치과교정용 NiTi 합금계 선재의 탄성과 상변태 거동에 대한 열처리 효과

이진숙,김광만,김경남 대한치과기재학회 1997 대한치과재료학회지 Vol.24 No.1

Due to unique property of superelasticity, NiTi has been used widely since their introduction to the orthodontic specialty by Andreasen and Hillmann. But sufficent evaluation of superelasticity of domestic marketed wires has not yet been made. It has been known that heat treatment caused changes not only of elastic behavior but also of phase transformation behavior, an important factor of superelasticity. So, this study was investigated into varied ways of heat treatment of wires for orthodontic force proper for each clinical case. Each elastic behavior of 6 commercial NiTi alloy orthodontic arch wires(LG's ORTHOLLOY, G & H's Nickel Titanium arch wire, ORMCO's NI-TI and COPPER NI-TI, TOMY's SENTALLOY and 3M Unitek's Nitinol) were examined, and in order to study the effect of heat treatment on elasticity and phase transformation behavior, 3-point bending test, differential scanning calorimetry and X-ray diffraction with each wire heated at 350℃, 450℃ and 550℃ for 1hour were carried out compared with a as-recieved group. The results were as follows : 1. As a result of 3-point bending test in a control group, all wires had superelasticity and COPPER NI-TI showed the lowest maximum load as well as minimum(P<0.05). 2. As a result of 3-point bending est, except Nitinol and COPPER NI-TI, the wires in the group heated at 450℃ had lowest maximum and minimum load than that of a control group, and higher maximum and minimum load that of COPPER NI-TI in control group, and had superelasticity without and permanent deformation(P<0.05). 3. Phase transition temperature of all wires heated at 350℃ except COPPER NI-TI became higher but it became lower when they were heated at 450℃ and 550℃. 4. All wires in control group had austenite structure and when they were heated, martensite phase increased, and R phase appeared when heated at 550℃. The wires used in this study were changed in phase transition temperature, structure and elastic behavior as well by heat treatment. So this study showed that even the same kind of wire could be varied and used after heat treated, choosing proper load in accordance with each orthodontic clinic case.

Shape memory and superelasticity of nanograined Ti-51.2 at.% Ni alloy processed by severe plastic deformation via high-ratio differential speed rolling

Lim, Y.G.,Han, S.H.,Choi, E.,Kim, W.J. Elsevier 2018 Materials characterization Vol.145 No.-

<P><B>Abstract</B></P> <P>A novel method of producing nanograined Ni-rich superelastic NiTi alloys in sheet form was proposed using a combination of severe plastic deformation via high-ratio differential speed rolling (HRDSR) and post-deformation annealing. The HRDSR-processed microstructure was composed of heavily deformed austenite and martensite grains, and amorphous phases. After annealing at 673 K, the severely deformed microstructure with no functional properties evolved to the nanograined structure (20–70 nm) composed of austenite and martensite nanograins and sub-nanograins through static recovery or continuous static recrystallization process. The nanograined microstructure had a high resistance to martensitic transformation upon cooling and slip deformation during straining. As a result, the HRDSR-processed alloy annealed at 673K exhibited superior superelasticity compared to the alloys with coarse grains. At the higher annealing temperature of 873 K, the micron-sized recrystallized grains with low dislocations developed through discontinuous static recrystallization process. In this case, deformation during straining was governed by the detwinning of twinned martensite, and as a result, shape memory effect was more significantly pronounced than superelasticity.</P>

Shape memory properties of TiNbMo biomedical alloys

Al-Zain, Y.,Kim, H.Y.,Hosoda, H.,Nam, T.H.,Miyazaki, S. Elsevier Science 2010 Acta materialia Vol.58 No.12

Mo is added to Ti-Nb alloys in order to enhance their superelasticity. The shape memory properties of Ti-(12-28)Nb-(0-4)Mo alloys are investigated in this paper. The Ti-27Nb, Ti-24Nb-1Mo, Ti-21Nb-2Mo and Ti-18Nb-3Mo alloys exhibit the most stable superelasticity with a narrow stress hysteresis among Ti-Nb-Mo alloys with Mo contents of 0, 1, 2 and 3at.%, respectively. The ternary alloys reveal better superelasticity due to a higher critical stress for slip deformation and a larger transformation strain. A Ti-15Nb-4Mo alloy heat-treated at 973K undergoes (211)<111>-type twinning during tensile testing. Twinning is suppressed in the alloy heat-treated at 923K due to the precipitation of the α phase, allowing the alloy to deform via a martensitic transformation process. The Ti-15Nb-4Mo alloy exhibits stable superelasticity with a critical stress for slip deformation of 582MPa and a total recovery strain of 3.5%.

