hpulcas™

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High Purity Nickel (Ni 99.98) in form of Plate, Strip and Wire:

Properties, Applications and Fabrication

Table of Contents

Summary ............................................................................................................................................1

A. Grade and norms ........................................................................................................................2

B. Properties of high purity nickel ..................................................................................................2

I. Lacking trace elements ............................................................................................................3

II. Softness ..................................................................................................................................3

III. Low recrystallization temperature of high purity nickel and melting point of other metals ..4

IV. Function as diffusion barrier ................................................................................................4

V. Stable properties .....................................................................................................................4

C. Applications ................................................................................................................................5

I. Properties of high purity nickel and their applications .............................................................5

II. Applications in detail ...............................................................................................................6

1. Batteries and capacitors ......................................................................................................6

2. Clad materials ......................................................................................................................6

3. Welding and brazing ............................................................................................................6

4. Sensors and controls............................................................................................................7

D. Production of strip and wire from cathode plates ......................................................................7

I. Starting material .....................................................................................................................7

II. Fabrication process .................................................................................................................7

III. Structure of the weld zone ..................................................................................................9

IV. Delivery program .................................................................................................................9

Contacts ........................................................................................................................................... 10

Keywords: high purity nickel, nickel strip, nickel wire, cathode plates, trace elements in nickel,

properties of nickel, applications of nickel

Summary

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GmbH has developed and implemented a new process to fabricate high purity nickel. The

new grade meets and surpasses the requirements for Ni 270. The key to the process is the use of

high purity cathode plates instead of nickel powder. The high degree of purity results in special and

reproducible properties, which are used in demanding applications ranging from temperature

sensors and controls, welding and brazing products, battery and supercapacitor components,

diffusion barriers in roll bonded clad metals, contacts and thermobimetals.

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hpulcas is an acronym for high purity ultra low carbon and sulfur

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A. Grade and norms

Hpulcas nickel with a purity of 99.98 % meets the composition requirements laid down by the norms

and technical documentations as UNS N02270, Nickel 270, W.Nr. 2.4050, Ni 99.98, ASTM F3 Grade 4

(“Standard Specification for Nickel Strip for Electron Tubes”) and JIS H 4501:1990 (“Nickel Sheets And

Strips For Electronic Tube”). However, the level of trace elements allowed by these norms is drastic-

cally reduced in hpulcas nickel:

Trace

element

Ni 99.98

(hpulcas)

Nickel

270

ASTM F3

Grade 4

W.Nr.

2.4050

JIS H 4501

VNiR/VNiP

C wt. % < 0,002 0.01 0.02 0.08 0.1

S wt. % < 0,0002 0.001 0.001 0.005 0.008

Cu wt. % < 0,00022 0.001 0.001 0.03 0.1

Fe wt. % < 0,00022 0.03 0.005 0.07 0.2

Mg wt. % < 0,0001 0.001 0.001 0.04 0.1

Mn wt. % < 0,0001 0.001 0.001 0.01 0.3

Si wt. % < 0,0003 0.001 0.001 0.03 0.2

Ti wt. % < 0.0002 0.001 0.001

Table 1: Trace elements allowed by high purity nickel grades

Whereas the norms assume, that this nickel grade is produced by powder metallurgy, hpulcas uses a

proprietary process.

B. Properties of high purity nickel

Standard grades of Nickel already possess an exceptional range of properties: very good corrosion

resistance, good creep resistance

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and high temperature coefficient of electrical resistance. High

purity nickel even shows substantially improved properties. These properties are:

Property Unit Degree of purity

Ni 99.98 Ni 99.6 Ni 99.2

Trace elements

- C wt. % < 0,002 0.036 0.034

- Al wt. % < 0.0001 0.005 0.005

- Ti wt. % <0.0002 < 0.02 0.045

- Si wt. % < 0,0003 0.07 0.13

- Mn wt. % < 0.0001 0.01 0.066

- Mg wt. % < 0.0001 0.01 0.01

Tensile Strength

- soft temper Rm [MPa] 300 - 350 370 - 400 370 - 450

- hard Rm [MPa] 600 - 900 590 - 700 590 - 700

Elongation (soft temper) % > 95 25 - 40 10 - 25

Recrystallisation temperature °C 300 - 350 690 - 720 690 - 720

Electrical resistance µΩ*cm 7.1 8.0 9.0

Temperature coefficient of

electrical resistance

10

-6

K +6,600 +5,300 to 6,400 +4,700 to +5,800

Curie temperature °C 360 +/- 1 354 - 360 350 - 370

Table 2: Properties of various grades of nickel

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caused by the large number of twins, which hinder dislocation jumps

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I. Lacking trace elements

If Nickel is produced by conventional melt metallurgy, C, Al, Si and/or Ti are added to deoxidize the

melt, Mn and Mg are added to globalize S. These elements are supposed to be slagged out, but

remain partly in the melt.

