Lamellar Bands Research Articles

Influence of the thermal treatment on the microstructure and hardness evolution of 7075 aluminium layers in a hot-rolled multilayer laminate composite

The microstructure and mechanical properties of the Al 7075 alloy present in a hot roll-bonded laminate consisting of Al 7075/Al 2024 layers have been characterized by high resolution electron backscattering diffraction (EBSD) analysis and Vickers microhardness, respectively. The as-rolled deformation structure consisted in lamellar bands aligned parallel to the rolling direction. It was found that a post-rolling tempering at 175 °C/6 h, prior to the T6 treatment has a profound effect on the microstructure and the mechanical properties of the Al 7075 alloy. This tempering reduces the driving force for recrystallization during the usual solution treatment of 30 min that is part of the T6 treatment. The performed procedures favour a more homogeneous precipitation during the following age hardening step and the achievement of a noticeable increase in Vickers microhardness.

Adiabatic shear banding in a tungsten heavy alloy processed by hot-hydrostatic extrusion and hot torsion

The dynamic behaviors of tungsten heavy alloy (WHA) processed by hot-hydrostatic extrusion (HE) and hot torsion (HT) were investigated. The HE + HT WHAs exhibit significant improved susceptibility to forming adiabatic shear bands (ASBs) and a remarkably high flow stress of 2400 MPa under uniaxial dynamic compression. With increasing plastic strain of HT, an obviously increasing tendency of localized shearing was observed. Elongated subgrains with an average width of 200–300 nm bonded together and formed parallel lamellar bands within the ASBs of WHA.

Formation of a Recrystallized and Recovered Multilayered Microstructure in a Hybrid Aluminium Alloy

Sheets of high purity aluminium and an Al-0.3wt.% Sc alloy in the supersaturated solid solution were roll bonded to generate 32 alternating Al-Al(Sc) layers in a 0.5 mm thickness strip. The Al layers produced lamellar bands that were aligned along the rolling direction and contained a complete β-fibre texture. Annealing at 350 °C led to complete recrystallization in the Al layers with a brass-free β-fibre texture. The recrystallization mechanism is likely to be a combination of continuous and discontinuous modes. Because the A1(Sc) layers retained much of their deformation structure after annealing the final result was a novel layered composite material.

Processing of Multi-Layered Al-Al(Sc) Hybrid Sheet by Accumulative Roll Bonding

A high-purity Al alloy and a supersaturated Al-0.3wt.% Sc alloy were accumulative roll bonded (ARB) at 200 °C to generate 0.5 mm gauge sheet consisting of 32 alternating layers of Al and Al(Sc). The material was subsequently annealed for 6h at 350 °C. The deformation and annealed microstructures were investigated using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The deformation microstructure composed primarily of lamellar bands of unequal fineness with shear bands and deformation bands being additional substructural features in the Al(Sc) layers. The high strain deformation generated Al layers containing lamellar boundaries separated by a large fraction of high angle grain boundaries, thereby creating the ideal microstructure for continuous recrystallization. Annealing of the as-deformed material generated a hybrid microstructure consisting of alternating layers consisting of ~20 0m grains produced by continuous recrystallization (Al layers) and a lightly recovered substructure (Al(Sc) layers); the latter were highly resistant to recrystallization due to precipitation of nanosized Al3Sc particles during annealing.

Development of a recovered/recrystallized multilayered microstructure in Al alloys by accumulative roll bonding

A high-purity Al alloy and a supersaturated Al–0.3 wt.% Sc alloy (Al(Sc)) were accumulative roll bonded at 200 °C to generate sheet material consisting of alternating layers of Al and Al(Sc). The deformation structure within these layers consisted of lamellar bands aligned parallel to the rolling direction. Compared with those bands in Al(Sc), the bands in the Al layers were less refined but contained a larger fraction of high angle grain boundaries (HAGBs). Subsequent annealing at 350 °C generated alternating layers of coarse grains (Al layers) and a recovered substructure (Al(Sc) layers); the latter were stabilized by the precipitation of Al 3Sc particles. Within the Al layers, annealing did not significantly alter the rolling texture (β-fibre), although the strong Brass component was largely eliminated; this behaviour has been explained using the “ReNuc” model of recrystallization whereby nucleation is deemed to occur on HAGBs between the β-fibre components of the lamellar bands in conjunction with orientation dependent recovery.

