of the wear resistance (10-11 times) are observed by laser in-situ synthesizing TiCN/TiN composite coating.     

Microstructure and properties of laser cladding FeCrBSi composite powder coatings with higher Cr content

FeCrBSi alloy powder with higher Cr content was used for laser cladding by employing a 3 kW solid-state laser. Ni- and Fe-based alloy powders, which were more resistant to cracking, were added into FeCrBSi alloy powder with higher Cr content to increase the ductile phases, lower thermal expansion coefficient, and reduce the crack sensitivity of the cladding layer. FeCrBSi alloy powder with higher Cr content combined Ni- and Fe-based alloy powder were cladded on the substrates, which yield two different phases. The hard phases of the cladding layer were mainly composed of carbide phase M₂₃C₆, and the ductile phases which played a lubrication function in the cladding layer were mainly composed of austenite γ-Fe and γ-Ni. The ductile phases increased by adding Ni- and Fe-based alloy powder into FeCrBSi alloy powder with higher Cr content, and the hard phases became sparser relatively. Smooth cladding layers, which were free of macroscopic pores, cracks and void between the adjacent tracks, were achieved. Therefore, the toughness of the cladding layer was improved, and the crack tendency was reduced. Three kinds of composite powder were obtained. The composition and morphology of the cladding layer were analyzed, and the microhardness between the hard phases and the ductile phases was compared. The average microhardnesses of the three cladding layers varied from HV_0.2 760 to HV_0.2 950.     

High temperature behaviour of NiCrAlY coatings made by laser cladding

The oxidation behaviour of NiCrAlY coatings made by laser cladding on Hastelloy X is presented in this study. Laser cladding is an alternative method to thermal spraying for the production of bond coats. Comparable dense layers with approximately zero porosity should improve the oxidation behaviour. The oxidation behaviour of the coated specimens was assessed by air furnace oxidation tests at 1100 °C for up to 450 h. The coatings were analysed by means of light and electron microscopy techniques, microprobe analysis and X-ray diffraction analysis. The analysis was performed before and after the oxidation tests. The as-clad coating had a columnar dendritic structure and it did not show the presence of the relevant defects. After the oxidation tests an oxide scale was present which consisted of two distinct layers. The layers consisted of an outer layer of mixed spinel-type oxides and an inner continuous layer, in which alumina was present. The obtained results suggested that up to 450 h the system was able to form a continuous alumina layer that could protect the substrate from oxygen diffusion.     

Microstructure and dry sliding wear resistance of laser clad TiC reinforced Ti–Ni–Si intermetallic composite coating

Wear resistant TiC reinforced Ti–Ni–Si intermetallic composite coating with a microstructure consisting of TiC uniformly distributed in Ti₂Ni₃Si–NiTi–Ti₂Ni multi-phase intermetallic matrix was fabricated on a substrate of TA15 titanium alloy by the laser cladding process using TiC/Ti–Ni–Si alloy powders as the precursor materials. Microstructure of the coating was characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray energy dispersive spectrometer (EDS). Dry sliding wear resistance of the laser clad TiC reinforced Ti–Ni–Si intermetallic composite coating was evaluated at room temperature. Results indicated that the TiC/(Ti₂Ni₃Si–NiTi–Ti₂Ni) intermetallic composite coating exhibited excellent abrasive and adhesive wear resistance.     

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.     

Synthesis and coating of micro-metal-matrix composite by combined laser sol-gel processing

Of the many methods of laser treatment for improving materials surface properties that have been reported, very few have addressed laser-assisted chemical reaction. In this work laser deposition of metal-matrix composites is reported, using chromium oxide and silicon carbide powders mixed in silica sol-gel mixtures, on EN43 mild steel substrates. Very fine SiC particles ≤ 1 μm and M₇C₃ carbides were synthesised in situ and dispersed in ferrite matrix by this process. A diode laser at different powers and scanning speeds was applied to specimens coated with slurries of different chemical compositions. The effect of solution composition and bath depths were examined in order to achieve optimum experimental parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscopy (SEM) and field emission gun scanning electron microscope (FEG-SEM). Chemical composition was determined by energy dispersive X-ray analysis (EDX). The different phases were identified by X-ray diffraction (XRD). Results of microhardness measurements and wear properties of the coatings are also reported. Thermodynamic analysis of the reactions taking place is also given.     

Tribological properties of titanium aluminides coatings produced on pure Ti by laser surface alloying

Titanium aluminides coatings were in-situ synthesized on a pure Ti substrate with a preplaced Al powder layer by laser surface alloying. The friction and wear properties of the titanium aluminides coatings at different normal loads and sliding speeds were investigated. It was found that the hardness of the titanium aluminides coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating. Friction and wear tests revealed that, at a given sliding speed of 0.10 m/s, the wear volume of pure Ti and the titanium aluminum coatings all increased with increasing normal load. At a given normal load of 2 N, for pure Ti, its wear volume increased with increasing sliding speed; for the titanium aluminides coatings, the wear volume of Ti₃Al coating and TiAl coating first increased and then decreased, while the wear volume of TiAl₃ coating first decreased and then increased with increasing sliding speed. In addition, the friction coefficients of pure Ti and the titanium aluminides coating decreased drastically with increasing sliding speed. Under the same dry sliding test conditions, the wear resistance of the titanium aluminium coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating.     

