Fracture Toughness Of Al2O3 Research Articles

Low temperature synthesized high entropy carbide composites: A potential high temperature anti-wear material

Bulk Al2O3/(NbTaMoW)C composites with uniform distribution of Al2O3 were designed and fabricated based on thermite reaction. The optimized composites were subjected to mechanical/tribological performance testing and directly compared to (NbTaMoW)C, revealing a significantly enhanced mechanical properties and wear resistance at high temperature. Compared to (NbTaMoW)C, the flexural strength and fracture toughness of Al2O3/(NbTaMoW)C composites significantly enhanced. The measured hardness value is 8% higher than that of (NbTaMoW)C. For the first time, the tribological behavior of Al2O3/(NbTaMoW)C and (NbTaMoW)C was studied systematically at temperatures from 25 °C to 800 °C. Al2O3/(NbTaMoW)C and (NbTaMoW)C present excellent wear resistance below 600 °C, while the wear rate exhibited an obvious increasing at 600 °C–800 °C. The specific wear rate of Al2O3/(NbTaMoW)C is much lower than that of (NbTaMoW)C at 600–800 °C. Al2O3/(NbTaMoW)C exhibits remarkable anti-wear performance at high temperature because the presence of Al2O3 improves oxidation resistance and decreases oxidation wear.

Dynamic Fracture Toughness Behaviour of CFRP-Foam-CFRP Sandwich Composite and Particles Filled Hybrid Glass Fiber Cloth, Graphene Nanoplates Coated Glass Fiber Strand Composite Materials under Low Impact Velocity

The main objective of the present study is to investigate the dynamic fracture toughness behaviors of CFRP-Foam-CFRP sandwich composite of V-notched through -thickness, surface, and un-notched specimens under Izod, and Charpy impact tests.  The sandwich composite structures are made of cross-plied carbon fiber reinforced plastic (CFRP) composite faces with polyurethane foam core. CFRP composites are used to combine the upper face and the lower face through the core in stitched sandwich structures. Compressive strength of weight drop impact perforated and un-perforated sandwich composite specimens are measured from a universal testing machine. Also, particles (Al2O3, CNTs, and cement) filled glass fiber cloth and graphene nanoplates coated glass fiber strands reinforced polymer hybrid composite are fabricated for V-notched, un-notched Izod impact and Charpy impact tests. The results show that weight drop impact energy is lower than the Izod impact energy but higher than the Charpy impact energy, whereas the dynamic fracture toughness of Izod impact energy is more than the Charpy and weight drop impact energy due to geometry of impactor and sandwich specimen. However energy and dynamic fracture toughness of Al2O3, CNTs, and Cement filled un-notched hybrid composites higher than the notched hybrid composites under Izod Impact. The dynamic fracture toughness and energy of CNTs filled hybrid composites is higher than the sandwich composites, Al2O3, and Cement filled hybrid composites under Charpy Impact.

Making Ultra-Tough Nanoceramics by Columnar Submicrocrystals with Three-Level Micro-Nano Structures.

The low fracture toughness of equiaxed nanocrystalline ceramics is the main bottleneck of its wide range of commercial applications. Here, the authors report a method to overcome this limitation for preparing ultra-tough nanoceramics from using amorphous and supersaturated Al2 O3 /ZrO2 solid solution micro-powders, which is fabricated by Al-O2 ultrahigh-temperature combustion synthesis assisted rapid water cooling. The Al2 O3 /ZrO2 micro-powders containing amorphous and metastable dendritic solid solutions can induce the three-level micro-nano structure (submicro/nano/supra-nano) of the high-content (up to 70-90%) columnar submicro-crystals accompanied with high-density nanoprecipitation after sintering or annealing, which makes the fracture toughness of Al2 O3 /ZrO2 ceramics with a unique combination of high-strength and high-hardness increased by 50-100%. This method is beneficial to microstructural design of high-performance ceramics and can be widely applied to various ceramic systems, coupled with simplicity, low-cost, and high-efficiency, making it suitable to industrially produce large-sized nanoceramics with specific grain geometry in large quantities.

