Ceramic Coating Barrier for Alpha Case-Free Titanium Surfaces

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Solution Overview

Problem

Current methods for inhibiting alpha case on titanium alloy surfaces, such as chemical milling, result in increased costs, production time, stress ratios, thermal gradients, and surface defects, and involve hazardous chemicals like hydrofluoric acid, leading to NOx emissions and hydrogen embrittlement.

Innovation Solution

Applying a ceramic coating to titanium or titanium alloy surfaces, followed by heating and subsequent removal, using a slurry composition comprising silicate, calcium, aluminum, iron, and titanium, and optionally subjecting the coated article to hot isostatic pressing to relieve stresses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If chemical milling is used to remove alpha case, then alpha case can be removed from the surface, but production time increases and hazardous chemicals are required

Engineering Contradiction:

Improvealpha case removalVSAvoidproduction time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies a ceramic coating to the titanium alloy surface before heating to prevent alpha case formation in the first place. This preliminary protective action eliminates the need for subsequent removal processes like chemical milling, thereby reducing production time while maintaining surface quality

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The ceramic coating acts as an intermediary barrier between the titanium alloy surface and the harmful environment during heating. This mediator prevents direct interaction between oxygen/carbon/nitrogen and the metal surface, preventing alpha case formation without requiring hazardous chemicals for removal

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If extra layers are printed to compensate for alpha case thickness, then final part dimensions can be maintained, but stress ratio and thermal gradient increase

Engineering Contradiction:

Improvefinal part dimensionsVSAvoidstress ratio

Core Design Contradiction:

Manufacturing precisionVSStress or pressure

Solution Approach 1:

By applying the ceramic coating before the heating process, the patent prevents alpha case formation proactively. This eliminates the need to print extra compensatory layers, thereby maintaining dimensional precision without introducing additional stress ratios and thermal gradients associated with extra printing cycles

Inventive Principle:

Principle #10Preliminary action

3Reliability

If chemical milling is used, then alpha case can be removed, but exposure to hydrofluoric acid causes hydrogen embrittlement

Engineering Contradiction:

Improvesurface qualityVSAvoidhydrogen embrittlement

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The ceramic coating serves as a protective intermediary during the heating process, preventing alpha case formation without requiring exposure to hydrofluoric acid. This eliminates the harmful side effect of hydrogen embrittlement while still achieving the desired surface quality through prevention rather than removal

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the potentially harmful heating process into a beneficial opportunity by applying the ceramic coating first. The coating transforms the heating environment from harmful (causing alpha case) to beneficial (maintaining surface integrity), eliminating the need for hazardous chemical treatments

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 effectively prevents alpha case formation by diffusing oxygen, nitrogen, and carbon at elevated temperatures, reducing production time and costs, and eliminating hazardous chemical exposure.

Implementation Method 1

The method effectively prevents alpha case formation by diffusing oxygen, nitrogen, and carbon at elevated temperatures

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

subjecting the preform to hot isostatic pressing while the ceramic coating is applied to the surface

Methodology Applied

Scientific EffectHot isostatic pressing: Hot Isostatic Pressing

Data Source

PatentUS12559434B2Methods and compositions for inhibiting alpha case on titanium alloy surfaces

Publication Date: 2026.02.24 THE BOEING CO

AI summary

A method for inhibiting alpha case on a titanium or titanium alloy article includes applying a ceramic coating to a surface of the article. The method further includes heating the article to a temperature of at least 800° F. while the ceramic coating is applied to the surface of the article. A method for manufacturing a titanium article that is substantially free of alpha case includes fabricating a preform by additive manufacturing, applying a ceramic coating to a surface of the preform, the ceramic coating having a nominal coating thickness of at least about 1 mil, subjecting the preform to hot isostatic pressing while the ceramic coating is applied to the surface, and removing the ceramic coating after hot isostatic pressing.