Meta l Powder Techno logyVacuum Induct ion Mel t ing and Iner t Gas Atomizat ion

Ceramic -Free Meta l Powder Product ionIner t Gas Recyc l ing

METAL POWDER TECHNOLOGY

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Metal powder technology is one of the most estab-

lished production methods nowadays in all kinds of

industries.

The process steps involved in the production of metal

powders are melting, atomizing and solidifying of

the respective metals and alloys. Metal powder

production methods such as oxide reduction and

water atomization, are limited with respect to special

powder quality criteria, such as particle geometry,

particle morphology and chemical purity.

Inert gas atomization, combined with melting under

vacuum or under protective atmosphere therefore

is the leading powder-making process for the

production of high-grade metal powders which have

to meet specific quality criteria such as:

n Spherical shape;

n High cleanliness;

n Rapid solidification;

n Homogeneous microstructure.

ALD has the capability to combine various melting

technologies with inert gas atomization which

enables the production of superalloys, superclean

materials and additionally reactive metals.

Metal powder technology - an established productionmethod for all kind of industrial applications

VIGA EIGA

VIGA Production UnitInert Gas Atomization Plant

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ALD has developed through over 30 years in gas

atomization technology process know-how to atomize

a broad range of materials for various applications.

Each particular application needs a special particle

shape and powder morphology.

With the right adjustment of the process parameters

it is possible to cover a wide range of desired powder

size distributions and to meet the demands for

various applications.

The following pictures show some examples for

different types of alloys.

n Solder/Brazing/Precious Alloys

n Iron-based- and Superalloys

n Refractory and Reactive Metals

Metal Powder Applications:

n Ni-base superalloys for the aviation industry

and power engineering;

n Solders and brazing metals;

n Hydrogen-storage alloys;

n Wear-protection coatings;

n Thermal Spray coatings;

n MIM powders for components;

n Magnetic alloys;

n Sputter target production for electronics.

Melting Alternatives in

Metal Powder Production

n VIGA: Vacuum Induction Melting combined

with Inert Gas Atomization;

n EIGA: Electrode Induction Melting Gas

Atomization;

n PIGA: Plasma Melting Induction Guiding Gas

Atomization;

n ESR-CIG: Electroslag Remelting Coldwall

Induction Guiding;

n VIGA-CC: Vacuum Induction Melting

based on Coldwall Crucible Melting Technology

combined with Inert Gas Atomization.

n Solder/Brazing/Precious AlloysSolder, Brazing and Precious Alloys have a high quality demand with regard to particle size and particle morphology. Especially solder/brazing alloys need fine powders with a low percentage ofagglomerated particles.

n Iron-based- and SuperalloysPlasma Spray powders for special coatings, powdersfor MIM applications as well as Superalloy powder for aerospace applications are covered by ALD’satomization technology.

n Refractory and Reactive MetalsAtomization of refractory and reactive metals withhigh melting temperatures (up to 2000 °C) is carriedout with a ceramic free melting and atomization technology. The atomization takes place in a speciallydesigned free-fall-atomization nozzle configuration.

PIGA ESR-CIG VIGA-CC

Particle Size Distribution of various Alloys

Aluminium-Alloy

Precious Metal-Alloy

Fe-based Alloy

Ni-based Alloy

Co-based Alloy

Titanium-Alloy

TiAl-AlloySolder/Brazing-Alloy

Particle Diameter [µm]

Cum. Volume Percentage [%]

Particle Diameter [µm]

Cum. Volume Percentage [%]

Particle Diameter [µm]

Cum. Volume Percentage [%] Zirkon-Alloy

Vacuum Iner t Gas Atomizat ion Sys tem (VIGA)

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With Tilting Crucible With Bottom PouringCrucible

VIGA

Vacuum Inert Gas Atomizat ionSystem (VIGA)

The standard design of a vacuum inert gasatomization (VIGA) system comprises a VacuumInduction Melting (VIM) furnace where thealloys are melted, refined and degassed. Therefined melt is poured through a preheatedtundish system into a gas nozzle where themelt stream is disintegrated by the kineticenergy of a high pressure inert gas stream.The metal powder produced solidifies in flightin the atomization tower located directlyunderneath the atomization nozzle. The powder gas mixture is transported via a conveying tube to the cyclone where the coarseand the fine powder fractions are separatedfrom the atomization gas. The metal powder iscollected in sealed containers which are locateddirectly below the cyclones.

