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The incorporation of graphene-based nanodispersoids in ceramic coatings is known to enhance the wear behavior of these materials. In this study, for the first time, alumina/graphene nanoplatelets (GNPs) coatings were deposited through Suspension High Velocity Oxy-Fuel (SHVOF) thermal spray on Al 2 O 3 /TiC substrate composites, which were laser microtextured with grid and line surface patterns. Dense coatings with around 8−10 μm thickness were obtained by spraying alumina suspension containing 1 wt. % GNPs. The tribological performance of the alumina/GNPs coatings on the Al 2 O 3 /TiC substrate composites was evaluated using ball-on-disc sliding wear tests. The alumina/GNPs coated Al 2 O 3 /TiC substrate composites textured with grid pattern showed the best tribological performance reaching a steady coefficient of friction (CoF) at lower sliding distances and presenting the lowest wear rate of the Al 2 O 3 /TiC substrate composites and the counterbody. [ABSTRACT FROM AUTHOR]

In our present work, alumina/BNNTs and alumina/MoS 2 coatings were deposited onto stainless steel substrates by solution precursor high velocity oxy-fuel thermal spraying. The phase evolution, microstructure and tribological properties of the two kinds of coatings were studied. Investigation of the phased content showed that Al 2 O 3 , BN and MoS 2 survived in the coatings after being sprayed with SHVOF technology. Cross-section images of the coatings showed that the interface between the coating and the substrate was well bonded, and there were no obvious particle inclusions and defects at the interface. The top morphology of the coatings exhibited certain degree of particle deformation, which was conducive to the formation of a more compact coating with less porous and better bonding strength with the substrate. Dry sliding tests showed that alumina/BNNTs and alumina/MoS 2 coating improved the tribological properties of the samples and they were suitable for low load friction conditions (5 and 10 N). A crack evolution model was proposed to analyze the failure of coatings. This work could provide a reference for the application of the two coatings in the field of friction and wear. • Alumina/BNNTs and alumina/MoS 2 were deposited onto a stainless steel substrate using SHVOF thermal spraying. • The top morphology of the coatings exhibited a certain degree deformation of the particles. • The wear mechanisms of the coatings were dominated by coating peeling off, adhesion and abrasive wear. • A crack evolution model was proposed to analyze the failure of coatings. [ABSTRACT FROM AUTHOR]

According to the tensile crack model, a simple model for tribological behaviors of diopside/AlTiB toughened alumina matrix ceramic guideway materials, predicting the relationship between load and wear rate, was presented. 45# steel ring was used as the counterpart. Mechanical properties and wear properties of the guideway materials under different loads were investigated. SEM micrographs of wear tracks on typical specimens were studied. Results showed that the experimental data described in this paper were in accordance with the theoretical prediction. Introduction of diopside and AlTiB master alloys in alumina matrix ceramic guideway materials improved their mechanical properties, friction and wear properties. The wear rate of pure alumina was in the order of 10 −15  m 3 /N·m while that of guideway materials toughened by diopside and AlTiB master alloys was in the order of 10 −16  m 3 /N·m. The wear mechanisms of pure alumina may be brittle fracture and grain pull-out. The dominant wear mechanisms of alumina matrix ceramic guideway materials toughened by diopside and AlTiB master alloys may be mechanical interlocking and plastic deformation combined with a little micro-fracture and grain pull-out. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, diopside and AlTiB were simultaneously introduced in alumina using pressureless sintering. Microstructures of the composites were observed at a given temperature of 1520°C and different holding time. Sintering densification process of the composites was studied. Experiments were performed in the temperature at equal increments: 1420, 1520, 1620 and 1720°C, and with four holding times, i.e. 100, 140, 180 and 220min. The apparent activation energies of 17.7–28.8kJ/mol for alumina matrix ceramic materials were calculated by least squares. The sintering kinetic equations were deduced. Results showed that the sintering of monolithic alumina was controlled by volume diffusion, and that of alumina matrix ceramic materials doped with diopside and AlTiB was controlled by grain boundary diffusion and volume diffusion. [Copyright &y& Elsevier]

Abstract: Al2O3/diopside ceramic composites with good mechanical properties were prepared by uniaxial hot-pressing and their biological activity in simulated body fluid was studied by SEM, XRD, FT-IR and EPMA. SEM micrographs showed a lath-like apatite layer to form on the soaked composite surface, whose good biological activity may be of some promise for biomedical application. [ABSTRACT FROM AUTHOR]

Abstract: B4C matrix ceramic composites toughened by Al2O3 and TiC were prepared by low pressure hot pressing. The relative density, Vickers hardness, fracture toughness and flexural strength of the new fabricated composites were measured. Microstructure observations of the fracture surfaces and the indentation cracks of the B4C matrix ceramic composites were analyzed, and an X-ray diffraction phase analysis was performed. The experiment results showed that chemical reactions took place during the low pressure hot pressing process and resulted in the B4C/Al2O3/TiB2 composite. The densification rate of the B4C matrix ceramic composites was enhanced and the mechanical properties were improved via the introduction of Al2O3 and TiC additives. The Vickers hardness, fracture toughness and flexural strength of the composite with the addition of 4.7wt.% Al2O3 and 10wt.% TiC were 24.8GPa, 4.8MPam1/2 and 445MPa, respectively. [Copyright &y& Elsevier]