Review of the Clinicopathologic Features of Fibrolamellar Carcinoma

Since its first description 50 years ago, fibrolamellar carcinomas (FLCs) have been recognized as a unique type of primary liver cancer. FLCs occur principally in children and young adults and are not associated with chronic liver disease. Their etiology is unknown. The tumor is made up of large polygonal cells containing abundant eosinophilic cytoplasm, large vesiculated nuclei, and large nucleoli, with tumor cells that are embedded in lamellar bands of fibrosis. Although rare, the most common variant of FLC shows areas of glandular type differentiation with mucin production. The uniqueness of FLC extends to their molecular findings, as they show no evidence for involvement by many of the major pathways and genes that are dysregulated in typical hepatocellular carcinoma, including alpha-fetoprotein, TP53 mutations, and beta catenin mutations. FLCs are not indolent tumors, but have an overall better prognosis than hepatocellular carcinomas of the usual sort because of the younger age at presentation and lack of cirrhosis. The most important prognostic feature is resectability. Although their morphologic appearance on routine stains is well defined, their etiology is still unknown and much of their molecular biology remains poorly described and awaits future investigation.

Relation between the deformation sub-structure after rolling or tension and the recrystallization mechanisms of an IF steel

The characteristics of the deformation microstructure of an IF steel sample have been studied using TEM after 40% cold rolling and 35% strain in tension. Different microstructures can be distinguished: lamellar bands for the {1 1 1} 〈1 1 2〉 grains belonging to the γ fibre and equiaxed cells for the {1 1 1} 〈1 1 0〉 grains that belong to both γ and α fibres as well as the {0 0 1} 〈1 1 0〉 grains that belong exclusively to the α fibre. Whatever the initial dislocation structure, the first steps of nucleus formation are characterized by coalescence and growth of deformation cells. The first steps of recrystallization mainly take place via continuous growth of subgrains for both orientations and are followed by bulging of grain boundaries in the case of the {1 1 1} 〈1 1 0〉 subgrains. The role of the morphology and size of the subgrains as well as that of the deformation energy stored by the sub-boundaries are discussed within the framework of the nucleation processes of low carbon steels.

Identification and quantification of stress concentrations in ferroelectrics using Kikuchi pattern indexing

Transmission electron microscopy has been used to investigate the junction between two lamellar bands in a tetragonal lead zirconate titanate (PZT) ceramic. It is found that significant bending occurs in the area due to the matching of different domains on <101> planes. Analysis of CBED patterns shows that the orientation relationships between the long boundaries between lamellae is much as expected and allows quantification of local c/a ratios. The short boundaries at the band junction, however, are highly stressed and deviate significantly from ideal misorientation values. This reveals that the areas between the 4- domain junctions in the band junction are highly stressed with peak stresses in the GPa range, which are highly likely to function as the source of microcracks under the additional strains found in device application.

Grain Refinement by High Temperature Plane-Strain Compression of Fe-2%Si Steel

An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series of plane strain compression (PSC) tests with reductions of 25, 35 and 75% at temperatures varying from 800 to 1,100°C and at a constant engineering strain rate corresponding to a constant cross velocity of 20 mm/s. The initial structure of the material displayed nearly equi-axed grains with an average size of 80 μm. The as-received texture was characterised by a nearly random cube fibre (&lt;100&gt;//ND) with a relatively weak maximum on the rotated cube component ({001}&lt;110&gt;). After deformation the samples were water quenched in order to avoid post-process static recrystallization events. The microstructures were analysed by orientation imaging microscopy (OIM) revealing that the zone of PSC was restricted to the central layers of the sample but minimally covering 50% of the sample thickness. After deformation at 800°C the conventional lamellar deformation structures were observed on the sections perpendicular to the transverse direction of PSC. At higher deformation temperatures the structure was of a bimodal nature consisting of lamellar deformation bands and equi-axed small grains. The volume fraction of these small equi-axed grains increased from 19.9% after 75%reduction at 800°C to 67.8% after 75% reduction at 1.100°C. After 75% reduction the equi-axed grains exhibited an average size of 10 μm which represents a strong grain refinement with respect to the initial size of 80 μm prior to PSC. Ferrite Silicon steels undergo extensive dynamic recovery during hot working. Dynamic recrystallization (DRX), though, has not yet been reported for these alloys although the present data suggest that a DRX mechanism might be responsible for the remarkable grain refinement after relatively low amounts of strain applied at high temperatures.

