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Analysis of Solidification of High Manganese Steels Using Improved Differential Thermal Analysis Method

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Journal of Iron and Steel Research International 2015年第8期22卷 709-714页

作者： Chang-ling ZHUANG Jian-hua LIU Christian BERNHARD Peter PRESOLY Engineering Research Institute University of Science and Technology Beijing Chair of Metallurgy Montanuniversitat Leoben

High manganese steels can damage the differential thermal analysis （DTA） instrument due to the manganese evaporation during high temperature experiments. After analyzing the relationship between residual oxygen and manganese evaporation, tanta- lum metal was employed to modify the crucible of DTA, and zirconium getter together with strict gas purification measures were applied to control the volatilization of manganese. By these modifications, problems of thermocouple damage and DTA instrument contamination were successfully resolved. Cobalt samples were adopted to calibrate the accuracy of DTA instruments under the same trial condition of high manganese steel samples, and the detection error was confirmed to be less than 1 ℃. Liquidus and soli- dus temperatures of high Mn steels were measured by improved DTA method. It was found that the liquidus temperatures of sam- ples tested by experiments increased linearly with the heating rates. To eliminate the effects of the heating rate, equilibrium liquidus temperature was determined by fitting the liquidus temperatures at different heating rates, and referred as real liquidus temperature. No clear relationship between solidus temperatures and heating rates was found, and the solidus temperature was finally set as the average value of several experimental data.

关键词： DTA high manganese steel solidification liquidus temperature solidus temperature

Determining casting defects in near-net shape casting aluminum parts by computed tomography

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Frontiers of Mechanical Engineering 2018年第1期13卷 48-52页

作者： Jiehua LI Bernd OBERDORFER Daniel HABE Peter SCHUMACHER Institute of Casting Research Montanuniversitat Leoben LeobenA-8700 Austria Austrian Foundry Research Institute Leoben A-8700 Austria

Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting （Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy）, die casting （A356, A1-7Si-0.3Mg）, and semi-solid casting （A356, A1-TSi-0.3Mg）, respectively. Unlike die casting （second part）, low-pressure die casting （first part） sig- nificantly reduced the formation of casting defects （i.e., porosity） due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi- solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.

关键词： near-net shape casting aluminum parts cast-ing defects low pressure die casting die casting semi-solidcasting computed tomography

Rapid solidification and metastable phase formation during surface modifications of composite Al-Cr cathodes exposed to cathodic arc plasma

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Journal of Materials Science & Technology 2021年第35期94卷 147-163页

作者： Mehran Golizadeh Francisca Mendez Martin Stefan Wurster Johann P.Mogeritsch Abdellah Kharicha Szilard Kolozsvári Christian Mitterer Robert Franz Department of Materials Science Montanuniversitat LeobenFranz Josef-Straβe 188700 LeobenAustria Erich Schmid Institute of Materials Science Austrian Academy of SciencesJahnstraβe 12.8700 LeobenAustria Department of Metallurgy Montanuniversitat LeobenFranz Josef-Straβe 188700 LeobenAustria Plansee Composite Materials GmbH Siebenbiirgerstraβe 2386983 Lechbruck am SeeCermany

A combination of both conventional and advanced high-resolution characterization techniques was applied to study the modified layers on the surface of three composite Al-Cr arc cathodes with identical nominal composition of Al-50 at.%Cr but varying powder grain *** results revealed that the modified layers consist mainly of metastable phases such as Cr solid solution,high temperature cubic Al8 Cr5,supersaturated Al solid solution,and icosahedral *** metastable phase formation indicates that high cooling rates were involved during the solidification of molten material produced in the arc craters during cathode spot *** average cooling rate was estimated to be 10^(6)K/s based on secondary dendrite arm spacing measurements and supporting phase-field based *** formation mechanisms of the modified layers are discussed based on the obtained results and the current literature.

