Titanium Alloy Surface Hardening With Luster-Preserving Oxide Layers
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Solution Overview
Problem
Existing surface hardening methods for titanium materials used in ornamental items result in reduced luster, surface discoloration, and poor external appearance quality due to improper control of nitrogen and oxygen diffusion, leading to low surface hardness and roughness.
Innovation Solution
A surface hardening method for titanium or titanium alloy members involving the diffusion of oxygen and optionally nitrogen into the surface, forming a hardened layer with a transparent oxide layer and internal diffusion layers, controlled under specific gas atmospheres to maintain high hardness and luster, using a heating and cooling process to manage oxide layer thickness and prevent discoloration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If vacuum thermal oxidation nitrification diffusion processing is used to improve surface hardness, then surface hardness increases, but surface luster deteriorates and surface becomes rough
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thermal processing temperature (600-750°C), oxygen concentration (1000-15000 ppm), and processing time (1-24 hours) to achieve optimal balance between surface hardness and surface quality. By adjusting these parameters, the patent forms a hardened layer with appropriate oxide composition that provides both hardness and good surface appearance.
Solution Approach 2:
The patent applies local quality by creating a gradient structure in the hardened layer, with different oxide compositions at different depths. The surface region contains a controlled amount of oxide (5-20 at%) that maintains luster, while deeper regions have higher oxide content for hardness. This local variation in oxide concentration resolves the contradiction between surface quality and hardness.
2Strength
If nitrogen solid solution is increased to improve surface hardness, then surface hardness increases, but surface discoloration occurs and external appearance quality deteriorates
Solution Approach 1:
The patent controls the oxygen concentration parameter (1000-15000 ppm) and processing temperature (600-750°C) to limit nitrogen diffusion while still achieving sufficient hardening. This parameter control prevents excessive nitrogen incorporation that would cause discoloration, while maintaining adequate surface hardness through controlled oxide diffusion.
Solution Approach 2:
The patent creates a localized hardened layer with controlled oxide concentration (5-20 at%) at the surface region, separating the functional requirement (hardness) from the aesthetic requirement (appearance). This local quality control ensures that only the necessary amount of oxide is present at the surface for hardening, minimizing discoloration while maintaining hardness.
3Strength
If atmospheric thermal oxidation processing is used to harden surface, then surface hardness increases, but surface becomes gray colored and metallic luster is lost
Solution Approach 1:
The patent uses a controlled vacuum atmosphere with limited oxygen (1000-15000 ppm) instead of atmospheric oxidation. This controlled inert environment prevents excessive oxide formation that would cause gray discoloration, while still providing sufficient oxygen for surface hardening through diffusion.
Solution Approach 2:
The patent changes the oxygen concentration parameter from atmospheric levels to controlled vacuum levels (1000-15000 ppm) and controls temperature (600-750°C) to achieve selective oxide diffusion. This parameter change allows surface hardening while preventing the formation of thick, discolored oxide layers that characterize atmospheric oxidation.
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 method achieves high surface hardness, maintains metallic luster, and ensures good external appearance by controlling the thickness of the transparent oxide layer to less than 10 nm, preventing discoloration and enhancing the durability of titanium-based ornamental items.
Implementation Method 1
a hardened layer formed by diffusion of oxygen into the surface
Implementation Method 2
a surface hardening method involving the diffusion of oxygen and optionally nitrogen into the surface, forming a hardened layer
Data Source
AI summary
The present disclosure relates to a titanium or titanium alloy member and to a surface hardening method for the titanium or titanium alloy member. The titanium or titanium alloy member includes a base material of titanium or titanium alloy, and at a surface of the base material, a hardened layer formed by diffusion of oxygen into the surface.