The capability of hibonite elongated grains to influence physical,microstructural, and mechanical properties of zirconia toughened alumina–CeO2–MgO ceramics

This work investigated the capability of hibonite (CaAl₁₂O₁₉) phase on structure and microstructure of zirconia toughened alumina–CeO₂–MgO ceramics. Three different additives (CeO₂, MgO and CaCO₃) were introduced into zirconia toughened alumina ceramics prepared by solid state reaction. X-ray diffraction and FESEM analyses were employed to observe the role of secondary phases especially hibonite and its influence on the microstructural features and other properties. Among the secondary phases present, EDX analysis revealed that hibonite phase contributed to elongated grains. Vickers indentations hinted a strong difference in the efficiency of compositional adjustment among the composites. The excellent Vickers hardness and fracture toughness results obtained for 3 wt.% CaCO₃ additions showed the appearance of 5.9% hibonite with the value of 1485 HV and 7.10 MPa·√m, respectively.     

Effect of stacking fault energy on mechanical behavior of cold-forging Cu and Cu alloys

Cu, Cu–2.87 wt% Mn, Cu–4.40 wt% Mn and Cu-10.19 wt% Mn were prepared by cold-forging. The deformation behavior of Cu–Mn alloys is consistent with the Cu-Al alloys and Cu–Zn alloys but without lowering the stacking fault energy to simultaneously increase the strength and ductility. A series of analysis demonstrate that Cu–Mn alloys have a much smaller twin density than low stacking fault energy (SFE) metals, and dislocation strengthening is the major reason for the higher strength. The role of short range order (SRO) in promoting the mechanical properties has also been briefly discussed.     

Quantitative Analysis of Work Hardening and Dynamic Softening Behavior of low carbon alloy Steel Based on the Flow Stress

In this study, the constitutive equation and DRX(Dynamic recrystallization) model of Nuclear Pressure Vessel Material 20MnNiMo steel were established to study the work hardening and dynamic softening behavior based on the flow behavior, which was investigated by hot compression experiment at temperature of 950 °C, 1050 °C, 1150 °C and 1250 °C with strain rate of 0.01 s⁻¹, 0.1 s⁻¹ and 10 s⁻¹ on a thermo-mechanical simulator THE RMECMASTOR-Z. The critical conditions for the occurence of dynamic recrystallization were determined based on the strain hardening rate curves of 20MnNiMo steel. Then the model of volume fraction of DRX was established to analyze the DRX behavior based on flow curves. At last, the strain rate sensitivity and activation volume V^* of 20MnNiMo steel were calculated to discuss the mechanisms of work hardening and dynamic softening during the hot forming process. The results show that the volume fraction of DRX is lower with the higher value of Z (Zener–Hollomon parameter), which indicated that the DRX fraction curves can accurately predicte the DRX behavior of 20MnNiMo steel. The storage and annihilation of dislocation at off-equilibrium saturation situation is the main reason that the strain has significant effects on SRS(Strain rate sensitivity) at the low strain rate of 0.01 s⁻¹ and 0.1 s⁻¹. While, the effects of temperature on the SRS are caused by the uniformity of microstructure distribution. And the cross-slip caused by dislocation piled up which beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions. Otherwise, the coarsening of DRX grains is the main reason for the high activation volume at low Z under the same strain conditions.     

Origin of radial breathing mode in multiwall carbon nanotubes synthesized by catalytic chemical vapor deposition

The origin of radial breathing mode (RBM) in the Raman spectra of multiwall carbon nanotubes (MWNCTs) is discussed. In general, RBM is characteristics of single wall carbon nanotube (SWCNT). With the help of transmission electron microscope (TEM) and Raman spectroscopic studies, it is established that the presence of SWCNT in the cavity of MWCNT is responsible for the appearance of RBM in MWCNT (synthesized by low temperature catalytic chemical vapor deposition technique). The estimated diameter of 8.2 Å (from Raman study) of SWCNT is almost same as that observed (∼8.3 Å) in TEM studies.     

Effects of vertical electromagnetic stirring on grain refinement and macrosegregation control of bearing steel billet in continuous casting

The grain refinement and macrosegregation control of GCr15 bearing steel were investigated under a type of rarely-used electromagnetic stirring, vertical electromagnetic stirring (V-EMS), in continuous casting. V-EMS can create an upward electromagnetic force and generate longitudinal loop convection, which ena-bles the better mixing of the upper part with the lower part of the liquid steel.The results showed that ap-plying V-EMS can enlarge the region of the equiaxed grain, decrease the secondary dendrite arm spacing (SDAS) and reduce the segregation of both carbon and sulfur.After applying V-EMS, liquid steel with a high solute concentration is brought to the dendrite tips, making the dendrite arms partially melt.The length of the dendrite fragment is approximately 1.8 mm, 10 to 12 times the SDAS.Upon increasing the amount of cooling water from 2.0 to 3.5 m3/h, the dendrite fragments exhibit an obvious aggregation fol-lowing V-EMS.Finally, a criterion for dendrite fragmentation under V-EMS was derived based on the dendrite fragmentation theory of Campanella et al.     

