The Experts below are selected from a list of 2532 Experts worldwide ranked by ideXlab platform

Markus Haapasalo - One of the best experts on this subject based on the ideXlab platform.

  • metallurgical characterization of controlled memory Wire nickel titanium rotary instruments
    Journal of Endodontics, 2011
    Co-Authors: Ya Shen, Huimin Zhou, Yufeng Zheng, Les Campbell, Bin Peng, Markus Haapasalo
    Abstract:

    Introduction: To improve the fracture resistance of nickel-titanium (Niti) files, manufacturers have intro- duced new alloys and developed new manufacturing processes for the fabrication of Niti files. This study aimed to examine the phase transformation behavior and microstructure of Niti instruments from a novel controlled memory Niti Wire (CM Wire). Methods: Instruments of EndoSequence (ES), ProFile (PF), ProFile Vortex (Vortex), Twisted Files (TF), Typhoon (TYP), and TyphoonCM (TYP CM), all size 25/.04, were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Microstructures of etched instruments were observed by optical microscopy and scanning elec- tron microscopy with x-ray energy-dispersive spectro- metric (EDS) analyses. Results: The DSC analyses showed that each segment of the TYP CM and Vortex instruments hadanaustenitetransformation completion or austenite-finish (Af) temperature exceeding 37C, whereas the Niti instruments made from conventional superelastic Niti Wire (ES, PF, and TYP) and TF had Af temperatures substantially below mouth temperature. The higher Af temperature of TYP CM instruments was consistent with a mixture of austenite and martensite structure, which was observed at room temperature with XRD. All Niti instruments had room temperature martensite microstructures consisting of colonies of lenticular features with substantial twinning. EDS anal- ysisindicated thatthe precipitates inallNiti instruments were titanium-rich, with an approximate composition of Ti2Ni. Conclusions: The TYP CM and Vortex instru- ments with heat treatment contribute to increase austenite transformation temperature. The CM instru- ment has significant changes in the phase transforma- tion behavior, compared with conventional superelastic Niti instruments. (J Endod 2011;37:1566- 1571)

  • fatigue testing of controlled memory Wire nickel titanium rotary instruments
    Journal of Endodontics, 2011
    Co-Authors: Ya Shen, Wei Qian, Houman Abtin, Markus Haapasalo
    Abstract:

    Introduction: To improve the fracture resistance of nickel-titanium (Niti) files, manufacturers have introduced new alloys to manufacture Niti files and developed new manufacturing processes. This study was aimed to examine the fatigue behavior of Niti instruments from a novel controlled memory Niti Wire (CM Wire). Methods: Instruments of ProFile, Typhoon (TYP), Typhoon CM (TYP CM), DS-SS0250425NEYY (NEYY), and DS-SS0250425NEYY CM (NEYY CM) (DS Dental, Johnson City, TN) all size 25/.04 were subjected to rotational bending at the curvature of 35 and 45 in air at the temperature of 23 2C, and the number of revolutions to fracture (Nf) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. The crack-iNitiation sites, the percentage of dimple area to the whole fracture crosssection, and the surface strain amplitude (ea) were noted. Results: The new alloy yielded an improvement of over three to eight times in Nf of CM files than that of conventional Nitifiles(P<.05). ThevastmajorityofCM instruments (50%-92%) showed multiple crack origins, whereas most instruments made from conventional Niti Wire (58%-100%) had one crack origin. The values of the fraction area occupied by the dimple region were significantly smaller on CM Niti instruments compared withconventionalNitiinstruments(P<.01).Thesquare (NEYY CM) versus the triangular (TYP CM) configuration showed a significantly different lifetime on CM Wire at both curvatures (P < .01). Conclusions: The material property had a substantial impact on fatigue lifetime. Instruments made from CM Wire had a significantly higher Nf and lower surface strain amplitude than the conventional Niti Wire files with identical design. (J Endod 2011;37:997‐1001)

Petr Šittner - One of the best experts on this subject based on the ideXlab platform.

