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 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.     

TC4钛合金激光熔覆TiC+M涂层组织和耐磨性能研究

用CO2激光在TC4合金表面熔覆TiC＋髓和TiC＋NiCrBSi金属陶瓷涂层,分析了熔覆层的微观组织,测试了熔覆层的干滑动磨损性能。结果表明,在TiC＋Ti激光熔覆层中,TiC颗粒全部溶解,熔覆层的组织是在β-Ti基体上分布着TiC树枝晶;在TiC＋NiCrBSi激光熔覆层中,TiC颗粒部分溶解,熔覆层的组织是在γ-Ni树枝晶和卜Ni＋M23（CB）6共晶的基体上分布着细小的TiC颗粒和TiC树枝晶。TiC＋骶激光熔覆层的显微硬度在500～700HV之间,质量磨损率约为TC4合金的1／3;TiC＋NiCrBSi激光熔覆层的显微硬度在900～1100HV之间,质量磨损率约为TC4合金的1／10。     

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 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.     

Dry coatings and ecodesign: Part. 2 — Tribological performances

The goal of this study is to find an industrial alternative application to hard chromium plating. The first part presents the appropriate environmental and chemical behaviour of NiCrBSi alloy and AISI 316L stainless steel coated by thermal spraying and laser cladding. This paper will concern the wear resistance of these dry coatings. However, stainless steel has awful performance in friction contacts, and this material cannot be suggested as a substitute solution to hard chromium coating for applications where the wear resistance is an important issue. Therefore the tribological pin-on-disc tests will only concern the NiCrBSi coatings. Consequently in the second part, tribological characterizations were carried out in order to determine the alternative potential of NiCrBSi coatings compared to electrolytic hard chromium plating, in applications to resist wear. The coatings are sprayed by Atmospheric Plasma Spraying (APS) and laser cladding (with a diode laser). Especially, the dry coated samples present a good tribological behaviour, whereas the wear mechanisms are different between APS and laser cladding coated samples. Laser cladding allows the manufacture of denser coatings, thus the mechanical properties are increased while the wear rate was reduced. At the same time, APS coated samples show a lower value of shear strength in comparison with laser cladding. That is the reason why fatigue is the main wear mechanism, and this process is called splat delamination.     

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.     

Indentation size effect in nickel and cobalt laser clad coatings

In this work it is reported a comparative study of the indentation response at different length scales in nickel and cobalt samples produced by laser cladding. The indentation tests were carried out in the load range 57 μN to 2 N. Both in Ni and Co, the indentation hardness increases as the indentation dimension decreases from the micrometer to the nanometer range. It is shown that the experimental results can be accurately described by an analytical function, whose terms account for the contributions of dislocation density and surface free energy to the material's hardness. Although the good relation between the model and the experimental points is not a fully evidence, it strongly suggests that, as the hardness scale decreases, the increase of dislocation density and the increase of the surface-to-volume ratio of the plastically deformed region are the most important causes for the observed indentation size effect.     

Microstructure and wear property of laser-clad Co3Mo2Si/Coss wear resistant coatings

Novel wear resistant Co₃Mo₂Si/Co_ss coatings consisting of a microstructure of hard and strong Co₃Mo₂Si intermetallic phases embedded in the ductile Co-base matrix were fabricated on austenite stainless steel by the laser cladding process from the Co-Mo-Si powder blend precursor. The microstructures of the coatings were characterized by optical microscopy (MO), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with an energy-dispersive X-ray analysis (EDX). The wear resistance of the coatings was evaluated in a dry sliding wear test condition at room temperature. Results indicated that the laser-clad Co₃Mo₂Si/Co_ss coatings exhibited very excellent wear resistance against abrasive and adhesive wear.     

Effect of Nb addition on microstructure and properties of laser cladding NiCrBSi coatings

NiCrBSi coatings with different Nb additions have been prepared by laser cladding. The microstructure, phase composition, hardness, and wear resistance of the coatings were studied by scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. The results show that the phases in the NiCrBSi coating without Nb addition include γ-Ni, Cr₂₃C₆, Cr₇C₃, Ni₃B, Ni₃Si₂ and CrB. The NbC phase appears in coatings after the addition of Nb element. When the addition of Nb is 2?wt-%, the NbC particles with a size of about 1.2?μm were found in the coating, and the amount of NbC is about 1.8?vol.-%. With the increase of Nb addition, the size and amount of NbC in the coatings also increased. When the addition of Nb is 6?wt-%, the size of NbC is about 2.3–6.1?μm and the morphology of NbC changed from particle to quadrangular and petaloid shaped. In addition, when the addition of Nb is 2?wt-%, the hardness and wear resistance of the coating are the best, and the wear resistance of the coating is 104% higher than that without Nb addition.     

