Experimental verification of hematite ingot mould heat capacity and its direct utilisation in simulation of casting process

Heat capacity of alloys (metals) is one of the crucial thermophysical parameters used for process behaviour prediction in many applications. Heat capacity is an input variable for many thermodynamical (e.g. Thermocalc, Pandat, MTData, …) and kinetic programs (e.g. IDS-Solidification analysis package, …). The dependences of heat capacity on common variables (temperature, pressure, ...) are also commonly used as the input data in software packages (e.g. ProCast, Magmasoft, ANSYS Fluent, …) that are applicable in the field of applied research for simulations of technological processes. It follows from the above that the heat capacities of materials, alloys in our case, play a very important role in the field of basic and applied research. Generally speaking, experimental data can be found in the literature, but corresponding (needed) data for the given alloy can very seldom be found or can differ from the tabulated ones. The knowledge of proper values of heat capacities of alloys at the corresponding temperature can be substantially used for addition to and thus towards the precision of the existing database and simulation software. This study presents the values of C _p measured for the hematite ingot mould and comparison of the measured data with the C _p values obtained using the software CompuTherm with respect to simulation of technological casting process.     

Investigation on solidification conditions in functionally Si-gradient Al alloys using simulation and cooling curve analysis methods

During recent years, functionally graded alloys have been widely produced by melt processing routes to achieve advanced material properties. In this paper, the new cast-decant-cast (CDC) method has been used to produce the gradient in concentration of Si particles in cross section of final Al–Si castings. For this purpose, the hypereutectic LM28 and hypoeutectic LM25 alloys were selected for each step casting into the steel mold. Cooling curve thermal analysis and simulation methods were applied to investigate the cooling behavior of first poured LM28 alloy and improve the accuracy of CDC process by determining the curves of solid fraction and temperature profiles. The final products were studied through optical microscopy, image analysis, and Brinell hardness measurement. The results showed that the silicon concentration decreased along transition zone between two alloys by increasing the decanting time in the order of 25, 40, and 50 s. This can be due to the lower temperature of exterior LM28 alloy in semi-solid state and shorter solidification time of interior LM25 alloy. This can lead a to reduction of the diffusion rate of elemental silicon along the transition zone. The microscopic scale of transition zone between two alloys developed the maximum thickness of 438 μm and hardness value of 83 HB comparing with the hardness of 88 and 62 HB for external and internal alloys, respectively. The microscopic observations and hardness evaluations confirmed the creation of functionally Si-gradient products.     

Systemic approach to design of liquid cleaning compositions and practical implementation of the method

The scientific basis of the development of liquid cleaning compositions is physicochemical analysis of multicomponent systems that comprise the major components of detergents. The method was implemented in Optimum software for the sulfirol-8–isobutanol–turpentine–water four-component system. After solubility in the system was studied, homogeneous mixtures were optimized by their physicochemical and functional properties (viscosity, density, refractive index, pH, detergency, and corrosion activity). The compositions having the highest detergency and neutral pH and not causing corrosion on titanium and aluminum alloys were selected and recommended for use as technical detergents.     

液体和非晶态NiAl3合金结构的从头算分子动力学模拟

应用从头算分子动力学方法模拟了液体以及淬冷形成的NiAl₃合金体系,得到了它们的对相关函数、结构因子、键对分析信息.结果分析表明,在淬冷条件下得到的体系呈现非晶态性质,且非晶态结构类似于液态NiAl₃合金的结构,可以用液体结构近似描述非晶态性质.还进行了电子结构分析,得到液体NiAl₃合金的电子态密度和电荷分布.在液体镍铝合金中,镍为电子受体,部分电子由铝向镍转移,支持了Candy等人的XPS实验结果.镍铝间强烈作用,形成带有弱共价键性质的金属键.镍在合金中相当分散,这能部分解释由淬冷形成的NiAl₃合金制得的骨架镍催化剂活性增强的原因.     

