Metal Powder

What is metal powder?

Metal powder refers to a group of metal particles with a size of less than 1 mm. Including single metal powder, alloy powder and some refractory compound powder with metallic properties, it is the main raw material for powder metallurgy and metal powder additive manufacturing, mainly including aluminum powder, titanium powder, copper powder, nickel powder, stainless steel powder, cobalt powder Powder, tungsten powder, magnesium powder, nickel powder, manganese powder, etc.

Metal powder properties

Metal powder is a loose substance, and its properties comprehensively reflect the properties of the metal itself, the properties of individual particles and the characteristics of particle groups. The properties of metal powders are generally divided into chemical properties, physical properties and process properties. Chemical properties refer to metal content and impurity content. Physical properties include the average particle size and particle size distribution of the powder, the specific surface and true density of the powder, the shape, surface morphology and internal microstructure of the particles. Process performance is a comprehensive performance, including powder fluidity, bulk density, tap density, compressibility, formability, and sintered dimensional changes. In addition, powders are also required to have other chemical and physical properties for some special purposes, such as catalytic properties, electrochemical activity, corrosion resistance, electromagnetic properties, internal friction coefficient, etc. The properties of metal powders depend to a large extent on the production method of the powder and its preparation process. The basic properties of powders can be determined by specific standard test methods. There are many methods for the determination of powder particle size and distribution, generally using sieve analysis method (>44μm), sedimentation analysis method (0.5 ~ 100μm), gas permeation method, microscope method, etc. Ultrafine powders (<0.5 μm) were determined by electron microscopy and X-ray small angle scattering. Metal powder is customarily divided into five grades: coarse powder, medium powder, fine powder, fine powder and ultrafine powder.

Application of metal powder

Metal powders can be used as industrial raw materials for powder metallurgy products, and can also be used directly.

Industrial raw materials

The metal powders used in this regard mainly include iron, tungsten, molybdenum, copper, cobalt, nickel, titanium, tantalum, aluminum, tin, lead and other powders, and the consumption accounts for more than 2/3 of the total output of metal powders.

Direct application

The direct application of metal powder is very extensive. E.g:
①Welding rod, iron powder for flame cutting process.
②Ni-Cr-B-Si, Fe-Cr-B-Si, Co-Cr-W and other alloy powders and nickel-coated aluminum or aluminum oxide, nickel or cobalt-coated tungsten carbide for spraying, spray welding and fusion welding etc. Coated powder. It is used to strengthen the wear resistance, heat resistance and corrosion resistance of the workpiece surface.
③Ultrafine aluminum powder for rocket solid fuel.
④Nickel, iron, cobalt powder for catalyst.
⑤ Magnetic powders for clutches, tapes, and copiers, such as iron-based alloy powders.
⑥ explosives, iron, nickel, cobalt, manganese, magnesium, aluminum, aluminum-magnesium alloy and other powders for fireworks.
⑦ Deoxidizers, chemical reagents, metal thermal reducing agents, replacement agents, etc. use aluminum, magnesium, iron powder, etc.
⑧ Surface coloring, decoration, paint pigments, aluminum, copper and other powders for paint.
⑨Steel shot, bronze shot peening, etc. for surface processing.
⑩ Iron powder and copper powder for metal electrochemical deposition.

In addition to the above applications, metal powders are increasingly used in 3D printing – Metal Powder Additive Manufacturing.

The advantages of Metal Powder Additive Manufacturing（3D Print） are:

01. Lightweight can be achieved

Due to the small molding restrictions, 3D printing can give full play to the role of generative design and topology optimization. In the design stage, algorithms are used to reduce unnecessary parts of parts, so as to achieve lightweight printed parts, and then manufacture them through 3D printing.

02. Can build complex shapes

Metal 3D printers create objects layer-by-layer, and in the most common form of powder bed fusion, objects are made by repeatedly melting and solidifying metal powder with a laser, bit by bit. The molding limit is relatively small, and complex structures such as lattices can be fabricated.

Therefore, some parts that cannot be demolded and the tool cannot enter for cutting can be manufactured by 3D printing. Additionally, metal 3D printed parts are already stronger than cast parts, and are approaching forged strength as technology continues to advance.

03. The number of parts is small, the work efficiency is high, and flexible production is possible

The 3D printing process has a high degree of design freedom and can give full play to the role of design. It can not only reduce unnecessary parts, but also integrate multiple parts into a whole, improve work efficiency and reduce energy consumption.

