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Electroless Nickel/EN: Also known as Autocatalytic Nickel

Electroless Nickel/EN: Also known as Autocatalytic Nickel

Techmetals is one of the largest platers in the world specializing in quality electroless nickel and is recognized as an industry leader. We do virtually every type of electroless nickel plating, from the most corrosion-resistant, high-phosphorous coatings to teflon-nickel and other co-deposits. We can handle one or one million pieces weighing up to 10,000 pounds. Our tanks are  10 feet deep for barrel or rack plating. Our state-of-the-art facilities offer complete metallurgical back-up. We know the best plating specifications and will stand behind the results.

  • High volume Lines for large and small parts
  • 40 tons & 55 vertical lift if job and project are large enough

This coating covers even the most complex shapes uniformly. Deposits exhibit superior corrosion resistance and are often used as reduced-cost replacements for stainless steel. Electroless nickel’s high lubricity makes it ideal for molding applications. It is an alloy coating available in many different formulations. It exhibits a wide range of characteristics, making the choice of suppliers and specifications critical.

From the formulation of the finest plating solutions to in process quality control, it takes the finest technology and resources to maintain consistent quality. Techmetals combines technology and resources to handle challenges and solve problems with an understanding and sensitivity to our customers’ needs.

Standard EN options and capacity varies based on options

  • Electroless Nickel  High Phosphorous (ENHP)
  • Electroless Nickle Medium Phosphorous (ENMP)
  • Electroless Nickel Low Phosphorous (ENLP)
  • Electroless Nickel Teflon (EN Teflon)
  • Electroless Nickel Boron (ENB)
  • Ni-P-B Electroless Nickel (Ni P B)
  • Electroless Nickel Composite Coatings

Standard Electroless Nickel Specifications

AMS-C-26074, AMS-2404, AMS-2405, ASTM-B-733, MIL-C-26074, MIL-DTL-32119, AMS 2433, and ASTM B 607

We can run our processes to customer specifications and have OEM and end customer approvals.

EN Plating and Engineered Performance Coatings

TM 103 A high phosphorous electroless nickel free of heavy metal contaminants. It is a uniform coating for corrosion resistance, hardness and lubricity.  It can be plated on all ferrous metals & most non-ferrous metals.  Uniformity & accuracy of the deposit of TM 103 can be maintained within .0001. It covers hard-to-reach areas that are difficult or impossible to coat with electrolytic processes.

  • Superior Corrosion Resistance & good wear resistance

ASTM B 117 95 ° F, 5% NaCL, .001″ TM103 coating thickness

1,000 + hours plus salt spray testing

Knoop Hardness as plated                  = 500 to 580

Knoop Harness after heat treating    = 800 to 950

en-1
TM 104 is  a medium electroless nickel phosphorus metallic coating that has good corrosion and hardness properties used on ferrous and non-ferrous metals.

  • As plated it has  micro hardness around 48  Rockwell-C
  • It Increases the wear-life on aluminum parts

TM 129 is  a low  nickel phosphorus metallic coating that work hardens and has wear resistance.

  • Low Coefficient of Friction
  • Greatly Increases wear-life of parts
  • Good Resistance to abrasion and erosion

Electroless Nickel Teflon Processes

TM 117C is a uniform co-deposition composite coating of nickel phosphorus and composite matrix of : Teflon,  nylon, and other polymer like particles.

  • Great release coating and Self Lubricating
  • Low Coefficient of Friction
  • Greatly reduces wear of sliding parts
  • NSF FDA approved applications

TM 117P is  a uniform nickel alloy infused with teflon and polymer type matrix with the nickel deposit  having a high Rockwell-C hardness around 62 to 68.

  • Best on Ferrous alloys and Self Lubricating
  • Good for mold release applications
  • Great for plastic extrusion and sliding wear

TM 133 electroless nickel boron process is a hard chrome replacement technology and a great process for solder ability.