  • Environmental fatigue of superelastic Niti Wire with two surface finishes
    Journal of the mechanical behavior of biomedical materials, 2020
    Co-Authors: Jan Racek, Petr Šittner
    Abstract:

    Abstract Surface finish of Niti is widely perceived to affect its biocompatibility and corrosion fatigue performance. The aim of this work was to find out, whether a carefully engineered surface oxide shows any beneficial effect over electropolished surface on the fatigue performance of superelastic Niti Wire mechanically cycled in simulated biofluid. Series of corrosion and environmental fatigue tensile tests was performed on superelastic Niti Wire with two different surface finishes frequently used in medical device industry. Open Circuit Potential reflecting the activity of chemical reactions on the surface of the Wire cycled in electrochemical cell was continuously monitored during the fatigue tests. Microcracks at the surface of the fatigued Niti Wires were characterized by SEM and TEM. It was found that the carefully engineered 70 nm thick TiO2 oxide provides the Niti Wire with similar level of protection against the static corrosion as the less than 10 nm thin natural oxide on the electropolished Wire and that it does not have any positive effect on its performance in environmental fatigue tests, whatsoever. On the contrary, the Wire covered by the carefully engineered 70 nm thick TiO2 oxide displayed systematically poorer fatigue performance upon tensile cycling under specific critical loading conditions (strain amplitude

  • B2 ⇒ B19′ ⇒ B2^T Martensitic Transformation as a Mechanism of Plastic Deformation of Niti
    Shape Memory and Superelasticity, 2019
    Co-Authors: Petr Šittner, O. Tyc, L. Kadeřávek, Orsolya Molnárová, Petr Sedlak, L. Heller, Hanuš Seiner
    Abstract:

    Deformation of superelastic Niti Wire with tailored microstructure was investigated in tensile loading–unloading tests up to the end of the stress plateau in wide temperature range from room temperature up to 200 °C. Lattice defects left in the microstructure of deformed Wires were investigated by transmission electron microscopy. Tensile deformation is localized up to the highest test temperatures, even if practically no martensite phase exists in the Wire at the end of the stress plateau. In tensile tests at elevated temperatures around 100 °C, at which the upper plateau stress approaches the yield stress for plastic deformation of martensite, upper plateau strains become unusually long, transformation strains become unrecoverable and deformation bands containing {114} austenite twins appear in the microstructure of deformed Wires. These observations were rationalized by assuming activity of B2 ⇒ B19′ ⇒ B2^T martensitic transformation into the austenite twins representing a new mechanism of plastic deformation of Niti, additional to the dislocation slip in austenite and/or martensite. It is claimed that this transformation becomes activated in any thermomechanical load in which the oriented B19′ martensite is exposed to high stress at high temperatures, as e.g., during shape setting or actuator cycling at high applied stress.

  • SMA Constitutive Modeling Backed Up by 3D-XRD Experiments: Transformation Front in Stretched Niti Wire
    Shape Memory and Superelasticity, 2018
    Co-Authors: M. Frost, P. Sedlák, L. Heller, P. Sedmák, Petr Šittner
    Abstract:

    It has been known for a long time that martensitic phase transformation in Niti shape memory alloys loaded in tension develops inhomogeneously via formation and propagation of macroscopic deformation bands resembling well-known Lüders bands. Growing literature evidence supports the view that Niti, in fact, develops a variety of localized deformation phenomena in particular geometries and loading modes. Coupling of cutting-edge experimental methods with dedicated modeling techniques can bring new insight into such a type of behavior. In this short review of our recent study, we demonstrate this synergic approach on the investigation of the martensite band in a stretched Niti superelastic Wire, in which the advanced technique of three-dimensional X-ray diffraction was complemented by Niti-tailored constitutive model. We focus mainly on the modeling part, but the experimental background motivating and validating the chosen numerical approach is also briefly presented.

  • Laser Annealing on the Surface Treatment of Thin Super Elastic Niti Wire
    IOP Conference Series: Materials Science and Engineering, 2018
    Co-Authors: Sneha Samal, O. Tyc, Ludek Heller, J. Brajer, L Kadrevek, Petr Šittner
    Abstract:

    Here the aim of this research is annealing the surface of Niti Wire for shape memory alloy, super-elastic Wire by solid state laser beam. The laser surface treatment was carried out on the Niti Wire locally with fast, selective, surface heat treatment that enables precisely tune the localized material properties without any precipitation. Both as drawn (hard) and straight annealing Niti Wire were considered for laser annealing with input power 3 W, with precisely focusing the laser beam height 14.3 % of the Z-axis with a spot size of 1 mm. However, straight annealing Wire is more interest due to its low temperature shape setting behavior and used by companies for stent materials. The variable parameter such as speed of the laser scanning and tensile stress on the Niti Wire were optimized to observe the effect of laser response on the sample. Superelastic, straight annealed Niti Wires (d: 0.10 mm) were held prestrained at the end of the superelastic plateau (e: 5 ~6.5 %) above the superelastic region by a tensile machine ( Mitter: miniature testing rig) at room temperature (RT). Simultaneously, the hardness of the Wires along the cross-section was performed by nano-indentation (NI) method. The hardness of the Niti Wire corresponds to phase changes were correlated with NI test. The laser induced Niti Wire shows better fatigue performance with improved 6500 cycles.

