Abstract
Microstructural stability is a critical factor to consider when designing new alloys for high-temperature applications. An Al-Cu alloy with Mn and Zr additions has recently been developed to withstand extended exposures of up to 350 °C. The addition of Mn in combination with Zr and their segregation to precipitate interfaces play a significant role in stabilizing the metastable θ′ precipitates responsible for the alloy's hardness; however, adding Zr and Mn separately only improves the stability to 200 °C and 300 °C, respectively. To this end, the effect of the synergistic additions on interfacial structure and chemistry was studied in detail using atom probe tomography (APT) and scanning transmission electron microscopy (STEM) for Al-Cu-Mn-Zr/Ti-containing alloys subjected to long-term annealing (up to 2,100 h) in the critical temperature range, 300 °C and 350 °C, to investigate the role of Zr/Ti in increasing the θ′-precipitate stability. The APT and STEM results reveal that Mn additions stabilize θ′ long enough for the slower diffusing Zr atoms to segregate to coherent θ′ interfaces that eventually create a θ′/ L12-Al3(Zrx,Ti1-x) co-precipitate structure. The co-precipitate is highly stable, as shown by density functional theory calculations, and is a key factor that governs microstructural stability beyond 300 °C. This study reveals how solute additions with different stabilization mechanisms can work in concert to stabilize a desired microstructure, and the results provide insights that can be applied to other high-temperature alloy systems.
| Original language | English |
|---|---|
| Pages (from-to) | 577-586 |
| Number of pages | 10 |
| Journal | Acta Materialia |
| Volume | 194 |
| DOIs | |
| State | Published - Aug 1 2020 |
Funding
This research was supported by the DOE Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office, Propulsion Materials Program and the DOE Basic Energy Sciences, Materials Sciences and Engineering Division. APT was conducted at ORNL's Center for Nanophase Materials Sciences (CNMS), which is a US DOE Office of Science User Facility. The authors appreciate the support provided by the Oak Ridge Leadership Computing Facility at the ORNL. Earlier research was supported by the Department of Energy, Laboratory Directed Research and Development program at Oak Ridge National Laboratory. The authors thank Ray Unocic and Allen Haynes (ORNL) for reviewing the manuscript. The authors would also like to thank Dana McClurg for heat treatments and hardness measurements and James Burns for APT sample preparation and APT operation. This research was supported by the DOE Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office, Propulsion Materials Program and the DOE Basic Energy Sciences, Materials Sciences and Engineering Division. APT was conducted at ORNL's Center for Nanophase Materials Sciences (CNMS), which is a US DOE Office of Science User Facility. The authors appreciate the support provided by the Oak Ridge Leadership Computing Facility at the ORNL. Earlier research was supported by the Department of Energy, Laboratory Directed Research and Development program at Oak Ridge National Laboratory. The authors thank Ray Unocic and Allen Haynes (ORNL) for reviewing the manuscript. The authors would also like to thank Dana McClurg for heat treatments and hardness measurements and James Burns for APT sample preparation and APT operation.
Keywords
- Aluminum alloy
- Atom probe tomography
- Density functional theory
- Microalloying
- Precipitate stability