Effects of aging treatment on microstructure and tribological properties of nickel-based high-temperature self-lubrication wear resistant composite coatings by laser cladding

The NiCr/Cr₃C₂–WS₂ high-temperature self-lubrication wear resistant composite coatings were fabricated on substrate of a hot-rolled AISI304 austenitic stainless steel by laser cladding. The high-temperature phase stability of the composite coatings was evaluated by aging at 600 °C for 10 h, 30 h, 50 h, and the microstructures of the as-laser clad and aged coatings were examined by means of XRD, SEM, EDS, respectively. The sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 °C. The results show that NiCr/Cr₃C₂–WS₂ composite coating has excellent high-temperature phase stability, the γ-(Fe,Ni)/Cr₇C₃ eutectic phases, Cr₇C₃ and (Cr,W)C hard phases, CrS/WS₂ mixed solid lubricant phases all existed in the as-laser clad and aged coatings. The volume fraction of eutectic phases decreased gradually with the increasing of aged time due to their dissolution. The microhardness of the aged coating decreased slightly after aging the coating 50 h at 600 °C due to the dissolution of the eutectic phases and notable breaking or granulation of the Cr₇C₃ hard phase, but the tribological properties were not significantly affected by aging treatment.     

Wear behavior of light-weight and high strength Fe-Mn-Ni-Al matrix self-lubricating steels

The good combination of mechanical and tribological properties for self-lubricating materials is crucial. In this work, novel self-lubricating Fe-16.4 Mn-4.8 Ni-9.9 Al-xC(wt%) steels containing graphite phase were fabricated using mechanical alloying and spark plasma sintering. The compositions of the steels were designed by using thermodynamic calculation, and the effect of carbon addition on the microstructure was further investigated. The steel possesses high hardness of 621 HV, high yield strength of 1437 MPa and good fracture toughness at room temperature. The yield strengths are still above 600 MPa at 600?C.The tribological behavior and mechanical properties from room temperature to 800?C were studied, and the wear mechanisms at elevated temperatures were discussed. The steel has a stable friction coefficient of 0.4 and wear rate in a magnitude of 10~(-6) mm~3/N·m below 600?C. The good tribological properties of the steels were mainly attributed to the high hardness, lubrication of graphite and stable surface oxide layer.     

Pulse current co-deposition of Ni-WS2 nano-composite film for solid lubrication

This study was undertaken to observe the effect of nano-composite coating on steel surface for enhancing its tribological properties. In the investigation, EN31 steel surfaces were coated with nano-composite (Ni-WS₂) by pulse current co-deposition process in order to improve the tribological properties of the surface. The coatings were prepared according to different parameter settings. The effect of variations on coating thickness, microstructure, surface morphology, microhardness and tribological properties was observed. The maximum coating thickness of 117?µm with 8% by weight of WS₂ particle concentration could be attained with the following parameter settings: applied voltage: 5?V; pulse frequency: 20?Hz; WS₂ concentration: 20?g/l; duty factor: 0.6 and bath temperature: 50°C. The average friction coefficient of the deposited surface was 0.11, which is significantly less than that of the EN31 steel surface (average coefficient of friction >?0.5).     

Microstructure and oxidation-resistant of ZrO2/Ni coatings applied by high-speed jet electroplating

ZrO₂/Ni composite coatings with different contents of ZrO₂ particles were deposited on superalloy K17 substrate using high-speed jet electroplating process. The microhardness and microstructure of composite coatings were studied. The oxidation kinetic curves of uncoated and coated K17 alloys were obtained. The results indicated that ZrO₂/Ni composite coatings exhibit higher microhardness than that of pure nickel coatings under the same high-speed jet electrodeposition conditions. ZrO₂/Ni composite coatings exposure to air at 1000 °C for 5 h formed scale containing NiO and Cr₂O₃; after exposure to air at 1000 °C for 100 h the scale was comprised NiO, NiCr₂O₄, and Cr₂O₃. The formation of Cr₂O₃ scales on the ZrO₂/Ni composite coating directly improved the oxidation resistance of superalloy K17.     

