A comparative study of austenitic structure in NiTi and Fe based shape memory alloys after severe plastic deformation

The effect of high speed high pressure torsion (HS-HPT) was studied in NiTi and FeMnSiCr SMAs, by comparison. Severe plastic deformation was performed in austenite state for both types of alloys. The alloys subjected to HS-HPT, reduced their grain size due to microstructure fragmentation by compression and torsion. The active elements were achieved being able to support variable ranges of processing parameters like force, pressure, rotation speed and time of torsion. The evolution of microstructural refinement in the samples subjected to different deformation by HS-HPT, were studied by optical and scanning electron microscopy observation and the thermal effect was reveled using differential scanning calorimetry (DSC). (C) 2015 The Authors. Published by Elsevier Ltd.publishersversionpublishe

An experimental study on the response of equal channel angular pressed aluminium subjected to cold rolling

253-258The present paper aims to identify a sequence of bulk-deformation processes able to produce sufficient quantities of ultra fine grained volume. Samples of aluminium Al 1100 alloy (98.41% Al) are subjected to repetitive equal channel angular pressing (ECAP) at room temperature, repeated up to eight passes. Severely plastic deformed specimens are cold rolled in thin strips which are subjected to structural characterization, calorimetric evaluation and mechanical testing with the aim of monitoring microstructural evolution. The X-ray diffraction studies and differential scanning calorimetry tests reveal the influence of cold rolling on ECAP’d samples, while tensile testing reveal marked strength increases with the number of rolling passes. Finally, an alternative technology is introduced which is easy to implement in metallurgical industry in order to provide large amounts of nanostructured strips

Study of the tensile constrained recovery behavior of a Fe-Mn-Si shape memory alloy

Free- and constrained recovery behaviors of a Fe-23.3 Mn-2.8 Si (wt.%) Shape Memory Alloy (SMA) were revealed by uncoiling experiments and tensile tests, respectively. With the enhancement of plastic deformation degree, including by additionally elongating the hot rolled specimens, the increase of the amount of ε stress induced martensite (SIM) plates in the detriment if γ austenite, was emphasized by means of optical microscopy and XRD. The tensile-stress variation was analyzed during complex cycling by constrained recovery of the alloy under study, with a tensile strength of 670 MPa and an ultimate strain of 8%. The cycles were composed of: (i) room temperature (RT) loading; (ii) RT partial unloading; (iii) constant strain heating and (iv) constant strain cooling to RT. During the cycles, characterized by average maximum stresses above 500 MPa and recovery stresses above 260 MPa, the observed stress-temperature evolution confirmed the four stage stress variation reported in literature [Z.Z. Dong et al., Acta Mater. 53, 4009 (2005)]. In order to maintain the above stress levels, constrained-recovery strain had to be increased with an average of 1.1% per cycle, between 1 and 3%

Latest Trends in Retinopathy of Prematurity: Research on Risk Factors, Diagnostic Methods and Therapies

Laura Bujoreanu Bezman,1,2 Carmen Tiutiuca,1,3 Geanina Totolici,1,3 Nicoleta Carneciu,1,2 Florin Ciprian Bujoreanu,4 Diana Andreea Ciortea,5,6 Elena Niculet,2,4 Ana Fulga,3,4 Anamaria Madalina Alexandru,4,7 Daniela Jicman Stan,4 Aurel Nechita5,6 1Department of Ophthalmology, “Sfantul Apostol Andrei” Emergency Clinical Hospital, Galati, Romania; 2Department of Morphological and Functional Sciences, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, Romania; 3Clinical Surgical Department, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, Romania; 4Doctoral School of Biomedical Sciences, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, Romania; 5Department of Pediatrics, “Sfantul Ioan” Emergency Clinical Hospital for Children, Galati, Romania; 6Clinical Medical Department, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, Romania; 7Department of Neonatology, “Sfantul Apostol Andrei” Emergency Clinical Hospital, Galati, RomaniaCorrespondence: Carmen Tiutiuca, Clinical Surgical Department, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, 800008, Romania, Tel +40741330788, Email [email protected] Florin Ciprian Bujoreanu, Doctoral School of Biomedical Sciences, Faculty of Medicine and Pharmacy, “Dunărea de Jos” University, Galati, 800008, Romania, Tel +40741395844, Email [email protected]: Retinopathy of prematurity (ROP) is a vasoproliferative disorder with an imminent risk of blindness, in cases where early diagnosis and treatment are not performed. The doctors’ constant motivation to give these fragile beings a chance at life with optimal visual acuity has never stopped, since Terry first described this condition. Thus, throughout time, several specific advancements have been made in the management of ROP. Apart from the most known risk factors, this narrative review brings to light the latest research about new potential risk factors, such as: proteinuria, insulin-like growth factor 1 (IGF-1) and blood transfusions. Digital imaging has revolutionized the management of retinal pathologies, and it is more and more used in identifying and staging ROP, particularly in the disadvantaged regions by the means of telescreening. Moreover, optical coherence tomography (OCT) and automated diagnostic tools based on deep learning offer new perspectives on the ROP diagnosis. The new therapeutical trend based on the use of anti-VEGF agents is increasingly used in the treatment of ROP patients, and recent research sustains the theory according to which these agents do not interfere with the neurodevelopment of premature babies.Keywords: retinopathy of prematurity, risk factors, optical coherence tomography, telescreening, artificial intelligence, anti-VEG

