The Effect of Combined Recrystallization and Precipitation Processes on the Functional and Structural Properties in NiTi Alloys

Treppmann, D.; Hornbogen, Erhard; Wurzel, D.

doi:10.1051/jp4/199558569

Cited by 23 publications

(27 citation statements)

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“…Our results with DSC, XRD and microhardness show that new specimens are significantly workhardened : microhardness mesure is twice than a sample fully recrystallized (8). Moreover machining marks and cracks on the surface observed by SEM contribute largely to fatigue failure by crack propagation process.…”

Section: Discussion -Conclusionmentioning

confidence: 64%

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: 64%

Microstructural effects on Ni-Ti endodontic instruments failure

Kuhn

Jordan

2001

J. Phys. IV France

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“…It has been determined by Treppmann et al [37] that the Ni4Ti3 precipitates are perfectly coherent with the matrix at about 10 nm and completely lose the coherency at about 300 nm.…”

Section: Discussionmentioning

confidence: 98%

Reduction of environmentally induced cracking of laser-welded shape memory NiTi wires via post-weld heat-treatment

Chan

Man

2013

Materials Science and Engineering: A

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In this study, the environmentally induced cracking behaviour of the NiTi weldment with and without post-weld heat-treatment (PWHT) in Hanks' solution at 37.5 °C at OCP were studied by tensile and cyclic slow-strain-rate tests (SSRT), and compared with those tested in oil (an inert environment). Our previous results in the tensile and cyclic SSRT showed that the weldment without PWHT showed high susceptibility to the hydrogen cracking, as evidenced by the degradation of tensile and super-elastic properties when testing in Hanks' solution. The weldment after PWHT was much less susceptible to hydrogen attack in Hanks' solution as no obvious degradation in the tensile and super-elastic properties was observed, and only a very small amount of micro-cracks were found in the fracture surface. The susceptibility to hydrogen cracking of the NiTi weldment could be alleviated by applying PWHT at the optimized temperature of 350 °C after laser welding.

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“…In the first cycle, the R-phase transformation is observed. The reason is internal stress fields induced by dislocations or precipitates due to the hardening treatment [1]. The austenite peak-(A m ) and martensite peak temperature (M m ) of the recrystallized state decrease with increasing number of cycles (Fig.…”

Section: Thermal Fatiguementioning

confidence: 99%

“…Range I (MF) and II (XF): Depending on the annealing conditions, favorable functional and structural properties were created [1,2]. Range III (AF): Only pseudo plasticity is improved.…”

Section: Introductionmentioning

confidence: 99%

Effects of different thermomechanical treatments on fatigue of NiTi shape memory alloys

Wurzel

2001

J. Phys. IV France

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Fully recrystallized NiTi sheets were deformed in four different temperature ranges: fully transformed martensite (T < M f ), transforming austenite (M s < T < Md), low temperature, stable austenite (M d < T < 1/3 T s ) and austenite at elevated temperatures (T > 1/3 T m ). The types and distributions of defects produced in these materials depend on the deformation temperature. The characteristic defect structures resulting from the low temperature deformation lead to different microstructures even after annealing. The thermomechanically treated as compared to the fully recrystallized NiTi alloys were subjected to thermal, mechanical and thermomechanical fatigue tests. Their microstructural origin was interpreted by TEM investigations. In conclusion it is proposed that a low ratio of pseudo-yield stress to true yield stress is responsible for good fatigue resistance. Regarding fatigue it is better to increase the yield stress by a small grain size than by a high dislocation density (work hardening).

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The Effect of Combined Recrystallization and Precipitation Processes on the Functional and Structural Properties in NiTi Alloys

Cited by 23 publications

References 0 publications

Microstructural effects on Ni-Ti endodontic instruments failure

Microstructural effects on Ni-Ti endodontic instruments failure

Reduction of environmentally induced cracking of laser-welded shape memory NiTi wires via post-weld heat-treatment

Effects of different thermomechanical treatments on fatigue of NiTi shape memory alloys

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