Studies on TiNiSi Ternary Shape Memory Alloys
Date Issued
2014
Date
2014
Author(s)
Lee, Tsung-Ching
Abstract
In this study, four kinds of Ti-rich and Ni-rich TiNiSi ternary shape memory alloys (SMAs) are investigated for their precipitates, transformation behavior and microstructure. The effects of aging, thermal cycling and cold working on their transformation temperatures are also studied. The Si added in TiNi SMAs has a tendency to substitute for the Ni. But the solubility of Si in the TiNi matrix is low, which gives a significant TiNi-silicides precipitation. Four different TiNi-silicides are observed, in which Ti5Ni4Si and Ti2Ni3Si are formed in three Ni-rich TiNiSi SMAs, while Ti2Ni and Ti5Si3 are found in a Ti-rich TiNiSi SMA. The TiNiSi SMAs exhibit a B2↔B19’ transformation after solution treatment, and their transformation temperatures are related to the Ti/(Si+Ni) ratio in the matrix. The tanδ values of TiNiSi SMAs reach 0.098~0.162, which indicate that these SMAs exhibit excellent damping performance. Transformation temperatures of TiNiSi SMAs decrease 10~20℃ after 100 thermal cycling, but they still remain B2↔B19’. Due to different precipitation rates occurred at the grain boundaries and inside the grains, the Ni-rich Ti48Ni50Si2 SMA behaves a multi-stage transformation after 300~550℃ aging. Furthermore, the precipitation hardening of Ti48Ni50Si2 SMA depends on the size and distribution of Ti3Ni4 precipitates, and the maximum hardness of 422Hv is found after the SMA is aged at 300℃×24hr, in which the recovery can reach 96.5%. Under 350~650℃ aging temperature, the DSC results show the appearance of the R phase peak in 20% and 40% cold-rolled Ti49Ni50Si1 and Ti49.5Ni50Si0.5 SMAs, respectively, due to the coherent strain around precipitations and the existing residual strain after cold working.
Subjects
鈦鎳矽形狀記憶合金
多階相變態
Ti3Ni4析出物
時效處理
制震能
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-103-R01527006-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):f686ef48a6cd6c825a78fa1eadfd5111