Develop the manufacturing process to improve the properties of medical Ni-Ti memory alloy wire

  • 黃 弋銘

Student thesis: Doctoral Thesis

Abstract

Nickel- Titanium(Ni-Ti) alloy is one of shape memory alloys (SMA) which are a distinct class of smart and functional material and have two unique properties shape memory and superelasticity Besides Ni-Ti alloy also possesses high mechanical strength good corrosion resistance good workability and biocompatibility so it has been used for a wide range of applications in various fields in recent years It can form a Ni-free TiO2 layer on the surface of the Ni-Ti alloy through a variety of surface modifications further improving its corrosion resistance surface hydrophilicity and biocompatibility to make the applications of the Ni-Ti alloy in medical devices more suitable Some literatures indicate that the properties of Ni-Ti could be manipulated through cold work heat treatment or a combination of both for applicable medical devices including vascular stents orthodontic wires and guide wires In this study the Ni-Ti wire (54 1%) was subjected to a series of cold drawing process and annealing heat treatment to evaluate their influence in mechanical alternation and shape memory transformation temperature A series of diamond dies were used to draw Ni-Ti wire in gradual reduction in cross sections to obtain desirable dimension and the effect of cold working A continuous furnace which was different from the box furnace in common research was used to adjust the straightness and recover the properties of the wires by annealing Diameter at 0 62 mm Ni-Ti wire were annealed at 800 ℃ for different times to find the relation between the annealing time and the properties of Ni-Ti wire All the treatment in Ni-Ti wires were analyzed by surface morphology oxide layer thickness tensile properties hardness value and phase transformation temperature The results showed that the cold drawing process possessed excellent dimensional control and the wires were not twisted after multiple stages drawing The ductility of annealed Ni-Ti wires successfully returned so that next cold drawing process could be continued After the drawing process the strength and hardness of Ni-Ti wires were greatly enhanced It could be observed that annealed wires had good straightness As the annealing time increases the coverage and thickness of the oxide layer that can suppress Ni ion release also increased The relationship between the annealing time and the properties of Ni-Ti wires was evaluated from the results so it provided the guidance to control the desired properties of Ni-Ti wires as well as the proper phase transformation temperature for various applications
Date of Award2020
Original languageEnglish
SupervisorMing-Long Yeh (Supervisor)

Cite this

'