  • Extreme hardness
  • Anti-galling and self lubricating.

Electroless nickel is a term used to describe plating of a nickel-phosphorus coatings onto a suitable substrate by chemical reduction. Unlike electroplated coatings, electroless nickel is applied without an externally applied electric current. Instead, the coating is deposited onto a part’s surface by reducing nickel ions to metallic nickel with sodium hypophosphite or boron hydrate. This chemical process avoids many of the problems associated with most metallic coatings and provides deposits with many unique characteristics.

As applied, electroless nickel coatings are uniform, hard, relatively brittle, lubricious, easily solder able, and highly corrosion resistant. They can be precipitation hardened to very high levels through the use of low temperature treatments, producing wear resistance equal to that of commercial hard chrome coatings. This combination makes the coating well suited for many severe applications and often allows it to be used in place of more expensive or less readily available alloys. The engineering properties of electroless nickel deposits and how they relate to the use of the coating are discussed in the following sections.

en-2

STRUCTURE

Hypophosphite reduced electroless nickel is one of the very few metallic glasses used as an engineering material. Depending on the formulation of the plating solution, commercial coatings may contain 5 to 12 percent phosphorus dissolved in nickel and as much as 0.25 percent of other elements. The structure of these coatings depends upon their composition. Coatings containing up to 5 percent phosphorus consist of crystalline B nickel with phosphorus in solid solution. Those with phosphorus content between 5 and 8 percent, contain a mixture of phases and are partly crystalline. Coatings containing more than 8 percent phosphorus consist only of a phase nickel-phosphorus and are normally amorphous to x-rays. These high phosphorus deposits have no crystal structure or separate phases 1, 2, 3. Electron diffraction studies of TM 103 deposits have confirmed their lack of crystal structure at magnifications up to 150,000 X.  The continuity of electroless nickel coatings also depends upon their composition. Coatings like TM-103 containing more than 10 percent phosphorus and less than 0.05 percent of impurities are typically continuous.

Lower phosphorus coatings, and especially those applied from baths stabilized or brightened with heavy metals or sulfur compounds, are often porous. These deposits consist of columns separated by cracks and holes. The presence of such discontinuities has a severe effect on the deposit’s properties, especially on its ductility and corrosion resistance.

Lower phosphorus and heavy metal stabilized deposits also frequently appear to have a laminar structure parallel to their substrate.  These laminations result from variations in the phosphorus content of the different layers of the coating, which in turn are due to changes in the pH or stabilizer content of the bath during plating. The more sophisticated complexing and stabilizing systems used to apply high phosphorus deposits, eliminate these variations and produce the more homogeneous structure.

mountingcopper  plasticmountcopperplatingplasticmount
hardnessbaseAs electroless nickel deposits are heated to temperatures above structural changes begin to occur.  First, coherent and then distinct particles of nickel phosphite (Ni3P) form within the alloy. Then at temperatures above 320°C/600°F the deposit begins to crystallize and to lose its amorphous character. With continued heating the nickel phosphite particles conglomerate and a two phase alloy forms. With coatings containing more than 8 percent phosphorus a matrix of Ni3P forms, while almost pure nickel is the predominate phase in lower phosphorus deposits. These changes cause a rapid increase in the hardness and wear resistance of the coating, but cause its corrosion resistance and ductility to be reduced. A cross sectional view of a fully hardened, TM-103 coating. Heating also causes the deposit to shrink and can result in cracking through the coating to the substrate.

coatedcomponentsINTERNAL STRESS

The internal stress in electroless nickel coatings consists of two components: A thermal stress due to the difference in thermal expansion between the coating and the substrate and a structure stress due to structural mismatch within the deposit caused by non-homogeneity. Both are primarily a function of the coating’s composition.  For example…on steel the stress in coatings containing more than 10 percent phosphorus is neutral or compressive. With lower phosphorus deposits, however, tensile stresses of 15 to 45 MPa (2 to 6 ksi) occur. The high level of stress in these coatings promotes their cracking and porosity.

