JP2001020055A - Chromium boride coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new kind of chromium boride coating having excellent sticking wear resistance and corrosion resistance. SOLUTION: This coating is composed in such a manner that superfine hard chromium boride particles having the average particle size of <1 μ are dispersed into a metallic matrix, the above particles occupy about <30 vol.% of the coating, and the balance is composed of a metallic matrix. The metallic matrix can be composed of nickel or an alloy consisting of nickel as a base and contg. metals selected from the group consisting of chromium, silicon and iron. The coating can be produced by a method in which a mechanically blended powdery mixture of a chromium metal or a chromium alloy or a mixture thereof and a boron-contg. alloy is deposited on a base material, and the coating as-deposited is subjected to heat treatment. The heat treatment causes duffusion reaction between the deposited elements, and as a result, the formation of the fine particles of chromium boride dispersed into the metallic matrix is caused. The coating can be deposited on the base material by using optional well-known depositing technique.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to chromium boride coatings having excellent anti-adhesive and anti-corrosion properties and to a method for producing such coatings. More specifically, the present invention relates to hard, dense, low porosity, abrasion and corrosion resistant coatings containing ultrafine chromium boride particles dispersed in a metal matrix. The invention also relates to a method for producing such a coating in situ by thermal spray and diffusion reaction techniques.

[0002] Throughout this specification, the application of a coating will be described using plasma arc spray and detonation gun (D-gun) techniques as examples. A typical detonation gun technique is described in US Pat.
No. 563 and No. 2950867. Plasma arc spray technology is disclosed in US Pat.
Nos. 58411 and 3016447. Other thermal spray techniques are also well known, for example, so-called "high-speed" plasma and "hypersonic" combustion spray methods, and various flame spray methods. The coating requires heat treatment, which can be performed after deposition in a vacuum or inert gas furnace or by electron beam, laser beam, induction heating, transfer plasma arc or other techniques. It is also known to perform the heat treatment after another deposition technique such as slurry, filled fabric or electrophoresis. Still other methods include simultaneous deposition and melting using a plasma transfer arc, laser or electron beam surface melting (with or without post-deposition heat treatment).

[0003]

BACKGROUND OF THE INVENTION In the petroleum industry, mechanical gate valves are commonly used to handle various corrosive liquids under high hydraulic pressure. When activating these valves,
It is required that the gate move very quickly against the valve seat under high mechanical force to close and close the valve. Such conditions can create severe sticking and corrosive wear on both the gate and valve seat metal surfaces, leading to premature valve failure.

[0004] In the petroleum industry, it is common to use a mechanical gate valve in which an adhesive and corrosion resistant coating is applied to the mating surface of the metal gate and the valve seat. Due to differences in the material of the substrate and the type of accompanying wear mechanism,
The coating applied to the gate surface and the coating applied to the valve seat surface are usually different. For example, detonation gun tungsten carbide based coatings (tungsten carbide based coatings) have been successfully used to protect metal gate surfaces against sticky wear, while valve seats are known from known welding techniques. Ni-Cr-BS applied as an overcoat layer by
It has been protected by i-Fe alloys.

[0005]

A problem with these particular coating combinations is that valve seat coatings are not compatible with many heat treated hardenable alloys useful as substrate materials. That is. For example,
Conventional Ni-Cr-B-Si-Fe coating alloys generally fail by cracking or fracturing after heat treatment when applied as a topcoat to AISI 410 stainless steel or AISI 4130 steel valve seats. Would. This is due to an incompatibility in the coefficient of expansion between the substrate and the coating. Accordingly, there is a need to develop new coatings that can be used with a wider variety of substrate materials.

