Solid State Phenomena Vol. 294

Abstract: The objective of this study was to compare the cytotoxicity of a domestically-made light-cured orthodontic adhesive to a commercial adhesive, Transbond XT (3M Unitek, USA). An in-house orthodontic adhesive composed of a filler 60-70 weight % and a monomer ratio (BisGMA:TEGDMA) of 6:4 with 0.5% of photoinitiator was mixed. The potential cytotoxic effect of this experimental and a control adhesive was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay according to ISO 10993-5: 2009(E). The L929 cell line was grown in 96-well tissue culture plates (1x10⁵ cells/mm³). Thin cured-resin discs of each material weighing 0.4 gram were prepared and incubated for 1, 3, 5, 7, 14, and 30 days in Dulbecco’s modified Eagle medium (DMEM) at 37°C and 95% humidity with 5% CO₂. The percentage of cell viability was reported by descriptive statistics. The result showed that the cell viability of the experimental adhesive was higher than Transbond XT in all measured periods. The cytotoxicity of both the adhesives gradually decreased with the progression of time. In conclusion, the in-house adhesive showed a good biocompatibility since the first day following polymerization. On the other hand, Transbond XT started with a cytotoxic potential, then, turned to be non-cytotoxic after 5 days of curing.

Abstract: Titanium alloy & stainless steel are major materials for bone fracture fixation such as bone screws and plates in today's medical devices. However, the fixation devices made of metal not only have the risk of metal ion release to cause human allergies, but they also need to be removed by a second surgical operation making pain and the risk of the patient’s wound infection after the bone fracture healing. The biodegradable Polylactic Acid (PLA) bone screws & bone plates have the great advantage of not needing a second operation, but their insufficient strengths make them not be widely used in the current bone fracture fixation. In the study, we use PLA as the matrix and in-mod heat treatment with induction coils to increase the strength of bone screw & plate by improving crystallinity of material. Regarding ASTM F2502 “Standard Specification and Test Methods for Absorbable Plates and Screws for Internal Fixation Implants”, we measure bending loads of test pieces before and after in-mold heat treatment, and obtain the optimized process parameters by Taguchi method that will increase the bend load of PLA bone plates by 34.82%. These optimal parameters are the injection speed of 80 mm/s, the melt temperature of 205 °C, the heat treatment temperature of 110 °C and heat treatment time of 20 min.

Abstract: Facing the current inefficiency of boron extraction from boron concentrate, this paper used mechanical activation as a pretreatment method to improve the extraction of B₂O₃ from boron concentrate, and researched the influences of milling conditions, including the ball-sample mass ratio, the diameter of milling ball, and filling ratio of chamber, on the B₂O₃ activity. The changes in the properties of the milled products were investigated to analyze the mechanism of activation. These three milling conditions all affected the B₂O₃ activity more or less, as evidenced by the changes of B₂O₃ activity with these milling factors. Under optimized milling conditions, the B₂O₃ activity could be enhanced from 67.52% of the non-activated boron concentrate to 85.01%. The results also showed that the specific surface area increased and the crystal structure was damaged, which accelerated the reaction between the alkaline leaching solution and boron concentrate samples and enhanced the B₂O₃ activity of the samples.

Abstract: In this study, microwave irradiation technology was used for the calcification roasting followed by sulfuric acid leaching process. The effect of roasting temperature, m (CaO)/m (V₂O₅), and roasting time on the leaching ratio of vanadium were investigated and the roasted samples were characterized by TG-DSC, XRD, and SEM. The leaching ratio of vanadium can be significantly enhanced with the increasing in roasting temperature, m (CaO)/m (V₂O₅), and roasting time. The leaching ratio of chromium decreased with roasting temperature and increased with m (CaO)/m (V₂O₅), and roasting time. The optimal roasting parameters were roasting temperature of 850 °C, the m (CaO)/m (V₂O₅) of 0.85, and roasting time of 90 min. Under the optimal roasting parameters, the leaching ratio of vanadium reached 88.81%. While the leaching ratio of chromium is 3.98%. During roasting process, vanadium is oxidized to acid-soluble CaV₂O₅, Ca₂V₂O₇, and CaMgV₂O₇. After leaching, chromium mainly exists in form of chromohercynite (FeCr₂O₄) and chrome-manganese spinel (Mn_1.5Cr_1.5O₄) in leaching residues.

Abstract: Nowadays, by increase in using structural materials, the high temperature properties of these materials are became an important issue within different aspects of engineering. The new Oxide Precipitation Hardened (OPH) steel generated by the authors based on Fe-Al-O matrix which prepared by mechanical alloying and hot consolidation. These new OPH steels showed a better oxidation resistant and creep, compare to similar ones. In order to investigate the thermomechanical and microstructure of these materials, a series of different tests were performed on three different OPH steels variant which developed and manufactured by the authors. The results show that the heating temperature has a significant influence on these properties while almost total recrystallization of grains and subgrains were observed during the investigation.