X射线荧光光谱法测定超硬铝合金中成分

叙述了用SRS 300型X射线荧光光谱仪测定超硬铝合金中铜、镁、锌、铁、硅、锰、铬、镍、钛、锆的X射线荧光光谱分析方法。试样用车床加工至表面平整、光滑,采用强度校正模型,由计算机拟合回归曲线。此法测定结果与常规湿法化学法测定结果相符。     

A method for more accurate FEA results on a medical device developed by 3D technologies

At present, 3‐dimensional models of all additive manufactured objects (AMOs) are accepted as a solid model for finite element analysis (FEA). FEA of AMOs may not reveal the real results because mechanical properties of default materials in CAD software and newly built AMOs are not equal to each other. This may produce problems especially for the end user due to unexpected failure or wear off. The aim of this study was to compare FEA results of an additive manufactured Ankle Foot Orthosis model under 2 different value sets, namely default material‐based mechanical properties and measured mechanical properties. In order to determine the real mechanical properties of the additive manufactured Ankle Foot Orthosis, 3‐dimensional printed test specimens with different infill densities were prepared and tested according to the recommended standards. Mechanical test results were then loaded in the CAD software and FEA was performed. This study illustrated that default mechanical properties of existing materials in CAD software produce misleading simulation results for AMOs, ie, real mechanical properties should be used to get more accurate results.     

SIMS investigations on the growth mechanisms of protective chromia and alumina surface scales

The oxidation behaviour of the oxide-dispersion strengthened (ODS) high-temperature alloys MA 956 (an aluminium oxide former) and MA 754 (a chromium oxide former) has been compared with that of two model alloys, Fe-20Cr-5Al and Ni-25Cr. The morphology and composition of the oxide scales were investigated by metallography, X-ray diffraction analysis and scanning electron microscopy. For analysis of the oxide layer growth mechanisms, twostage oxidation experiments with¹⁸O as tracer were used, the distribution of the oxygen isotopes in the oxide scale being determined by SIMS. The ODS alloys show a more selective oxidation than the two model alloys; moreover, the protective oxides on the ODS alloys have a lower growth rate and better adhesion than those on the two model alloys. From the SIMS investigations it can be deduced that the improved properties of the layers on the ODS alloys result from a change in the transport processes in the protective layer; whereas the aluminium and chromium oxide films on the conventional alloys grow by cation and anion transport, the scales on the ODS alloys grow almost exclusively by anion transport. It is shown that the observed properties of the oxide scales on the ODS alloys can be explained by this change in transport mechanism.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

A Study of Precipitates Formation in AA 380.0 Aluminium Alloys Modified by the Addition of Magnesium

A data acquisition system and the SAD2 software, that provide characteristic cooling curves, in combination with microstructure analysis were used to study precipitates formation in the AA380.0 aluminium alloys modified by adding extra magnesium. The samples were solidified with distinct cooling rates caused by carrying out the solidification in shell and permanent molds. The mathematics processing of the cooling curves in agreement with the microstructure analysis have confirmed the remarkable presence of both the Al–Si dendrite network and the Mg2Si interdendritic phase in the alloys with the addition of extra magnesium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electrodeposition of cobalt–tungsten alloys and their application for surface engineering

Applying electrochemically deposited coatings is a convenient way to improve surface properties of a substrate metal. Today materials for applications are frequently selected according to their functional properties. Nowadays theoretical and practical studies of the co-deposition of tungsten with iron group metals are conducted worldwide, and interest for these studies increases. Tungsten alloys of iron group metals have a high melting point and are often considered high-performance alloys, and the attractiveness in those has been driven by their outstanding properties and multiple possible applications. That research is encouraged by the pronounced mechanical, tribological, and magnetic properties as well as the corrosion resistance of tungsten alloys. The magnetic properties of electrodeposited Co–W alloys are of interest in recording media and remotely-actuated micro-/nano-electromechanical systems. The given research presents an overview of versatile possibilities of Co–W alloys as multiscale materials obtained by electrodeposition from citrate solutions at pH 5–8 and temperatures 20–60°C. The paper discusses electrodeposited tungsten alloys as suitable candidates to meet many technological demands at macro-, micro- and nano-scale as coating films, microbumps and nanowires.     

Electrochemical deposition and corrosion stability of Zn–Co alloys

Electrochemically deposited Zn–Co alloys under various deposition conditions were investigated using anodic linear sweep voltammetry for phase structure determination, scanning electron microscopy for surface morphology analysis, atomic absorption spectroscopy for determination of chemical composition, and polarization measurements and open circuit potential measurements for determination of corrosion properties. The influence of deposition current density, temperature, and composition of deposition solution on the phase structure and corrosion properties of Zn–Co alloys was studied. It was shown that the ratio of cobalt to zinc ions in the plating bath strongly affects the chemical content and phase structure, as well as corrosion stability, of Zn–Co alloys. Zn–Co alloys deposited from plating baths with the lowest and the highest ratios of cobalt and zinc ions exhibited the lowest corrosion rate.     

