Refractory and ceramic materials

The paper examines the consolidation of 95 mole% ZrO₂-2 mole% CeO₂-3 mole% Y₂O₃ nanocrystalline powder in cold uniaxial double-action pressing, cold isostatic pressing (60 and 120 MPa), and sintering. Five starting powders are produced by processing a suspension after hydrothermal decomposition in different conditions. It is established that a homogeneous microstructure forms only in a material from the powder subjected to two homogenizing grindings. After cold uniaxial pressing and cold isostatic pressing, the sintered samples reach a relative density of 0.96 to 0.94. The bending strength is 600 to 660 MPa. The efficient consolidation of ceramics requires comprehensive processing of starting nanocrystalline powders to modify their morphology. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 45–58, 2007.     

陶瓷刀具材料的研究进展

陶瓷刀具材料是一种先进的刀具材料.文章介绍了陶瓷刀具材料的特点和种类,指出了陶瓷刀具材料发展方向,并展望了其发展前景.     

Primary recrystallization mechanisms in ceramic materials

Data on the mechanisms of primary recrystallization in covalent type ceramics under temperature-and-pressure treatment are generalized and discussed. There are three types of structural transformations governing nucleation during primary recrystallization. I. Formation of intragrain boundaries. As a result of plastic shears boundaries appear to be kinked due to dislocation pile-ups (materials based on 2H BN, 6H SiC). With deformation by total dislocations the boundaries arise as a result of dynamic recovery due to rebuilding of dislocation pile-ups (AlN, β-Si₃N₄, TiB₂). II. Twinning. This structural transformation promotes the formation of recrystallization nuclei in the following cases: a) with insertion of lattice dislocations into the boundaries of strain-induced twins; b) with formation of annealing twins; c) with development of multiple twinning near grain boundaries (3C BN). III. Structural transformations in migrating boundaries: a) splitting of boundaries and ternary junctions (3C BN); b) local bulging of boundaries (3C BN); c) generation of high-angle and platelet twins (3C BN); d) plastic rotation of material microvolumes near grain boundaries (3C BN, SiC). Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya. Nos. 1-2, pp. 63–77, January–February, 1998.     

Ultradispersed nitride powder-base ceramic tool materials

Translated from Poroshkovaya Metallurgiya, No. 12, pp. 78–82, December, 1990.     

Fatigue limit of ceramic materials at elevated temperatures

Translated from Poroshkovaya Metallurgiya, No. 2(350), pp. 42–47, February, 1992.     

Anelastic relaxation controlled cyclic creep and cyclic stress rupture behavior of an oxide dispersion strengthened alloy

Cyclic creep deceleration relative to static creep was observed in oxide dispersion strengthened alloy Inconel MA 754 at 760 °C and cyclic stresses of 221 MPa-41 MPa, 231 MPa-41 MPa, and 241 MPa-41 MPa. Tests were run over the range of frequency from 0.05 cycles per hour to six cycles per hour. The maximum cyclic deceleration, which was manifested as a reduced net creep rate and increased rupture life, was observed at the highest cyclic frequency. Considerable anelastic strain, having a magnitude of ε_a/ε_e～ 1/3, is stored in MA 754 at 760 °C under these creep loads, and this strain may be recovered in the off-load half cycle of a cyclic creep test. During the higher frequency tests, the effect of an incomplete storage of anelastic strain on the accompanying nonrecoverable creep rate provides a mechanism for the frequency dependent cyclic creep deceleration. The proposed mechanism is in agreement with mixed-mode test results and with TEM examination of interrupted-test specimens.     

Depletion of high-energy carriers in YAG optical ceramic materials

The scintillation properties of YAG:Ce transparent ceramic material prepared by a hot-pressing technique have been characterized and compared with those of a chemically identical specimen of single crystal. Each of the scintillation steps (conversion, energy transfer and luminescence) has been selectively investigated using appropriate spectroscopic techniques. The light output from the ceramic specimen was measured at approximately 1500 photons/MeV, only 10% of that from the single crystal. This drastic decrease in the ceramic reflects the inefficient transfer of energy from the excited host to the Ce ion. The inefficiency can be attributed to the presence in the ceramic material of a high population of lattice defects, as demonstrated by the UV absorption spectra. Thermoluminescence experiments show that these defects can serve as sinks for free carriers (electrons and holes), providing sites for their nonradiative recombination and preventing them from conveying their energy to the emitting centers.     

Non-linear behavior in advanced materials

<正>The 17th IUMRS International Conference in Asia was held in Qingdao from October 20th to 24th,2016.This conference contained 28international symposia.One of symposia,titled as Serration and Noise Behavior in Advanced Materials,was well organized,which provided an effective platform to discuss the non-linear behavior in advanced materials including high-entropy alloys,bulk metallic glasses,and lightweight alloys,etc.Generally speaking,serration and noise phenomenon exist everywhere,such as,the crackling noise     

Slow crack growth in ceramic materials at elevated temperatures

Techniques for studying slow crack growth at high temperatures are described. The techniques are used to obtain crack growth data for a range of silicon nitrides between 1100 and 1400°C. For these materials the data suggest that the slow crack growth may be effectively characterized by the relation between crack velocity and stress intensity factor. Data obtained for mechanical and thermal fatigue modes indicate that these behaviors can be predicted with moderate accuracy from the isothermal, static stress parameters (for the range of conditions investigated). Finally, the application of slow crack growth data to failure prediction is described and illustrated using data for one of the materials tested.     

Low-temperature ceramic materials based on chemically precipitated solid solutions

Translated from Poroshkovaya Metallurgiya, No. 1(325), pp. 19–21, January 1990.     

Slow crack growth in ceramic materials at elevated temperatures

Techniques for studying slow crack growth at high temperatures are described. The techniques are used to obtain crack growth data for a range of silicon nitrides between 1100 and 1400°C. For these materials the data suggest that the slow crack growth may be effectively characterized by the relation between crack velocity and stress intensity factor. Data obtained for mechanical and thermal fatigue modes indicate that these behaviors can be predicted with moderate accuracy from the isothermal, static stress parameters (for the range of conditions investigated). Finally, the application of slow crack growth data to failure prediction is described and illustrated using data for one of the materials tested.     

New water-soluble acrylic bonding agents for shaping ceramic materials

Preliminary results are reported on the synthesis and use of new water-soluble polymer binders for making ceramic films from Al ₂O₃ by casting. The binders produce cast materials having high contents of the solid phase and with rheological properties that provide for good flow of the cast mass and for easy separation of the film from the substrate. The emulsions wet Al₂O₃ well, so one can make ceramic films with appropriate densities, elasticities, and mechanical strength in the raw state, and these can be fired to make planeparallel specimens free from cracks and having high density, good mechanical strength, and low roughness. Warsaw Polytechnic. Translated from Poroskhovaya Metallurgiya, Nos. 5–6(407), pp. 15–20, May–June, 1999.     

Crack propagation in ceramic materials under cyclic loading conditions

An analysis is presented which enables crack propagation rates under cyclic loading condiditions to be predicted from static slow crack growth parameters. A comparison of the predicted times to failure under cyclic conditions with available measured failure times, for several ceramic materials at ambient temperatures, suggests that there is no significant enhancement of the slow crack growth rate due to cycling. This is verified in a series of measurements of slow crack growth rates under static and cyclic conditions.