Microstructure Evolution of Mechanically-Alloying and Its Subsequently-Annealed AlCrCu0.5Mo0.5Ni High-Entropy Alloy
LEI Yunlong1, YANG Kang1(), XIN Yue1, JIANG Zitao1, TONG Baohong2, ZHANG Shihong1()
1 Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials, Ministry of Education, Anhui University of Technology, Ma'anshan 243000, China 2 School of Mechanical Engineering, Anhui University of Technology, Ma'anshan 243032, China
Cite this article:
LEI Yunlong, YANG Kang, XIN Yue, JIANG Zitao, TONG Baohong, ZHANG Shihong. Microstructure Evolution of Mechanically-Alloying and Its Subsequently-Annealed AlCrCu0.5Mo0.5Ni High-Entropy Alloy. Acta Metall Sin, 2025, 61(5): 731-743.
Boiler steel is prone to thermal corrosion and abrasion in high-temperature environments, making thermal spray protective coatings a vital solution for enhancing the corrosion and abrasion resistance of boilers. This study focuses on the development of a novel AlCrCu0.5Mo0.5Ni high-entropy alloy powder synthesized through mechanical alloying (MA) using monolithic metal powders as starting materials. The effects of milling time on the phase structure, grain size, and microstructure evolution of the MA powder were investigated. Phase characterization was performed using XRD; grain size, lattice strain, and lattice constant were measured; morphological and microstructural analyses were performed using SEM and TEM. Phase regulation through vacuum isothermal annealing techniques was also explored. The findings indicated the formation of two bcc (bcc1, bcc2) and one fcc solid solution phases within the high-entropy alloy powder. With increased milling time, the MA powder experienced plastic deformation, which led to a reduction in grain size and an augmentation of lattice strain. Powder particle fragmentation and refinement of the element-enriched zones facilitated enhanced diffusion and alloying of the elements. At 40 h of milling, the powder particles exhibited a more homogeneous elemental distribution, with phase contents of 41% bcc1, 37% bcc2, and 22% fcc, and an average particle size of 24 μm, making them suitable for thermal spray applications. Annealing at 800 oC led to the decomposition of the bcc2 solid solution structure after 40 h of ball milling. Upon increasing the annealing temperature to 1000 oC, complete decomposition of the bcc2 solid solution was observed, resulting in 68% bcc1 and 21% fcc phases, with the emergence of 11% CrMo phase. As the annealing temperature was increased, the MA powder released significant strain energy, increasing grain size and a reduction in lattice strain. The maximum hardness and elasticity modulus were achieved after annealing at 800 oC, recorded at (6.54 ± 0.58) and (65.62 ± 3.07) GPa, respectively.
Table 1 Characteristic parameters of each element in mechanical alloying (MA) powders
Fig.1 XRD spectra of mechanical alloying (MA) powders at different ball milling time (a) 2θ = 20°-90° (b) 2θ = 39°-46°
Fig.2 Mixing enthalpies between component elements (unit: kJ/mol)
Fig.3 Evolutions of grain size and lattice strain (a, b) and lattice parameters (c, d) with ball milling time (a, c) bcc1 phase (b, d) bcc2 phase
Fig.4 Phase contents in MA powders after different ball milling time calculated by XRD data
Fig.5 Surface morphologies of MA powder after different ball milling time (a) 10 h (b) 20 h (c) 40 h (d) 60 h
Fig.6 Cross-sectional morphologies and EDS element distributions of MA powder after different ball milling time (a) 10 h (b) 20 h (c) 40 h
Fig.7 Variation trends of particle size distributions (a) and average particle sizes (D50) (b) of MA powders after different ball milling time
Fig.8 TG-DSC curves (Inset is the localized enlargement of DSC curve) (a), XRD spectra (b), grain sizes and lattice strains(c), and phase contents (d) of MA 40 h powders after annealing at several temperatures
Fig.9 Surface morphologies of MA 40 h powders after annealing at different temperatures (a) 800 oC (b) 1000 oC (c) 1200 oC
Fig.10 Cross-sectional morphologies and EDS element distributions of MA 40 h powders after annealing at different temperatures (a) 800 oC (b) 1000 oC (c) 1200 oC
Fig.11 Bright-field TEM image (a), selected area electron diffraction (SAED) patterns of the areas B (b) and C (c) in Fig.11a, and dark-field TEM image and EDS elemental distributions (d) of MA 40 h powders after annealing at 1200 oC
Fig.12 Typical HRTEM image of the two-phase interface in MA powders after annealing at 1200 oC and corresponding fast Fourier transform (FFT) and inverse FFT (IFFT) (d—interplanar spacing)
Fig.13 Mechanical properties of MA powders in ball-milled and annealing states (H i represent MA powders annealed at i temperature) (a) load-depth curves (b) hardness and elasticity modulus
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