- •Microstructure and martensitic transformation and mechanical properties of cast Ni-rich NiTiCo shape memory alloys Nader El-Bagoury 1, 2
- •Introduction
- •Experimental procedures
- •Results and discussion
- •Microstructure
- •Fig. 1 Microstructure of investigated Ni51-xTi49Cox alloys.
- •Ni51Ti49Co0 alloy (b) Ni50.5Ti49Co0.5 alloy
- •Ni49.5Ti49Co1.5 alloy (d) Ni47Ti49Co4 alloy
- •Fig. 3 Ti2Ni ratio versus Co content in NiTi alloy.
- •Fig. 4 Ni3Ti2 precipitates in the microstructure of Ni51Ti49Co0 alloy.
- •Ni3Ti2 precipitates in small round shape.
- •Higher magnification of (a) Ni3Ti2 precipitates in needle like-shape.
- •Fig. 5 Colonies of NiTi phase inside Ti2Ni precipitates in the microstructure of Ni51Ti47Co4 alloy.
- •Ni51Ti49Co0 alloy (b) Ni50.5Ti49Co0.5 alloy
- •Fig. 6 edx of phases in Ni52Ti48Co0
- •Fig. 7 X ray diffraction patterns for NiTiCo shape memory alloys.
- •Phase transformation
- •Fig. 8 Martensitic and austenitic transformation temperatures of Ni50.5Ti49Co0.5 alloy.
- •Mechanical properties
- •Fig. 9 Hardness measurements versus Co content in NiTi alloy.
- •Conclusions
- •References
Conclusions
The effect of Co additions on the microstructure, martensitic transformation and mechanical properties of Ni51-xTi49Cox shape memory alloy was investigated and the results are as follows:
In addition to martensite phase in both Ni51Ti49Co0 and Ni50.5Ti49Co0.5 alloys, the microstructure contains B2 and NiTi intermetallic compound phases. However the microstructure of both Ni49.5Ti49Co1.5 and Ni47Ti49Co4 alloys consists of martensite and Ti2Ni phase only.
Ni3Ti2 phase was precipitated only in the microstructure of Ni51Ti49Co0 alloy.
The volume fraction of Ti2Ni phase sharply decreased by the addition of 0.5 and 1.5 at% Co before rising again with 4 at% Co content.
Most of Ti2Ni phase in the microstructure of Ni49.5Ti49Co1.5 alloy precipitates in flakes shape.
The martensitic-austenitic phase transformation temperature increases as the Co content increase.
Hardness value was slightly improved by adding 0.5 at% Co to Ni51Ti49Co0 alloy. On the other hand it was dramatically deteriorated by more additions of Co.
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