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To improve the wear resistance of 6061 aluminum alloys, we reported the fabrication of Fe–Al coatings by laser surface alloying with mixed Fe and Al powders. The alloyed coatings mainly consisted of Fe4Al13, FeAl, Fe3Al and α-Al phases. Due to its high specific gravity, the Fe-rich melt segregated at the bottom of the molten pool during the laser process, and special microstructures characterized by a bright white stripe at the interfacial zone were formed. Additionally, the nonuniform exothermic reactions occurring along the width of the interfacial zone resulted in the formation of a rough sawtooth interface. The typical microstructures from the top layer to the interfacial zone of the alloyed coatings were investigated to explore the formation and solidification processes of the molten pool. Additionally, the microhardness of the coatings markedly improved with increasing Fe concentration in the mixed powders, reaching 720 HV0.2. Moreover, a 92.3% reduction in the volume loss of the 70Fe–30Al coating compared with that of the substrate significantly enhanced the wear resistance. [ABSTRACT FROM AUTHOR]

Ni35 coatings were fabricated on 45 steel using a CO2 laser at various parameters. A relatively large spot (10 mm diameter) was adopted, which was beneficial to the coating quality and the cladding efficiency. The cross-sectional geometry, phase constituent, and microstructure of the coatings were investigated. With a lower specific energy, coating height increased, while coating width, melted depth, dilution rate, width to height ratio and contact angle decreased. Ni35 coating primarily consisted of γ-Ni, FeNi3, Ni3B, Cr23C6, and Cr5B3. Dendrites with flower-like, fishbone-like, pearl-like, and column-like morphologies were observed. The fraction of flower-like dendrites increased gradually with the decrease in scanning velocity due to the dendrite growth direction evolution. With the decrease in scanning velocity, the microstructure of the heat-affected zone transformed from martensite to martensite + sorbite and finally sorbite. The maximum microhardness of the Ni35 coating reached 451.8 HV0.2, which was about double that of the substrate (220 HV0.2). [ABSTRACT FROM AUTHOR]

Laser alloying has attracted significant attentions due to the advantages of high processing precision, good controllability and low heat effects on the substrate. However, the complexity of laser alloying requires further attentions on its processing parameters. This study aims at improving the wear resistance of the Ti-6Al-4V substrate by means of laser surface alloying with Ni-coated graphite (G@Ni). The effect of laser scanning speed is explored. The result suggests that the coating has a high surface quality and excellent metallurgical bonding with the substrate. NiTi and NiTi2 have a eutectic microstructure as well as in the TiC ceramic-reinforced phase as dendrites distribute in the γ-Ni matrix of the coatings. At higher scanning speeds, the lower energy density and shorter existence time of the molten pool refines the microstructure of the coating, improving its microhardness. At the scanning speed of 15 mm/s, the coating has the lowest wear weight loss due to its high microhardness and dense structure. This paper explores the influence of scanning speed on the microstructure and properties of the coatings, expanding the application of laser alloying on the surface modification of Ti-6Al-4V alloys. [ABSTRACT FROM AUTHOR]

In this study, Co-based laser cladding coatings reinforced by multiple phases were fabricated on titanium alloy. Co42 Co-based self-fluxing alloy, B4C, and CeO2mixed powders were used as the precursor materials. The coatings were mainly composed of γ-Co/Ni, CoTi2, CoTi, NiTi, TiC, Cr7C3, TiB2, and TiB phases. A typical TiB2/Cr7C3/TiC composite structure was chosen. It was found that CeO2did not influence the phase types of the coating significantly, but was effective in refining the microstructure and enhancing the microhardness and dry sliding wear resistance. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced by 3.44–4.21 times and 14.26–16.87 times, respectively. [ABSTRACT FROM PUBLISHER]

Ti-Al alloyed coating reinforced by nitrides was fabricated by laser surface alloying technique to improve mechanical properties and high temperature oxidation resistance of Ti-6Al-4V titanium alloy. Microstructures, mechanical properties and high temperature oxidation behavior of the alloyed coating were analyzed. The results show that the alloyed coating consisted of Ti3Al, TiAl2, TiN and Ti2AlN phases. Nitrides with different morphologies were dispersed in the alloyed coating. The maximum microhardness of the alloyed coating was 906HV. The friction coefficients of the alloyed coating at room temperature and high temperature were both one-fourth of the substrate. Mass gain of the alloyed coating oxidized at 800C for 1000h in static air was mg/mm2, which was 1/35th of the substrate. No obvious spallation was observed for the alloyed coating after oxidation. The alloyed coating exhibited excellent mechanical properties and long-term high temperature oxidation resistance, which improved surface properties of Ti-6Al-4V titanium alloy significantly. [ABSTRACT FROM AUTHOR]