[0006]

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a new class of chromium boride coatings that have excellent anti-adhesion and corrosion resistance and are compatible with many alloy substrates. You. These coatings consist of a dispersion of hard ultrafine chromium boride particles in a metal matrix, which make up less than about 30% by volume of the coating, with the remainder being the metal matrix. The atomic ratio of chromium metal to boron in the coating ranges from about 0.8 to 1.5. The metal matrix can be composed of nickel or an alloy based on nickel and containing a metal selected from the group consisting of chromium, silicon and iron.

The coating of the present invention comprises depositing a mechanically blended powder mixture of chromium metal or a chromium alloy or a mixture of both and a boron-containing alloy on a substrate.
The as-deposited coating can then be manufactured by a method that includes heat treating. This heat treatment results in a diffusion reaction between the deposited elements, resulting in the formation of ultrafine chromium boride particles dispersed in the metal matrix. The coating can be deposited on the substrate using any of the previously reported known deposition techniques.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating of the present invention is preferably applied to a substrate using a thermal spray method. In one such method, plasma spraying, an electric arc is established between one non-consumable electrode and a second non-consumable electrode spaced therefrom. Gas is passed through and brought into contact with the non-consumable electrode to contain an electric arc. The arc-containing gas is compressed by the nozzle,
This results in an effluent with a high heat content. A powdery coating material is injected into this high heat content effluent and deposited on the surface to be coated. This method and the plasma arc torch used therein are described in U.S. Pat. No. 2,858,411. Plasma spraying produces a firm, dense, adherent adherent coating to the substrate. The applied coating is
Irregularly shaped microscope-sized vertical splats
Or the leaves are entangled and mechanically connected to each other and to the substrate.

[0009] Another method of applying a coating to a substrate is by detonation gun (D-gun) deposition. A typical D-gun is several feet long and has an inside diameter of about 1
Consists essentially of an inch water cooled barrel. In operation, a mixture of oxygen and a fuel gas (eg, acetylene) in a particular ratio (typically about 1: 1) is fed into a barrel with a charge of powder to be coated. The gas is then ignited and a detonation wave dissolves the powder for about 2
While accelerating to 400 feet / second (730 m / s)
The powder is heated to near or above its melting point. After the powder exits the barrel, a pulse of nitrogen purges the barrel and prepares the system for the next detonation. This cycle is then repeated many times.

The D-gun deposits one coating circle on the substrate for each detonation. The ring of the coating is typically about 1 inch (25 mm) in diameter and several ten thousandths of an inch (or a few microns) thick. Each annular coating is composed of a number of microscopic sized slabs corresponding to the individual powder particles, partially overlapping (hereinafter, partially overlapping is simply referred to as overlapping). These overlapping elongated plates entangle and bond to each other and to the substrate substantially without alloying at their interfaces. In order to deposit a smooth coating of uniform thickness and to minimize residual stresses during heating of the substrate and applied coating, the arrangement of rings in the coating deposition is adjusted to be tight.

In principle, the powdery coating material used in the thermal spraying process will have essentially the same composition as the applied coating itself. However, when a certain type of thermal spraying device is used, a change in composition may be expected. In such cases, the composition of the powder is adjusted to achieve the desired coating composition.

In the following, the invention will be described with particular reference to coatings produced by the plasma arc spray method, but it will be understood that any of the previously known deposition techniques reported above may be used.

According to the present invention, a mechanically blended powder mixture containing particles of chromium metal or a chromium alloy or a mixture of both and particles of a boron-containing alloy or alloy mixture is plasma sprayed and then heated to a high temperature (eg, About 900
(~ 1100 ° C) to apply a wear and corrosion resistant coating to the metal substrate.
At these temperatures, diffusion and chemical reactions between thin overlapping elongated plates (some of which contain a chromium metal component and others of which contain a boron-containing alloy or alloy mixture) deposited by a thermal spray process. Happens. These diffusions and chemical reactions result in the formation of chromium boride (CrB) precipitates dispersed in the metal matrix. The precipitate is usually evenly dispersed throughout the matrix, but in some cases can agglomerate into a plurality of small colonies that are evenly dispersed throughout the matrix. During adhesion, essentially no reaction occurs between the powder particles,
Prior to heat treatment, the elongated plates maintain their initial powder composition.