Al, Si and Ti remaining in the melt are mostly present in oxidized form, which makes these particles

very hard. As a consequence, the particles don’t deform at the same rate as the surrounding metal,

resulting in holes, when foil is rolled or in wire breaks, when thin wire is drawn.

During the annealing process, the trace elements segregate to the surface, internal layers and grain

boundaries. Segregation to layer boundaries is particularly harmful in clad metals, as brittle

intermetallic phases impair bond strength and support delamination.

High purity nickel is nearly free from trace elements, so little, if any, segregation occurs.

II. Softness

High purity nickel in the annealed state is extraordinarily soft. The consequences of softness are:

- heavy reduction possible between annealing steps

- less frequent interim annealing necessary

- if nickel is a top and /or bottom layer in clad composites, softness is a critical factor to achieve

“green” bonding and bond strength. This is already the case if the core material is relatively hard

in comparison to nickel, as is the case for titanium, stainless steel and steel. It is even more

important if the core layer is a soft material as copper or aluminum.

Figure 1: Strength and hardness of high purity nickel

Even though high purity nickel made by powder metallurgy can be produced having the same degree

of purity as hpulcas strip and wire, comparison of the mechanical properties shows that hpulcas

nickel products made from cathodes is softer in all tempers. Table 2 represents the comparison of

the range of mechanical properties, such as tensile strength (R

m

), 0.2% yield strength (R

0.2

),

elongation and Vickers hardness for hpulcas high purity nickel wire, to wire produced by means of

powder metallurgy.

0

100

200

300

400

500

600

700

800

14

25

33

,3

43

,5

52

55

,5

60

64

,7

68

,6

70

,6

72

,4

74

,1

75

,5

Stre

ng

th

, M

Pa

Vick

ers h

ard

ne

ss

Cold work, %

hpulcas 99.98

Tensile strength

0,2 yield

strength

Vickers hardness

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Condition Process R

0.2

[MPa] R

m

[MPa] Elongation [%] Hardness [HV]

Soft annealed

hpulcas process 100-200 300-350 >45 <65

Powder

metallurgy

105-140 345-400 40-45 64-90

Half hard

hpulcas process >300 >450 >15 >100

Powder

metallurgy

345-520 413-550 79-86 148-171

Full hard

hpulcas process >500 600-900 >5 >150

Powder

metallurgy

620-690 650-710 12 >203

Table 3: Range of typical mechanical properties of hpulcas Ni 99.98% wire and wire made by powder

metallurgy

III. Low recrystallization temperature of high purity nickel and melting point of other metals

A low recrystallization temperature

- is beneficial when nickel is annealed

From 500 °C upwards, nickel tends to stick, requiring strip annealing. As high purity nickel

recrystallizes below 500 °C, it can be bell annealed. Bell annealing is more economical than

continuous annealing.

- is necessary if nickel is clad to a metal with a low melting point

Combinations between standard nickel grades and aluminum or magnesium can be clad, but

they cannot be subsequently soft annealed due to the low melting points of the Al or Mg. The

low recrystallization temperature is even more important, if the metal with a low melting

temperature reacts exothermically with nickel upon melting. In addition, magnesium has a

tendency to autoignite; the autoignition temperature of magnesium ribbon is approximately 473

°C (746 K; 883 °F).

Metal Melting point Recrystallization

°C °C

Less pure Nickel 690 - 720

High purity Nickel 300 - 350

Magnesium 650

Aluminum 660

Table 4: Recrystallization temperature and melting points of selected metals

If aluminum or magnesium are clad to high purity nickel, the composite can be soft annealed.

IV. Function as diffusion barrier

If clad metals are exposed to elevated temperatures, its layers may diffuse into each other. This is

the case for copper and gold, especially, when the gold layer is electrolytically deposited and

therefore porous. In addition, constituents of layers may migrate from one layer into another. This

happens with C, if high carbon steel and low carbon steel are cladded. Nickel can be used as an

interlayer hindering diffusion.

