Titanium Alloy Surface Microstructure for Hardness and Fatigue Strength
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Solution Overview
Problem
Conventional surface treatments for titanium alloy mechanical components enhance hardness but lead to coarsening of crystal grains, reducing fatigue strength.
Innovation Solution
A mechanical component with a titanium alloy surface comprising primary and secondary α crystal grains, where primary α crystal grains have an area ratio of 10-30% and secondary α crystal grains have diameters ≤75 μm, combined with an oxygen concentration of ≥1% by mass, achieved through a solution treatment, aging treatment, and oxygen permeation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If surface treatment is performed to form a solid solution of oxygen in the surface of the titanium alloy mechanical component, then hardness of the surface is enhanced, but crystal grains in the surface coarsen resulting in reduced fatigue strength
Solution Approach 1:
The patent applies local quality by creating distinct regions with different crystal grain characteristics: primary α crystal grains (10-30% area ratio) provide a refined structure that maintains fatigue strength, while secondary α crystal grains provide hardness. The oxygen concentration is also localized to 1% or more in the surface region, achieving surface hardening without compromising the underlying microstructure. This spatial differentiation of properties resolves the contradiction between surface hardness and fatigue strength.
2Strength
If solution treatment is performed to increase hardness through phase transformation, then mechanical hardness improves, but crystal grain structure coarsens reducing fatigue resistance
Solution Approach 1:
The patent employs parameter changes by precisely controlling the heating temperature range (β transformation starting temperature to β single phase transformation temperature) and duration during solution treatment. This controlled thermal parameter adjustment enables partial phase transformation that increases hardness while limiting excessive grain growth. The subsequent cooling rate is also controlled to produce the desired secondary α crystal grain size (75 μm or less), thereby achieving hardness improvement without significant fatigue strength degradation.
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 approach results in a surface with enhanced hardness and fatigue strength by preventing crystal grain coarsening and reinforcing with oxygen, effectively coestablishing hardness and fatigue strength.
Implementation Method 1
a portion of an α phase in the titanium alloy forming the mechanical component undergoes α phase transformation to a β phase
Implementation Method 2
the β phase generated in the heating step undergoes a phase transformation to a secondary α phase
Implementation Method 3
a surface treatment may further be performed to form a solid solution of oxygen in the surface of the mechanical component made of the titanium alloy
Data Source
AI summary
A mechanical component according to one aspect of the present invention is made of a titanium alloy and has a surface. The mechanical component includes a plurality of primary α crystal grains and a plurality of secondary α crystal grains. At the surface of the mechanical component the primary α crystal grains have an area ratio of 10% or more and 30% or less. At the surface of the mechanical component the secondary α crystal grains have a major diameter of 75 μm or less and a minor diameter of 10 μm or less. At the surface of the mechanical component 1% by mass or more of oxygen is included.