  • Monitoring Tensile Fatigue of Superelastic Niti Wire in Liquids by Electrochemical Potential
    Shape Memory and Superelasticity, 2015
    Co-Authors: Jan Racek, Petr Šittner, Marc Stora, Luděk Heller, Jaromir Kopeček, Martin Petrenec
    Abstract:

    Fatigue of superelastic Niti Wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued Niti Wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO_2 oxide layer on the Niti Wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled Wire surface develops mechanochemical reactions at the Niti/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the Niti matrix, local loss of the matrix strength, crack transfer into the Niti matrix, accelerated crack growth, and ultimately to the brittle fracture of the Wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of Niti—superelasticity due to martensitic transformation and biocompatibility due to the protective TiO_2 surface oxide layer—leads to excessive fatigue damage during cyclic mechanical loading in biofluids.

Vicente Tadeu Lopes Buono - One of the best experts on this subject based on the ideXlab platform.

  • Effects of aging treatments on the fatigue resistance of superelastic Niti Wires
    Materials Science and Engineering: A, 2019
    Co-Authors: Jéssica Dornelas Silva, Suzanny Cristina Soares Martins, Natalia Isabel De Azevedo Lopes, Pedro Damas Resende, Leandro De Arruda Santos, Vicente Tadeu Lopes Buono
    Abstract:

    Abstract Thermomechanical and aging treatments can be powerful tools to improve the fatigue life of Niti Wires submitted to severe conditions of cyclic deformation. In this work, aging treatments were performed in an iNitially superelastic Niti Wire in temperatures ranging from 300oC until 600oC for 30 min. The as-received and heat-treated Wires’ microstructures were characterized by XRD, the transformation temperatures were obtained by DSC and the mechanical characterization was performed in tensile tests. The Wires were then submitted to low-cycle fatigue tests in a rotating-bending machine at a maximum strain of 4%. The heat treatments were effective on improving the fatigue resistance, especially when the R-phase was formed. The highest number of cycles to failure was obtained in the samples heat treated at 400oC and 450oC.

  • Mechanical behavior of M-Wire and conventional Niti Wire used to manufacture rotary endodontic instruments.
    Dental materials : official publication of the Academy of Dental Materials, 2013
    Co-Authors: Érika Sales Joviano Pereira, Renata O. Gomes, Rupinderpal Singh, Ove A. Peters, Agnès M F Leroy, Maria G A Bahia, Vicente Tadeu Lopes Buono
    Abstract:

    Comparison of physical and mechanical properties of one conventional and a new Niti Wire, which had received an additional thermomechanical treatment. Specimens of both conventional (Niti) and the new type of Wire, called M-Wire (MW), were subjected to tensile and three-point bending tests, Vickers microhardness measurements, and to rotating-bending fatigue tests at a strain-controlled level of 6%. Fracture surfaces were observed by scanning electron microscopy and the non-deformed microstructures by transmission electron microscopy. The thermomechanical treatment applied to produce the M-Wire apparently increased the tensile strength and Vickers microhardness of the material, but its apparent Young modulus was smaller than that of conventionally treated Niti. The three-point bending tests showed a higher flexibility for MW which also exhibited a significantly higher number of cycles to failure. M-Wire presented mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed Niti Wires. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  • Mechanical behavior of M-Wire and conventional Niti Wire used to manufacture rotary endodontic instruments.
    Dental Materials, 2013
    Co-Authors: Érika Sales Joviano Pereira, Maria Guiomar De Azevedo Bahia, Renata O. Gomes, Agnès Leroy, Rupinderpal Singh, Ove A. Peters, Vicente Tadeu Lopes Buono
    Abstract:

    Abstract Objective Comparison of physical and mechanical properties of one conventional and a new Niti Wire, which had received an additional thermomechanical treatment. Methods Specimens of both conventional (Niti) and the new type of Wire, called M-Wire (MW), were subjected to tensile and three-point bending tests, Vickers microhardness measurements, and to rotating-bending fatigue tests at a strain-controlled level of 6%. Fracture surfaces were observed by scanning electron microscopy and the non-deformed microstructures by transmission electron microscopy. Results The thermomechanical treatment applied to produce the M-Wire apparently increased the tensile strength and Vickers microhardness of the material, but its apparent Young modulus was smaller than that of conventionally treated Niti. The three-point bending tests showed a higher flexibility for MW which also exhibited a significantly higher number of cycles to failure. Significance M-Wire presented mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed Niti Wires.

