Aluminum-nickel alloy 4. Nickel-based aluminum alloy

An intermetallic alloy based on nickel-aluminium contains predominantly the binary phase NiAl, as well as additionally chromium and tantalum with a total fraction of up to 12 at. %. Optionally, the alloy may further contain at least one element from the group consisting of iron, molybdenum, tungsten, niobium and hafnium with a corresponding proportion of up to 1 at.% and a total of not more than 3 at.%. The alloy is used as a material for the manufacture of products with a 0.2% tensile strength at room temperature above 600 MPa, at 800°C - above 200 MPa and at 1000°C - above 90 MPa, viscosity K to less at least 7 MPa/m, oxidation resistance of about 510 -14 g 2 cm -4 s and good resistance to thermal shock. 10 salary, 5 tab.

The invention relates to an intermetallic alloy based on nickel-aluminium, which contains a binary phase NiAl. The invention further relates to the use of an intermetallic alloy based on nickel-aluminium. Such an intermetallic nickel-aluminum alloy follows from the article "NiAl Alloys for High Temperature Structural Applications", Journal of Metals, March 1991, p. 44, etc. DE-AS 18 12 144 describes a method for producing a high-strength nickel-aluminium material with good oxidation resistance. In this method, nickel powder and aluminum powder are mixed and then pressed and cold formed so that a self-supporting and interlocking molded article with a fibrous or laminar structure is obtained. The share of nickel is at least 80% and the share of aluminum is maximum at 20%. The interconnected product is then successively subjected to hot deformation at suitably elevated temperatures. Along with the solid solution of aluminum in nickel, the compound Ni 3 Al additionally appears in this case. This solid solution, as well as the Ni 3 Al compound, can be detected by X-ray analysis. To what extent other compounds between nickel and aluminum can be obtained by this method does not appear from this published application. The invention is based on the task of improving the thermomechanical characteristics of a nickel-aluminum alloy. These include primarily heat resistance, oxidation resistance and thermal shock resistance. Another object of the invention is to indicate the use of such an improved nickel-aluminum alloy. To solve this problem, an intermetallic alloy based on nickel-aluminum is specified, which predominantly contains the binary phase NIAI, as well as additionally chromium and tantalum, wherein chromium and tantalum are contained in a total proportion of up to 12 at.% and which optionally contains additionally at least one an element from the group iron, molybdenum, tungsten, niobium and hafnium, respectively, with a proportion of up to 1 at.%, in total, however, no more than 3 at.%. The proportion of the NiAl binary phase preferably lies between 70 and 95 at.%, in particular between 85 and 90 at.%. Preferred content ranges for tantalum or chromium are 0.3 to 3.8 at.% or 1.0 to 9.0 at.%. Within these ranges, 0.3 to 0.9 atm is preferably used. % tantalum and 1.0 to 3.0 at.% chromium or, respectively, 1.7 to 3.0 at.% tantalum and 6.0 to 9.0 at.% chromium. The ratio of tantalum to chromium is preferably 1:3 or less. At this ratio, the concentration of substituting elements in NiAl reaches a maximum. Due to the addition of tantalum and chromium in an intermetallic alloy based on nickel-aluminum, deposits of a coarse multiple Laves-Phase appear at the grain boundaries of the NiAl binary phase, in which the elements Ni, Al, Cr and Ta can participate. In addition, inside the NiAl grains there are deposits of the fine-grained Laves phase and chromium. In this case, they prefer that the structure consist of 5 to 11 volumes. % Laves phase, 3 to 10 vol.% precipitation in NiAl, as well as residue from NiAl. Particularly preferred is a structure that contains about 11 vol.% Laves phase at the grain boundaries and about 10 vol.% precipitation in NiAl, as well as NiAl as a residue. A further improvement in certain characteristics is obtained if the alloy additionally contains at least one element from the group iron, molybdenum, tungsten and hafnium in quantities up to 1 at.%, respectively, but in total not more than 3 at.%. The alloy may also contain residual elements such as oxygen, nitrogen and sulfur, as well as contamination caused by manufacturing. By adding tantalum and chromium in the specified content ranges, the already mentioned coarse or respectively fine-grained multiple phases of Laves and -chromium are formed. These deposits can typically be found at the wedge points (grain contact points) of various NiAl grains. Higher amounts of tantalum or chromium alloying elements than the specified amounts can lead to an undesirable increase in the amount of precipitation. If the volume fraction of the Laves phase increases too much, a cellular structure appears in which the Laves phase takes on the function of a matrix. Too much of the Laves phase in the structure makes the intermetallic alloy brittle and difficult to process. By adding one or more elements from the group iron, molybdenum, tungsten, niobium and hafnium, respectively, up to 1 at. %, in total however not more than 3 at.