Variant selection in surface martensite.

Area of Science:

• Materials Science
• Crystallography
• Phase Transformations

Background:

• Isothermal martensite formation in Fe-Ni alloys is crucial for material properties.
• Understanding variant selection in martensite is key to controlling microstructure.
• Surface martensite exhibits unique crystallographic features and transformation behaviors.

Purpose of the Study:

• To model and compare different theoretical descriptions of variant selection in surface martensite.
• To evaluate the ability of various models to predict experimental observations.
• To identify the most suitable model for explaining the {225} habit plane and twinning mechanisms.

Main Methods:

• Modeling martensitic phase transformation using phenomenological theory of martensite crystallography (PTMC).
• Applying Jaswon and Wheeler distortion model.
• Utilizing continuous face-centered cubic (FCC) to body-centered cubic (BCC) distortion model.
• Comparing model predictions with experimental observations of surface martensite in Fe-30%Ni.

Main Results:

• All tested models predicted variant selection in isothermal martensite.
• The Jaswon and Wheeler distortion and continuous FCC-BCC distortion models provided superior predictions.
• These advanced models accurately accounted for the {225}_γ habit plane and twin-related variant pairing accommodation mechanism.

Conclusions:

• The Jaswon and Wheeler and continuous FCC-BCC distortion models are highly effective for describing variant selection in surface martensite.
• These models offer deeper insights into the crystallographic and mechanistic aspects of martensitic transformations.
• Accurate modeling is essential for tailoring material properties through controlled martensite formation.