Effect of heat treatment on microstructure and mechanical properties of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy

ABSTRACT

The effect of heat treatment on the mechanical properties and microstructures of Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloys was investigated. The results show that the microstructure of the as-cast alloy mainly consists of an alpha-copper matrix and γ-phase Ni₃Al particles. The microstructure of the alloy after solution treatment at 950°C for 2?h is a single-phase alpha-copper supersaturated solid solution and the second-phase strengthening disappears. After ageing treatment at 550°C for 6?h, the γ-phase particles are fully precipitated, and the mechanical properties of the alloy are significantly improved. The tensile strength is increased from 305 to 588?MPa. Quasi-cleavage fracture with shallow dimples appeared in the Cu–6.9Ni–2.97Al–0.99Fe–1.06Mn alloy aged at 550°C for 6?h.     

Effect of firing temperature on microstructure and dielectric properties of chromium oxide based glass composite thick films on stainless steel substrate

We report the influence of firing temperature on Al₂O₃–chromium oxide based (Cr₂O₃–Bi₂O₃–B₂O₃–SiO₂–Al₂O₃) glass composite (named as GC-1 composite) thick films of thickness (27?±?3) µm deposited onto 0.6 mm thick austenitic grade stainless steel (DIN 1.4301/AISI 304) substrate by screen printing technique, which can be used as a substitute to alumina substrate. Prior to formulation of glass composite, the chromium oxide based glass (named as GC-1) phase was prepared separately by melt-quench technique. X-ray diffraction analysis confirmed amorphous nature of the GC-1 glass. The thermo gravimetric analysis and differential scanning calorimetry of the GC-1 glass shows thermal stability over the temperature range of 20–1000 °C. We observed that the firing temperature significantly influences microstructural and dielectric properties of the GC-1 composite film. The deposited GC-1 composite films onto stainless steel base were fired at temperatures between the range of 550–750 °C, showed the surface resistivity in the range of (1.0–6.9?±?0.2) × 10¹² ohms per square. The microstructure of these composite films recorded using scanning electron microscopy and electrical properties recorded using LCR meter were correlated with each other. The study revealed that the film fired at 600 °C were found to be superior among the samples under investigation in terms of microstructure, stable relative permittivity [36 (±?1)] and low loss tangent [0.02 (±?0.002)] in frequency range of 1–200 kHz, and surface resistivity (~?5.1?×?10¹² ohms per square).     

Joining of Cf/SiBCN composite with CuPd-V filler alloy

Two compositions of CuPd-V system filler alloy were designed for joining the Cf/SiBCN composite. Their dynamic wettability on the Cf/SiBCN composite was studied with the sessile drop method. The CuPd-8 V alloy exhibited a contact angle of 57° after holding at 1170℃ for 30 min, whereas for CuPd-13 V alloy,a lower contact angle of 28°can be achieved after heating at 1200 ℃ for 20 min. Sound C_f/SiBCN joints were successfully produced using the latter filler alloy under the brazing condition of(1170-1230)℃for 10 min. The results showed that the active element V strongly diffused to the surface of Cf/SiBCN composite, with the formation of V_2 C/VN reaction layer. The microstructure in the central part of the joint brazed at 1200 ℃ was characterized by the V_2 C/VN particles distributing scatteringly in CuPd matrix. The corresponding joints showed the maximum three-point bend strength of 82.4 MPa at room temperature.When the testing temperature was increased to 600 0 C, the joint strength was even elevated to 108.8 MPa.Furthermore, the joints exhibited the strength of 92.4 MPa and 39.8 MPa at 800 ℃ and 900 ℃, respectively.     

Room and high temperature tensile behaviour of a P/M 2124/MoSi2 composite at different heat treatment conditions

In the present work, a 2124/15 vol%MoSi₂ composite was obtained by powder metallurgy. Its microstructure and mechanical properties were investigated at room and at high temperature (up to 200°C) in conditions T351, T4 and after heat treatments at 495°C for up to 100 h. Up to 150°C, tensile properties of 2124/MoSi₂ in T351 resulted similar to those of a ceramic reinforced 2124/SiC composite. Yield stress of the 2124/MoSi₂ material, after heating at 495°C for up to 100 h, resulted higher than that of the monolith 2124 alloy heated for the same periods. No diffusion reaction phases were formed surrounding the MoSi₂ reinforcing particles during such long exposures to high temperature. Only at 100 h, large plate-like precipitates that contain Al, Cu, Mg and Si appeared. The high thermal stability of this 2124/MoSi₂ composite and its good mechanical properties at room and at elevated temperature makes MoSi₂ intermetallic a competitor of ceramic reinforcements.     

