Study of Lithium Disilicate Based Nano Glass Ceramics Containing P2O5.

Multi component Lithium disilicate based glasses containing P2O5 have been synthesized by conventional melt quenching technique. The replacement of (Li2O+SiO2) by P2O5 and its nucleating effect has been discussed. Structural features of glasses were evaluated by DTA, FTIR and Raman spectroscopy. The glass samples have been converted into glass ceramics by following three stage heat treatment schedule. XRD, FESEM, HAADF imaging and EDX analysis has been carried out for glass ceramics. Vickers microhardness and Vickers indentation fracture toughness of all the glass ceramics have been measured. UV–Visible spectroscopy study has been carried out for glass ceramics to investigate the optical properties. The glass ceramic with 1.5 mol % P2O5 has highest transmittance. Glass ceramics with P2O5 ≥1 mol % having Li2Si2O5 as main phase exhibit high Vickers microhardness (Hv) about 6.71-6.82 GPa which is suitable for dental and armor applications.

Sliding Wear Properties of HVOF Sprayed WC-10Co4Cr Coatings With Conventional Structure and Bimodal Structure Under Different Loads

The WC-10Co4Cr coatings with conventional structure and bimodal structure were sprayed by high-velocity oxygen fuel (HVOF) technology. The phase compositions and morphologies of the WC-10Co4Cr powders and coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microhardness, porosity, bonding strength, elastic modulus, and indentation fracture toughness of the conventional coating (Conventional) and the bimodal coating (Bimodal) were also studied. The sliding wear properties of the Conventional and the Bimodal against Si3N4 counterballs under different loads at room temperature (∼25 °C) were investigated using a friction and wear tester. Compared with the Conventional, the Bimodal has denser microstructure, lower porosity, more excellent mechanical properties, and the Bimodal has better wear resistance than the Conventional under different loads. The two coatings under 15 N and 30 N only exhibit abrasive and slightly adhesive wear mechanism, while in the load application of 45 N, additional mechanism which is fatigue is detected and causes flaking of the coating.

Comparison of Different Cermet Coatings Sprayed on Magnesium Alloy by HVOF

In the present study, two different cermet coatings, WC–CrC–Ni and Cr3C2–NiCr, manufactured by the high-velocity oxy-fuel (HVOF) method were studied. They are labeled as follows: WC–CrC–Ni coating—WC and Cr3C2–NiCr coating—CrC. These coatings were deposited onto a magnesium alloy (AZ31) substrate. The goal of the study was to compare these two types of cermet coating, which were investigated in terms of microstructure features and selected mechanical properties, such as hardness, instrumented indentation, fracture toughness, and wear resistance. The results reveal that the WC content influenced the hardness and Young’s modulus. The most noticeable effect of WC addition was observed for the wear resistance. WC coatings had a wear intensity value that was almost two times lower, equal to 6.5·10−6 mm3/N·m, whereas for CrC ones it was equal to 12.6·10−6 mm3/N·m. On the other hand, the WC coating exhibited a lower value of fracture toughness.

Effect of particle size of Y2O3-Al2O3 additives on microstructure and mechanical properties of Si3N4 ceramic balls for bearing applications

Si3N4 ceramic balls were prepared by gas pressure sintering with Y2O3 and Al2O3 as sintering additives. The effects of particle size of Y2O3-Al2O3 additives on densification, microstructure and mechanical properties of Si3N4 ceramic balls were investigated. The reliability of Si3N4 ceramic balls was evaluated through the Weibull modulus. The results showed that Si3N4 ceramic balls containing nanosized Y2O3-Al2O3 additives have a higher relative density and better comprehensivemechanical properties compared with the samples containing microsized additives, with relative density of 98.9 ? 0.2%TD, Vickers hardness of 14.7 ? 0.1GPa, indentation fracture toughness of 6.5 ? 0.1MPa?m1/2 and crushing strength of 254 ? 8.5MPa. The more homogeneous and extensive dispersion of the nanosized sintering additives in the Si3N4 matrix is the main reason for the enhancement in density and mechanical properties of the Si3N4 ceramic balls.

