Titanium Alloy Outer Hardened Layer Fatigue Strength
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Solution Overview
Problem
Conventional titanium alloy members with outer hardened layers suffer from reduced fatigue strength and inadequate wear resistance, particularly in automotive applications, due to excessive surface hardness and notch susceptibility, and existing methods for improving these properties are costly and inefficient.
Innovation Solution
A titanium alloy member with a base metal portion having a cross-sectional hardness of 330 HV to 400 HV and an outer hardened layer with a controlled hardness distribution, featuring an oxygen diffusion layer at 40-80 μm depth and a nitrogen diffusion layer at 2-5 μm depth, formed through specific heat treatment processes in an oxygen-contained and nitrogen atmosphere, to achieve balanced fatigue strength and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If an oxidized hardened layer is formed on the surface of a titanium alloy member to improve wear resistance, then wear resistance is improved, but fatigue strength is reduced due to excessive surface hardness and notch susceptibility
Solution Approach 1:
The patent applies local quality by creating a dual-layer diffusion structure where the outermost layer (5-20 μm) has lower oxygen concentration (0.5-2.0 mass%) to reduce surface hardness and notch susceptibility, while the inner layer (20-80 μm) has higher oxygen concentration (2.0-5.0 mass%) to provide wear resistance. This spatial differentiation of oxygen concentration resolves the contradiction between wear resistance and fatigue strength.
Solution Approach 2:
The patent changes the parameter of oxygen concentration distribution through a two-stage diffusion process: first stage creates a deep oxygen diffusion layer (20-80 μm) for wear resistance, then the second stage with controlled oxygen potential creates a low-oxygen outer layer (5-20 μm) to reduce surface hardness. This parameter transformation resolves the contradiction by optimizing oxygen distribution at different depths.
2Strength
If the thickness of an oxidized hardened layer is reduced to suppress fatigue strength reduction, then fatigue strength is improved, but wear resistance becomes insufficient
Solution Approach 1:
The patent creates different oxygen concentration zones at different depths: the outer layer (5-20 μm) has low oxygen concentration to maintain fatigue strength, while the inner layer (20-80 μm) has high oxygen concentration to provide wear resistance. This resolves the contradiction by providing both properties at different locations within the hardened layer.
Solution Approach 2:
The patent creates a composite diffusion layer structure with two distinct regions: an outer low-oxygen region and an inner high-oxygen region. This composite structure combines the benefits of low surface hardness (for fatigue strength) and high bulk hardness (for wear resistance) within a single hardened layer, resolving the thickness contradiction.
3Force
If conventional coating methods are used to improve wear resistance of titanium alloy members, then wear resistance is improved, but treatment costs increase significantly
Solution Approach 1:
The patent uses self-service by utilizing the titanium alloy's own material to form the hardened layer through oxygen diffusion. The base metal serves as the source of titanium atoms that diffuse oxygen to form the hardened layer, eliminating the need for external coating materials and complex coating equipment, thereby reducing treatment costs while improving wear resistance.
Solution Approach 2:
The patent replaces mechanical coating systems (PVD, spraying) with a thermal diffusion process. Instead of mechanically depositing coating materials, the patent uses controlled heat treatment to enable oxygen diffusion into the titanium alloy surface, creating a hardened layer through chemical diffusion rather than mechanical deposition, thereby simplifying the manufacturing process and reducing costs.
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 provides a titanium alloy member with enhanced wear resistance and fatigue strength, reducing the margin of fatigue strength reduction compared to conventional methods, while being industrially inexpensive and applicable to various automotive components, contributing to improved fuel efficiency and environmental sustainability.
Implementation Method 1
forming an oxidized hardened layer by causing oxygen to diffuse from a surface into an inside of a titanium alloy starting material
Implementation Method 2
performing heat treatment in an oxygen-contained atmosphere
Data Source
AI summary
There is provided a titanium alloy member including a base metal portion, and an outer hardened layer formed on an outer layer of the base metal portion, the cross sectional hardness of the base metal portion is 330 HV or higher and lower than 400 HV, the cross sectional hardnesses at positions 5 μm and 15 μm from the surface of the outer hardened layer are 450 HV or higher and lower than 600 HV, the outer hardened layer includes an oxygen diffusion layer and a nitrogen diffusion layer, the oxygen diffusion layer is at a depth of 40 to 80 μm from the surface of the outer hardened layer, and the nitrogen diffusion layer is at a depth of 2 to 5 μm from surface of the outer hardened layer. This titanium alloy member includes an outer hardened layer, is high in cross sectional hardness of the base metal portion, and is excellent in fatigue strength and wear resistance.