Intermetallic Composite Coatings Research Articles

Fabrication of In Situ rGO Reinforced Ni-Al Intermetallic Composite Coatings by Low Pressure Cold Spraying with Desired High Temperature Wear Characteristics.

In this study, the surface of aluminum powder was uniformly coated with in situ reduced graphene oxide (r-GO) sheets (Al/r-GO). The Ni powder, Al2O3 powder, and Al/r-GO powders were mixed uniformly in a mass ratio of 20:6:4. In situ rGO-reinforced Ni-Al intermetallic composite coatings were successfully prepared using low-pressure cold spraying and subsequent heat treatment. The microstructure and phase of the composite coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The high-temperature wear test was conducted at 200 °C, 400 °C, and 600 °C to understand the mechanism. The results indicate that the in situ rGO-reinforced Ni-Al intermetallic composite coatings exhibit a 33.3% lower friction coefficient and 26% lower wear rate in comparison to pure Ni-Al intermetallic coatings, which could be attributed to the generation of an easy-shearing transferred film between the coating and grinding ball.

Core-shell ZrC/Ti2AlC reinforced composite coatings prepared by laser cladding on Zr-alloy substrates

Core-shell ZrC/Ti2AlC reinforced intermetallic composite coatings were successfully prepared by laser cladding in-situ reaction using TiAl–TiC–Al powder preset on R60702 zirconium alloy surface. As-obtained coatings showed good metallurgical bonding with substrates. Composite coatings mainly contained dendritic ZrC/Ti2AlC reinforced phase with core-shell structure and intermetallic matrix of TixAly and ZrxAly, with small amounts of Ti3AlC. During laser pool solidification, TiC nucleated at boundary of primary precipitated ZrC dendrite. Al atoms then diffused into TiC outer layer during subsequent solidification process to finally form core-shell structure with ZrC as core and Ti2AlC as outer layer. Ti2AlC phase of shell structure improved physical performance between hard ZrC particles and matrix in terms of hardness and thermal expansion coefficient. The maximum hardness of cladding layer (848.8 HV) was 5-fold higher than that of zirconium alloy substrate. Also, no cracking was found inside the coatings or at the junction with substrates. In sum, these findings look promising for future applications of MAX phase composite coatings in nuclear power equipment.

Microstructure and high temperature oxidation resistance of in-situ synthesized TiN/Ti3Al intermetallic composite coatings on Ti6Al4V alloy by laser cladding process

High temperature anti-oxidation TiN/Ti3Al intermetallic composite coatings were fabricated with the powder and AlN powder on Ti6Al4V titanium alloy surface by 6 kW transverse-flow CO2 laser apparatus. The chemical composition, morphology and microstructure of the TiN/Ti3Al composite coatings were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). In order to evaluate the high temperature oxidation resistance of TiN/Ti3Al coating, the isothermal oxidation test was performed in a high temperature resistance furnace at 600 °C and 800 °C, respectively. The result shows that the composite coating has a rapidly solidified fine microstructure consisting of TiN primary phase (granular-like, flake-like or dendrites), with an even distribution in Ti3Al matrix. It indicates that a physical and chemical reaction between Ti powder and AlN powder has completely occurred under the laser irradiation condition. In addition, the microhardness of the TiN/Ti3Al intermetallic composite coating is 3.4 times higher than that of the Ti6Al4V alloy substrate and reaches 844 HV0.2. The high temperature oxidation behavior test reveals that the high temperature oxidation resistance of TiN/Ti3Al composite coating is much better than that of titanium alloy substrate. The excellent high temperature oxidation resistance of TiN/Ti3Al intermetallic composite coating is attributed to the formation of reinforced phases TiN, Al2O3 and TiO2. The laser cladding TiN/Ti3Al intermetallic composite coating is anticipated to be a promising high temperature oxidation resistance coating for Ti6Al4V alloy.

Microstructure and Wear Properties of Ni-W-Si Coatings by Laser Cladding

Ni-W-Si intermetallic composite coatings consisting of primary tungsten dendrites and eutectic W/WSi2 were fabricated on 45 steel by laser cladding process using Ni-W-Si powder. The microstructure and composition of the coatings were characterized by SEM, XRD and EDS. The effect of the W content on the hardness and wear resistance of coatings was investigated. Results indicate that attributed to the high hardness and toughness of tungsten dendrites and fine and compact eutectic W/WSi2, coatings had high hardness being 950HV in maximum and the wear resistance was elevated to 4-8 times higher.