%, an increase in strength under short-term load can be achieved. However, the creep resistance is reduced. Due to the addition of hafnium after the first corrosion, improved adhesion of the oxide layer is achieved. The problem of using the alloy is solved according to the invention by using a NiAl-based alloy to produce gas turbine parts, in particular parts subject to high temperature loads, such as gas turbine blades. A gas turbine part made from a base alloy, in particular a turbine blade, is, due to its high oxidation resistance, particularly suitable for long-term use at high temperatures, for example above 1100 o C, in particular at 1350 o C. Depending on the requirements in the case of such a part, in contrast For superalloys, additional coating with protective layers can be dispensed with. A turbine blade manufactured in this way, consisting of a single alloy without additionally applied layers, is much easier to manufacture and, in comparison with turbine blades consisting of several layers, is free from the problems of connection between the individual layers. The nickel-aluminum intermetallic alloy is generally also suitable as a material for the manufacture of objects that need to have high strength, high heat resistance, good toughness, good oxidation resistance and good thermal shock resistance. In this case, the strength lies with 0.2% tensile strength at room temperature above 600 MPa. Thermal resistance with 0.2% tensile strength is above 200 MPa at 800 o C and above 90 MPa at 1000 o C. Viscosity is at least 7 MPa/m and oxidation resistance is on the order of 510 -14 g 2 cm -4 s. Using the following examples, the nickel-aluminum intermetallic alloy is explained in more detail. The composition (in at.%) of the studied alloys is given in the following Table 1. The structure execution, that is, the grain size, the distribution of precipitation and the magnitude of precipitation are highly dependent on the manufacturing process. By thermodynamic treatments, profile pressing (SP) or using a powder metallurgy (PM) manufacturing route, the particle distribution of the Laves phases is homogenized. Also, the mechanical properties of alloys are highly dependent on the chosen manufacturing process. The following manufacturing paths for these alloys can be traced: - directional solidification as a possibility of obtaining a structure with small defects due to casting technology. The process parameters correspond to those for superalloys (cf. U. Paul, VDI-Fortschrittbericht Nr. 264, VDI publishing house), - powder metallurgy: by atomization in an inert gas through nozzles and subsequent hot isostatic pressing at 1250 o C, - profile pressing to homogenize the structure and regulation of certain sizes of grain diameters at 1250 o C, - hot pressing in a multiaxial state of stress and 1100 o C. Directional-cured samples have a clearly higher strength, while material obtained by profile pressing has reduced or very low strength. The following Table 2 shows the 0.2% tensile strength under pressure test for various alloys as well as for NIAI. The creep resistance (in MPa) of the studied alloys in pressure testing (secondary steady-state creep resistance as a function of tensile rate [in 1/s] at 1000 o C and 1100 o C is presented in Table 3. The creep resistance of these alloys is higher than the creep resistance of comparable intermetallic phases, for example, higher than the creep resistance of binary NiAl or respectively NiAI-Cr alloys. Table 4a gives a comparison of the 0.2% tensile strength (in MPa) pressure test of a conventional superalloy, binary NiAl alloy and NiAI-Ta-Cr alloy. With respect to 0.2% tensile strength, the alloy according to the invention is superior at temperatures above 1000 o C. Comparison of steady-state creep resistance at 10 -7 1/s (in MPa). ) in the pressure test of the superalloy, the binary NiAl alloy and the developed NiAI-Ta-Cr alloy is conveyed by the following table 4b: Here the abbreviation n.o. means that the value has not been determined. Compared to conventional superalloys, the NiAl-Ta-Cr alloy has the advantage that it also has sufficient strength above 1050 o C - 1100 o C. In this alloy there is no sudden decrease in strength, which can be explained by the decomposition of the strengthened phase. Table 5 shows a comparison of the K IC -values of various ceramics known from industrial data, as well as a powder metallurgical NiAI-Ta-Cr alloy. The toughness of the NiAl-based intermetallic alloy is significantly better than the measured data for binary NiAl and SiC. The alloy has a good oxidation resistance of the order of 510 -14 g 2 cm -4 s, which is therefore equal to or even better than the oxidation resistance of binary NiAl. In contrast to a superalloy, therefore, at high temperatures no protective layers, for example made of ceramic material, are needed. This eliminates the problem of connections between ceramic and metal components. There is also sufficient resistance to thermal shock. At 1350 o C the alloy achieves 500 temperature cycles without damaging the material.

