Publisher: German Copper Institute

• 1. General information on Cu-Ni alloys
  • 1.1 Historical
  • 1.2 The Cu-Ni equilibrium diagram
  • 1.3 Effect of alloying elements
  • 1.4 Cu-Ni alloys in EN standards
  • 1.5 Comparison between related material designations in different countries

• 2. Properties
  • 2.1 Physical properties
  • 2.2 Mechanical properties
  • 2.3 Corrosion resistance

• 3. Manufacture and processing
  • 3.1 Melting
  • 3.2 Casting
  • 3.3 Working
  • 3.4 Heat treatment
  • 3.5 Machining
  • 3.6 Joining
  • 3.7 Surface treatment

• 4. Application

• 5. References

   1. GENERAL INFORMATION ON Cu-Ni ALLOYS

In 1751, A.F. Cronstedt succeeded in isolating nickel. However, Cu-Ni alloys were in existence much earlier, mostly prepared by processing ores. Today, Cu-Ni alloys have gained a variety of interesting applications because of their specific characteristics [1].

Copper and nickel are adjacent to one another in the periodic system of elements, with atomic numbers 29 and 28 and atomic weights 63.54 and 68.71.The two elements are closely related and are completely miscible in both the liquid and solid state. Cu-Ni alloys crystallise over the whole concentration range in a face-centred cubic lattice. The lattice spacing of the face-centre cubic solid solution varies almost linearly with atomic concentration between the values for copper (3.1653 . 10^-8 cm) and that for nickel (3.5238 . 10^-8 cm).

Cu-Ni alloys are alloys of copper (base metal with the largest individual content) and nickel with or without other elements, whereby the zinc content may not be more than 1%. When other elements are present, nickel has the largest individual content after copper, compared with each other element.

As with other copper alloys, it is necessary to distinguish between wrought alloys, which are processed to semi-finished products, and cast alloys, from which castings are produced by various casting processes.

Apart from 8.5 to 45% Ni, most commercial alloys usually contain manganese, iron and tin to improve specific properties, cast alloys also have additions of niobium and silicon.

The age-hardenable copper-nickel-silicon alloys with 1.0 to 4.5% Ni and 0.2 to 0.6% Be are not dealt with here. In European standards, these alloys are assigned to ‘low-alloyed copper alloys’ (see CR 13388 and relevant product standards).

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   1.1 Historical

Although elemental nickel was only discovered relatively late on, its use in alloys – without knowledge of the alloy composition – goes back at least two thousand years. This is confirmed by finds of coins from antiquity, which contain up to 10% nickel in addition to copper [2].

The most ancient Cu-Ni coin that has been saved for posterity comes from the period around BC 235. It was found in Bactria and consists of an alloy similar e.g. to the former German 50-Pfennig and 1 DM pieces (approximately 75% Cu and 25% Ni). These and many other old coins are outstanding examples for the high corrosion resistance of Cu-Ni alloys.

In the Middle Ages, Saxon miners gave a mineral, from whose red colour they inferred a copper ore, the nickname ‘coppernickel’ (nickel = goblin = mountain troll). However, they would not succeed in extracting copper from it – a spell was cast on the ore by a ‘nickel’. It was only red nickel pyrites (NiAs), for the veins of ore worked in seams also incorporated copper and iron sulphides as well as arsenides.

In England, the term ‘cupronickel’ was used at the start of the 20th century for an alloy of 80% Cu and 20% Ni. In Germany, the description ‘Cu-Ni alloys’ was in general use for the group of materials containing less than 50% Ni (see 1.).

The Cu-Ni alloys with additions of manganese that are important in electrical engineering were first referred to in 1895 in a paper of the Physikalisch-Technischen Reichsanstalt in Berlin on ‘Electrical properties of Cu-Ni alloys’. Around 1925, it was recognised that additions of iron significantly improve the resistance of Cu-Ni alloys to erosion corrosion in flowing seawater and other aggressive waters.

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   1.2 The Cu-Ni equilibrium diagram

The equilibrium diagram was first established by Gürtler and Tammann and was later improved by Pilling and Kihlgren, among others. Fig. 1 shows the Cu-Ni equilibrium diagram [3].

Alloys of the two metals form a continuous series of solid solutions having a face-centred cubic lattice, i.e. the Cu-Ni system exhibits complete solubility in both liquid and solid states. The equilibrium diagram is therefore very simple. The melting points of the two components broaden to a melting range in the alloys. The upper curve, which forms the lower boundary of the liquid melt, is called the ‘liquidus’. The curve which forms the upper boundary of the area of a crystals is termed the ‘solidus’. A two-phase area in which liquid and a crystals co-exist is formed between liquidus and solidus.

Below a dotted straight line at the bottom right, behaviour is ferromagnetic, above it is paramagnetic. Thus, for example all alloys up to 80% Ni are paramagnetic at 150 ºC while at 20 ºC alloys containing more than 68.5% nickel exhibit ferromagnetic behaviour.

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   1.3 Effect of alloying elements

Nickel has a significant effect on the physical and mechanical properties of Cu-Ni alloys (see 2.). While tensile strength, 0.2% proof strength, hot strength, solidus and liquidus temperature and corrosion resistance increase with nickel content, thermal and electrical conductivity decrease. Tensile strength and elongation are shown in Fig. 2 as a function of nickel content. Tensile strength increases with nickel content, elongation remains almost constant after a slight decrease (up to 5% Ni).

Manganese is added to the melt for deoxidation. It ties up sulphur, which is detrimental to hot working, as harmless manganese sulphide, improves casting characteristics, increases strength, and especially the softening temperature (Fig. 3).