Thermal analysis of Cu-14.82 wt% Al-0.4 wt% Be shape memory alloy

The phase transitions proceeding during melting of selected Sn–Ag–Cu alloys were determined by means of the DSC technique. Twelve compositions were studied along two cross-sections with silver to copper molar ratios X(Ag)/X(Cu) = 1 and 7/3 and tin concentration from 0.4 to 0.9 mol fraction. The transition temperatures were calculated using Pandat software package and thermodynamic parameters from the SOLDERS database. The experimental results were compared with both available literature data and calculation results, and a good agreement was observed. Deconvolution of DSC complex curves was performed using PeakFit v.4.12 software package. Eutectic mixture mass fractions involved in the eutectic transformation were determined. The obtained results were compared with the data calculated using thermodynamic parameters and good agreement was achieved in the case of alloys of higher content of Sn. The discrepancy was found in the case of alloys with lower Sn content where initial structure of the samples subjected to DCS analysis was partly a result of the occurrence of peritectic transformation.     

Modeling of Thermodynamic Properties of Liquid Alloys in the System Magnesium-Tin

The results obtained in studying experimentally the thermodynamic properties of liquid alloys in the system magnesium-tin are analyzed. The concentration dependences of the excess molar Gibbs energy and the enthalpy of mixing of the magnesium-tin system in the liquid state are described in terms of the ideal and regular solution models, using modified software.     

热处理对La4MgNi19储氢电极合金结构和性能的影响

以感应熔炼和不同的热处理工艺制备了La₄MgNi₁₉合金, 用X射线衍射(XRD)和电化学测试系统研究了该合金的相结构和电化学性能. 结构分析表明: 当热处理工艺为900 °C+水淬时, 合金主要由CaCu₅结构的LaNi₅相和少量未知相组成; 当热处理工艺为900 °C退火时, 合金主要由Pr₅Co₁₉、Ce₅Co₉结构的(La, Mg)₅Ni₁₉相及少量CaCu₅结构的LaNi₅相组成. 淬火和退火后合金的电化学循环稳定性(S₁₀₀)分别为49.7%及76.0%, 合金电极的电化学性能和相结构密切相关. 退火热处理有利于生成Pr₅Co₁₉、Ce₅Co₉型相. 在La-Mg-Ni 系储氢合金中, La₄MgNi₁₉合金电化学循环稳定性不及La₃MgNi₁₄合金.     

Physical Stability and the Droplet Distribution of Rice Oil–in–Water Emulsion

The objective of the current study was to evaluate long-term stability of emulsions with rice oil by assessing their physical properties. For this purpose, six emulsions were prepared, their stability was examined empirically, and the most correctly formulated emulsion composition was determined using a computer simulation. Variable parameters (oil and thickener content) were indicated with optimization software based on Kleeman's method. Synthesized emulsions were studied by numerous techniques involving determination of particle size and distribution of emulsion, optical microscopy, viscosity, and novelty analysis—Turbiscan test.

The emulsion containing 50 g of oil and 1.2 g of thickener had the highest stability. Empirically determined parameters proved to be consistent with the results obtained using the computer software. The computer simulation showed that the most stable emulsion should contain from 35.93 to 50 g of oil and 0.94 to 1.19 g of thickener. The computer software based on Kleeman's method proved to be useful for fast optimization of the composition and providing parameters of stable emulsion systems. Forming emulsions based on rice oil is a chance to introduce a new, interesting representative of functional food as well as a cosmetic product.     

Molecular simulation of aromatic polyesters containing oxetane rings in the main chain

Molecular simulation is a powerful research tool for gaining new insights into polymer chemical structures and processes. This paper presents a computational conformational analysis of some aromatic polyesters containing either an oxetane ring or propylene moieties in the main chain. The studied polyesters were synthesised by phase transfer catalysis using 3,3-bis-(chloromethyl)-oxetane, 1,3-dibromopropane and various aromatic diacids. The computational analysis and calculations were performed using the Cerius² program (version 3.5), molecular simulation software for material science, designed by Molecular Simulations Incorporated. This study elucidates some aspects and properties dependent upon supramolecular arrangement of the macromolecular chains. In order to verify the agreement between simulated and experimental results the coefficient of asymmetry, order parameter and glass transition temperature were calculated for each studied aromatic polymer.     

