Pt-Cr-Free TiAl Coating for High-Temperature Oxidation
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Solution Overview
Problem
TiAl alloys face limitations in high-temperature oxidation resistance and mechanical property preservation due to rapid oxidation and oxygen diffusion at temperatures above 700°C, with existing coatings like platinum-based and chromium-containing layers causing phase transformations that impair strength.
Innovation Solution
A Pt- and Cr-free TiAl alloy coating with a higher aluminum content, deposited by physical vapor deposition at ≤600°C, forming a slowly growing aluminum oxide layer with additives like silicon and erbium to inhibit oxygen diffusion, maintaining mechanical properties and preventing microstructural destabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum layer is deposited and heat treated to form aluminum oxide layer, then high-temperature oxidation protection is achieved, but aluminum diffuses into the TiAl base material forming brittle intermetallic phases that impair strength
Solution Approach 1:
The invention changes the compositional parameters of the coating layer by incorporating refractory elements (W, Mo, Nb, Ta) with specific atomic percentages (W: 1-20 at.%, Mo: 1-20 at.%, Nb: 1-20 at.%, Ta: 1-20 at.%) to modify diffusion behavior and phase stability, preventing aluminum diffusion into the base material while maintaining oxidation protection
Solution Approach 2:
The invention creates a composite coating system consisting of multiple elements (Al, W, Mo, Nb, Ta, and TiAl base material) that work synergistically: aluminum provides oxidation resistance through Al2O3 formation, while refractory elements control diffusion and stabilize the microstructure, preventing brittle phase formation at the interface
2Reliability
If platinum-based or chromium-containing protective layers are applied, then high-temperature protection is achieved, but phase transformations occur in the surface region of the TiAl base material that impair mechanical properties
Solution Approach 1:
The invention replaces Pt and Cr with refractory elements (W, Mo, Nb, Ta) that have different physical and chemical properties, specifically lower reactivity with TiAl base material and different melting points, which prevent phase transformations while maintaining high-temperature protection capabilities
Solution Approach 2:
The invention substitutes expensive platinum and chromium materials with more cost-effective refractory elements that achieve similar or superior protection performance without the harmful phase transformation side effects, making the coating more economically viable
3Strength
If TiAl alloys are used for high-strength, low-density components, then mechanical properties are improved, but oxidation resistance deteriorates at temperatures above 700°C
Solution Approach 1:
The invention applies a localized protective coating with specific compositional characteristics (high aluminum content 60-80 at.%, plus refractory elements) only on the surface region of the TiAl component, preserving the bulk material's excellent strength-to-weight ratio while providing targeted oxidation resistance where it is most needed
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 coating effectively increases the use temperature of TiAl components without impairing mechanical properties, forming a stable, impermeable aluminum oxide layer that prevents oxygen penetration and microstructural transformations, ensuring reliable high-temperature protection.
Implementation Method 1
depositing on the component by physical vapor deposition at a temperature of less than or equal to about 600° C. a Pt- and Cr-free protective layer TiAl alloy
Implementation Method 2
the aluminum is oxidized and the TiAl material underneath becomes enriched in this as a result of diffusion
Implementation Method 3
the TiAl material underneath becomes enriched in this as a result of diffusion
Data Source
AI summary
Disclosed is a process for coating a component of a TiAl alloy in order to improve the high-temperature resistance of the component. The process comprises depositing a Pt- and Cr-free protective layer alloy comprising Ti, Al, Nb, Mo and B and optionally one or more of W, Si, C, Zr, Y, Hf, Er and Gd on the component by physical vapor deposition at a temperature of less than or equal to 600° C. The protective layer alloy has a higher Al content than the TiAl alloy of the component. A coated component made by this process is also disclosed.