Formation and performance of an Fe-based amorphous-nanocrystalline composite coating by laser cladding and remelting

Abstract

A very important research topic in the area of the surface performance of engineering components, in particular their wear properties, recently has been the application of high quality surface layers on relatively cheap substrates. An Fe-based composite coating with both amorphous and nanocrystalline structures on a mild steel substrate offers a combination of high quality coating and low materials cost, at the same time extending the range of applications of traditional materials. The difficulties posed by preparation of Fe-based amorphous alloys have limited progress for many years. However, the recent development of high power lasers, and of laser material processing technology in general, has made the preparation of a Fe-based amorphous and nanocrystalline composite coatings over a large area a real possibility.     

Microstructure and wear studies of laser clad Al-Si/SiC(p) composite coatings

Coatings of a composite material consisting of an Al-Si matrix reinforced with SiC particles were produced by laser cladding on UNS A03560 cast Al-alloy substrates from mixtures of powders of Al-12 wt.% Si alloy and SiC. The influence of the processing parameters on the microstructure and abrasive wear resistance of the coatings was studied. For an interaction time of 0.08 s and a power density of 330 MW/m², corresponding to a specific energy of 26 MJ/m², the interaction between SiC and liquid Al is limited and the reinforcement particles remain essentially undissolved. The coating's microstructure is formed of SiC particles dispersed in a matrix consisting of primary α-Al dendrites and interdendritic α-Al + Si eutectic. For interaction times of 0.3 and 0.45 s and a power density of 193 MW/m², corresponding to specific energies of 58 and 87 MJ/m², SiC reacts with molten Al and partially dissolves. The resulting microstructure consists of undissolved SiC particles, found mainly at the bottom of the clad tracks, where the maximum temperature reached during processing is lower, and Al₄SiC₄ and Si particles dispersed in a matrix of α-Al + Si eutectic. The coatings prepared with higher specific energy (58 MJ/m²) present a hardness of 250 V and an abrasive wear rate in three-body abrasion tests with SiC as abrasive of 1.7 × 10^− 4 mm³/m, while those produced with 26 MJ/m² present a hardness of 120 V and a wear rate of 0.43 × 10^− 4 mm³/m. These results show that Al₄SiC₄ and Si increase the hardness of the material by dispersion hardening but do not contribute to its abrasive wear resistance, because they are softer than the abrasive particles, and confirm that the parameters used to prepare Al-Si-SiC composite coatings by laser cladding must be selected so that only minimal reactions occur between SiC and molten Al.     

Synthesis by sol-gel route and characterization of Yttria Stabilized Zirconia coatings for thermal barrier applications

This paper deals with the development of new synthesis techniques for functional materials such as Yttria Stabilized Zirconia (YSZ) used in the field of thermal barriers coatings. Currently, Thermal Barrier Coatings (TBCs) are manufactured by dry route technologies (EB-PVD or plasma spray) but such methods are directional and often require costly investments and complicated operations. We have carried out significant work aimed at developing sol-gel routes, which are nondirectional methods, to prepare, by suitable chemical modifications, nanocrystalline materials with a controlled morphology. The main advantage of this method is to decrease the crystallization temperature, much lower than the conventional processes, allowing the synthesis of reactive powders with nanometric particles size. In this paper, the formulation of an alkoxide sol has been optimized in order to obtain homogeneous YSZ films. Nature and quantity of binders have been studied. Superalloys have been then immersed in the sol and withdrawn at several controlled rates before being annealed at different temperatures. The films microstructures have been investigated using scanning electron microscopy. It appears that the combination of a slower withdrawal speed (17 cm/min) with a 3 wt.% content of DBP allows to obtain the most homogeneous and the thicker coatings. Moreover, SEM-FEG observations have shown that the deposit is present all over the rough surface of the substrate and is composed of two morphologies: a YSZ thin covering film and a thicker discontinuous layer duplicating the substrate topography.     

Microstructure and properties of WC-12Co composite coatings prepared by laser cladding

A comprehensive study of the phase composition, microstructure evolution, microhardness and wear performance of WC-12Co composite coatings fabricated by laser cladding using coaxial powder-feed mode was presented. It was shown that a combination of high scan speed and high laser energy density made WC on the edge of WC-12Co composite powders partially melt in liquid Co and 304 stainless steel matrix, and then new carbides consisting of lamellar WC and herringbone M₃W₃C (M=Fe, Co) were formed. Meanwhile, WC-12Co composite coatings with no porosity, cracks and drawbacks like decarburization were obtained, showing high densification and good metallurgical bonding with the substrate. Furthermore, a considerably high microhardness of HV_0.3 1500-1600, low coefficient of friction of 0.55 and wear rate of (2.15±0.31)×10^-7 mm³/(N·m) were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of composite coating under laser power of 1500 W.     

Wear resistance of WCp/Duplex Stainless Steel metal matrix composite layers prepared by laser melt injection

Laser Melt Injection (LMI) was used to prepare metal matrix composite layers with a thickness of about 0.7 mm and approximately 10% volume fraction of WC particles in three kinds of Cast Duplex Stainless Steels (CDSSs). WC particles were injected into the molten surface layer using Nd:YAG high power laser beam. As a result the microstructure characterized by hard ceramic particles distributed in a metal matrix with the strong bonding to substrate is formed in the surface layer of the treated metal.Dry sliding wear properties of these metal matrix composites layers were measured and compared with the wear properties of the substrate and with surfaces simply remelted by the laser beam. The observed wear mechanisms are summarized and related to detailed microstructural observations. The layers have been found to show excellent interfacial bonding, coupled with substantially improved tribological properties expressed through the wear resistance increase of 8 times. The amount of WC particles was sufficient to reinforce the matrix and the particles have shown a good bonding to the matrix to support the contact stress in the layer.