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高温材料处理:国际期刊
SJR: 0.137 SNIP: 0.341 CiteScore™: 0.43

ISSN 打印: 1093-3611
ISSN 在线: 1940-4360

高温材料处理:国际期刊

DOI: 10.1615/HighTempMatProc.v4.i4.20
10 pages

THE WIRE ELECTRO-DISCHARGE MACHINING CHARACTERISTICS OF TiNi SHAPE MEMORY ALLOYS

H. C. Lin
Department of Materials Science, Feng Chia University, 100 Wen-Hua Road,Taichung 407, Taiwan, Republic of China
K. M. Lin
Department of Materials Science, Feng Chia University, 100 Wen-Hua Road,Taichung 407, Taiwan, Republic of China
I. S. Cheng
Department of Materials Science, Feng Chia University, 100 Wen-Hua Road,Taichung 407, Taiwan, Republic of China

ABSTRACT

The wire electro-discharge machining (WEDM) characteristics of TiNi shape memory alloys (SMAs) have been investigated in this study. The maximum feeding rate without breakage of wire electrode increases with increasing pulse duration τP for the TiNi SMAs. The wire electrode will easily break off if the pulse duration τP raises up to 0.7-0.8 μs due to the excessive discharge energy produced in the over-long pulse duration. The maximum feeding rate of wire electrode has a reverse relationship to the product of the melting temperature (λ) and thermal conductivity (θ) of machined materials. Besides, longer pulse duration τP will have rougher WEDM surfaces of TiNi SMAs. Many electro-discharge craters and re-cast materials are observed in the WEDM surface of TiNi SMAs. The re-cast layer consists of the oxides TiO2, TiNiO3 and the deposition particles of consumed brass electrode. The thickness of re-cast layer decreases with increasing pulse duration τP. The specimen's hardness near the outer surface can reach 730 Hv for TiNi SMAs. This hardening effect arises from the formation of the oxides TiO2, TiNiO3 and the deposition particles of consumed electrode in the re-cast layer. The WEDM TiNi SMAs still exhibit a nearly perfect shape recovery at a normal bending strain, but a slightly reduced shape recovery at a higher bending strain due to the depression of the re-cast layer. All the Ti49Ni51, Ti50Ni50 and Ti50Ni40Cu10 SMAs exhibit similar WEDM characteristics although they have different crystal structures and mechanical properties at room temperature.