The Experts below are selected from a list of 17079 Experts worldwide ranked by ideXlab platform

J D Embury - One of the best experts on this subject based on the ideXlab platform.

  • the strain induced Martensite Transformation in austenitic stainless steels part 1 influence of temperature and strain history
    Materials Science and Technology, 2009
    Co-Authors: K Spencer, M Veron, K Yuzhang, J D Embury
    Abstract:

    The strain induced Martensite Transformation in austenitic stainless steels is of considerable interest, because it results in materials with attractive combinations of strength and ductility. The present work examines the mechanical response for a variety of strain and temperature paths, and relates these to microstructural observations. New evidence of the detailed Transformation sequence is presented, along with direct evidence of codeformation of the austenite and Martensite. Using different deformation temperature sequences enables the Transformation to be changed from one that is heterogeneous to one that propagates axially along the sample. The strain hardening that occurs due to combined plasticity and martensitic Transformation results in high kinematic hardening that is revealed by microstructural observations here, and which are linked directly to the mechanical response of these materials described in Part II of the present work.

  • the strain induced Martensite Transformation in austenitic stainless steels part 2 effect of internal stresses on mechanical response
    Materials Science and Technology, 2009
    Co-Authors: K Spencer, J D Embury, K T Conlon, Y Brechet
    Abstract:

    In Part 1 of the present study attention was given to the influence of the deformation temperature on the structural aspects of the strain induced Martensite Transformation in austenitic stainless steels. In this part the mechanical response is examined, both during and after the Martensite Transformation, with particular attention to the development of internal stress. The influence of internal stresses on the bulk mechanical response concerns both the nature of the elastoplastic transition and the extent of kinematic hardening. The approach taken to assess the development of internal stresses is to use strain reversal (Bauschinger) tests and tensile experiments performed on a neutron diffractometer. In this way the evolution of stresses in partially transformed samples can be measured in the absence of any further Martensite Transformation.

Junichi Sakai - One of the best experts on this subject based on the ideXlab platform.

  • hydrogen embrittlement behavior induced by dynamic Martensite Transformation of ni ti superelastic alloy
    Acta Materialia, 2009
    Co-Authors: Kenichi Yokoyama, Miho Tomita, Junichi Sakai
    Abstract:

    Abstract The hydrogen embrittlement behavior induced by the Martensite Transformation of Ni–Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the Martensite Transformation steeply decreases with increasing number of deformation cycles, whereas the critical stress for the reverse Transformation only slightly changes. The dynamic stress-induced Martensite Transformation markedly enhances hydrogen absorption, compared with that of the Martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm; nevertheless, no fracture associated with the stress-induced Martensite Transformation occurs. In addition, no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally desorbed at a low temperature markedly increases, indicating that the hydrogen states are changed by the dynamic Martensite Transformation. Note that interactions between hydrogen and the phase Transformation are probably irreversible, although the phase Transformation is reversible. The present study shows, for the first time, that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the Martensite Transformation.

  • hydrogen embrittlement of ni ti superelastic alloy aged at room temperature after hydrogen charging
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: Kenichi Yokoyama, Kenzo Asaoka, Toshio Ogawa, Katsutoshi Takashima, Junichi Sakai
    Abstract:

    Abstract The hydrogen embrittlement of a Ni–Ti superelastic alloy aged at room temperature (25 °C) in air after hydrogen charging is examined using tensile test and hydrogen thermal desorption analysis (TDA). Cathodic hydrogen charging is performed at a current density of 10 A/m 2 for 6 h in 0.9% NaCl aqueous solution at room temperature. For the specimen immediately after hydrogen charging, tensile fracture occurs near the critical stress for Martensite Transformation without stress-induced Martensite Transformation. Hydrogen thermal desorption is observed from room temperature to 400 °C. Charged hydrogen exists within approximately 50 μm from the surface of the specimen. Hydride formation is confirmed by X-ray diffraction (XRD) analysis. In contrast, the specimens aged at room temperature after hydrogen charging fracture during or after stress-induced Martensite Transformation. The amount of hydrogen desorbed at low temperatures (room temperature to 200 °C) decreases. Charged hydrogen diffuses toward the center part of the specimen, and some charged hydrogen diffuses out in the early stage of aging at room temperature. In addition, no XRD peaks corresponding to hydrides are detected. The present results suggest that aging at room temperature in air after hydrogen charging changes the distribution and state of hydrogen in Ni–Ti superelastic alloy, thereby leading to a partial recovery of the tensile properties of the alloy.

