Fine Metal Powders

Ralph H. Hershberger, UltraFine Powder Technology Inc.

Fine metals have been commercially available for years by various methods. One of the earliest methods was the precipitation of elemental precious metal powders. Fine refractory metal powders are also produced by milling.

Elemental iron or nickel powders are also produced to fine particle distributions with the carbonyl process. On a tonnage basis, carbonyl iron still accounts for a large percentage of fine powders used for metal injection molding. Carbonyl iron is produced to very tight distributions (Table 1) with typical particle sizes ranging from 3 to 8 i'm. Tables 2 and 3

summarize carbonyl iron grades from BASF, which is the world's largest supplier of carbonyl iron. More information on carbonyl iron is also contained in the article "Production of Iron Powder" in this Volume.

Table 1 Typical composition and particle size distribution of carbonyl iron powder

BASF grade

Mean

Iron,

Carbon(a),

Nitrogen(a),

Oxygen(a),

Other

Particle size distribution

size,

wt%

wt%

wt%

wt%

10%

50%

90%

P m

less than

less than

less than

Reduced standard powders

CL

7-8

>99.5

0.05

0.01

0.2

5.0 .'■m

10.0 .'-m

25.0 .'-m

CM

5-6

>99.5

0.05

0.01

0.2

4.0 .'-m

9.0 .'-m

22.0 .'-m

CS

4-5

>99.5

0.05

0.01

0.2

4.0 .'-m

8.0 .'-m

18.0 .'-m

CN

5-6

>99.5

0.04

0.01

0.2

3.5 .'-m

8.0 .'-m

18.0 .'-m

CC

4-6

>99.5

0.05

0.01

0.3

0.1 wt% coating

SiO2 3.0 .'-m

6.0 .'-m

11.0 .'-m

SU

1-1.5

99.4

0.1

0.01

0.5

0.70 .'-m

1.67 .'-m

3.43 .'-m

SM

1-1.6

99.4

0.1

0.01

0.5

0.81 .'-m

1.91 .'-m

3.66 .'-m

Iron-

3-5

88

0.3-0.7

0.1

0.4-0.6

9-10 wt% P

1.5 .''-m

4.0 .''-m

10.0 .'-'m

Maximum wt% unless a range is specified

Maximum wt% unless a range is specified

Table 2 Carbonyl iron powders for powder metallurgy and injection molding

BASF Mean grade size, tlm

(max), wt%

Characteristic properties

Reduced standard powders

CL 7-8

>99.5

^0.05

:l0.01

:l0.2

Soft, spherical powder

CM 5-6

>99.5

<0.05

ll0.01

£j0.2

Soft, spherical powder

CS 4-5

>99.5

<0.05

0.01

:l0.2

Soft, spherical powder

CN 5-6

>99.5

<0.04

ij 0.01

:l0.2

Soft, spherical powder

Unreduced standard powders for injection molding

OM 4-5

>97.8

<0.9

<0.9

:l0.4

Unreduced, hard powder; agglomerates broken up by grinding

ON 4-5

>97.5

■ 1.2

■ 0.1

<12

Unreduced, hard powder with low N content and higher

O content

OS 4-5

>97.3

0.9

ij 0.9

0.7% SiO2

Unreduced, hard powder; SiO2 coated

OX 3-4

>96.2

<0.9

ij 0.9

5% i 1 -Fe2O3

More stable form in debinding with improved sinter properties

OX 3-4

>94.7

^0.9

Fe203

With lower or higher £V-Fe203 content on request

Table 3 Carbonyl iron powders for electronic and microwave applications

BASF Mean grade(a) size, /'m

Iron min, wt%

Carbon max, wt%

Nitrogen max, wt%

Oxygen max, wt%

Bulk, density, g/cm3

Characteristic properties

For electronic parts

EN 4-5

>97.4

<1.0

<1.0

<0.4

2.6

General-purpose product

EW 4-5

>97.3

<1.0

<1.0

<0.8

2.3

High ohmic resistance and high Q factor at 5-10 MHz

EQ 3-5

>97.2

<1.0

<1.0

<0.4

2.7

High Q factor at 4-15 MHz

ES 3-4

>97.4

<1.1

<1.1

<0.4

2.2

High Q factor at 30-100 MHz

SP 4-6

>99.5

<0.05

<0.01

<0.2

2.2

Ductile attainable toroidal / 'm = 75(b)

