Advanced Materials Research Vol. 906

Abstract: Isothermal compression tests were carried out on Ti-6.0Al-7.0Nb biomedical titanium alloy at the temperatures of 750900°C (all below β phase transition temperature about 1010°C) and strain rates of 0.0011.0s^-1. The processing maps were constructed to evaluate the efficiency of power dissipation (η) and recognize the flow instability regimes. True strain takes great effect on the efficiency of power dissipation η under the different temperatures and strain rates. The value of power dissipation η increases from 0.1 to 0.7 in most areas. When the strain is 0.9, the value of power dissipation η in most regimes is from 30% to 40%. There are two instability regimes respectively located around 780°C/1.0s^-1 and 860-900°C/0.001-0.01s^-1 when the strains are below 0.5. One of the instability regimes disappears when the strains are 0.5-0.7. When the strain is 0.9, there are still two instability regimes. The safe regime located around 780-840°C/0.1-0.01s^-1, and hot deformation can be carried out in this area.

Abstract: Aluminum alloy 7075-T6 specimens were corroded in 3.5% NaCl solution for 120 hours and 240 hours, respectively. Morphology and dimensions of corrosion pits on specimen surface were inspected with white light confocal profiler. Statistical analysis shows that pit dimensions can be fitted well with log-normal and Gumbel distribution. After surface inspections, we performed high-cycle fatigue tests for the specimens. Fracture analysis shows that fatigue cracks initiate from single pit or two adjacent pits, and the crack-initiation pit shape and dimensions were examined with SEM. It is found that initiation pit dimensions can be well described with the log-normal distribution. Additionally, initiation pit dimensions are significantly larger than those measured on specimen surface before fatigue tests.

Abstract: Corrosion morphology image is one of the most important features for the evaluation of the corrosion damage of materials. By using white light confocal profiler, the corrosion morphologies of AA2524 aluminum alloy specimen are obtained after full immersion to experimental 3.5% salt solution for different time. Through digital image processing, typical corrosion morphology characteristics are extracted, such as the fractal dimension, the depth of pit, the area of pit. By extended 3D box-dimension method, the fractal dimensions of the corrosion surface under immersing time of 24 and 120 hours are determined. The statistical analyses show that the corrosion areas and the characterization parameters ab/2c² obey Gumma distribution, and the corrosion depth obeys Gumbel, normal, Weibul and log-normal distributions.

Abstract: The grain oriented silicon steel slabs were reheated at 1323K~1623K with different soaking time in this study. The precipitation behavior of the second phase particles in the steel slabs was investigated by using SEM/EDS combined with other analytic tools. The results show that the main precipitations in samples are MnS and AlN bearing a little of Cu_xS, and they frequently aggregate with each other by two or three types of precipitations. The quantities of the above three types of precipitations are up to 90% in each sample. These complex precipitations change into AlN bearing a little of Cu_xS or single AlN after being reheated. The shapes of MnS or AlN havent the common spherical or quadrilateral characteristic outline. There are a few of spherical or irregular shape inclusions such as SiO₂, Al₂O₃, TiO₂, CaO, CaS and their complex in the samples. Part of MnS or AlN can also grow around with these particles and then dissolves after being reheated. The sizes of the particles are main in the range of 0.05~0.2μm. There are no inclusions larger than 5.0μm in size observed in the fields of view. The volume density of the precipitations 0.05~0.2μm in size extracted from the quenched samples at 1523K using non aqueous solution electroextraction are 4.04×10⁴ /mm³, 4.73×10⁴ /mm³, 3.70×10⁴ /mm³, 3.33×10⁴ /mm³, 3.10×10⁴ /mm³ and 1.56×10⁴ /mm³ as the corresponding reheating time is 10min, 30min, 60min, 90min, 120min and 240min at 1523K respectively. The average size of them is 0.108μm. It is more precise to statistics the volume density of the particles in the steel by electrolysis extracting method than that of using metallogrphical analysis. No obvious microstructure variation was observed in the quenched samples after annealing different time. When the reheating temperature reaches 1523K and 1623 K, the grain size grows more easily and the grain boundary gets smoothly. The grain boundary of the samples becomes clear with the increase of the annealing temperature during the same annealing time. The reheating temperature in the present slab is chosen at 1523K and the reheating time is kept for 120 min, which will insure the particles in the slab to dissolve more completely and avoid grain growth abnormally at high temperature.

