Search

A novel Al 27 Cr 25 Ti 18 Nb 18 Zr 12 eutectic high entropy alloy (EHEA) coating with BCC/B2 and Laves phase has been developed by laser cladding on Ti–6Al–4V alloys. The average microhardness of EHEA coating was ∼697.6HV 0.3 , which significantly surpasses the values reported for most eutectic high-entropy alloy coatings. The strengthening effect and additional strain hardening sources generated by the intersecting nanometer-spaced stacking faults and Lomer-Cotrell locks which found in BCC/B2 phase are important reasons for the superior hardness. And the adhesive problem of Ti–6Al–4V alloy was ameliorated by the EHEA coating with lower friction coefficient (83.05 % of the Ti–6Al–4V alloy) and volumetric loss (27.75 % of the Ti–6Al–4V alloy). • A novel eutectic high entropy alloy (EHEA) coating consisting of BCC/B2 and Laves phases was firstly reported. • A large number of intersecting nanometer-spaced lattice imperfections were found inside the BCC/B2 phase. • Due to the rigid eutectic phases and lattice imperfections, microhardness in this work exceeds the majority of EHEAs. • The adhesive problem of Ti–6Al–4V alloy was ameliorated by this coating and the effect mechanism was investigated. [ABSTRACT FROM AUTHOR]

In this work, the fabrication of supersonic fine particle bombardment (SFPB)-doped rare-earth pretreatment modified vacuum carburized layers were applied. The SFPB-doped La 2 O 3 pretreated vacuum carburized reinforced layer was explored by common testing methods such as XRD, XPS, SEM, and TEM, focusing on the effects of La 2 O 3 -doped SFPB pretreatment on the decomposition, adsorption and diffusion of active carbon atoms and the diffusion mechanism. The composite carburizing behavior of La 2 O 3 -doped SFPB pretreatment modified layer under the action of thermal coupling is explored, and the influence law of rare earth modified carburizing and nano-modified carburizing on the thickness, residual stress, impact toughness, tribological properties of the carburized layer were clarified. The mechanism of mass transfer under the coupling role of pre-set surface defects and rare earth pinning was revealed. The case depth of the LSPC layer was increased by 14.3%, and the residual stress was significantly higher. The carbon diffusion coefficients of LSPC were 1.31 times superior to that of the vacuum carburizing layer, which is mainly attributed to the formation of a large number of nanocrystals with high-angle grain boundaries (HAGBs) by the rare-earth doped nanosized pretreatment, and the multiple synergistic strengthening effects of rare-earth oxides and nanocrystals. [Display omitted] • SFPB pretreatment introduces both La 2 O 3 and diffusion channels into the surface/subsurface layer. • Enhancement of carbon diffusion driving force by La 2 O 3. • High dislocation density and LAGBs provide fast diffusion channels for carbon diffusion. • The pretreatment increased the thickness of the carburized layer by 14.3%. [ABSTRACT FROM AUTHOR]

In this work, the Co 25 Ni 45 Al 30 and Co 25 Ni 50 Al 25 magnetic shape memory alloy (MSMAs) coatings were successfully synthesized on 38CrMoAl by laser cladding technology. By regulating the composition, β phase transformed to M phase due to the martensitic transformation, and the structure presented M phase and γ phase layered eutectic in Co 25 Ni 50 Al 25 coating. The analysis of microstructure, mechanical property, and frictional property was investigated in detail. The results showed that with β phase transformed to M phase and layered eutectic appeared in Co 25 Ni 50 Al 25 , the coating changed from brittle material to plastic material while the hardness increased. The friction property promoted, Co 25 Ni 50 Al 25 coating showed lower friction coefficient of 0.5, lower weight loss of 10 mg and lower wear rate of 5.9·10−14 m3 N−1 m−1. The wear mechanism of Co 25 Ni 45 Al 30 were abrasive wear and oxidation wear, while the wear mechanism of Co 25 Ni 50 Al 25 were adhesive wear and oxidation wear. • Martensite transformation was occurred in Co 25 Ni 50 Al 25 coating. • M phase and the eutectic structure were found in Co 25 Ni 50 Al 25 coating. • Co 25 Ni 50 Al 25 coating changed from brittle material to plastic material. • The weight loss of Co 25 Ni 50 Al 25 coating is 1/3 of Co 25 Ni 45 Al 30 coating. [ABSTRACT FROM AUTHOR]