04. Short lead time

When the number of parts is relatively small, or only one piece is required, 3D printing not only shortens the production time, but also costs less per unit. Therefore, metal 3D printing is suitable for making prototypes or small batch production.

What are the requirements for the performance of metal powders in 3D printing?

We just mentioned a lot of metal powders that can be used for 3D printing. So, to meet the material requirements of 3D printing, what conditions do metal powders need to meet?

1. Purity

Ceramic inclusions can significantly reduce the performance of the final part, and these inclusions generally have a high melting point and are difficult to sinter, so there must be no ceramic inclusions in the powder.

In addition, oxygen and nitrogen content also need to be strictly controlled. At present, the powder preparation technology for metal 3D printing is mainly based on the atomization method. The powder has a large specific surface area and is easy to oxidize. In special application fields such as aerospace, customers have stricter requirements for this index, such as superalloy powder. The oxygen content is 0.006%-0.018%, the oxygen content of titanium alloy powder is 0.007%-0.013%, and the oxygen content of stainless steel powder is 0.010%-0.025%.

2. Powder particle size distribution

Different 3D printing equipment and forming processes have different requirements for powder particle size distribution. At present, the powder particle size range commonly used in metal 3D printing is 15-53 μm (fine powder), 53-105 μm (coarse powder), and can be relaxed to 105-150 μm (coarse powder) in some cases.

The selection of metal powder particle size for 3D printing is mainly based on metal printers with different energy sources. Printers using lasers as energy sources are suitable for using 15-53μm powder as consumables because of their fine focusing spot and easy melting of fine powders. The powder supply method is layer-by-layer powder coating; the powder coating type printer using electron beam as the energy source has a slightly thicker focusing spot, which is more suitable for melting coarse powder, and is suitable for the use of 53-105μm coarse powder; for coaxial powder feeding type For printers, powders with a particle size of 105-150 μm can be used as consumables.

3. Powder morphology

The powder morphology is closely related to the preparation method of the powder. Generally, when the metal gaseous or molten liquid is converted into powder, the shape of the powder particles tends to be spherical. When the solid state is changed to powder, the powder particles are mostly irregular in shape, while most of the powders prepared by aqueous electrolysis are dendritic.

In general, the higher the sphericity, the better the fluidity of the powder particles. 3D printing metal powder requires a sphericity of more than 98%, which makes it easier to spread and feed powder during printing.

The above table shows the morphologies of metal powders corresponding to different milling methods. It can be seen that, except for the gas atomization method and the rotating electrode method, the morphologies of the powders prepared by the other methods are all non-spherical. Electrode method is the main preparation method for high-quality 3D printing metal powder.

Microstructure of stainless steel powder: 

Powder particle size distribution

Through our flexible and efficient work, we are able to supply high-quality metal powders with a wide range of particle size distributions, as well as customized particle size distributions on request.

Powder particle classification

• 1000~50µm conventional powder
• 50~10µm finepowder
• 10~0.5µm very fine powder
• <0.5µm ultrafine powder
• 0.1~100nm nanometer powder

How to choose particle size for spherical alloy powder?

In the process of use, due to the different powder particle sizes used in each process, for example, the selective laser melting process uses 15-53 μm powder, the thermal spraying process uses 15-45 μm powder, electron beam printing uses 45-105 μm powder, and ordinary powder metallurgy uses 0- 150μm powder, so we need to physically sort the powder, and the graded powder material can be used in aerospace, biomedical, automotive electronics, machinery manufacturing and other fields.

What kind of spherical alloy powder is of good quality?

1: High density, low porosity, reduce product cost and improve working speed.
2: High sphericity, uniform particle size, better process efficiency and finished product performance.
3: Low oxygen content, no hollow powder satellite powder.
4: Good fluidity, suitable for complex products.

What are the spherical alloy powders?

