Cold Gas Spraying Mo-W Layers Using Porous Aggregates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cold gas spraying (CGS) technologies face challenges in producing dense, well-adhering layers of molybdenum (Mo) and tungsten (W) with high thickness and low residual stresses, often resulting in poor adhesion and high defect densities, particularly with brittle materials like Mo and W, which are difficult to deposit using conventional CGS methods.
Innovation Solution
A process involving a coating material composed of Mo or W particles, presented as aggregates and/or agglomerates with high porosity, injected into a high-pressure process gas (>10 bar) within a convergent-divergent nozzle, where the gas is heated to >800°C, allowing for efficient deposition of layers with improved adhesion and density using nitrogen as the process gas, eliminating the need for expensive helium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cold gas spraying is used for brittle materials like Mo and W, then the process is simple and inexpensive, but the layer adhesion is poor and defect density is high
Solution Approach 1:
The invention changes the physical state parameters of the coating material by using aggregates and agglomerates with controlled porosity (10-80%) instead of conventional fine powders. This parameter change enables brittle materials like Mo and W to achieve adequate adhesion through controlled deformation and mechanical interlocking, resolving the adhesion problem without requiring complex process modifications
Solution Approach 2:
The invention creates a composite structure within the coating material by forming aggregates and agglomerates consisting of multiple particles bound together. This composite approach allows the material to exhibit both strength from the particle bonds and ductility from the overall aggregate structure, improving adhesion of brittle materials while maintaining process simplicity
2Manufacturing precision
If fine powders are used for coating material, then the particle size is small and deposition is easier, but the layers have high defect densities and poor adhesion
Solution Approach 1:
The invention segments the coating material into aggregates and agglomerates composed of multiple fine particles bound together. This segmentation approach allows the benefits of fine particle deposition while avoiding the drawbacks of poor adhesion, as the aggregate structure provides mechanical interlocking and distributed stress pathways that reduce defect density and improve overall layer quality
3Reliability
If helium is used as process gas, then particle velocity and deposition quality are improved, but the process cost increases significantly
Solution Approach 1:
The invention replaces expensive helium gas with cheaper alternative gases (air, nitrogen, or their mixtures). By combining this gas substitution with the use of aggregates and agglomerates, the process achieves adequate deposition quality at significantly reduced cost, making the technology economically viable for industrial applications
4Reliability
If high gas pressure is used to increase particle velocity, then adhesion improves, but residual stresses in the layer increase
Solution Approach 1:
The invention changes the particle morphology parameter by using aggregates and agglomerates with specific porosity ranges (10-80%). This parameter change allows the particles to deform more effectively upon impact, achieving adequate adhesion through mechanical interlocking and plastic deformation at lower gas pressures, thereby reducing residual stresses in the deposited layer
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 process achieves dense, firmly-adhering layers with low residual stresses and defect densities, enabling the production of thick, high-quality layers and self-supporting bodies with Mo or W content exceeding 80% at a lower cost, using nitrogen as the process gas and achieving particle velocities necessary for effective adhesion without the limitations of fine powders.
Implementation Method 1
A process gas (for example air, He, N2 or mixtures thereof) under high pressure is depressurized by means of a convergent-divergent nozzle (also referred to as supersonic nozzle)... Gas velocities of, for example, from 900 m/s (in the case of N2) to 2500 m/s (in the case of He) can be achieved
Implementation Method 2
Heating of the gas before the convergent-divergent nozzle increases the flow velocity of the gas and thus also the particle velocity in the expansion of the gas in the nozzle... the gas is heated in a heater immediately after leaving the gas buffer and the heated gas is fed to the spray gun
Implementation Method 3
Coating processes in which powder particles are applied with very high kinetic energy and low thermal energy to a support material are subsumed under the term cold gas spraying (CGS)... The coating material is, for example, injected into the gas stream before the narrowest cross section of the convergent-divergent nozzle which forms part of the spray gun, typically accelerated to a velocity of from 300 to 1200 m/s and deposited on the substrate
Data Source
AI summary
A process for producing a layer or a body built up of layers. A process gas which has a pressure of >10 bar is accelerated in a convergent-divergent nozzle and a coating material which is formed by particles and is composed of Mo, W, an Mo-based alloy or a W-based alloy is injected into the process gas. The particles are at least partly present as aggregates and/or agglomerates. It is possible to produce dense layers and components in this way. We also describe layers and components having a microstructure with cold-deformed grains having a high aspect ratio.