Improvement of toughness and ductility of a cryomilled Al-Mg alloy via microstructural modification

The effect of annealing treatment on microstructure, fracture toughness, and tensile and compression behavior of a cryomilled Al-7.5 pct Mg alloy was investigated in the present study. Inspection of the mechanical performance reveals that there is a significant effect of annealing on fracture toughness and ductility. After annealing treatment, the value of fracture toughness increases from 8.3 to 17.5 MPa $$\sqrt m $$ , and the value of ductility increases from 4.4 to 14 pct, while the decrease of strength is slight. The improvement of ductility and toughness is attributed to the existence of lamellar coarsegrain bands that effectively blunt the crack tip and slow propagation. These bands have widths of approximately 500 nm and are parallel to the extrusion direction. They were produced in the microstructure, which has a typical grain size of approximately 260 nm as a result of the annealing at 773 K.

TEM study of recovery and recrystallization mechanisms after 40% cold rolling in an IF-Ti steel

Abstract The deformed microstructure of an IF-Ti steel has been characterized by TEM observations after 40% cold rolling. Different substructures can be distinguished: lamellar bands for the {1 1 1}〈1 1 2〉 grains belonging to the γ fibre ND∥〈1 1 1〉 and equiaxed cells for the {1 1 1}〈1 1 0〉 orientation that belong to both γ and α fibres (α fibre RD∥〈1 1 0〉). Whatever the initial dislocation structure, the first steps of nucleus formation is characterized by coalescence and growth of existing cells in the recovered matrix. Then, nucleus growth occurs by sub-boundary migration. Nucleation is mainly intragranular for the {1 1 1}〈1 1 2〉 grains and it is widely observed at the grain boundaries or at the vicinity of the grain boundaries for the {1 1 1}〈1 1 0〉 grains. Therefore, first steps of recrystallization mainly take place by continuous growth of subgrains followed quickly or not by bulging of grain boundaries.

Experimental measurement of stress at a four-domain junction in lead zirconate titanate

A junction between two lamellar bands of ferroelectric domains in a lead zirconate titanate ceramic is analyzed using Kikuchi diffraction patterns in the transmission electron microscope. Indexing of the diffraction patterns allowed the determination of the three-dimensional relative orientation of the four different domains at the junction and thus the characterization of the domain boundaries. The local c∕a ratio could also be determined from the misorientations at the domain boundaries. Analysis of the data showed that large stresses were concentrated at the junction, and that this is inevitable at such band junctions. Such stress concentrations could act as nuclei for cracking of the ceramic under additional loading in service, perhaps particularly as a consequence of extended electromechanical cycling. Moreover, the stresses would increase with increasing c∕a, making the issues all the more serious for Ti-rich compositions having larger c∕a ratios.

Recovery and Recrystallization Study after Low Deformation Amount by Cold Rolling in an IF-Ti Steel

The first steps of recovery and recrystallization in an IF-Ti steel after 40% cold rolling have been studied using the Electron Back Scattered Diffraction (EBSD), Orientation Imaging Microscopy(™) (OIM) and the Transmission Electron Microscopy (TEM). As it is well known, for low deformation amounts by cold rolling, recrystallization texture exhibits the g fiber (ND // &lt;111&gt;) with a reinforcement of the {111}&lt;110&gt; orientation. In order to understand this {111}&lt;110&gt; development during recrystallization, characterization of the deformed state was performed. Different microstructures were distinguished: lamellar bands for the {111}&lt;112&gt; grains of the g fiber and coarse elongated cells for the {111}&lt;110&gt; orientation that belongs to the a and g fibers. Whatever the initial dislocation structure, the recovery step seems to be characterized by coalescence and growth of existing cells in the recovered matrix. Then nucleus growth seems to occur by sub-boundary migration. The first steps of recrystallization mainly take place by continuous growth of subgrains including or not the bulging of grain boundaries.

Disc morphology in health and disease.

