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Production of Ti-Ni Intermetallic Compounds by High Temperature Ball Milling Method
Hojaji Najafabadi, Alireza | 2014
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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 46233 (07)
- University: Sharif University of Technology
- Department: Material Science and Engineering
- Advisor(s): Sadrnezhad, Khatiboleslam
- Abstract:
- NiTi intermetallic is well known for its unique physical and mechanical properties, such as superelasticity, shape memory effect, good tribological properties, excellent corrosion resistance and biocompatibility. It is widely used in several areas including aerospace and medical applications and surface engineering. Several approaches, such as casting, powder metallurgy, self-propagating high-temperature synthesis, mechanical alloying and explosive shock-wave compression have been used to produce NiTi alloys. However the formation of the undesirable phases such as NiTi2 and Ni3Ti still is the biggest concern. According to Ni-Ti phase diagram, stability region of NiTi compound is at temperatures above 650 ̊C, that may have a wide stability region at elevated temperatures for non-equilibrium states. The aim of this work is to investigate the feasibility of using high temperature ball milling method (above 700 ̊C) to synthesis of pure NiTi for the first time. For this purpose, we have designed and made a high temperature ball mill. By using elemental Ni and Ti, the effect of temperature of milling, time, and chemical compound of primary mixed powders as well as cooling rate of milling medium has been evaluated with XRD, SEM and EDS analysis techniques. Also coated layer on balls and internal medium surface was assessed with optical microscopy, Vickers microhardness method and wear analysis. After using Nickel balls in high temperature process for several times, the Shell separation phenomena was happened on Nickel balls that this might be happened for the extreme difference in thermal expansion coefficient for Nickel at curie temperature. The results show that Ni3Ti, NiTi and NiTi2 are the main phases obtained by high temperature ball milling method. The kinetic of formation of these compounds is improved due to high temperatures and the required time is decreased. Finally the obtained results shows that the coated layer on balls and internal medium surface is a high strength coating, so the high temperature ball milling is a novel coating method to deposition of different compounds on balls and aspheric surfaces
- Keywords:
- Nickel-Titanium Alloy ; Mechanical Alloying ; Intermetallic Compounds ; Hot Milling ; High Temperature Ball Milling ; Shell Separation Phenomen in Nickel Ball ; Coating Process on Ball
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