Production de poudres métalliques

Vue d'ensemble

Poudres métalliques are fine metal particles used as feedstock for manufacturing techniques like additive manufacturing, metal injection molding, and powder metallurgy pressing and sintering. Producing advanced specialty metal powders with precise control of chemistry, particle size distribution, morphology, and microstructure is critical to properties of finished components.

There are various methods used for large scale production of metal powder production from different alloy systems including:

• Atomisation du gaz
• Vaporisation de l'eau
• Atomisation par plasma
• Electrode induction melting gas atomization
• Procédé d'électrode rotative
• Processus de carbonylation
• Procédé électrolytique
• Metal reduction processes

Each process results in powders with different characteristics suited to specific applications.

Méthodes de production de poudre métallique

Poudre de métal Méthodes de production

There are a variety of commercial methods used for producing metallic powders from different alloy systems. The choice of production method depends on factors like:

• Type of alloy material
• Purity requirements
• Desired powder characteristics like particle size, shape, grain structure
• Scale of production in tons per year
• Powder end use application

Here are some of the most common industrial processes for metal powder production:

Processus d'atomisation des gaz

In gas atomization process, a stream of molten metal alloy is disintegrated by high pressure jets of gas, usually nitrogen or argon. The metal stream breaks up into fine droplets, which solidify into powder particles.

Gas atomized powders have a spherical shape and smooth surface morphology. Particle size distribution can be controlled by adjusting process parameters. This is a widely used technique for reactive materials like titanium, aluminum, magnesium alloys as well as stainless steels, tool steels and nickel superalloys.

Atomisation de l'eau

In water atomization, the molten metal stream is hit by high velocity water jets. The sudden cooling causes an explosion that breaks the metal into fine particles. The powders have irregular shapes and contain higher oxygen content from water contact.

Water atomization is lower cost process used for producing large volumes of stainless steel, alloy steel, iron and copper powders for pressing and sintering type applications.

Plasma Atomization Process

In plasma atomization process, a plasma torch is used to melt the metal alloy before disintegration into fine droplets through gas jets. The ultra-high temperatures enable highly reactive elements like titanium aluminides to be successfully atomized.

The powders have a very spherical shape and narrow size distribution suitable for additive manufacturing methods like laser melting and electron beam melting.

Rotating Electrode Process (REP)

In the rotating electrode process, a cylindrical metallic electrode is spun at high speeds in an evacuated chamber. It is melted using an electric arc and the molten metal droplets flung off through centrifugal forces cool to form powders.

REP powders have a grain structure and morphology ideal for hot extrusion into fine wires and rods for aerospace alloys like tungsten, molybdenum, tantalum.

Atomisation par induction de gaz par électrodes (EIGA)

Le procédé EIGA utilise le chauffage par induction pour faire fondre les pointes d'électrodes consommables dans une atmosphère de gaz inerte. Les gouttelettes sont ensuite atomisées par des jets d'argon pour former de fines poudres sphériques.

L'EIGA permet d'obtenir des superalliages de nickel réactif d'une très grande pureté pour les composants critiques de l'aérospatiale grâce à une fusion contrôlée et à une minimisation de la contamination.

Processus de carbonylation

Dans le processus de carbonylation, le métal est converti en un carbonyle volatil, qui se décompose dans des conditions contrôlées pour produire des particules métalliques uniformes et ultrafines. Cette approche permet de produire des poudres de fer, de nickel et de cobalt très pures.

Autres méthodes de production de poudre

Parmi les autres techniques utilisées pour la production de poudres de métaux spéciaux, on peut citer les suivantes :

• Procédé électrolytique: Utilisé pour produire des poudres de cuivre et de nickel de forme irrégulière et de morphologie dendritique par électrodéposition.
• Procédés de réduction des métaux: Réduction d'oxydes métalliques à l'aide d'hydrogène ou de carbone pour produire des poudres de titane, de zirconium, de tungstène et de molybdène.
• Alliage mécanique: Broyage à haute énergie pour synthétiser des alliages composites et nanostructurés

Poudre de métal Spécifications

Les attributs de qualité critiques et les spécifications testées pour les poudres métalliques dépendent de la méthode de production et de l'application finale, mais comprennent généralement les éléments suivants :

Chimie des poudres

• Composition des alliages par spectroscopie d'émission optique ou de fluorescence X
• Éléments d'alliage mineurs
• Éléments d'impureté tels que l'oxygène, l'azote et l'hydrogène
• Essai de perte au feu à haute température

Distribution de la taille des particules

• Taille moyenne des particules en volume
• Largeurs de distribution telles que D10, D50, D90

Caractérisation de la forme des particules

• Microscopie électronique à balayage pour la morphologie
• Facteurs de forme tels que le rapport d'aspect et le facteur de forme

Microstructure

• Phases présentes par diffraction des rayons X
• Caractéristiques des grains à partir de l'imagerie

Propriétés des poudres

• Densité apparente/tap
• Débit dans les essais de débitmètre à entonnoir de Hall
• Niveaux de compressibilité

Les exigences en matière de spécifications pour les poudres varient considérablement en fonction de l'utilisation finale dans différentes applications :

Méthodes de caractérisation

Plusieurs méthodes analytiques sont utilisées pour caractériser les propriétés des poudres métalliques essentielles à la performance des produits :

Analyse de la taille des particules

Laser diffraction methods are most widely used to characterize the particle size distribution. This technique passes a laser beam through a dispersed powder sample which scatters light at an angle dependent on particle sizes. Computer analysis of the diffraction pattern provides detailed statistically relevant size distribution data within seconds.

