Papers by Keyword: Pinning

Abstract: The properties of alloys depend on its microstructure, such as the size of grains. In general, the balanced mechanical properties of alloys can be obtained with small grain size. While the grain size of alloys may increases under heat treatment, thermal mechanical processing and service condition of high temperature, i.e., the grain growth is inevitable. The effort of most research is to control the rate of grain growth and avoid abnormal grain growth. For example, pinning the grain boundary and reduce its mobility with the second phase particles in order to prevent grain growth. Therefore, the properties of the alloys will not decreases dramatically and the structure retains a high degree of integrity. The details of grain growth with particle pinning were investigated by phase field simulations in the present paper. It is found that, with the same size of pinning particles, the pinning effect increases with the increases of the pinning particle number. With the same pinning particle number, the pinning effect increases with the increases of pinning particle size. Under the same total volume of pinning particles while different particle size and number, the pinning effect is complicated and it will be discussed in details. The pinning effect decreases with the increases of grain boundary energy. These findings could shed light on the understanding of the grain growth kinetics with particle pinning.

Abstract: This paper presents an experimental study of the evaporation of a sessile water-sodium chlorides solution drop to open atmosphere on the solid substrate (anodized aluminum) under the varying heat flux. The main parameters defining drop profile, i. e., contact diameter, contact angle, and height of the drop have been obtained. Specific evaporation rate has been calculated. According to the data analysis it was found, that the sessile water-sodium chlorides solution drop with the highest concentration (16.7%) evaporates in the "reverse depinning" mode. So, there is movement of the contact line in the direction of increasing the surface occupied by the drop. The sessile water and water-sodium chlorides solution drop with 4.8% and 9.1% concentration evaporates in the contact line pinning mode. The influence of the initial concentration of the evaporated solution on the contact angle and the specific evaporation rate was found out.

Abstract: Spatial distribution of microalloy precipitates have been characterized in a low carbon microalloyed steel containing Nb, Ti and V. Micro-segregation during casting resulted in an inhomogeneous distribution of Nb (and also Ti) precipitates in the as-cast slab. Austenite grain growth has been investigated in the above mentioned steel, using different reheating temperatures between 1000°C and 1250°C for 1 h. Inhomogeneous distribution of Nb-rich precipitates created austenite grain size bimodality after reheating to an intermediate temperature range (1150-1200°C). Uniformly fine and uniformly coarse grain structures were found after reheating at lower- (≤ 1075°C) and higher-reheating temperatures (≥ 1250°C). A model has been proposed for the prediction of austenite grain size variation in the reheated steel.

Abstract: This paper presents the work done for the preparation of precursor for producing Ti-Al-V-Y alloy via FFC Cambridge process. The aim of the work is also to investigate the uniformity of the phases formed during the pre-processing of the precursor.The importance of the alloy for mechanical and medical applications is well known. Titanium oxide (TiO₂), vanadium oxide (V₂O₅), aluminium oxide (Al₂O₃) and yttrium oxide (Y₂O₃) were selected as raw materials for precursor. The expected composition for the new alloy is Ti-6Al-4V-0.5Y. Water was used as a binder for the precursor. The materials were pre-mixed by ball milling for 24 hours and pressed using 13 mm die. The pressed mixtures were then sintered in the furnace at 900°C for 24 hours. The sintered samples were analysed using the optical microscope, electron micrograph with EDX and XRD. The result of the optical micrograph showed that the raw materials were uniformly mixed and well distributed with the presence of porosities. Electron micrograph further verified the morphology of the materials and the elements distribution in the precursor. The overlapping of yttrium and vanadium, Y(VO₄) was observed and verified by XRD. The derived formulated precursor was then ready for further work of reduction to Ti-Al-V-Y alloy using FFC Cambridge process.

Abstract: Effect of carbide precipitation on pinning force and migration mechanism of boundaries of martensite laths was considered in a 3%Co modified P911. The dimensions of second phase precipitations, martensite laths and dislocation densities were measured by means of transmission electron microscopy. The pinning forces retarding the motion of the lath boundaries, that arise from M(C,N) nanoscale precipitations and M₂₃C₆ particles were evaluated by using different models. The pinning pressure evaluated by taking into account a non-uniform distribution of M₂₃C₆ particles was high enough to stabilize the lath martensite structure during tempering and long term ageing. On the other hand, significant coarsening of martensite laths occurred in neck portions of samples subjected to long-term creep tests. Additional effects from dislocation density and applied stress on the motion of lath boundaries are considered in some details.

Abstract: The effects of long-range atomic order and pinning of interfaces on anelastic properties of Cu-based martensite have been distinguished by means of studying strain amplitude dependences of internal friction and Young’s modulus defect, assuming that low-and high-amplitude stages of the strain amplitude dependence correspond to the oscillations within and beyond pinning atmospheres.

Abstract: In this paper, pinning synchronization of complex dynamical with time delay was considered. We proved that the dynamical complex network can achieve synchronization with small time delay. Then we give some simulations to illustrate the theoretical result.

Abstract: Analytical and numerical methods are used to study the process of motion of domain walls in an individual nanowire consisting of ferromagnetic crystallites with a chaotic crystallographic anisotropy. The influence of magnetostatic interaction on the motion is considered. The force profile of the domain wall pinning, caused by stochastic crystallographic anisotropy, is examined. The magnetization curve is analytically constructed and the coercive force is calculated. The Barkhausen jumps of domain walls are investigated. The result is verified by numerically modeling.

Abstract: New thermo-mechanical processes (TMPs) to produce ultrafine-grained copper alloys utilizing continuous recrystallization (cRX) were proposed. These methods stand on our hypothesis that the evolution of ultrafine grains can be evolved by a mechanism of cRX even during severe plastic deformation at ambient temperature. A TMP of warm compression of 10 to 20 % of Cu-1.7mass%Fe alloy followed by annealing was cyclically repeated. The slight reduction, low-temperature annealing and pinning of grain boundaries by precipitates efficiently impeded occurrence of discontinuous recrystallization (dRX). The evolved substructures with nodes of the Fe precipitates gradually changed to new grains surrounded by low- and high-angle boundaries with increasing number of the repeated processes. Ultrafine grains with average size of 0.7 m were successfully evolved. However, the onset of dRX triggered extended grain coarsening accompanied by grain-boundary migration under conditions of insufficient annealing temperature and large pass stain. Another TMP cycles of cold rolling and annealing also induced fine-grained structure of about 0.6 m. The above results improved that ultrafine grain refinement can be realized simply by a mechanism of cRX even in the metallic materials with low stacking fault energy.

Abstract: We investigated the durability of giant magnetoresistive (GMR) heads to nanoscale scratches created during the lapping process. Analysis using high-field transfer curves after deliberate scratching with an atomic force microscope (AFM) identified changes in the magnetization of the head and a reduction in pinning strength, which is a magnetic performance indicator. Additionally, finite element method (FEM) analysis suggested that the overall effects on the GMR head following nanoscale scratching increased with scratch depth.