Fatigue of NITI thermoelastic martensites

Melton, K.N.; Mercier, O.

doi:10.1016/0001-6160(79)90065-8

Cited by 293 publications

(145 citation statements)

References 5 publications

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“…Mechanical fatigue of Ni-Ti alloys was studied: fatigue crack growth rates were measured and formed to be lower than predicted from the phenomenological law relating growth rates to the elastic modulus (7). A deviation of a factor of 3 is observed with conventionnal metals or alloys.…”

Section: Discussion -Conclusionmentioning

confidence: 99%

Microstructural effects on Ni-Ti endodontic instruments failure

Kuhn

Jordan

2001

J. Phys. IV France

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Abstract. Endodontic treatments consist to eliminate the vascular nervous system of the tooth. The objectives of this treatment are adequate cleaning and shaping the root canals of the tooth. The endodontic treatment is essential to the success of prosthetics therapy and the lifetime of the tooth. The difficulties of endodontic treatments lie in the abruptness of canal curvature. Ni-Ti endodontic instruments were introduced to facilitate instrumentation of curved canals. They are superelastic and flex far more than stainless-steel instruments. Despite the increased flexibility we can observe unexpected fractures of these Ni-Ti files. The purpose of this work is to understand the process history on fracture life. Our results are based on microstructural and mechanical investigations of Ni-Ti engine-driven rotary files: X-ray diffraction, SEM, DSC, microhardness and bending tests. Thus, and as we expected, endodontic files are very work-hardened: there is a high density of defects in the alloy, which will impede the phase transformation. DSC : the phase transformation A/R-Phase is predominant, the martensitic transformation is difficult to observe. The microvickers hardness confirms these observations (dislocations and precipitates). The X-rays show that the experimental peaks are broad, which is typical of a distorted lattice. Morover, machining resulted in the work hardening of files. Some thermal treatments are involved in promoting some changes in the mechanical properties and transformation characteristics. Annealing around 400°C shows good results : the recovery allows a compromise between an adequate density of defects to see the R-Phase germination and a low density to limit the brittleness of these instruments. The surface state of the endodontic files is an important factor for failures and fractures initiation. In these applications, it is very critical to predict the service life based on the theoretical modeling.

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Section: Discussion -Conclusionmentioning

confidence: 99%

Microstructural effects on Ni-Ti endodontic instruments failure

Kuhn

Jordan

2001

J. Phys. IV France

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“…From these results, it is understood that the amount of the stressinduced martensites influences the degree of functional degradations. It is reported that slip deformation occurs during the deformation process of specimens, 11) all of the stress-induced martensites do not disappear, and the residual martensites remain after unloading. The residual martensites increase with the number of cycles.…”

Section: Cyclic Behavior 321 Effect Of Maximum Shear Strainmentioning

confidence: 99%

Superelastic Behavior under Cyclic Loading for Coil Spring of Ti-Ni Shape Memory Alloy

Sakuma

Suzuki

2007

Mater. Trans.

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The superelastic behavior of coil springs of a Ti-Ni shape memory alloy was investigated using loading-unloading cycling tests under isothemal temperatures. The effects of the Ni content and shape memory treatment temperatures on the cyclic behavior in the superelastic deformation were investigated. The deformation behavior within the elastic region of the parent phase scarcely changes during tensile cyclic loading. However, when a martensitic phase is induced by the stress, the deformation behavior changes considerably during cyclic loading. The critical shear stress for inducing martensites and the dissipated strain energy per cycle decrease with an increase in the number of cyclic loadings. Such changes in the superelastic behavior under cyclic loading become large with a decrease in the Ni content of the Ti-Ni shape memory alloy and the increase in the shape memory treatment temperature.

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“…Where authors find decreasing M s temperatures [4] [6] it tends to be associated with pure thermal cycling or very low stress levels and implies that dislocations within the microstructure interfere with the transformation and increase the degree of under-cooling required for the transformation to proceed. Similarly, where authors find increasing M s temperatures [6] [7][8] it tends to be associated with an applied stress either prior to or during thermal cycling. In this case the changing microstructure appears to assist the transformation resulting in a decrease of the required under-cooling.…”

Section: Thermal Cyclingmentioning

confidence: 99%

“…The cause of residual strain in superelastic alloys is also probably due to the occurrence of slip during the transformation as demonstrated by Melton and Mercier [7]. The internal stress caused by slip can also assist the stress-induced martensite transformation by reducing the critical applied stress -CTM [3].…”

Section: Superelastic Cyclingmentioning

confidence: 99%

A review of shape memory stability in NiTi alloys

Morgan

Friend

2001

J. Phys. IV France

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Stability and fatigue are terms often referred to when discussing the durability of the shape memory effect. This paper considers the meaning of these terms and how they relate to the macroscopic memory response and the microstructural accommodation response of NiTi alloys. The results of previous workers are analysed and compared to establish how the three parameters that apparently control the macroscopic memory effect -temperature, stress and strain, are controlled themselves by the alloy's microstructure. It will be shown that repeated phase changes will alter the microstructure and hysteresis of the transformation and in turn this will lead to changes in transformation temperatures, transformation stresses and transformation strains. Both superelastic and memory effects are considered simultaneously so as to emphasise the similarities between the respective stress/strain and strain/temperature degradation effects. Although the mechanisms of both are often regarded as physically separate it is shown that in fact the macroscopic changes observed during cycling are a result of similar microstructural changes. It is also shown how as a result of the inherently large transformation strains internal cracking may occur and that even apparently stable microstructures can fail catastrophically via conventional crack growth mechanisms.

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Fatigue of NITI thermoelastic martensites

Cited by 293 publications

References 5 publications

Microstructural effects on Ni-Ti endodontic instruments failure

Microstructural effects on Ni-Ti endodontic instruments failure

Superelastic Behavior under Cyclic Loading for Coil Spring of Ti-Ni Shape Memory Alloy

A review of shape memory stability in NiTi alloys

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