Plasma-sprayed graphene oxide reinforced alumina composite coatings on low carbon steel with improved fracture toughness, brittleness index, and microhardness

In this work, the mechanical properties of atmospheric plasma-sprayed Al2O3 and Al2O3-xGO (x = 0.5, 1.0, 1.5, and 2.0 wt%) coatings on low carbon steel was evaluated using the Vickers indentation technique, and the effects of GO addition in microhardness brittleness index and fracture toughness were investigated. The Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) techniques were employed to analyze the microstructural characterization of the plasma-sprayed coatings and to confirm the retention of GO in the Al2O3-xGO composite after the plasma spray. It was found that the Vicker’s microhardness of as-sprayed Al2O3 is 4.148 GPa and it decreased with the increase in the addition of GO and for Al2O3-2.0GO, it is 3.305 GPa. The fracture toughness of Al2O3 is 4.86 (MPa m1/2) whereas for Al2O3-2.0GO is 16.85 (MPa m1/2). The fracture toughness has increased whereas the brittleness index has decreased as the weight percentage of GO addition is increased in the Al2O3-GO composite. Thus, the plasma-sprayed Al2O3 and Al2O3-xGO coatings suggest that 2 wt% GO addition helps in the improvement of brittleness, fracture toughness, and the microhardness.

Effect of Ni on mechanical behavior of Al2O3/(W,Ti)C ceramic tool materials at ambient and elevated temperatures

Two types of Al2O3/(W0.5,Ti0.5)C ceramic composites with and without metal phase Ni were studied in this research. The evolution mechanism of bending strength and fracture toughness at both ambient and high temperature(600 ∼ 1000 °C) was studied. The influence of nickel on mechanical behavior and microstructure of composites was also analyzed in the test temperature range. The results showed that the bending strength of both ceramic composites decreased with gradually increased temperature. The bending strength of Al2O3/(W0.5,Ti0.5)C/Ni was greater than that of Al2O3/(W0.5,Ti0.5)C ceramic composites at room temperature. However, the bending strength of Al2O3/(W0.5,Ti0.5)C/Ni decreased more rapidly at high temperature. The fracture toughness of Al2O3/(W0.5,Ti0.5)C/Ni was always greater than that of Al2O3/(W0.5,Ti0.5)C at different temperatures. The addition of metal phase had a positive impact on the fracture toughness at different temperatures. It was found that the matrix and the toughening phase were well combined by the metal phase, so the room temperature bending strength of Al2O3/(W0.5,Ti0.5)C/Ni was enhanced. However, the decrease of interfacial bonding strength caused by the low-melting metal phase led to the fracture mode changed. Moreover, the elastic modulus of Al2O3/(W0.5,Ti0.5)C/Ni decreased faster at elevated temperatures, which resulted in lower bending strength. The research on the evolution law of mechanical behavior of composites at elevated temperatures has important guiding significance for the design of materials and the choice of cutting parameters.

Preparation of Al<sub>2</sub>O<sub>3</sub> Based Nano-Micro Composite Gradient Self-Lubricating Ceramic Tool Materials

Aiming at the low mechanical property of existing self-lubricating ceramic cutting tool material, a new Al2O3 based nanomicro composite gradient self-lubricating ceramic tool material was developed by applying the design concept of nanomicro composite. The self-lubricating ceramics was composed of ceramic matrix and self-lubricating component, and was prepared by hot pressing technology at a hot-pressing temperature of 1650°C, pressure of 30MPa, and duration of 15min. The model of gradient ceramic tool material is symmetrical composition distribution, and the compositional distribution n and layer number are 1.8 and 7, respectively. The result shows that the interfaces between layers are bonded well and no cracks or defects can be observed. Compare with the homogeneous material, the flexural strength, hardness and fracture toughness of Al2O3 based graded material increase by 74%, 5.2% and 3.9%, respectively.

Effect of LiTaO3grain sizes on microstructure and properties of Al2O3

To investigate the relationship in LiTaO3 between the non-180° domains and the grain size, nano LiTaO3 powders were synthesized by sol–gel methods and added into Al2O3 to prepare LiTaO3–Al2O3 ceramic composites by hot pressing. The effect of LiTaO3 grain size on microstructure and properties of Al2O3 was investigated. The addition of nano LiTaO3 powders contributed to the sintering of Al2O3 and the relative density of the LiTaO3–Al2O3 ceramic composites was more than 96%. Non-180° domains also formed in the composite and were nearly independent on the grain sizes of LiTaO3. The bending strength and fracture toughness of Al2O3 were improved by adding nano LiTaO3. A typical “second-phase grain size threshold effect” at around 310 nm grain size of LiTaO3 additions appeared for the mechanical properties of LiTaO3–Al2O3 ceramic composites.