SQ 4-6

>99.5

<0.06

<0.01

<0.4

1.9

Specially insulated; high Q factor at 100-200 KHz; attainable toroidal tl: 68<b)

SL 7-8

>99.5

<0.05

<0.01

<0.2

2.6

attainable toroidal : 65(b)

SD

5-6

>99.5

<0.06

<0.01

<0.2

2.4

attainable toroidal !■: 60(b)

SB

5-6

>99.5

<0.1

<0.01

<0.2

2.6

attainable toroidal ^: 55(b)

HM

2.6-3.5

>96.0

<2.0

<2.0

<0.4

2.9

High permeability; high Q factor; wide particle size distribution

HL

2.8-3.5

>97.0

<1.0

<1.0

<0.5

2.7

General-purpose H product

HS

2.4-3.3

>97.0

<1.0

<1.0

<0.5

2.2

High Q factor, particularly at 10 MHz

HF

2.0-2.5

>97.0

<1.0

<1.0

<0.7

2.0

High Q factor, 30 to 100 MHz

HQ

1.6-1.9

>97.0

<1.0

<1.0

<1.0

1.9

High Q factor, 10 to 100 MHz

For microwave absorption

EA

3-4

>97.3

<1.2

<1.2

<0.4

Narrow particle size distribution

EB

3-4

>97.3

<1.0

<1.0

<0.4

Somewhat wider particle size distribution

(a) E brands: mechanically hard, mean particle size 3-8 /■'m; H brands: mechanically hard, mean particle size

1.6-3.5 P-rcv, S brands: mechanically soft, mean particle size 3-8 /'m; in each case, the second letter indicates the properties, for example, L, large; S, small; Q, high quality; M, medium; P, good permeability; W, high resistance.

(a) E brands: mechanically hard, mean particle size 3-8 /■'m; H brands: mechanically hard, mean particle size

1.6-3.5 P-rcv, S brands: mechanically soft, mean particle size 3-8 /'m; in each case, the second letter indicates the properties, for example, L, large; S, small; Q, high quality; M, medium; P, good permeability; W, high resistance.

(b) With 0.3% of binder and 1.5 GPa pressure

Some alloy parts are produced using elemental carbonyl iron and/or nickel as a base, but this method has obvious chemical limitations. In this regard, prealloyed powders from atomization offer more flexibility in alloy composition. So-called "residual products" met the initial demand for fine, prealloyed powders. Prior to 1980, the demands for fine alloy powders were satisfied by screening the fine residuals from a standard as-atomized distribution. Although this method avoided investment in technology development and dedicated equipment, it had several weaknesses. First, the supply of fine powders was constantly at risk. The available fine powders were a function of the production and sales of a coarse powder stream. This dependency jeopardized the supply continuity. Secondly, the powders frequently were not discrete particles and had satellites or were dog-boned shaped. Finally, if the products were sold on an as-yielded basis, the prices were prohibitively high and few markets could support production. Until manufacturers became convinced that a sustainable fine powder market existed, end users had to contend with these limitations. Ultimately, the limitations of residual fines prevented further growth.

Today a full range of fine alloy powders are produced by atomization methods (Table 4). Ametek, Specialty Metals Division in the United States, uses a specialized high-pressure, water-atomized system. Pacific Metals (PAMCO) of Japan uses high-pressure water and a recently announced combination water- and gas-atomization system (Ref 1). Mitsubishi employs a water-atomized process to create a feedstock, which is subsequently cold worked to create nodular shape powders. The primary commercial gas-atomization operations include UltraFine Powder Technology in the United States, Anval in Sweden, and Osprey Metals in Wales.

Table 4 Major commercial fine atomized powder producers, systems, and products

Country

Producer

Powder production system

Grades produced

Japan

Pacific Metals (PAMCO)

High-pressure water

Stainless, tool steels, nickel and cobalt alloys

Mitsubishi

High-pressure water, shape modified

Stainless, tool steels, nickel and cobalt alloys

Kobe

Water atomization

Stainless and tool steels

Sweden

Anval

Nitrogen gas atomization

Stainless steels

Plasma-heated tundish

United Kingdom

Osprey

Proprietary gas atomization

Stainless, tool steels, low alloy, and cobalt alloys

United States

UltraFine Powder Technology

Proprietary gas atomization

Stainless, tool steel, low alloy steels, copper, nickel, and cobalt alloys

Ametek

High-pressure water atomization

Stainless, tool steels, and nickel alloys

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