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Interplay between microstructural evolution and tribo-chemistry during dry sliding of metals

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Friction 2019年第6期7卷 637-650页

作者： Philipp GGRÜTZMACHER Sebastian RAMMACHER Dominic RATHMANN Christian MOTZ FrankMÜCKLICH Sebastian SUAREZ chair of Functional materials Saarland UniversityCampus D3.3Saarbrücken 66123Germany chair of Experimental Methodology of Material science Saarland UniversityCampus D2.2Saarbrücken 66123Germany

Understanding the microstructural and tribo-chemical processes during tribological loading is of utmost importance to further improve the tribological behavior of metals. In this study, the friction, wear and tribo-chemical behavior of Ni with different initial microstructures(nanocrystalline, bi-modal, coarse-grained) is investigated under dry sliding conditions. In particular, the interplay be-tween frictional response, microstructural evolution and tribo-oxidation is considered. Friction tests are carried out using ball-on-disk experiments with alumina balls as counter-bodies, varying the load between 1 and 5 N. The microstructural evolution as well as the chemical reactions beneath the samples’ surface is investigated by means of cross-sections. The samples with finer microstructures show a faster run-in and lower maximum values of the coefficient of friction(COF) which can be attributed to higher oxidation kinetics and a higher hardness. It is observed that with increasing sliding cycles, a stable oxide layer is formed. Furthermore, initially coarse-grained samples show grain refinement, whereas initially finer microstructures undergo grain coarsening converging towards the same superficial grain size after 2,000 sliding cycles. Consequently, the experimental evidence supports that, irrespective of the initial microstructure, after a certain deformation almost identical steady-state COF values for all samples are achieved.

关键词： dry sliding microstructural analysis tribo‐oxidation wear

Fluidization behavior of graphitized glassy particles in a fluidized carbon bed cooling process for investment casting

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Particuology 2022年第6期20卷 32-38页

作者： Paul Git Matthias Hofmeister Robert F.Singer Carolin Körner chair of materials science and Engineering for Metals(WTM) Friedrich-Alexander UniversitätErlangen-Nürnberg(FAU)Martensstr.591058 ErlangenGermany

Fluidized Carbon Bed Cooling(FCBC)is an innovative investment casting process for directional solidification of superalloy *** takes advantage of a fluidized bed with a base of small glassy carbon beads for cooling and other low-density particles that form an insulating layer by floating to the bed *** so-called“Dynamic Baffle”protects the fluidized bed from the direct heat input from the high-temperature heating zone and provides the basis for an improved bed *** prerequisites for a stable casting process are stable fluidization conditions where neither collapse of the bed nor particle blow out at excessive bubble formation *** work aimed to investigate the fluidization behavior of spherical carbon bed material in argon and air at temperatures between 20 to 350℃.Systematic studies at reduced pressures using the FCBC prototype device were performed to understand the stable fluidization conditions at all stages of the investment casting *** particle shape factor and size distribution characterization and the measurement of the powder’s minimum fluidization velocity and bed voidage show that this material can be fully utilized as a cooling and buoyancy medium during the FCBC process.

关键词： Gas-solid fluidization Glassy carbon Reduced pressure Increased temperature Fluidized carbon bed

INTERNAL FRICTION OF 51CrV4 SHAFT INFLUENCED BY THERMO-MECHANICAL COUPLING

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Acta Metallurgica Sinica(English Letters) 2008年第2期21卷 79-84页

作者： J.Gken M.Maikranz-Valentin K.Steinhoff T.S.Pavlova T.V.Ivleva I.S.Golovin chair of Metal Forming Technology University of Kassel KasselGermany Physics of Metals and materials science Department Tula State University TulaRussia

The simultaneous influence of thermal and mechanical treatment was applied to produce a geometrically complex shaft from 51CrV4 steel leading to the formation of mierostruetures which were significantly different from each other. These mierostrue- rural differences were accompanied by a local change of mechanical properties in terms of hardness, electrical resistivity and especially internal friction. The Snoek-KSster peak was recognized and analyzed in the structure of this steel.

关键词： 51CRV4 steel Functionally graded material (FGM) Internalfriction Snoek- KSster peak

Strengthening and deformation mechanism of high-strength CrMnFeCoNi high entropy alloy prepared by powder metallurgy

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Journal of materials science & Technology 2023年第1期132卷 119-131页

作者： Y.Xing C.J.Li Y.K.Mu Y.D.Jia K.K.Song J.Tan G.Wang Z.Q.Zhang J.H.Yi J.Eckert Faculty of materials science and Engineering Kunming University of Science and TechnologyKunming 650093China Laboratory for Microstructures Institute of MaterialsShanghai UniversityShanghai 200444China School of Mechanical Electrical&Information EngineeringShandong UniversityWeihai 264209China College of materials science and Engineering Chongqing UniversityChongqing 400044China Erich Schmid Institute of materials science Austrian Academy of SciencesJahnstraße 12Leoben A-8700Austria Department of materials science Chair of Materials PhysicsMontanuniversität LeobenJahnstraße 12Leoben A-8700Austria Adjunct with National University of science and Technology«MISiS» Leninsky Prosp.4Moscow 119049Russia

