Microstructures and Enhanced Mechanical Properties of (Zr, Ti)(C, N)-Based Nanocomposites Fabricated by Reactive Hot-Pressing at Low Temperature.

Dense and enhanced mechanical properties (Zr, Ti)(C, N)-based composites were fabricated using ZrC, TiC0.5N0.5, and Si powders as the raw powders by reactive hot-pressing at 1500-1700 °C. At the low sintering temperature, both (Zr, Ti)(C, N) and (Ti, Zr)(C, N) solid solutions were formed in the composites by adjusting the ratio of ZrC to TiC0.5N0.5. During the sintering process, the Si added at a rate of 5 mol% reacted with ZrC and TiC0.5N0.5 to generate SiC. With the increase in Si addition, it was found that the residual ß-ZrSi was formed, which greatly reduced the flexural strength of composites but improved their toughness. The reaction and solid-solution-driven inter-diffusion processes enhanced mass transfer and promote densification. The solid solution strengthening and grain refinement improved the mechanical properties. The ZrC-47.5 mol% TiC0.5N0.5-5 mol% Si (raw powder) composite possessed excellent comprehensive performance. Its flexural strength, Vickers hardness, and fracture toughness were 508 ± 33 MPa, 24.5 ± 0.7 GPa, and 3.8 ± 0.1 MPa·m1/2, respectively. These reached or exceeded the performance of most (Zr, Ti)(C, N) ceramics reported in previous studies. The lattice distortion, abundant grain boundaries, and fine-grained microstructure may make it possible for the material to be resistant to radiation.

Biologically competitive effect of Desulfovibrio desulfurican and Pseudomonas stutzeri on corrosion of X80 pipeline steel in the Shenyang soil solution.

In this paper, we have investigated the corrosion mechanism of X80 carbon steel in the presence of nitrate reducing bacteria (NRB), sulfate reducing bacteria (SRB) or both in the Shenyang soil solution. The results show that both SRB and NRB increase the corrosion rate of steel specimens and cause pitting corrosion of steel. Electrochemical tests and weight-loss data show that the addition of NRB in the SRB-containing environment leads to the reduction of corrosion. The thermodynamic analyses confirm the competitive advantage of NRB for the nutrients (organic carbon sources and irons) and the chemical oxidation of ferrous sulfide by nitrite, which results in a mitigation in the microbiologically influence corrosion (MIC) of SRB.

Synergistic effect of alternating current and sulfate-reducing bacteria on corrosion behavior of X80 steel in coastal saline soil.

With the development of electrified railways and high-voltage transmission lines, it is often inevitable that buried metal structures are subjected to interference from the alternating current (AC) induced by the neighboring power facilities. Commonly found in soil, sulfate-reducing bacteria (SRB) have the capability to accelerate metal corrosion. In this paper, with electrochemical methods, surface analysis techniques, and weight-loss test, the influence of AC and SRB on the X80 steel corrosion behavior was explored in coastal saline soil. The results revealed that the 100 A m-2 AC inhibited the growth of the sessile and planktonic SRB cell. Under the action of 100 A m-2 AC, the metabolic activity of viable bacteria was enhanced, and the process of extracellular electron transfer was accelerated. When both AC and SRB were introduced, the maximum pit depth (76.2 µm) increased significantly to be 15 times higher than in the control condition (4.9 µm). Both SRB and AC played a role in enhancing corrosion. The corrosion rate of the AC-influenced specimen was far higher than that of the SRB-influenced specimen, while SRB and AC produced a synergistic effect on the enhanced corrosion of the specimen.

Microstructure Evolution in ZrCx with Different Stoichiometries Irradiated by Four MeV Au Ions.

ZrCx ceramics with different stoichiometries were irradiated under a four MeV Au ion beam in doses of 2 × 1016 ions/cm2 at room temperature, corresponding to ~130 dpa. Grazing incidence, X-ray diffraction and transmission electron microscopy were performed to study the radiation damage and microstructure evolution in ZrCx ceramics. With the decrease in C/Zr ratio, the expansion of ZrCx lattice became smaller after irradiation. Some long dislocation lines formed at the near-surface, while, in the area with the greatest damage (depth of ~400 nm), large amounts of dislocation loops formed in ZrC, ZrC0.9 and ZrC0.8. With the increase in carbon vacancy concentration, the size of the dislocation loops gradually decreased. Few dislocation loops were found in ZrC0.7 after irradiation, and only black-dot defects were found in the area with the greatest damage. For the non-stoichiometric ZrCx, with the increase of the intrinsic vacancies, the number of C interstitials caused by irradiation decreased, and the recombination barrier of C Frenkel pairs reduced. The above factors will reduce the total number of C interstitials after cascade cooling, suppressing the formation and growth of dislocation loops, which is significant for the enhancement of the tolerance of radiation damage.

Corrosion kinetics and mechanisms of ZrC1-x ceramics in high temperature water vapor.

The corrosion kinetics and mechanisms of ZrC1-x ceramics in water vapor between 800 and 1200 °C were investigated. The results showed that there was only cubic ZrO2 phase in the corrosion layer when corroded at 800 °C, while a scale layer consisted of a mixture of cubic and monoclinic ZrO2 phases when corroded at 1000 °C and 1200 °C. A series of crystallographic relationships at the ZrC/c-ZrO2 interface were detected. The c-ZrO2 formed near the interface retained some crystallographic orientations of the initial ZrC before corrosion, presenting an "inheritance in microstructure" between c-ZrO2 and ZrC. The corrosion behavior mainly followed a parabolic relationship. The incremental rate of weight gain increased with increased corrosion temperature and decreased C/Zr ratio and the carbon vacancy was passive to the decrease of corrosion rate. The main corrosion controlling mechanism changed from phase boundary reactions to surface diffusion and then to grain boundary diffusion with increased temperature.