Microstructure and dry sliding wear behavior of plasma transferred arc clad Ti5Si3 reinforced intermetallic composite coatings

In order to modify the tribological properties of titanium alloy, Ti53–Si32–Ni15, Ti43–Si26–Ni31 and Ti30–Si18–Ni52 (at.%) elemental powders blends were designed to fabricate Ti5Si3 reinforced intermetallic composite coatings on Ti–6Al–4V titanium alloy substrate by plasma transferred arc (PTA) cladding process. Microstructure of the PTA cladding coatings was characterized by SEM, XRD and EDS. The relationship between Ti/Si/Ni atomic ratios of the Ti–Si–Ni elemental powders blends and microstructure of the PTA cladding coatings was investigated in detail. The effect of volume fraction of the Ti5Si3 primary phases on microhardness and room temperature dry sliding wear behavior of the PTA cladding coatings was discussed. Results show that the PTA clad intermetallic composite coatings have a non-equilibrium solidified super-fine microstructure consisting of Ti5Si3 primary phases, NiTi2/α-Ti/Ti5Si3 ternary eutectics and a small amount of NiTi2/Ti5Si3 binary eutectics. The PTA clad composite coatings are metallurgically bonded to the Ti–6Al–4V titanium alloy substrate. The Ti/Si/Ni atomic ratios of the Ti–Si–Ni elemental powders blends have a noticeable effect on grain size, volume fraction and solidification morphologies of the Ti5Si3 primary phases. With increasing the Ni content of the elemental powder blends, grain size and volume fraction of the Ti5Si3 primary phases decrease significantly. Microhardness values of the PTA clad intermetallic composite coatings are remarkable influenced by the volume fraction of the Ti5Si3 primary phases. The higher the volume fraction of the Ti5Si3 primary phases, the higher the microhardness value of the PTA cladding coatings. Room temperature dry sliding wear properties of the PTA cladding coatings are significantly affected by both the solidification morphologies and volume fraction of the Ti5Si3 primary phases.

Microstructure and properties of intermetallic composite coatings fabricated by selective laser melting of Ti–SiC powder mixtures

Transition metal silicides and carbides are attractive advanced materials possessing unique combinations of physical and mechanical properties. However, conventional synthesis of bulk intermetallics is a challenging task because of their high melting point. In the present research, titanium carbides and silicides composites were fabricated on the titanium substrate by a selective laser melting (SLM) of Ti–(20,30,40wt.%)SiC powder mixtures by an Ytterbium fiber laser with 1.075μm wavelength, operating at 50W power, with the laser scanning speed of 120mm/s. Phase analysis of the fabricated coatings showed that the initial powders remelted and new multiphase structures containing TiCx, Ti5Si3Cx, TiSi2 and SiC phases in situ formed. Investigation of the microstructure revealed two main types of inhomogeneities in the composites, (i) SiC particles at the interlayer interfaces and, (ii) chemical segregation of the elements in the central areas of the tracks. It was suggested and experimentally proven that an increase in laser power to 80W was an efficient way to improve the laser penetration depth and the mass transport in the liquid phase, and therefore, to fabricate more homogeneous composite. The SLM Ti–(20,30,40wt.%)SiC composites demonstrated high hardness (11–17GPa) and high abrasive wear resistance (3.99×10−7–9.51×10−7g/Nm) properties, promising for the applications involving abrasive wear.

Microstructure and Properties of Fe–Al/Cr<sub>3</sub>C<sub>2</sub>RE Composite Coating Produced by HVFS