Ceramic coatings were deposited on 2A12 aluminum alloys using micro-arc oxidation (MAO) technology in CHCOONa-NaWO electrolyte. The MAO process was studied by recording the current-time curve. The influences of NaWO concentrations on the coatings in CHCOONa electrolyte were investigated. The results show that the NaWO concentrations affect the MAO process and performances of the coatings directly. NaWO in excess is harmful for the formation of AlO in this electrolyte. The corrosion resistance was enhanced with the decrease of NaWO concentration. [ABSTRACT FROM AUTHOR]

Abstract: Laser cladding of the Fe3Al+TiB2/Al2O3 pre-placed alloy powder on Ti–6Al–4V alloy can form the Ti3Al/Fe3Al+TiB2/Al2O3 ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti3Al/Fe3Al+TiB2/Al2O3 ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al2O3 can react with TiB2 leading to formation of amount of Ti3Al and B. This principle can be used to improve the Fe3Al+TiB2 laser cladded coating, it was found that with addition of Al2O3, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al–Ti–B system and hard phases. [Copyright &y& Elsevier]

Thermal barrier coatings of Al2O3–ZrO2 were prepared by air plasma spraying on the surface of 20G steel. Phase constitution, microstructures and elemental distributions of the coatings were studied by X-ray diffraction, scanning electron microscope and electron probe X-ray microanalysis. The results show that the plasma spray coating mainly consists of α-Al2O3, c-ZrO2, and t-ZrO2. The bond state of the interface between the top layer and bond layer is fine, and the bond layer has a good combination with the substrate. ZrO2 and Al2O3 structures can closely integrate together and form compact top layer system. [ABSTRACT FROM AUTHOR]

The oxidation behavior of the coatings at 1100°C in air was investigated using electron probe microanalyzer, scanning electron microscopy, and X-ray diffractometer. Compacted oxide scales, mainly consisting of oxides of Al and Y, were formed on the coating surface, and thus the oxidation resistance of the coatings was enhanced. Cone oxides are formed on the scale surface and normal to the coating surface due to the characterization of preferential growth. [ABSTRACT FROM AUTHOR]

It is thought that the PEO (plasma electrolysis oxidation) coatings are difficult to be prepared on the cast Al–Si alloys because these alloys contain lots of pure silicon phases. In the present study, oxide coatings with a thickness of about 10 μm were deposited on the substrate of the ZL109 Al–Si alloy by a PEO treatment. XRD showed that the phase composition of the coating was γ-Al2O3. SEM showed that the coating surface was porous, and the pore diameter was in the range of 1–5 μm. The cross-section view by EDS indicated that the coating matrix is quite dense, and there are few defects. Phosphorus from the applied electrolyte could be incorporated into the coating during the PEO process. A transitional zone with a thickness of about 3 μm was observed on the interface between the coating and substrate, and a high adhesive strength was expected. The average hardness of the coating was 576 HV0.025, which was 7.2 times higher than that of the substrate. High alloy element content of the substrate seems to have no remarkable and adverse influence on the structure and composition of the PEO coating. [ABSTRACT FROM AUTHOR]

Laser cladding is one kind of advanced surface modification technology and has the abroad prospect in making the wear-resistant coating on metal substrates. However, the application of laser cladding technology does not achieve the people's expectation in the practical production because of many defects such as cracks, pores and so on. The addiction of rare earth can effectively reduce the number of cracks in the clad coating and enhance the coating wear-resistance. In the paper, the effects of rare earth on metallurgical quality, microstructure, phase structure and wear-resistance are analyzed in turns. The preliminary discussion is also carried out on the effect mechanism of rare earth. At last, the development tendency of rare earth in the laser cladding has been briefly elaborated. [ABSTRACT FROM AUTHOR]

Ceramic-like coatings were deposited on the substrate of the AZ91 alloy by micro-arc oxidation (MAO). Many methods like X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDS) were used to analyze the structure and composition of the coating. XRD showed that the MAO coating was mainly composed of MgO. The results of SEM showed that the coating surface possessed a porous microstructure and the pore size was in the range of 1–3 μm. EDS indicated that the coating matrix was relatively dense and had a homogeneous thickness. The element silicon from the applied electrolyte could be absorbed into the coating in the MAO process. The hardness of the MgO coatings could reach 513 HV0.025 that was about four times higher than that of the substrate. It is expected that the coatings have a great potential in the surface protection of magnesium alloys. [ABSTRACT FROM AUTHOR]