Claim

1. An intermetallic alloy based on nickel-aluminium, containing predominantly the binary phase NiAl, as well as additionally chromium and tantalum, the total proportion of chromium and tantalum being up to 12 at.% and at least optionally one additional element selected from the group containing iron, molybdenum, tungsten, niobium and hafnium with a corresponding proportion of up to 1 at.% and a total of not more than 3 at.%. 2. The alloy according to claim 1, characterized in that it contains 70 - 95 at.% of the NiAl binary phase, in particular 85 - 90 at.%. 3. The alloy according to claim 1 or 2, characterized in that it contains 0.3 - 3.8 12 at.% tantalum and 1.0 - 9.0 at.% chromium. 4. The alloy according to claim 3, characterized in that it contains 0.3 - 0.9 at.% tantalum and 1.0 - 3.0 at.% chromium. 5. The alloy according to claim 3, characterized in that it contains 1.7 - 3.0 at.% tantalum and 6.0 - 9.0 at.% chromium. 6. An alloy according to any of the previous paragraphs, characterized in that it contains tantalum and chromium in a ratio of 1: 3 or less. 7. The alloy according to any of the previous paragraphs, characterized in that on at least some grain boundaries of NiAl there are deposits of a coarse Laves phase and inside at least some grains of nickel-aluminum there are deposits of a fine-grained Laves phase and chromium. 8. The alloy according to claim 7, characterized in that its structure contains 5 - 11 vol. % precipitation of the coarse Laves phase at grain boundaries and 3 - 10 vol.% precipitation of the fine-grained Laves phase and -chromium in NiAl. 9. The alloy according to claim 8, characterized in that its structure contains about 11 vol. % precipitation of the Laves phase at grain boundaries and about 10 vol.% precipitation in the binary NiAl phase. 10. An alloy according to any of the previous claims, characterized in that it is used as a material for the manufacture of gas turbine parts, such as gas turbine rotor blades and gas turbine guide vanes. 11. An alloy according to any of the previous paragraphs, characterized in that it is used as a material for the manufacture of products having a 0.2% tensile strength at room temperature above 600 MPa, at 800 o C - above 200 MPa and at 1000 o C - above 90 MPa, viscosity K to at least 7 MPa/m, oxidation resistance of the order of 5 10 -14 g 2 cm -4 s and good resistance to thermal shock.

Similar patents:

The invention relates to the metallurgy of alloys, namely to the production of heat-resistant nickel-based alloys used for the manufacture of parts, such as gas turbine blades, operating for a long time at high temperatures (1000-1100°C) using directional crystallization and single-crystal casting methods.

The invention relates to methods for heat treatment of nickel-based superalloys with the following chemical composition, wt.%: Cr 11-13, Co 8-17, Mo 6-8, Ti 4-5, Al 4-5, Nb 1.5, Hf 1 , C, B, Zr each 510-4, Ni - the rest up to 100, or Cr 12-15, Co 14.5-15.5, Mo 2-4.5, W 4.5, Al 2.5-4 , Ti 4-6, Hf 0.5, C 110-4-310-4, B 110-4-510-4, Zr 210-4-710-4, Ni - rest up to 100

Permissible metal contacts according to GOST 9.005-72

Any electrician knows that copper and aluminum wires should not be twisted together. A copper ground bus or brass board stand does not fit well with galvanized screws purchased at the nearest hardware store - corrosion can destroy the electrical contact. A bare aluminum part can generally gradually turn into dust if even a low voltage voltage is applied to it.

