Ceramic Oxide Layer Research Articles

Rheological Modeling and Fracture of Hard Oxide Ceramics Modified by Ultra-Dispersed Diamond Nanoparticles

Fracture of Al-Al 2 O 3 -diamond-containing composite coating was investigated using rheological models for principal Hertzian contact of a sphere and a plate. The crystallographic and morphologic texture was characterized and the fracture resistance was measured using fracture mechanics. A rheological model of the composite coating was proposed and confirmed by in situ experiments. Examination of the composite coating showed a hardness value of 25 GPa (about 25% higher than for an alumina-based layer) and fracture resistance (about 50% higher than for a single oxide ceramic layer) as compared to prior alumina-based coatings on a soft substrate. Experiments revealed ultimate stresses and stress-strain modes of the coating. Diamond nanoparticles improved fracture resistance of an alumina-based layer. It is also thought that the composite coatings will have higher thermal conductivity and thermal shock resistance than alumina-based layers. Such physical characteristics suggest a number of possible commercial applications for the composite coatings, particularly for wear-resistant and related applications. The higher hardness and toughness of the coatings make them very attractive as substitutes for alumina-based and other ceramic-based composite coatings in these applications. composite rheology fracture stress indentation diamonds

Preparation of microarc oxidation layer containing hydroxyapatite crystals on Ti6Al4V by hydrothermal synthesis

Titanium alloys are widely applied in producing hard tissue implants (such as bone, joint, and teeth), but they are bioinert materials and fail to form chemical bond with host bone. Bioactive hydroxyapatite (HA) coatings can form bony contact with bone tissue and shorten the healing period, but their dissolution and fracture limit their wide application [1]. It is essential to prepare bioactively modified layer on titanium alloy with high bond strength. Microarc oxidation (MO) is a technique of ingrowing oxidation ceramic layer on nonferrous metals, which was firstly developed in 1970s [2]. The antiscuff and anticorrosion properties of titanium alloys were improved after MO treatment [3, 4]. As for biomedical application, Ca2+ and PO3− 4 ions in electrolyte could enter the ceramic layer during MO process and existed in amorphous form, so that the bioactivity potential of titanium alloys was increased [5]. But unfortunately, HA crystals were not formed on the surface of MO layer, which makes it difficult for bone tissue to attach on the implants. Hydrothermal synthesis (HS) can convert other calcium phosphates to HA [6]. Here, the MO layer containing Ca and P on Ti6Al4V was hydrothermally treated to obtain surface modified bioactive layer containing HA crystals on titanium alloy. The study also showed that the MO-HS layer has high bond strength (above 25 MPa) with biologically favorable roughness and porosity. 25 × 2.5 titanium alloy (Ti6Al4V) plates were used as substrates. They were polished with 600 and 1000# abrasive paper, ultrasonically washed with deionized water and acetone. The electrolyte was prepared by calcium salt and phosphate salt with a Ca/P mole ratio 3. Ti6Al4V plate was anode and stainless plate cathode. Pulse-direct power resource was used with voltage 350 V and occupancy/(occupancy + void) ratio 60%. The oxidation time was 3 min. The samples by MO was hydrothermally treated in an autoclave at 160, 180 for 2 or 4 h, and the pH of water was adjusted to 11–12 by adding ammonia. Scanning electron microscopy (SEM) was used to analyze the surface and profile morphology, and X-ray diffraction (XRD) and electron dispersive X-ray analysis (EDXA) were used to analyze the phase and element composition. Tensile bond strength test was carried out

Thickness effects on the mechanical properties of micro-arc discharge oxide coatings on aluminium alloys