Multiphase CrMnFeCoNi high-entropy alloys(HEAs)were prepared by a powder metallurgy process com-bining mechanical alloying(MA)and vacuum hot-pressing sintering(HPS).The single-phase face-centered cubic(FCC)HEA powder prepared by MA was sintered into a bulk HEA specimen containing FCC phase matrix along with precipitated M 23 C 6 phase and nanoscaleσphase *** the sintering temper-ature was 1223 K,the ultimate strength reaches 1300±11.6 MPa,and the elongation exceeds 4%±0.6%.Microstructural characterization reveals that the formation of nanoscale particles and deformation twins play critical roles in improving the strain hardening(SH)*** the MA time promoted the formation of the precipitated phase and enhanced the SH ability by increasing the number of precip-itated *** SH capacity increases significantly with increasing sintering temperature,which is attributed to a significant enhancement in the twinning capacity due to grain growth and the reduced number ofσphase *** systematic studies,the planar glide of dislocations was found to be the main mode of deformation,while deformation twinning appeared as an auxiliary deformation mode when the twinning stress was *** the formation of precipitates leads to grain bound-ary and precipitation strengthening effects,crack initiation is more prominent owing to increased grain boundary brittleness around the precipitated M 23 C 6 *** prominence of crack initiation is a contra-diction that must be reconciled with regard to precipitation *** work serves as a useful reference for the preparation of high-strength HEA parts by powder metallurgy.

关键词： High entropy alloy Powder processing Grain reﬁnement Precipitation strengthening Deformation twinning

Recent advancements in thermal conductivity of magnesium alloys

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Journal of Magnesium and Alloys 2024年第5期12卷 1687-1708页

作者： Hao Lv Jun Tan Qian Yuan Fanglei Wang Yunxuan Zhou Quan Dong Aitao Tang Jürgen Eckert Bin Jiang Fusheng Pan National Engineering Research Center for Magnesium Alloys College of Materials Science and EngineeringChongqing UniversityChongqing 400044China National Key Laboratory of Advanced Casting Technologies Chongqing UniversityChongqing 400044China Department of materials science Chair of Materials PhysicsMontanuniversität LeobenJahnstraße 12Leoben A-8700Austria Erich Schmid Institute of materials science Austrian Academy of SciencesJahnstraße 12Leoben A-8700Austria

As highly integrated circuits continue to advance,accompanied by a growing demand for energy efficiency and weight reduction,materials are confronted with mounting challenges pertaining to thermal conductivity and lightweight *** virtue of numerous intrinsic mechanisms,as a result,the thermal conductivity and mechanical properties of the Mg alloys are often inversely related,which becomes a bottleneck limiting the application of Mg *** on several effective modification methods to improve the thermal conductivity of Mg alloys,this paper describes the law of how they affect the mechanical properties,and clearly indicates that peak aging treatment is one of the best ways to simultaneously enhance an alloy's thermal conductivity and mechanical *** the most frequently used Mg alloy,cast alloys exhibit substantial potential for achieving high thermal ***,recent reports indicate that hot deformation can significantly improve the mechanical properties while maintaining,and potentially slightly enhancing,the alloy's thermal *** presents a meaningful way to develop Mg alloys for applications in the field of small-volume heat dissipation components that require high *** comprehensive review begins by outlining standard testing and prediction methods,followed by the theoretical models used to predict thermal conductivity,and then explores the primary influencing factors affecting thermal *** review summarizes the current development status of Mg alloys,focusing on the quest for alloys that offer both high thermal conductivity and high *** concludes by providing insights into forthcoming prospects and challenges within this field.

关键词： Mg alloy Thermal conductivity Mechanical properties Solute atom Second phase

Bulk amorphous Al_(85)Ni_(10)Ce_5 composite fabricated by cold hydromechanical pressing of partially amorphous powders

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Chinese science Bulletin 2011年第36期56卷 3965-3971页

作者： WEI XianShun HUANG YongJiang VEKSHIN BorisSergeevitch KRAPOSHIN ValentinSidorovitch SHEN Jun School of materials science and Engineering Harbin Institute of Technology Harbin 150001 China Material science chair Bauman Moscow State Technical University Moscow 105005 Russia

Gas atomized Al85Ni10Ce5 partially amorphous alloy powders were successfully consolidated into bulk alloy specimens with high relative density at room temperature by cold hydromechanical pressing. The consolidated specimens have a high fracture strength of up to 1.1 GPa. Two densification mechanisms are proposed to explain the consolidation process. The viscous flow of the amorphous phase because of local heating facilities the elimination of residual pores.

