Electrochemical and Friction Characteristics of Metallic Glass Composites at the Microstructural Length-scales

Abstract

Metallic glass composites represent a unique alloy design strategy comprising of in situ crystalline dendrites in an amorphous matrix to achieve damage tolerance unseen in conventional structural materials. They are promising for a range of advanced applications including spacecraft gears, high-performance sporting goods and bio-implants, all of which demand high surface degradation resistance. Here, we evaluated the phase-specific electrochemical and friction characteristics of a Zr-based metallic glass composite, Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5, which comprised roughly of 40% by volume crystalline dendrites in an amorphous matrix. The amorphous matrix showed higher hardness and friction coefficient compared to the crystalline dendrites. But sliding reciprocating tests for the composite revealed inter-phase delamination rather than preferred wearing of one phase. Pitting during potentiodynamic polarization in NaCl solution was prevalent at the inter-phase boundary, confirming that galvanic coupling was the predominant corrosion mechanism. Scanning vibration electrode technique demonstrated that the amorphous matrix corroded much faster than the crystalline dendrites due to its unfavorable chemistry. Relative work function values measured using scanning kelvin probe showed the amorphous matrix to be more electropositive, which explain its preferred corrosion over the crystalline dendrites as well as its characteristic friction behavior. This study paves the way for careful partitioning of elements between the two phases in a metallic glass composite to tune its surface degradation behavior for a range of advanced applications.

Surface degradation mechanisms in a eutectic high entropy alloy at microstructural length-scales and correlation with phase-specific work function

“…The correlation between corrosion potential and work function investigated for crystalline 32 and amorphous 33 materials show that metallic alloys with higher work function typically show better corrosion resistance due to lower electropositivity. 34 In other words, corrosion is affected by the Fig. 8 a Low magnification SEM image of E-HEA after polarization test in 3.5 wt.% NaCl solution; b high magnification SEM image corresponding to the black box in the previous image showing preferential dissolution of B2 phase; c pitting in the corroded sample with pit initiation in the region with high B2 phase fraction surface electron behavior or electron activity, which may be characterized by work function.…”

“…Higher adhesion for metal-on-metal wear has been reported for more electropositive alloys. 34 Buckley's hypothesis 37 suggests that chemically active metals (i.e., electron donors) are prone to strong adhesion as opposed to inert metals. 38 Therefore, it can be concluded that the more electropositive nature of B2 phase might have resulted in a stronger adhesion to the cube-corner indenter and resulted in higher localized stresses (Fig.…”

Bio‐electrochemical response to sense implant degradation

“…Therefore, it is paramount to investigate and understand the electrochemical response during mechanochemical degradation in vivo under dynamic loading. In terms of design and development of new metallic biomaterials, a new generation of biocompatible alloys named high‐entropy alloys (HEAs) and bulk metallic glasses (BMG) show excellent mechanical and corrosion behaviour that is superior in many cases compared to presently used bioimplant materials (A. Ayyagari, Hasannaeimi, Arora, Hasannaeimi, Arora, & Mukherjee, 2018; A. Ayyagari, Hasannaeimi, Grewal, et al., 2018; Ren et al., 2019; Todai et al., 2017). HEAs are composed of multiple principal elements that result in unique strengthening mechanisms and resistance to failure under dynamic loading.…”

Corrosion, Erosion and Wear Behavior of Complex Concentrated Alloys: A Review

“…This may be of interest in tribology for developing super-lubricity complex composition coatings. Phase-specific friction studies will provide significant insights into surface degradation from multi-body wear in multi-phase CCAs [101]. Ni free complex alloys might be attractive for biomedical applications.…”