[Paper Review] Orientation gradients in rapidly solidified pure aluminum thin films: comparison of experiments and phase-field crystal simulations

Paul Jreidini, Tatu Pinomaa+4 more|arXiv (Cornell University)|Mar 31, 2021

Solidification and crystal growth phenomena37 references35 citations

TL;DR

This study proposes a single-component phase-field crystal (PFC) model that captures solid, liquid, and vapor phases to simulate rapid solidification in pure aluminum thin films. Using a coarse-grained amplitude representation, the model reproduces experimentally observed orientation gradients within single grains during ultrafast quenching, linking them causally to defect formation such as dislocations and voids.

ABSTRACT

Rapid solidification experiments on thin film aluminum samples reveal the presence of lattice orientation gradients within crystallizing grains. To study this phenomenon, a single-component phase-field crystal (PFC) model that captures the properties of solid, liquid, and vapor phases is proposed to model pure aluminium quantitatively. A coarse-grained amplitude representation of this model is used to simulate solidification in samples approaching micrometer scales. The simulations reproduce the experimentally observed orientation gradients within crystallizing grains when grown at experimentally relevant rapid quenches. We propose a causal connection between formation of defects and orientation gradients.

Motivation & Objective

• To investigate the origin of lattice orientation gradients in rapidly solidified pure aluminum thin films.
• To bridge the gap between experimental observations and atomistic-scale mechanisms in ultrafast solidification.
• To develop a quantitative PFC model capable of simulating microstructure evolution at experimentally relevant quench rates.
• To establish a causal link between defect formation and the emergence of orientation gradients.

Proposed method

• A single-component PFC model is employed, based on a free energy functional that includes liquid, vapor, and solid phases.
• The model uses a coarse-grained amplitude expansion to simulate large-scale systems at micrometer scales.
• The free energy functional incorporates temperature-dependent parameters (pl, ql) and a two-point correlation function C(2) to stabilize a 2D triangular lattice structure.
• The model is calibrated to match the thermodynamic phase diagram of pure aluminum near the triple point.
• Simulations are performed under rapid quenching conditions to mimic experimental laser-induced resolidification.
• Defect structures such as dislocations, voids, and sub-boundaries are analyzed in relation to orientation gradients.

Experimental results

Research questions

• RQ1 What causes the formation of orientation gradients within single grains during rapid solidification of aluminum thin films?
• RQ2 How do defect structures such as dislocations and voids correlate with the development of orientation gradients?
• RQ3 Can a phase-field crystal model quantitatively reproduce experimentally observed orientation gradients in pure aluminum?
• RQ4 What is the role of vapor phase trapping in the formation of orientation gradients and defect arrays?
• RQ5 How do defect dynamics evolve over time during ultrafast solidification?

Key findings

• The PFC simulations successfully reproduce experimentally observed orientation gradients within single grains during rapid solidification.
• The simulations reveal that orientation gradients are strongly correlated with the presence of dislocation arrays and voids, particularly in regions of high defect density.
• Rows of dislocations with dipolar strain fields and irregularly spaced defects are observed to form within single grains, coinciding with orientation gradients.
• Voids and dislocation arrays are found to evolve dynamically, with some defect arrays showing interconversion between dislocations and voids over time.
• The formation of sub-boundaries—misoriented regions within a single grain—correlates with localized defect clustering and lattice misfit accommodation.
• The model demonstrates that orientation gradients emerge as a consequence of complex defect dynamics during ultrafast solidification, rather than as a result of grain boundary motion.