Grades of spherical alloy powder Superalloy powder: GH4169, GH3625, GH3536, GH5188, GH3230, GH4099, GH1131, K418, K438 (In738), K477, K447A, DD4, DD5, DD6, DZ125 Titanium alloy powder: TA1, TA15, TC4 , TC17, TC18, TC21 steel powder: M2, H13, M42, 316L, 304, 17-4PH, 15-5PH, 310, 420, CPM10V cobalt chromium alloy powder: CoCrMoW, CoCRW, CoCrMo aluminum alloy powder: AISi10Mg, AlMgScZr , AISi12, 2024, 6061, 7075 refractory powder: W, Mo, Ta, Nb, V, Si, Hf, Re

Application of spherical alloy powder

1. Aerospace field: used in aircraft fan blades, compressor blades, fuselage bearing structural parts, landing gear, and high thrust-to-weight ratio engine turbine disks, compressor disks, turbine baffles, rocket nozzles, etc.
2. Nuclear industry: used in nuclear fuel, neutron control materials and shielding materials, neutron deceleration materials and reflector materials, nuclear reactor fuel element cladding and bearings, etc.
3. Biomedical field
4. 3D printing field: metal printing consumables for LENs (DMD), EBDM, SLM technology, and also for high-performance direct forming and rapid repair of complex integral components, cladding and adding feature structures.
5. Automotive industry: such as auto parts and so on.
6. In other fields, it is used for powder metallurgy dense parts such as metal powder injection molding and laser forming.

How to deal with the risks of metal additive manufacturing powder handling?

Handling metal powder is inherently dangerous because of its susceptibility to fire and explosion, as well as physical health problems associated with prolonged inhalation and exposure to metal powder.

From production, blending and screening to shipping, safety must be a top priority, including equipment maintenance, handling procedures and employee safety.

This is why closed procedures are preferable. Pressurized production of metal fines with an inert gas such as argon greatly reduces some of the safety risks.

We also absolutely avoid producing multiple alloys in the same location to prevent the risk of powder metal contamination with each other.

In addition to this, we can share specific best practices for handling powders if you want.

Metal Powder Packaging Options

Our packaging of metal powders is suitable for air, sea and ground transportation with a variety of packaging options

Packaging materials are:

Special plastic bottle
Metal cans
Special steel drum

Packaging weight is divided into:

5 kg (11 lb) pack
6 kg (13 lb) pack
10 kg (22 lb) pack
20 kg (44 lb) pack
100 kg (220 lb) pack
150 kg (330 lb) pack
250 kg (551 lb) pack

In addition, we can also customize packaging as required

How is metal powder made?

It is usually divided into two categories: mechanical method and physical chemical method according to the principle of transformation, which can be obtained directly from solid, liquid and gaseous metals, and can be transformed from metal compounds in different states by reduction, pyrolysis and electrolysis. made. Carbides, nitrides, borides and silicides of refractory metals can generally be prepared directly by compounding or reduction-compounding methods. Due to different preparation methods, the shape, structure and particle size of the same powder are often very different (Figure 2). The preparation methods of powder are listed below, among which reduction method, atomization method and electrolysis method are the most widely used.

Reduction method

The oxygen in the metal oxide powder is captured by a reducing agent, and the metal is reduced into powder. Gas reducing agents include hydrogen, ammonia, coal gas, converted natural gas, etc. Solid reducing agents include carbon and metals such as sodium, calcium, and magnesium. Hydrogen or ammonia reduction is often used to produce tungsten, molybdenum, iron, copper, nickel, cobalt and other metal powders. Carbon reduction is often used to produce iron powder. Metal powders such as tantalum, niobium, titanium, zirconium, vanadium, beryllium, thorium and uranium can be produced by using strong metal reducing agents such as sodium, magnesium and calcium (see metal thermal reduction). Using high-pressure hydrogen to reduce the aqueous solution of metal salts, nickel, copper, cobalt and their alloys or coated powders can be obtained (see hydrometallurgy). Most of the powder particles produced by the reduction method are irregular shapes of sponge structure. Powder particle size mainly depends on factors such as reduction temperature, time and particle size of raw materials. The reduction method can produce powders of most metals and is a widely used method.

