Microstructure of cryogenically treated martensitic shape memory nickel-titanium alloy

Area of Science:

• Materials Science
• Metallurgy
• Biomaterials

Background:

• Shape memory (SM) nickel-titanium (NiTi) alloy is crucial in endodontics.
• Instrument fracture remains a challenge despite enhanced flexibility.
• Improved fatigue life through supplementary manufacturing is desirable.

Purpose of the Study:

• Investigate the effect of dry cryogenic treatment (CT) on martensitic SM NiTi alloy microstructure.
• Determine optimal CT conditions for enhancing NiTi alloy properties.

Main Methods:

• Tested Ni-51 wt% Ti-49 wt% SM alloy under various CT conditions (Deep CT -185°C for 24h/6h, Shallow CT -80°C for 24h/6h).
• Analyzed surface microstructure using optical and scanning electron microscopy.
• Examined subsurface structure via X-ray diffraction (XRD).

Main Results:

• All SM NiTi specimens exhibited equiaxed grains (approx. 25 μm) with precipitates.
• Cryogenic treatment accentuated austenite and martensite peaks in XRD patterns.
• Deep CT (DCT) for 24 hours resulted in increased martensite volume and crystallite size.

Conclusions:

• Deep cryogenic treatment (DCT) for 24 hours increases martensite content in SM NiTi alloy.
• DCT does not alter the grain size of the SM NiTi alloy.
• Optimized CT conditions can enhance NiTi alloy performance for endodontic applications.