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Friction Stir Radial Backward Extrusion (FSRBE) as a new grain refining technique

Jafarzadeh H., Babaei A., Esmaeili-Goldarag F.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1374--1385

EN

A new method entitled Friction Stir Radial Backward Extrusion (FSRBE) is presented for processing fine-grained tubes. In FSRBE technique, an initial pure copper billet is placed inside a cylindrical chamber. The billet is pushed toward a rotating tool which results in radial and backward flow of the material while is frictionally stirred. The microstructure evolution during FSRBE was investigated through experimental observations and cellular automaton (CA) modeling. The observations reveal that the microstructure with initial grain size of 75 μm was refined to a fine-grained structure with an average grain size of 12 μm. The results of tensile tests demonstrate slight improvement in the value of yield and ultimate strength, elongation and microhardness. The microstructural evolution during FSRBE processing in the micro-level was studied using a coupled cellular automaton algorithm and finite element model. First, the macroscopic plastic flow behavior of material during FSRBE was calculated using FEM simulation method. Next, by tracing the plastic strain, the strain rate and temperature, in the deformation domain of cellular automaton, the DRX kinetics of pure copper is obtained in a devised post-processing step. The microstructure observations showed that the proposed model predictions were in reasonably good agreement with the experimentally obtained results.

2

Ultra-fine grain structure of AA3104 alloy analyzed by TEM and SEM orientation mappings

Paul H., Baudin T., Tarasek A.

Inżynieria Materiałowa

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2010

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Vol. 31, nr 3

531-534

EN

Commercial purity AA3104 aluminum alloy was deformed via equal channel angular pressing through different routes up to 10 passes and then annealed to obtain the state of partial recrystallization. The microstructure and the crystallographic texture were analyzed using scanning (SEM) and transmission (TEM) electron microscopes equipped with orientation measurement facilities. The nucleation of new grains was observed in bulk samples and during in situ recrystallization in TEM. In most of the observed cases, the growth of recrystallized grains occurred by the coalescence of neighboring subcells. This process usually led to nearly homogeneous structure of fine grains of similar size. Irrespective of the applied deformation mode, a large non-deformable second phase particles (SPP) strongly influenced strengthening of the matrix through deformation zones around them. After annealing the diameter of grains in the vicinity of large SPP was only occasionally significantly larger than the average grain size. Large grains were most often observed in places far from the large SPP. TEM orientation mapping of highly deformed zones around particles showed that orientations of new grains were not random and only strictly defined groups of orientations were observed.

PL

Materiał o czystości technicznej przeciskano w matrycy równokątowej do 10 przepustów, a następnie poddawano wyżarzaniu dla uzyskania stanu częściowej rekrystalizacji. Rozwój mikrostruktury i tekstury analizowano, wykorzystując techniki pomiaru orientacji lokalnych w transmisyjnej (TEM) i wysokorozdzielczej skaningowej (SEM) mikroskopii elektronowej. Proces zarodkowania analizowano na masywnych próbkach oraz w eksperymentach rekrystalizacji in situ w TEM. W szczególności systematyczne pomiary orientacji lokalnych w TEM są niezwykle użyteczną techniką w analizie zmian teksturowych, jakie dokonują się w ultra drobnokrystalicznych obszarach, w pobliżu dużych cząstek drugiej fazy. liczba błędnie zindeksowanych punktów map orientacji uzyskanych za pomocą TEM nie przekraczała zwykle 10÷15%, co pozwala na stwierdzenie, że technika ta może być rozważana, jako komplementarna dla pomiarów SEMFEG/ EBSD. W większości obserwowanych przypadków, wzrost nowych zrekrystalizowanych ziaren następował drogą koalescencji sąsiadujących komórek dyslokacyjnych. Niezależnie od zastosowanej drogi odkształcenia, duże wydzielenia cząstek drugiej fazy silnie wpływały na formowanie się strefy zlokalizowanego odkształcenia w ich bezpośrednim sąsiedztwie. W strefach tych w procesie rekrystalizacji nowe ziarna jedynie sporadycznie osiągały rozmiary większe od średniej. Duże ziarna najczęściej obserwowano w obszarach 'znacznie' oddalonych od dużych cząstek, a ich orientacje nie były przypadkowe.