Atomization

The molten metal is atomized into fine droplets, which solidify into a powder in a cooling medium (Figure 3). Figure 4 The widely used two-flow (melt flow and high-speed fluid medium) atomization method uses high-pressure air, nitrogen, argon, etc. (gas atomization) and high-pressure water (water atomization) as the spray medium to break the metal liquid flow . There are also centrifugal atomization methods that utilize rotating disk pulverization and the rotation of the melt itself (consumable electrodes and crucibles), as well as other atomization methods such as dissolved hydrogen vacuum atomization, ultrasonic atomization, etc. Due to the small droplets and good heat exchange conditions, the condensation speed of droplets can generally reach 100-10000K/s, which is several orders of magnitude higher than that of ingot casting. Therefore, the composition of the alloy is uniform, the structure is small, and the alloy material made of it has no macrosegregation and excellent performance. Gas atomized powder is generally nearly spherical, and water atomization can produce irregular shapes. The characteristics of powder such as particle size, shape and crystalline structure mainly depend on the properties of the melt (viscosity, surface tension, superheat) and atomization process parameters (such as melt flow diameter, nozzle structure, pressure of spray medium, flow rate, etc.) . Almost all metals that can be melted can be produced by atomization, especially for the production of alloy powders. This method has high production efficiency and is easy to expand the industrial scale. It is not only used for mass production of industrial iron, copper, aluminum powder and various alloy powders, but also for the production of high-purity (O2<100ppm) superalloy, high-speed steel, stainless steel and titanium alloy powders. In addition, the preparation of rapidly condensing powders (condensation rate > 100,000K/s) by chilling technology has received increasing attention. It can be used to produce high-performance microcrystalline materials (see fast cooling microcrystalline alloys).

Electrolysis

When direct current is applied to the metal salt aqueous solution, metal ions are discharged and precipitated on the cathode, forming a deposit layer that is easily broken into powder. Metal ions generally originate from the dissolution of the same metal anode and migrate from the anode to the cathode under the action of current. The factors affecting the particle size of the powder are mainly the composition of the electrolyte and the electrolysis conditions (see electrolysis of aqueous solutions). Generally, electrolytic powders are mostly dendritic and have high purity, but this method consumes a lot of electricity and costs more. Electrolysis is also widely used, and is often used to produce copper, nickel, iron, silver, tin, lead, chromium, manganese and other metal powders; alloy powders can also be prepared under certain conditions. For rare refractory metals such as tantalum, niobium, titanium, zirconium, beryllium, thorium, and uranium, composite molten salts are often used as electrolytes (see molten salt electrolysis) to prepare powders.

Mechanical crushing

The solid metal is mainly broken into powder by crushing, crushing and grinding. The equipment is divided into two categories: coarse crushing and fine crushing. Crushing equipment mainly includes crushers, rolling mills, jaw crushers and other coarse crushing equipment. The main functions of crushing and grinding are hammer crushers, rod mills, ball mills, vibrating ball mills, stirring ball mills and other fine crushing equipment. The mechanical crushing method is mainly suitable for crushing brittle and easy work-hardening metals and alloys, such as tin, manganese, chromium, high-carbon iron, iron alloys, etc. It is also used to crush the brittle titanium after hydrogenation, and then dehydrogenation to produce fine titanium powder. The mechanical pulverization method has low efficiency and high energy consumption, and is mostly used as a supplementary method for other pulverizing methods, or for mixing powders of different properties. In addition, the mechanical pulverization method also includes a vortex mill, which relies on two impellers to create a vortex, so that the particles trapped by the airflow collide with each other at high speed and pulverize, which can be used for the pulverization of plastic metals. The cold flow crushing method uses a high-speed and high-pressure inert gas stream to carry coarse powder and spray it onto a metal target. Due to the adiabatic expansion of the airflow at the outlet of the nozzle, the temperature drops sharply below 0 °C, so that the coarse powder of metals and alloys with low temperature brittleness is pulverized into fine powder. The mechanical alloying method uses a high-energy ball mill to grind different metals and refractory compounds into a solid solution or finely dispersed alloy state.

Carbonyl method

Some metals (iron, nickel, etc.) and carbon monoxide are synthesized into metal carbonyl compounds, and then thermally decomposed into metal powder and carbon monoxide. The powder thus obtained is very fine (particle size ranging from several hundred angstroms to several microns) and high purity, but also high cost. It is mainly used in industry to produce fine and ultra-fine powders of nickel and iron, as well as alloy powders such as Fe-Ni, Fe-Co, and Ni-Co.

Direct legalization

Carbon, nitrogen, boron, and silicon are directly combined with refractory metals at high temperatures. The reduction-chemical method uses carbon, nitrogen, boron carbide, silicon and refractory metal oxides. Both methods are commonly used to produce carbide, nitride, boride and silicide powders.