Systematic investigation of mechanically alloyed Ti-Mg-Ni used as negative electrode in Ni-MH battery

In this study, a series of Ti-Mg-Ni alloys have been synthesized by mechanical alloying using a planetary high-energy ball mill. The effect of varied composition on the microstructure and electrochemical hydrogenation properties of Ti-Mg-Ni system have been investigated through the compared analysis of Ti_1-xMgNi_x and TiMg_1-xNi_x alloys. The structural transformation and discharge capacities were characterized by XRD and electrochemical measurements at galvanostatic conditions, respectively. Additionally, a separate milling process has been employed for improving the electrochemical properties of Ti-Mg-Ni alloys. It is shown that the separated milling process can extremely enhance the discharge capacities of Ti-Mg-Ni composite materials.     

Online Monitoring of the Atmospheric Corrosion of Aluminium Alloys Using Electrochemical Noise Technique

In this work, an electrochemical system based on electrochemical noise (EN) technique for online detection and monitoring of atmospheric corrosion of LY12CZ aluminium alloys has been established. A detecting probe and a monitoring instrument with a software have been developed to perform the electrochemical noise measurements with zero resistance ammeter (ZRA) mode. Experimental results show that the atmospheric corrosion behaviour of aluminium could be effectively detected and monitored by the analysis of the electrochemical potential and current noise, also by the noise resistance variation.     

Calorimetric study and thermal analysis of Al–Sn system

The results of calorimetric study and thermal analysis of binary Al–Sn system are presented in this paper. The Oelsen calorimetry was used in thermodynamic analysis. Following thermodynamic properties were determined at 727 °C: activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies. The energetics of mixing in liquid Al–Sn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit. Thermal analysis of selected alloys in Al–Sn system was done using differential thermal analysis. Defined characteristic phase transition temperatures were used for comparison with calculated phase diagram of investigated system. Good agreement with available literature data was obtained. Structural analysis of selected alloys was done using optic microscopy.     

Mechanical properties of UV‐curable carbon fiber‐reinforced polymer composite patch: Repair evaluation of damaged aluminum alloy

Epoxy resin composite patches reinforced by carbon fiber were prepared through ultraviolet (UV)–curing method, and the damaged aluminum alloy plates are rapidly repaired by means of adhesively bonding method. Mechanical properties of the composite patches and damaged aluminum alloy plates before and after repair were studied by experiment and numerical simulation. Results indicated that the tensile properties of carbon fiber/epoxy resin composite patches presented the tendency of first increase and then decrease with the increase of layer numbers of reinforced fiber. The composite patches with two layers fiber showed the best tensile properties, and the tensile strength and modulus reached 1.13 GPa and 27.79 GPa, respectively. However, the bending strength of composite patches decreased with the increase of layer numbers. Results of performance evaluation on the mechanical properties of damaged aluminum alloy plates repaired by the two layers carbon fiber/epoxy resin composite patches showed that the repair efficiency of tensile and bending properties of the repaired aluminum alloys reached more than 83% and 160%, respectively, compared with the undamaged aluminum alloys. Besides, results of numerical simulation showed that the stress intensity factor (SIF) of the crack tip on repaired aluminum alloy plates decreased significantly in comparison with the unrepaired aluminum alloy plates, which further revealing the reinforced mechanism of composite patches on the bending properties of repaired aluminum alloy plates.     

Oxidation behaviour and kinetic properties of shape memory CuAlxNi4 (x=13.0 and 13.5) alloys

Although the copper-based shape memory alloys (SMA) have some important problems such as controlling of the kinetic properties in the shape memory ability, they have relatively more advantages when compared to nitinol, such as lower price and simpler production technology. In order to determine the kinetic properties and oxidation rates of shape memory CuAl_xNi₄ (x=13 and 13.5) alloys with polycrystalline forms, the alloys have been homogenized in β-phase field at 930 °C for 30 min and immediately quenched in iced-brine water at −3 °C. The transformation temperatures in a period of three thermal cycles which include heating and cooling processes have been determined through Shimadzu DSC-50 differential scanning calorimeter. Activation energies of forward and reverse martensitic transformations have been calculated by using the Kissenger method. Thermogravimetric analysis with Shimadzu TGA-50 have been carried out for the determination of mass changes of alloys during heating and cooling cycles with two temperature rates selected as 10 and 30 °C/min up to 900 °C. It has been shown that increasing aluminium content reduces the oxidation rates of the alloys. It has also been established that CuAlNi shape memory alloys have a good stabilization in martensitic phase.