ALD has developed atomization systems where a variety of melting processes can becombined with inert gas atomization. Theatomization systems built by ALD have a modular design and are applicable from laboratory scale (1 – 8 l crucible volume),through pilot production (10 – 50 l cruciblevolume) up to large-scale atomization systems(with 300 l crucible volume).

Operator platform with state-of-the-artprocess visualization

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Large Sca le VIGA Atomizat ionUni t

The photo on this page shows a large scaleinert gas atomization system. The melting cru-cible of this production atomization system hasa maximum capacity of 2 tons. The atomiza-tion tower is connected to a melt chamber witha double-crucible door arrangement. Each fur-nace door is equipped with a vacuum inductionmelting furnace. This design allows very fastcrucible changing. While one crucible is in pro-duction the second crucible can be cleaned orrelined in stand-by position. This minimizes thedown time for furnace change operations.Additionally, the double-door design enhancesthe production flexibility, because differentfurnace sizes can be used in the same equip-ment. The melting chamber is equipped with abulk charger, two temperature measuringdevices and a redundant tundish system.

The redundant tundish configuration allows ahigh flexibility in case clogging of the outletnozzle occurs. In that situation, the secondpreheated tundish nozzle system which is instand-by position can be moved into the atomization position to continue the process.Each pouring tundish, including the gas nozzlearrangement, is mounted on a tundish cart.

Double-door crucible VIGA atomization unit with redundant tundish systemsEach vacuum induction furnace has a rated batch capacity of 2,000 kg. A gas recycling system recovers the inert gas for reuse.

Schematic design of a large scale atomization unit with adouble-door melting furnace chamber

Powder collection system of a large-scaleatomization unit

The tundish cart can be moved sideways to alocation for loading and unloading withoutventing the system and without breaking theambient atmosphere.

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Due to the contact between the melt and theceramic lining and nozzle material, in stan-dard VIGA systems ceramic inclusions in themelt can occur, which influence the materialproperties of high-strength PM-components ina negative manner. Reactive metal powders,such as titanium based alloys, can not be produced with this method at all, due to thereactions between the reactive melt and theceramic lining. In order to overcome the“ceramic problem” it is necessary to use melt-ing techniques where the melt is not in contactwith ceramic lining material. Additionally, arefining of the melt during the melting processwould be desirable. Typical materials thatneed ceramic-free production processes arerefractory and reactive materials, such as Ti,TiAl, FeGd, FeTb, Zr and other materials.

E IGA

In the EIGA process, prealloyed rods in formof an electrode are inductively melted andatomized without any melting crucible at all.The melting of the electrode is accomplishedby lowering the slowly rotating metal electrode into an annular induction coil.

E IGA PIGA

Ceramic -Free Meta l Powder Product ion

Electrode Induction Melting GasAtomization System

Electrode Induction Melting Gas Atomization (EIGA)

Plasma Melting Induction Guiding Gas Atomization (PIGA)

The melt droplets from the electrode fall intothe gas atomization nozzle system and areatomized with inert gas. The EIGA process wasoriginally developed for reactive alloys such astitanium and high-melting alloys. It can alsobe applied to many other materials.

PIGA

For the production of ceramic-free powdersand for the atomization of reactive, and/orhigh-melting alloys, melting can also beaccomplished by means of a plasma burnerin a water-cooled copper crucible. PIGA standsfor plasma-melting induction-guiding gasatomization.

The bottom of the PIGA crucible shown below isconnected with an inductively heated dischargenozzle, also made of a copper base material.This ceramic-free discharge nozzle systemguides the liquid metal stream into the gasatomization nozzle, where it is disintegratedby the inert gas.

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Besides powder production, the disintegrationprocess of the liquid metal stream can be usedto collect the spray droplets to form a so-called spray formed billet. The collection dur-ing the sprayforming process is shown in thepicture below.

VIGA-CC

Reactive alloys like titanium or intermetallicTiAl alloys can also be melted in a copper-based cold wall induction crucible which isequipped with a bottom pouring system. Thebottom pouring opening of the cold crucible isattached to a CIG system. The bottom pouringopening of the cold crucible is attached to aColdwall Induction Guiding (CIG) System.

ESR-CIG

High performance superalloys for the aircraftindustry are typically produced via the so-called “triple melt process”. In the triplemelt process the refining of the material iscarried out by the reactive slag in the ESRmelting step. The combination of the ESRremelting technique with a ceramic-free meltguiding system (CIG) represents a processtechnology to produce powder material with ahigh level of cleanliness and chemical homo-geneity.