The role of oxidation and counterface in the high temperature tribological properties of TiAl intermetallics

Clarification of how oxidation and counterface materials influence the high temperature tribological properties of TiAl alloy is the main object of this research. As evident from the comparison tests in air and argon, surface oxidation is detrimental to the tribological properties of the alloy at low temperature, but favorable above 600 °C.Counterface (Si₃N₄, SiC and Al₂O₃) is an important factor that largely affects the tribological properties of TiAl alloys, and this effect is strongly dependent on the system environment. In general, TiAl alloy shows superior tribological properties when Al₂O₃ is mating surface, excluding at 800 °C in argon.     

Precipitation of second phases in aged Ni rich NiTiRe shape memory alloy

Abstract

This study investigated the effect of aging on the structure and precipitation of second phases of Ni₅₂Ti_47·7Re_0·3 shape memory alloys. The alloy was solutionised at 1000°C for 24 h before aging at various temperatures ranging from 300 to 600°C for 3 h. The matrix phase in both solutionised and aged specimens was martensite. Ti₂Ni phase was also present in the microstructure of both solutionised and aged specimens and its volume fraction decreased as the aging temperature increased. Ni₄Ti₃ phase began in appearance by increasing aging temperature to 400°C. Ni₄Ti₃ precipitates had lenticular and non-geometry shapes. Aging at 600°C led to precipitation of Ni₃Ti phase in the microstructure. This precipitated phase formed in white blocky shapes. Ti/Ni ratio increased and/or Ni content decreased in the matrix with increasing in aging temperature.     

Effect of Zr on microstructure and mechanical properties of the Al–Cu–Er alloy

ABSTRACT

The microstructure and mechanical properties of the Al–4Cu–2.7Er–0.3Zr alloy were investigated. The precipitates of the L1₂ structured phase with sizes 37?±?12?nm were formed in lines and homogenously distributed inside the aluminium matrix after annealing at 605°C for 1?h. The as-rolled Al–4Cu–2.7Er–0.3Zr alloy developed an increased hardness after 1?h annealing at 100–550°C and 0.5–6?h annealing at 150–250°C due to precipitation of the Al₃(Er,Zr) phase. Addition of Zirconium improved the tensile properties relative to those of the Zr-free alloy by approximately 20?MPa: yield strength?=?273–296?MPa and ultimate tensile strength?=?296–328?MPa in the alloys annealed at 100–150°C.     

Hybrid effect of an in situ multilayer Zn–ZnO–Cr2O3 electrodeposited nanocomposite coatings for extended application

Multifunctional composite coatings of Zn?ZnO?Cr₂O₃ were deposited electrolytically on prepared carbon mild steel (CS) from Zn electrolyte, having Zn²⁺ ions and uniformly dispersed nano ZnO?Cr₂O₃ particulates. The corrosion resistance characteristics of the deposited coatings were evaluated using the linear polarization measurement method in 3.65% NaCl. The microstructural properties of the produced multilayered coatings were evaluated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), x-ray diffraction (XRD), and atomic force microscope (AFM). Thermal deformations were observed after 4 h at 250°C and the mechanical response of the coated samples was investigated using a diamond-based Dura Scan microhardness tester and a MTR-300dry abrasive wear tester. From the results, a significant improvement in the corrosion performance of coatings was observed with bath containing less than 2 g/L. The microhardness, thermal stability, and anti-wear properties of Zn?ZnO?Cr₂O₃ shows improved performance against Zn?ZnO coating matrixes, which was attributed to dispersive strengthening effect and grain induced effect of the ZnO/Cr₂O₃ particulate.     

Preparation and high-temperature tribological properties of CrAlVYN-Ag nanocomposite coatings

CrAlVYN-Ag coatings were successfully deposited by introducing the elements of V and Ag into CrAlYN hard coatings. Their microstructure and mechanical property as a function of the annealing temperature were investigated from room temperature (RT) (～25°C) to 800°C. Besides, the worn surfaces were analyzed after combined effects of temperature and friction to figure out the wear mechanisms at different temperatures. The coatings exhibited special surface morphologies and Ag diffusion after annealing at different temperatures. In addition, the x-ray diffraction results showed that the coatings suffered obvious oxidation once the temperature exceeded 600°C; as a result of this, the coating hardness decreased sharply. The friction coefficients were relatively high during the tribological tests from RT to 400°C because the abrasive wear mechanisms played a dominant role. The lower friction coefficients obtained at 600 and 700°C were mainly due to the self-lubricating mechanisms. However, the coating exhibited higher friction coefficient at 800°C, which was mainly ascribed to the severe oxidation wear of the coating.     