Iron – dissolved in the solid solution – increases the corrosion resistance of Cu-Ni alloys. It promotes the formation of an adherent, uniform protective coating in water and thus improves corrosion resistance, primarily in fast-flowing seawater (see 2.3). The solubility of iron in the Cu-Ni solid solution decreases as temperature is lowered (Fig. 4), i.e. these alloys – preferably with higher iron contents - are age-hardenable. The solubility of iron also depends on the nickel content of the alloy, increasing with nickel content to reach a maximum at 30% nickel and falling again as nickel content continues to increase. Fig. 5 shows the effect of iron on hardness. Mechanical properties are improved somewhat by iron. Cold workability is slightly worsened.

Tin as an addition element raises tensile strength, tarnish resistance and wear resistance of Cu-Ni alloys. Cu-Ni alloys containing c. 2% Sn are distinguished by very good resistance to stress relaxation and therefore are used a spring materials. Alloys with even higher tin contents (4 to 10%) can also be age-hardened (Fig. 6).

Silicon improves the castability of casting alloys and at the same time acts as deoxidant. In the Cu-Ni system, the solubility of silicon increases with nickel content. Up to the solubility limit, increasing silicon contents raise strength and reduce ductility.

Niobium increases tensile strength and proof strength, while elongation drops. The favourable effect of niobium on the weldability of cast alloys is crucial (see 3.6.1).

Lead is kept below 0.02% in wrought alloys intended for hot working. Even lead contents of more than 0.01% impair weldability. However, cast alloys with high lead contents, e.g. in ASTM B 584 from 1 to 11% Pb (C97300 to C97800), are well-known and are used for machining.

Zinc is a main constituent of copper-nickel-zinc alloys (previously ‘nickel silver’ or German silver), which are dealt with in a special DKI information booklet. In contrast, the zinc content of Cu-Ni alloys is restricted to 1% max. Zinc-free alloys are required as materials for fittings in electron tubes to avoid zinc vaporisation.

Titanium promotes the formation of pore-free welds because it can tie up oxygen, hydrogen and nitrogen, due to its high affinity for these gases. Therefore titanium is an essential constituent of welding consumables.

Phosphorus has a strongly embrittling effect in Cu-Ni alloys and decreases weldability (hot shortness and crack formation). Therefore phosphorus content is kept as low as possible, but at most 0.015 to 0.05%.

Furthermore, chromium, aluminium and beryllium are interesting as alloying elements. These additions make Cu-Ni alloys age-hardenable. Chromium increases strength and has a surprisingly favourable effect on resistance to erosion corrosion in fast-flowing seawater and to erosion by solids. Aluminium increases strength, seawater and scaling resistance. Beryllium has the strongest effect on mechanical properties after age-hardening.

The solubility of carbon in nickel (max. 0.18%) is severely reduced as copper content increases – it is about 0.01% with a copper content of 90%. Carbon is not detrimental in Cu-Ni alloys.

Cobalt can often occur as an uncontrolled constituent in Cu-Ni alloys depending on the cobalt content of the nickel used.

Antimony, arsenic, sulphur, tellurium and bismuth are embrittling in small quantities, alone or in combinations, and should not be present in practice in Cu-Ni alloys.

Table 1. Wrought Cu-Ni alloys to EN; Composition

Material Designation 1 in accordance with EN
Symbol	Number	Mean composition 2 (Mass %)
CuNi9Sn2	2.0875	9.5 Ni4; 2.3 Sn; Rem. Cu
CuNi10Fe1Mn3	2.0872	10 Ni4; 1.5 Fe; 0.8 Mn; Rem. Cu
CuNi25	2.0830	25 Ni4; Rem. Cu
CuNi30Mn1Fe3	2.0882	31 Ni4; 0.7 Fe; 1 Mn; Rem. Cu
CuNi30Fe2Mn2	2.0883	30 Ni4; 2 Fe; 2 Mn; Rem. Cu
1 In accordance with EN 1412; the same identification symbols are used in ISO 429-1983 2 See EN product standards or CR 13388 for precise compositions and permissible impurities 3 Where order requirements include welding characteristics: P 0.02% max., S 0.02% max. 4 Ni includes 0.5 % Co.

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   1.4 Cu-Ni alloys in EN and former DIN standards

Wrought Cu-Ni alloys are standardised in different EN standards. Table 1 shows the composition of these alloys. According to the ISO 1190-1, the identification symbol CuNi is applied to wrought Cu-Ni alloys, followed by a number which denotes the mean nickel content. Thus CuNi25 contains approx. 75% Cu and 25% Ni. Further addition elements are indicated in the identification symbol by attaching the chemical symbol and very often by stating the mean contents. Cu-Ni wrought alloys are supplied in the form of strip, sheet, plate, tube, bar, wire and drop forgings (Table 2). Data on mechanical properties are given in the corresponding semi-fabrications standards for the respective alloys.

EN only contains the binary alloy CuNi25. Further binary alloys containing 2, 6 and 10% Ni can be used at application temperatures of 300 to 400ºC max. and are standardised as resistance alloys in DIN 17 471 among others. The standard alloys containing manganese and iron which are also included are characterised by the following chemical symbol for manganese or iron if and insofar as this is necessary for differentiation of similar materials, e.g. CuNi23Mn (23% Ni, 1.5% Mn and therefore about 75.5% Cu), CuNi30Mn (30% Ni, 3% Mn and about 67% Cu) or CuNi44 for the alloy containing 44% Ni, 1% Mn and 55% Cu, in the identification symbol of which only the number of the mean nickel content is stated. The last three materials specified are suitable for maximum application temperatures of 500 to 600ºC.