Effect of silver addition on the properties of nickel–titanium alloys for dental application

Oh, Keun-Taek,Joo, Uk-Hyon,Park, Gee-Ho,Hwang, Chung-Ju,Kim, Kyoung-Nam Wiley Subscription Services, Inc., A Wiley Company 2006 Journal of Biomedical Materials Research Part B Vol. No.

<P>Equiatomic and near-equiatomic nickel–titanium alloys exhibit a shape-memory effect and superelasticity. However, the properties of such alloys are extremely sensitive to the precise nickel–titanium ratio and the addition of alloying elements. High corrosion resistance is necessary for biomedical applications, especially orthodontic. The purpose of this study was to investigate the effect of silver addition to nickel–titanium alloys for dental and medical application. Arc melting, homogenization, hot rolling, and solution heat treatment were performed to prepare the nickel–titanium–silver (NiTi-Ag) specimens. The properties of the ternary NiTi–Ag alloys such as phase-transformation temperature, microstructure, microhardness, corrosion resistance, and cytotoxicity were investigated. The NiTi-Ag alloys showed low silver recovery rate for the cast alloy, due to silver's low evaporation temperature, and low silver solubility in nickel–titanium. Silver addition to nickel–titanium increased the transition temperature range to 100°C and stabilized the martensitic phase (monoclinic structure) at room temperature, because the martensitic transformation starting temperature (M<SUB>s</SUB>) was above room temperature. Martensitic and austenitic phases existed in X-ray diffraction patterns of solution-annealed NiTi-Ag alloys. The silver addition was considered to improve the corrosion resistance and form a stable passive film. Significantly, the mechanical properties of the silver-added alloys were dependent upon the amount of alloying addition. There was no toxicity in the NiTi-Ag alloys, as the response index showed none or mild levels. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006</P>

Effect of annealing temperature on shape memory characteristics in Ti-20Nb-6Zr-0.5O(at%) biomedical alloy

Kim, J.I.,Park, Y.C.,Ock, J.M. Elsevier Sequoia 2013 JOURNAL OF ALLOYS AND COMPOUNDS Vol.577 No.suppl1

Effect of annealing on shape memory characteristics of Ti-20Nb-6Zr-0.5O(at%) biomedical alloys was investigated by using tensile test and optical microscopy (OM). The ingots were cold-rolled with a reduction up to 95% in thickness. After severe cold-rolling, the plate was annealed at 923-1173K. The martensitic transformation start temperature (M<SUB>s</SUB>) is hardly affected by annealing temperature. The superior shape memory properties and cyclic deformation behavior were observed at room temperature in all specimens. The specimen annealing at 923K exhibits the most stabilized superelasticity. The maximum shape recovery strain of 4.2% and the critical stress for slip of 780MPa were obtained in the specimen annealed at 923K. Maximum recovery strain and critical stress for slip decrease with increasing annealing temperature. According to OM observation the grain size increases from 10 to 47μm with increasing annealing temperature. It is considered that the critical stress for slip and the stability of superelasticity was considerably affected by grain size. This indicates that grain refinement is important method to improve shape memory characteristics.

Energy-balance assessment of shape memory alloy-based seismic isolation devices

O.E. Ozbulut,S. Hurlebaus 국제구조공학회 2011 Smart Structures and Systems, An International Jou Vol.8 No.4

