Details
| Original language | English |
|---|---|
| Pages (from-to) | 3205-3217 |
| Number of pages | 13 |
| Journal | Acta materialia |
| Volume | 49 |
| Issue number | 16 |
| Publication status | Published - 20 Sept 2001 |
| Externally published | Yes |
Abstract
We study the instrumented Vickers micro-indentation of single-crystal Ti-50.9 at% Ni shape-memory alloys with systematically varied surface normal orientations ([100], [210], [111] and [221]) and Ti3Ni4 precipitate sizes (0 nm, 10 nm, 50 nm, 100 nm, 300 nm and 500 nm). Based on transmission electron microscopy observations, indentation of solutionized NiTi induces inelastic deformation via dislocation activity and a stress-induced martensitic transformation. The room-temperature hardness, Hv, and recoverable energy, Er, of NiTi are shown to be a maximum for very small precipitate sizes, decrease for intermediate precipitate sizes, and increase for large precipitate sizes. The maximization of Hv and Er at small precipitate sizes (10 nm) is attributed to the relatively high resistance to both dislocation motion and a recoverable stress-induced martensitic transformation. The decreases in Hv and Er at intermediate precipitate sizes (50-300 nm) are attri buted to a decrease in the resistance to dislocation motion and a measured increase in the transformation temperatures with respect to the indentation temperature. The increases in Hv and Er at large precipitate sizes (500 nm) are attributed solely to measured decreases in the transformation temperatures with respect to the indentation temperature, since the resistance to dislocation motion remains constant as the precipitates grow from 300 nm to 500 nm. For nearly all heat treatments, the [100] and [221] surfaces demonstrate the highest and lowest values of Hv and Er, respectively, an effect attributed primarily to orientation of favorable slip systems.
Keywords
- Annealing, Dislocations, Hardness testing, NiTi shape-memory alloys, Phase transformations, Transmission electron microscopy (TEM)
ASJC Scopus subject areas
- Materials Science(all)
- Electronic, Optical and Magnetic Materials
- Materials Science(all)
- Ceramics and Composites
- Materials Science(all)
- Polymers and Plastics
- Materials Science(all)
- Metals and Alloys
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In: Acta materialia, Vol. 49, No. 16, 20.09.2001, p. 3205-3217.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Instrumented micro-indentation of NiTi shape-memory alloys
AU - Gall, K.
AU - Juntunen, K.
AU - Maier, H. J.
AU - Sehitoglu, H.
AU - Chumlyakov, Y. I.
N1 - Funding Information: The work of Y. Chumlyakov is supported by grants from the Russian Fund for Basic Researches, grant # 02-95-00350, MOPO (MGTU, Moscow) and from fund 99-03-32579a. The authors gratefully thank A. Lerche for her meticulous TEM work. We also thank Subash Gupta at Special Metals for providing the NiTi material and DSC results on the solutionized single crystals. Mark Stavig at Sandia National Laboratory, Mark Polinsky at Memry Corporation, and Stephen Kelley at NREL are thanked for providing DSC results on the aged materials.
PY - 2001/9/20
Y1 - 2001/9/20
N2 - We study the instrumented Vickers micro-indentation of single-crystal Ti-50.9 at% Ni shape-memory alloys with systematically varied surface normal orientations ([100], [210], [111] and [221]) and Ti3Ni4 precipitate sizes (0 nm, 10 nm, 50 nm, 100 nm, 300 nm and 500 nm). Based on transmission electron microscopy observations, indentation of solutionized NiTi induces inelastic deformation via dislocation activity and a stress-induced martensitic transformation. The room-temperature hardness, Hv, and recoverable energy, Er, of NiTi are shown to be a maximum for very small precipitate sizes, decrease for intermediate precipitate sizes, and increase for large precipitate sizes. The maximization of Hv and Er at small precipitate sizes (10 nm) is attributed to the relatively high resistance to both dislocation motion and a recoverable stress-induced martensitic transformation. The decreases in Hv and Er at intermediate precipitate sizes (50-300 nm) are attri buted to a decrease in the resistance to dislocation motion and a measured increase in the transformation temperatures with respect to the indentation temperature. The increases in Hv and Er at large precipitate sizes (500 nm) are attributed solely to measured decreases in the transformation temperatures with respect to the indentation temperature, since the resistance to dislocation motion remains constant as the precipitates grow from 300 nm to 500 nm. For nearly all heat treatments, the [100] and [221] surfaces demonstrate the highest and lowest values of Hv and Er, respectively, an effect attributed primarily to orientation of favorable slip systems.
AB - We study the instrumented Vickers micro-indentation of single-crystal Ti-50.9 at% Ni shape-memory alloys with systematically varied surface normal orientations ([100], [210], [111] and [221]) and Ti3Ni4 precipitate sizes (0 nm, 10 nm, 50 nm, 100 nm, 300 nm and 500 nm). Based on transmission electron microscopy observations, indentation of solutionized NiTi induces inelastic deformation via dislocation activity and a stress-induced martensitic transformation. The room-temperature hardness, Hv, and recoverable energy, Er, of NiTi are shown to be a maximum for very small precipitate sizes, decrease for intermediate precipitate sizes, and increase for large precipitate sizes. The maximization of Hv and Er at small precipitate sizes (10 nm) is attributed to the relatively high resistance to both dislocation motion and a recoverable stress-induced martensitic transformation. The decreases in Hv and Er at intermediate precipitate sizes (50-300 nm) are attri buted to a decrease in the resistance to dislocation motion and a measured increase in the transformation temperatures with respect to the indentation temperature. The increases in Hv and Er at large precipitate sizes (500 nm) are attributed solely to measured decreases in the transformation temperatures with respect to the indentation temperature, since the resistance to dislocation motion remains constant as the precipitates grow from 300 nm to 500 nm. For nearly all heat treatments, the [100] and [221] surfaces demonstrate the highest and lowest values of Hv and Er, respectively, an effect attributed primarily to orientation of favorable slip systems.
KW - Annealing
KW - Dislocations
KW - Hardness testing
KW - NiTi shape-memory alloys
KW - Phase transformations
KW - Transmission electron microscopy (TEM)
UR - http://www.scopus.com/inward/record.url?scp=0035922148&partnerID=8YFLogxK
U2 - 10.1016/S1359-6454(01)00223-3
DO - 10.1016/S1359-6454(01)00223-3
M3 - Article
AN - SCOPUS:0035922148
VL - 49
SP - 3205
EP - 3217
JO - Acta materialia
JF - Acta materialia
SN - 1359-6454
IS - 16
ER -