Laboratory HPT study links kinks and dislocations to alloy strengthening

Room-temperature high-pressure torsion increased the microhardness of a near-single-phase Mg-18Y-8Ni magnesium alloy, measured in weight percent, by producing extensive kink bands, fragmented regions of its long-period stacking-ordered phase and organized dislocation structures. The laboratory study found that microhardness rose by approximately 50 HV after one-eighth turn of processing and by about 70 HV relative to the as-cast state after 20 turns, when the sample edge reached 173 HV. The alloy contained approximately 95 vol% long-period stacking-ordered, or LPSO, phase.

The experiment examined how the LPSO-dominated material responded to increasing equivalent strain under high-pressure torsion. High hydrostatic pressure and intense shear deformation induced numerous kink bands within the LPSO phase. As equivalent strain increased, the fraction of high-angle kinks rose continuously.

Portions of the ordered phase were also refined through two observed fragmentation modes: blocky fragmentation and delamination tearing. Alongside the changes within the LPSO phase, severe plastic deformation generated a high density of dislocations. Numerous dislocation substructures formed as strain increased, with initially tangled dislocations gradually becoming more organized.

The observed configurations included dislocation cells and dislocation walls. Regularly arranged dislocation walls subsequently developed into lamellar boundaries. The reported hardness gains were associated with the combined effects of dislocation strengthening and kink strengthening, rather than with a single microstructural mechanism.

The alloy also exhibited a strain-hardening exponent of 0.09, which the researchers described as excellent in comparison with conventional magnesium alloys. The results are limited to a laboratory Mg-18Y-8Ni alloy processed by high-pressure torsion at room temperature, and the principal mechanical measure reported is microhardness. The study does not establish whether the same response will occur in large components or persist under service conditions.

Its central result is a measured connection between increasing deformation, the formation of high-angle kinks and fragmented LPSO regions, the development of organized dislocation structures, and increased microhardness in this LPSO-dominated magnesium alloy.

Subject of Research: Microstructural evolution and strengthening of an LPSO-dominated magnesium alloy during high-pressure torsion

Article Title: Evolution of microstructure and mechanical properties of LPSO-dominated Mg-18Y-8Ni (wt.%) processed via high-pressure torsion

Article References: Yin, R. R., Qiao, X. G., Enikeev, N. A., Valiev, R. Z., & Zheng, M. Y. (2026). Evolution of microstructure and mechanical properties of LPSO-dominated Mg-18Y-8Ni (wt.%) processed via high-pressure torsion. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13966-4

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13966-4

Keywords: high-pressure torsion, magnesium alloy, LPSO phase, microstructure, microhardness, kink bands, dislocations, strain hardening, severe deformation, materials science, Evolution, mechanical