Almost everything about permissible metal-to-metal contacts was written in Soviet GOSTs, but now it can be very inconvenient to look for information about connections in old documents. Habrauser @teleghost collected all the data in one table.

The letter "A" means "limited permissible in atmospheric conditions." The definition of this concept from GOST is under the spoiler.

These contacts can be used in products whose design features and operating conditions make it possible to periodically renew the protection of contact surfaces by applying working or conservation lubricants, paint coatings, or provided that corrosion damage to the contacting materials is acceptable for the designated service life of the product.

A few words about metals.

Cink Steel- the main workhorse of the national economy. In the form of various hardware, “galvanization” is found in building materials stores much more often than, for example, stainless steel. Factory PC cases, technological boxes and cabinets for equipment are most often made of galvanized cold-rolled steel with a thickness of about 1 mm.

Stainless steel- the queen of steels: strong, ductile, corrosion-resistant, electrically conductive, looks cool. Too tight to cut and bend at home on an industrial scale. Chromium and chromium-nickel stainless steels are electrically poorly compatible with zinc and “bare” steel, but they provide reliable contact with copper without the help of tin. Aluminum and nitrided, oxidized and phosphated low alloy steel have limited compatibility under standard atmospheric conditions. A2 grade stainless steel is not “magnetic”, but there are also stainless steels with magnetic properties. Magnetic properties do not affect the corrosion resistance of stainless steel.

Aluminum and its alloys are anodized (with a protective layer) and conventional (non-anodized). Aluminum is easy to process at home, but you need to be aware of corrosion. Don't use bare aluminum as a conductor, even at low voltage, or the current will slowly turn the part into dust. Aluminum and duralumin parts processed in the workshop are shown to be fully equipotential (field-induced currents seem to be okay, they can also be grounded). Aluminum is compatible with zinc coating, but contact with copper, bare or nickel-plated steel requires a tin "spacer". Contact between aluminum and stainless steel in atmospheric conditions is allowed to a limited extent. For simplicity, we can assume that when in contact with other metals and coatings, aluminum will corrode on its own, without the help of external electricity.

Copper soft and oxidizes rather unappetizingly in air, so copper products are enclosed in a hermetically sealed shell or varnished. Brass plaques for soldiers' belts and racks for electronic printed circuit boards resist oxidation better and look more appetizing than greened copper, especially if they are periodically polished (I'm talking about plaques, of course). At the same time, neither copper nor its alloy with zinc (brass) is “friendly” with pure zinc and its coatings. But copper is combined with chromium, nickel and stainless steel. And if you hold any terminal in your hands, then it is probably made of tinned (tin-coated) copper.

Tin relatively resistant to corrosion (in room conditions) and electrically compatible with almost everything except cast iron, low-alloy and carbon steels and magnesium. You should not solder tin and beryllium; be careful when assembling a home nuclear reactor. Tin is used to turn an unacceptable electrical contact into an acceptable one, i.e. as a "gasket". Tinned copper terminals are a great example.

Tin should not be used at low temperatures - the so-called tin has been known since the last century. “tin plague” - a polymorphic transformation of the so-called. “white tin” to “gray” (b-Sn → a-Sn), in which the metal crumbles into gray powder. The reason for the destruction is a sharp increase in the specific volume of the metal (the density of b-Sn is greater than that of a-Sn). The transition is facilitated by contact of tin with a-Sn particles and spreads like a “disease”. The tin plague has the highest rate of spread at a temperature of -33°C; lead and many other impurities delay it. As a result of the destruction of tin-soldered liquid fuel vessels by the “plague” in 1912, R. Scott’s expedition to the South Pole perished.

Nickel covered with shiny “computer” screws. This coating is compatible with copper and bronze, brass, tin, chrome and stainless steel. Nickel is incompatible with zinc and aluminum (for aluminum, contact with stainless steel is better, see below).