The coatings of the present invention can be made using a two-component system, a first chromium metal or chromium alloy component and a second boron-containing alloy component, or a multi-component system can be used. . The multi-component system can include additional chromium metal or chromium alloys, which can be used, for example, when it is desired to add chromium metal in the alloy matrix to increase corrosion resistance. it can.

The formation of the coating containing the chromium boride precipitate in the metal matrix can proceed according to one of the following equations:

Embedded image (Where M ₁ and M ₂ are nickel and optionally one or more metals selected from the group consisting of chromium, silicon, phosphorus, aluminum, manganese, cobalt and iron;
B is boron).

As mentioned above, the purpose of the metal M ₂ is to change the properties of the matrix, eg to include additional chromium to improve corrosion resistance.

In addition to the above elements, M ₁ and M ₂ are carbon,
Small amounts of other elements such as oxygen and nitrogen can also be included.

The proportions of chromium metal and boron used in the powder mixture determine the volume fraction of chromium boride that precipitates in the metal matrix. Generally, this ratio is about 0.8
Should be kept in the range of ~ 1.5.

For optimal cohesive wear properties, the volume fraction of chromium boride precipitate in the coating should be kept in the range of about 12 to about 30% by volume, and in the range of about 15 to 25% by volume. Is preferred.

The elements in the boron-containing alloy are in the following proportions: about 2.5 to about 10% by weight Born 0 to about 25% by weight Chromium 0 to about 2% by weight Manganese 0 to about 2% by weight Aluminum 0 to about 1% by weight % Carbon 0 to about 5% by weight Silicon 0 to about 5% by weight Phosphorus 0 to about 2% by weight Copper 0 to about 5% by weight Iron Remaining nickel if kept within the range of chromium boride in the above range A coating having a high modulus can be produced.

As the boron-containing alloy, the above formulas (1) to (1)
Use of almost any boron-containing alloy in the preparation of the coating of the present invention, as long as it satisfies the reaction requirements for one of (3) and provides the desired components in the metal matrix. Can be. Particularly suitable alloys for use in producing the coating according to the invention are given in Table I below.

[0022]

[Table 1]

Generally, the powder mixture used to make the coating has a particle size of less than about 200 mesh.

In practicing the present invention, the as-deposited coating is heat treated at a temperature high enough for the boron-containing alloy to be sufficiently fluid to promote the diffusion reaction (typically about 900 ° C.). It is important to. This heat treatment temperature can be much higher than 900 ° C. if desired, for example about 1100 ° C., but this temperature should not be so high as to have a detrimental effect on the substrate. The as-deposited coating should be kept at the heat treatment temperature for a time sufficient to promote reaction and / or diffusion between the components of the coating. Also, for the substrate, a limited but significant amount of diffusion reaction occurs.

The heat treatment of the coating is generally carried out in a vacuum or inert gas furnace. Also, as long as the time at high temperatures is sufficiently short or a protective atmosphere is provided such that no significant oxidation of the coating occurs,
Electron beam, laser beam, transitional plasma arc,
Heat treatment can also be achieved by a surface melting process such as induction heating or other techniques.

The coatings of the present invention can be successfully applied to many different types of substrates using the known deposition techniques described above. However, the substrate must be able to withstand the effects of the heat treatment without any detrimental consequences. Suitable substrate materials that can be coated according to the present invention include, for example, steel, stainless steel, iron-based alloys (iron-based alloys; hereafter, all base alloys are based on ...) Alloys), nickel, nickel-based alloys, cobalt, cobalt-based alloys, chromium, chromium-based alloys, titanium, titanium-based alloys, refractory metals and refractory metal-based alloys.