High Velocity Oxygen Liquid-Fuel (HVOLF) Spraying of WC-Based Coatings for Transport Industrial Applications

In this article, we analyse five types of coatings, in terms of their microstructure, hardness, porosity, and wear resistance, in the as-sprayed state. The coatings are WC-based (WC-FeCrAl, WC-WB-Co, and WC-NiMoCrFeCo), alloy-based (Co-MoCrSi), or nanoWC coating-based (nanoWC-CoCr). Two tests were applied to assess the wear resistance of the coatings: a dry-pot wear test with two impact angles and an abrasive test using an abrasive cloth with two grit sizes. Porosity was determined by image analysis. Vickers impression was performed on cross-sections of the coatings, in order to determine their indentation fracture toughness. The highest hardness of the tested coatings was recorded for the nanoWC coating, followed by the rest of the WC-based coatings; meanwhile, the lowest hardness was recorded for the alloy coating. Minimal porosity was achieved by the alloy coating, due to its different nature and the absence of hard particles with a higher melting point. The NanoWC coating and other WC-based coatings had a higher porosity; however, porosity did not exceed 1% for each coating. The best wear resistance was achieved by the nanoWC coating, followed by the other WC-based coatings, with the lowest obtained by the alloy coating. The same tendency was recorded when determining the indentation fracture toughness. From a microscopic point of view, the structure of the evaluated coatings is not compact; nevertheless, their properties are excellent, and they act as compact coatings under load.

Characterization of Thermochemical and Thermomechanical Properties of Eyjafjallajökull Volcanic Ash Glass

The properties of a volcanic ash glass obtained from the Eyjafjallajökull eruption of 2010 were studied. Crystallization experiments were carried out on bulk and powdered glass samples at temperatures between 900 and 1300 °C. Iron oxides, Fe3O4 and Fe2O3, and a silicate plagioclase, (Na,Ca)(Si,Al)4O8, were observed. Bulk samples remained mostly amorphous after up to 40 h at temperature. Powdered glass samples showed increased crystallinity after heat treatment compared to bulk samples. The average coefficient of thermal expansion of the glass was 7.00 × 10−6 K−1 over 25–720 °C. The Vickers hardness of the glass was 6–7 GPa and the indentation fracture toughness, 1–2 MPa √m Values for density, elastic modulus, and Poisson’s ratio were 2.52 g/cm3, 75 GPa, and 0.24, respectively. The viscosity of the glass was determined experimentally and compared to three common models from the literature. The implications for the deposition of volcanic ash on hot section components of aircraft turbine engines are discussed.

Hardness and Indentation Fracture Toughness of Slip Cast Alumina and Alumina-Zirconia Ceramics

Alumina (Al2O3) and zirconia (ZrO2) have good overall properties and thus are widely used oxide technical ceramics. The biggest drawback of Al2O3 is its low fracture toughness. In contrast, ZrO2 is relatively tough, but is also much more expensive. In order to improve the alumina toughness, composite ceramics are being developed. Slip casting technology has economic advantages over the conventional hot isostatic pressure technology, but problems may arise when preparing stable highly-concentrated suspensions (slip) for filling the mold. The purpose of this study is to prepare aqueous suspensions using 70 wt. % α-Al2O3, with 0, 1, 5 and 10 wt. % of added t-ZrO2. Suspensions were electrosterically stabilized using the ammonium salt of polymethylacrylic acid, an alkali-free anionic polyelectrolyte dispersant. Also, magnesium oxide in form of magnesium aluminate spinel (MgAl2O4) was used to inhibit the abnormal alumina grain growth during the sintering process. Minimum viscosities were used as stability estimators, where an increase in ZrO2 content required adding more dispersant. After sintering, the Vickers indentation test was used to determine the hardness and the indentation fracture toughness from the measurement of the crack length. Also, the brittleness index (Bi, μm−1/2) was calculated from values of Vickers hardness and the Vickers indentation fracture toughness. It was found that with increasing ZrO2 content the fracture toughness increased, while the hardness as well as the brittleness index decreased. Zirconia loading reduces the crystallite sizes of alumina, as confirmed by the X-ray diffraction analysis. SEM/EDS analysis showed that ZrO2 grains are distributed in the Al2O3 matrix, forming some agglomerates of ZrO2 and some pores, with ZrO2 having a smaller grain size than Al2O3.