High-Strength Electroplated Au–Cu Alloys as Micro-Components in MEMS Devices

Tang, Haochun; Chen, Chun-Yi; Yoshiba, Masaharu; Nagoshi, Takashi; Chang, Tso-Fu Mark; Yamane, Daisuke; Machida, Katsuyuki; Masu, Kazuya; Sone, Masato

doi:10.1149/2.141704jes

Cited by 9 publications

(13 citation statements)

References 26 publications

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“…Binary AuCu nanocrystals have attracted significant interest in various structural and functional applications including stomatology, [ 27 ] flexible electronics, [ 28 ] and microelectromechanical systems, [ 36 ] owing to their high wear resistance, high strength, and low contact stress relaxation. Understanding the plastic behavior of crack tips is important in the design of AuCu alloys for numerous applications; however, most previous studies investigated pure metals, in which plastic deformation at the crack tip is governed by deformation‐twin generation in a layer‐by‐layer fashion.…”

Section: Resultsmentioning

confidence: 99%

In Situ Atomic‐Scale Evidence of Unconventional Plastic Behavior at The Crack Tip in AuCu Nanocrystals

Yang,

Fu,

et al. 2023

Adv Funct Materials

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Understanding the plastic behavior of crack tips is crucial for improving the fracture toughness of nanometals. Although many studies are carried out, most previous studies focus on pure metals, and how the crack tip accommodates the plastic deformation of highly concentrated solid‐solution alloys is unclear owing to a lack of direct atomic‐scale evidence. In this study, the atomic‐scale plastic behavior of the crack tip in face‐centered cubic (FCC) AuCu alloy nanocrystals is observed in situ, which provides direct evidence that plastic deformation is governed by the generation of deformation twins and hexagonal close‐packed (HCP) 2H and 4H phases, recurrence of reversible FCC‐HCP phase transitions, and detwinning, which are rarely observed in pure metals. This unusual behavior originates from the inherent chemical inhomogeneity of the AuCu alloy, which inhibits twin thickening via partial dislocations on the adjacent plane, instead of random generation of deformation twins, phase transitions, and reversible processes. This naturally implies a similar behavior at the crack tip in other highly concentrated solid‐solution alloys, including high‐medium‐entropy alloys, providing important insights that greatly improve the understanding of the fracture toughness of metallic materials.

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Section: Resultsmentioning

confidence: 99%

In Situ Atomic‐Scale Evidence of Unconventional Plastic Behavior at The Crack Tip in AuCu Nanocrystals

Yang,

Fu,

et al. 2023

Adv Funct Materials

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“…Increasing the current density would make the applied potential to be more negative, hence reduction of copper was gradually favored and lead to an increase in the copper content. 15 Engineering stress-engineering strain (SS) curves generated from bending test of the micro-cantilevers are shown in Fig. 7.…”

Section: Resultsmentioning

confidence: 99%

High Strength Electrodeposited Au-Cu Alloys Evaluated by Bending Test toward Movable Micro-Components

Asano

Chang

Tang

et al. 2019

ECS J. Solid State Sci. Technol.

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Au-Cu alloy micro-cantilevers are fabricated from Au-Cu alloy films electrodeposited at different current density. Bending deformation behaviors of the Au-Cu alloy micro-cantilevers are evaluated for applications as components in MEMS devices. Au-Cu alloy films with smaller grain size and higher copper content are obtained when a higher current density is used. The Au-Cu alloy film electrodeposited at 5 mA/cm 2 has the finest average grain size among films prepared in this work, which the grain size is 4.76 nm. Bending test of a micro-cantilever prepared from this film shows a high yield stress at 1826 MPa. The high strength is contributed by synergetic effects of the grain boundary strengthening and the solid solution strengthening mechanisms. The deformation behavior changes from ductile to brittle as the copper content increased. The capability to control the grain size and copper concentration simply by adjusting the current density and the high strength are both advantageous in fabrication of MEMS components.

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“…Au-Cu alloy films were electrodeposited with an electrolyte containing X 3 Au(SO 3 ) 2 (X = Na, K) and CuSO 4 . Details of the electrodeposition procedures are reported in previous studies [21,22]. The chemical composition and crystal structure were characterized by energy-dispersive spectroscopy in a scanning electron microscope (SEM, Hitachi SU4300SE, Tokyo, Japan) and X-ray diffraction (XRD, Rigaku Ultima IV, Tokyo, Japan).…”

Section: Methodsmentioning

confidence: 99%

“…Enhancement of the mechanical strength by solid solution strengthening can be achieved by alloying of the nanocrystalline Au [11][12][13]. The yield strength reaches 1.0 GPa in Au-Cu alloys prepared by electrodeposition and evaluated by uniaxial micro-compression tests [21,22]. The high yield strength is a result of synergistic effects of grain boundary and solid solution strengthening mechanisms and the sample size effect [23].…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Hierarchical Structure of Twins in Nanograins Embedded with Twins and the Strengthening Effect

Tang

Chang

Chai

et al. 2019

Metals

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Hierarchical structures of 20 nm grains embedded with twins are realized in electrodeposited Au–Cu alloys. The electrodeposition method allows refinement of the average grain size to 20 nm order, and the alloying stabilizes the nanoscale grain structure. Au–Cu alloys are face-centered cubic (FCC) metals with low stacking fault energy that favors formation of growth twins. Due to the hierarchical structure, the Hall–Petch relationship is still observed when the crystalline size (average twin space) is refined to sub 10 nm region. The yield strength reaches 1.50 GPa in an electrodeposited Au–Cu alloy composed of 16.6 ± 1.1 nm grains and the average twin spacing at 4.7 nm.

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High-Strength Electroplated Au–Cu Alloys as Micro-Components in MEMS Devices

Cited by 9 publications

References 26 publications

In Situ Atomic‐Scale Evidence of Unconventional Plastic Behavior at The Crack Tip in AuCu Nanocrystals

In Situ Atomic‐Scale Evidence of Unconventional Plastic Behavior at The Crack Tip in AuCu Nanocrystals

High Strength Electrodeposited Au-Cu Alloys Evaluated by Bending Test toward Movable Micro-Components

Nanoscale Hierarchical Structure of Twins in Nanograins Embedded with Twins and the Strengthening Effect

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