关键词： Cathodic arc Rapid solidification Quasicrystal Arc crater Macroparticle Phase-field simulation

Norton-Hoff model for deformation of growing solid shell of thin slab casting in funnel-shape mold

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Journal of Iron and Steel Research International 2022年第1期29卷 88-102页

作者： Alexander Vakhrushev Abdellah Kharicha Menghuai Wu Andreas Ludwig Gerald Nitzl Yong Tang Gernot Hackl Josef Watzinger Christian M.G.Rodrigues Christian-Doppler Laboratory for Metallurgical Applications of Magnetohydrodynamics Montanuniversitat Leoben8700 LeobenAustria Primetals Technologies 4031 LinzAustria Chair of Simulation and Modeling of Metallurgical Processes Department of MetallurgyMontanuniversit?t Leoben8700 LeobenAustria RHI Magnesita GmbH 1120 ViennaAustria RHI Magnesita GmbH 8700 LeobenAustria

A funnel-type mold is commonly used to provide necessary clearance for the submerged entry nozzle in the thin slab casting(TSC).The partially solidified shell is subjected to the mechanical deformations,which can lead to the defects formation and,as a results,to a ***,the results of the flow simulation,performed by the finite volume method(FVM),are fed to the external package for the finite element analysis of stress and strain.A coupled model was assembled using“creeping solid”approach by blending the Norton-Hoff viscoplastic stress for the solidifying shell with the Newtonian viscous stress of the liquid *** FVM was used to combine both liquid and solid stress models within a single *** iterative procedure based on the improved both side diffusion method was introduced to treat the nonlinear relation between the viscoplastic stress and the strain *** modeled shell thickness was verified by previously published breakout measurements and the simulation *** distribution,obtained during the TSC simulation,dominantly corresponds to the viscoplastic *** numerical approach is robust and has direct industrial application.

关键词： Solid shell Viscoplastic stress Solidification Norton-Hoff model Thin slab Continuous casting Improved both side diffusion method OpenFOAM

A comparative study of stress influence on fracture apertures in fragmented rocks

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第1期11卷 38-45页

作者： Hossein Agheshlui Mohammad H.Sedaghat Siroos Azizmohammadi Department of Infrastructure Engineering The University of Melbourne Centre for Coal Seam Cas The University of Queensland Department of Petroleum Engineering Montanuniversitat Leoben

This study compares the calculated fracture apertures in a fragmented rock layer under different stress scenarios using two different approaches. Approach 1 is a simplified method using a two-dimensional(2 D) mapping of the fracture network and projects the far-field stresses to individual fractures, and calculates the dilation, normal and shear displacements using experimental stiffnesses available in the literature. Approach 2 employs a three-dimensional(3 D) finite element method(FEM) for the mechanical analysis of the fragmented rock layer considering the interaction with the neighbouring rock layers, frictional interfaces between the rock blocks, stress variations within the fragmented rock layer,and displacements, rotations and deformations of rock blocks. After calculating the fracture apertures using either of the approaches, the permeability of the fragmented rock layer is calculated by running flow simulations using the updated fracture apertures. The comparison between the results demonstrates an example of the inaccuracies that may exist in methods that use simplified assumptions such as2 D modelling, ignoring the block rotations and displacements, projected far-field stresses on fractures,and the stress variations within the rock layer. It is found that for the cases considered here, the permeability results based on apertures obtained from the simplified approach could be 40 times different from the results from apertures calculated using a full mechanical approach. Hence, 3 D mechanical modelling implementing realistic boundary conditions, while considering the displacements and rotations of rock blocks, is suggested for the calculation of apertures in fragmented rocks.

关键词： Fracture aperture change In situ stresses Frictional interfaces Ensemble permeability

Ballistic tests on hot-rolled Ti-6Al-4V plates:Experiments and numerical approaches

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Defence Technology（防务技术） 2023年第8期26卷 39-53页

作者： Alexander Janda Benjamin James Ralph Yael Demarty Marcel Sorger Stefan Ebenbauer Aude Prestl Ingo Siller Martin Stockinger Helmut Clemens Department of Materials Science Montanuniversitat LeobenFranz Josef-Straße 188700 LeobenAustria Department Product Engineering Montanuniversitat LeobenFranz Josef-Straße 188700 LeobenAustria French-German Research Institute of Saint-Louis 5 Rue du General Cassagnou68300 Saint-LouisFrance voestalpine BOEHLER Bleche GmbH&Co KG Boehler-Gasse 18680MürzzuschlagAustria

