Improvement of mechanical properties of zirconia-toughened alumina by sinter forging

ZTA powder with a composition of 85 wt% alumina/15 wt% zirconia was prepared by a gel precipitation method. Sinter forging was performed with this powder to enhance the mechanical properties of ZTA materials. The influence of processing flaws on mechanical properties of sinter forged materials and pressureless sintered materials was investigated. Sinter forging at 40 MPa effectively decreases process flaw sizes resulting in a homogeneous microstructure and improves the grain boundary structure because of large shear applied in this process. Sinter forging resulted in an increase in strength and toughness by a factor of 1.5–2 when compared with pressureless sintered compacts. The fracture energy is enhanced by a factor of two. The predominate mechanism for improvement of mechanical properties of these sinter-forged ZTA materials is grain boundary strengthening

Sinter forging of zirconia toughened alumina

Sinter forging experiments have been carried out on powder compacts of zirconia toughened alumina (ZTA) Ceramics Alumina-15 wt% zirconia was prepared by a gel precipitation method and calcined at temperatures of 900 or 1100°C. Full densification of ZTA ceramics was obtained within 15 min at 1400°C and 40 MPa. A homogeneous microstructure can be observed with an alumina grain size of 0.7 mgrm and a zirconia grain size of 0.2 mgrm. Almost no textural evolution occurred in the microstructure. During sinter forging the densification behaviour of the compacts was improved by an effective shear strain, for which values of more than 100% could be obtained. As a result of the shear deformation the densification of ZTA in the agr alumina phase stage shifted to lower temperature. During pressureless sintering the gamma to agr alumina transformation temperature was dependent of the preceding calcination temperature, while during sinter forging this phase transformation was independent of calcination temperature and took place at a lower temperature

Plasticity of nanocrystalline zirconia ceramics and composites

The deformation strain rate of nanocrystalline Y-TZP shows an increase by a factor 4 if the grain size decreases from 200 to 100 nm. Real superplastic deformation (strain rate > 10−4 s−1) is observed in these materials at relative low temperature (1100–1200 °C). Grain-boundary analysis indicates (partial) removal of an ultra-thin (1 nm), yttrium-rich grain boundary layer after deformation.\ud \ud Uniaxial pressure-assisted sintering techniques (=sinter-forging) provide the opportunity of large shear strains during densification. Sinter-forging experiments on zirconia-toughened alumina (15 wt% ZrO2/85 wt% Al2O3) resulted in a dense composite within 15 min at 1400 °C and 40 MPa, with effective shear strains up to 100%. Sinter-forging of Y-TZP and ZTA gives an increase in strength, reliability and fracture toughness. These improvements are caused by the large shear strains that result from the removal of processing flaws. Also, the number of microcraks at the grain boundaries and the interatomic spacing between the grains are reduced by the forging techniques, resulting in a strengthening of the grain boundaries if compared with pressureless sintering. K1C values of 10 MPa√m are obtained for Y-TZP, while no classical stress-induced phase transformation toughening is observed. Sinter-forged ZTA samples showed a better wear resistance than free sintered ones.\u

Effects of a second phase on the tribological properties of Al2O3 and ZrO2 ceramics

The tribological properties of four different materials are investigated, tetragonal zirconia (Y-ZTP), Al2O3 dispersed in Y-TZP (ADZ), ZrO2 dispersed in Al2O3 (ZTA) and Al2O3 (with 300 ppm MgO). These materials are used as a cylinder sliding against a plate of Y-TZP (TZ-3Y)). Compared to Y-TZP, the wear resistance of ADZ composites is increased by a factor of 4¿10. At a contact pressure of 230 MPa, a wear transition for Y-TZP is observed from plastic deformation to microchipping and microfracture due to the high interfacial temperature (450°C¿550°C) generated by frictional heating. Because of the higher elastic modulus, hardness and fracture toughness at high temperature, ADZ composites show better wear resistance and a higher transition contact pressure (over 400 MPa) under the present conditions. For Al2O3, the transition from mild to severe wear occurs when the contact pressure is changed from 250 to 400 MPa. For ZTA ceramics, the wear behaviour does not change because of the presence of a compressive layer due to the zirconia phase transformation during sliding.\ud \ud In water the wear resistance for ADZ and ZY5 is almost two orders of magnitude higher than the results under dry conditions. Reduction of the interfacial temperature by using water and the formation of a hydroxide layer at the contact surface by the tribochemical reaction of water with the ceramic, as observed by XPS, gives a positive effect on wear resistance

Friction and wear behaviour of ceramic-hardened steel couples under reciprocating sliding motion

The friction and wear behaviour of ZrO2-Y203, ZrO2-Y203-CeO2 and ZrO2-A1203 composite ceramics against hardened steel AISI-52100 were investigated using a pin on plate configuration under reciprocating motion. The reproducibility of the results was examined in this configuration. Wear characteristics were separated into system and material contributions. Under the conditions used, all the ceramic components exhibited rather low wear rates (less than 10-6mm3N-1m-1). The frictional behaviour of ceramic-metal couples depended on a metallic layer transferred from the steel plate to the ceramic pin. A relation was determined between surface hardness and friction of ceramic-metal pairs. It was shown that the affinity for the transfer of the metal towards ceramic surfaces depended on the physical properties of the materials. In the tribosystems investigated, the effect of the hardness of the ceramics on friction and wear behaviour is found to be more important than that of toughness of the ceramics

Carboplatin/taxane-induced gastrointestinal toxicity: a pharmacogenomics study on the SCOTROC1 trial