Aluminum bronze coatings were prepared on MBLS10A-200 magnesium-lithium alloy substrate by cold spraying technology to improve the surface properties of Mg–Li alloys. The microstructure, phase composition, microhardness, tribological properties and corrosion resistance of the coatings were systematically analyzed. The results show that aluminum bronze coatings are mainly composed of α phase. β phase in the original aluminum bronze powder disappeared in the coating due to the eutectoid transition of β→α + γ 2 during the cold spraying. Compared with the Mg–Li alloy substrate, the aluminum bronze coating exhibits the higher microhardness (222.88 HV 0.3) and wear resistance (friction coefficients, wear track widths and wear mass losses are 0.37, 0.79 mm and 2.47 mg, respectively). The dominant wear mechanism of the coatings was abrasive wear. In the electrochemical test, the corrosion current density of the aluminum bronze coating (3.07 × 10−5 A/cm2) was an order of magnitude lower than that of Mg–Li alloy substrate (6.15 × 10−4 A/cm2), indicating that the coating had superior corrosion resistance. The above analysis confirms that preparing a cold sprayed aluminum bronze coating has outstanding tribological and corrosion resistance properties. • Aluminum bronze coatings were prepared on Mg–Li alloy by cold spraying. • Aluminum bronze coatings are mainly composed of α phase. • The eutectoid transformation of β. →α + γ 2 occurred during the cold spraying process. • The wear and corrosion resistance of Mg–Li alloy are comprehensively improved. [ABSTRACT FROM AUTHOR]

Abstract: A phytic acid conversion film with especial functional groups was proposed as the pretreatment layer between Ni–P coating and AZ91D magnesium alloy substrate, to replace the traditional pretreatment. In the process, the silane coupling agent was adopted as connector between conversion film and palladium ion with catalysis. The microstructure of the phytic acid conversion coatings was observed using scanning electronic microscopy, while the composition and functional groups were analyzed by energy dispersive spectrometer and Fourier transform infrared spectroscopy. The bonding between Si–OH of the silane coupling agent and hydroxyl of phytic acid was validated by X-ray photoelectron spectroscopy, and the existence of palladium ion was also verified. The subsequent Ni–P deposited on the layer was also characterized by its structure, morphology, and corrosion resistance. The results show that the Ni–P coatings with the phytic acid pretreatment on AZ91D magnesium alloy have good corrosion resistance. [Copyright &y& Elsevier]

Abstract: In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES). The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5gl−1 corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1–5gl−1 are integrated and uniform. However, those formed in 20–50gl−1 have some micro-cracks on the α phase. The coating formed in 5gl−1 has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1–20gl−1 can all improve the corrosion resistance of AZ91D. [Copyright &y& Elsevier]

Refractory High Entropy Alloys (RHEAs) have great potential for ultra-high temperature environments and are one of the potential candidates for high temperature applications. In this work, a series of Al 0.75 NbNi 0.1 Mo 0.1 Cr 0.5 Si 0.1 W x (x = 1, 1.5, 2) refractory high-entropy alloy coatings is prepared by laser cladding technology. The microstructure and oxidation behavior at 1000 °C and effect of changing oxidation temperature on oxidation behavior of the coatings is investigated. The results show that Al 0.75 NbNi 0.1 Mo 0.1 Cr 0.5 Si 0.1 W x RHEA coatings are composed of BCC, W 5 Si 3 and AlNi 3 phases. The microstructure of RHEA coatings exhibits dendritic-cellular grain transition with increasing W content. The specific mass gains of coatings due to high temperature oxidation is 65.5 mg/cm2 for x = 1, 8.5 mg/cm2 for x = 1.5 and 14.5 mg/cm2 for x = 2 at 1000 °C for 70 h. After oxidation in 1000 °C for 70 h under air atmosphere, a protective oxide film (such as Al 2 O 3 and SiO 2) adhere around NiWO 4 on the alloy coatings, which impedes the inward oxygen transport. Moderate addition of W elements is found to be beneficial in enhancing the oxidation resistance of coatings. However, excessive addition of W elements prevents the formation of protective oxides (Al 2 O 3 and SiO 2) and reduces the high-temperature oxidation resistance of the coatings. With the increase of oxidation temperature, simple oxides are significantly reduced while compound oxides are increased on the surface of the coatings. The surface appears hill-shaped oxides with the increase of NiWO 4. • The increase in W element content promotes the formation of cellular crystal structure. • The combination of SiO 2 and Al 2 O 3 can form a dense oxide layer. • Al diffuses rapidly to the top of the oxide layer during the oxidation process. • Part of the elemental distribution shows a continuous horizontal band in the oxide film. [ABSTRACT FROM AUTHOR]

