<p>Applications of Aluminum (Al) alloys in harsh
environments involving high stress and high temperatures are often hindered
because of their inherently low strength and poor performance at high
temperatures. The strongest commercial Al alloys reported up to date have a
maximum strength less than 700 MPa. Although ultrafine grained Al alloys
prepared by severe plastic deformation have higher strength, they encounter
grain growth at moderate temperatures. </p>
<p>This thesis focuses on adopting transition metal
solutes and non-equilibrium approach to fabricate high-strength, thermally
stable nanotwinned Al alloys. To understand the underlying deformation
mechanisms of nanotwinned Al alloys, <i>in-situ</i>
micromechanical tests, high resolution and analytical transmission microscopy
and atomistic simulations were used. Our studies show that nanotwinned
supersaturated Al-Fe alloys have a maximum hardness and flow stress of ~ 5.5
GPa and 1.6 GPa, respectively. The apparent directionality of the vertical
incoherent twin boundaries renders plastic anisotropy and compression-tension
asymmetry in the nanotwinned Al-Fe alloys, revealed by systematic <i>in-situ</i> tensile and compressive
micromechanical experiments conducted from both in-plane and out-of-plane
directions. Moreover, the nanotwinned Al-Fe alloys experience no apparent
softening when tested at 200 °C. When selectively incorporating with one
additional solute as stabilizer, the ternary nanotwinned Al alloys can preserve
an exceptionally high flow stress, exceeding 2 GPa, prior to precipitous
softening at an annealing temperature of > 400 °C. The thesis offers a
new perspective to the design of future strong, deformable and thermally stable
nanostructured Al alloys. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/9107918 |
| Date | 12 October 2021 |
| Creators | Qiang Li (7041092) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/FABRICATION_PLASTICITY_AND_THERMAL_STABILITY_OF_NANOTWINNED_AL_ALLOYS/9107918 |
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