The composition of Cu-Ni cast alloys standardised in EN 1982 is given in Table 4. EN 1982 also contains characteristic mechanical properties. The number following the identification symbol CuNi represents the mean nickel content. A C with a hyphen is placed afterwards, as the identification symbol for casting alloys – e.g. CuNi10Fe1Mn1-C. Cu-Ni alloys with higher lead contents are standardised in the USA, but not in Germany.

Of the standards which include Cu-Ni alloys, among others, particular mention should be made of EN 12451 (Tubes for condensers and heat exchangers), DIN 1653 (Plate for condensers and heat exchangers), EN 12452 (Tubes with rolled fins for heat exchangers), DIN 74 234 (Hydraulic braking systems, tubes, flanges), DIN 1733 (Welding consumables for copper and copper alloys), DIN 46 460, DIN 46 461, DIN 46 462, and DIN 46 464 (Round wire of resistance alloys) and DIN 46 465 (Flat wire of resistance alloys).

   

Table 2. Wrought Cu-Ni alloys to EN product standards; Available semi-fabricated forms

Symbol	Strip and sheet to EN 1652	Spring strip to EN 1654	Cond-enser plates to EN 1653	Tubes to EN 12 449	Cond-enser tubes to EN 12 451 and EN 12 452	Bar to EN 12 163	Wires to EN 12 1661	Die forg-ings to EN 12 420
CuNi9Sn2	X	X					X1
CuNi10Fe1Mn3	X		X	X	X	X		X
CuNi25	X
CuNi30Mn1Fe3			X	X	X	X		X
CuNi30Fe2Mn2	X1				X2
1 Formerly manufactured according to DIN 17677 to small extent for special purposes. Mechanical properties were not included in the specified standard. 2 Only included in EN 12451

   

Table 3. Cu-Ni alloys as resistance alloys to DIN 17 471 (04.1983); Composition

Identification symbol in accordance with DIN 17471	Material number	Mean composition (Mass %)
CuNi2	2.0802	2 Ni; Rem. Cu
CuNi6	2.0807	6 Ni; Rem. Cu
CuNi10	2.0811	10 Ni; Rem. Cu
CuNi23Mn	2.0881	23 Ni; 1.5 Mn; Rem. Cu
CuNi30Mn	2.0890	30 Ni; 3 Mn; Rem. Cu
CuNi44*	2.0842	44 Ni; 1 Mn; Rem. Cu
*This alloy is also standardized in DIN 17 664 as CuNi44Mn1

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   1.5 Comparison between related material designations in different countries

The tolerance ranges of the composition of alloys standardised in different countries are not the same as those specified in EN and former national standards in all cases. Therefore Table 5 contains a comparison of the approximately related materials designations for different countries (including ISO) for Cu-Ni alloys.

   

Table 4. Cast copper-nickel alloys¹ to EN 1982; Composition

Material designation
Symbol	Number	Mean composition (Mass %)
CuNi10Fe1Mn1-C2	CC380H	10 Ni; 1.5 Fe; 1 Mn; max. 1.0 Nb; max. 0.10 Si; Rem. Cu
CuNi30Fe1Mn1-C	CC381H	30 Ni; 1 Fe; 1 Mn; 0.5 Si; Rem. Cu
CuNi30Cr2FeMnSi-C	CC382H	30 Ni, 2 Cr, 1 Fe, 1 Mn, 0,5 Si, 0,25 Ti, 0,15 Zr
CuNi30Fe1Mn1NbSi-C	CC383H	30 Ni; 1 Fe; 1 Mn; 0.75 Nb; 0.5 Si; Rem. Cu
1 A shrinkage value of 1.9 to 2% should be taken into account when making patterns. 2 According to former DIN 17658, for weldable castings: % Nb > 1.55 . Si - 0.1

   

Table 5. Comparison of related material designations in different countries (including ISO)

Europe EN	Germany DIN	Great Britain BS2	France NF3	USA UNS1	International Stand-ardization ISO4
CuNi9Sn2	CuNi9Sn2	-	-	C 72500	CuNi9Sn2
CuNi10Fe1-Mn	CuNi10Fe1Mn	CN 102	CuNi10Fe1Mn	C 70600	CuNi10Fe1Mn
CuNi25	CuNi25	CN 105	CuNi25	C 71300	CuNi25
CuNi30Mn1-Fe	CuNi30Mn1Fe	CN 107	CuNi30Mn1Fe	C 71500	CuNi30Mn1Fe
CuNi30Fe2-Mn2	CuNi30Fe2Mn2	CN 108	CuNi30Fe2Mn2	C 71640	CuNi30Fe2Mn2
CuNi44Mn1	CuNi44Mn1	-	CuNi44	C 72150	CuNi44Mn1
CuNi10Fe1-Mn1-C	G-CuNi10	-	-	C 96200	-
CuNi30Fe1-Mn1-C	-	-	?	-	?
CuNi30Cr2-FeMnSi-C	-	-	?	-	?
CuNi30Fe1-Mn1NbSi-C	G-CuNi30	CN 2	-	C 96400	G-CuNi30Nb
1 UNS = United Numbering System. 2 BS = British Standards. 3 NF = Norme Franaise 4 ISO = International Organisation for Standardization

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      2. PROPERTIES

Cu-Ni alloys have interesting physical properties, good mechanical properties – even under continuous loading and at elevated temperatures – together with high resistance to corrosion in many media – especially seawater.