High Cr ODS steels performance under supercritical water environment

This paper summarizes the results of supercritical water corrosion studies of two ferritic oxide dispersion strengthen (ODS) steels MA956 and PM2000 at the temperature of the upper limit of potential peak cladding temperature under normal operation, according to the conceptual design being developed in the EU. As the high temperature and pressure above the thermodynamic critical point of water result in higher oxidation rate for conventional austenitic alloys than observed in sub-critical light water reactor (LWR) conditions, ensuring adequate corrosion resistance is critical for thin-wall components like fuel cladding. This study concentrated on the investigation of two effects, surface finish and orientation of the cuts. Two different surface treated coupons were prepared in order to study the effect of cold work in sample surface on corrosion resistance. Samples were exposed in supercritical water at 650 °C and 25 MPa, for up to 1800 h. The corrosion rate was evaluated by measuring the weight change of the samples and by cross-section examinations. The microstructure of the oxide layers was analyzed using a scanning electron microscope (SEM) in conjunction with energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). Weight gain results of both ODS steels proved a good resistance to general corrosion. Nevertheless the cross-sectional SEM study showed signs of nodular corrosion, observed mostly on the ground specimens after long exposure times.     

Constitutive analysis of the hot deformation behavior of Fe–23Mn–2Al–0.2C twinning induced plasticity steel in consideration of strain

In this study, constitutive analysis has been carried out on Fe–23Mn–2Al–0.2C twinning induced plasticity (TWIP) steel. For this purpose, hot compression tests were conducted on a Gleeble-3500 thermo-mechanical simulator in the temperature range of 900–1150 °C and the strain rate range of 0.001–20 s⁻¹. The effects of deformation heating and friction on flow stress were analyzed and corrected. On the basis of Sellars–Tegart–Garofalo equation, the strain-dependent constitutive equations of the steel were derived. The results show that deformation heating has a significant influence on the flow stress at lower temperatures and higher strain rates, while the frictional effect is slight even at the highest strain level investigated. Comparison of the calculated flow stress with the experimental data suggests that the developed constitutive equations can adequately describe the relationships between the flow stress, strain rate, temperature and strain of the steel during hot deformation. This is supported by a high correlation coefficient (R = 0.996) and a low average absolute relative error (AARE = 3.31%) for the entire deformation condition range investigated.     

A recursive algorithm for the reliability of a circular connected-(r,s)-out-of-(m,n):F lattice system

A circular connected-(r, s)-out-of-(m, n):F lattice system consists of m×n components arranged in a cylindrical grid. Each of m circles has n components, and this system fails if and only if there exists a grid of size r ×s which all components are failed. A circular connected-(r, s)-out-of-(m, n):F lattice system might be used in reliability models for ‘Feelers for measuring temperature on reaction chamber’ and ‘TFT Liquid Crystal Display system with 360° wide area’.In this study, we proposed a new recursive algorithm for obtaining the reliability of a circular connected-(r, s)-out-of-(m, n):F lattice system. We evaluated our proposed algorithms in terms of computing time and memory capacity. Furthermore, a numerical experiment comparing our proposed algorithm with Yamamoto and Miyakawa's algorithm [Yamamoto, H., & Miyakawa, M. (1996). Reliability of circular connected-(r, s)-out-of-(m, n):F lattice system. Journal of the Operations Research Society of Japan, 39(3), 389–406] showed that our proposed algorithm is more effective for systems with a large n.     

An investigation on effects of various parameters on viscosities of coal–water mixture prepared with Erzurum–Aşkale lignite coal

In this study the effects of parameters such as coal loading (wt.%), the initial pH of mixture, the addition of various electrolytes, surfactants and temperature on the viscosity and rheologic parameters of coal–water mixture (CWM) have been investigated. The apparent viscosity was measured with a RV8-Brookfield rotating type viscosimeter. The additives used were AlCl₃ and K₂HPO₄ as the electrolytes and Cetyltrimethyl Ammonium Bromide (CTAB), Sodium Dodecyl Sulphate (SDS) and Borrosperse NA-3A as the surfactants. It was found that the most effective additives, in terms of the viscosity reduction, were CTAB and K₂HPO₄, and that the CWM which had coal concentrations up to 50% (based on the weight of dry coal) could be prepared by using each additives. In addition, the viscosities of CWM with increasing temperature were found to increase at low speed, and decrease at high speed.