Deformation of Ti-6Al-4V micro-pillars with different β phase contents

Wu, Zhaoxuan (2023). Deformation of Ti-6Al-4V micro-pillars with different β phase contents. University of Birmingham. Ph.D.

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Abstract

Compressions of Ti-6Al-4V micro-pillars with increasing number of α/β interfaces or β fillets, orientated for prismatic <a\(_2\)>, prismatic<a\(_3\)>, pyramidal <a\(_3\)>, basal <a\(_1\)> and basal <a\(_3\)> slips have been carried out to study the role of α/β interface and its number in the plastic deformation of the alloy.

Micro-compression has been used to quantify the effect of the number of interfaces on CRSS for different slip systems. Following that, SEM was used to observe the distribution of shear bands across the pillars while TEM has been used to examine the interaction between dislocations and interfaces assisted with FIB sample preparation.

The strengthening effect of α/β interface has been considered in light of the lattice parameter mismatch \(\tau_{misfit}\) Koehler stress \(\tau_k\) due to shear modulus mismatch, interface stress \(\tau_f\) related to the interface energy and interface strain tensor, and \(w\) interaction \(\tau_w\) that is slip system change from one phase to another. The total CRSS of micropillars was estimated by considering the contributions from α and β phases based on their volume fractions and α/β interface strengthening effect.

The interface strengthening estimated for prismatic <a\(_2\)> and <a\(_3\)> slips are 46 MPa and 18 MPa respectively, close to the experimental determined values of 49 MPa and 20 MPa. There is a significant strengthening effect of α/β interface on the CRSS values.

Slip band nucleation, formation and distribution are strongly affected by the number of α/β interfaces or β fillets. More shear bands nucleate and form, and their distribution becomes more homogeneous with increasing the number of interfaces. Likely caused by stress and strain localization as well as the dislocation pile-up at interfaces.

For the micropillars containing 2 β fillets, the CRSS of prismatic <a\(_3\)> slip is 7-9% higher than that of prismatic <a\(_2\)> slip.

For the pillars containing multiple (~10) β fillets, the CRSS value for basal <a\(_3\)> slip, which reaches 699 MPa, is higher than that for basal <a\(_1\)> and <a\(_3\)> slips which are all much higher than the those reported for the micro-pillars without the α/β interface.

Pillar size effect on the CRSS value is sensitive to the number of α/β interfaces. The percentage increment of CRSS values from 10 μm to 5 μm sized pillars drops significantly from 14.2% to 3.4% with increasing the number of β fillets in the current work.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):