Superior ballistic performance and the lightweight character of Ti alloys are considered as main reasons for their use in armour applications against a broad spectrum of ballistic threats,***,fragment or blast *** dynamic loading caused by typical penetrators is characterized by high strain rates,only specific test methods allow a closer investigation of the respective material *** the present study,quasi-static and dynamic compression tests as well as ballistic tests were conducted on a twophase a+βalloy Ti-6Al-4V(in m%)manufactured by ***-deformation heat treatments,influencing microstructure and mechanical properties were applied in order to compare three different microstructural configurations:as-rolled,mill-annealed and ***,on the one hand,ballistic tests were employed for the determination of the ballistic limit velocity v_(50),compression tests,on the other hand,delivered essential input parameters for the application of the Johnson-Cook constitutive model in a finite element simulation of the impact *** comparison of experimental results to simulation results was supplemented by means of microstructural characterization of tested samples with the focus set on the prevalently observed deformation and damage mechanisms,as for example adiabatic shearing.

关键词： Ti-6Al-4V Ballistic performance Split Hopkinson pressure bar FE simulation Adiabatic shear bands Intermetallic phase

Effects of weathering depth and thickness on rock failure:Experimental approach and particle flow code simulation

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第11期16卷 4638-4653页

作者： Vahab Sarfarazi Mehdi Torabi-Kaveh Arsham Moayedi Far Mining Engineering Department Hamedan University of TechnologyHamedan57965155Iran Department of Geology Yazd UniversityYazd***Iran montanuniversitat leoben Franz Josef Straße 18Leoben8700Austria

This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical *** first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 *** mechanical parameters of the samples were measured at the end of the 40th *** the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 *** results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were *** weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure *** results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering *** numerical results revealed that the tension crack was the dominant ***,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering *** results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.

关键词： Limestone Weathering depth Weathering thickness Failure pattern Particle flow code in two dimensions(PFC2D)

Creep Modeling of Magnesia-chromite Bricks in a RH Snorkel During a Process Cycle

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China's Refractories 2015年第1期24卷 22-25页

作者： JIN Shengli Harald HARMUTH Dietmar GRUBER Roman RSSLER Chair of Ceramics Montanuniversitat LeobenA-8700Austria Voestalpine Stahl GmbH

In this paper both experimental and analytical approaches to provide the inputs for creep modeling of refractories including a newly developed high temperature compressive creep machine and an inverse estimation procedure of creep law parameters are briefly ***,a modified shear test is applied to determine the cohesion and friction angle of refractories under shear state. A RH snorkel equipped with magnesia- chromite bricks is chosen for a case study of thermomechanical simulation applying the classical creep model and Drucker-Prager creep model available in the finite element code ABAQUS,respectively. Afterwards,thermal stresses and joint opening of magnesia- chromite bricks during a process cycle are compared to distinguish the impact of these two creep models.

关键词： creep shear failure thermomechanical modeling RH snorkel

Understanding formation of Mg-depletion zones in Al-Mg alloys under high pressure torsion

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Journal of Materials Science & Technology 2019年第5期35卷 858-864页

作者： Jing Xue Shenbao Jin Xianghai An Xiaozhou Liao Jiehua Li Gang Sha Herbert Gleiter Institute of Nanoscience School of Materials Science and Engineering Nanjing University of Science and Technology Nanjing 210094 China School of Aerospace Mechanical and Mechatronic Engineering The University of Sydney Sydney NSW 2006 Australia Institute of Casting Research Montanuniversitat Leoben A-8700 Leoben Austria

Redistribution of elements may take place in alloys during severe plastic deformation, which significantly alters the mechanical properties of the alloys. Therefore, comprehensive knowledge about deformationinduced redistribution of elements has to be established. In the present paper, the distribution of Mg in an Al-Mg alloy processed by high pressure torsion was examined using atom probe tomography(APT).With crystallographic information extracted by APT data analysis, this research reveals that the movement of dislocations plays an important role in the formation of Mg-depletion zones in the deformed microstructure.

关键词： High-pressure torsion Atom probe tomography Aluminum alloys Grain boundary diffusion Dislocation