Weight-saving materials are becoming increasingly important, especially in the automotive and aerospace industries. Design engineers would thus like to make more extensive use of light metals such as aluminium, titanium, magnesium and their alloys; however, these materials tend to have poor wear resistance. Previous treatments and coatings applied to aluminium alloys, for example by traditional processes such as hard anodising and thermal spraying, have suffered from the low load support from the underlying material and/or insufficient adhesion, which reduces their durability. Also, although TiN-, CrN- or DLC-coated aluminium alloys (using various PVD methods) can achieve a high surface hardness, in practice they often exhibit poor performance under mechanical loading, since the coatings are usually too thin to protect the substrate from the contact conditions.In the work reported here, a plasma electrolysis technique known as micro-arc discharge oxidation (MDO) was investigated; thick and hard oxide ceramic layers were fabricated on BS Al-6082 aluminium alloy by this method. The phase composition and microstructure of the MDO coatings were investigated by XRD, SEM and EDX analyses. A number of adhesion and tribological sliding and impact wear tests were also performed. It was found that Al–Si–O coatings with a hardness of up to 2400 HV and with excellent wear resistance and load support could be formed. The thickness of the coatings significantly influenced the mechanical properties. In terms of tribological performance, the thicker coatings performed best in sliding, scratch and impact tests whilst thin coatings were also surprisingly effective in both impact and low-load sliding. Coatings of intermediate thickness provided relatively poor performance in all tribological tests.

Plasma electrolytic fabrication of oxide ceramic surface layers for tribotechnical purposes on aluminium alloys

Abstract The problem of technical and economical optimization of the process of micro-arc discharge oxidation of high-strength aluminium for the fabrication of oxide ceramic layers for tribotechnical purposes is considered in terms of experimental design. To estimate the effectiveness of the process, a generalized parameter is used which accounts for oxide mass yield as a principal parameter, and mechanical and geometrical characteristics of the layer as restricting parameters. The methods of chemical weight, scanning electron microscopy, optical and durometric analyses are used. The influence of the silicate–alkali electrolyte composition and the amount of electricity carried through the cell on the layer properties is discussed. The response surface of the generalized parameter is plotted with the aid of desirability functions. The area of regimes corresponding to 2–3 g l −1 KOH and 2–3 g l −1 Na 2 SiO 3 electrolyte composition and (2.50–3.33)×10 3 C m −2 of carried electricity is outlined for the most effective fabrication of uniform oxide layers with 165–190 μm thickness and 18–23 GPa hardness.

Oxygen Diffusion Hardening of Ti-Nb-Zr Alloys

Abstract Ti-13Nb-13Zr (Ti-13-13TM) is a new titanium alloy developed for medical implant applications. In the oxygen diffusion hardened condition, Ti-13-13 and titanium alloys which possess zirconium, are hardenable at temperatures of 400 to 600°C with the end result being a passive, mechanically stable, abrasion resistant oxide ceramic surface layer of about 0.2 to 2 μm in thickness. The thickness of this surface layer depends on the concentration of zirconium, time, temperature, and partial pressure of oxygen. This paper describes the results of x-ray diffraction analysis, secondary ion mass spectroscopy, x-ray photoelectron spectroscopy, Knoop and Nano hardness measurements, and reciprocal polarization resistance measurements of hardened Ti-13-13, and selected Ti-Nb-Zr alloys. The results of this work suggest that zirconium plays a key role for effective oxygen diffusion hardening at 500°C for Ti- ] 3-13 and similar Ti-Nb-Zr alloys.

Oxide Matrix Composite by Directional Oxidation of a Commercial Aluminum‐Magnesium Alloy

Oxidation rates of a commercial Al‐Mg alloy, Al‐5083, were investigated to understand the synthesis of an oxide‐based composite. In some experiments, the oxide layer was grown with several platinum wires embedded in the matrix to facilitate transport of electrons. The oxidation rate was not controlled by the rate of transport of the electrons and positive holes through the ceramic oxide layer. In the initial phase of the composite growth, an incubation period was observed due to formation of MgO on the alloy surface. At 1273 K or higher, the incubation period was followed by a period of sustained oxidation after MgO was converted to a spinel layer. It is demonstrated that, after the initial incubation period, the rate of oxidation is influenced by the rate of transport of ions through the oxidematrix composite.

Electrophoretic deposition - a method for preparation of semiconducting oxide ceramic layers

Electrophoretic deposition has been used as a method for the preparation of layers, based on NiMn 2O 4 and related compounds. The deposition was carried out in a suspension of a precursor powder dispersed in butanol. After deposition the layers were sintered. The morphology and the conductivity behaviour of the layers have been investigated.