  • fracture of nickel titanium superelastic alloy in sodium hypochlorite solution
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Kenichi Yokoyama, Kazuyuki Kaneko, Eiji Yabuta, Kenzo Asaoka, Junichi Sakai
    Abstract:

    Abstract Fracture of the Ni–Ti superelastic alloy for endodontic instruments such as files was investigated with a sustained tensile-loading test in sodium hypochlorite (NaOCl) solution of various concentrations. It was found that the time to fracture was reduced when the applied stress exceeded the critical stress for Martensite Transformation. When the applied stress was higher than the critical stress, the 0.3 mm diameter wires of the Ni–Ti superelastic alloy sometimes fractured within 60 min. From the results of observations of the fracture surface using a scanning electron microscope, it was revealed that the fracture of the Ni–Ti superelastic alloy is significantly influenced by corrosion when the applied stress was higher than the critical stress for Martensite Transformation. The results of the present study suggest that one of the causes of the fracture of Ni–Ti files during clinical use is corrosion under the applied stress above the critical stress for Martensite Transformation in NaOCl solution.

K Spencer - One of the best experts on this subject based on the ideXlab platform.

  • the strain induced Martensite Transformation in austenitic stainless steels part 1 influence of temperature and strain history
    Materials Science and Technology, 2009
    Co-Authors: K Spencer, M Veron, K Yuzhang, J D Embury
    Abstract:

    The strain induced Martensite Transformation in austenitic stainless steels is of considerable interest, because it results in materials with attractive combinations of strength and ductility. The present work examines the mechanical response for a variety of strain and temperature paths, and relates these to microstructural observations. New evidence of the detailed Transformation sequence is presented, along with direct evidence of codeformation of the austenite and Martensite. Using different deformation temperature sequences enables the Transformation to be changed from one that is heterogeneous to one that propagates axially along the sample. The strain hardening that occurs due to combined plasticity and martensitic Transformation results in high kinematic hardening that is revealed by microstructural observations here, and which are linked directly to the mechanical response of these materials described in Part II of the present work.

  • the strain induced Martensite Transformation in austenitic stainless steels part 2 effect of internal stresses on mechanical response
    Materials Science and Technology, 2009
    Co-Authors: K Spencer, J D Embury, K T Conlon, Y Brechet
    Abstract:

    In Part 1 of the present study attention was given to the influence of the deformation temperature on the structural aspects of the strain induced Martensite Transformation in austenitic stainless steels. In this part the mechanical response is examined, both during and after the Martensite Transformation, with particular attention to the development of internal stress. The influence of internal stresses on the bulk mechanical response concerns both the nature of the elastoplastic transition and the extent of kinematic hardening. The approach taken to assess the development of internal stresses is to use strain reversal (Bauschinger) tests and tensile experiments performed on a neutron diffractometer. In this way the evolution of stresses in partially transformed samples can be measured in the absence of any further Martensite Transformation.

Kenichi Yokoyama - One of the best experts on this subject based on the ideXlab platform.

  • marked degradation of tensile properties induced by plastic deformation after interactions between strain induced Martensite Transformation and hydrogen for type 316l stainless steel
    Metals, 2020
    Co-Authors: Keisuke Nicho, Kenichi Yokoyama
    Abstract:

    Marked degradation of tensile properties induced by plastic deformation after dynamic interactions between strain-induced Martensite Transformation and hydrogen has been investigated for type 316L stainless steel by hydrogen thermal desorption analysis. Upon modified hydrogen charging reported previously, the amount of hydrogen desorbed in the low temperature range increases; the degradation of tensile properties induced by interactions between plastic deformation and hydrogen at 25 °C or induced by interactions between Martensite Transformation and hydrogen at −196 °C occurs even for the stainless steel with high resistance to hydrogen embrittlement. The hydrogen thermal desorption behavior is changed by each interaction, suggesting changes in hydrogen states. For specimen fractured at 25 °C, the facet-like morphology and transgranular fracture are observed on the outer part of the fracture surface. At −196 °C, a quasi-cleave fracture is observed at the initiation area. Modified hydrogen charging significantly interacts both plastic deformation and Martensite Transformation, eventually enhancing the degradation of tensile properties. Upon plastic deformation at 25° C after the interactions between Martensite Transformation and hydrogen by straining to 0.2 at −196 °C, cracks nucleate in association with Martensite formed by the interactions at −196 °C and marked degradation of tensile properties occurs. It is likely that the interactions between Martensite Transformation and hydrogen induce damage directly related to the degradation, thereby affecting subsequent deformation. Upon dehydrogenation after the interactions between the Martensite Transformation and hydrogen, no degradation of tensile properties is observed. The damage induced by the interactions between Martensite Transformation and hydrogen probably changes to harmless defects during dehydrogenation.

  • hydrogen embrittlement behavior induced by dynamic Martensite Transformation of ni ti superelastic alloy
    Acta Materialia, 2009
    Co-Authors: Kenichi Yokoyama, Miho Tomita, Junichi Sakai
    Abstract:

    Abstract The hydrogen embrittlement behavior induced by the Martensite Transformation of Ni–Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the Martensite Transformation steeply decreases with increasing number of deformation cycles, whereas the critical stress for the reverse Transformation only slightly changes. The dynamic stress-induced Martensite Transformation markedly enhances hydrogen absorption, compared with that of the Martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm; nevertheless, no fracture associated with the stress-induced Martensite Transformation occurs. In addition, no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally desorbed at a low temperature markedly increases, indicating that the hydrogen states are changed by the dynamic Martensite Transformation. Note that interactions between hydrogen and the phase Transformation are probably irreversible, although the phase Transformation is reversible. The present study shows, for the first time, that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the Martensite Transformation.

  • hydrogen embrittlement of ni ti superelastic alloy aged at room temperature after hydrogen charging
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: Kenichi Yokoyama, Kenzo Asaoka, Toshio Ogawa, Katsutoshi Takashima, Junichi Sakai
    Abstract:

    Abstract The hydrogen embrittlement of a Ni–Ti superelastic alloy aged at room temperature (25 °C) in air after hydrogen charging is examined using tensile test and hydrogen thermal desorption analysis (TDA). Cathodic hydrogen charging is performed at a current density of 10 A/m 2 for 6 h in 0.9% NaCl aqueous solution at room temperature. For the specimen immediately after hydrogen charging, tensile fracture occurs near the critical stress for Martensite Transformation without stress-induced Martensite Transformation. Hydrogen thermal desorption is observed from room temperature to 400 °C. Charged hydrogen exists within approximately 50 μm from the surface of the specimen. Hydride formation is confirmed by X-ray diffraction (XRD) analysis. In contrast, the specimens aged at room temperature after hydrogen charging fracture during or after stress-induced Martensite Transformation. The amount of hydrogen desorbed at low temperatures (room temperature to 200 °C) decreases. Charged hydrogen diffuses toward the center part of the specimen, and some charged hydrogen diffuses out in the early stage of aging at room temperature. In addition, no XRD peaks corresponding to hydrides are detected. The present results suggest that aging at room temperature in air after hydrogen charging changes the distribution and state of hydrogen in Ni–Ti superelastic alloy, thereby leading to a partial recovery of the tensile properties of the alloy.