The properties of the binary Cu-Ni alloys are not adequate for many applications. Certain properties of Cu-Ni alloys can be significantly increased by several additions. Among the addition elements, manganese, iron and tin and niobium and silicon are technically important, also chromium, beryllium and aluminium (see 1.3).

   

Table 6. Wrought Cu-Ni alloys to EN; Physical properties (guide values)

Symbol EN	Melting range °C	Electrical conductivity at 20°C (m/Ω . mm2)	Thermal conductivity at 20°C W/(m . K)	Coefficient of expansion (25 to 300°C) 10-6/K	Elastic modulus Ε kN/mm2
CuNi9Sn2	1060-1130	6.4	48	17.6	140
CuNi10Fe1Mn3	1100-1145	5.3	46	17.0	130
CuNi25	1150-1210	3.1	29	15.5	145
CuNi30Mn1Fe3	1180-1240	2.7	29	16.0	150
CuNi30Fe2Mn2	1160-1240	2.0	21	15.0	140

   

Table 7. Cu-Ni resistance alloys to DIN 17471; Physical properties¹ (guide values)

Identification symbol DIN 17471	Density at 20°C ρ20 kg/dm3	Solidus temp °C	Specific heat at 20°C J/(g . K)	Thermal conductivity at 20°C W/(m . K)	Mean of coefficient expansion		Thermo-electric voltage versus copper μV/K
					(20 to 100°C) 10-6/K	(20 to 400°C) 10-6/K
CuNi2	8.9	1090	0.38	130	16.5	17.5	-15
CuNi6	8.9	1095	0.38	92	16	17.5	-20
CuNi10	8.9	1100	0.38	59	16	17.5	-25
CuNi23Mn	8.9	1150	0.37	33	16	17.5	-30
CuNi30Mn	8.8	1180	0.40	25	14.5	16	-25
CuNi44	8.9	1230-12902	0.41	23	13.5	15	-40
1 See Table 8 for electrical resistivity 2 Melting range

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   2.1 Physical properties

Nickel has a marked effect on the colour of Cu-Ni alloys. The copper colour becomes lighter as nickel is added. Alloys are almost silvery white from about 15% nickel. The lustre and purity of the colour increases with nickel content; from about 40% nickel, a polished surface can hardly be distinguished from that of silver.

   

Table 8. Cu-Ni resistance alloys to DIN 17471; Electrical resistivity in annealed condition and upper application temperatures (guide values)

Identification symbol DIN 17471	Electrical resistivity in Ω . mm2/m						Temperature coefficient of electrical resistance between 20 and 105° C 10-6/K	Upper appl-ication limit in air °C
	20°C	100°C	200°C	300°C	400°C	500°C
CuNi2	0.051	0.057	0.064	-	-	-	+1000 to +1600	300
CuNi6	0.101	0.107	0.114	0.123	-	-	+500 to +900	300
CuNi10	0.151	0.156	0.162	0.169	0.175	-	+350 to +450	400
CuNi23-Mn	0.302	0.308	0.315	0.323	0.331	0.339	+220 to +280	500
CuNi30-Mn	0.402	0.404	0.410	0.417	0.424	0.432	+80 to +130	500
CuNi44	0.492	0.49	0.49	0.49	0.49	0.49	-80 to +40	600
1 Allowable deviation 10% 2 Allowable deviation 5%

The important physical properties of the wrought Cu-Ni alloys standardised in EN are summarised in Table 6 and those of the Cu-Ni resistance alloys standardised in DIN 17 471 are shown in Table 7.

The density of copper (8.93 kg/dm³ at 20 °C) varies only slightly with increasing nickel content (density of nickel at 20 °C = 8.9 kg/dm³) and is 8.9 kg/dm3 for all Cu-Ni alloys specified in DIN 17 664. This aspect can also be seen in Table 7 with the physical properties of the Cu-Ni resistance alloys to DIN 17 471. The high thermal conductivity of pure copper of 394 W/(m.K) is severely reduced by nickel (Fig. 7); it reaches a minimum of c. 21 W/(m.K) at about 45% Ni. The coefficient of linear expansion initially decreases sharply with addition of nickel, then more slowly (Fig. 8). The specific heat (at 20 °C) of copper is 0.385 J/(g.K) and of nickel is 0.452 J/(g. K). As nickel content increases, it first diminishes slightly and a mean value of 0.377 J/(g.K) can be expected.

       

The electrical resistivity of Cu-Ni resistance alloys at different temperatures is shown in Table 8. It rises steeply with nickel content, so that Cu-Ni alloys are suitable as resistance materials. A maximum occurs at c. 45% Ni. The minimum of the temperature coefficient of electric resistance is in approximately the same concentration range.

   

The high thermoelectric power of Cu-Ni alloys in the range between 40 and 50% Ni is particularly noteworthy compared with other metals such as iron (Fig. 10), copper, platinum etc. They are therefore especially suitable for use in thermocouples for temperature measurements in a moderate temperature range. Fig. 11 shows the thermoelectric power of CuNi44 versus copper and iron as a function of temperature. The high thermoelectric force of CuNi44 excludes its use as resistance material in low-voltage appliances, because the copper connections to CuNi44 form a thermocouple.

   

The elastic modulus (see Table 6) increases with nickel content (CuNi10FeMn: 130 kN/mm²; CuNi44Mn1: 165 kN/mm²).

Cu-Ni alloys do not exhibit any ferromagnetism. Copper is diamagnetic, nickel is ferromagnetic. Nickel-copper alloys change from diamagnetic via paramagnetic to ferromagnetic as nickel content increases. Depending on the alloy, iron has a small effect when it is present in solid solution. If iron is precipitated, these ferromagnetic microscopic particles lead to a macroscopic increase of ferromagnetism.