Features of corrosion aggressiveness of non-metals. Appendix 3b to GOST 9.005-72:

The corrosive aggressiveness of organic materials is determined by the activity of released aging products.
- The corrosive aggressiveness of phenoplasts, aminoplasts, foam plastics, and formaldehyde adhesives is determined by the release of formaldehyde and the possibility of its oxidation to formic acid and hexamine, which can be a source of ammonia.
- The corrosive aggressiveness of wood materials is determined by the release of solutions of acetic and formic acids.
- The corrosive aggressiveness of epoxy materials is determined by the presence in them of free chlorine and hydrogen chloride, carboxylic and dicarboxylic acids.
- The corrosive aggressiveness of rubber products is determined by the content of sulfur and its compounds, hydrogen compounds with halides, and organic compounds with oxidizing properties.
Polymer materials obtained by condensation reaction (epoxy, polyester, etc.) have the greatest corrosiveness during the curing period. It is not recommended to carry out the curing process in confined spaces of the structure.
Irradiation of a non-metal with ionizing radiation (ultraviolet, gamma irradiation, etc.) can increase its corrosiveness.
The corrosive aggressiveness of a non-metal in direct contact with metal is determined by its water and oxygen permeability. The values of water and oxygen permeability for a number of non-metals are given in Tables 4 and 5.

The first three were the main coin metals, although there have been a few attempts to use some other metals for coins since ancient times. In ancient Byzantium, in medieval China and Japan, iron coins were in use. In the last years of the Roman Republic, in China IX-X centuries. Coins made of lead are found in Eki, and on the islands of Sicily, Java, Borneo and Sumatra - made of tin. In ancient Bactria, coins were made from an almost modern copper-nickel alloy containing 20% nickel; this composition corresponded to the natural ore deposits from which the metal was smelted.

At the end of the 19th century, a fourth metal, nickel, was added to the three main coin metals. This metal was discovered in 1751 by the Swedish mineralogist Axel Frederik Kronstedt (1722−1765). He examined the reddish-brown ore. Its color resembles copper, and when medieval German miners were unable to smelt metal from this ore, they called it “kupfernickel”, that is, “devil’s copper” (from German. Kupfer- copper and Nickel- evil mountain spirit, or gnome). By the way, once in Russian (for example, in Mendeleev’s “Fundamentals of Chemistry”) they wrote “nikkel” according to the German template. Canada is one of the world's leading nickel-mining countries. And in 1951, in honor of the 200th anniversary of the discovery of this important metal for the country, a five-cent nickel coin was issued in Canada. Rice. 1. Nickel Five-Cent Coin (Canada) In the United States, five-cent coins are traditionally called “nickels”, although in fact they are minted from a copper-nickel alloy, which contains only 25% nickel (Fig. 2). But already 15% nickel completely masks the color of copper in the alloy, making it pure white. The first copper-nickel coins in the United States had a different denomination - three cents; they replaced the earlier silver three-cent coins and were minted from 1865 to 1889. Interestingly, on October 8, 1942, “nickel-free nickels” appeared in circulation in the United States - they contained 56% copper, 9% manganese and... 35% silver! The reason is simple: at the end of 1941, the United States entered World War II, and the military needed large quantities of nickel to make steel armor. Such coins were minted until 1945. How much nickel could have been saved? In 1941 alone, 300,152,000 five-cent coins were minted, weighing 5 g each and totaling 1,500.76 tons, of which pure nickel accounted for more than 375 tons. This made it possible to produce almost 10 thousand tons of Krupp armor!

Rice. 3. Three cents Coins made from a copper-nickel alloy were first minted in Switzerland in 1850.

And from nickel - in the Austro-Hungarian Empire since 1892 (10 and 20 hellers). Coins made of almost pure (99%) nickel were minted in 1923-1943 in Italy (two lire), and coins of one lira, 50, 25 and 20 centesimo contained 97.5% nickel in different years. In the twentieth century, nickel coins were minted in many countries - Belgium, France, Switzerland, Germany, Hungary, Luxembourg, the Netherlands, etc.