Since the discovery of Bioglass® by Hench, bioactive glasses have been used in many medical applications, such as drug delivery systems, nonload-bearing implants, and bone cements because of their excellent bioactivity and biocompatibility. However, due to their poor mechanical properties, these glasses cannot be used in load-bearing applications, where the metallic alloys are still main materials. One useful approach to solving the mechanical limitations of bioactive glasses is to apply the glasses as the coating on mechanically tough substrates; it was also recognized early that bioactive glasses could be used as coatings for prosthetic metallic implants. In this paper, the mechanism, characterization, and current status of some methods of preparation for bioactive glass coating on implants are introduced. In the end, to get the homogeneous and compact coating with perfect bonding strength, some ideas of improving the performance of coatings are also presented. [ABSTRACT FROM AUTHOR]

Electrophoretic deposition (EPD) is a good method in the fabrication of the coating materials. Its processing parameters are easy to be operate. It is a nonbeeline process and can be used in the deposition on complex shape and porous surface. It has been widely used in many ways. This paper reviews the principles and fabrication steps of EPD and points out the influencing factors. The developments of EPD in the fabrication of materials, such as solid surface coatings, porous structure materials and gradient materials, are introduced in detail. The future of the application of EPD is also discussed. [ABSTRACT FROM AUTHOR]

Hopeite (Zn3(PO4)2·4H2O) conversion coating was prepared on pure titanium using mild phosphate chemical conversion technology. In this investigation the effect of post-processing after phosphating was focused on coating microstructure, chemical composition, adherence and corrosion resistance. Different sequential order of drying and rinsing of the coated samples were carried out. The results demonstrated that the priority shift of rinsing or drying did not change the hopeite phase of the conversion coating, but played a significant role in the crystal size and coating microstructure. Compared with the traditional preparation of the coating, a more compact and uniform coating with finer crystals grains (3–5 μm) was obtained by the unconventional post-treatment of drying before rinsing, along with a higher bonding strength and corrosion resistance. [ABSTRACT FROM AUTHOR]

A porous bioceramic containing tricalcium phosphatein (TCP) coating was prepared by micro-arc oxidation (MAO) with different voltages. The degradability and bioactivity of the coatings were measured by immersion tests in the stimulated body fluid (SBF). The thickness, phase composition and morphology of the oxide coating were monitored with X-ray diffraction (XRD), fourier transform infrared spectrometer (FT–IR) and scanning electron microscopes (SEM) with energy energy-disperse spectrometer (EDS). The results show that the TCP-containing coating can be influenced by the increasing applied voltages through affecting the energy of sparking and the effect of electrical field. The MAO coatings have porous surface morphologies with uniform and compact micropores. The results of immersion tests confirm that the TCP-containing MAO coating has bioactivity and could protect Mg–4.75Zn–0.55Ca alloy from corrosion effectively. [ABSTRACT FROM AUTHOR]

Laser-alloyed composite coatings were fabricated on Ti–6Al–4V by using Ni60A + micro-sized B 4 C particles as the precursor material. The composite coatings were mainly comprised of a kind of TiB 2 /TiC complex structure, assembled by TiB 2 lamellae and TiC pillars. In this study, the formation mechanism of the TiB 2 /TiC complex structure was discussed intensively. TiB 2 lamellae were firstly precipitated from the melt pool. Subsequently, TiC particles nucleated heterogeneously and grew on the TiB 2 plates. The nucleation and growth of TiB 2 and TiC proceeded synchronously, further forming the TiB 2 /TiC complex structure. The composite coating fabricated under a moderate scan velocity (450 mm⋅min−1) exhibited a good combination of high micro-hardness and wear resistance. [ABSTRACT FROM AUTHOR]