Carboplatin/taxane combination is first-line therapy for ovarian cancer. However, patients can encounter treatment delays, impaired quality of life, even death because of chemotherapy-induced gastrointestinal (GI) toxicity. A candidate gene study was conducted to assess potential association of genetic variants with GI toxicity in 808 patients who received carboplatin/taxane in the Scottish Randomized Trial in Ovarian Cancer 1 (SCOTROC1). Patients were randomized into discovery and validation cohorts consisting of 404 patients each. Clinical covariates and genetic variants associated with grade III/IV GI toxicity in discovery cohort were evaluated in replication cohort. Chemotherapy-induced GI toxicity was significantly associated with seven single-nucleotide polymorphisms in the ATP7B, GSR, VEGFA and SCN10A genes. Patients with risk genotypes were at 1.53 to 18.01 higher odds to develop carboplatin/taxane-induced GI toxicity (P<0.01). Variants in the VEGF gene were marginally associated with survival time. Our data provide potential targets for modulation/inhibition of GI toxicity in ovarian cancer patients

Technical note: Characterization of key volatile odorants in rabbit meat using gas chromatography mass spectrometry with simultaneous distillation extraction

[EN] This study explored the key volatile compounds in both male and female rabbit meat. Simultaneous distillation extraction with dichloromethane was adopted to extract the volatile compounds in Hyla rabbit meat. A total of 35 volatile compounds were identified by gas chromatography–mass spectrometry and quantified with 2, 4, 6-thimethylpyridine as internal standard. Seventeen volatile aldehydes, 4 alcohols, 2 ketones, 2 acids, 1 heterocyclic compound, 2 alkanes and 7 esters were detected. Hexanal, heptanal, octanal, nonanal, (E, E)-2, 4-decadienal, 1-octen-3-ol and (Z)-2-decenal were the key odorant compounds, with high relative odour activity value. Furthermore, the concentration of volatile compounds in male rabbit meat was higher than that in female rabbit meat.This work was supported by the National Natural Science Foundation of China (31671787), the Chinese Rabbit Industry System of Education Ministry (100030-40305411) and Fundamental Research Funds for the Central Universities (XDJK2014D042).Xie, Y.; He, Z.; Zhang, E.; Li, H. (2016). Technical note: Characterization of key volatile odorants in rabbit meat using gas chromatography mass spectrometry with simultaneous distillation extraction. World Rabbit Science. 24(4):313-320. https://doi.org/10.4995/wrs.2016.4464SWORD31332024

Modelling a real rockslide as a static-dynamic transition using a material instability criterion

747-757Failures at geological discontinuities often play a dominant role in the prediction of rockslides. In this study, a second order work criterion was used to analyze this type of problem by its constitutive instabilities, as it can expound all physical instabilities by divergence, except flutter instabilities. Derived from vanishing of the second order work, a matrix analysis focusing on the instability of geological discontinuities in two dimensions was performed. A real rockslide was simulated in a 2-D framework, and the second order work criterion was used to predict the occurrence of the rockslide. The numerical results were compared to monitoring data. Rockslides could be considered as processes involving a transition from a static loading to a dynamic response including a sudden burst of kinetic energy. Furthermore, a relationship existed between the second order work and second order kinetic energy. Hence, kinetic energy estimation was performed using two numerical approaches derived from this relationship and compared

High-pressure behaviors of carbon nanotubes

In this paper, we have reviewed the experimental and theoretical studies on pressure-induced polygonization, ovalization, racetrack–shape deformation, and polymerization of carbon nanotubes (CNTs). The corresponding electronic, optical, and mechanical changes accompanying these behaviors have been discussed. The transformations of armchair (n, n) CNT bundles (n = 2, 3, 4, 6, and 8) under hydrostatic or nonhydrostatic pressure into new carbons, including recently proposed superhard bct-C₄, Cco-C₈, and B-B1AL2R2 carbon phases have also been demonstrated. Given the diversity of CNTs from various chiralities, diameters, and arrangements, pressure-induced CNT polymerization provides a promising approach to produce numerous novel metastable carbons exhibiting unique electronic, optical, and mechanical characteristics.Розглянуто експериментальні та теоретичні дослідження з індукованою тиском полігонізації, овалізації, деформації у формі бігової доріжки і полімеризації вуглецевих нанотрубок (ВНТ). Обговорено відповідні електронні, оптичні і механічні зміни, що супроводжують ці процеси. Також продемонстровано перетворення в ВНТ у формі крісла (n, n), зібраних в пучок (n = 2, 3, 4, 6 і 8) під гідростатичним або негідростатичним тиском в нові вуглецеві алотропи, в тому числі недавно запропоновані надтверді bct-C₄, Cco-C₈ і B-B1AL2R2-вуглецеві фази. Різноманітність ВНТ з різними хіральністю, діаметрами та упаковками, а також полімеризація ВНТ, викликана тиском, забезпечує перспективний підхід для отримання численних нових метастабільних вуглецевих фаз, що демонструють унікальні електронні, оптичні і механічні характеристики.Рассмотрены экспериментальные и теоретические исследования по индуцированной давлением полигонизации, овализации, деформации в форме беговой дорожки и полимеризации углеродных нанотрубок (УНТ). Обсуждены соответствующие электронные, оптические и механические изменения, сопровождающие эти процессы. Также продемонстрированы преобразования в УНТ в форме кресла (n, n), собранных в пучок (n = 2, 3, 4, 6 и 8) под гидростатическим или негидростатическим давлением в новые углеродные аллотропы, в том числе недавно предложенные сверхтвердые bct-C₄, Cco-C₈ и B-B1AL2R2-углеродные фазы. Разнообразие УНТ с различными хиральностью, диаметрами и упаковками, а также полимеризация УНТ, вызванная давлением, обеспечивает перспективный подход для получения многочисленных новых метастабильных углеродных фаз, демонстрирующих уникальные электронные, оптические и механические характеристики