Fe–Al/Cr3C2composite coatings produced from high-velocity flame spraying (HVFS) are Fe–Al intermetallic composite coatings with remarkable room-temperature and high-temperature properties. However, Fe–Al/Cr3C2composite coatings have a Cr3C2content of 50%. This causes the coatings to become porous and limits its room-temperature and high-temperature properties. In order to improve microstructure and properties of Fe–Al/Cr3C2composite coatings, Fe–Al/Cr3C2RE, including Fe–Al/Cr3C2and CeO2, is sprayed by HVFS technology onto AISI 1020 steel. The properties including bonding strength and high-temperature corrosion-resistance of Fe–Al/Cr3C2RE composite coating are tested at 25°C and 650 °C. For comparison, two other materials, substrate AISI 1020 steel and Fe–Al/Cr3C2composite coating, are tested under the same experimental conditions. The microstructures of the coatings are analyzed by scanning electronic microscopy (SEM), the cross-section morphology of Fe–Al/Cr3C2RE composite coating is analyzed by energy-dispersive spectroscopy (EDS), and the existing states of oxides are analyzed by transmission electron microscopy (TEM). The phases of the composite coating after corrosion are analyzed by X-ray diffraction (XRD). The results demonstrate that the properties of Fe–Al/Cr3C2RE composite coatings is better than that of either AISI 1020 steel or the Fe–Al/Cr3C2composite coating. CeO2is a surface-active agent, and it significantly improves the microstructure and properties of Fe–Al/Cr3C2RE composite coating. CeO2improves the bonding strength of Fe–Al/Cr3C2RE composite coating by reducing the surface tension of droplet and enhancing its fluidity as well as wetting capacity on the surface of the substrate, decreasing the internal stress of coating.Adding CeO2to the coating produces Al2O3and Cr2O3oxide films, which protect the substrate AISI 1020 steel from corrosion more efficiently.

Heat treatment induced intermetallic phase transition of arc-sprayed coating prepared by the wires combination of aluminum-cathode and steel-anode

A method to prepare intermetallic composite coatings employing the cost-efficient electric arc spraying twin wires assistant with suitable heat treatment was developed. In this study, a Fe–Al composite coating was produced by spraying twin wires, i.e. a carbon steel wire as the anode and an aluminum wire as the cathode. The inter-deposited Fe–Al coating was transformed in-situ to Fe–Al intermetallic composite coating after a post annealing treatment. The effect of annealing treatment conditions on phase composition, microstructure and mechanical properties of the coating was investigated by using XRD, SEM, EDS and OM as well as microhardness tester. The results show that the desirable intermetallic phases such as Fe 2Al 5, FeAl and Fe 3Al are obtained under the annealing condition. The main oxide in the coating is FeO which can partially transform to Fe 3O 4 up to the annealing condition.

Effect of Annealing Treatment on the Structure and Microhardness of Cold-Sprayed Nanostructured FeAl/WC Composite Coating

Nanostructured FeAl/WC intermetallic composite coatings were prepared by cold spaying of the ball-milled powders. The effect of annealing on the coating structure and microhardness was examined. It was found that the nanocrystalline structure of the milled feedstock was retained in the cold sprayed coatings. The FeAl intermetallic phases were formed from the milled Fe(Al) solid solution during the post-spraying annealing at 550oC. The microhardness of the as-sprayed coating was about 680HV0.1 and it decreased a little with increasing the annealing time at 550oC.

Oxidation performance of Fe-Al/WC composite coatings produced by high velocity arc spraying

Fe-Al intermetallics with remarkable high-temperature intensity and excellent erosion, high-temperature oxidation and sulfuration resistance are potential low cost high-temperature structural materials. But the room temperature brittleness induces shape difficult and limits its industrial application. The Fe-Al intermetallic coatings were prepared by high velocity arc spraying technology with cored wire on 20G steel, which will not only obviate the problems faced in fabrication of these alloys into useful shapes, but also allow the effective use of their outstanding high-temperature performance. The Fe-Al/WC intermetallic composite coatings were prepared by high velocity arc spraying technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings was studied by means of thermogrativmetic analyzer at 450, 650 and 800°C. The results demonstrate that the kinetics curve of oxidation at three temperatures approximately follows the logarithmic law. The composition of the oxidized coating is mainly composed of Al2O3, Fe2O3, Fe3O4 and FeO. These phases distribute unevenly. The protective Al2O3 film firstly forms and preserves the coatings from further oxidation.