Abstract Ti-Al- x Nb- y Si coatings were fabricated by laser surface alloying on a Ti-6Al-4V alloy substrate. The high-temperature oxidation behavior of the coatings was investigated at 800 °C. The coatings mainly consisted of TiAl x and Ti 5 Si 3. Compared with the substrate and Ti-Al coatings, the Ti-Al- x Nb- y Si coatings showed better oxidation resistance. The synergistic effect of Nb and Si on improving high temperature oxidation resistance of the coatings included changing the control mechanism of the oxidation process, promoting the formation of Al 2 O 3 in the oxide scales, inhibiting the diffusion of oxygen and increasing the adhesion of the oxide scales. Highlights • Ti-Al-xNb-ySi coatings with different Nb and Si content were fabricated. • The coatings consisted of TiAl x and Ti 5 Si 3 and were free of cracks. • Ti-Al-xNb-ySi coatings had good high temperature oxidation resistance. • The addition of Nb and Si promoted the formation of Al 2 O 3 in the oxide scales. • The addition of Nb and Si improved the adhesion of the oxide scales. [ABSTRACT FROM AUTHOR]

In this study, Ti-Al- x Nb coatings were deposited on a Ti-6Al-4V alloy by laser surface alloying in order to investigate their oxidation resistance. A Ti-Al coating was fabricated for comparison. It was found that the Ti-Al and Ti-Al- x Nb coatings were composed of TiAl and Ti 3 Al phases. Nb addition reduced the cracking tendency of the Ti-Al- x Nb coatings. The Ti-Al and Ti-Al- x Nb coatings exhibited good high-temperature oxidation resistance at 800 °C. In comparison, Ti-Al- x Nb ( x  = 10, 20, 30 and 40) coatings had better high-temperature oxidation resistance and Ti-Al-40Nb coating had the best high-temperature oxidation resistance. The mechanism of Nb that improves the high-temperature oxidation resistance of Ti-Al- x Nb coatings includes preventing the internal diffusion of oxygen, inhibiting the formation of TiO 2 , promoting the formation of Al 2 O 3 and increasing the adhesion of the oxide scales. [ABSTRACT FROM AUTHOR]

Si-CaP containing coatings were deposited on a Mg-Zn-Ca alloy by the two-step micro-arc oxidation processes. The surface and cross-section morphologies, EDS analysis, phase composition and polarization curves of MAO coatings were investigated. With the increasing of the two-step voltages, the number of micro-pores tended to decrease and the surfaces became more compact while the thickness of coatings continually increased. In addition, the corrosion resistance of Mg alloy was greatly improved with the Si-CaP coatings, and the Mg alloy with Si-CaP coating prepared at 400 V had the best corrosion resistance. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) is a promising surface treatment technique to enhance the corrosion resistance of Mg alloy. However, the micro-pores and micro-cracks of the PEO coating limit its anti-corrosion protection capability. In this study, a dense Ca 3 Al 2 (OH) 12 layer was fabricated on the PEO coating surface by hydrothermal treatment (HT), forming a PEO/HT composite coating. Surface morphologies, chemical composition, phase composition and growth process of the PEO/HT composite coating were characterized using Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FT-IR). Corrosion resistance of the samples was studied through immersion test, hydrogen evolution test, and electrochemical test. Results demonstrated that the PEO/HT coating possessed a polyhedral structure and the micro-pores and micro-cracks of the PEO coating were sealed. The PEO/HT composite coating showed improved bioactivity in comparison with PEO coating and Mg alloy after immersion in Hanks' solution. Moreover, the Ca 3 Al 2 (OH) 12 crystals layer improved the corrosion resistance of PEO coating significantly. Furthermore, the growth process of Ca 3 Al 2 (OH) 12 layer was discussed. [Display omitted] • A dense Ca 3 Al 2 (OH) 12 layer was fabricated on the PEO coating surface by HT. • The anti-corrosion property of the PEO/HT coating was significantly higher than that of both Mg alloy and PEO coating. • The formation mechanism of Ca 3 Al 2 (OH) 12 structure layer was proposed. [ABSTRACT FROM AUTHOR]

• TiAl coatings with different Nb and Si content were fabricated. • Hot corrosion behaviors of the coatings were investigated. • High Si addition improved hot corrosion resistance of the coatings. • Co-addition of Nb and Si improved hot corrosion resistance of the coatings. • Mechanism of Nb and Si on hot corrosion resistance of the coatings was investigated. Hot corrosion behaviors of TiAl coatings with different Nb and Si additions in a Na 2 SO 4 + NaCl salt mixture at 800 °C were investigated. Corrosion kinetics was evaluated based on mass change measurements. The corrosion products and morphologies of the corrosion scales were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The adhesion strength of the corrosion scales was evaluated by acoustic emission (AE). High Si addition on its own and a co-addition of a high content of Si and an appropriate content of Nb improved the hot corrosion resistance of the coatings. [ABSTRACT FROM AUTHOR]