New insights on tensile plasticity of ultrafine-grained metallic materials

ABSTRACT

The tensile properties of TiNi_43.5Fe_6.5 alloy samples having different grain sizes (0.16, 0.35, 1.7, 2.3, and 3.9 μm) and fabricated by severe plastic deformation and annealing were investigated. It was observed that both the strength and the elongation of the alloy increase with a decrease in the grain size until the average size reaches 1.7 μm. However, for average grain sizes smaller than 1.7 μm, the elongation decreases continuously with further grain refinement. On the other hand, the strain-hardening rate does not decrease with the decrease in plasticity but instead increases slightly. The poor ductility of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is accompanied by a high degree of strain hardening. This newly observed ductility behaviour of the ultrafine-grained TiNi_43.5Fe_6.5 alloy is elucidated by characterising the intragranular and grain boundaries.

KEYWORDS:

• Ultrafine-grained metallic materials
• amorphous crystallisation
• strain hardening
• ductility
• tensile properties

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Yongqiang Wang http://orcid.org/0000-0003-1082-046X

Additional information

Funding

This work was supported by State Key Lab of Advanced Metals and Materials [Grant No. 2016-Z02].