Explaining absence of texture development in cold rolled two-phase Zr–2.5 wt% Nb alloy

Abstract

In the present study, two distinct starting microstructures of Zr-2.5 wt% Nb have been used: (1) single-phase α hcp martensitic structure; and (2) two-phase, 10% bcc β and rest hcp α, Widmanstätten structure. In the second case, two types of α were present-near grain boundary predominantly single-phase α (about 5% of the total α) and α plates in an apparently continuous β matrix. Both (1) and (2) had similar starting crystallographic texture of the hcp α phase and were deformed by unidirectional and cross rolling. In the two-phase structure the changes in the bulk texture on cold rolling was found to be insignificant, while in the single-phase material noticeable textural changes were observed. Taylor type deformation texture models predicted textural changes in single-phase structure but failed to predict the observed lack of textural development in the two-phase material. Microtexture observations showed that α plates remained approximately single crystalline after cold rolling, while the β matrix underwent significant orientational changes. Relative hardening, estimated by X-ray peak broadening, was observed mainly in β phase; while aspect ratio of α plates remained unchanged with cold rolling-indicating absence of effective macroscopic strain in the hcp α plates. Based on microstructural and microtextural observations, a simple model is proposed in which the plastic flow is mainly confined to the β matrix within which the α plates are subjected to 'in-plane rigid body rotation'. The model explains the observed lack of textural developments in the two-phase structure.

The effect of cooling rates on the microstructure and mechanical properties of thermo-mechanically processed Ti–Al–Mo–V–Cr–Fe alloys

“…There are two reasons for this observation: (i) the bcc crystal structure of β phase have more active slip systems than the hcp α phase. Thus, dislocation assisted slip activities during deformation at 1073 K occurs mostly in the β phase [65]. In addition, (ii) the remaining β phase is subjected to two deformations at 1173 K and 1073 K, whereas the α phase formed during holding at 1073 K is subjected only to single deformation (1073 K) and the α phase formed during cooling is not deformed.…”

Heterogeneous Deformation in Single‐Phase Zircaloy 2

“…For example, in any commercial alloy the hard constituent or dispersoid particles are often non-shearable and strain is accommodated mainly by the matrix phase [12]. In two-phase Zr [14], the softer second phase of only 15% of the total volume can effectively accommodate the entire strain.Zircaloy 2, the chemical composition of which is given in Table 1, is used in nuclear power reactors for tubes and claddings [15]. Its typical microstructure involves equiaxed or elongated grains (based on prior processing) of a hexagonal close packed (hcp) structure, with submicron intermetallic precipitates.…”

“…1a), was cold rolled in a laboratory rolling mill to 20% and 50% reductions. Samples from the mid-thickness sections of the rolled plates were electropolished using standard techniques [14] and then subjected to electron backscattered diffraction (EBSD) measurements and X-ray diffraction (XRD). The EBSD were performed using a TSL-OIM package on a Fei quanta-200 HV scanning electron microscope (SEM), while a panalytical MRD system was used for XRD measurements.…”

“…Real heterogeneous deformation, where different grains/phases of the microstructure have remarkably different strains, has been reported [12][13][14] only in multi-phase alloys. For example, in any commercial alloy the hard constituent or dispersoid particles are often non-shearable and strain is accommodated mainly by the matrix phase [12].…”

“…For example, in any commercial alloy the hard constituent or dispersoid particles are often non-shearable and strain is accommodated mainly by the matrix phase [12]. In two-phase Zr [14], the softer second phase of only 15% of the total volume can effectively accommodate the entire strain.…”