Titanium Alloy Alpha Case Removal via Machining
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Solution Overview
Problem
The formation of a hard, brittle alpha case layer on titanium alloys when exposed to high temperatures in the presence of oxygen compromises their fatigue strength, corrosion resistance, and high-temperature mechanical properties, necessitating effective prevention, minimization, or removal methods, with existing solutions being costly, environmentally hazardous, or difficult to implement.
Innovation Solution
A method involving heat treating titanium alloys above 1200 degrees F, followed by machining to remove at least 0.007 inches of material from all surfaces to ensure complete removal of the alpha case layer, thereby mitigating contamination risks and reducing the need for subjective inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If titanium is heat treated to increase strength, then the strength of the material is improved, but an alpha case layer forms on the surface that compromises fatigue strength and corrosion resistance
Solution Approach 1:
The patent applies preliminary action by machining the titanium part to its final dimensions before heat treatment. This ensures that when the alpha case forms during subsequent heat treatment, it only forms on the final surface, minimizing the amount of material that needs to be removed later and ensuring complete removal of the alpha case layer without affecting the final part dimensions or requiring additional machining operations.
2Object-generated harmful factors
If chemical milling is used to remove the alpha case layer, then the alpha case is removed, but the process becomes expensive and environmentally hazardous
Solution Approach 1:
The patent replaces the chemical milling process with a mechanical machining approach. By machining the part to final dimensions before heat treatment, the subsequent alpha case removal can be accomplished through standard mechanical machining operations rather than expensive and environmentally hazardous chemical processes involving hydrofluoric or nitric acids.
3Object-generated harmful factors
If mechanical milling is used to remove the alpha case layer, then the alpha case is removed, but additional machining passes are required that significantly increase manufacturing costs
Solution Approach 1:
The patent applies preliminary action by completing all machining operations to final dimensions before heat treatment. This eliminates the need for subsequent alpha case removal machining passes, thereby improving manufacturing efficiency and reducing production time and costs.
4Object-generated harmful factors
If the part is manufactured oversized and then machined to remove the alpha case, then the alpha case can be removed, but the process requires additional material removal that increases manufacturing complexity
Solution Approach 1:
The patent applies inversion by reversing the conventional sequence of operations. Instead of manufacturing the part oversized, heat treating it, and then removing the alpha case, the patent machines the part to final dimensions first, then heat treats it. This inverts the traditional approach and eliminates the need for additional material removal operations, simplifying the manufacturing process.
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 approach effectively removes the alpha case layer, ensuring a finished surface with reduced manufacturing costs and environmental risks, while enhancing the mechanical properties of titanium parts.
Implementation Method 1
when titanium is exposed to high temperatures in the presence of oxygen, a hard brittle layer caused by oxygen diffusing into the titanium, called an alpha case, is formed
Implementation Method 2
Titanium and titanium-alloys can be heat treated to increase the strength of the material
Data Source
AI summary
Disclosed is a method for manufacturing titanium-alloy articles that includes, before machining, heat treating a slug of titanium-alloy at a temperature sufficient to form a layer of alpha case on the surface of the slug of titanium-alloy, then, after heat treating, machining the slug of titanium-alloy to form a finished part while removing material from all surfaces of the slug of titanium-alloy.Also disclosed is an article of manufacture made with the described method.