Title: Tuning martensitic transformations via coherent second phases in nanolaminates using free energy landscape engineering

Abstract

In this work we explore the possibilities and limitations of using a coherent second phase to engineer the thermo-mechanical properties of a martensitic alloy by modifying the underlying free energy landscape that controls the transformation. We use molecular dynamics simulations of a model atomistic system where the properties of a coherent, nanoscale second phase can be varied systematically. With a base martensitic material that undergoes a temperature-induced transformation from a cubic austenite to a monoclinic martensite, simulations show significant ability to engineer the transformation temperatures, from a ~50% reduction to a ~200% increase, with 50 at.% of the cubic second phase. We establish correlations between the properties of the second phase, the transformation characteristics, and the microstructure via the free energy landscape of the twophase systems. Coherency stresses have a strong influence on the martensitic variants observed and can even cause the non-martensitic second phase to undergo a transformation. Reducing the stiffness of the second phase increases the transformation strain and modifies the martensitic microstructure, increasing the volume fraction of the transformed material. This increase in transformation strain is accompanied by a significant increase in Af and thermal hysteresis, while Ms remains unaltered. Our findings on the tunability of martensiticmore » transformations can be used for informed searches of second phases to achieve desired material properties, such as achieving room temperature, lightweight shape memory alloys.« less

Authors:

Desai, Saaketh  ^[1];

• Search DOE PAGES for author "Desai, Saaketh"
• Search DOE PAGES for ORCID "0000-0003-2719-0185"

Reeve, Samuel Temple  ^[2];

• Search DOE PAGES for author "Reeve, Samuel Temple"
• Search DOE PAGES for ORCID "0000-0002-4250-9476"

Vishnu, Karthik Guda  ^[1];

• Search DOE PAGES for author "Vishnu, Karthik Guda"
• Search DOE PAGES for ORCID "0000-0002-5212-3331"

Strachan, Alejandro ^[1]

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+ Show Author Affiliations

1. Purdue Univ., West Lafayette, IN (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Fri Mar 27 00:00:00 EDT 2020

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1631091

Alternate Identifier(s):

OSTI ID: 1606605

Report Number(s):

LLNL-JRNL-781798
Journal ID: ISSN 0021-8979; 975952; TRN: US2200954

Grant/Contract Number:  

AC52-07NA27344; FG02-07ER46399

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Applied Physics

Additional Journal Information:

Journal Volume: 127; Journal Issue: 12; Journal ID: ISSN 0021-8979

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Shape memory effect; Nanomaterials; Molecular dynamics; Phase transitions; Free energy landscapes