Effects of thermal and thermomechanical cycling on the phase transformations in NiTi and NiTiCo shape-memory alloys

Jordan, Laurence; Masse, M.; Collier, John; Bouquet, G.

doi:10.1016/0925-8388(94)90483-9

Cited by 22 publications

(9 citation statements)

References 1 publication

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“…The choice of only one manufacturer is appropriate because the mechanical properties of NiTi orthodontic wire products are affected by the chemical composition, process fabrication and heat treatment of the alloy (Guénin, 1986;Jordan et al, 1994;Thayer et al, 1995), and thus will vary among manufacturers. These parameters are not discussed in this study.…”

Section: Methodsmentioning

confidence: 99%

Evolution of flexural rigidity according to the cross-sectional dimension of a superelastic nickel titanium orthodontic wire

Garrec¹,

Tavernier²,

Jordan³

2005

European Journal of Orthodontics

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SUMMARY The choice of the most suitable orthodontic wire for each stage of treatment requires estimation of the forces generated. In theory, the selection of wire sequences should initially utilize a lower fl exural rigidity; thus clinicians use smaller round cross-sectional dimension wires to generate lighter forces during the preliminary alignment stage. This assessment is true for conventional alloys, but not necessarily for superelastic nickel titanium (NiTi). In this case, the fl exural rigidity dependence on cross-sectional dimension differs from the linear elasticity prediction because of the martensitic transformation process. It decreases with increasing defl ection and this phenomenon is accentuated in the unloading process. This behaviour should lead us to consider differently the biomechanical approach to orthodontic treatment.The present study compared bending in 10 archwires made from NiTi orthodontics alloy of two crosssectional dimensions. The results were based on microstructural and mechanical investigations. With conventional alloys, the fl exural rigidity was constant for each wire and increased largely with the crosssectional dimension for the same strain. With NiTi alloys, the fl exural rigidity is not constant and the infl uence of size was not as important as it should be. This result can be explained by the non-constant elastic modulus during the martensite transformation process. Thus, in some cases, treatment can begin with full-size (rectangular) wires that nearly fi ll the bracket slot with a force application deemed to be physiologically desirable for tooth movement and compatible with patient comfort.

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Section: Methodsmentioning

confidence: 99%

Evolution of flexural rigidity according to the cross-sectional dimension of a superelastic nickel titanium orthodontic wire

Garrec¹,

Tavernier²,

Jordan³

2005

European Journal of Orthodontics

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“…The effect of cold rolling in the range 10-50% on the transformation characteristics of NiTi has been studied by many researchers ( Ref 4,[8][9][10][11][12][13][14]. Mithwally and Farag (Ref 4) through XRD and microstructural study on 10-50% cold worked NiTi SMA have reported an increase in volume fraction of martensite with increase in percentage of cold roll resulting in an increase of recoverable strain, tensile strength, and hardness.…”

Section: Introductionmentioning

confidence: 97%

Effect of Cold Rolling on Phase Transformation Temperatures of NiTi Shape Memory Alloy

Pattabi

Murari

2014

J. of Materi Eng and Perform

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The effect of cold rolling and heat treatment on the phase transformation behavior of NiTi shape memory alloy (SMA) heat treated at 660°C has been investigated. Four sets of samples were cold rolled after heat treatment. The austenite-to-martensite and martensite-to-austenite transformation temperatures for samples without any cold rolling are determined through differential scanning calorimetry (DSC). The austenitic start temperature gets shifted to the higher temperature side with increase in the percentage of the cold rolling up to 12.5%. Austenitic finish temperature could not be detected in cold-rolled samples. Martensitic start temperature increases slightly with increased cold rolling while martensitc finish temperature slightly decreases. Beyond 12.5% cold work, the shape memory effect (SME) is completely lost. The evolution of austenitic phase in SMA subjected to cold rolling was studied through powder x-ray diffraction (XRD) at different temperatures in the range 25 to 160°C at intervals of 10°C, during heating and cooling. The XRD results agree with those of DSC. Two sets of cold-rolled samples were again heat treated to 300 and 500°C and the transformation behavior was studied using DSC. Heat treatment at 300°C brings back the SME, but with the presence of an intermediate R-Phase due to the additional dislocations present. Even with a heat treatment at 500°C, the effect of cold work is not completely removed and a single-step transformation is not observed. Another set of samples subjected to cold work were heat treated at 660°C and the transformation is studied. The effect of cold work even up to 25% is completely removed with this heat treatment as indicated by DSC. The complete regaining of the SME is further confirmed by electrical resistivity measurements also.

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“…These treatments have focused mainly on the equiatomic Ti-Ni [16][17][18][19] or Ni-rich alloys [20][21][22][23][24]. Very few studies concern similar attempts in the case of Ti-rich Ti-Ni alloys [25][26][27][28].…”

Section: Introductionmentioning

confidence: 97%

Mechanical properties of Ti–(∼49at%) Ni shape memory alloy, part II: Effect of ageing treatment

Sinha

Mondal

Chattopadhyay

2013

Materials Science and Engineering: A

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Effects of thermal and thermomechanical cycling on the phase transformations in NiTi and NiTiCo shape-memory alloys

Cited by 22 publications

References 1 publication

Evolution of flexural rigidity according to the cross-sectional dimension of a superelastic nickel titanium orthodontic wire

Evolution of flexural rigidity according to the cross-sectional dimension of a superelastic nickel titanium orthodontic wire

Effect of Cold Rolling on Phase Transformation Temperatures of NiTi Shape Memory Alloy

Mechanical properties of Ti–(∼49at%) Ni shape memory alloy, part II: Effect of ageing treatment

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