Effect of Ni4Ti3 precipitation on martensitic transformation in Ti-Ni

• Published in: Acta materialia Vol. 58; no. 20; pp. 6685 - 6694
• Main Authors: ZHOU, N, SHEN, C, WAGNER, M. F.-X, EGGELER, G, MILLS, M. J, WANG, Y
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01-12-2010
• Subjects: Applied sciences; Exact sciences and technology; Intermetallic compounds; Martensitic transformations; Metals. Metallurgy; Nickel; Nucleation; Precipitates; Precipitation; Stress concentration; Stresses; Titanium base alloys; Shape memory alloys; Intermetallic compound; Heterogeneous nucleation; Modeling; Heterogeneous nucleation of phase transformations; Phase transformation; Precipitation; Phase field models; Shape memory alloy; Internal stress; Simulation; Internal stresses; Titanium; Martensitic transformation; Nickel; Microstructure
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2010.08.033

Precipitation of Ni4Ti3 plays a critical role in determining the martensitic transformation path and temperature in Ni-Ti shape memory alloys. In this study, the equilibrium shape of a coherent Ni4Ti3 precipitate and the concentration and stress fields around it are determined quantitatively using the phase field method. Most recent experimental data on lattice parameters, elastic constants, precipitate-matrix orientation relationship and thermodynamic database are used as model inputs. The effects of the concentration and stress fields on subsequent martensitic transformations are analyzed through interaction energy between a nucleating martensitic particle and the existing microstructure. Results indicate that R-phase formation prior to B19a super(2) phase could be attributed to both direct elastic interaction and stress-induced spatial variation in concentration near Ni4Ti3 precipitates. The preferred nucleation sites for the R-phase are close to the broad side of the lenticular-shaped Ni4Ti3 precipitates, where tension normal to the habit plane is highest, and Ni concentration is lowest.