Iron-Based Alloy Stent Nitriding and Ion Etching
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Solution Overview
Problem
Current methods for manufacturing iron-based alloy medical apparatuses, such as stents, face challenges in efficiently removing the corrosion-resistant compound layer formed during nitriding, which affects the absorption rate and performance of the stents, particularly due to limitations in mechanical polishing, electrochemical polishing, vacuum denitriding, and low nitrogen potential nitriding methods.
Innovation Solution
A manufacturing method involving ion nitriding followed by ion etching, where the preformed medical device is heated to 350-550°C and nitrided for 30-100 minutes, then ion-etched with a mixed gas of argon and hydrogen, effectively removing the compound layer while maintaining the hardness and strength of the stent surface, and allowing for subsequent normal-temperature chemical polishing to achieve mirror polishing effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical polishing is used to remove the compound layer, then the removal speed is fast, but the dimensional precision of the medical instrument cannot be ensured
Solution Approach 1:
The patent replaces mechanical polishing with electrochemical polishing, substituting a mechanical removal system with an electrochemical dissolution system. This allows the compound layer to be removed through electrochemical reactions rather than mechanical abrasion, thereby avoiding dimensional errors while achieving effective removal.
Solution Approach 2:
The patent changes the removal mechanism from mechanical to electrochemical by adjusting process parameters such as electrolyte composition, voltage, and current density. This parameter change enables precise control over the removal process, maintaining dimensional accuracy while achieving compound layer removal.
2Manufacturing precision
If electrochemical polishing is used to remove the compound layer, then the dimensional precision is maintained, but the surface of the diffusion layer becomes bright and flat only after excessive removal, causing the diffusion layer to become very thin
Solution Approach 1:
The patent applies electrochemical polishing with controlled parameters to achieve partial removal of the compound layer without excessive action. By optimizing voltage, current density, and electrolyte composition, the process removes the compound layer effectively while limiting diffusion layer removal to minimal amounts, preventing the diffusion layer from becoming too thin.
Solution Approach 2:
The patent optimizes electrochemical polishing parameters including using lower voltage (1-5V), specific electrolyte compositions (citric acid, acetic acid, or sulfuric acid solutions), and controlled current densities to achieve selective removal of the compound layer while preserving the diffusion layer thickness.
3Manufacturing precision
If vacuum de-nitriding is used to remove the compound layer, then the phase structure can be changed, but the required temperature holding time is too long, reducing surface hardness and performance
Solution Approach 1:
The patent replaces vacuum de-nitriding with electrochemical polishing, substituting a thermal process with an electrochemical process. This eliminates the need for long temperature holding times (6-9 hours) required by vacuum de-nitriding, thereby preserving surface hardness and mechanical performance while achieving compound layer removal.
Solution Approach 2:
The patent changes the removal mechanism from thermal (vacuum de-nitriding requiring 500-550°C for 6-9 hours) to electrochemical (polishing at room temperature or elevated temperature with electrolytes), dramatically reducing process time from hours to minutes while maintaining removal effectiveness.
4Object-generated harmful factors
If nitriding is performed at low nitrogen potential to prevent compound layer formation, then the compound layer is avoided, but the nitriding efficiency is greatly reduced and basic performance is weakened
Solution Approach 1:
The patent segments the nitriding process into two distinct stages: first, high nitrogen potential nitriding to form the compound layer and diffusion layer with adequate nitrogen content; second, electrochemical polishing to remove the compound layer. This segmentation allows each stage to be optimized independently, maintaining nitriding efficiency while eliminating the harmful compound layer.
Solution Approach 2:
The patent extracts the harmful compound layer from the nitrided surface through electrochemical polishing after forming it during nitriding. This approach allows the compound layer to be formed (maintaining nitriding efficiency) and then selectively removed (eliminating harmful effects), rather than trying to prevent its formation entirely.
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
This method enhances the production efficiency of iron-based alloy medical apparatuses by ensuring quick and effective removal of the compound layer, meeting both performance and manufacturing efficiency requirements, and facilitating the absorption of the stent by the human body while maintaining surface hardness and strength.
Implementation Method 1
the preformed unit is heated to 350-550°C and the surface of the preformed unit is nitrided for 30-100 minutes
Implementation Method 2
by surface alloying the iron-based alloy stent, for example, nitriding from a surface to inside to form a readily-corrodible diffusion layer
Implementation Method 3
The preformed unit is then ion-etched with an ion etching time of 80-110% of the nitriding time
Implementation Method 4
ion bombardment treatment is performed on the chemical compound layer formed on the surface of the steel during nitriding
Implementation Method 5
ion-etched with an ion etching time of 80-110% of the nitriding time
Implementation Method 6
ion bombardment treatment is performed on the chemical compound layer formed on the surface of the steel during nitriding
Data Source
Figure 1~2
Figure 3~4
AI summary
Disclosed is a manufacturing method of an iron-based alloy medical apparatus, comprising: nitriding the iron-based alloy preformed unit at 350-550°C for 30- 100 minutes; and ion etching the iron-based alloy preformed unit with an ion etching time of 80-110% of the nitriding time. Ion nitriding and ion etching can be performed in situ in the same equipment using this manufacture method with high production efficiency, and in the ion nitriding and ion etching process, nitrogen atoms continuously permeate the preformed unit, making the time it takes for the medical apparatus to be absorbed by the human body and both the hardness and strength of the instrument surface achieve requirements.