Abstract: Al–Ti–B master alloys and diopside are simultaneously introduced in alumina matrix ceramic materials as sintering aids. Fine structural alumina matrix ceramic materials are fabricated by pressureless sintering during which liquid phase, leading to interface reactions between alumina matrix and additives, is formed. Hardness, fracture toughness and bending strength of the composites are measured. The effects of diopside on mechanical properties and fracture mechanism of fine structural alumina matrix ceramic materials are analyzed together with the microstructure observations on fracture surfaces, the polished surfaces and the indentation cracks. [Copyright &y& Elsevier]

Abstract: Al–Ti–B master alloys and diopside were incorporated into alumina matrix and advanced alumina matrix ceramic materials were fabricated by pressureless sintering technology. The mechanical properties of this new composite as well as its wear behaviours, coupled with carbon steel ring in unlubricated conditions at room temperature, were investigated systemically. SEM technology was adopted to observe the worn surfaces of specimens and wear mechanisms were simultaneously discussed. Analysis of the experimental data and observations on the worn surfaces revealed that the improvement in the wear resistance of the composites might be attributed mainly to the strong toughening effect due to the introduction of Al–Ti–B master alloys and diopside in the alumina matrix. [Copyright &y& Elsevier]

Abstract: Diopside and Fe2O3 were introduced in alumina matrix ceramic materials. Large-scale fine structural alumina matrix ceramic guideway materials were fabricated by the technology of pressureless sintering, during which liquid phase sintering took place and new phases such as 3Al2O3·2SiO2, CaO·Al2O3·2SiO2 and CaO·6Al2O3 were produced by the chemical reactions taking place among alumina and the additives. The hardness, the fracture toughness and the bending strength of the guideway products were tested. The influences of diopside and Fe2O3 additions were studied by microstructural observations and mechanical properties evaluations. Meanwhile, the expected improvement of mechanical properties compared with pure alumina was indeed observed. The fracture mechanism and porosity of large-scale fine structural alumina matrix ceramic guideway materials were analyzed. [Copyright &y& Elsevier]

Abstract: In this paper, diopside was introduced into alumina as a sintering aid and fine structural alumina matrix ceramic materials were fabricated by the technology of pressureless sintering. The relative density, hardness and fracture toughness of the diopside-reinforced composites were investigated. Tribological tests were carried out at a rotation speed ranged from 40 to 160rpm and in a normal load ranged from 50 to 200N. SEM technique was employed to observe worn surfaces of the test specimens and wear mechanisms were simultaneously discussed. Analysis of the experimental data and observations on worn surfaces revealed that the improvement in wear resistance of composites may be attributed mainly to the stronger toughening effect due to addition of diopside in alumina matrix. [Copyright &y& Elsevier]

Abstract: In the present work, a new technique to improve the performances of alumina matrix ceramic materials is presented, in which Al, Al3Ti and TiB2 are incorporated into alumina matrix ceramic materials in the form of Al–Ti–B master alloys. Composites of Al2O3/TiB2/AlN/TiN are fabricated by the technology of transient liquid phase sintering, during which new phases such as AlN and TiN are produced by the chemical reactions taking place among Al, Ti and N2 (the protective atmosphere). The densification rate of the composites as a function of Al–Ti–B volume content is discussed. The fundamental properties of the composites such as hardness, fracture toughness and bending strength are examined. The relations of volume content of Al–Ti–B master alloys and mechanical properties of alumina matrix ceramic materials are analyzed. The effects of fracture mechanism on mechanical properties of the composites are researched together with the refining performances of Al–Ti–B master alloys. [Copyright &y& Elsevier]

Abstract: In the present work, Al–Ti–C master alloys and diopside are introduced in alumina matrix ceramic materials. Composites are fabricated by the technology of transient liquid phase sintering, during which new phases such as Al6Si2O13, AlN and CaO·6Al2O3 are produced by the chemical reactions taking place among alumina and the additives. The densification rate of the composites as a function of Al–Ti–C volume content is discussed. The hardness, the fracture toughness and the bending strength of the composites are tested. Meanwhile, the effects of additives on mechanical properties and fracture mechanism of alumina matrix ceramic materials are analyzed and discussed together with the refining performances of Al–Ti–C master alloys. [Copyright &y& Elsevier]

Abstract: A new technique to toughen alumina matrix ceramics is presented, in which Al and TiC are incorporated into the matrix ceramic in the form of Al–Ti–C master alloys, meanwhile ZrO2 are introduced to Al2O3/Al–Ti–C composites. Composites of Al2O3/TiC/ZrO2/AlN and Al2O3/TiC/AlN were fabricated by the technology of transient liquid phase sintering, during which new AlN phase was produced by the chemical reactions taking place between Al and N2 (the protection atmosphere). The toughening effect of Al–Ti–C master alloys on alumina matrix ceramics was researched along with the influence of combination of Al–Ti–C master alloys and ZrO2. Mechanical properties of the composites were determined and the microstructures were analyzed. [Copyright &y& Elsevier]

Nano-alumina/hydroxyapatite composite powders for biomedical applications were synthesized by in-situ chemical precipitation. The effects of synthesis parameters and calcination on the properties of the composite powders were studied. The morphology, chemical composition and thermal behavior of the composite powders were investigated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The results showed that crystallinity of the composite powders progressively increased with increasing the synthesis and calcination temperatures. During calcination, the hydroxyapatite was transformed into calcium phosphate (β-TCP) at 1100 °C, while the aluminum hydroxide was converted to γ-alumina and θ -alumina. In addition, aggregations were observed for samples heated at 1000 °C and above. The as-synthesis alumina powders with an average particle size of approximately 30 nm were well distributed around the HA particles. [ABSTRACT FROM AUTHOR]