Bulk Metallic Glass Corrosion Resistance via Selective Anodization
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Solution Overview
Problem
Bulk metallic glasses (BMG) suffer from reduced corrosion resistance, particularly to pitting corrosion, due to the presence of non-passivable elements like copper and nickel, which hinder the formation of a stable passivation layer during conventional anodization, leading to aesthetic and structural issues.
Innovation Solution
An electrochemical anodic treatment with selective extraction of non-passivable elements and enrichment of passivable elements like zirconium, titanium, and aluminum, applied at specific current densities to enhance corrosion resistance while preserving the substrate's aesthetic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional anodization is applied to BMG substrates containing non-passivable elements (Cu, Ni), then the substrate undergoes surface treatment, but the current density does not significantly decrease and a stable passivation layer is not formed
Solution Approach 1:
The patent applies a two-stage anodization process with specific parameter changes: first stage at 10-100 mA/cm² for 5-30 minutes to remove non-passivable elements, then second stage at 1-10 mA/cm² for 10-60 minutes to form the passivation layer. This parameter modification enables successful passivation that conventional single-stage anodization cannot achieve.
Solution Approach 2:
The first anodization stage acts as a preliminary action to selectively remove non-passivable elements (Cu, Ni) from the BMG surface before the second stage forms the passivation layer. This preliminary removal of harmful elements is essential for subsequent successful passivation.
2Strength
If BMG substrates contain non-passivable elements (Cu, Ni), then the alloy exhibits good mechanical properties, but the corrosion resistance is reduced due to inability to form stable passivation layer
Solution Approach 1:
The patent creates local quality differentiation by selectively removing non-passivable elements from the surface layer while preserving the bulk alloy composition. The surface becomes enriched in passivable elements (Zr, Ti, Al) forming a protective layer, while the bulk retains the original mechanical properties from Cu and Ni content.
Solution Approach 2:
The first anodization stage extracts non-passivable elements (Cu, Ni) from the BMG surface through selective dissolution. This extraction removes the corrosive elements while preserving the beneficial mechanical properties contributed by these elements in the bulk material.
3Shape
If the surface of BMG is polished to be fine (0.02 μm SiO2 abrasive), then the surface is smooth, but copper enrichment occurs with low resistance to pitting corrosion
Solution Approach 1:
The patent converts the harmful copper enrichment that occurs during fine polishing into a benefit by subsequently using controlled anodization to selectively remove this surface copper. The harmful copper-rich surface layer is transformed into a controlled process that ultimately creates a copper-depleted, corrosion-resistant surface.
4Productivity
If the current density is kept high during anodization of BMG, then the treatment is efficient, but non-passivable elements dissolve selectively and prevent stable passivation layer formation
Solution Approach 1:
The patent uses periodic action by dividing the anodization process into two distinct stages with different current densities. The first stage uses high current density (10-100 mA/cm²) for efficient removal of non-passivable elements, then the second stage uses low current density (1-10 mA/cm²) for stable passivation layer formation. This periodic variation in current density achieves both efficiency and stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process significantly improves the corrosion resistance of BMG alloys by forming a stable metal oxide layer enriched in passivable elements, reducing pitting corrosion and maintaining the substrate's visual integrity.
Implementation Method 1
an electrochemical anodic treatment applying a current density of from 0.2 mA.cm-2 to 200 mA.cm-2 for a duration of from 5 seconds to 2 hours
Implementation Method 2
conventional anodisation on Vit105, the formation of a typical passivation layer is not usually achieved
Implementation Method 3
forming a stable metal oxide layer enriched in passivable elements
Data Source
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AI summary
The invention relates to a process for enhancing corrosion resistance of a metal-based glass substrate, wherein the metal of the metal-based glass is one or more of zirconium, titanium, hafnium, aluminium, magnesium, and gold, and wherein the process comprises a step of exposing the substrate to an electrochemical anodic treatment applying a current density from 0.5 mA.cm-2 to 1000 mA.cm-2.