Nitrided PVD Coating for Steam Turbine Erosion Resistance
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Solution Overview
Problem
Current surface treatments for 12% chromium stainless steel components in steam turbines, such as boronizing and diamond-like carbon membranes, fail to provide sufficient solid particle erosion resistance, oxidation resistance, and fatigue strength, especially for rotating parts, leading to reduced lifespan and performance.
Innovation Solution
A solid particle erosion-resistant surface treatment comprising a nitrided hard layer and a Physical Vapor Deposition (PVD) hard layer, with the nitrided hard layer having a thickness of at least 30 μm and the PVD hard layer at least 10 μm, featuring materials like CrN, TiN, AlCrN, and TiAlN, applied in multi-layer forms to enhance hardness and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If boronizing treatment is applied to 12% chromium stainless steel, then erosion resistance is improved, but fatigue strength deteriorates and sufficient erosion resistance is still not obtained
Solution Approach 1:
The patent applies a composite surface treatment consisting of multiple layers: a nitrided hard layer (30-100 μm) formed by radical nitriding, and a PVD hard layer (10-50 μm) containing CrN, TiN, AlCrN, or TiAlN. This multi-layer composite structure provides both high hardness for erosion resistance and sufficient fatigue strength, resolving the contradiction between erosion protection and fatigue strength deterioration.
Solution Approach 2:
The patent changes the surface treatment parameters by using radical nitriding to form a thick nitrided hard layer (30 μm or more) instead of conventional boronizing. The PVD layer thickness is controlled at 10 μm or more. These parameter changes result in a surface layer with Vickers hardness of 1200-1500 that achieves both erosion resistance and fatigue strength.
2Object-affected harmful factors
If diamond-like carbon membrane is applied to base material, then erosion resistance is improved, but oxidation resistance and fatigue strength are insufficient for steam turbine applications
Solution Approach 1:
The patent replaces the single-layer diamond-like carbon membrane with a composite structure of nitrided hard layer plus PVD hard layer. The PVD layer materials (CrN, TiN, AlCrN, TiAlN) provide both erosion resistance and oxidation resistance at high temperatures, while the thick nitrided hard layer (30-100 μm) ensures fatigue strength. This composite approach achieves all three required properties for steam turbine applications.
3Object-affected harmful factors
If thick nitrided hard layer is formed, then erosion resistance is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent performs radical nitriding as a preliminary treatment to form a thick nitrided hard layer (30-100 μm) before applying the PVD hard layer. This preliminary action creates a strong foundation that reduces the required PVD layer thickness and ensures proper adhesion. The nitrided hard layer is formed by diffusion of nitrogen into the steel substrate, a well-established process that can be integrated into existing manufacturing lines.
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 treatment significantly enhances solid particle erosion resistance, oxidation resistance, and fatigue strength, extending the lifespan of components and improving the performance of rotating machines like steam turbines by preventing deformation and cracking from collisions.
Implementation Method 1
the nitrided hard layer is formed by a radical nitriding method
Implementation Method 2
a PVD (physical vapor deposition) hard layer of at least one layer formed on the nitrided hard layer by a PVD method
Data Source
AI summary
A solid particle erosion resistant surface treated coating has a solid particle erosion resistance that is largely enhanced and a rotating member having the coating gains oxidation resistance without deteriorating a fatigue strength. Also, a rotating machine can have this coating applied thereto. The solid particle erosion resistant surface treated coating has a nitrided hard layer formed on a surface of a base material and a PVD (physical vapor deposition) hard layer of at least one layer formed on the nitrided hard layer by a PVD method. Deformation of the base material by collisions by solid particles is prevented and cracking of the coating is prevented. Thereby, the solid particle erosion resistance is secured, life of the solid particle erosion resistant surface treated coating can be increased and oxidation resistance and fatigue strength are enhanced.