Comparative study of the structures of Fe-Mn-Si-Cr-Ni shape memory alloys obtained by classical and by powder metallurgy, respectively

Hot rolled specimens of low-manganese Fe-Mn-Si-Cr-Ni shape memory alloys, produced by classical and by powder metallurgy (CM and PM) with mechanical alloying, respectively, were analysed by tensile loadingunloading tests (TENS), by dilatometry (DIL), by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Solution annealed specimens had two-phase structure, comprising γ-austenite and thermally induced α-martensite. The formation of γ’-stress-induced martensite during TENS was ascertained by SEM and XRD being accompanied by rounded loading portions on stress-strain curves, characteristic to transformation induced plasticity, which preceded long stress plateaus with low tilt. Even if loading behaviour changed from transformation induced plasticity, on first loading, to slip induced plasticity, during subsequent ones, the specimens maintained their pseudoelastic behaviour on each unloading. DIL responses of the elongated CM and PM specimens emphasised a thermallyinduced reversion, noticeable only during first heating, which was associated with thermally induced reversion of γstress-induced martensite

Influence of mechanically alloyed fraction and hot rolling temperature in the last pass on the structure of Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloys processed by powder metallurgy

Samples of Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloy were sintered from two powder mixtures: (i) as blended (0_MA) and (ii) equal amounts of as blended and mechanically alloyed (MA’d) powders (50_MA). In order to increase the compactness degree, different specimens were hot rolled at 1373 K and the last rolling pass was performed at four different temperatures: (i) room temperature (RT); (ii) 873 K; (iii) 1073 K and (iv) 1373 K. In order to emphasize the influence of both MA’d fraction and rolling final temperature, the eight resulting specimens were analysed by X-ray diffraction (XRD) as well as by scanning electron microscopy (SEM). XRD results allowed the qualitative and quantitative identification of the three component phases, namely γ (face centred cubic, fcc)-parent phase, ε-(hexagonal close packed, hcp) martensite and α’- (body centred tetragonal, bct) martensite. SEM micrographs enabled to observe the influence of MA’d fraction on the relative amounts of the three phases. The results suggest that the presence of MA’d fraction contributes to destabilization of α’(bct) martensite and increase of the amount of ε(hcp) martensite, with favourable effects on shape memory behaviour.status: publishe

Particularities of phase transitions in thermomechanically processed Cu-Al-Mn shape memory alloys

The thermally and stress induced phase transitions occurring in a Cu-Al-Mn Shape Memory Alloy (SMA) have been investigated by means of thermal analysis techniques, tensile testing and microscopic observations. On heating a hot rolled solution annealed Cu-Al-Mn SMA, up to 873 K, two phase transformations, related to equilibrium phase precipitation and to 2-step order-disorder transition, respectively, were revealed by Differential Scanning Calorimetry (DSC). During tensile testing, the Cu-Al-Mn SMA under study experienced almost complete superelasticity, after five mechanical training cycles, as well as good ductility and tensile resistance. On trained specimens the formation of stress induced martensite was revealed by optical microscopy (OM) observations. The reversion to austenite of stress induced martensite was accompanied by relatively large increases of elastic modulus and internal friction, determined on Dynamic Mechanical Analyzer (DMA) and by marked variations of relative elongation, thermal expansion coefficient and elongation rate, determined by dilatometry. Since it is a two step transition, it was associated with the two morphologies of stress induced martensite observed by Scanning Electron Microscopy (SEM)

Structural changes caused by high-temperature holding of powder shape memory alloy 66% Fe - 14% Mn - 6% Si - 9% Cr - 5% Ni

Shape memory alloy Fe – 14Mn – 6Si – 9Cr – 5Ni (wt.%) obtained by cold pressing and sintering of a mixture of powder elements or of mechanically alloyed powder is studied. To compact the alloy additionally the specimens are subjected to hot rolling. Solution treatment of different duration (0.6 – 4.8 ksec) at 1473 K in low vacuum, nitrogen or argon is performed. The structure of the alloy after such treatments is studied by the methods of x-ray diffraction and optical and scanning electron microscopy.status: publishe