Rice. 5. One lira 1922 In the Russian Empire, the famous physicist who discovered electroplating, academician Boris Jacobi, advocated the minting of a nickel coin. He represented Russia in the international commission to develop common units of measures, weights and coins. At his request, in 1871, test samples of the proposed coins were minted at the Brussels Mint. However, the Ministry of Finance rejected this proposal, as well as subsequent ones coming from England, France and Germany. At the beginning of the twentieth century, rich nickel ores were discovered in Russia, and a proposal to begin minting nickel coins came in 1911, now from the St. Petersburg Mint. But the war that began soon buried this initiative too. Coins from a copper-nickel alloy began to be minted in the USSR only in 1931. The composition of the alloy changed with the redesign of Soviet coins in 1961. Thus, an analysis of the alloy of the 20-kopeck coin of 1978 showed that it contains 52.77% copper, 31.72% zinc, 11.40% nickel, 3.85% manganese and 0.26% iron.

Rice. 6. 1871 Proof Nickel Coins

Rice. 8. Twenty kopecks 1931 Aluminum coins are very light, cheap and look good, but only while they are new. Soft aluminum wears out quickly, corrodes easily, and coins become quite unsightly. Aluminum coins were minted (and in some places are still minted) in the GDR, Poland, Czechoslovakia, Albania, Hungary, Mongolia, Austria and a number of other countries.
Rice. 9. On the right is an uncirculated aluminum coin (Cuba, five centavos, 1971), on the left is a corroded aluminum coin (France, two francs, 1943) An amazing story happened with Italian aluminum coins. (Strictly speaking, they were minted not from pure aluminum, but from an alloy italma- from “Italy”, “aluminum” and “magnesium”, but this alloy contains 96.2% aluminum, and only 3.5% magnesium, and 0.3% manganese.) Coins were minted from this right in the post-war Italian Republic the smallest denominations: 1, 2, 5 and 10 liras. As mentioned in the first article about coins made of gold, silver and copper, the price of the metal in the coin once corresponded to the face value. The so-called deterioration of coins is known, when rulers maliciously reduced the standard of the precious metal. But history also knows exactly the opposite cases, when the value of the metal exceeded the face value of the coin. As a rule, this is due to inflation and the slowness of officials who do not stop minting coins in a timely manner, as they say, at a loss. In Italy in the 1970s of the twentieth century, there was an acute shortage of small change coins - the smallest denominations almost disappeared from circulation. It turned out that some companies were buying up these cheap coins, the metal of which was worth more than the face value, and using them for various purposes, for example as the basis for buttons - this was cheaper than stamping mugs from even inexpensive aluminum. As a result, the Italian government took urgent measures to mass mint small coins. So, if in 1970 3.1 million five-lire coins were minted, then in 1972 - already 16.4 million, and in 1973 - 28.8 million! And although back in 1976 the lira was worth only 0.0012 US dollars, i.e. it could not buy anything, the mass minting of small coins continued almost until the transition to the euro in 2002. As if in mockery, a cornucopia was depicted on the one lira coin. To be fair, it should be said that the circulation of aluminum coins at the end of the 20th and beginning of the 21st centuries was, of course, modest. Thus, in 2001, only 110 thousand five-lira coins were minted, but not for circulation, but for collectors - of improved quality.

Ilya Leenson,
Ph.D. chem. Sciences, Associate Professor, Higher Chemical College of the Russian Academy of Sciences

1 Abstract 2

2 Introduction 3

3 Part characteristics 4

4 Choosing a nickel plating method 5

4.2 Electrolytic method 5

4.2 Chemical method 5

5 Requirements for coating and selection of its thickness 6

6 Selection of technological process implementation 7

7 Theory of the electroless nickel plating process 8

8 Selection of solution 10

9 Selection of basic technical operations 12

9.1 Chemical degreasing 12

9.2 Electrochemical degreasing 13

9.3 Etching 13

9.4 Lightening 14

9.6 Electroless nickel plating 14

9.7 Flushing 14

10 Process diagram 16

11 Compositions of solutions and modes of their operation 17

12.1 Calculation of the dimensions of pendants and chemical baths

nickel plating 19

12.2 Calculation of equipment operating time funds 21

12.3 Annual production volume of one bath of chemical

nickel plating 22

12.4 Chemical consumption 22

12.5 Adjusting solutions 24

12.6 Water consumption 28

12.7 Water consumption for washing 30

13 References 33

2 Introduction

The use of aluminum alloys for the manufacture of machine parts is increasing every year, which is due to a number of specific properties of aluminum (lightness, malleability for stamping, corrosion resistance (in air, aluminum is instantly covered with a durable film of Al 2 O 3, which prevents its further oxidation), high thermal conductivity, non-toxicity its compounds. But aluminum has a significant drawback - low hardness (100-150 MPa), as a result of which the surface of parts working on friction quickly wears out. Therefore, hardening the surface of parts made of aluminum alloys by applying a harder layer of another metal is of great practical importance. In this regard, the nickel coating, which has high hardness and adhesion to the base, is of great practical interest, especially after heat treatment.