Morphology and Surface Imaging

Scanning electron microscopy (SEM) provides high resolution images of powder particle shape, surface topographies and features at much higher magnification and depth of focus compared to optical microscopy.

SEM imaging is used to study particle rounding, satellite formation, surface smoothness and defects like porosity.

Density and Flow Property Measurement

Standard test methods have been established to quantify bulk behavior using:

• Hall flowmetry funnel to measure powder flow rates through an orifice
• Carney funnel to assess flowability by angle of repose
• Scott volumeter to determine tap density and compressibility

These methods help predict ease of handling, blending, die filling and spreading during component manufacturing.

X-ray Methods for Composition and Crystal Structure

• X-ray fluorescence spectroscopy accurately identifies and quantifies elemental composition of metals
• X-ray diffraction analyzes the atomic arrangements and phases present by diffraction peak patterns

Applications des poudres métalliques

Some major end uses of engineering metal powders include:

Fabrication additive

Also known as 3D printing techniques like selective laser melting (SLM), direct metal laser sintering (DMLS) and electron beam melting (EBM) to build complex geometries from titanium, aluminum, stainless steel, superalloy, cobalt chrome powders.

Moulage par injection de métal (MIM)

Powders like stainless steels, titanium alloys and tool steels are combined with a binder, injection molded then sintered to manufacture small, complex parts at high volumes for lower costs.

Presse et frittage pour la métallurgie des poudres

Compacting and sintering iron, copper and alloy steel powders into high volume components like gears, bushings and magnets.

There are also niche applications in areas like welding, diamond tools, electronics and surface coatings that use specialty metal powders.

Fournisseurs et prix

Some leading global suppliers of various metal powders are:

Pricing for metal powders varies widely by:

• Alloy material and composition
• Méthode de production utilisée
• Processing to achieve particle characteristics
• Purity levels and degree of contamination
• Purchase volumes – very high volume contracts bring lower pricing

Typical base prices per kilogram are:

Prices go up significantly for highly customized particle size distributions, controlled oxygen and nitrogen levels below 100 ppm, and small lot purchases.

Advantages and Limitations of Powder Metallurgy

Benefits of Powder Metallurgy

• Ability to produce complex geometries not possible through casting or machining
• Near-net-shape manufacturing reduces material waste
• Higher performance metals and alloys can be used
• Consistent porosity structures not possible in ingot metallurgy
• Components can be mass customized

Limitations of Powder Production and Processing

• Capital investment for production and handling equipment is very high
• Increased surface area makes handling pyrophoric reactive powders risky
• Achieving high compaction densities can require high pressures
• Additional process steps compared to casting
• Portability of AM machines due to powder being LO/NO

Here is a quick comparison of powder metallurgy against the conventional casting process:

FAQ

Q: What is the typical particle size range used in metal 3D printing powders?

A: In powder bed technologies like selective laser melting (SLM) and electron beam melting (EBM), the optimal particle size range is 15-45 microns. Finer powders improve resolution but can be challenging to handle and process.

Q: What determines morphology of metal powders from different methods?

A: Production factors like intensity of melt stream breakdown forces from gas jets or water impacts and subsequent cooling rates determine particle shapes. Faster cooling produces irregular, dendritic particles while slower solidification (spherical atomization) enables smooth rounded structures.

Q: Why is high purity important for metal powders in additive manufacturing?

A: Impurities can cause defects, porosity issues, alter alloy microstructures, reduce density, affect performance under loads and temperatures – negatively impacting mechanical properties. Target oxygen levels below 500 ppm and nitrogen levels below 100 ppm have become typical.

Q: How are metal powders handled safely during transportation and storage?

A: Reactive metal powders are passivated to create oxidized surfaces minimizing flammability risk. Powders are sealed in drums under inert gases like argon instead of air during shipment to prevent ignition. Storage containers must be properly grounded. Personnel wear specialized PPE while handling.

Q: What are common powder characterization methods?

A: Hall flowmetry, tap density tests, pycnometry, LOI testing, spectrographic analysis, metallography and particle size distribution using laser or sieve techniques are vital to quantifying behavior, building quality process control for metal powder production and assessing batch suitability for given applications.

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