When the coating according to the invention is applied to a heat-treated, hardenable alloy substrate such as, for example, AISI 4140/4130 steel, the volume fraction of the hard phase can be as high as 20% or more. it can. AISI 4 coating
When applied to 10 stainless steel, the volume fraction of the hard phase should be kept below about 20%. It has been found that coatings having a volume fraction of CrB above these levels are not sufficiently ductile to withstand the high internal stresses imposed by the expansion of the substrate. This is particularly troublesome for certain alloys, such as AISI 410, which undergo thermal expansion due to martensitic phase deformation. (AI
The nominal composition of SI410 is 12.5 wt% Cr, 0.15 wt% maximum C, and the balance is iron, the nominal composition of AISI 4130 is 0.3 C, 0.5 Mn, 0.2 Si, 1.0 Cr, 0 .
2Mo, balance iron, AISI 4140 nominal composition is 0.
4C, 0.9Mn, 0.2Si, 1.0Cr, 0.2M
o, the rest is iron. )

[0028] The thickness of the coating produced according to the present invention generally ranges from about 0.005 to about 0.040 inches (0.1 to 1.0 mm).

The microstructure of the coatings of the present invention is somewhat complicated and is not well understood. However, studies performed to date have shown that the coating contains a hard phase containing ultrafine particles of chromium boride in a metal matrix. The metal matrix is crystalline in nature, relatively dense, softer and less permeable than the hard phase.

Depending on the volume fraction of the hard phase in the coating, the chromium boride particles may be substantially evenly dispersed throughout the matrix, and the particles aggregate to form a plurality of small colonies (these are referred to as chromium boride particles). The colonies are usually evenly distributed in the matrix). Generally, CrB
Particle clusters form in the coating as the volume fraction approaches the upper limit of about 30% by volume.

The size of the chromium boride particles will vary depending on several factors, including heat treatment temperature and time. Generally, the average particle size will be below μ, typically from about 0.1 to about 1.0μ.

The hardness of the coating changes in proportion to the volume fraction of the hard phase. Thus, by varying the atomic ratio of chromium metal to boron in the powder mixture, the hardness can be tailored to a specific range of values. Generally, the hardness of the coating ranges from about 250 to about 700 DPH ₃₀₀ (HV.3).

A significant advantage of the present invention is that the diffusion reaction between chromium or a chromium alloy and a boron-containing alloy occurs at relatively low heat treatment temperatures, eg, about 1000 ° C. The exact reason for this phenomenon is unknown, but is believed to be due to the accumulation and dislocation of high internal stresses within the layered elongated plate or leaf deposited on the substrate by thermal spraying. In contrast, conventional casting or hot pressing methods have produced chromium boride at significantly higher temperatures, above about 1150 ° C. These high temperatures are usually harmful for most steels. Since only low heat treatment temperatures are required for the coating method of the present invention, these substrates can be coated without any adverse effects.

[0034]

The following examples further illustrate the practice of the present invention.

EXAMPLE I A powder mixture of an alloy of nickel-20 chromium and alloy No. 2 was placed in a 1 / 2.times.3 / 4.times. (2 + 3/4) inch (13.times.19.times.70 m
m) dimensioned low carbon AISI 1018 steel specimen, 5/8 × 1 ×
AISI 4 with dimensions of 2 inches (16 x 25 x 51 mm)
10 stainless steel specimens, 1/2 × 1 × (2 + 3/4) inch (1
Inconel 718 superalloy specimens sized 3x25x70mm) and AISI sized 1 / 2x1x (2 + 3/4) inches
Approximately 0.020 inch (0.5m
m) by plasma spraying to a series of C
An rB coating was produced. (The nominal composition of AISI 1018 is 0.18C, the balance is Fe, and the nominal composition of Inconel 718 is 19Cr, 3.0Mo, 5.1Nb, 0.8
Ti, 0.5Al, 18.5Fe, 0.08Cmax, the balance being Ni. Inconel is International Nickel Co
mpany is a trademark. ) The atomic ratio of Cr to B in the powder mixture was about 1. These as-deposited coatings were heat treated for 1 hour at a temperature of about 970-1020 ° C. in vacuum or argon and then subjected to a series of heat treatments depending on the substrate material. The deposited and heat treated coating had an apparent porosity of less than about 0.5%. In these heat treated coatings, very fine CrB precipitates were uniformly dispersed throughout the Ni-Cr-Si-Fe matrix. The coating / substrate interdiffusion zone had a thickness of about 30-40 μm.