Nickel coatings are used in various industries both as a sublayer and independently for protective, decorative and special purposes. They are characterized by hardness, significant corrosion resistance and good reflectivity (58 - 62%), electrical resistivity of 8.3-10 -2 Ohm m.

Nickel coatings are used in industry for protective, decorative and decorative finishing of products and parts of machines, apparatus, and instruments; for protection against corrosion at elevated temperatures and in special environments (alkalies, some acids), as an intermediate sublayer for applying other coatings to steel in order to ensure strong adhesion of the coatings to the base, to increase the wear resistance of rubbing surfaces.

Currently, two methods of applying nickel coating are used: electrochemical and chemical. Only with the help of chemical nickel plating is it possible to obtain a coating for complexly profiled parts. By introducing inorganic additives containing phosphorus and boron, it is possible to regulate the hardness of the resulting coating, which is important for parts made of aluminum alloys. It should be taken into account that coatings obtained by chemical nickel plating have high corrosion resistance.

3 Part characteristics

The body of the radio-electronic device, made by milling and made of D16 aluminum alloy, was selected as a part for coating.

The part is coated both from the outside and from the outside; characteristic is the presence of various holes for the output of wires and bolted connections.

This housing with the radio-electronic device is subsequently sealed using a bolted connection or low-temperature soldering. To ensure reliable operation of the device, the coating applied to the body must provide corrosion resistance, wear resistance, optimal hardness and be uniform in thickness.

Typically, cases made of aluminum alloys are subjected to nickel plating followed by the application of other functional coatings, such as tin, bismuth, and silver coatings.

Part Dimensions:

l=5.4cm 2 , h=8.8cm 2 , b=1.3cm 2

Since the part is coated both from the outside and from the inside, the coverage area of one part will be equal to:

S cover =168 cm 2

4 Choosing a nickel plating method

There are two possible ways to apply nickel coatings:

4.1 Electrolytic method

The electrolytic method is the application of nickel coatings to the surface of an electrolyte product under the influence of an electric current. The advantage of this method is that the thickness of the coating is clearly controlled and the consumption of coating metal is minimal. In addition, by selecting the type of electrolyte and the deposition mode, it is possible to obtain deposits of the desired structure, appearance and with different mechanical properties. The disadvantage of electrolytic nickel plating is the uneven deposition of nickel when applied to a relief surface, as well as the impossibility of coating narrow and deep holes and cavities.

4.2 Chemical method

In the chemical method, the product to be coated is placed in an aqueous solution containing a dissolved metal salt and a reducing agent. A layer of metal is deposited on the surface of the product.

The coating deposited during electroless nickel plating is not pure nickel, as in electroplating, but consists of an alloy of nickel and phosphorus. Coating with this alloy has nothing in common with coating with pure nickel, both in terms of physical-mechanical and chemical-corrosion properties.

The coating can be applied to products of complex configuration with a high degree of uniformity. It can be applied to the internal cavities and channels of the product, which is almost impossible to achieve with galvanic application.

The wide range of applications of chemically deposited nickel-phosphorus coating is explained by its impressive set of useful properties: hardness from 6000 to 10000 MPa, high corrosion resistance, antifriction (low wear during dry friction), the ability to shield high-frequency electromagnetic radiation, low contact resistance on electrical contacts, good solderability.

The mechanical properties of nickel plating do not depend on thickness: for example, coatings with a thickness of 1 micron and 100 microns have the same specific wear resistance.

In this case, it is more advisable to use chemical nickel plating. This is due to the fact that the part has a complex configuration (the presence of holes, recesses, cavities), and also requires coating both on the outside and on the inside.

5 Coating requirements and choice of thickness

The thickness of the coating is set depending on the operating conditions, the purpose of the coating according to regulatory and technical documentation, as well as the method of applying the coating.