Abstract: The effect of graphite shapes on the electrochemical corrosion behavior of cast iron was studied by means of weight loss tests, electrochemical measurements and electron microscopy. It was found that the electrochemical corrosion behavior of graphite is significantly different from one other, and the corrosive potential difference between carbide ad the matrix is the main driving force of the different phase corrosions. Among them, the center A type and edge D type graphite exhibited the highest corrosion resistance. The corrosion of white iron is worst, because there are so many type carbides in white iron and so there is an obvious tendency to produce micro-cell in white iron.

Abstract: The three-dimensional finite element (FE) numerical simulation of extrusion forming of AZ31 matrix magnesium alloy was analyzed in four extrusion velocities. The flow pattern and the influence of extrusion velocity for the temperature, the distribution of effective stress and strain of composites were analyzed. The results showed that, when the extrusion velocity increased from 1.5 mm/s to 4.5 mm/s, the heat flux under steady extrusion state would change from-2.77e+004 (Wm²) to 1.14e+005 (Wm²), meanwhile the effective stress and strain increased at first and then decreased, and the average effective strain and stress value were smallest when v = 4.5 mm/s. It showed that along with the increase of the extrusion velocity, the rise degree of the temperature increased and the distribution of the effective stress and strain tended to be more evenly. Finally, the best extrusion technical parameters of AZ31 magnesium alloy were determined, that was the extrusion velocity was equal to 4.5 mm/s when extrusion ratio was 25 and extrusion temperature was 350 °C.

Abstract: The interpenetrating magnesium composites reinforced by three-dimensional braided stainless steel wire reinforcement were fabricated. And, the deformation behavior of materials was analyzed in four extrusion velocities by DEFORM-3D software. The results show that with the increases of extrusion velocities, the equivalent stress values exhibit a gradually increasing and then decreasing trend. Owing to the effect of three dimensional reinforcement, the basal plane orientation occur tilt. And, the microstructure turns refined.

Abstract: Costs with the polishing process represent nearly a third of what costumers pay for polished floor tiles. This is in part due to the high consumption of cemented-matrix abrasive tools, whose demand is about half kilogram per square meter final product. The present study addresses the wear of such abrasive tools, colloquially known as fickerts in the industrial polishing process of ceramic tiles. The focus was set on the evolution of the fickert ́s surface during polishing. The fickert ́s topography was periodically measured by both optical and confocal microscopy. The abrasive tool was submitted to a sequence of ten polishing steps of one second each. All variations were quantitatively characterized and were successfully represented by means of the morphological space. Such space is in turn composed by two statistical parameters: the skewness and kurtosis, both based on the distribution of heights collected from roughness profiles taken along the fickert ́s active surface. The experimental points showed a linear relationship between skewness and kurtosis, in a very good accordance with the behavior expected for typical abrasive wear.

Abstract: This paper built the three dimension mechanics model of CRTSII slab ballastless track structure on subgrade with ANSYS software. Analysis the influence of deformation and stress characteristics caused by different temperature gradients and the coupling action of temperature gradients and train loads under different work conditions, including no-separated, separated, and multiple-slabs separated with the cement asphalt mortar layer. The results show that, temperature gradients on track slab is one of the main reasons which caused the gap appearing between the bottom of slab track and cement asphalt mortar elastic cushion. And the joint main cause the deterioration of vibration of track slab, accelerating the deterioration of the cement asphalt mortar layer.

Abstract: In order to focus on hybrid fiber reinforced concrete flexural toughness,mixed 0.7% steel fiber/0.3% modified polypropylene fiber reinforced concrete, mixed 0.89% steel fiber/0.11% Dura fiber reinforced concrete were chosen to perform flexural toughness test. The test method is giving a central point load to the notched beam specimens (H*B*L1:150mm*150mm*550mm, h1*B1:2mm*25mm) with a 0.2 mm/min loading rate. The load we carry out should not stop until the mid span deflection is more than 3mm.Based on calculating the contribution of the fiber to the energy absorption value Dcr when the concrete cracking,the contribution of the fiber to the energy absorption value D_1f when mid-span deflection is δ₁,the contribution of the fiber to the energy absorption value D_2f when mid-span deflection isδ₂ and the equivalent flexural tensile strength feq₁,feq₂,the effect of the way use to hybrid fiber on the flexural toughness of concrete were investigated. The results shows that the hybrid fiber can significantly improve the flexural toughness of concrete, have favorable deformability and the ability to control crack. The result of 0.7% steel fiber/0.3% modified polypropylene fiber reinforced concrete is shown: D_cr=2185 Nmm,D_1f=7634.26 Nmm,D_2f=2198.67 Nmm, feq₁=4.89 MPa,feq₂=2.83 MPa, hence it shows the positive enhancement effect of hybrid fiber and flexural toughness increase significantly.