Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite $\Rightarrow$ martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe₇Pd₃ ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the facecentered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ionirradiation-induced austenite⇒martensite and inter-martensite transitions, explore the multivariant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiationinduced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite⇔martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys

Structural defects in Fe-Pd-based ferromagnetic shape memory alloys: Tuning transformation properties by ion irradiation and severe plastic deformation

Fe-Pd-based ferromagnetic shape memory alloys constitute an exciting class of magnetically switchable smart materials that reveal excellent mechanical properties and biocompatibility. However, their application is severely hampered by a lack of understanding of the physics at the atomic scale. A many-body potential is presented that matched ab inito calculations and can account for the energetics of martensite ↔ austenite transition along the Bain path and relative phase stabilities in the ordered and disordered phases of Fe-Pd. Employed in massively parallel classical molecular dynamics simulations, the impact of order/disorder, point defects and severe plastic deformation in the presence of single- and polycrystalline microstructures are explored as a function of temperature. The model predictions are in agreement with experiments on phase changes induced by ion irradiation, cold rolling and hammering, which are also presented

Creep and stress relaxation of a FeMnSi-based shape memory alloy at low temperatures

The creep and stress relaxation behavior of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (wt%) shape memory alloy at low homologous temperatures (-45 degrees C < T < 50 degrees C) was systematically studied in stress and strain controlled tensile tests. At constant stresses at -45 degrees C, the alloy exhibits pronounced creep up to 0.6% at 600 MPa after only 30 min holding time. If the strain is kept constant, a pronounced stress relaxation of up to 10% of the initial stress was observed. The final creep strains, the creep rates at a constant stress as well as the stress relaxation at a constant strain increase with decreasing temperature. In addition, the change of the recovery stress as a function of time in a restrained sample after 4% elongation and heating to different constant temperatures was monitored. It was observed that the increase of the final recovery stress is more pronounced when the holding temperature is increased. This behavior was explained with the time and temperature dependent formation of stress induced epsilon-martensite from the parent gamma-austenite phase during mechanical loading according to the model of Kajiwara et al. as well as with the increased number of stacking faults at lower temperatures, which serve as nucleation sites for the epsilon-martensite formation. (C) 2016 Elsevier B.V. All rights reserved

The effects of low calorie, high protein diet on body composition, duration and sleep quality on obese adults: A randomized clinical trial

Abstract Background and Aims The effects of high‐protein diets on regulating sleep have received research attention in recent decades. However, no studies have examined the effects of these diets in obese adults. Therefore, this study was conducted to investigate the effects of low‐calorie high protein diets on sleep quality in obese adults. Methods This study is a randomized clinical trial conducted on 60 obese adults (BMI > 29.9 kg/m2) diagnosed with low‐quality sleep. All participants were given a diet with a 750‐calorie energy deficit. While the control group was given a normal diet, the intervention group received a diet with 30% more protein. Results The results showed a significant difference between the control group and intervention group with respect to sleep apnea at 30‐, 60‐, and 90‐day follow‐up (p < 0.01). Sleep quality, apnea‐hypopnea index (AHI), sleep latency (SL), and polysomnography were significantly different between the two groups (p < 0.05), showing an improvement in sleep quality and obstructive sleep apnea in the intervention group (p < 0.05). Conclusion This study shows that low‐calorie high‐protein diets can effectively improve apnea, sleep quality, and body composition indices in obese adults

Characterization of the deformation and phase transformation behavior of VC-free and VC-containing FeMnSi-based shape memory alloys by in situ neutron diffraction

The stress-induced fcc-austenite to hcp-martensite transformation in the iron based shape memory alloy (SMA) Fe-17Mn-5Si-10Cr-4Ni with and without VC precipitates is investigated by in-situ neutron diffraction measurements upon uniaxial loading and unloading. Based on experimentally derived elastic moduli the critical resolved shear stress (CRSS) for the fcc to hcp phase transformation was calculated. VC precipitates promote the martensite transformation by shifting the CRSS from 152 MPa to 85 MPa. A nearly perfect plastic behavior is found for the (220) grains with a high Schmid factor of 0.47. While (220), (111) and (200) oriented grains exhibit a phase transformation, (311) grains plastically deform solely by slip. During plastic deformation a load redistribution from soft behaving (220) grains to hard behaving (200) orientated grains takes place. The presence of VC precipitates leads to a broadening of the stress interval at which a martensite transformation is induced. This is explained by spatially heterogeneously distributed martensite transformation temperatures which are caused by VC precipitates. The microstructural reason for pseudo-elasticity is found to be a combination of back transformation from hcp to fcc and a reversible motion of Shockley partial dislocations

Fatigue crack propagation behavior of a micro-bainitic TRIP steel

Controlling the grain size of steels is an effective way for tailoring their mechanical properties, such as yield strength, impact toughness, and ductility. In this study, a new industrial thermomechanical treatment was applied to a low-alloyed TRIP-assisted bainitic steel 13MnSiCr7 to achieve a substantial microstructural refinement. In this way the average grain size of the new micro-bainitic steel was decreased from ∼25 μm to ∼5 $μ$m. Fatigue tests were carried out in order to investigate the influence of this new thermomechanical treatment on crack propagation behavior. Besides electron backscatter diffraction (EBSD), vibrating sample magnetometry (VSM), and high-energy synchrotron X-ray diffraction (HEXRD) were used to study the microstructure in the vicinity of the fatigue crack tip. The applicability of each method for detecting the martensitic transformation is discussed. In addition, the contribution of the martensitic transformation to fracture toughness was assessed on the basis of the results obtained by HEXRD