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The development of high-strength cold spray deposits using amorphous/nanocrystalline aluminum high-entropy alloy (Al HEA) powder is hindered by the lack of understanding of correlations between powder microstructure and its deformation behavior. In this study, gas-atomized Al HEA powder (Al90.05-Y4.4-Ni4.3-Co0.9-Sc0.35 at.%) is devitrified at 298, 345, 362, and 450 °C to optimize strength and deformation for cold spraying. Devitrification-induced atomic rearrangement developed equiaxed Al grains and Al3Ni and Al3Sc precipitates. The amorphous content, growth of grains, hard precipitates, and reduced dislocation density increased the hardness by 16% to 515 HV at 298 °C and decreased the hardness by 55% to 190 HV at 450 °C. The compressive strength of Al HEA powder increased by 5% to 1559 MPa at 298 °C and decreased by 49% to 760 MPa at 450 °C. To enhance the limited sprayability of Al HEA powder, compressive strength is used to model optimized cold spray process maps. Helium gas with temperatures from 300 to 800 °C and a pressure of 40 bar can produce cold spray deposits with deposition efficiency greater than 70%. The scientific insights acquired from the present study provide a gateway toward developing novel lightweight and high-strength aluminum alloy deposits, thus marking an advancement in cold spray technology. [ABSTRACT FROM AUTHOR]

The lack of a comprehensive understanding of the role of heat treatments on microstructure and multiscale mechanical properties of powders and their interrelatedness with cold spray process parameters severely impedes the manufacturing of high-strength aluminum coatings. For the first time, this study develops customized heat treatment protocols for controlling microstructure homogenization and intermetallic precipitation in Al 6061 and Al 7075 powders for cold spray. Solution treatment at 505-545 °C, followed by precipitation hardening at 130-160 °C, enables controlled precipitation of hard intermetallic Mg2Si and MgZn2 phases in Al 6061 and Al 7075, respectively. Strengthening by these phases enhances powder nanohardness of Al 6061 and Al 7075 from 1.0 and 1.5 to 1.6 and 1.8 GPa, respectively. The cumulative response from multiple grains at the micrometer length scale carries the trend to improve microhardness to 131.2 and 177 HV. These characteristics of the precipitation-hardened powder encompass improvements of 13-60% above their pristine gas-atomized counterparts. Experimentally measured powder hardness was employed as input in a cold spray simulation tool to develop process maps for manufacturing high-quality coatings. The optimum temperature for deposition with 75-98% efficiencies was established to be 100-300 °C with helium and 500-600 °C with nitrogen and air. In this process window, the particle velocity and critical velocity range of the powders are 998 to 1237 ms−1 and 548 to 858 ms−1 for helium and 580 to 663 ms−1 and 400 to 594 ms−1 for air and nitrogen, respectively. [ABSTRACT FROM AUTHOR]

This article is the first report on the role of ultrasonic treatment (UST) on microstructural evolution, multiscale mechanical behavior, and tribological response in 2D tungsten disulfide (WS2) reinforced aluminum (Al6061) matrix composites. Delaunay triangulation calculations show that UST for 45 s enables a fourfold enhancement in the dispersion parameter of WS2 reinforcements in the Al6061 matrix from 0.08 to 0.32. Improved WS2 dispersion contributes to higher nucleation density with 52.7% grain refinement efficiency, achieving a fine‐grained Al6061–WS2 composite. The role of UST‐induced 2D reinforcement dispersion on the elastic deformation is established at progressively increasing length scales from individual grains to the bulk composite. It is accomplished by integrating the nanodynamic modulus mapping technique with a finite element modeling framework built on experimentally acquired microstructures and localized elastic moduli. It delineates a directly proportional relationship between UST‐induced dispersion and elastic modulus enhancement at all length scales from 10 to 700 μm. Excellent dispersion of the 2D layered WS2 homogenizes the tribological response of the composite material with a tenfold reduction in the volume of material lost during wear. [ABSTRACT FROM AUTHOR]

This paper presents the first report of ultrasonic treatment (UST) assisted casting of independent 2D layered hexagonal boron nitride (hBN) reinforced aluminum matrix composites. A linear enhancement of nucleation density is obtained with treatment time from 0 to 90 s from dispersion of hBN platelets by UST. Outstanding grain refinement of 72% from 375.3 to 103.6 μm is obtained from UST for 90 s. The corresponding nanohardness is 709.2 MPa, a hardening of 36% due to symbiotic refinement and dispersion contributions. Anchoring and orientation of hBN platelets dictate that the elastic modulus improved up to 150% by ultrasonication for 90 s. The exfoliated 2D reinforcement layers reduce the coefficient of friction during sliding wear by 15% and loss of worn material by 46% in these composites. The mechanism of dispersion, improvement of properties, and quantitative correlations constitute a step of advancement towards understanding the role of 2D particle morphology and dimensionality on the ultrasonic casting of metal matrix composites. [ABSTRACT FROM AUTHOR]

This study shows the beneficial effect of Pt addition to the (β+γ)-NiCrAlY coating. Adding Y in NiCrAl increases oxide growth kinetics but improves spallation resistance. Pt with Y does not change the oxidation rate compared to only adding Y but significantly reduces spallation when cooled to room temperature. Continuous layers of Al 2 O 3 and Cr 2 O 3 , along with other oxides such as YAlO 3 , NiCr 2 O 4 , and NiAl 2 O 4, are observed. Moreover, Pt addition reduces the thickness of the interdiffusion zone where Al goes through an uphill diffusion profile, minimizing Al loss and significantly decreasing the growth of deleterious TCP phases. [Display omitted] • Pt addition to (β+γ)-NiCrAl improves spallation resistance without affecting oxide growth kinetics. • Y addition increases oxide growth kinetics but improves spallation resistance. • Combined Pt and Y additions markedly enhance oxide layer spallation resistance. • TEM reveals α-Al 2 O 3 and Cr 2 O 3 oxide layers, spinels and Y-Al-rich oxide pegs at the bond-coat/Al 2 O 3 interface. [ABSTRACT FROM AUTHOR]