Effect of molybdenum on the microstructure and corrosive wear resistance of laser clad Ni-based coatings

Five kinds of Ni-based coatings with 0 wt%, 2.5 wt%, 5.0 wt%,7.5wt% and 10.0wt% molybdenum were prepared on 45CrNi steel plates by using laser cladding technique. The effect of Mo on the microstructure of Ni-based coatings was investigated by using scanning electron microscopy. The corrosive wear resistance and the corrosion resistance of five coatings were tested. The results show that the corrosive wear resistance of the coating with 5.0wt% Mo is better than those of other coatings. During the corrosive wear process, the corrosion and wear effects are combined. The corrosive wear resistance is closely related to the microstructure of the coating.     

Abrasive wear resistance of plasma-sprayed glass-composite coatings

A ball-milled mixture of glass and alumina powders has been plasma sprayed to produce alumina-glass composite coatings. The coatings have the unique advantage of a melted, ceramic secondary phase parallel to the surface in an aligned plateletlike-composite structure. The alumina raises the hardness from 300 HV for pure glass coatings to 900 HV for a 60 wt.% alumina-glass composite coating. The scratch resistance increases by a factor of 3, and the wear resistance increases by a factor of 5. The glass wears by the formation and intersection of cracks, while the alumina wears by fine abrasion and supports most of the sliding load. The wear resistance reaches a maximum at 40 to 50 vol.% alumina, above which there is little further improvement. This critical alumina content corresponds to the changeover from a glass to a ceramic matrix.     

耐磨陶瓷涂层的研究与发展

从涂层用原材料、制备方法、涂层特点等几个方面介绍了耐磨陶瓷涂层的近期研究进展及发展趋势.     

TiAl合金激光熔覆复合材料涂层耐磨性研究

利用预涂NiCr-Cr3C2复合粉末对γ-TiAl合金（简称TiAl合金）进行激光熔覆处理,制得了以Cr7C3、TiC硬质相为耐磨增强相,以γ-NiCrAl镍基固溶体为基体的复合材料涂层,研究了原始TiAl合金和激光熔覆涂层的室温和高温（600℃）滑动磨损性能,并讨论了原始TiAl合金和所制备涂层的室温和高温滑动磨损机理。结果表明：激光熔覆复合材料涂层均具有较好的室温和高温滑动磨损耐磨性。室温下涂层的耐磨性先随着其中硬质耐磨增强相体积分数的增加而提高,但当耐磨相体积分数过高时,由于涂层脆性增大,其耐磨性反而下降。     

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.     

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.     

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.     

Laser-assisted spraying and laser treatment of thermally sprayed coatings

In the present study, surface engineering research related to thermally sprayed wear and corrosion resistant coatings modified by in-situ and post-treatment by novel high power lasers (Nd:YAG and diode lasers) has been carried out. The main aim of the study was to create experimental based information and knowledge on simultaneous remelting of thermally sprayed (plasma, HVOF, flame) single layers for production of metallurgically bonded, dense corrosion and wear resistant coatings on surfaces of steels. The main focus of research was to estimate the needed processing parameters, which enable simultaneous laser-assisted thermal spraying. The microstructures and hardness-profiles for the coatings prepared by laser-assisted thermal spraying are also introduced.     

Microstructure and wear resistance of TaC reinforced Ni-based coating by laser cladding

The in situ synthesized TaC particulate reinforced Ni-based composite coating was fabricated on a mild steel by laser cladding of powder mixture of Ni60 alloy powder with (Ta₂O₅ + C)-doping. The microstructure and wear resistance of the TaC/Ni60 composite coating were investigated. It is shown that the coating is bonded metallurgically to the substrate and has a homogeneous fine microstructure containing both approximate cubic TaC particle and acicular chromium carbide uniformly dispersed in the dual phase matrix of γ(Ni) solid solution and eutectic of Cr₃C₂, Fe₂B with γ(Ni). Compared to a Ni60 coating, the hardness of the TaC/Ni60 composite coating was enhanced by a factor of 1.38, could achieve a Vicker microhardness of Hv_0.31100. And the wear rate in a block on ring test against hardened steel was reduced by a factor of five. This is attributed to the presence of in situ synthesized TaC particles and their well distribution in the coating.     

SiCp增强铝基复合激光熔覆层组织和磨损性能研究

采用CO2激光器在ZL102合金表面熔覆SiCp-Al基复合涂层,利用SEM和XRD等分析了激光熔覆层的微观组织,测试了激光熔覆层的硬度和磨损性能.结果表明,激光熔覆层表层呈过共晶组织形态,由针状Si、α-Al Si共晶和少量的SiC颗粒组成,底层呈亚共晶组织形态,由α-Al树枝晶,α-Al Si共晶和SiC颗粒组成.激光熔覆层与基材结合区组织为定向生长的树枝晶,且与基材呈联生结晶特征.激光熔覆层的硬度在220～280HV之间,显著提高了ZL102合金的耐磨性能.