Experimental and molecular dynamics studies of phase transformations during cryogenic thermal cycling in complex TiNi-based crystalline/amorphous alloys

In TiNi-based crystalline/amorphous alloys, superelasticity in crystalline phase coordinating the dislocation sinking in amorphous phase lead to a high ductility and outstanding anti-fatigue properties. We performed cryogenic thermal cycling, between 77 K and 303 K, on the complex TiNi-based alloys consisting of a major B2 austenite phase, an interdendritic amorphous phase, and a minor B190 martensite phase in the as-cast state. The critical martensitic phase transformation stress (sigma(m)) increased with the number of thermal cycles, reaching a maximum at 10 cycles. The initial B19' martensite which is confined in the amorphous phase transformed to B2 austenite due to thermal induced stable transformation. A lamellar structure of alternating amorphous and crystalline layers dominantly grew into the amorphous matrix as a consequence of the thermal fatigue during the cryogenic thermal cycling. Initial cell for the molecular dynamic simulations was carefully prepared to contain three different phases. Cyclic compressive loading and cryogenic thermal cycling simulations were consistent with the experimental results. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In TiNi-based crystalline/amorphous alloys, superelasticity in the crystalline phase and dislocation sinking in the amorphous phase lead to high ductility and outstanding anti-fatigue properties. Cryogenic thermal cycling experiments on complex TiNi-based alloys showed an increase in critical martensitic phase transformation stress with the number of cycles, reaching a maximum at 10 cycles, and initial B19' martensite transformed to B2 austenite due to thermal induced stable transformation. Thermal fatigue during cryogenic cycling resulted in a lamellar structure of alternating amorphous and crystalline layers growing dominantly into the amorphous matrix.