A series of heat treatment experiments were performed on the coated specimens in a horizontal furnace equipped with an oil quenching apparatus and a constant flow of 10 cfh (0.28 m ³ / h) argon gas. The heat treatment applied to the coating / substrate system is outlined in Table II below.

[Table 2]

In Table II above, the first heat treatment step (1) promotes the diffusion reaction in the coating, and the second heat treatment step (2) achieves the desired mechanical properties of the substrate.

After completion of the heat treatment cycle, metallographic and penetrant techniques were used to find any defects in the coating or substrate. It was found that the coating was essentially unaffected by the second heat treatment, except that the coating on AISI 410 stainless steel showed evidence of cracking.

In subsequent experiments on this same coating on 410 stainless steel, a crack-free coating was produced by adjusting the heat treatment schedule. However, this change requires very precise control of the heat treatment, which makes it unsuitable for practical use in production.

EXAMPLE II A powder mixture of nickel-20 chromium and alloy No. 1 was mixed with 5 /
Approximately 0.020 inch (0.2 mm) on AISI 410 stainless steel sized 8 × 1 × 2 inch (16 × 25 × 51 mm).
A series of CrB coatings were produced by plasma spraying at a thickness of 5 mm). The composition of the mixture is as follows: Alloy No. 1 + 39.3 (Ni-20C
r). In the following, all compositions are expressed in weight%,
For example, 60.7% by weight of alloy No. 1 + 39.3% by weight (Ni
-20Cr) is alloy No. 1 + 39.3 (Ni-20Cr)
It is expressed as The atomic ratio of Cr to B was about 1.4. These as-deposited coatings were heat treated for 1 hour at a temperature of about 970-1020 ° C. in vacuum or argon. During these coatings, the CrB precipitate was Ni-
It was uniformly dispersed throughout the Cr-Si-Fe matrix.

The volume fraction of CrB precipitate in these coatings was 15.5% by volume. This was lower than the volume fraction of precipitate in the coating of Example 1.

The coating produced in this example was subjected to the same heat treatment schedule as for the AISI 410 stainless steel substrate as outlined in Table II. After heat treatment, the coating was inspected and found to be free of cracks and defects. This indicates that this particular coating is compatible with the 410 stainless steel substrate.

The hardness of these CrB coatings is about 3
40 DPH ₃₀₀ (HV.3). This was lower than the hardness of the coating made in Example 1. However, the coating in this case was more ductile and strain resistant.

EXAMPLE III A powder mixture of chromium metal or nickel-20 chromium and a boron-containing alloy was placed on an AISI 1018 steel specimen sized 3 / 4.times.1 / 2.times. (2 + 1/2) inches by about 0.020. Inches (0.
5 mm) by plasma spraying,
A B coating was produced. This powder mixture was based on a stoichiometric CrB incorporation in the coating such that the calculated chromium boride volume fraction was in the range of about 13.4-42.6%. The composition of this mixture was as follows. (1) Alloy No. 1 + 50 (Ni-20Cr) (2) Alloy No. 1 + 39.3 (Ni-20Cr) (3) Alloy No. 2 + 56 (Ni-20Cr) (4) Alloy No. 3 + 35 (Ni-20Cr) + 15Cr (5) Alloy No.3 + 30Cr

The as-deposited coatings were heat treated for 1 hour at a temperature of about 960-1020 ° C. in vacuum or argon and then oil quenched. These coatings contain fine Cr in Ni-Cr-Si-Fe.
The B precipitate consisted of a dispersion. Formulations (1) to (5)
The calculated volume fraction of the hard phase in the coatings made from each of 13.4, 15.5, and 19.
7, 32.5 and 42.6%. The hardness of the CrB coating ranged from about 280-740 DPH ₃₀₀ (HV.3).

