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Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy.

Vinothkumar TS, Kandaswamy D, Prabhakaran G, Rajadurai A - J Conserv Dent (2015 Jul-Aug)

Bottom Line: XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks.The volume of martensite and its crystallite size was relatively more in DCT 24 specimen.DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size.

View Article: PubMed Central - PubMed

Affiliation: Department of Restorative Dental Sciences, College of Dentistry, Jazan Universtiy, Jazan, Kingdom of Saudi Arabia.

ABSTRACT

Context: Recent introduction of shape memory (SM) nickel-titanium (NiTi) alloy into endodontics is a major breakthrough. Although the flexibility of these instruments was enhanced, fracture of rotary endodontic instruments during instrumentation is an important challenge for the operator. Implementation of supplementary manufacturing methods that would improve the fatigue life of the instrument is desirable.

Aim: The purpose of this study was to investigate the role of dry cryogenic treatment (CT) conditions on the microstructure of martensitic SM NiTi alloy.

Materials and methods: Experiments were conducted on Ni-51 wt% Ti-49 wt% SM alloy. Five cylindrical specimens and five sheet specimens were subjected to different CT conditions: Deep CT (DCT) 24 group: -185°C; 24 h, DCT 6 group: -185°C; 6 h, shallow CT (SCT) 24 group: -80°C, 24 h, SCT 6 group: -80°C, 6 h and control group. Microstructure of surface was observed on cylindrical specimens with an optical microscope and scanning electron microscope at different magnifications. Subsurface structure was analyzed on sheet specimens using X-ray diffraction (XRD).

Results: Microstructures of all SM NiTi specimens had equiaxed grains (approximately 25 μm) with well-defined boundaries and precipitates. XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks. The volume of martensite and its crystallite size was relatively more in DCT 24 specimen.

Conclusions: DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size.

No MeSH data available.


Related in: MedlinePlus

(a) Optical micrograph of shape memory nickeltitanium (NiTi) alloy (black circle denotes the martensite variant of the grain), (b) scanning electron microscope micrograph (white circle denotes the martensite variant); holes (black arrow) and precipitates (white arrow) in the NiTi matrix are present, (c) EDS spectrum showing the elemental composition
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Figure 1: (a) Optical micrograph of shape memory nickeltitanium (NiTi) alloy (black circle denotes the martensite variant of the grain), (b) scanning electron microscope micrograph (white circle denotes the martensite variant); holes (black arrow) and precipitates (white arrow) in the NiTi matrix are present, (c) EDS spectrum showing the elemental composition

Mentions: Optical microscopic images [Figure 1a] of all etched specimens showed equiaxed grains with well-defined boundaries. The average diameter of the grains was approximately 25 μm with ASTM grain size number of 7.7 in all the groups. The size distribution of the grains in all the groups was uneven. Few grains revealed some martensite variants while other grains remained free of martensite. The martensite variants within the grains showed the characteristic substantial twinning. Table 1 shows the volume of martensite that is observed in the images of different groups.


Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy.

Vinothkumar TS, Kandaswamy D, Prabhakaran G, Rajadurai A - J Conserv Dent (2015 Jul-Aug)

(a) Optical micrograph of shape memory nickeltitanium (NiTi) alloy (black circle denotes the martensite variant of the grain), (b) scanning electron microscope micrograph (white circle denotes the martensite variant); holes (black arrow) and precipitates (white arrow) in the NiTi matrix are present, (c) EDS spectrum showing the elemental composition
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4502124&req=5

Figure 1: (a) Optical micrograph of shape memory nickeltitanium (NiTi) alloy (black circle denotes the martensite variant of the grain), (b) scanning electron microscope micrograph (white circle denotes the martensite variant); holes (black arrow) and precipitates (white arrow) in the NiTi matrix are present, (c) EDS spectrum showing the elemental composition
Mentions: Optical microscopic images [Figure 1a] of all etched specimens showed equiaxed grains with well-defined boundaries. The average diameter of the grains was approximately 25 μm with ASTM grain size number of 7.7 in all the groups. The size distribution of the grains in all the groups was uneven. Few grains revealed some martensite variants while other grains remained free of martensite. The martensite variants within the grains showed the characteristic substantial twinning. Table 1 shows the volume of martensite that is observed in the images of different groups.

Bottom Line: XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks.The volume of martensite and its crystallite size was relatively more in DCT 24 specimen.DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size.

View Article: PubMed Central - PubMed

Affiliation: Department of Restorative Dental Sciences, College of Dentistry, Jazan Universtiy, Jazan, Kingdom of Saudi Arabia.

ABSTRACT

Context: Recent introduction of shape memory (SM) nickel-titanium (NiTi) alloy into endodontics is a major breakthrough. Although the flexibility of these instruments was enhanced, fracture of rotary endodontic instruments during instrumentation is an important challenge for the operator. Implementation of supplementary manufacturing methods that would improve the fatigue life of the instrument is desirable.

Aim: The purpose of this study was to investigate the role of dry cryogenic treatment (CT) conditions on the microstructure of martensitic SM NiTi alloy.

Materials and methods: Experiments were conducted on Ni-51 wt% Ti-49 wt% SM alloy. Five cylindrical specimens and five sheet specimens were subjected to different CT conditions: Deep CT (DCT) 24 group: -185°C; 24 h, DCT 6 group: -185°C; 6 h, shallow CT (SCT) 24 group: -80°C, 24 h, SCT 6 group: -80°C, 6 h and control group. Microstructure of surface was observed on cylindrical specimens with an optical microscope and scanning electron microscope at different magnifications. Subsurface structure was analyzed on sheet specimens using X-ray diffraction (XRD).

Results: Microstructures of all SM NiTi specimens had equiaxed grains (approximately 25 μm) with well-defined boundaries and precipitates. XRD patterns of cryogenically treated specimens revealed accentuation of austenite and martensite peaks. The volume of martensite and its crystallite size was relatively more in DCT 24 specimen.

Conclusions: DCT with 24 h soaking period increases the martensite content of the SM NiTi alloy without altering the grain size.

No MeSH data available.


Related in: MedlinePlus