Precipitation kinetics of Ti3Ni4 in polycrystalline Ni-rich TiNi alloys and its relation to abnormal multi-stage transformation behavior
✍ Scribed by G. Fan; Y. Zhou; W. Chen; S. Yang; X. Ren; K. Otsuka
- Publisher
- Elsevier Science
- Year
- 2006
- Tongue
- English
- Weight
- 133 KB
- Volume
- 438-440
- Category
- Article
- ISSN
- 0921-5093
No coin nor oath required. For personal study only.
✦ Synopsis
Normally, martensitic transformation occurs in two stages (B2-R-B19 ) in aged Ni-rich TiNi alloys. But a three-stage martensitic transformation was also reported. The origin of this abnormal transformation behavior has remained controversial, and in particular it is difficult to understand why in some cases the three-stage transformation occurs while in other cases normal two-stage transformation appears. Very recently by considering the kinetics features of Ti 3 Ni 4 precipitation in polycrystalline Ni-rich TiNi, we propose a general mechanism, which is able to explain not only abnormal three-stage transformation but also normal two-stage transformation. In the present study, we made further experimental effort to critically verify the proposed mechanism by studying the transformation behavior of low Ni-rich polycrystals and intermediate Ni-rich polycrystals. We have found that low Ni-rich polycrystals exhibit three-stage transformation and the number of transformation peaks is independent of aging time; intermediate Ni-rich samples exhibit three-stage transformation after short time aging and two-stage transformation after longer time aging; but all the high Ni-rich samples show two-stage transformation, being independent of aging time. These results are consistent with our mechanism that different transformation behaviors are a result of competition between preferential grain boundary precipitation of Ti 3 Ni 4 particles and a tendency for homogeneous precipitation when supersaturation of Ni is large.