Author
Kaka Ma
Other affiliations: University of California, Davis, University of California, Irvine
Bio: Kaka Ma is an academic researcher from Colorado State University. The author has contributed to research in topics: Spark plasma sintering & Grain boundary. The author has an hindex of 18, co-authored 44 publications receiving 1580 citations. Previous affiliations of Kaka Ma include University of California, Davis & University of California, Irvine.
Papers
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TL;DR: In this article, the relationship between precipitation phenomena, grain size and mechanical behavior in a complex precipitation-strengthened alloy system, Al 7075 alloy, a commonly used aluminum alloy, was selected as a model system in the present study.
995 citations
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TL;DR: In this paper, a bulk Al 7075 alloy with an ultrafine grain (UFG) structure was fabricated via cryomilling, hot isostatic pressing and extrusion, followed by solution treatment and artificial aging.
193 citations
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TL;DR: In this paper, the authors show that coupling of dislocations and precipitates within the ultrafine grains has a beneficial impact on the mechanical behavior and results in an extremely high strength, i.e., ultimate tensile strength ∼878 MPa, with uniform elongation of 4.1% strain at fracture.
171 citations
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15 Oct 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the influence of reinforcement particle size on the microstructure and mechanical behavior of Al metal matrix composites was investigated, and the composite with the smallest B 4 C particles possessed the highest yield strength and fracture strength.
Abstract: We report on an investigation of the influence of reinforcement particle size on the microstructure and mechanical behavior of Al metal matrix composites. In our work, Al 7075/B 4 C composites containing three types of B 4 C particle sizes (56.9 µm, 4.2 µm and 2.0 µm) were synthesized and studied. For a constant value of volume fraction of B 4 C, the composite with coarse reinforcement particles exhibited a relatively homogeneous and discrete distribution of the B 4 C particles while the composites with fine reinforcement exhibited agglomeration of the B 4 C particles. The composite with the smallest B 4 C particles possessed the highest yield strength and fracture strength. Quantitative analysis of the strengthening mechanisms revealed that smaller B 4 C particles lead to larger values in strain gradient strengthening as well as CTE mismatch strengthening, which are significantly correlated to the geometrically necessary dislocations caused by the presence of B 4 C. In addition, the different spatial distributions of the B 4 C particles contributed to different fracture mechanisms in the composites.
86 citations
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TL;DR: In this article, the growth rate and homogeneity of the thermally grown oxide (TGO) were quantified and characterized through rigorous statistical evaluation, and the initial TGO growth follows parabolic growth kinetics in both systems.
Abstract: Isothermal oxidation behavior of thermal barrier coatings (TBCs) with cryomilled NiCrAlY bond coats, in comparison with equivalent TBCs with conventional bond coats was investigated The growth rate and homogeneity of the thermally grown oxide (TGO) were quantified and characterized through rigorous statistical evaluation The initial TGO growth follows parabolic growth kinetics in both systems, but the cryomilled coatings exhibit improved homogeneity in TGO thickness, thinner TGO layers after long-term exposure, slower TGO growth rate, and uniformity in TGO composition consisting primarily of α-Al 2 O 3 with a limited presence of other oxides such as Ni(Cr, Al) 2 O 4 spinel Results indicate that the distinct bond coat structure derived from cryomilling, ie, the creation of a thermally stable, uniform distribution of ultrafine Al- or Y- rich oxide dispersoids within the bond coat layer, may affect the Al outward diffusion from the bond coat to the bond coat/top coat interface, which ultimately influences the TGO growth behavior In addition, computational simulation is applied using the commercially available Thermo-calc® software to provide further insight into the chemical composition of the TGO layers
83 citations
Cited by
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TL;DR: In this paper, the authors demonstrate the possibility to precipitate a coherent reinforcing phase in a fcc-FeCoNiCr HEA matrix using minor additions of Ti and Al, and demonstrate that extraordinary balanced tensile properties at room temperature were achieved, which was due to a well combination of various hardening mechanisms, particularly precipitation hardening.
1,486 citations
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TL;DR: In this article, the relationship between precipitation phenomena, grain size and mechanical behavior in a complex precipitation-strengthened alloy system, Al 7075 alloy, a commonly used aluminum alloy, was selected as a model system in the present study.
995 citations
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TL;DR: In this paper, the authors review recent advances in overcoming this tradeoff, by purposely deploying heterogeneous nanostructures in an otherwise single-phase metal, and advocate this broad vision to help guide future innovations towards a synergy between high strength and high ductility.
611 citations
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TL;DR: In this paper, the microstructures of HESAs consisting of γ and γ′ phases are similar to that of Ni-base superalloys and refractory HEAs.
441 citations
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North Carolina State University1, Ritsumeikan University2, Ohio State University3, University of California, Santa Barbara4, Institute of High Performance Computing Singapore5, Pohang University of Science and Technology6, University of California, Irvine7, University of California, Riverside8, Lawrence Berkeley National Laboratory9, Kyoto University10, Yanshan University11, Chinese Academy of Sciences12
Abstract: Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones wi...
392 citations