internalstressgraph
The structural changes during heat treatment at temperatures above 220°C (420°F) , cause a volumetric shrinkage of up to 4 to 6 percent within electroless nickel deposit. This increases tensile stress or reduces compressive stress in the coatings.Deposit stress is also increased by the co-deposition of orthophosphates or contaminants, or by the presence of excess complexing agents in the plating solution. Even small quantities of some metals can produce a severe increase in stress. For instance, the addition of only 5 mg/l of bismuth and antimony to most baths will cause the deposit stress to increase to as much as 350 MPa (50 ksi) tensile. High levels of internal stress also reduce the coating’s ductility and increase its porosity.

UNIFORMITY

One especially beneficial property of electroless nickel is its uniform coating thickness. With electroplated coatings, thickness can vary significantly depending upon the part’s configuration and its proximity to the anodes. Not only can these variations effect the ultimate performance of the coating, but they can also cause additional finishing to be required after plating.

With electroless nickel the plating rate and coating thickness are the same on any section of the part exposed to fresh plating solution. Grooves, slots, blind holes, and even the inside of tubing will have the same amount of coating as the outside of a part.

Because of its uniformity, often the overall finishing cost of a part will be less with electroless nickel than with electro- plated coatings, even though the material cost of the process is higher. For example, the substitution of electroless nickel for hard chromium on many of the cylinders and rolls used in the printing and textile industries has not only reduced the cost of plating by 40 percent, but also has allowed 55 percent of the grinding time to be saved.

With electroless nickel, coating thickness can be controlled to suit the application. Coatings as thin as 2-1/2 μm (0.1 mil) are commonly applied for electronic components, while those as thick as 75 to 125 μm (3 to 5 mils) are typical for corrosive environments. Coatings thicker than 250 μm (10 mils) are used for salvage or repair of worn or miss-machined parts.

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ADHESION

The adhesion of electroless nickel coatings to most metals is excellent. The initial replacement reaction, which occurs with catalytic metals, together with the associated ability of the baths to remove submicroscopic soils, allows the deposit to establish metallic as well as mechanical bonds with the substrate. The bond strength of ELMIC coatings to properly cleaned steel has been found to be 400 MPa (60 ksi) or more.  The adhesion to aluminum and aluminum alloys is less, but usually exceeds 300 MPa (40 ksi).

With non-catalytic or passive metals, such as stainless steel, an initial replacement reaction does not occur and adhesion is reduced. With proper pretreatment and activation, however, the bond strength of the coating normally is at least 140 MPa (20 ksi). The adhesion to the copper alloys is usually between 300 and 150 MPa (40 and 50 ksi).

With metals such as aluminum it is common practice to bake parts after plating for 1 to 4 hours at 130°+ 200°C (270° to 4000F) to increase the adhesion of the coating. These treatments relieve hydrogen from the part and the deposit and provide a very minor amount of co-diffusion between the coating and substrate. They are most useful where pretreatment has been less than adequate and adhesion is marginal. With properly applied coatings, baking will have only a minimal effect upon bond strength.

MELTING POINT

Electroless nickel is an eutectic alloy with a wide melting range. Unlike a pure compound, it does not have a true melting point. This is illustrated by the phase diagram for nickel-phosphorus alloys.

The melting range for electroless nickel coatings varies depending upon the phosphorus content of the deposit. All electroless nickel coatings begin to melt at approximately 880 degrees C (l6200F), which is the eutectic temperature for nickel phosphide (Ni3P). The temperature at which the coating is completely liquid, however, increases with decreasing phosphorus content from about 880°C (16200F) at 11 percent — the eutectic point — to approximately 1450°C (2640°)  for pure nickel. Thus, the melting range becomes wider as the phosphorus content is reduced.