The morphology of the intervertebral disc is dependent on the type of components present and the manner in which they are assembled. This, in turn, will determine how the tissue carries out its primary physiological functions of load bearing and allowing movement in all directions of the otherwise rigid spine. The disc starts its life in an ordered fashion, with the outer annulus fibrosus consisting of a series of regular concentric bundles of collagen fibres around the central gelatinous nucleus pulposus. With advancing age there is increased complexity of lamellae, with more bifurcations, interdigitations and irregularity in number and size of lamellar bands, probably as a result of the disc cells' synthetic response to variations in incident loads. This change in organization itself will lead to altered load bearing, hence possibly establishing a self-perpetuating cycle of disruption to disc morphology, which, once started, may be irreversible. There are also alterations to cell organization with disease and degeneration. There may be increased cell number, with clusters of cells forming by cell proliferation, or increased cell death, whether by necrosis or apoptosis, in degenerate or deformed discs such as are found in spinal deformities; for example, scoliosis. Any change in cell number is likely to alter the nutritive requirements and concentration gradients of both nutrients and metabolites. The normally avascular disc in the healthy adult can become increasingly vascularized and innervated with degeneration and disease. This may lead to an increased supply of oxygen and nutrients to the disc, but can also introduce other cells types and molecules such as cytokines and growth factors.

Anisotropy in the shape memory effect in thermomechanically treated Fe-Mn-Si alloys

The experimerttal results on anisotropic shape memory in a training-treated Fe-Mn-Si alloys were presented. The training for improving the shape memory provides a large number of stacking faults that are distributed in the y matrix. When tests are carried out parallel to the training direction, these stacking faults make the stress-induced e martensite formation easier and the resultant y/e lamellar structure bands are postulated to favor the reversible motion of Shockley partial dislocations. On the contrary, when tests are performed vertical to the training direction, the pre-existing stacking faults are of no use or are rather harmful for the formation of stress-induced e martensite.

The effect of fluoride on bone histology in postmenopausal osteoporosis depends on adequate fluoride absorption and retention.

Forty-one women with idiopathic postmenopausal osteoporosis have been followed for 2 years after initiation of sodium fluoride at 40-50 mg/day, given together with a daily calcium supplement of 1 gram and vitamin D2, at 50,000 IU weekly. Histological and histomorphometric analyses were done on bone biopsies taken prior to and after 1 year of treatment (mean 1.25 +/- 0.35 years). Thirty patients (74%) developed the histological fluoride effect of hyperosteoidosis, while the remaining 11 patients (26%) had no change from pretreatment biopsies. Hyperosteoidosis was based on increased values for osteoid volume and/or thickened osteoid with greater than 3 lamellar bands. Based on previously reported findings, this histological evidence of hypersoteoidosis within 12-18 months of initiation of therapy provides a useful predictor of ultimate satisfactory fluoride response in terms of bone mineral accretion. No increases in bone mass (measured by neutron activation analysis) were observed at the time of the posttreatment biopsy but, according to this previous work, increases are anticipated over a further 2-3 years of treatment. Factors affecting the development of hyperosteoidosis were analyzed. Hyperosteoidosis was associated with a significantly higher dose of sodium fluoride and a significantly higher level of bone fluoride retention but without significant increase in fasting serum fluoride. Results suggest that fluoride retention depends not only on fluoride dose but also on body size, renal function, and intestinal absorptions of calcium and fluoride. There were no differences in the initial investigations between patients with and without hyperosteoidosis, with respect to age, years of postmenopause, estrogen use, initial biochemistry, or initial bone histology.(ABSTRACT TRUNCATED AT 250 WORDS)

MELTING BEHAVIOR OF COMPRESSED MATS OF POLYETHYLENE SINGLE-CRYSTALS

Structural change of Polyethylene single crystal mats by hot pressing was investigated by means of x-ray diffraction and differential scanning calorimetry. X-ray data showed that the deformation of the mat proceeded through the following stages. For a specimen pressed with lower compression ratios (C. R.) 1-5.3, the intra-lamellar slip or the chain tilting developed resulting in a decrease of the lamellar thickness. With higher C. R. 5.3-11.7, locally concentated slips occurred in the mat and blocks of lamellar fragments rotated so as to decrease the angle between the chain axis and the direction of the deformation.In melting experiments, (1) a remarkable increase of the melting points occurred at higher compression stages (C. R.>5.3), (2) both of minimum half width of melting peak and minimum heat of fusion appeared at intermediate stages (C. R.=3.0_??_5.3), and (3) superheating effects became obvious at higher compression stages (C. R.>5.3).These results suggested that the structural and melting behaviors of compressed mats differed from that of drawn mats. The discussion was made on the assumption that a small number of tiechains in compressed mats mainly existed in the lamellar slip bands.