V. Stable properties

A substantial change in the content of trace elements as carbon, sulfur and silicon has substantial

influence on the mechanical as well as electrical properties of pure nickel.

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For high precision electronic applications such as sensing or regulating devices, not only certain

properties, but also the stability and reproducibility of the properties are decisive. Standard nickel

grades lack stable properties. By ensuring a low content of trace elements stability and reproduci-

bility of the properties are realized.

Property Unit Degree of purity

Ni 99.98 Ni 99.6 Ni 99.2

Temperature coefficient of

electrical resistance

(between 0 and 100 °C)

10

-6

K +6,600 +5,300 to 6,400 +4,700 to +5,800

Curie temperature °C 360 +/- 1 354 - 360 350 - 370

Table 5: Stability of properties

C. Applications

I. Properties of high purity nickel and their applications

The special properties of high purity nickel are used in the following applications:

Property

Value/characteristics Significance Application

Ni 99.98 Ni 99.2

Degree of purity

(Ni-content)

99.98% 99.2%

Decreased amount of impurities

drastically influences the

mechanical properties of pure

metal.

Segregations of impurities

facilitate stress corrosion fracture

and inter-granular corrosion.

Sputtering targets

C-Content <20 ppm 1000 ppm

Carbon results in hot-shortness

and increases hardness and

electrical resistance.

Deep drawn products,

as electrode shells

S-content <2 ppm 50 ppm

Surface segregation of sulfur

results into a sulfur induced

breakdown of the passive film on

nickel facilitating corrosion.

Segregation to boundaries results

into hot-shortness and reduced

mechanical stress.

Products relying on

catalytically active

surfaces.

Si-content 0.2 ppm 1000 ppm

In the presence of silica (as well as

Al and Ti oxides) thin products are

exposed to breaking (wire) or

developing holes (strip).

Oxides increase die wear.

Foil, thin wire.

Glass molds for optical

quality glass.

Expanded metal

Tensile strength,

MPa

300-350 450

High purity nickel (HPN) can be

deformed by up to 98% without

intermediate annealing.

Deep drawn parts (as

CCFL-electrodes);

brazing spacer taking

up compressive stress

Recrystallisation

temperature,

°C

350 690

Starting from about 500 °C, nickel

tends to sticking, when bell-

annealed. HPN annealing

HPN can be annealed

after cladding to

metals with low

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Property

Value/characteristics Significance Application

Ni 99.98 Ni 99.2

temperatures are below the

temperature, where sticking

starts.

melting points as Al

and Mg.

Curie-point,

°C

360±1 354 - 358

Consistent Curie temperature HPN can be used for

temperature sensing.

Electrical

resistance,

µΩ*cm

7.1 9.0

HPN nickel component can be

reduced in size. Less Joule heating

during charging and discharging of

batteries.

current collectors in

batteries, battery

tabs; Litz wire for use

in aggressive climate

and high temperature

Temperature

coefficient of

electrical

resistance

Sensors: Resistance

thermometers, e.g. in

E-Cigs

Controls:

Regulator coil in glow

plugs for Diesel

engines

Table 6: Properties of high purity nickel, significance and use

II. Applications in detail

1. Batteries and capacitors

Nickel is used as

- electrode substrate in hearing aid batteries and supercapacitors

- anode current collector in rechargeable batteries

- battery tabs

2. Clad materials

Metal combination Application

Ni/Al Terminal for prismatic batteries with aluminum case

Examples:

Ni/FeNi36

MnCu18Ni10/Ni/FeNi36

Thermobimetals

In a two layer composite, the layer with the high coefficient of expansion

may consist of nickel, e.g. ASTM TM22.

In case of a three layer structure, an intermediate layer consisting of

copper or nickel is used either to reduce the electrical resistance or to

increase thermal conductivity. For interlayers of nickel see: ASTM B388-06

TM9 to TM17; DIN 1715, Tl. 1 TB 1425, 1435, 1555).

Ni/Ti/Ni Brazing material for ceramics and metals

CuNi25/Ni/CuZn20Ni5 Magnetic signature as a security feature in coinage

Table 7: Clad metal combinations using Ni as one of the layers

3. Welding and brazing

Pure nickel is used for welding in form of electrodes, wire and sheath for cored wire.