  • Physical and mechanical properties of a thermomechanically treated Niti Wire used in the manufacture of rotary endodontic instruments
    International endodontic journal, 2011
    Co-Authors: Érika Sales Joviano Pereira, Isabella Faria Da Cunha Peixoto, Ana Cecília Diniz Viana, I. I. Oliveira, Berenice Mendonça Gonzalez, Vicente Tadeu Lopes Buono, Maria Guiomar De Azevedo Bahia
    Abstract:

    Pereira ESJ, Peixoto IFC, Viana ACD, Oliveira II, Gonzalez BM, Buono VTL, Bahia MGA. Physical and mechanical properties of a thermomechanically treated Niti Wire used in the manufacture of rotary endodontic instruments. International Endodontic Journal, 45, 469–474, 2012. Abstract Aim  To compare physical and mechanical properties of one conventional and one thermomechanically treated nickel–titanium (Niti) Wire used to manufacture rotary endodontic instruments. Methodology  Two Niti Wires 1.0 mm in diameter were characterized; one of them, C-Wire (CW), was processed in the conventional manner, and the other, termed M-Wire (MW), received an additional heat treatment according to the manufacturer. Chemical composition was determined by energy-dispersive X-ray spectroscopy, phase constitution by XRD and the transformation temperatures by DSC. Tensile loading/unloading tests and Vickers microhardness measurements were performed to assess the mechanical behaviour. Data were analysed using analysis of variance (α = 0.05). Results  The two Wires showed approximately the same chemical composition, close to the 1 : 1 atomic ratio, and the β-phase was the predominant phase present. B19′ martensite and the R-phase were found in MW, in agreement with the higher transformation temperatures found in this Wire compared with CW, whose transformation temperatures were below room temperature. Average Vickers microhardness values were similar for MW and CW (P = 0.91). The stress at the transformation plateau in the tensile load–unload curves was lower and more uniform in the M-Wire, which also showed the smallest stress hysteresis and apparent elastic modulus. Conclusions  The M-Wire had physical and mechanical properties that can render endodontic instruments more flexible and fatigue resistant than those made with conventionally processed Niti Wires.

Ya Shen - One of the best experts on this subject based on the ideXlab platform.

  • metallurgical characterization of controlled memory Wire nickel titanium rotary instruments
    Journal of Endodontics, 2011
    Co-Authors: Ya Shen, Huimin Zhou, Yufeng Zheng, Les Campbell, Bin Peng, Markus Haapasalo
    Abstract:

    Introduction: To improve the fracture resistance of nickel-titanium (Niti) files, manufacturers have intro- duced new alloys and developed new manufacturing processes for the fabrication of Niti files. This study aimed to examine the phase transformation behavior and microstructure of Niti instruments from a novel controlled memory Niti Wire (CM Wire). Methods: Instruments of EndoSequence (ES), ProFile (PF), ProFile Vortex (Vortex), Twisted Files (TF), Typhoon (TYP), and TyphoonCM (TYP CM), all size 25/.04, were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Microstructures of etched instruments were observed by optical microscopy and scanning elec- tron microscopy with x-ray energy-dispersive spectro- metric (EDS) analyses. Results: The DSC analyses showed that each segment of the TYP CM and Vortex instruments hadanaustenitetransformation completion or austenite-finish (Af) temperature exceeding 37C, whereas the Niti instruments made from conventional superelastic Niti Wire (ES, PF, and TYP) and TF had Af temperatures substantially below mouth temperature. The higher Af temperature of TYP CM instruments was consistent with a mixture of austenite and martensite structure, which was observed at room temperature with XRD. All Niti instruments had room temperature martensite microstructures consisting of colonies of lenticular features with substantial twinning. EDS anal- ysisindicated thatthe precipitates inallNiti instruments were titanium-rich, with an approximate composition of Ti2Ni. Conclusions: The TYP CM and Vortex instru- ments with heat treatment contribute to increase austenite transformation temperature. The CM instru- ment has significant changes in the phase transforma- tion behavior, compared with conventional superelastic Niti instruments. (J Endod 2011;37:1566- 1571)

  • fatigue testing of controlled memory Wire nickel titanium rotary instruments
    Journal of Endodontics, 2011
    Co-Authors: Ya Shen, Wei Qian, Houman Abtin, Markus Haapasalo
    Abstract:

    Introduction: To improve the fracture resistance of nickel-titanium (Niti) files, manufacturers have introduced new alloys to manufacture Niti files and developed new manufacturing processes. This study was aimed to examine the fatigue behavior of Niti instruments from a novel controlled memory Niti Wire (CM Wire). Methods: Instruments of ProFile, Typhoon (TYP), Typhoon CM (TYP CM), DS-SS0250425NEYY (NEYY), and DS-SS0250425NEYY CM (NEYY CM) (DS Dental, Johnson City, TN) all size 25/.04 were subjected to rotational bending at the curvature of 35 and 45 in air at the temperature of 23 2C, and the number of revolutions to fracture (Nf) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. The crack-iNitiation sites, the percentage of dimple area to the whole fracture crosssection, and the surface strain amplitude (ea) were noted. Results: The new alloy yielded an improvement of over three to eight times in Nf of CM files than that of conventional Nitifiles(P<.05). ThevastmajorityofCM instruments (50%-92%) showed multiple crack origins, whereas most instruments made from conventional Niti Wire (58%-100%) had one crack origin. The values of the fraction area occupied by the dimple region were significantly smaller on CM Niti instruments compared withconventionalNitiinstruments(P<.01).Thesquare (NEYY CM) versus the triangular (TYP CM) configuration showed a significantly different lifetime on CM Wire at both curvatures (P < .01). Conclusions: The material property had a substantial impact on fatigue lifetime. Instruments made from CM Wire had a significantly higher Nf and lower surface strain amplitude than the conventional Niti Wire files with identical design. (J Endod 2011;37:997‐1001)

Jan Racek - One of the best experts on this subject based on the ideXlab platform.

  • Environmental fatigue of superelastic Niti Wire with two surface finishes
    Journal of the mechanical behavior of biomedical materials, 2020
    Co-Authors: Jan Racek, Petr Šittner
    Abstract:

    Abstract Surface finish of Niti is widely perceived to affect its biocompatibility and corrosion fatigue performance. The aim of this work was to find out, whether a carefully engineered surface oxide shows any beneficial effect over electropolished surface on the fatigue performance of superelastic Niti Wire mechanically cycled in simulated biofluid. Series of corrosion and environmental fatigue tensile tests was performed on superelastic Niti Wire with two different surface finishes frequently used in medical device industry. Open Circuit Potential reflecting the activity of chemical reactions on the surface of the Wire cycled in electrochemical cell was continuously monitored during the fatigue tests. Microcracks at the surface of the fatigued Niti Wires were characterized by SEM and TEM. It was found that the carefully engineered 70 nm thick TiO2 oxide provides the Niti Wire with similar level of protection against the static corrosion as the less than 10 nm thin natural oxide on the electropolished Wire and that it does not have any positive effect on its performance in environmental fatigue tests, whatsoever. On the contrary, the Wire covered by the carefully engineered 70 nm thick TiO2 oxide displayed systematically poorer fatigue performance upon tensile cycling under specific critical loading conditions (strain amplitude

  • TEM observation of twins in surface grains of superelastic Niti Wire after cyclic loading
    Materials Science and Engineering: A, 2020
    Co-Authors: Jan Racek, Jan Duchoň, Marek Vronka, Miroslav Cieslar
    Abstract:

    Abstract Since the surface dominates fatigue of medical grade Niti Wire by yet unexplained causes, for comparison, we carried out a TEM observation of surface grains, both after one thousand superelastic cycles and on the unloaded Wire. Crystallographic defects consisting of aggregates of austenite twins stacked in the bands were observed after cycling deformation. The nuclei of aggregates are already present in an unloaded Wire that originates from cold drawing or heat treatment. Severe plastic deformation induced by a stress increasing in the surface during a cyclic phase transformation enables an accumulation of these aggregates into bands at inclined angle of 55° to the Wire axis corresponding to the spreading of diffused martensite band front paths during their propagation. An unrecovered strain, suppression of transformation and acceleration of crack propagation can be expected while the aggregates grow. Based on investigation of the grain orientation and boundaries in the twin lamellae using nano beam diffraction mapping, it can be proposed that, with exceeding martensite twin variant stress, twinning plane {1 1 4}B2 is a result of non-transforming pathway.

  • Monitoring Tensile Fatigue of Superelastic Niti Wire in Liquids by Electrochemical Potential
    Shape Memory and Superelasticity, 2015
    Co-Authors: Jan Racek, Petr Šittner, Marc Stora, Luděk Heller, Jaromir Kopeček, Martin Petrenec
    Abstract:

    Fatigue of superelastic Niti Wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued Niti Wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO_2 oxide layer on the Niti Wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled Wire surface develops mechanochemical reactions at the Niti/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the Niti matrix, local loss of the matrix strength, crack transfer into the Niti matrix, accelerated crack growth, and ultimately to the brittle fracture of the Wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of Niti—superelasticity due to martensitic transformation and biocompatibility due to the protective TiO_2 surface oxide layer—leads to excessive fatigue damage during cyclic mechanical loading in biofluids.