关键词：流体力学粉末制备无定形非晶合金粉末复合致密化机制相对密度断裂强度

Continuous cooling precipitation diagram of high alloyed Al-Zn-Mg-Cu 7049A alloy

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Transactions of Nonferrous Metals Society of China 2014年第7期24卷 2018-2024页

作者： Davit ZOHRABYAN Benjamin MILKEREIT Christoph SCHICK Olaf KESSLER chair of materials science University of Rostock Polymer-Physics Group University of Rostock

The precipitation behaviour during cooling from solution annealing of high alloyed 7049A aluminium alloy was investigated, covering the complete cooling-rate-range of technical interest. This ranges from slow cooling rates close to equilibrium up to rates above complete supersaturation and is covering seven orders of magnitude in cooling rate （0.0005 to 5000 K/s）. The continuous cooling precipitation behaviour of 7049A alloy was recorded by combining different differential scanning calorimetry （DSC） techniques and microstructure analysis by SEM and Vickers hardness testing. The high alloyed, high strength and quench sensitive wrought aluminium alloy 7049A was investigated during quenching from solution annealing by conventional DSC in the cooling rate range of 0.0005 to 4 K/s. In this range at least two exothermal precipitation reactions were observed： a high temperature reaction in a narrow temperature interval of 450-430℃, and a low temperature reaction in a broad temperature interval down to about 200 ℃. Intensities of both reactions decreased with increasing cooling rate. Quenching from solution annealing with rates up to 1000 K/s was investigated by differential fast scanning calorimetry （DFSC） and the differential reheating method （DRM）. A critical quenching rate to suppress all precipitation reactions of 100-300 K/s was been determined.

关键词： differential scanning calorimetry (DSC) differential fast scanning calorimetry (DFSC) 7049A alloy differentialreheating method continuous cooling precipitation

Tailoring the microstructure， tensile properties， and creep resistance of additively manufactured Inconel 718 superalloy by post-processing

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Transactions of Nonferrous Metals Society of China 2024年

作者： Sajad Ghaemifar Milad Roostaei Mohammad Reza Zamani Stefan Wurster Hamed Mirzadeh School of Metallurgy and materials Engineering， College of Engineering， University of Tehran Erich Schmid Institute of materials science， Austrian Academy of sciences Department of materials science， chair of materials Physics， Montanuniversit?t Leoben

Effects of post-processing heat treatments on the microstructure， aging kinetics， and room/elevated temperature mechanical properties of additively manufactured Inconel 718 superalloy were investigated. Scanning electron microscopy (SEM)， electron backscattered diffraction (EBSD)， and X-ray diffraction (XRD)， as well as hardness， tensile， and creep testing were used for characterization. At temperatures higher than 1100 °C， homogenization treatment resulted in the appearance of equiaxed grains by recrystallization and diminishing the dislocation density. The precipitation activation energy for the homogenized aged condition was obtained as 203 kJ/mol， which was higher than the value of ～160 kJ/mol for the as-built IN718 superalloy. Therefore， direct aging resulted in a faster aging response， which led to a significant improvement in tensile properties， as rationalized by the strengthening mechanisms. Direct aging treatment resulted in a higher elevated-temperature ultimate tensile strength (UTS) as well as the optimum creep life and lowest minimum creep rate in comparison with other heat treating routes， which were attributed to the presence of fine and uniformly dispersed strengthening precipitates in conjunction with the high dislocation density.

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Influence of structural depth of laser-patterned steel surfaces on the solid lubricity of carbon nanoparticle coatings

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Friction 2023年第7期11卷 1276-1291页

作者： Timothy MACLUCAS Lukas DAUT Philipp GRÜTZMACHER Maria Agustina GUITAR Volker PRESSER Carsten GACHOT Sebastian SUAREZ Frank MÜCKLICH chair of Functional materials Saarland UniversitySaarbrücken 66123Germany Institute for Engineering Design and Product Development TU WienWien 1060Austria INM–Leibniz Institute for New materials Saarbrücken 66123Germany Department of materials science&Engineering Saarland UniversitySaarbrücken 66123Germany Saarene-Saarland Center for Energy materials and Sustainability Saarbrücken 66123Germany

Carbon nanoparticle coatings on laser-patterned stainless-steel surfaces present a solid lubrication system where the pattern's recessions act as lubricant-retaining *** study investigates the influence of the structural depth of line patterns coated with multi-walled carbon nanotubes(CNTs)and carbon onions(COs)on their respective potential to reduce friction and *** laser interference patterning(DLIP)with a pulse duration of 12 ps is used to create line patterns with three different structural depths at a periodicity of 3.5μm on AISI 304 steel ***,electrophoretic deposition(EPD)is applied to form homogeneous carbon nanoparticle coatings on the patterned *** ball-on-disc experiments are conducted on the as-described surfaces with an alumina counter body at a load of 100 *** results show that the shallower the coated structure,the lower its coefficient of friction(COF),regardless of the particle ***,with a minimum of just below 0.20,CNTs reach lower COF values than COs over most of the testing *** resulting wear tracks are characterized by scanning electron microscopy,transmission electron microscopy,and energy-dispersive X-ray *** friction testing,the CNTs remain in contact,and the immediate proximity,whereas the CO coating is largely *** of structural depth,no oxidation occurs on CNT-coated surfaces,whereas minor oxidation is detected on CO-coated wear tracks.

关键词： solid lubricant coatings carbon nanotubes carbon onions direct laser interference patterning(DLIP)surface structuring electrophoretic deposition(EPD)