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Title: Hardenability and microstructural evolution of a precipitation strengthened Ni50Ti21Hf25Al4 alloy

Journal Article · · Journal of Alloys and Compounds
 [1];  [1];  [1];  [1];  [2];  [3];  [1];  [4]
  1. Univ. of Florida, Gainesville, FL (United States)
  2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
  3. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
  4. Univ. of Pittsburgh, PA (United States)

NiTi-based quaternary alloys are used in a variety of mechanical components, such as bearings, actuators, and dampers, owing to their good hardenability, wear resistance, and corrosion resistance. Additionally, one of the most notable characteristics of NiTi-based alloys is their shape memory effect and pseudoelastic properties. Connecting the macroscopic processing parameters employed in the design of new intermetallic alloys to the nanoscale structural characteristics dictating their behavior is crucial for improving their mechanical properties and expanding the spectrum of potential applications. Here, in this work, an arc melted Ni50Ti21Hf25Al4 (at%) alloy was solution treated at 1050 °C followed by quenching and aging at 600 °C to investigate the effect of aging time on the microstructure and mechanical properties. Two types of nano-sized precipitates were observed and determined as face-centered orthorhombic H-phase (TiHf)Ni and L21 Heusler precipitates Ni2TiAl. The morphology and orientation of the H-phase were investigated using scanning and transmission electron microscopy (SEM and TEM), elucidating the coarsening kinetics and strengthening contribution of that phase to the intermetallic mechanical behavior. Following coarsening, the presence of Heusler nanoprecipitates was detected under overaged conditions through TEM imaging and nanobeam electron diffraction patterns. A peak hardness condition of 756 HV was achieved after 70 h of aging, indicating that the co-precipitation of H-phase and Heusler precipitates through a well-designed aging treatment can lead to optimal mechanical performance, thus elevating the alloy’s potential as a viable material for industrial applications.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
2491458
Journal Information:
Journal of Alloys and Compounds, Journal Name: Journal of Alloys and Compounds Vol. 1010; ISSN 0925-8388
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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