Effect of Post-Deformation Annealing on Structure and Properties of Nickel-Enriched Ti-Ni Shape Memory Alloy Deformed in Various Initially Deformation-Induced Structure States

Abstract

The effect of post-deformation annealing (PDA) of nickel-enriched Ti-50.9 at.% Ni shape memory alloy deformed in various initially deformation-induced structure states on the structure and properties was studied. The phase composition, temperature ranges of martensitic transformations and structure were studied using X-ray diffractometry and TEM. Mechanical and functional properties were determined using Vickers hardness tests and thermomechanical method using a bending mode for recovery strain inducing. The PDA at 430 °C (1 h) of the nickel-enriched Ti-Ni SMA with the dynamically recovered, dynamically polygonized or dynamically recrystallized structures after compressing deformation leads to the precipitation of finely dispersed (nanosized) Ti3Ni4 particles. The most significant increase of the completely recoverable strain (from 8.8 to 11.8%) and shape recovery rate (from 88 to 100%) as compared to the reference treatment is observed after PDA of the alloy with the dynamically polygonized structure.

Evolution of Structure and Properties of Nickel-Enriched NiTi Shape Memory Alloy Subjected to Bi-Axial Deformation

“…It can be consequently concluded that the dynamic recovery and polygonization processes in nickel-enriched NiTi SMA in the same thermomechanical conditions are less developed compared to those of an equiatomic NiTi alloy. This can be explained by the retarding effect of the finely dispersed Ni 4 Ti 3 phase particles that were precipitated during dynamic strain aging [ 19 , 20 ].…”

“…The present work continues the previous studies, and it is focused on the investigation of the effect of bi-axial deformation on the structural phase state and properties of bulk nickel-enriched NiTi SMA. In these alloys, deformation in the temperature range of dynamic polygonization is accompanied by dynamic strain aging with the precipitation of Ni 4 Ti 3 particles, which cannot occur in non-aging equiatomic NiTi SMA, and it has a great impact on the structure’s formation and properties [ 18 , 19 , 20 , 21 ]. The precipitated particles restrict the grain growth, however, they can lead to earlier sample destruction compared to that of equiatomic alloy and the accumulation of a lowered value of true strain.…”

Structure and Properties of TiNi Shape Memory Alloy after Quasi-Continuous Equal-Channel Angular Pressing in Various Aged States

“…It should be noted that, in itself, obtaining a mixed nanograined and nanosubgrained structure in titanium nickelide bulk samples is an important scientific and technological result [27][28][29]. During pre-aging for 1 h, the growth of Ti 3 Ni 4 phase particles proceeds less intensively than that after pre-aging for 5 h [30][31][32]. Thus, during QC ECAP, finer Ni 4 Ti 3 particles after pre-aging for 1 h provide higher resistance to grain boundary migration and the formation of a finer matrix structure, while after pre-aging for 5 h coarser and rarer Ti 3 Ni 4 particles inhibit matrix structure refinement to a lesser extent.…”

Effect of Severe Torsion Deformation on Structure and Properties of Titanium–Nickel Shape Memory Alloy

“…Binary NiTi alloys provide remarkable shape memory characteristics in combination with extraordinary mechanical properties; therefore, they are the most widely used shape memory alloys (SMAs) for industrial purposes. Severe plastic deformation (SPD) is commonly applied to NiTi SMA for the formation of an ultrafine-grained (UFG) structure, e.g., submicrocrustalline (SMCS) and nanocrystalline structures (NCSs), and to improve the combination of its properties [4][5][6][7][8][9][10]. However, the formation of an NCS in bulk NiTi samples after SPD is a difficult scientific challenge [11,12].…”