In the ESR-CIG process, the material to beatomized is fed in form of an electrode. Theelectrode is lowered into the metallurgicalrefining slag. As the electrode tip is melted at its point of contact with the slag, droplets of the refined metal are formed and thesedroplets pass down through the reactive slaglayer.

The refined metal droplets which pass throughthe reactive slag form a liquid melt poolunderneath the slag layer. The melt pool isenclosed by a water-cooled crucible made ofcopper. The refined liquid metal is guidedthrough the cold-wall induction guiding system and is disintegrated by a high kineticinert gas stream in a free-fall-type gas nozzle.

ESR-CIG VIGA-CC

Electroslag Remelting Coldwall Induction Guiding (ESR-CIG)

Vacuum Induction GasAtomization based on ColdwallCrucible Melting Technology(VIGA-CC)

Collection of atomized particles to a sprayformed billet

Molten metal stream out of CIG system before entering the high pressure gas nozzle

Particle shape of high grade metal powder

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Iner t Gas Recyc l ingAt a certain batch size of the atomization sys-tem, recycling of the inert gas is recommended,to reduce the total inert gas consumption andthus achieve a more economical productionprocess. ALD offers two different process technologies to recycle the inert gas.

Inert Gas Recycling Based onCompressor Technology

One method of reusing the inert gas is to“drive” the gas in a closed gas circulation loop,using a suitable compressor unit. Behind thecyclone and the filter system, the “dust-free”gas is repressurized using a 2-stage compressorunit. The compressors have to be gastight toprevent contamination of the recirculated inertgas. After each compressor, a gas buffer tank isused to minimize pressure fluctuations duringthe atomization process. This results in stableatomizing process conditions with respect toatomization pressure and gas-flow rate.

In case the permissible impurity levels in theatomization gas are set very low, the oxygen,hydrogen and nitrogen contents can be mea-sured at several locations in the gas circulationloop.

For large-scale atomizing systems this type ofgas recycling is economically operated in apressure range up to 50 bar.

Argon Recyc l ing Based onL iquefact ion

To achieve a higher gas supply pressure, therecycling concept described above has to bechanged to the principle of reliquefying theargon by using evaporating liquid nitrogen asthe refrigerant. In this situation, the 2-stagecompressors with the pulsation buffer arereplaced by a concurrent flow argon liquifierand a set of high-pressure liquid argon pumps.

Compressor Technology

Liquefaction Technology

1 Atomization tower2 Cyclone3 Heat Exchanger4 Cyclone Filter

5 Fine Filter6 Blower7 Compressor System8 Gas Buffer Tank

1 Atomization tower2 Cyclone3 Heat Exchanger4 Cyclone Filter5 Fine Filter6 Liquefied-argon tank7 Evaporator8 Fresh gas storagevessel

Argon recycling system based on liquefaction

Great BritainALD Vacuum Technologies Ltd.First Floor276 High StreetGuildford, Surrey GU 1 3JL, UKPhone +44 (1483) 45 44 34e-mail: info@aldvactech.co.uk

RussiaALD Vacuumyje Technologii OOOul. Bolschaja Ordynka 40, str. 2109017 Moskau, RussiaPhone +7 (495) 787 6733e-mail: ald@metallurg.com.ru

ALD Vacuum Technologies GmbHWilhelm-Rohn-Strasse 35D-63450 Hanau, GermanyPhone: +49 (0) 6181 - 307-0Fax: +49 (0) 6181 - 307-3290e-mail: solar@ald-vt.deInternet: www.ald-vt.de

ChinaALD Liaison Officec/o C&K Development Co., Ltd.Rm. 1102, South Office TowerHong Kong Plaza283 Huai Hai Zhong Rd. Shanghai, 200021, ChinaPhone +86 (21) 63 85 - 55 00e-mail: ald@ald-vt.cn

Far EastALD Thermo Technologies Far East Co., Ltd.10F. Shinjuku Nomura Bldg.1-26-2 Nishi-Shinjuku, Shinjuku-KuTokyo 163-0558, JapanPhone +81 (3) 33 40 37 26e-mail: Peter.Lang@ald-vt.de

USA / CanadaALD Vacuum Technologies, Inc.18, Thompson RoadEast Windsor, CT 06088, USAPhone +1 (860) 386 72 - 27e-mail: info@ald-usa.com