Microstructure and mechanical properties of an ultrafine grained Ti5Si3-TiC composite fabricated by spark plasma sintering

The purpose of this study was to investigate mechanical properties, microstructure and sintering behavior of ultrafine grained Ti₅Si₃-TiC composite synthesized by mechanically activated self-propagating high-temperature synthesis method. For this purpose, the composite was sintered at 1450?°C at constant pressure of 50?MPa and reached to 97% of theoretical density by spark plasma sintering technique. The XRD pattern of the sintered sample is composed of the same peaks as the synthesized sample which means that the composite is stable at high temperature. The microstructure analyses illustrate that the composite retained its fine microstructure during the sintering process. The results also show that the amount of C atoms in the structure of titanium silicide slightly increased during the sintering process. The Young’s modulus and nanohardness of the composite reached 281?±?15.5?GPa and 16.6?±?0.8?GPa, respectively. In addition, Vickers indentation test results show that the composite possesses hardness and fracture toughness of 13.2?±?0.6?GPa and 4.7?±?0.1?MPa.m^1/2, respectively. Formation of microstructure with low microcracks and homogenous distribution of TiC through the matrix are responsible for relative high mechanical properties of the composite. The crack deflection is observed as the main toughening mechanism.     

Microwave dielectric properties of (1 − x)(Mg0.4Zn0.6)2SiO4–xCaTiO3 composite ceramics

Phase formation, microstructure and microwave dielectric properties of (1 ? x)(Mg_0.4Zn_0.6)₂SiO₄–xCaTiO₃ (MZS-C) composite ceramics synthesized by using the conventional solid-state method were systematically investigated. Three phase structure was observed in all samples by using X-ray diffraction and the back scattering electron images. Mg₂SiO₄ can form a solid solution with Zn₂SiO₄, which improved sinterability of the MZS-C composite ceramics. As the CaTiO₃ content was increased from 0.06 to 0.14, dielectric constant ε _r and temperature coefficient of resonant frequency τ _f values of the MZS-C ceramics sintered at 1,180 °C for 4 h increased from 6.74 to 8.35 and ?41.5 to ?6.46 ppm/°C, respectively. Zero τ _f value can be obtained by properly adjusting the x value of the (1 ? x)MZS–xC ceramics. With increasing content of CaTiO₃, densification temperatures of the composite ceramics were decreased. The composite ceramic with x = 0.14 sintered at 1,180 °C for 4 h exhibited excellent microwave dielectric properties of ε _r = 8.35, Q × f = 28,125 GHz and τ _f = ?6.46 ppm/°C.     

Structural analysis and corrosion studies on an ISO 5832-9 biomedical alloy with TiO2 sol–gel layers

The aim of this study was to demonstrate the relationship between the structural and corrosion properties of an ISO 5832-9 biomedical alloy modified with titanium dioxide (TiO₂) layers. These layers were obtained via the sol–gel method by acid-catalyzed hydrolysis of titanium isopropoxide in isopropanol solution. To obtain TiO₂ layers with different structural properties, the coated samples were annealed at temperatures of 200, 300, 400, 450, 500, 600 and 800 °C for 2 h. For all the prepared samples, accelerated corrosion measurements were performed in Tyrode’s physiological solution using electrochemical methods. The most important corrosion parameters were determined: corrosion potential, polarization resistance, corrosion rate, breakdown and repassivation potentials. Corrosion damage was analyzed using scanning electron microscopy. Structural analysis was carried out for selected TiO₂ coatings annealed at 200, 400, 600 and 800 °C. In addition, the morphology, chemical composition, crystallinity, thickness and density of the deposited TiO₂ layers were determined using suitable electron and X-ray measurement methods. It was shown that the structure and character of interactions between substrate and deposited TiO₂ layers depended on annealing temperature. All the obtained TiO₂ coatings exhibit anticorrosion properties, but these properties are related to the crystalline structure and character of substrate–layer interaction. From the point of view of corrosion, the best TiO₂ sol–gel coatings for stainless steel intended for biomedical applications seem to be those obtained at 400 °C.     

