Papers by Keyword: Grain Coarsening

Abstract: This study investigates the mechanical properties and microstructure of sintered tungsten under varying sintering conditions. Bending strength tests revealed that sintering at 1400 °C resulted in low flexural strength due to inadequate temperature, whereas sintered tungsten at 1500 °C exhibited improved strength attributed to grain growth. However, temperatures exceeding 1600 °C led to excessive grain growth and a subsequent decline in strength, indicative of grain coarsening and potential localized bonding. Additionally, analysis of holding times at 1500 °C demonstrated that extended durations promoted neck bonding between grains, contributing to the formation of interconnected grains and enhanced mechanical properties. This study underscores the importance of optimizing sintering parameters to control grain growth and achieve desired mechanical properties in sintered tungsten materials.

Abstract: Thermal crack initiation and pitting corrosion are frequently caused by the formation of the secondary phases such as sigma phase, delta-ferrite phase, carbides and secondary austenite phase in steel. Traditionally, heat treatment is used to minimize these detrimental effects of the secondary phases. In this study, we have applied pulse to the 316L stainless steel and observed the considerable effects. In comparison to the heat treatment, the electropulsing can effectively suppress the precipitation of the secondary phases in a temperature range (1161 K–1173 K). Austenite grain size becomes larger under electropulsing compared to the heat treatment at annealing temperatures due to enhanced interface migration. The kinetic and thermodynamic aspects of electropulsing can be used to explain the effects of electropulsing on the evolution of microstructure for 316L stainless steel.

Abstract: The hot rolling at temperature range of 1100 °C to 862 °C and subsequent air-cooling induce a formation of the coarse ferrite grains in the 9CrODS steels. This coarse ferrite is produced by transformation from the severely hot rolled γ-grains to ferrite. Formation process and mechanism of the transformed coarse ferrite are interpreted in terms of a nucleation, growth and coalescence of the same variant ferrite grains under a variant restriction rule.

Abstract: Modern steelmaking technologies utilizing microalloyed steel designs have been responsible for enormous economic benefits for both the steelmaker and fabricator. What has not been acknowledged is the environmental benefit that high strength steels have produced in terms of reduced steel usage in major infrastructure projects. The judicial use of microalloying has the potential to further reduce total tonnage requirements while delivering enhanced operational performance and service life. Various projects around the world have begun to recognize these recent microalloying developments. This paper will present the grain coarsening behavior of the new generation of Nb bearing steels, which have been used in major international steel fabrication projects.

Abstract: Numerous literature [1,4,5] has reported on the effective use of cellular automaton method for the simulation of short-range diffusion. Using this model for the simulation of short-range diffusional phase transformations therefore is a resolved issue. It is proven that two- or three-dimensional automata can reflect the course of the abovementioned processes realistically. What our study demonstrates more than in the past [1] is that two-dimensional stochastic cellular automaton simulation already presented before has been simplified. This time our automaton operates in one dimension [2], which has consequently reduced running time, thus, made it possible to enhance the efficiency of the scaling of simulation. In our previous work the results of scaling of one-dimensional simulation of the recrystallization process [3] were demonstrated, in our current study fitting is performed for measurement results of grain coarsening using one-dimensional cellular automaton.

Abstract: Electrochemical performance of solid oxide fuel cells based on Ni_0.75Co_0.25-GDC (Gd_0.1Ce_0.9O_1.95) and Ni-GDC anodes were investigated and compared in order to understand the effects of (i) alloying Ni with Co and (ii) anode microstructure on the cell performance under hydrogen fuel. At the sintering temperature of 1300°C for 5 h, the Ni_0.75Co_0.25-GDC anode showed a superior distribution and connection of grains to the Ni-GDC anode which had grain clustering structure in general. Grain growth and connection were found in both anodes when the sintering temperature was increased to 1350°C for 3 h. This resulted in significant improvement of the anodic polarization resistance for the Ni-GDC anode but only minor change for the Ni_0.75Co_0.25-GDC anode. This research, however, showed that the Ni-GDC anode had higher anodic polarization resistance than the Ni_0.75Co_0.25-GDC anode, resulting in the better cell power density at all sintering conditions. The maximum power density obtained at 800°C for the cell with the Ni_0.75Co_0.25-GDC anode was 118 mW•cm^-2. Impedance spectroscopy analysis showed that the total cell resistance of both cell types became progressively larger when the operation time was prolonged to 10 h at 800°C, while the microstructure change was not observable by the SEM. The reason for the fast degradation will thus require further investigation.

Abstract: With the process parameters and processing conditions in the mill, a systematic experimental research were conducted to Q345 steel containing niobium austenite grain growth law, and analysis the dissolution and precipitation behavior of Nb carbonitride. The results shows that Nb-microalloyed steel heated to 1180 ~ 1230 °C can significantly improve strength and toughness of steel and performance.

Abstract: The grain structure and texture evolution during annealing an Al-0.13%Mg submicron grained alloy, deformed by plane strain compression (PSC) at cryogenic temperatures, has been investigated. On annealing the grain structure coarsened and transformed from lamellar to equiaxed. But, remarkably, the fraction of low angle boundaries (LABs) increased, from less than ~ 25% to ~50% above 300 °C, leading to instability and discontinuous coarsening at higher temperatures. The surprisingly large increase in LAB fraction on annealing is shown to be related to orientation impingement originating from the strong texture present after PSC in liquid nitrogen.

Abstract: Normal and abnormal grain coarsening, NGC and AGC, are briefly reviewed and discussed in the light of grain curvature and kinetic models - notably those of Mullins. The critical importance of the log-normal grain size distribution determined by Hull and the grain shapes measured by Rhines and Craig are reviewed. It is shown that in NGC, as in particle coarsening, the largest grains or particles in their respective distributions grow at the rates, larger by a factor of the ratio of the largest to average size, required to maintain the size distributions during coarsening. The particle curvature removal model for NGC anchorage, giving = 0.2 r/f, developed here, matches surprisingly well the data reviewed by Manohar et al. Finally the need is indicated for further experimental and modeling studies to test the current ideas and to answer the many remaining questions.

Abstract: Amorphous silicon (a-Si) film crystallized by Ni-induced lateral crystallization under static electric field was analyzed. It has been demonstrated that Ni-induced lateral crystallization of a-Si is directional with electric field. Moreover, there exists a critical value of electric field strength, below which the rate of Ni-induced lateral crystallization of a-Si increases remarkably with the increase of field strength, while above which the rate will decrease instead. This phenomenon can be interpreted well based on electromigration effect.