The precipitate-free matrix remains diamagnetic or paramagnetic. Cu-Ni alloys containing 20 to 25% Ni and 20% Fe or about 25% Co are pronounced magnetic materials. As a result of their high remanence and coercive force, they are also suitable for permanent magnets.

All physical properties of the two wrought Cu-Ni alloys CuNi10Fe1Mn and CuNi30Mn1Fe have been investigated thoroughly and are well known from room temperature to 1000°C [8].

Some physical properties of Cu-Ni casting alloys to DIN 1982 are shown in Table 9.

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2.2    Mechanical properties

   

Table 9. Cast Cu-Ni alloys to EN 1982; Physical properties¹ of two generally known alloys

Symbol	Melting range °C	Electrical conductivity at 20°C m/( Ω . mm2)	Thermal conductivity at 20°C W/(m . K)	Coefficient of expansion (25 to 300°C) 10-6/K	Elastic modulus Ε kN/mm2
CuNi10Fe1Mn1-C	1105-1140	5.5	59	17	123
CuNi30Fe1Mn1NbSi-C	1170-1240	2.5	29	16	145
1 Density of both materials is 8.9 kg/dm3

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2.2.1 Mechanical properties at room temperature

2.2.1.1 Wrought Cu-Ni alloys

Table 10 contains characteristic mechanical properties for wrought Cu-Ni alloy sheet and strip conforming to EN 1652. Further data are given in the respective semi-fabricated product standards. Material condition is indicated in the mechanical property standards by adding the letter R to the alloy identification symbol, with a following number, e.g. CuNi10Fe1Mn R320. A tensile strength of at least 320 N/mm² is guaranteed for the strength level R320. The 0.2% proof stress and elongation are also defined by the strength level. A minimum hardness (Vickers hardness) is guaranteed by adding the letter H with a following number, e.g. CuNi19Fe1Mn H100.

Table 11 shows the tensile strength and elongation of Cu-Ni resistance alloys.

   

Table 10. Mechanical properties of wrought Cu-Ni alloy strip and sheet to EN 1652

Symbol		Number	Thick mm	Tensile strength Rm N/mm2	0.2% Proof stress Rp0.2 N/mm2	Elongation		Vickers hardness HV
						A50mm for thickness up to 2.5 mm %min.	A for thickness above 2.5 mm %min.
CuNi9Sn2	R340	CW351H	0.2 to 5	340 to 410	(max. 250)	30	40	-
	H075			-	-	-	-	75 to 110
	R380		0.2 to 5	380 to 470	(min. 200)	8	10	-
	H110			-	-	-	-	110 to 150
	R450		0.2 to 2	450 to 530	(min. 370)	4	-	-
	H140			-	-	-	-	140 to 170
	R500		0.2 to 2	500 to 580	(min. 450)	2	-	-
	H160			-	-	-	-	160 to 190
	R560		0.2 to 2	560 to 650	(min. 520)	-	-	-
	H180			-	-	-	-	180 to 210
CuNi10-Fe1Mn	R300	CW352H	0.3 to 15	min. 300	(min. 100)	20	30	-
	H070			-	-	-	-	70 to 120
	R320		0.3 to 15	min. 320	(min. 200)	-	15	-
	H100			-	-	-	-	min. 100
CuNi25	R290	CW350H	0.3 to 15	min. 290	(min. 100)	-	-	-
	H070			-	-	-	-	70 to 100
CuNi30-Mn1Fe	R350	CW354H	0.3 to 15	350 to 420	(min. 120)	-	35	-
	H080			-	-	-	-	80 to 120
	R410		0.3 to 15	min. 410	(min. 300)	-	14	-
	H110			-	-	-	-	min. 110

   

Table 11. Cu-Ni resistance alloys to DIN 17 471; Mechanical properties at 20 C in annealed condition

Identification symbol	Tensile strength1 Rm N/mm2 min.	Elongation (Lo = 100 mm) A % for nominal diameter in mm
		0.02 to 0.0632	>0.063 to 0.1252	>0.125 to 0.52	>0.5 to 1	>13
CuNi2	220	-	approx. 15	approx. 18	≥18	≥25
CuNi6	250	-	approx. 15	approx. 18	≥18	≥25
CuNi10	290	-	approx. 15	approx. 20	≥20	≥25
CuNi23Mn	350	approx. 12	approx. 18	approx. 20	≥20	≥25
CuNi30Mn	400	approx. 12	approx. 18	approx. 20	≥20	≥25
CuNi44*	420	approx. 12	approx. 18	approx. 20	≥20	≥25
1 Values are applicable to wire with diameter more than 2 mm; values are substantially higher for smaller diameters. Values also apply to flat wire and strip whose thickness is equal to diameter. 2 Only guide values. 3 Measurement length Lo can be agreed for wire diameters more than 3 mm.

Fig. 12 shows the increase of tensile strength, 0.2% proof stress and hardness with nickel content. There is only a relatively small drop in elongation and reduction of area with the rise in tensile strength. On the other hand, hardness increases strongly with nickel content. The notched-bar impact toughness is only slightly affected by nickel content.

   

Iron has a favourable effect on the mechanical properties of Cu-Ni alloys. Fig. 13 shows this with an example of an alloy containing 10% Ni. Additional improvements of the mechanical properties of CuNi30Mn1Fe are obtained by increasing the iron and manganese contents each to 2%; thus, for example, strip and sheet of the alloy CuNi30Fe2Mn² have a tensile strength of 440 N/mm² and a 0.2% proof stress of 145 N/mm².