Development and characterization of laser clad high temperature self-lubricating wear resistant composite coatings on Ti–6Al–4V alloy

To enhance the wear resistance and friction-reducing capability of titanium alloy, a process of laser cladding γ-NiCrAlTi/TiC + TiWC₂/CrS + Ti₂CS coatings on Ti–6Al–4V alloy substrate with preplaced NiCr/Cr₃C₂–WS₂ mixed powders was studied. A novel coating without cracks and few pores was obtained in a proper laser processing. The composition and microstructure of the fabricated coating were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) techniques, and tribological properties were evaluated using a ball-on-disc tribometer under dry sliding wear test conditions at 20 °C (room-temperature), 300 °C, 600 °C, respectively. The results show that the coating has unique microstructure consisting of α-Ti, TiC, TiWC₂, γ-NiCrAlTi, Ti₂CS and CrS phases. Average microhardness of the composite coating is 1005 HV_0.2, which is about 3-factor higher than that of Ti–6Al–4V substrate (360 HV_0.2). The friction coefficient and wear rate of the coating are greatly decreased due to the combined effects of the dominating anti-wear capabilities of reinforced TiC and TiWC₂ carbides and the CrS and Ti₂CS sulfides which have excellent self-lubricating property.     

Microstructural study of oxidation of carbon-rich amorphous boron carbide coating

Carbon-rich amorphous boron carbide (B _x C) coatings were annealed at 400°C, 700°C, 1000°C and 1200°C for 2 h in air atmosphere. The microstructure and composition of the as-deposited and annealed coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS). All of the post-anneal characterizations demonstrated the ability of carbon-rich B _x C coatings to protect the graphite substrate against oxidation. Different oxidation modes of the coatings were found at low temperature (400°C), moderate temperature (700°C) and high temperature (1000°C and 1200°C). Finally, the feasibility of the application of carbon-rich BxC instead of pyrolytic carbon (PyC) as a fiber/matrix interlayer in ceramics-matrix composites (CMCs) is discussed here.     

Plasma- and vacuum-plasma-sprayed Cr3C2 composite coatings

Plasma- and detonation-sprayed chromium carbide-Nichrome coatings have long been used for applications requiring superior wear resistance at temperatures up to 820°C. The coatings are typically sprayed from mechanical blends of powder containing from 17 to 35 wt.% Nichrome. These coatings are susceptible to non-uniformity of microstructure because of segregation of the blended powders. Oxide formation occurs in both ambient atmosphere plasma and detonation-applied coatings.A new Cr₃C₂Nichrome composite powder was developed for application by the plasma and vacuum plasma processes. The developed material consists of 50 wt.% Cr₃C₂ clad with 50 wt.% 80-20 Nichrome. Unlike powder blends, each Cr₃C₂ powder particle is clad with an essentially continuous layer of Nichrome. The developed material is sized ?270 mesh + 5 μm.Coatings of the composite Cr₃C₂ material were sprayed using the conventional non-transferred arc plasma and the low pressure low oxygen vacuum plasma processes. These coatings were compared with coatings sprayed from a commercially available blend of 75 wt.% Cr₃C₂25wt.% Nichrome. Unlike the blend, the microstructure of both composite coatings showed Cr₃C₂ to be present as discrete second-phase particles embedded in the Nichrome matrix. The vacuum-plasma-sprayed composite coating showed no visible oxide. Macrohardness (Rockwell C hardness) and microhardness (diamond pyramid hardness for a load of 300 gf) readings of the conventionally sprayed coatings were 50 HRC and 600 HDP 300 respectively. The hardness values for the vacuum-plasma-sprayed composite were 60 HRC and 860 HDP 300. The abrasive slurry wear resistance of the conventionally sprayed composite was three times that of the blend, while the wear resistance of the vacuum-plasma-sprayed composite was four times that of the standard blend coatings.The air-plasma-sprayed composite Cr₃C₂Nichrome coatings are expected to exhibit performance characteristics comparable with similar detonation-applied coatings. The vacuum-plasma-sprayed composite coatings combine superior wear resistance with low oxide and are recommended for severe high temperature wear environments.     

The chemical vapor deposition of TiB2 from diborane

In this paper we describe an experimental study of the chemical vapor deposition of titanium diboride on graphite using the reaction of TiCl₄ with B₂H₆ in a hydrogen atmosphere in the temperature range 600–900 °C. Dense and adherent coatings were obtained varying in composition from boron rich at 600 °C (TiB_3.12) to stoichiometric above 700°C. There was a gradual increase in crystalline size with increasing deposition temperature. Chlorine tended to remain incorporated in the deposit (1.86 at.% at 600 °C decreasing to 0.51% at 900 °C). The coatings were very hard ($\text{HV = 3715 kgf mm}{}^{\mathrm{?2}}$).