This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

치과 재료용 NiTi 합금의 특성에 대한 Ag 첨가의 영향

오근택,박기호,심형민,황충주,김경남 大韓齒科器材學會 2001 대한치과재료학회지 Vol.28 No.4

Equiatomic and near-equiatomic nickel-titanium alloys have shape memory effect and superelasticity. However nickel-titanium alloys are extremely sensitive to the precise nickel-titanium ratio and alloying additions. There are many reports on the alloying additions such as Fe, Al, Cr, Co, V, Pt, Pd, Zr, Hf, Nb and Cu. The purpose of this study was to investigate the effect of silver addition to nickel-titanium alloy for dental and medical application.Arc melting process was used to fabricate nickel-titanium alloys. The casts were heat-treated in a vacuum furnace at 950℃ for 72 hours to homogenize their composition. Subsequently, they were hot-rolled at 950℃ to obtain the plate samples and annealed in a vacuum furnace at 950℃. To investigate the properties of nickel-titanium alloys, phases, transformation temperature, compositions, corrosion resistance and hardness were evaluated using X-ray diffractometer, differential scanning calorimeter, energy dispersive spectroscopy or atomic absorption spectroscopy, potentiostat and micro-vickers hardness tester, respectively. NiTiAg alloys showed the low silver recovery rate for the cast due to its low evaporation temperature, and showed low silver solubility to NiTi alloy. Silver addition to NiTi alloy increased transition temperature range (TTR) above 100℃ and stabilized martensitic phase(monoclinic structure) at room temperature because Ms temperature was above room temperature. Martensitic and austenitic phase existed in x-ray diffraction pattern of solution annealed NiTiAg alloys. The Silver addition is considered to improve corrosion resistance and change largely the mechanical properties depending upon the amount of alloying addition and types of addition elements.

Energy-balance assessment of shape memory alloy-based seismic isolation devices

Ozbulut, O.E.,Hurlebaus, S. Techno-Press 2011 Smart Structures and Systems, An International Jou Vol.8 No.4

This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

Shape memory alloy (SMA)-based Superelasticity-assisted Slider (SSS): an engineering solution for practical aseismic isolation with advanced materials

Peyman Narjabadifam,Mohammad Noori,Donatello Cardone,Rasa Eradat,Mehrdad Kiani 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.1

Shape memory alloy (SMA)-based Superelasticity-assisted Slider (SSS) is proposed as an engineering solution to practically exploit the well-accepted advantages of both sliding isolation and SMA-based recentering. Self-centering capability in SSS is provided by austenitic SMA cables (or wire ropes), recently attracting a lot of interest and attention in earthquake engineering and seismic isolation. The cables are arranged in various novel and conventional configurations to make SSS versatile for aseismic design and retrofit of structures. All the configurations are detailed with thorough technical drawings. It is shown that SSS is applicable without the need for Isolation Units (IUs). IUs, at the same time, are devised for industrialized applications. The proof-ofconcept study is carried out through the examination of mechanical behavior in all the alternative configurations. Forcedisplacement relations are determined. Isolation capabilities are predicted based on the decreases in seismic demands, estimated by the increases in effective periods and equivalent damping ratios. Restoring forces normalized relative to resisting forces are assessed as the criteria for self-centering capabilities. Lengths of SMA cables required in each configuration are calculated to assess the cost and practicality. Practical implementation is realized by setting up a small-scale IU. The effectiveness of SSS under seismic actions is evaluated using an innovative computer model and compared to those of well-known Isolation Systems (ISs) protecting a reference building. Comparisons show that SSS seems to be an effective IS and suitable for earthquake protection of both structural and non-structural elements. Further research aimed at additional validation of the system are outlined.

니켈-고함량 니켈-타이타늄 박막 합금의 기계적 거동

김지영(Ji-Young Kim),Abdul Rheman,심기동(Gi-Dong Sim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11

Nickel-titanium (NiTi) alloy thin films are attractive for micro-scale applications because of its fast response on temperature by high surface area, large work output, and higher strain recovery. In terms of superelasticity, Ni-rich NiTi alloys is primarily used due to enhanced phase transformation stability. As it is well known that the mechanical behavior of materials is scale dependent, it is crucial to understand size-effect on the mechanical behavior of NiTi for reliable operation in micro-scale devices. Therefore, in this study, mechanical behavior of Ni-rich NiTi thin films was characterized to identify the effect of the Ni concentration on superelasticity. Free-standing Ni-rich NiTi thin films were fabricated by sputter deposition followed by micro-electro-mechanicalsystem (MEMS) process. Tensile tests were conducted using a custom-built micro tensile tester. Films with higher Ni concentration showed improved strength with enhanced phase transformation stability.