In this study, graphite/CeO 2 reinforced Co-based coatings were prepared on the surface of HT250 gray cast iron by the plasma cladding technology. The influence of graphite and CeO 2 on microstructure and properties of Co-based coatings were studied in detail. The phase composition and microstructure of coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The micro-hardness, wear resistance and corrosion resistance of coatings were evaluated using micro-hardness tester, friction wear testing machine and electrochemical workstation. The results showed that the addition of graphite was beneficial to enhance micro-hardness and wear resistance of coatings, but there was still shortcoming in improving corrosion resistance. On this basis, CeO 2 was further introduced together with graphite. The microstructure of coatings was found to be more uniform under the synergy of graphite and CeO 2. The micro-hardness increased from 684.5 HV 0.3 (coatings adding graphite alone) to 767.4 HV 0.3 (coatings adding graphite and CeO 2), which was 29.7% and 115.1% higher than that of as-cladded coatings and substrate respectively. More importantly, the corrosion current density of coatings was an order of magnitude lower than that of coatings adding graphite alone. Therefore, adding CeO 2 together with graphite was beneficial to the synergistic improvement of micro-hardness, wear resistance and corrosion resistance of Co-based coatings. • Co-based coatings adding graphite/CeO 2 were prepared by plasma cladding. • The microstructure of coatings became uniform after adding graphite/CeO 2. • Wear resistance of coatings adding graphite together with CeO 2 was enhanced. • Corrosion resistance of coatings adding graphite together with CeO 2 was raised. [ABSTRACT FROM AUTHOR]

The improvement of wear resistance has a profound effect on the far-ranging application of aluminum alloy. In this study, the Al–Cu-based in-situ reinforced composite coating was successfully manufactured on the AlSi10Mg substrate by laser cladding. The microstructure, microhardness and wear resistance under gradient loading (3 N, 6 N, 9 N, 12 N and 15 N) and thermal conditions (200 °C, 300 °C and 400 °C) of the composite coating were studied. The research results showed that the composite coating exhibited a gradient distributed microstructure due to the different diffusion degrees of Cu and Al atoms. The composite coating was mainly composed of Al 4 Cu 9 , Al 7 Cu 4 Ni and α-Al in the bottom, center and top area, respectively, and Al 2 Cu evenly distributed in each area. The microhardness showed gradient distribution owing to the gradient microstructure. Compared with the AlSi10Mg substrate, the composite coating possessed higher microhardness and better wear resistance contributed by the gradient Al–Cu intermetallic compounds. At room temperature, the main wear mechanisms of the composite coating changed from abrasive wear to adhesive wear with the increase of loading condition. At high temperatures, the main wear mechanisms of the composite coating were adhesive wear and plastic flow. During the wear process, Al–Cu intermetallic compound was the key to improving the wear resistance and stabilizing the friction coefficient. • The Al–Cu-based composite coating with gradient distribution on Al alloy was prepared. • The diffusion properties of Al and Cu elements were briefly analyzed. • The friction property of the coating is improved than the substrate at room and high temperatures. • The increase of Al–Cu intermetallic and the transformation of microstructure make the coating have better properties. [ABSTRACT FROM AUTHOR]