Additions of aluminium or chromium, for example, produce a further strength increase; Table 12 contains two materials with improved mechanical properties.

As with all metallic materials, tensile strength, 0.2% proof stress and hardness increase with increasing cold deformation of wrought Cu-Ni alloys, while elongation decreases (Fig. 14).

           

2.2.1.2 Cu-Ni cast alloys

Table 13 contains mechanical properties of Cu-Ni cast alloys conforming to DIN 17 658.

Three age-hardenable Cu-Ni casting alloys with additions of aluminium, chromium or beryllium (Table 14) must also be mentioned. The alloy with 2% Al can be used in the as-cast state or age-hardened. The largest increase of strength is achieved by adding beryllium – after age hardening. An alloy of this type is already in use in the USA for seawater applications.

High-strength age-hardenable Cu-Ni casting alloys containing up to 6% tin, usually with further additions such as lead and zinc, are standardised in ASTM 584.

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2.2.2 Mechanical properties at low temperatures

Like other copper alloys, Cu-Ni alloys possess excellent mechanical properties at low temperatures, which are shown for an alloy containing 20% Ni in Fig. 15. Here tensile strength decreases with falling temperature without a marked reduction of elongation and reduction of area. Thus these alloys exhibit no embrittlement at low temperatures. They are therefore very suitable for applications in cryogenic engineering.

       

Table 12. Mean composition and mechanical properties of wrought Cu-Ni alloys proven in use but not standardised in DIN

Addition of	Mean composition (Mass %)	Material condition	Tensile strength Rm N/mm2	0.2% Proof stress Rp0.2 N/mm2	Elongation A5 %	Brinell hardness. HB
Al	5 Ni; 4 Al; 0.8 Cr; 2.5 Mn; Rem. Cu	Soft	450 to 550	170 to 230	35 to 50	110 to 130
		Age-hardened	1000 to 1090	940 to 1040	1 to 3	320 to 340
Cr	30 Ni; 3 Cr; 0.5 Fe; 0.5 Mn; Rem. Cu	Age-hardened	590	≥360	27	110

   

Table 13. Cast Cu-Ni alloys to EN 1982; Mechanical properties

Symbol	Form supplied	Supplement.	Tensile strength Rm N/mm2 min.	0.2% Proof stress Rp0.2 N/mm2 min.	Elongat. A % min.	Brinell hard. HB min.	Elastic modulus E KN/mm2 approx. 1
CuNi10-Fe1Mn1-C	Sand casting	-GS	280	120	20	70	1231
	Centri-fugal casting	-GZ	280	100	25	70	-
	Contin-uous casting	-GC	280	100	25	70	-
CuNi30-Fe1Mn1-C	Sand casting	-GS	340	120	18	80	-
	Centri-fugal casting	-GC	340	120	18	80	-
CuNi30Cr2-FeMnSi-C	San casting	-GS	440	250	18	115	-
CuNi30Fe1-Mn1NbSi-C	Sand casting	-GS	440	230	18	115	1451
1 according to former DIN 17658

   

Table 14. Mean composition and mechanical properties of some cast high-strength Cu-Ni alloys not standardised in DIN [11]

Addition of	Mean composition (Mass %)	Material condition	Tensile strength Rm N/mm2	0.2% Proof stress Rp0.2 N/mm2	Elongation A5 %
Al	14 Ni; 10 Mn; 5 Fe; 2 Al; Rem. Cu	As cast	460	260	35
		Heat treated	460 to 620	310 to 420	20 to 40
Cr	30 Ni; 2 Cr; 1 Mn; 1 Fe; 0.5 Si; Rem. Cu	As cast	520 to 580	330 to 380	22
Be	30 Ni; 1 Fe; 1 Mn; 0.5 Be; Rem. Cu	Heat treated	750 to 850	520 to 620	7 to 24

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2.2.3 Mechanical properties at elevated temperatures

Cu-Ni alloys retain good mechanical properties at elevated temperatures.

2.2.3.1 Hot strength

The hot strength of copper increases with only a small addition of nickel. The effect of nickel on the softening of cold-rolled Cu-Ni alloys at elevated temperatures is shown in Fig. 16. By adding iron, mechanical properties are improved, not only at room temperature, but also at elevated temperatures. Fig. 17 shows this with an example of an alloy containing 10% Ni. CuNi10Fe1Mn, for example, can be used in pressure vessel construction up to 300°C, CuNi30Mn1Fe up to 350°C. Above these limit temperatures, strength drops markedly, particularly the creep strength and creep strain limit (see 2.2.3.2).

   

Values for the elastic modulus decrease as temperature increases by about 50-100 N/mm² per °C.

2.2.3.2 Creep behaviour

Metallic materials are not infrequently exposed to continuous loading at elevated temperatures, so that knowledge of the creep behaviour of Cu-Ni alloys is necessary. The creep test gives values in this respect. It is used to determine material behaviour under static loading (creep loading) under conditions in which the time under stress has a substantial effect in addition to the stress level and the temperature, thus the term ‘creep behaviour’.

The creep rupture strength at a specific temperature is the static load (at test temperature) referred to the initial cross section of the test pieces at room temperature which causes fracture of the test piece after a specific time has elapsed. That maximum load which a workpiece (test piece) can withstand without fracture ‘for an infinitely long time’ is called the creep strength. The creep limit at a specific temperature is then that load which gives rise to a specific permanent strain after a specific time (and at the test temperature).

Values for creep strength and 1% creep limit for alloys CuNi10Fe1Mn and CuNi30Mn1Fe which determine the limit temperatures for the use of these alloys under long-term loading are given in Table 15.