For comparison, from a conventional alloy powder (referred to herein as C1), a brazing alloy (alloy No. 1) (C2), the alloy powder was plasma sprayed onto the same AISI 1018 steel specimen and then deposited. The coating was made by heat treating the as-coated coating in the same manner as described above. Another conventional alloy powder (Ni-Cr-B-Si-F
e) A coating made from (referred to herein as C3) was applied on steel specimens using standard weld adhesion techniques.

Table III below lists the nominal compositions for all coatings.

[Table 3]

From Table III, it can be seen that the mixed formulations (2) and (3)
It should be noted that the composition of the coatings produced from Co., Ltd. closely corresponds to the composition of conventional coatings, in particular coating C3. Although the compositions of coatings made according to the present invention are similar to those of conventional coatings, the structures of these coatings are significantly different microscopically.

The abrasive wear properties of the coatings prepared above were measured using the standard dry sand / rubber wheel polishing test described in ASTM Standard G65-80 (Procedure A). In this test, the coated specimen was loaded by a lever arm means against a rotating wheel having a chlorobutyl rubber rim around the wheel. An abrasive (50-70 mesh Ottawa silica sand) was introduced between the coating and the rubber wheels. The wheel was rotated in the direction of the abrasive flow. The specimen was weighed before and after the test and its weight loss was recorded. Because the densities of the various materials tested varied widely, their mass loss was typically converted to the material's capacity loss to evaluate the relative ranking of the material. The average volume loss for the coating of the present invention was in the range of about 5 to 50 mm ^3/1000 rotations. It was found that the volume loss decreased as the volume fraction of the hard phase in the coating increased.

[0050] These CrB coatings were also subjected to an erosion test. These tests were performed according to standard procedures using alumina particles with a nominal size of 27μ, a particle velocity of about 91 m / sec, and impact angles of 90 ° and 30 °. The average erosion rate is about 60 to 120 μm /
g and about 30-37 μm / g.

The dry tack and abrasion resistance of both chromium boride and conventional coatings was determined by block-on-ring (bloc).
Evaluation was performed using a k-on-ring (α) tester. Detonation gun (W, Cr) C-CO manufactured by Union Carbide Company under the name UCAR LW-15 ™
The coated ring with the coating was rotated against a stationary block coated with the test coating. The test conditions were 8 in dry air at room temperature.
0 ° vibration, 1000 and 2000 cycles, 164K
g (360 lbs) and a rotating speed of 18 m / min (60 ft / min). The abrasion resistance of the coating was determined by measuring the abrasion on the block, the volume loss based on the measurement of the length and width of the scratch, and the weight loss on the ring. The coatings produced using the blends (1) to (3) are 1
The conventional coating showed a weight loss of more than 2.0 mm ^{3 in the} 1000 cycle test, while the conventional coating showed a weight loss of about 1.3 mm ³ in the 000 cycle test. Each weight loss in 2000 cycle test was 1.4 to 1.9 and 1.8~3.4mm ^3.

Table IV summarizes the metallographic evaluation, sand polish, erosion and tack and abrasion resistance of all coatings tested.