  • fracture of nickel titanium superelastic alloy in sodium hypochlorite solution
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2004
    Co-Authors: Kenichi Yokoyama, Kazuyuki Kaneko, Eiji Yabuta, Kenzo Asaoka, Junichi Sakai
    Abstract:

    Abstract Fracture of the Ni–Ti superelastic alloy for endodontic instruments such as files was investigated with a sustained tensile-loading test in sodium hypochlorite (NaOCl) solution of various concentrations. It was found that the time to fracture was reduced when the applied stress exceeded the critical stress for Martensite Transformation. When the applied stress was higher than the critical stress, the 0.3 mm diameter wires of the Ni–Ti superelastic alloy sometimes fractured within 60 min. From the results of observations of the fracture surface using a scanning electron microscope, it was revealed that the fracture of the Ni–Ti superelastic alloy is significantly influenced by corrosion when the applied stress was higher than the critical stress for Martensite Transformation. The results of the present study suggest that one of the causes of the fracture of Ni–Ti files during clinical use is corrosion under the applied stress above the critical stress for Martensite Transformation in NaOCl solution.

Lin Geng - One of the best experts on this subject based on the ideXlab platform.

  • effect of si doping on microstructure and Martensite Transformation in ni mn sb ferromagnetic shape memory alloys
    Intermetallics, 2018
    Co-Authors: Ruochen Zhang, Mingfang Qian, Xuexi Zhang, Jianfei Sun, Lin Geng
    Abstract:

    Abstract We have recently reported that the quaternary Ni49.0Mn38.4Sb11.7Si0.9 alloy showed enhanced refrigeration capacity due to the wide working temperature interval and narrow magnetic hysteresis loss via Si-doping. Here we systematically investigate the microstructure, Martensite Transformation and magnetic transition behaviors of Ni50Mn38Sb12-xSix (x = 0, 1, 2, 3) alloys. Ni50Mn38Sb12-xSix (x = 0, 1, 2) alloys exhibited a full solid-solution state with a four-layer modulated orthorhombic (4O) Martensite structure. However, three phases formed in Ni50Mn38Sb9Si3 alloy, and lath-like Martensite twins existed only in α phase at room temperature. The Martensite Transformation temperature decreased with the increasing Si content when the Si atomic content increased from 0% to 2%, but significantly increased when Si content reached to 3% because of the increase of the valence electron concentration (e/a) of matrix phase (α phase). The martensitic Transformation also occurred in the β phase below room temperature in Ni50Mn38Sb9Si3 alloy. Furthermore, the Martensite Transformation temperature range enlarged and the thermal hysteresis narrowed with the addition of Si atomic content from 0% to 2%, of which Ni50Mn38Sb10Si2 alloy had the widest Martensite Transformation temperature range and narrowest thermal hysteresis, which was supposed to have great magnetocaloric effect (MCE). However, when x = 3, the thermal hysteresis increased significantly and the transition character changed to a second-order phase transition above room temperature; a magneto-structural coupling of the first-order martensitic Transformation and second-order magnetic transition also existed below room temperature, which all would result in low MCE.

  • magnetocaloric effect with low magnetic hysteresis loss in ferromagnetic ni mn sb si alloys
    Journal of Magnetism and Magnetic Materials, 2017
    Co-Authors: Ruochen Zhang, Mingfang Qian, Xuexi Zhang, F X Qin, Longsha Wei, Dawei Xing, Xiping Cui, Jianfei Sun, Lin Geng, Huaxin Peng
    Abstract:

    Abstract Giant magnetocaloric effect in Ni-Mn-X (X=In, Sn, Sb) Heusler alloys has been revealed due to the significant shift of the Martensite Transformation temperatures under a bias magnetic field. However, the magnetic hysteresis during the magnetization and demagnetization cycles creates a large hysteresis loss and reduces the refrigeration capacity. Here we demonstrated that the magnetic hysteresis loss in Ni-Mn-Sb alloys was effectively reduced by Si-doping. The quaternary Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy exhibited Martensite and magnetic transitions around room temperature. Maximum magnetic entropy change Δ S m 9.4 J/kg K and working temperature interval 7.0 K were achieved attributed to the Martensite Transformation under a magnetic field of 5 T. Meanwhile, the average magnetic hysteresis loss for Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy was 2.1 J/kg, much smaller than that for Ni 49.0 Mn 38.5 Sb 12.5 alloy, 11.4 J/kg. As a result, a refrigeration capacity of 50.2 J/kg was obtained in the Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy. This result shows that Si-doped Ni-Mn-Sb alloys may act as a potential material system for magnetic refrigeration.