Since our part must be coated with a functional coating, the coating must be uniform in thickness, and also provide corrosion resistance, wear resistance and hardness of the base metal under operating conditions.

According to GOST 9.303-84, the minimum coating thickness should be 9 microns. The permissible maximum coating thickness is 15 microns. The average thickness of nickel obtained in a nickel plating bath is 15 microns.

6 Selection of technological process implementation

There are three ways to carry out the technological process of chemical nickel plating, differing depending on the type of reagent chosen as a reducing agent.

1) hypophosphite method, characterized by the joint release of phosphorus into the nickel coating;

2) borohydride method, in which boron, which is part of the coating, is released;

3) hydrazine method, in which nickel is deposited with the least amount of impurities.

So far, only the hypophosphite method has received industrial application. This is due to the fact that the borohydride coating method is characterized by a highly alkaline environment (pH>13), which will lead to the dissolution of aluminum.

Despite the fact that the hydrazine method makes it possible to obtain high-quality nickel coating, its use is practically not widespread, due to the low deposition rate of nickel, the main component (hydrazine) is practically not commercially available, this method is very demanding in terms of compliance with safety regulations, because If operating conditions are violated, detonation is possible.

It is advisable to carry out chemical deposition of nickel onto aluminum alloys using a solution with sodium hypophosphite. The deposited coating has a semi-shiny metallic appearance, an amorphous structure and is an alloy of nickel and phosphorus.

7 Theory of the electroless nickel plating process

The mechanism for the reduction of nickel ions with the help of hypophosphite is electrochemical in nature, while on the surface of the catalyst - base, the anodic stage of oxidation of the reducing agent (5.1) and the cathodic stage of the reduction of nickel (5.6) and hydrogen (5.3) simultaneously occur (conjugate).

The anodic stage of hypophosphite oxidation - the reaction of sodium hypophosphite with water - is represented as the addition of an OH¯ ion from a water molecule to the site of bond rupture

P – H in the sodium hypophosphite molecule. This reaction, facilitated by the catalytic action of the nickel surface, can be expressed by the following equation:

H 2 O ↔ H + + OH¯, (5.1)

H 2 PO 2 ¯ + OH¯→ H 2 PO 3 ¯ + H + e. (5.2)

An electron released from the hypophosphite anion can be transferred through a metal surface to a hydrogen ion and convert it into an atomic one:

N + + e → N. (5.3)

Two hydrogen atoms, one of which was formed from the P–H bond of the hypophosphite anion, and the other from water, combine to form molecular hydrogen.

Alnwick (English Alnwick, ˈ listen [ˈænɨk]) is a small market town in the North-East of England in the county of Northumberland.
Alloy of Fe with Ni and Al
Hard magnetic alloy
Nickel-aluminum alloy
Alloy for permanent magnets
Alloy for making permanent magnets
Magnetic alloy
Alloy for manufacturing constant magnets
Alloy of iron with nickel and aluminum
Magnetic alloy of iron, nickel, aluminum
(from aluminum and nickel) magnetically hard alloys Fe (base) with Ni (20-34%) and Al (11-18%), sometimes with additions of Cu, Co, Si, Ti

Yuval Avital (Jerusalem, 1977) is an Israeli musician, composer and guitarist.
Aluminum alloy
Aluminum based alloy used in aviation
Light alloy
High ductility aluminum alloy
Aluminum alloy for aircraft
Light alloy for winged liners
Alloy, aircraft grade aluminum
Aviation aluminum

Cupronickel (German Melchior, distorted from the French Maillot-Chorier) is a single-phase alloy of copper, mainly with nickel, sometimes with the addition of iron and manganese, which received its name after the names of the French inventors from Lyon, Maillot and Chorier. , who created their alloy in 1819. Typically, cupronickel contains 5-30% nickel, ≤0.8% iron and ≤1% manganese, although in some cases it differs from these proportions.
Jewelry alloy
Tableware alloy
Copper-nickel alloy
Nickel-copper alloy
Silver-white copper-nickel alloy
A metal alloy plated with silver, better known as new silver
A heavy copper-nickel alloy similar to silver and widely used for cutlery and cookware.
Alloy for spoons and forks
Stainless alloy