3

Badania strukturalne mechanizmu odkształcenia na zimno stali specjalnych

Stępień J., Wojtas J.

Prace Instytutu Metalurgii Żelaza

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2006

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T. 58, nr 3

57-60

PL

Zgniatanie obrotowe na zimno stali niskowęglowej chromowo-manganowo-molibdenowo-wanadowej stosuje się w celu uzyskania w wyrobie gotowym struktury ultra drobnoziarnistej. W pracy po zgniataniu obrotowym uzyskano w wyrobie strukturę silnie rozdrobnionego martenzytu listwowego umocnionego wydzieleniami i pasmami odkształcenia ułożonymi przestrzenie w wielu kierunkach. Na podstawie przeprowadzonych badań strukturalnych stwierdzono, że struktura w wyrobach ze stali EŻP jest bardziej jednorodna i bardziej rozdrobniona niż struktura wyrobów ze stali VAD.

EN

The cold roll flowing of low-carbon chromium-manganese-molybdenum-vanadium steel is used to obtain the ultra-fine grained structure in the finished product. As a result of roll flowing, the structure of highly refined strip martensite strengthened with precipitations and deformation bands, arranged spatially in many different directions, was obtained in the product. On the basis of the structural tests it was found that the structure of ESR steel products was more homogeneous and refined than the structure of VAD steel products.

4

Strength enhancement possibilities of low carbon steels

Greger M., Kocich R., Kander L., Dorociáková G.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

359--362

EN

Purpose: The paper analyses methods of grain refinement and demonstrates development of structure and properties of metallic materials after severe plastic deformations (SPD). Design/methodology/approach: Technology ARB was experimentally verified. The material was rolled in 11 passes. Rolling proceeded at temperature 650 ̊C, with heating in furnace with inert atmosphere (Ar). Findings: True strain has achieved the value 9. Basic relations between magnitude of deformation, grain refinement and resulting mechanical properties were described. Bonding of degree was greater than 90%. Practical implications: ARB method is one of instrument for acquirement materials with ultrafine grain structure. Is it very simply apparatus, which can be used in practical technology (classical rolling mill). Originality/value: Development of structure was verified on low carbon steel. Obtained grain size was around 0.3 μm. Properties obtained by tensile test did not achieve the expected value. Grain size was homogenous in whole volume.

5

Refinement of steel microstructure by free-forging

Jandová D., Divišová R., Skálová L., Drnek J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 16, nr 1-2

17--24

EN

Purpose: Refinement of austenitic steel and low alloyed C-Mn-Si-Nb steel microstructure by free-forging. Design/methodology/approach: In this study severe hot deformation was applied on low alloyed 0.2C-1.5Mn-2Si-0.05Nb steel and austenitic 0.07C-18Cr-2Mn.-10Ni steel. Steels were processed in a full-hydraulic press. Different temperatures of preheating, dwells and strain levels were applied. Microstructure was characterised using optical metallography, scanning and transmission electron microscopy. Findings: After optimization of processing fine grained structures with convenient phase composition were obtained. Multiple free-forging followed by recrystallization annealing was successfully used for refinement of austenitic Cr-Ni steel and improvement of mechanical properties. While free-forging of low alloyed C-Mn-Si-Nb steel still has not satisfied expected increase of strength and ductility. Research limitations/implications: Free-forging usually results in formation of very heterogeneous structures. In submitted study relatively fine grained and uniform structures were obtained. Grain size below a few micrometers can not be probably achieved using above mentioned technology. Originality/value: Obtained results can be used for development of forging technology in service conditions.