       

Table 15a & 15b. creep strength1 and 1% creep limit¹ for CuNi10Fe1Mn and CuNi30Mn1Fe materials [12]

Temp. °C	Alloy CuNi10Fe1Mn2
	Creep strength in N/mm2 for time [h]				1% Creep limit in N/mm2 for the time [h]
	100	1000	10 000	100 000	100	1000	10 000	100 000
20	-	-	-	-	-	123	116	-
300	239	212	172	(121)	-	105	(93)	-
350	194	143	91	( 55)	-	108	65	-
400	121	73	41	-	-	76	45	-
450	-	-	-	-	-	-	-	-
500	-	-	-	-	-	-	-	-
550	-	-	-	-	-	-	-	-
600	-	-	-	-	-	-	-	-

   

Table 15b.

Temp. °C	Alloy CuNi30Mn1Fe3
	Creep strength in N/mm2 for time [h]				1% Creep limit in N/mm2 for time [h]
	100	1000	10 000	100 000	100	1000	10 000	100 000
20	-	-	-	-	-	-	-	-
300	-	-	-	-	-	-	-	-
350	(391)	(363)	(326)	-	361	317	(258)	-
400	351	305	244	-	299	232	(166)	-
450	292	221	153	-	211	145	(97)	-
500	208	139	92	-	138	87	(50)	-
550	133	85	50	-	83	44	(14)	-
600	84	46	18	-	44	12	-	-
1 Values in brackets are extrapolated 2 Material condition: annealed 3 Material condition: cold rolled, 40%

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2.2.4 Fatigue limit

Since many components are subjected to an oscillating load, the fatigue limit, called fatigue strength for short, is an important characteristic quantity for practical application. In contrast to creep behaviour (see 2.2), it is defined as the maximum stress amplitude oscillating about a given mean stress which can be withstood by a workpiece (test piece) ‘infinitely often’ without fracture and without unacceptable deformation.

Copper alloys do not have any pronounced limit value of stress but a steady fall in strength is observed with increasing number of load cycles followed by an imperceptibly small drop in the area of high load cycles. Fatigue strengths at high load cycles (c. 10⁸) are stated as fatigue limits.

Table 16 summarises fatigue limit values for CuNi10Fe1Mn. CuNi25, CuNi30Mn1Fe and CuNi44Mn1 for 10⁸ load cycles [13].

   

Table 16. Fatigue strength of various Cu-Ni alloys for 10⁸ load cycles [13]

Alloy	Fatigue strength in N/mm2 for 108 load cycles
CuNi10Fe1Mn1	150
CuNi252	275
CuNi30Mn1Fe3	245
CuNi44Mn14	290
1 No data on material form, cold rolled. 2 Wire (2 mm dia.), cold work: 88%. 3 Bar (14 mm dia.), cold drawn (33%). 4 Bar, cold drawn and stress-relief heat-treated.

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   2.3 Corrosion resistance

Cu-Ni alloys are among the corrosion-resistant copper alloys. They are resistant to moisture, non-oxidising acids, alkalis and salt solutions, organic acids and to gases such as oxygen, chlorine, hydrogen chloride, hydrogen fluoride, sulphur dioxide and carbon dioxide. There is no risk of stress corrosion cracking with them, the tendency to selective corrosion is extremely small and pitting corrosion is seldom observed. The resistance of these alloys – as with the Cu-Al alloys – relates to a stable protective coating on the surface due to the alloying metal.

   

Table 17. Corrosion rate of a Cu-Ni alloy containing 30% nickel and different iron contents in seawater at various flow rates; temperature 30 C, test duration 60 days [6]

Iron content %	Semi-fabricated form	Corrosion rate in g/m2 at a flow rate in m/s of
		3	4.12	6.1	8.23
0.04	Tube	27.5		35.5
0.49		2.2		2.7
0.03	Bar		24.7		22.9
0.48			2.5		3.2

Since copper and nickel form a continuous series of solid solutions, no heterogeneous structure can occur in these alloys. Alloys containing 10% and 30% Ni have good resistance even to hot seawater and at high flow rates. Thus these alloys are stable up to moderate flow rates of 6 m/s. It is necessary to maintain a minimum flow rate of 0.6 m/s to avoid corrosion problems. Rates are guide values.

The manganese-containing alloys CuNi44Mn1 and CuNi30Mn1Fe, as materials for electrical resistors, are scarcely attacked by dilute acids, more strongly by acid vapours – in particular hydrochloric acid vapours. They have good resistance to ammonia-containing air. The resistance of these resistance alloys to different atmospheres is given in DIN 17 471. In addition, CuNi44Mn1 is also resistant to alkali metals up to about 600 °C. Of the iron-containing wrought alloys, CuNi10Fe1Mn contains 0.5 to 1.0% Mn and 1.0-2.0% Fe and CuNi30Mn1Fe 0.5 to 1.5% Mn and 0.4-1.0% Fe (see Table 1). Iron contents at this level substantially improve the adherence of protective coatings against corrosion and thus markedly increase resistance to erosion corrosion, especially in seawater and other aggressive waters, e.g. brackish and mine waters. When iron contents are in this optimum range, copper alloys also do no not show any selective corrosion. Iron contents that are too low reduce the resistance to erosion in flowing seawater, excessive iron contents reduce resistance to deposit corrosion in static seawater. The importance of iron for the seawater resistance of CuNi30Mn1Fe can be seen in Fig. 19 and Table 17. CuNi30Mn1Fe is also resistant to ammoniacal condensates. By increasing each of the iron and manganese contents in the 30% Ni alloy to 2% (see CuNi30Fe2Mn2 in Table 1), mechanical wear by solids contained in cooling water (e.g. sand) is further reduced.

