Stress-induced strain glass to martensite (R) transition in a Ti50Ni44.5

Abstract

Strain glass (STG) in Ni-rich binary Ti-Ni possesses an R-like (rhombohedral) local strain order, but it transforms into B19' martensite under stress. It remains a puzzle why the local strain order in STG yields a different long-range strain order.Here, we systematically investigated a ternary Ti 50 Ni 44.5 Fe 5.5 STG, which exhibited the same STG features as the binary STG, and the local strain order is also an R-like one.Being different from the binary STG, under stress this ternary STG transforms into a normal R-phase rather than B19'. By considering that both systems have bi-instability with respect to both R and B19' martensites in the schematic free energy landscape, we provide a unified explanation for the different products of the stress-induced STG to martensite (STG-M) transition between Ti-Ni binary system and the present ternary system. We show that the difference stems from the competing thermodynamic stability between R-phase and B19' martensites.2

Influence of Zr content on β-phase stability in α-type Ti–Al alloys

“…According to the alculations and Although the β-martensite transformation in Ti alloy is dependant on the stability of β phase, it is also dependant on the formation of martensite. Previous reports [34][35][36] showed that the addition of Co or Mn to Ti alloy forms the formation of point defects and local stresses which suppress the formation of long range ordered martensites and even form glass state instead of martensitic phase. According to the Fleischer theory, the local stress resulted from alloying elements can be expressed as AG c…”

The transitions from glassy state to long‐range‐ordered state in ferroic glasses

“…This is a glassy state of local strain order, being analogous to the ferroelectric relaxor. Similar to the external‐field‐induced relaxor to normal ferroelectric transition, a stress‐induced transition from strain glass to long‐range strain‐ordered martensite has also been found in strain‐glass alloys .…”

“…Strain glass was recently found in several ferroelastic/martensite alloys by introducing point defects beyond a critical value . This is a glassy state of local strain order, being analogous to the ferroelectric relaxor.…”

Lattice deformations in quasi‐dynamic strain glass visualised and quantified by aberration corrected electron microscopy

“…. In recent years, a new glass state was observed in some martensitic and ferroelastic systems, including the widely used Ni–Ti , Ni–Ti–Fe , Ti–Pd–Cr , and Ni–Co–Mn–Ga . The strain glass state, considered to be a conjugate state to the martensite and ferroelastic state, has features of all glass behaviours such as dynamic freezing, ergodicity breaking and existence of local strain .…”

“…X‐ray diffraction (XRD) investigations show there is no average structure change or macroscopic symmetry change during the strain glass transition . Several transmission electron microscopy (TEM) investigations have been carried out in order to reveal the details of the strains, however, so far these have only revealed the existence of nanodomains or diffuse superlattice scattering in electron diffraction patterns, without providing true structural detail at the atomic level .…”