Correlating microstructure and superelasticity of directed energy deposition additive manufactured Ni-rich NiTi alloys

JOURNAL OF ALLOYS AND COMPOUNDS

卷:739

Article

Hamilton, Reginald F.^1,2  Bimber, Beth A.¹  Palmer, Todd A.^1,3 

[1] Penn State Univ, Engn Sci & Mech Dept, University Pk, PA 16802 USA

[2] Penn State Univ, Mat Res Inst, University Pk, PA 16802 USA

[3] Penn State Univ, Appl Res Lab, University Pk, PA 16802 USA

关键词: Metals and alloys;    Laser processing;    Microstructure;    Mechanical properties;    Shape memory;    Scanning electron microscopy;   

DOI  :  10.1016/j.jallcom.2017.12.270

来源: Elsevier

【 摘 要 】

Laser-based directed energy deposition (LDED) additive manufacturing of Ni-rich NiTi shape memory alloys was shown to produce inhomogeneous precipitate morphologies and characteristic grain structures consisting of columnar grains coexisting with equiaxed and subgrain structures. Post-processing solutionizing and aging heat treatments impacted microstructure and martensitic phase transformation (MT) responses underpinning superelastic shape memory responses. A solution treatment of 950 degrees C for 24 h was found to produce a uniform composition of the B2 austenite parent phase without affecting the coexistence of columnar and equiaxed substructures. Aging the solution treated material brought about a spatially uniform Ni4Ti3 precipitate morphology. Due to the uniform morphology, an underlying austenite-martensite interface motion accompanies the compressive stress-induced MT (SIMT). Reversible interface motion underpinned the compressive superelastic response for the solutionized and aged condition. On the other hand, strain concentrations existed at different spatial locations in the as built condition as well as when the as built material was aged. The stark contrasts in the SIMT exposed precipitate morphology as a controlling factor in tailoring the superelastic response of Ni-rich NiTi SMAs fabricated by LDED. (c) 2018 Elsevier B.V. All rights reserved.

【 授权许可】

Free