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In brazing, nickel is used in form of foil, expanded metal/metal mesh and layered or clad composite.

Nickel functions as solder and spacer to take up stress.

4. Sensors and controls

The temperature coefficient of electrical resistance is used for resistance thermometers and the

progressive limitation of current flowing through a wire subject to increasing temperature. The

magnetic properties (Curie point and Villari effect) are used for temperature sensing resp. as tensile

stress sensor.

D. Production of strip and wire from cathode plates

I. Starting material

hpulcas has developed a proprietary process to manufacture high purity nickel plate, strip, wire and

flatwire directly from full plate cathodes, avoiding melt metallurgy. Cathode plates are produced by

an electro-winning process resulting in fully dense nickel plates with a minimum of trace elements.

This method achieves an initial purity of 99.98% nickel.

Cathode plates are produced by inserting a thin starter sheet in the electrolytic bath, both sides of

which are receiving nickel ions in the process of the electrolytic deposition. Therefore, the cathode

plate has a three layer structure, the outer layers being composed of columnar grains, which resist

deformation against their axis.

The surface of the as-deposited material is covered with an orange peel, dotted with occasional

warts.

Cathode plates are offered in various sizes, e.g. 720 mm wide, 1280 mm long, 12 to 15 mm thick.

Figure 2: Full plate nickel cathode

II. Fabrication process

The surface defects are mechanically removed by milling.

Due to the stress resulting from the electrolytic deposition process, grain recrystallization can be

achieved by annealing without prior reduction. Through a proper choice of annealing parameters,

the grains, during recrystallization, grow across the layer boundaries, dissolving the previous layered

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structure. This is important, as otherwise the plates could delaminate or even split at the layer

boundaries.

The milled cathode plates are heat treated under ambient air at 1100°C in order to achieve

recrystallization. They are then hot rolled at about 1000 °C from 12 to 15 mm down to about 6 mm in

one pass. At this fabrication step, the three-layer structure is still noticeable but the previously sharp

separation of layers has disappeared.

Figure 3: Hot rolling of full plate nickel cathode

After cooling, the plates are leveled and the oxidized surface is removed by brushing. The plates are

then cut to a rectangle of constant width by a table shear.

For the production of strip, the plates are beveled,

frontally welded by TIG-welding with a high purity

nickel feed wire and coiled.

Figure 4: Coiler at the end of the welding line Figure 5: Cold rolled and slit coil

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The hot rolled coil is then cold rolled and slit by subcontractors.

For producing wire, the 6 mm thick plates are cut into 6 mm wide sticks. Special emphasis has to be

given in further processing to avoid edges being folded into the body, which would result in deep

reaching delamination. The sticks are frontally hot or cold pressure welded. Afterwards the raw wire

can be treated in the same way as hot rolled wire produced by melt metallurgy.

Figure 6: Spool with 0.2 mm diameter high purity nickel wire

III. Structure of the weld zone

The welding zones of both strip and wire have the same chemical composition as the starting

material. The difference between the structures of the welding zone, the heat affected zone and the

initial material can be removed by a multi-step reduction with in-between annealing. The resulting

microstructures are shown in Fig. 3.

(a) (b)

Figure 7: Microstructure of as-welded (a) and worked and annealed material (b)

IV. Delivery program

Product mm inch

Plate

Width up to 650 up to 25.6“

Thickness 6 - 10 0.236“ - 0.393“

Strip/Foil

Width 3 - 650 0.12“ - 25.6“

Thickness 0.05 - 2.5 0.002“ - 0.10“

Temper

- soft annealed

- quarter hard

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Product mm inch

- full hard

Surface

- mill finish

- mirror finish

- brush finish

Rod

Diameter up to 4 up to 0.157“

Length up to 2,500 up to 98.4“

Wire

Diameter 0.2 - 1.6 0.0078“ - 0.063“

Flat wire

Width 3 - 12 0.12“ - 0.47“

Thickness 0.25 - 2.5 0.01“ - 0.100“

Contacts

hpulcas GmbH

Frauensteiner Strasse 107

09599 Freiberg

Germany

Tel.: +49 3731 77494 40

Fax: +49 3731 77494 429

www.hpulcas.com

_______________________________

Angaben gemäß § 37a HGB, § 35a GmbHG:

Geschäftsführer: Ralf Lummer; Amtsgericht Chemnitz, Reg.-Nr. HRB 27024

USt-ID-Nr. DE 280822588