Practically, this means that all commercial coatings contain large quantities of liquid material at temperatures above 880°C (16200F). For example, at 900°C (16500F) coatings containing 5, 8 and 10 percent phosphorous are 46, 74 and 100 percent melted.

endepositsphasediagram

PHYSICAL PROPERTIES

The density of electroless nickel coatings is inversely proportional to their phosphorus content. For Example….density varies from about 8.5 gm/cm3 for very low phosphorus deposits, to 7.75 gm/cm3 for TM-103 containing about 10-1/2 percent phosphorus.

The thermal and electrical properties of these coatings also vary with composition. For high phosphorus coatings, like TM- 103 however, electrical resistivity and thermal conductivity are generally about 90 μm-cm and 0.08 W/cm-°K (4.6 Btu/ ft/hr-°F) respectively. Accordingly, these coatings are significantly less conductive than conventional conductors such as copper.

Because of the relatively thin layers used, however, for most applications the resistance of electroless nickel is not significant. TM-103 coatings are being successfully used for such applications as exchanger tubing and electrical switches and contacts.

Heat treatments precipitate phosphorus from the alloy and can increase the conductivity of electroless nickel by 3 to 4 times. The formulation of the plating solution can also affect conductivity. Tests with baths complexed with sodium acetate and with succinic acid showed electrical resistivity of 61 and 804 μm-cm respectively.

Phosphorus content also has a strong effect on the thermal expansion of electroless nickel.

The coefficient of thermal expansion of TM-103 coatings is approximately equal to that of steel.

thermalexpansion

Exhibits effects of deposit phosphorus content on the coefficient
of thermal expansion on electroless nickel.

 

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Exhibits effects of deposit phosphorus content
on the density of electroless nickel.
snowmobile
As deposited, coatings containing more than 10 percent phosphorus are completely non-magnetic. The magnetic susceptibility of TM-103 deposits is on the order of 10-4 mks at ambient temperature. Lower phosphorus coatings, however, have some magnetic susceptibility. The coercivity of 3 to 6 percent phosphorus coatings is about 20 to 80 oersteds, while that of deposits containing 7 to 9 percent phosphorus is typically 1 to 2 oersteds. Heat treatment at temperatures above 260°C (500°F) improve the magnetic response of all electroless nickels and can provide coercities of about 100 to 300 oersteds.

MECHANICAL PROPERTIES

The mechanical properties of electroless nickel deposits are similar to those of other glasses. They have high strength, limited ductility and a high modulus of elasticity. The ultimate tensile strength of most coatings exceeds 700 MPa (100 ksi). This is equal to that of many hardened steels and allows the coating to withstand a considerable amount of abuse without damage. The effect of phosphorus content upon the strength and strain at fracture of electroless nickel deposits.

The ductility of electroless nickel coatings also varies with composition.

The ductility of TM-103 coatings is about 1 to 1-1/2 percent (as elongation). While this is less than that of most engineering materials, it is adequate for most coating applications. Thin films of the deposit can be bent completely around themselves without fracture, and the coating has been used successfully for springs and bellows. Electroless nickel, however, should not be applied to articles which subsequently will be bent or drawn. Severe deformation will crack the deposit, reducing corrosion and abrasion resistance. With lower phosphorus deposits, or  with deposits containing metallic or sulfur impurities, ductility is greatly reduced and may approach zero. The effect of phosphorus content upon the strain at fracture of electroless nickel coatings.

Hardening type heat treatments reduce both the strength and the ductility of electroless nickel deposits. Exposure to temperatures above 2200C (4200F) cause a 80 to 90 percent reduction in strength and can destroy ductility, especially in lower phosphorus coatings. Because of their high phosphorus content and high purity, the effect of heat treatment on the ductility of TM-103 deposits is not as pronounced. The ductility of TM-103 coatings is not significantly reduced until it is heated to above 260°C (500°F).

fracturestrength
Effect of phosphorus content on strength
and stain at fracture of EN deposits
motor

HARDNESS AND WEAR RESISTANCE

Two of the most important properties for many applications are hardness and wear resistance. As deposited, the micro-hardness of electroless nickel coatings is about 500 to 600 VHN 100. This is approximately equal to 48 to 52 HRC and equivalent to many hardened alloy steels. Heat treatment causes these alloys to age harden and can produce hardness values as high as 1000 Hv. This is equal to most commercial hard chromium coatings.

