Features of galvanic treatments Electroless nickel

The chemical nickel-plating process (or electroless nickel plating) consists of a deposition of nickel without the use of electric current: the presence in the treating solution of a chemical reducing agent (typically sodium hypophosphite) triggers a controlled autocatalytic reaction, with a co-deposition of phosphorus (resulting from the reaction of the hypophosphite).
It is a process that is very developed in the last 15-20 years: in fact, in the late 1990s, the Galvanic Paciotti had two bathrooms to 400 liters, today there are nine, with volumes from 250 up to 2200 liters.

Nook for microelectronics/defense - Nickel chemistry on aluminum

Nook for microelectronics/defense - Nickel chemistry on aluminum


The chemical nickel can be deposited on a wide range of materials: aluminum alloys, copper and its alloys (including copper-tungsten), ferrous alloys (stainless steel, kovar, invar, mu-metal, ...) and titanium (Ti6Al4V alloy), with thicknesses ranging from 2-3μ up to 50μ (and beyond), according to the needs. The first advantage of chemical nickel plating is the distribution of the thickness on the treated objects, much more uniform compared to electrolytic nickel plating (with electric current), especially in the case of complex geometric shapes; for example you can nickel-plate the interior of tubes without the aid of auxiliary anodes (it’s sufficient to ensure a good handling of the piece).

 

Application in the marine environment - Ni-chemical high phosphorus on aluminum

Application in the marine environment
Ni-chemical high phosphorus on aluminum

Aluminum bushings treated with chemical nickel

Aluminum bushings treated with chemical nickel

Chromate + Ni-chemical fusion of aluminum alloy

Chromate + Ni-chemical fusion of aluminum alloy


The chemical nickel can be applied as a final treatment (corrosion protection, wear resistance, general improvement of the treated surfaces), or as an intermediate layer (barrier) before subsequent treatments such as gold, silver, tin, etc.


SVarious types of baths, which differ in the different percentage of co-deposited phosphor with different characteristics from the deposit obtained, are available (see table), providing the ideal solution for any type of application.
The average and high types phosphorus meet about 80% of the requests of our current customers.

Housing e cover per apparati di telecomunicazione civili e per difesa: nichelatura chimica su base alluminio

Housing and cover for civil telecommunications equipment and defense: Chemical nickel plating on aluminum basis.

 

Some general criteria for the choice of the type of chemical nickel:

  • LOW PHOSPHORUS (1-3%): 

a) when the main requirement is the hardness and wear resistance;
b) in presence of high mechanical and or thermal stresses (thermal shock): it limits the risk of cracking of the deposit, due to the compressive internal stresses;
c) when low electrical resistivity is required (in relation to the other types of chemical nickel).

 

  • MEDIUM-LOW (4-6%) AND MEDIUM PHOSPHORUS (7-9%):

a) general applications in mechanical, aeronautical industries, space and microelectronics sectors; 
b) good resistance to corrosion.
c) it is the most used as a substrate (or barrier layer) before subsequent treatments.

  • HIGH PHOSPHORUS (10-13%):

a) where the main requirement is the corrosion resistance;
b) applications requiring the absence of magnetism;
c) where it is required a relatively flexible coating, resistant to mechanical or thermal stress with limited risk of cracking.
d) applications in the food industry;
e) compliance with the European ROHS directive.

 



SPECIAL SOLUTIONS ON REQUEST

For special applications, evaluating the performance/cost ratio, the following offers may be available:

  • Nickel-boron: chemical nickel with co-deposition process with boron instead of phosphorus: the deposit is particularly suitable for the brazing of components especially in the field of microelectronics.

  • Nickel-PTFE: the co-deposition of particles of PTFE (Teflon®) in the chemical nickel-plating process allows to obtain deposits with a particularly low coefficient of friction, for applications where the smoothness is an essential requirement.

 


Characteristics

Basso fosforo
1-3% P

Medio-basso fosforo
4-6% P

Medio fosforo:
7-9% P

Alto fosforo:
10-13% P

Hardness as presented:       
Knoop (HK100)
Rockwell C (Rc)

 

700-800
56-61

 

600-700
51-56

 

500-600
45-51

 

450-500
41-45

Hardness after TT:
Knoop (HK100)
Rockwell C (Rc)

 

900-1000
65-69

 

850-950
63-67

 

800-900
60-65

 

750-900
57-65

Magnetic properties

Magnetic

Magnetic

Slightly magnetic

Non-magnetic

Electrical resistivity  (µΩ.cm)

10-30

15-45

40-70

80-110

Resist. Taber wear
(mg/1000 cycles-load 1000g)

7-12

10-14

16-20

22-24

Resist. Taber wear after TT. (1)

6-10

7-10

10-12

10-14

Corrosion resistance (2)

n.d.

12µ à 24 ore
25µ à 96 ore

12µ à 24 ore
25µ à 96 ore

12µ à 250 ore
25µ à 1000 ore

Nitric acid test (3)

Negative

Negative

Negative

Negative

Hydrochloric acid Test (4)

Positive

Positive

Positive

Positive

Internal tensions
(extensive/compression)

Slightly Compressive

Slightly expansionary

Slightly expansionary

Neutral or compressive

Thermal expansion coefficient (µ/m/°C)

12-15

11-14

10-15

8-10

Tensile strength (MPa)

200-400

350-600

800-1000

650-900

Elongation at break (%)

0.5-1.5

0.5-1

0.5-1

1-2.5

Density (g/cm3)

8.7

8.4

8.1

7.7

Melting point (°C)

1250-1350

1000-1300

880-980

880-900

Source of data in table: technical bulletins producers/suppliers of chemical nickel baths.


(1) The heat treatment at temperatures between 260 and 400°C, transforming the structure from amorphous to crystalline allows the increase of the hardness and wear resistance of the chemical nickel deposit, but reduces the resistance to corrosion and cancels the non-magnetic characteristics (especially for medium and high phosphorus types).

(2) Test run according to ASTM-B117 (test in fog 5% NaCl - 35°C) on lapped steel specimens, without heat treatment after nickel plating. The data indicated in the table shall be understood as a comparison, also with other types of treatment, and can vary in function of the base material, the degree of surface finish, the thickness of deposited nickel and the real geometry of the object.
Over the thickness of 25μ there are no significant improvements.


(3) Testing with concentrated nitric acid (42Bé) at room temperature for 1 minute.

(4) (4) Test with solution of hydrochloric acid in water (1: 1) at room temperature for 2 minutes.

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