Fracture surface morphology of some crystalline block copolymers—propylene/ethylene and tetramethyl-p-silphenylenesiloxane dimethylsiloxane

The fracture surface morphology of block copolymers of (i) tetramethyl-p-silphenylenesiloxane/dimethylsiloxane (TMPS/DMS) and (ii) propylene/ethylene (P/E) has been studied. The TMPS/DMS samples had compositions ranging from 90/10 to 30/70 wt% ratios. The ethylene content in the P/E samples ranged from 8 to 13%. A few polyolefin blends were also examined. Materials were fractured at liquid-nitrogen temperatures and studied under ambient conditions by scanning and transmission electron microscopy. X-ray methods and differential scanning calorimetry (DSC) techniques were also used. Copolymers with higher TMPS compositions exhibited a lamellar texture, but at high DMS contents fracture appeared ``glassy''. All TMPS/DMS samples exhibited spherulitic structures. Spherulites were mainly banded and were negatively birefringent. In samples with higher TMPS content, fracture occurred predominately between lamellar bands. The DMS component rejected by the crystalline TMPS hard segments is largely responsible for the observed fracture behavior and for the tensile properties of these copolymers particularly where this phase predominates. In the P/E copolymers both large and small globular particles are observed. Ethylene and propylene form separate crystalline phases. The interfacial characteristics between the large aggregates and the polypropylene matrix are believed to be responsible for impeding fracture porpagation in these materials, as assessed by impact tests. The influence of annealing conditions on the observed morphology has been investigated.

OBSERVATIONS ON THE FINE STRUCTURE OF DICTYOCHA FIBULA EHRENBERG. II. THE PROTOPLAST1

SUMMARY Dictyocha fibula in exponential phase cultures displays a range of morphological variants of which the “sunburst” is most common. In this form, the perinuclear cytoplasm (perikaryon) contains an average of 72 dictyosomes, assorted vesicles, mitochondria, endoplasmic reticulum, and ribosomes. Cytoplasmic processes, globose to irregular, extend on fine cytoplasmic strands from the perikaryon into an extensive, viscous wall, structureless in electron micrographs except for scattered electron‐opaque leaflets near the perikaryon. Mitochondria with tubular cristae occur within the globose process and occasionally within the connecting strands. Chloroplasts, with 3‐disk lamellar bands and with pyrenoids not crossed by lamellae, are confined to the cytoplasmic processes in the sunburst from. A structure which may be the “flagellum” occasionally occurs attached to the perikaryon. However, no flagellar structures containing microtubules, nor flagellar root structures, have been found.

Notch toughness and fracture characteristics of structural Al-Zn-Mg alloy welds

In this paper, there are investigated the notch toughness and fracture characteristics of Al-4%Zn-2%Mg alloy welds made with filler metals of Al-5%Mg, Al-4%Mg-2%Zn and Al-4%Zn-2%Mg alloys.The notch toughness was evaluated by the ratio of tensile strengths between notched and unnotched specimens and the Charpy impact values.The decreasing order of notch toughness of base metals by tensile tests was as follows, according to treatments of specimens :T6>T7>T4. Whereas, the reverse tendency was observed in Charpy impact tests. In any case, however, notch toughness was decreased, and notch sensitivity was increased with the drop of testing temperature.The decreasing order of notch toughness of welds by both of tensile and Charpy impact tests was as follows, according to filler metals: Al-5%Mg>Al-4%Mg-2%Zn>Al-4%Zn-2%Mg. However, the toughness was also decreased with the ageing after welding. The above tendencies were more remarkable in Charpy impact tests than in tensile tests. The Charpy impact values of welds were hyperbolically decreased with the increase of hardness, and they tended to approach approximately constant values in the lower limit.Uniform granular ruggedness was observed in the fracture of welds with excellent notch toughness, but lamellar bands peculiar to weld metals were likely to appear in that with poor notch toughness. By electron fractography, the former showed dimple patterns associated with ductile rupture and the latter showed cleavage patterns associated with brittle rupture.The notch toughness of welds was considerably improved by decreasing the heat input per one pass and increasing the number of passes. The reason of the above behavior would be due to the refining of dendrite cells and distribution of eutectic compounds following the mass transport theory, and the dissolution of the compounds into the matrix by the subsequent weld heat cycles.It was considered that the notch toughness and fracture characteristics of welds macroscopically depended upon the mutual relation between strength and ductility. However, they would also microscopically depend upon the state of precipitates and distribution of dendrite cells and eutectic compounds.