High Temperature Material Processes (An International Quarterly of High-Technology Plasma Processes) An International Journal

ISSN for PRINT: 1093-3611

For Online Access

Best Paper Award Selection - Editorial Board Site

2000, Volume4

Issue 4

132 pages

Issue price - $144.00

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

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 τ_P for the TiNi SMAs. The wire electrode will easily break off if the pulse duration τ_P 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 τ_P 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 τ_P. 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.

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