Evolution of the cold-rolling and recrystallization textures in FeNiCoAlNbB shape memory alloy

doi:10.1016/j.jallcom.2016.06.273

Journal of Alloys and Compounds

Volume 686, 25 November 2016, Pages 1008-1016

https://doi.org/10.1016/j.jallcom.2016.06.273 Get rights and content

Highlights

•
Cold-rolling FeNiCoAlNbB alloy with good superelasticity was investigated.
•
Evolution of cold-rolling and recrystallization textures was firstly revealed.
•
Improving mechanism on superelasticy of the severe rolling alloy was discussed.
•
Formation of textures and suppression of precipitations result in the improvement.

Abstract

The evolution of cold-rolling and recrystallization textures in the newly-developed ferrous shape memory alloy (FeNiCoAlNbB) was investigated and the improving mechanism on superelasticy of the severe cold-rolled alloy was discussed. A weaker copper rolling texture ({112}〈111〉) was formed in FeNiCoAlNbB alloy at relatively low rolling reductions (≤80%); the copper rolling texture transformed to the Goss {110}〈001〉 and brass {110}〈112〉 orientations through twinning and dislocation slipping with the rolling reductions of 90%–95%; significantly enhanced rolling texture of a strong brass orientation was obtained with the rolling reduction of 98.5%. The 98.5% cold-rolled FeNiCoAlNbB alloy after solution treatment at 1220 °C for 1 h with strong {hk0}〈001〉 recrystallization texture, followed by aging for 96 h at 600 °C exhibited good superelasticity of 3.2% with residual strain only 0.7%, and the tensile strength was approximately 960 MPa. Compared with the non-superelasticity in the as-forged FeNiCoAlNbB alloy, the considerably improving superelasticity in this alloy mainly attributes to the formation of strong favorable textures and the suppression of grain boundary precipitation.

Introduction

Shape memory alloys (SMAs), as one kind of intelligent functional materials with both shape memory effect (SME) and superelasticity (SE) [1], [2], [3], can be divided into three groups: NiTi-based [4], Cu-based [5] and Fe-based [6]. NiTi-based alloys are the most well-known SMAs owing to their excellent shape memory properties and corrosion resistance [7], [8]. However, their low cold-workability and high processing cost have limited the further large-scale application. In contrast, with high strength, excellent cold workability and low cost etc., the newly-developed Fe-based shape memory alloys enjoy a broad application prospect in industry [9].

Particularly the thermoelastic martensitic transformation in FeNiCoAlTaB alloy discovered by Kainuma et al. [10], the alloy showed huge superelastic strain, which was almost twice the maximum superelastic strain obtained in the NiTi-based alloy. Centering on this found, wide attentions and much research have recently been aroused and launched [11], [12], [13], [14], [15]. Afterwards, Kainuma’s group developed a new shape memory alloy FeNiCoAlNbB alloy with more cost-efficient and low-melting element Nb instead of Ta, and this alloy also showed superelasticity over 5% [16].

Relevant studies on FeNiCo-based SMAs fabricated by rolling + recrystallizing have confirmed that an excellent superelastic performance can be obtained only with cold-rolling reduction above 98% followed by advisable solution and aging treatments. The internal machnism of this critical reduction is not clear at present. Therefore, it is indicated that rolling reduction significantly influences the microstructure and superelasticity of the alloy. To reveal the improving mechanism on the superelastic properties of FeNiCo-based alloys with severe rolling deformation, clarifying the rolling and recrystallization texture evolution in these alloys is fundamentally important.

Thus, in the present paper, the effects of rolling deformation on microstructure and texture after cold-rolling and annealing in FeNiCoAlNbB alloy were investigated.

The reasons of excellent superelasticity at severe rolling deformation were also discussed, which could offer guidance for efficient manufacture of the alloy.

Section snippets

Experimental procedures

Pure iron (99.9 wt%), pure nickel (99.9 wt%), pure cobalt (99.9 wt%), pure aluminum (99.9 wt%), pure niobium (99.9 wt%) and ferroboron (17.5 wt% boron content, iron and boron content 99.95 wt%) were used as raw materials. Referring to the research results given by Omori et al. [16], the Fe-28Ni-17Co-11.5Al-2.5Nb-0.05B (at.%) alloy ingot was first induction melted and casted in a vacuum furnace. Its chemical composition is shown in Table 1.

The as-cast ingot was then homogenized and forged in the

Microstructure and texture evolution in cold-rolled alloy

Fig. 2 shows the microstructure of the as-forged and cold-rolled alloy with various rolling reductions of 60%,80%,90%,95% and 98.5%. It can be seen that the microstructure of the as-forged specimen was dominated by uniform equiaxed grains with an average size of ∼100 μm. After over 60% of the rolling deformation, grains were long rolled and increasing rolling deformation intensified the grain deformation and refinement. Severely fragmented and much finer microstructure developed in the 98.5%

Analysis on cold-rolling and recrystallization texture evolution

Polycrystalline deformation gives rise to the considerable grain rotations toward particular orientations inside alloys, thus various rolling texture types are closely related to main mechanisms of rolling deformation.

In the FeNiCoAlNbB alloy with relatively low stacking fault energy (SFE), dislocation slip and mechanical twinning are the two main deformation mechanisms. As for rolling reduction ≤80%, alloy deformation is characterized by normal dislocation slipping at active {111}〈110〉

Conclusions

(1)
At relatively lower cold rolling reduction (≤80%), a weak copper texture appeared in the FeNiCoAlNbB alloy. Stronger brass and Goss textures were formed in the alloy with cold-rolling reduction of 90–95%. With the cold-rolling reduction up to 98.5%, the alloy is characterized by the highly enhanced dominant brass texture, leading to the formation of strong (023) [100], (032) [100] and Goss textures after recrystallization.
(2)
The 98.5% cold-rolled FeNiCoAlNbB alloy after solution treatment at

Acknowledgements

This work was supported by the Major States Basic Research Development Program (973 Program) of China under contract number 2011CB606300, National Natural Science Foundation of China (No. 51504023), Fundamental Research Funds for the Central Universities (No. FRF-TP-15-051A2) and State Key Lab of Advanced Metals and Materials Foundation (2014-Z06).

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Evolution of the cold-rolling and recrystallization textures in FeNiCoAlNbB shape memory alloy

Highlights

Abstract

Introduction

Section snippets

Experimental procedures

Microstructure and texture evolution in cold-rolled alloy

Analysis on cold-rolling and recrystallization texture evolution

Conclusions

Acknowledgements

Mater. Des.

Acta Mater.

J. Alloys Compd.

Acta Mater.

Scr. Mater.

Acta Mater.

Scr. Mater.

Int. J. Mech. Sci.

Acta Mater.

Acta Metall. Mater.