The tarnish resistance of Cu-Ni alloys is additionally increased by tin (see 1.3). Resistance to fast-flowing seawater in particular can be increased still further by addition of chromium; aluminium contents have a favourable effect on corrosion and scaling resistance of wrought and cast Cu-Ni alloys.

Table 18 contains some comparable data on the behaviour of Cu-Ni alloys towards various agents.

   

Table 18. Corrosion resistance³ of Cu-Ni alloys to various agents [14]

Acetone	1	Iron(III) sulphate	4	Magnesium chloride	2	Nitric acid	4
Alcohol1)	1	Iron(III) chloride	2	Magnesium hydroxide	1	Hydrochloric acid, dry	2
Aluminium chloride	2	Iron(III) sulphate	2	Magnesium sulphate	1	Sulphur, solid	1
Aluminium sulphate	1	Natural gas	1	Molasses1)	1	Sulphur chloride, dry	1
Formic acid	2	Vinegar1)	1	Milk1)	1	Sulphur dioxide, dry	1
Ammonia, dry	1	Acetic acid (20-50%)1)	1	Lactic acid	1	Sulphur dioxide, wet	3
Ammonia, wet	3	Acetic acid ester	1			Sulphur trioxide, dry	1
Ammonium chloride	3			Sodium carbonate	1	Sulphuric acid (less than 78%)	2
Ammonium hydroxide	3	Boiled oil	1	Sodium bisulphate	1	Sulphuric acid (more than 78%)	3
Ammonium nitrate	3	Fluorosilicic acid	2	Sodium chloride	1	Seawater	1
Ammonium sulphate	2	Hydrofluoric acid	2	Sodium cyanide	4	Soap solution	1
Aniline and aniline dyes	1	Formaldehyde	1	Sodium hydroxide	1	Stearic acid	1
Asphalt	1	Freon	1	Sodium hypochlorite	2
Ether	1	Furfural	1	Sodium carbonate	1	Turpentine	1
Ethylene glycol	1			Sodium nitrate	1	Carbon tetrachloride, dry	1
Acetylene2)	4	Gelatine1)	1	Sodium peroxide	2	Carbon tetrachloride, wet	1
		Tannic acid	1	Sodium phosphate	1	Toluene	1
Barium chloride	2	Drinks containing. carbonic acid1)	1	Sodium silicate	1	Trichlorethylene, dry	1
Barium sulphate	1	Glucose1)	1	Sodium sulphate	1	Trichlorethylene, wet	1
Cotton seed oil	1	Glycerol	1	Sodium sulphide	1
Petrol	1			Sodium thiosulphate	1	Water, acidic mine water	3
Benzene	1	Heating oil	1	Sodium chloride	3	Water, condensate	1
Beer1)	1			Sodium sulphate	3	Water, drinking water	1
Boric acid	1	Potassium chloride	1			Hydrogen	1
Butane	1	Potassium cyanide	4	Oleic acid	2	Hydrogen peroxide	2
		Potassium hydroxide	1	Oxalic acid	1	Tartaric acid	1
Calcium bisulphate	2	Potassium sulphate	1			Whisky	1
Calcium chloride (acid)	2	Carbon dioxide, dry	1	Phosphoric acid	2
Calcium chloride (basic)	2	Carbon dioxide, wet1)	1	Picric acid	4	Zinc chloride	2
Calcium hydroxide	1	Creosote	1	Propane	1	Zinc sulphate	1
Calcium hypochlorite	2	Copper sulphate	1			Citric acid1)	1
Chlorine, dry	1			Mercury	4	Sugar beet syrup1)	1
Chlorine, wet	2	Paint	1	Mercury salts	4
Chromic acid	4	Paint thinners	1
		Glue	1	Raw sugar syrup1)	1
Iron(III) chloride	4	Linseed oil	2
1 Tinning is necessary in the drinks and foods industry 2 There is a risk of explosion due to the formation of copper acetylide 3 1 = very good resistance; 2 = resistant; 3 = acceptable; 4 = not recommended

   

Table 19a & 19b. Wrought Cu-Ni alloys to EN and cast alloys to EN 1982 - Information on further processing

Identification symbol	Castability	Working
		Cold	Hot
Wrought Cu-Ni alloys to EN
CuNi9Sn2		good	v. good
CuNi10Fe1Mn		good	v. good
CuNi25		good	good
CuNi30Mn1Fe		good	good
CuNi30Fe2Mn2		good	good
CuNi44Mn11		good	good
Cast Cu-Ni alloys to EN 1982
CuNi10Fe1Mn1-C	good
CuNi30Fe1Mn1 NbSi-C	good

   

Table 19b.

Identification symbol	Joining							Surface treatment
	Welding					Soldering and brazing		Mechanical polishing	Electrochemical polishing
	Gas	Metal arc	Gas-shielded		Resistance	Brazing	Soldering
Wrought Cu-Ni alloys to EN
CuNi9Sn2	poor	good	v. good	v. good	v. good	v. good	v. good	good	good
CuNi10Fe-1Mn	poor	good	v. good	v. good	v. good	v. good	v. good	good	good
CuNi25	poor	v. good	v. good	v. good	v. good	v. good	v. good	v. good	good
CuNi30Mn-1Fe	poor	v. good	v. good	v. good	v. good	v. good	v. good	good	good
CuNi30Fe-2Mn2		v. good	v. good	v. good	v. good	v. good	v. good	good	good
CuNi44Mn11