For some applications, high temperature treatments cannot be tolerated because of part warp-age or because of their effect on the substrate. For these, it is sometimes possible to use longer times and lower temperatures to obtain the desired hardness.

Treatments at 340°C (650°F) for 4 to 6 hours and at 290°C (550°F) for 10 to 12 hours are commonly used for electroless nickel deposits. These can produce hardness values of 950 to 1000 Hv. Treatments at 260°C (500°F) are also occasionally used, although the resulting hardness is lower. At temperatures of 230°C (450°F) and below, only a minimal increase in hardness is obtained. Accordingly such treatments are only rarely used, except for hydrogen relief or adhesion improvement.

Electroless nickel coatings also have excellent hot hardness. Up to about 4000C (7500F) the hardness of heat treated electroless nickel is around that of hard chromium coatings.

Because of their high hardness, electroless nickel coatings have excellent resistance to wear and abrasion, both in the as-deposited and hardened conditions. Laboratory tests have shown fully hardened coatings to have wear resistance comparable to hard chromium under both dry and lubricated conditions.

Comparison Of: Taber Abrasion Resistance of Different Engineering Coatings

Coating Heat Treatment TWI, mg/1000 cycles
Watts Nickel None 25
Electroless Ni-9%P None 17
Electroless Ni-9%P 300°C/1 hr. 10
Electroless Ni-9%P 500°C/1 hr. 6
Electroless Ni-9%P 650°C/1 hr. 4
Electroless Ni-5%B None 9
Electroless Ni-5%B 400°C/1 hr. 3
Hard Chromium None 3

1) Taber Wear Index, CS-10 abrasion wheels, 100 gram load determined as average weight loss per 1000 cycles for total test of 6000 cycles.

Tests with electroless nickel coated vee-blocks in a Falex Wear Tester have confirmed a similar relation between heat treatment and wear, and shown the coating to be more resistant than hard chrome under lubricated wear conditions.

COMPARISON OF FALEX WEAR RESISTANCE OF  CHROMIUM & ELECTROLESS NICKEL COATINGS

Coating Plated V-Blocks Un-plated steel pins
Heat Treatment HardnessVHN WearMg(1)
Chromium None 1100 .5 1.9
Electroless Nickel None 590 6.6 .2
Electroless Nickel 290°C/2 HRS 880 1.2 .1
Electroless Nickel 290°C/16 HRS 1050 .4 .1
Electroless Nickel 400°C/1 HR 1100 .5 .2
Electroless Nickel 540°C/1 HR 750 1.4 .1

FRICTIONAL PROPERTIES

The frictional characteristics of electroless nickel coatings are excellent. Their phosphorus content provides a natural lubricity, which helps to minimize heat buildup and reduces scoring and galling and which can be very useful for applications such as plastic molding.

The coefficient of friction for electroless nickel versus steel is about 0.13 for lubricated conditions and 0.4 for unlubricated conditions. This is approximately 20 percent lower than chromium, one-half of that of steel, and much lower than aluminum or stainless steel. The frictional properties of these coatings vary little with either phosphorus content or with heat treatment.

SOLDER-ABILITY AND WELDABILITY

Electroless nickel coatings can be easily soldered and are commonly used in electronic applications to facilitate soldering of light metals, like aluminum. For most components, mildly activated rosin (RMA) flux is specified together with conventional tin-lead solder. Pre-heating the component to 100° to 110°C (210° to 230°F) will improve the ease and speed of joining. With moderately oxidized surfaces, such as those resulting from steam aging, activated rosin (RA) flux is usually required to obtain wetting of the coating.