[Table 4]

The curves in FIG. 1 show the relationship between hardness, abrasive and cohesive wear in coatings made according to the present invention and the volume fraction of chromium boride in the coating. These curves show the various Cs produced in this example.
Based on the average of the test results obtained for the rB coating. It should first be noted that the hardness of the coating is linearly proportional to the volume fraction of CrB. Curve A represents the sand abrasive wear rate of the coating. It can be seen that the sand polishing wear rate is non-linear and varies inversely with the volume fraction of chromium boride. Curve B is 10
The adhesive wear rate at 00 cycles and curve C represents the adhesive wear rate at 200 cycles. Adhesive wear increases non-linearly with increasing boride content in the coating. These coatings show higher cohesive wear when tested at 2000 cycles. The chromium boride volume fraction in the coating is about 1
It should also be noted that the capacity loss is minimal when in the range of 2-30%. Coatings with a chromium boride volume fraction of about 30% or more show a significant increase in capacity loss.

The bar graph in FIG. 2 shows a comparison of the capacity loss between a chromium boride coating and a conventional alloy coating when combined with UCAR LW-15. CrB coatings M2, M3 and M4 are each a mixed formulation (2),
Represents those made from (3) and (4), which are superior to the conventional alloy coatings C1 and C2 and comparable or better than the conventional coating C3. LW when matched to CrB coating
The volume loss of the -15 coating is 1/3 to 1/10 of that when combined with a conventional alloy coating.

Micrographs of horizontal and vertical cross-sections relative to the surface of a series of chromium boride coatings made from blends (1)-(5) are shown in FIGS. 3 (a) and (b).
7 (a) and 7 (b). The volume fraction of chromium boride in coatings made from these blends (1) to (5) ranges from 13.4 to 42.6.

In all micrographs, C represents the coating, S represents the substrate, the dark areas represent the precipitate and the light areas represent the matrix.

As shown in FIGS. 3 (a), 4 (a) and 5 (a), the microstructure in a cross section perpendicular to the surface of the coating has a volume fraction of CrB of 13 respectively. In the case of coatings made from blends (1), (2) and (3) which are 0.4, 15.5 and 19.7%, the precipitation of chromium boride is substantially uniform throughout the matrix. It shows that it is distributed. The microstructure of the coatings made from the remaining blended formulations (4) and (5), as shown in FIG. 6 (a) and FIG. This indicates that the village is distributed throughout the matrix as settlements. These coatings have 32.5 and 42.6% C, respectively.
It had an rB volume fraction.

[0058] Cross sections horizontal to the surface of the coating are generally exposed to a wear environment. Thus, it is expected that the microstructure of the coating in a cross section horizontal to the surface will have a significant effect on the wear behavior of the coating. FIGS. 3 (b) to 7 (b) show the microstructure of the cross section horizontal to the surface of the coating made from the blended formulations (1) to (5), respectively. And shows the same type of precipitation that occurs in vertical sections. CrB volume fraction of 1
The coatings made from the blended formulations (1), (2) and (3), which are 3.4, 15.5 and 19.7%, are shown in FIGS. 3 (b), 4 (b) and 5 ( As shown in b), it shows that chromium boride is substantially uniformly precipitated throughout the matrix. In the remaining coatings made from the other mixed formulations (4) and (5), as shown in FIGS. 6 (b) and 7 (b),
The precipitate aggregated into colonies that were uniformly dispersed throughout the matrix. These coatings had a volume fraction higher than 30%.

For comparison, the microstructures in cross-section perpendicular to the surface of conventional plasma sprayed and heat treated C1 and C2 coatings and weld deposited C3 coatings are shown in FIGS. 8 (a), (b) and It is shown in (c).
Since these conventional alloy coatings were made using pre-alloyed powders, it is expected that the microstructure of the cross-section horizontal to the surface of each coating will be the same as that of the cross-section perpendicular to the surface. For coating C1, the relatively high boron content and low chromium content result in the formation of very fine Ni ₃ B structures, such as primary hard phases. As for the coating C2, FIG.
The chromium boride precipitate is in the form of needles, as shown in FIG. In the weld adhesion coating C3, the CrB precipitation was about 3μ.
It is a block with a particle size of m.

