Plasma-Nitrided Iron Lumen Stent Preform for Strength and Plasticity
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Solution Overview
Problem
Current nitriding methods for iron-based stents face challenges such as low production efficiency, toxicity risks, and unsuitable mechanical properties for lumen stents, particularly in achieving the required radial strength and plasticity for coronary and peripheral stents.
Innovation Solution
A lumen stent preform made of pure iron or iron alloy with specific impurity and alloy content, processed through plasma nitriding to achieve a hardness of 160-250 HV0.05/10 and a deformed microstructure, ensuring suitable radial strength and plasticity for both coronary and peripheral stents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If gas nitriding method is used to improve stent strength, then stent hardness increases, but production efficiency becomes too low for large-scale use
Solution Approach 1:
The patent changes the nitriding method from conventional gas nitriding to plasma nitriding, altering the physical and chemical parameters of the treatment process. Plasma nitriding uses ionized gas with higher energy density, enabling faster nitrogen diffusion into the iron alloy surface, thus achieving the required hardness with significantly reduced treatment time and improved production efficiency.
2Strength
If salt-bath nitriding method is used to improve stent strength, then stent hardness increases, but toxic molten cyanide salts are required causing high clinical risk
Solution Approach 1:
The patent eliminates the harmful cyanide salts by replacing salt-bath nitriding with plasma nitriding. The plasma process uses ionized nitrogen and hydrogen gases that can be precisely controlled and completely decomposed, leaving no toxic residues. This converts a harmful chemical process into a cleaner, safer physical-chemical process that maintains stent hardness while eliminating clinical toxicity risks.
3Strength
If conventional nitriding methods are used, then stent strength improves, but compound layers become too thick for subsequent polishing and fine structure design
Solution Approach 1:
The patent utilizes plasma nitriding parameters (ion energy, gas composition, treatment time, temperature) to precisely control the depth and uniformity of nitrogen diffusion. By optimizing these parameters, the process produces a thin, uniform compound layer (typically 1-5 micrometers) that provides sufficient surface hardness while remaining compatible with subsequent polishing and fine structure design of thin-wall lumen stents.
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 solution enables the production of stents with radial strength of 80-260 kPa and over-plasticity of 20-50%, meeting the mechanical property requirements for conventional lumen stents and allowing for commercial-scale plasma nitriding.
Implementation Method 1
The plasma nitriding method has high nitriding efficiency, which uses nitrogen and hydrogen as treatment gas without introducing any other toxic substances
Implementation Method 2
The plasma nitriding method has high nitriding efficiency, which uses nitrogen and hydrogen as treatment gas
Data Source
AI summary
A lumen stent preform is provided using a plasma nitriding technology, a preparation method thereof, a method for preparing a lumen stent by using the preform, and a lumen stent obtained according to the method. The preform is manufactured by using pure iron or an iron alloy containing no strong nitrogen compound, has a hardness of 160-250 HV0.05/10, and has a microstructure that is a deformed structure having a grain size scale greater than or equal to 9 or a deformed structure after cold machining. Alternatively, the preform is an iron alloy containing a strong nitrogen compound, and has a microstructure that is a deformed structure having a grain size scale greater than or equal to 9 or a deformed structure after cold machining. The lumen stent preform meets the requirements of a conventional stent for radial strength and plasticity, so that plasma nitriding is applicable to commercial preparation of a lumen stent.