Abstract: The uniaxial tensile tests were conducted at different temperatures to explore the coupled influence of stacking fault energy (SFE) and short-range clustering (SRC) on the plastic deformation behavior of Cu-Ni alloys. The results demonstrate that the ultimate tensile strength and uniform elongation decrease with increasing temperature due to the competitive influence of SFE and SRC. Dynamic strain aging (DSA) effect is observed at 200 and 250°C, and such an effect becomes more notable with increasing Ni content. The occurrence of DSA effect is thought to be caused by pinning of moving dislocations by SRC and diffusing solute atoms. The plastic deformation mechanisms for Cu-Ni alloys is mainly governed by wavy slip of dislocations at different temperatures, since the SFE of Cu-Ni alloys are very high especially at high temperatures, and the effect of SRC can be nearly ignored.

Abstract: To explore the role of dislocation slip mode playing in the size effect of mechanical behavior of metallic materials, the tensile behavior of Cu-5at.%Mn and Cu-20at.%Mn alloys with thickness (t) spanning from 0.1 to 2.0 mm is investigated. The results reveal that the yield strength σ_YS of Cu-5at.%Mn alloy displays an independence of thickness, whereas the ultimate tensile strength σ_UTS and the uniform elongation δ show an obvious size effect. The σ_UTS and δ first slightly decrease as t is reduced from 2.0 to 0.5 mm, but evidently drop when t is below 0.5 mm. A similar size effect is also exhibited in Cu-20at.%Mn alloy; however, the variation trend of “the smaller the weaker” in size effect can be weakened by the planar slip of dislocations occurring during the deformation of this alloy.

Abstract: Corner cracks are very likely to occur in the slabs when peritectic steels, medium carbon steels, boron or niobium micro-alloyed steels are being produced by continuous slab caster, which will lead to edge upwarping and edge cracking of the finished products in the rolling process. To stop the slabs with corner cracks from going down to the rolling mills and affecting the finished rolled product quality, the slabs must be flame scarfed in the continuous casting process, thus causing increases in the operational cost. In 2013, Baosteel decided to relocate the two single-strand 2,300mm slab casters from Luojing of Shanghai to Zhanjiang of Guangdong. The slabs produced by the slab casters at Baosteel Luojing were observed with serious corner crack problem. To solve the problem of corner cracks, CISDI worked hard together with Baosteel to extensively optimize and improve the bender roller arrangement, segment roller gap accuracy control, secondary cooling zoning, secondary cooling width control, dynamic cooling control model, dynamic soft reduction model, etc., and eventually the conundrum of corner cracks which were frequent in the slab casters when at Luojing was solved and the presence of corner cracks in slabs of peritectic steels, medium carbon steels, boron or niobium micro-alloyed steels has been decreased from over 90% to less than 1%. The present article focuses on the work done specifically on solving the problem of corner cracks in the designing stage.

Abstract: Generally, the welding parameters directly affect the weld forming and the joint performance. Because many parameters are involved in the automatic arc welding process, it is not realistic to use traditional experimental methods, such as full factorial design. Therefore, it is important to find out the good experimental design method to determine the welding parameters for optimal joint quality with a minimal number of experiments. Therefore, this study is aimed at investigating the effect of DOE (Design of Experiment) methods on bead width of mild steel parts welded by the automatic GMA (Gas Metal Arc) welding process. In this work, Taguchi method was used for studying the effect of the welding parameters on optimization of bead width, while Box-Behnken method was utilized to develop a mathematical model relating the bead width to welding parameters such as welding voltage, arc current, welding speed and CTWD (Contact Tip to Work Distance). The S/N (Signal-to-Noise) ratio and the ANOVA (Analysis of Variance) were employed to find the optimal bead width. Confirmation tests were carried out to validate the effectiveness of the Taguchi method. The experimental results show that welding current mainly affected the bead width. The predicted bead width of 3.12mm was in good agreement with the confirmation tests. With the regression coefficient analysis in the Box-Behnken design, a relationship between bead width and four significant welding parameters was obtained. A second-order model has also been established between the welding parameters and the bead width as welding quality. The developed model is adequate to navigate the design space.

Abstract: The process of cold die drawing of tubes is ranked among frequently used methods of production of seamless tubes and is performed in drawing tool which is characterized by simple design. Shape and dimensions of the drawing tool depend on tube reduction degree, i. e. on original diameter of initial tube and final internal diameter of the tube. Tube wall thickness is not determined by any tool. The technology of cold die drawing of tubes is influenced by various process parameters, i.e. geometry of the die itself, strain degree and strain rate, force conditions, conditions of friction, method of lubrication and the type of used lubricant. The contribution is concerned with evaluation of influence of the selected process parameters using FEM simulation. Designed graphs illustrate the impact of coefficient of friction and reduction cone of drawing tool on the size of drawing force.