Other methods

Due to the uniform composition, fine grain size and high activity of fine powders and ultrafine powders smaller than 10 μm, they are widely used in manufacturing materials (such as dispersion-strengthened alloys, ultra-microporous metals, metal tapes) and direct applications (such as rocket solid fuels and magnetic fluid seals). , magnetic ink, etc.) has a special status. In addition to carbonyl method and electrolysis method, vacuum evaporation condensation method, arc spraying, coprecipitation double salt decomposition, gas phase reduction and other methods are also used to manufacture such powders.
Coating powders are increasingly showing excellent performance in special applications such as thermal spraying and atomic energy engineering materials. By adopting two types of chemical powdering methods, gas phase and liquid deposition, such as hydrogen reduction thermal dissociation, high pressure hydrogen reduction, replacement, electrodeposition, etc., various coating powders mixed with metals and metals, metals and non-metals can be prepared.

Various standards for metal powders:

GB/T 11105-1989 Latola test of metal powder compacts
GB/T 11106-1989 Method for compressing cylindrical compacts for metal powders to determine compact strength
GB/T 13390-1992 Determination of specific surface area of ​​metal powder – Nitrogen adsorption method
GB/T 13390-2008 Determination of specific surface area of ​​metal powder – Nitrogen adsorption method
GB/T 1479-1984 Determination of bulk density of metal powders Part 1: Funnel method
GB 1480-1984 Determination of particle size composition of metal powder – Dry sieving method
GB/T 1480-1995 Determination of particle size composition of metal powder – Dry sieving method
GB 1481-1984 Determination of compressibility of metal powders (excluding powders for cemented carbide) in uniaxial pressing
GB/T 1481-1998 Determination of compressibility of metal powder (excluding cemented carbide powder) in uniaxial pressing
GB/T 1482-1984 Determination of fluidity of metal powder Standard funnel method (Hall flowmeter)
GB/T 1482-2010 Metal powder – Determination of fluidity – Standard funnel method (Hall flowmeter)
GB/T 21779-2008 Light scattering test method for particle size distribution of metal powders and related compounds
GB/T 4164-1984 Determination of hydrogen-reduced oxygen content in metal powders
GB/T 4164-2002 Determination of hydrogen-reduced oxygen content in metal powders
GB/T 4164-2008 Determination of hydrogen-reduced oxygen content in metal powders
GB/T 5060-1985 Determination of bulk density of metal powders Part 2: Scott volume meter method
GB 5061-1985 Determination of bulk density of metal powders Part 3: Vibrating funnel method
GB/T 5061-1998 Determination of bulk density of metal powders – Part 3: Vibrating funnel method
GB/T 5157-1985 Determination of particle size distribution of metal powder – sedimentation balance method
GB 5158-1985 Determination of weight loss of metal powder during reduction in hydrogen (hydrogen loss)
GB/T 5158-1999 Determination of mass loss of metal powder during reduction in hydrogen (hydrogen loss)
GB/T 5158.4-2001 Metal powder Determination of total oxygen content reduction-extraction method
GB/T 5159-1985 Determination method of dimensional change associated with forming and sintering of metal powder (excluding powder for cemented carbide)
GB/T 5160-1985 Metal Powder – Method for Determination of Compact Strength by Transverse Fracture of Rectangular Compacts
GB/T 5160-2002 Determination of green strength of metal powder – Transverse fracture method of rectangular compact
GB/T 5161-1985 Metal powder – Determination of effective density – Liquid immersion method
GB/T 5162-1985 Metal powder – Determination of tap density
GB/T 5162-2006 Metal powder – Determination of tap density
GB/T 6524-1986 Determination of particle size distribution of metal powders – Optical transmission method
GB/T 6524-2003 Metal powder – Measurement of particle size distribution – Gravity sedimentation light transmission method
GB/T 8643-1988 Determination of lubricant content in lubricant-containing metal powder Soxhlet extraction method
GB/T 8643-2002 Determination of lubricant content in lubricant-containing metal powders – Modified Soxhlet extraction method
SN/T 1138-2002 Dry sieving test method for particle size composition of import and export metal powders
YB/T 036.13-1992 General technical conditions for metallurgical equipment manufacturing Oxygen-acetylene flame metal powder spraying
YS/T 56-1993 Metal Powder – Determination of Natural Slope Angle