Welding of electroless nickel coated components is more difficult due to the low welding point of the alloy and because phosphorus can diffuse into an embrittled steel. Some success has been reported using special high purity stainless steel electrodes and inert gas shielding. With piping high nickel backup rings are also sometimes used.

CORROSION RESISTANCE

Electroless nickel is a barrier coating, it protects its substrate by sealing it off from the environment, rather than by sacrificial action. Because of its amorphous nature and passivity, however, the corrosion resistance of the coating is excellent and in many environments superior to that of pure nickel or chromium alloys. Amorphous alloys generally have better resistance to attack than equivalent polycrystalline materials because of their freedom from grain or phase boundaries, and because of the glassy films which form on and passivate their surfaces.

Effect of Environment
When properly applied, TM-103 Electroless Nickel is almost totally resistant to alkalies, to salt solutions and brines, to chemical and petroleum environments, and to all types of hydrocarbons and solvents. TM-103 deposits also have good resistance to ammonia solutions, to organic acids, and to reducing inorganic acids. They are only significantly attacked by strongly oxidizing media.

Effect of Composition
The corrosion resistance of an electroless nickel coating is a function of its composition. Most deposits are naturally passive and very resistant to attack in most environments. Their degree of passivity (and corrosion resistance), however, is greatly affected by their phosphorus content. Alloys like TM-103 containing more than 10 percent phosphorus are generally more resistant to attack than those with lower phosphorus contents.

CORROSION OF HIGH PHOSPHORUS ELECTROLESS NICKEL IN VARIOUS ENVIRONMENTS

ENVIRONMENT(AMOUNT) TEMP °C CORROSION RATE
μM/Y MPY
ACETIC ACID(GLACIAL) 20 08 .03
ACETONE 20 .08 .003
ALUMINUM SULFATE (27%) 20 5 .2
AMMONIA (25%) 20 16 .6
AMMONIUM NITRATE (20%) 20 15 .6
AMMONIUM SULFATE (SATURATED) 20 3 .1
BENZENE 20 NIL NIL
BRINE(3.5% SALT, CO2 SATURATED) 95 5 .2
BRINE(3.5% SALT, H2S SATURATED) 95 NIL NIL
CALCIUM CHLORIDE (42%) 20 .2 .01
CARBON TETRACHLORIDE 20 NIL NIL
CITRIC ACID (SATURATED) 20 7 .3
CUPRIC CHLORIDE (5%) 20 25 1.0
ETHYLENE GLYCOL 20 .6 .02
FERRIC CHLORIDE (1%) 20 200 8.0
FORMIC ACID (88%) 20 13 .5
HYDROCHLORIC ACID (5%) 20 24 .9
HYDROFLUORIC ACID (2%) 20 27 1.1
LACTIC ACID (85%) 20 1 .04
LEAD ACETATE(36%) 20 .2 .01
NITRIC ACID(1%) 20 25 1.0
OXALIC ACID (10%) 20 3 .1
PHENOL (90%) 20 .2 .01
PHOSPHORIC ACID (85%) 20 3 .1
POTASSIUM HYDROXIDE (50%) 20 NIL NIL
SODIUM CARBONATE (SATURATED) 20 1 .04
SODIUM HYDROXIDE (45%) 20 NIL NIL
SODIUM HYDROXIDE (50%) 95 .2 .01
SODIUM SULFATE (10%) 20 .8 .03
SULFURIC ACID (65%) 20 9 .4
WATER, ACID  MINE, 3.3pH 20 7 .3
WATER, DISTILLED, N2 DEAERATED 100 NIL NIL
WATER, DISTILLED, O2 SATURATED 95 NIL NIL
WATER, SEA (3.5% SALT) 95 NIL NIL