Effect of crosshead speed on the fracture toughness of soda-lime glass, Al2O3 and Si3N4 ceramics determined by the surface crack in flexure (SCF) method

The fracture toughness of soda-lime glass, Al2O3 and Si3N4 specimens was measured by the surface crack in flexure method. For the soda-lime glass specimens, the fracture toughness was calculated from the initial crack size and flexure strength, and the value increased with increasing crosshead speed. This trend seems to be related to the difficulty in determining the critical crack size at fracture, since slow crack growth occurs during bending test. For the Al2O3 specimens, a halo region (stable crack growth region) was formed around the initial precrack during bending test. The halo size increased and the resultant flexure strength decreased with decreasing in the crosshead speed. The halo region, however, could not be observed in the Si3N4 specimens. Despite of the difference in the appearance of halo region, the fracture toughness of the Al2O3 and Si3N4 specimens was constant irrespective of the crosshead speed when the values were calculated with the critical crack sizes at fracture (halo incorporated crack sizes). The constant fracture toughness with the crosshead speed could be explained by the relation between the changes of halo size (thus critical crack size at fracture) and resultant flexure strength.

SiC whisker toughened Al 2O 3-(Ti, W)C ceramic matrix composites

Nowadays, more and more researchers begin to utilize more than one type of reinforcing agent to fabricate ceramic matrix composites in order to improve the mechanical properties of ceramic materials to a greater degree 1 and 11. The aim of this research work is to use SiC whiskers to improve the fracture toughness and flexural strength of (Ti, W)C reinforced Al2O3 composite material. The effects of SiC whisker content and sintering temperature on the relative density, flexural strength and fracture toughness of Al2O3-(Ti, W) composites were investigated.

Effect of annealing on the microstructure, room-temperature strength, and fracture toughness of Al2O3−ZrO2−TiN ceramics

The microstructure, phase composition, room-temperature flexural strength, and fracture toughness of Al2O3−ZrO2−TiN (AZT) ceramics were studied on specimens annealed in air at 1000, 1200, and 1400°C. The strength of the ceramics decreased with annealing temperature. The degradation in strength was caused by defects formed on or near the surface of the ceramics during oxidation of TiN which started at 600–700°C. The surface defects after annealing are influenced by the formation of rutile (TiO2) at 1000 and 1200°C, aluminum titanate (Al2TiO5), and titanium suboxide Ti5O9 at 1400°C as well as by diffusion processes associated with ZrO2. If the annealing of smooth AZT specimens in air resulted in lower strength, specimens in the form of single-edge notched beam (SENB) exhibited a considerable increase in fracture toughness (KIc) with annealing temperature. Such behavior was caused by the formation of an oxide layer which hindered the propagation of the main crack from the notch base. Thermal treatment of the smooth AZT specimens and further edge notching and testing did not result in a change of KIc values. The Al2O3 and Al2O3−ZrO2 ceramics were also tested for comparison.

Fracture Toughness of Al2O3 with an Unstabilized ZrO2Dispersed Phase

The fracture toughness of Al2O3 is considerably increased by the incorporation of fine monoclinic ZrO2 particles. Hot‐pressed composites containing 15 vol % ZrO2 yield Klcvalues of ∼ 10 MN/m3/2, twice that of the A12O3 matrix. It is hypothesized that this increase results from a high density of small matrix microcracks absorbing energy by slow propagation. The microcracks are formed by the expansion of ZrO2during the tetragonal → monoclinic transformation. Since extremely high tensile stresses develop in the matrix, very small ZrO2 particles can act as crack formers, thus limiting the critical flaw size to small values.

Factor Analysis of Fracture-Toughness Test Parameters for Al2O3

The double-cantilever-beam technique was used to determine the effects of varying 6 factors related to specimen preparation, size, and testing conditions on the fracture toughness of polycrystalline Al2O3. Experimental design and statistical factor analysis techniques were used to investigate each factor at two levels. Direct fracture surface replication and electron microscopy provided supporting information about the fracture mode and fracture surface features for each test condition. The fracture toughness of Al2O3 was higher for 30-μm grain size than for 10-μm grain size. Pretest annealing (900°C) and specimen width were both significant factors for 10-μm Al2O3. The effects of variations of beam width, beam height, and test machine speed were masked by data scatter and are being studied further. The ratio of specimen width to fracture web width caused no effect in the range studied. The sensitivity of the test results to sample dimensions and surface finish is small enough that special care in cutting and measuring of samples is not required.