The morphology and particle size of the chromium boride precipitate were examined by scanning electron microscopy (SEM) in a cross section horizontal to the surface of the CrB coating.
It has been found that both the morphology and the particle size of the chromium boride precipitate depend on the formation mechanism. Two powder components,
That is, a low melting point boron-containing nickel base alloy and nickel
Coatings made from 20 chromium or chromium metal had a more uniform distribution of precipitates than those made from the three components, the boron-containing alloy, nickel-20 chromium and chromium metal. CrB volume fraction of 13.4, 15.5
And a coating of 19.7%, the diffusion reaction between boron from the low melting point nickel base alloy and chromium in the Ni-20 chromium solid solution has an average size of about 0.5 μm.
This results in m or rod-like or plate-like CrB precipitates (the average size is the length of the rod or the diameter of the plate).

In a 42.6% CrB volume fraction coating made from the two powder components using the blend formulation (5), the diffusion reaction between boron and pure chromium from the low melting point alloy is 1%. Block-shaped C having a particle size of ５5 μm
Leads to the formation of an rB precipitate. In a 32.5% CrB volume fraction coating made from the three powder components using the blended formulation (4), the formation of precipitate was controlled by both mechanisms. Thus, fine plate-like CrB precipitates were formed between the boride settlements containing block-like precipitates having a particle size of 1-5 μm in the matrix.

[Brief description of the drawings]

1 is a graph showing the relationship between the volume fraction of CrB particles in a coating according to the invention and hardness, polishing and cohesive wear.

FIG. 2 is a bar graph showing the anti-adhesion wear of various coatings tailored to a conventional detonation gun tungsten carbide base coating.

FIG. 3: Cr according to the invention produced from the blended formulation (1)
4 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular (a) or horizontal (b) to the surface of the B coating.

FIG. 4: Cr according to the invention produced from mixed formulation (2)
4 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular (a) or horizontal (b) to the surface of the B coating.

FIG. 5: Cr of the invention produced from the blended formulation (3)
4 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular (a) or horizontal (b) to the surface of the B coating.

FIG. 6: Cr of the present invention produced from mixed formulation (4)
4 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular (a) or horizontal (b) to the surface of the B coating.

FIG. 7: Cr according to the invention produced from the blended formulation (5)
4 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular (a) or horizontal (b) to the surface of the B coating.

FIG. 8 is a photomicrograph taken at 200 × magnification showing the microstructure of a cross section perpendicular to the surface of three prior art conventional coatings.

[Explanation of symbols]

 C: Coating S: Substrate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Robert Clark Tucker Jr., Inventor Ridgway Drive 61, Brownsburg, Indiana, USA (72) Inventor Joseph Patrick Nemes Hatteras Lane, Indianapolis, Indiana, USA 7201, Apartment 3B F-term (reference) 4K031 AA08 AB08 AB09 CB01 CB22 CB44 DA04 FA01

Claims (3)

[Claims] 1. An abrasion and corrosion resistant coating on a substrate comprising a plurality of thin irregularly shaped elongated plates overlapping and bonded to each other and to the substrate, wherein the elongated plates are The article comprises dispersed ultrafine hard chromium boride particles having an average particle size of less than about 1 micron in a metal matrix, said particles comprising less than about 30% by volume of the coating and the balance being the metal matrix; The coating. 2. depositing a mechanically blended powder mixture of at least two components comprising a first component containing chromium and a second component containing a boron-containing alloy on a substrate; The as-deposited coating is heated to a high enough temperature to cause a diffusion reaction between the deposited elements, resulting in the formation of ultrafine chromium boride particles dispersed in the metal matrix. Including
A method for producing an abrasion and corrosion resistant coating on a substrate. 3. An atomic ratio of chromium to boron comprising a mechanically blended powder mixture of at least two components including a first component containing chromium and a second component containing a boron-containing alloy. Wherein the is in the range of about 0.8 to 1.5.