Chromium Coating via Cold Gas Spraying
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Solution Overview
Problem
Current methods for producing chromium-containing layers via cold gas spraying face challenges such as poor adhesion, high porosity, and brittleness, particularly due to the high yield strength and work hardening of chromium, which limits the production of dense and crack-free layers with high chromium content.
Innovation Solution
A coating material with Cr-rich particles having a high Cr content (>95% by mass), characterized by specific surface area, porosity, and particle aggregation, which enhances spray behavior and adhesion, is used in cold gas spraying to produce layers with improved density and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chromium oxide is reduced using conventional methods (aluminothermal or electrolytic processes), then chromium powder is produced, but the powder exhibits poor spray behavior and high porosity in cold gas spraying
Solution Approach 1:
The invention changes the physical and chemical parameters of chromium powder production by using hydrogen reduction at controlled temperatures (800-1500°C) with specific hydrogen partial pressures (0.1-10 bar) and residence times (0.1-10 seconds). This produces chromium powder with optimized properties: lower hardness, higher ductility, and controlled particle morphology that enables dense, defect-free layers in cold gas spraying
Solution Approach 2:
The invention creates a composite approach by combining hydrogen reduction with controlled carbon contamination (adding 0.1-5 wt% carbon to the chromium powder). This composite material has improved spray behavior and forms dense layers without the porosity problems of conventional chromium powders
2Strength
If chromium powder with high yield strength is used, then adhesion may be improved, but flowability deteriorates and layer build-up becomes impossible
Solution Approach 1:
The invention optimizes chromium powder parameters by controlling particle size (5-50 μm), hardness (20-40 HV0.05), and ductility through hydrogen reduction conditions. This creates powder with balanced properties: sufficient adhesion strength while maintaining flowability for layer build-up
3Manufacturing precision
If chromium layers are deposited galvanically, then dense layers can be produced, but hydrogen is incorporated causing cracks and reduced corrosion resistance
Solution Approach 1:
The invention replaces the galvanic deposition process (electrochemical) with cold gas spraying (physical deposition). This substitution eliminates hydrogen incorporation during deposition while achieving dense layers through controlled particle impact and deformation at room temperature
Solution Approach 2:
The invention utilizes phase transition of chromium particles from powder state to deposited layer state through cold gas spraying. The particles undergo plastic deformation and densification upon impact, achieving dense structure without hydrogen embrittlement associated with galvanic processes
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 enables the production of dense, well-adhering, and crack-free chromium layers with high chromium content, overcoming the limitations of existing technologies by improving the flowability and mechanical interlocking of particles, resulting in enhanced layer quality and properties.
Implementation Method 1
The coating material is heated in a spray torch (thermal energy) and/or accelerated to high speeds (kinetic energy)
Implementation Method 2
a process gas brought to high pressure and heated (usually N 2 , He or mixtures thereof) is expanded using a convergent-divergent nozzle (also referred to as a supersonic nozzle). A typical nozzle shape is the Laval nozzle (also called De Laval nozzle). This generates the kinetic energy required for the spraying process
Implementation Method 3
The adhesion of the coating material to the substrate material and the cohesion between the particles of the coating material are crucial for the quality of a thermally sprayed layer
Data Source
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AI summary
The invention relates to a coating material comprising Cr-rich regions having a Cr-content of > 95 mass percent, which form Cr-containing particles. Said particles are, at least partially, in the form of aggregates or agglomerates, are provided, at least partially, with pores, have an average nano hardness HIT 0.005/5/1/5 of ≤ 4 gpa in the Cr-rich regions and/or an average surface > 0.05 m2/g measured by BET. The coating material is especially well suited for cold-gas spraying. The invention further relates to a method for producing a layer, and to a layer produced using said method.