Modeling the Melting and Dissolution Stages During Thermal Processing of Intermetallic Coatings from Layered Precursors

This paper presents a simple analytical model of the temperature and concentration dynamic distributions during thermal processing of intermetallic and metal-matrix composite coatings, such as nickel aluminide coatings on steel substrates, by melting, e.g., preplated aluminum/nickel layers using a moving heat source such as a plasma arc. Such a source of Gaussian power distribution scans the surface of the coating, giving rise to the temperature evolution and component dissolution during the thermal melting and reaction process. The model is based on a system of lumped energy and mass balances, and convolution expressions of distributed temperature and concentration Green’s fields (accounting for the orientation of their gradient and decomposing heat and mass transfer across the coating from substrate conduction), and is solved numerically in real-time. The simulation results are validated on Ni–Al coatings processed using a robotic plasma arc laboratory station, through in-process infrared thermal sensing and off-line metallographic analysis. It is shown that the predicted temperature and dissolution penetration values compare well with the experimentally obtained results, therefore supporting the model as a real-time basis for design and/or adaptation of a thermal control system for the coating process.

Microstructure and dry-sliding wear resistance of laser clad tungsten reinforced W 5Si 3/W 2Ni 3Si intermetallic coatings

Wear resistant tungsten reinforced W 5Si 3/W 2Ni 3Si intermetallic composite coatings consisting of small amount of well-developed tungsten primary dendrite and the metal silicides W 5Si 3/W 2Ni 3Si dual-phase structure were fabricated on a substrate of pure nickel plate by laser cladding process. Wear resistance of the coatings was evaluated under block-on-wheel dry-sliding wear test conditions at room temperature. Because of the strong covalent-dominant atomic bonds and the high hardness inherent to the tungsten silicides W 5Si 3 and W 2Ni 3Si, the intermetallic coatings have outstanding abrasive and adhesive wear resistance.

Wear resistance of laser clad Ti2Ni3Si reinforced intermetallic composite coatings on titanium alloy

Titanium alloys are restricted from industrial applications as tribological components because of their inherent poor wear resistance. In this paper, novel wear resistant Ti2Ni3Si reinforced 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 a titanium alloy BT9 by the laser cladding process. Wear resistance of the coating was evaluated under dry sliding wear tester condition at room temperature. Results indicated that the laser clad coatings have excellent wear resistance and very low load sensitivity under dry sliding wear test conditions.

Wear resistance of laser clad Ti2Ni3Si reinforced intermetallic composite coatings on titanium alloy

Titanium alloys are restricted from industrial applications as tribological components because of their inherent poor wear resistance. In this paper, novel wear resistant Ti2Ni3Si reinforced 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 a titanium alloy BT9 by the laser cladding process. Wear resistance of the coating was evaluated under dry sliding wear tester condition at room temperature. Results indicated that the laser clad coatings have excellent wear resistance and very low load sensitivity under dry sliding wear test conditions.

Microstructure and tribological properties of laser clad Ti 2Ni 3Si/NiTi intermetallic coatings

Wear resistant Ti 2Ni 3Si/NiTi full intermetallic composite coatings with a microstructure consisting of ternary metal silicide Ti 2Ni 3Si primary dendrites and interdendritic Ti 2Ni 3Si/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 Ti 2Ni 3Si/NiTi intermetallic coatings was evaluated under dry sliding wear test conditions at room temperature. Results indicate that the Ti 2Ni 3Si/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 Ti 2Ni 3Si with MgZn 2 type Laves crystal structure.

Wear and corrosion behavior of laser clad Cr 3Si reinforced intermetallic composite coatings

Wear and corrosion are two of the three most frequently encountered failure modes for mechanical components working under aggressive conditions. Extending the service life of mechanical components by surface engineering methods is of critical importance from both the technological and economical point of view. In this paper, novel rapidly solidified wear and corrosion resistant Cr 3Si reinforced intermetallic composite coatings were fabricated on a substrate of austenitic stainless steel 1Cr18Ni9Ti by laser cladding using Cr–Si–Ni elemental powder blends. Microstructure, hardness, room-temperature dry sliding wear and electrochemical corrosion behavior of the laser clad composite coatings were investigated as a function of the Cr 3Si volume fraction. Results show that the laser clad composite coatings have a rapidly solidified microstructure consisting of Cr 3Si primary dendrites and interdendritic matrix of Cr–Ni–Si ternary silicide. Volume fraction of the primary Cr 3Si dendrites was shown to have a remarkable influence on hardness, wear and corrosion resistance of the laser clad composite coatings. The higher the volume fraction of Cr 3Si, the higher the hardness and the wear and corrosion resistance of the laser clad composite coatings.