RU2521780C1 - Application method of heat-protective wear-resistant coating onto parts from cast iron and steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: abrasive-waterjet machining is performed by silicon carbide with size of particles of 1.5 mm; plasma sputtering of an intermediate layer consisting of Co-Cr-Al-Y and further sputtering of cermet composition of powder mixture containing components is performed at the following component ratio, wt %: nichrome 10-20, zirconium dioxide stabilised by yttrium oxide, 30-20, nickel-aluminium 30-40, nickel-titanium 20-10, chrome carbide 5, and tungsten carbide 5.

EFFECT: improving resistance of a coating to wear at friction, hardness of the coating, heat resistance and adhesion of the coating to the base alloy.

6 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of chemical-thermal treatment of metals and alloys and can be used in mechanical engineering to increase the wear resistance of parts of the cylinder-piston group of automotive vehicles.

Known methods for applying condensation and diffusion coatings, each of which has its own varieties (see Kolomytsev PT High-temperature protective coatings for nickel alloys. M: Metallurgy, 1991, 236 S.).

Thermal protective coatings are characterized by lower thermal conductivity, but crack and peel off during heat changes under the influence of thermomechanical loads.

To ensure the operability of parts of the piston and cylinder group, electrolytic chromium coatings and heat-shielding coatings obtained by electron beam spraying or plasma deposition in air or in vacuum are effectively used (see. Increasing the wear resistance of parts of internal combustion engines. M. Khrushchev. - M.: Mechanical Engineering , 1972).

Electrolytic chrome coatings generally satisfy the specified requirements of existing plants. The hardness of these coatings is at the level of 900-1000 HV, the adhesive strength is up to 700 kg / cm ² , a relatively low coefficient of friction, satisfactory break-in and oil absorption, high thermal conductivity.

However, due to the impossibility of applying electrolytic chromium precipitates of more than 200 microns, their resource is sometimes lower than the engine resource before the 1st repair. And increasing the hardness of the coating reduces the working life of the ring in the liner and requires high precision manufacturing rings. Due to the insufficient coating thickness, subsequent processing under the geometry of the liner is quite difficult and time-consuming.

Electrolytic chromium does not work satisfactorily at friction and wear at high temperatures due to a sharp decrease in hardness (at 300 ° C the hardness is 800 kg / mm ² , and at 700 ° C - 200 kg / mm ² ). Since there is no polymorphic transformation in chromium deposits, the hardness of coatings does not increase by heat treatment. If the coating has insufficient porosity, then at temperatures above 300 ° C, hard chromium is inoperative under conditions of unsatisfactory lubrication - there are burns, seizures. Local temperature increase leads to intense softening, setting, chipping of coatings. During production, the porous layer is significantly softened due to fatigue wear at elevated temperatures. Since the temperature coefficient of linear expansion (TEC) of chromium coatings is lower than the material of the ring (cast iron, steel), tensile stresses can occur in the coating, which contribute to thermocyclic and corrosion cracking of coatings. In diesel engines, as a result of the presence of sulfur in the fuel, the formation of sulfuric acid is possible, which can lead to the formation of galvanic pairs in contact with the cylinder and sulfide corrosion.

A known method of applying a chrome coating to steel parts (patent for the invention 2269608, publ. 02/10/2006, bull. No. 4). In this method, the wear resistance of the coating is not increased, but the adhesion of the coating and productivity are increased.

A known method of applying a high temperature composite material for a sealing coating (patent for the invention of the Russian Federation No. 2,303,649, publ. 07/27/2007, bull. No. 21) containing zirconia stabilized with yttrium oxide with the addition of boron nitride, and nichrome fiber. This coating increases heat resistance at high temperatures (1000 ° C), which is not necessary when working parts of automotive equipment.

Known heat-resistant cermet coating (patent for the invention of the Russian Federation No. 2309194, publ. 06/20/2006, bull. No. 30) with alternating heat-resistant and heat-resistant layers of cermets to resist thermal shock, but it is very expensive and not effective when working on friction and wear.

A known method of applying a combined heat-resistant coating to turbine blades, including chromoalithization in a powder mixture, followed by thermal vacuum treatment, followed by electron-beam spraying of a ZrO ₂ - 8Y ₂ O ₃ ceramic layer on the input edges of the blades, followed by annealing for the final coating formation (see patent for the invention of the Russian Federation No. 2272089, class C23C 28/00, publ. March 20, 2006, bull. No. 8), the composition of which corresponds to the working conditions of the outer surface of the turbine engine blades and is unacceptable for cylinder piston parts groups of automotive equipment.

A known method of producing erosion-resistant heat-resistant coatings based on the composition of ZrO ₂ and NiCr, including plasma spraying of a nichrome sublayer and subsequent spraying of a cermet composition from a mechanical powder mixture containing 50-80 wt.% Zirconia and 50-20 wt.% Nichrome (patent for the invention RF №2283363, publ. September 10, 2006, bull. No. 25). The invention provides increased erosion resistance, heat resistance and adhesive strength of the coating due to the composition and the creation of a phase transition zone. The coating obtained in this way works unsatisfactorily for friction and wear, has insufficient hardness, poor run-in.

A known method of applying a heat-resistant wear-resistant coating on parts made of cast iron and steel (patent for the invention of the Russian Federation No. 2455385, publ. July 10, 2012, bull. No. 19), including abrasive blasting with silicon carbide with a particle size of 1.5 mm, plasma spraying a cermet composition from a mechanical powder mixture containing zirconia with a stabilizing additive, nichrome, titanium carbide and boron carbide at a certain ratio of components, used to restore the wear resistance of milling mill rollers. In this method, the coating has high hardness, wear resistance, and the proposed coating composition does not allow technologically applying plastic coatings of large thickness.

The closest technical solution is a method of applying a heat-resistant wear-resistant coating to parts made of cast iron and steel, including plasma spraying of a sublayer of the composition: Co-Cr-Al-Y and subsequent spraying of the cermet composition from a mechanical powder mixture of 20-50 wt.% Nichrome, 50- 20 wt.% Zirconia with a stabilizing additive, 20 wt.% Chromium carbide, 10 wt.% Tungsten carbide. At the same time, yttrium oxide is used as a stabilizing additive in zirconia powder, the content of which is 4-7 wt.% (RF patent No. 2425906, publ. 08/10/2011, bull. No. 22), adopted as a prototype. The invention provides an increase in the resistance of the coating to wear during friction, the hardness of the coating, heat resistance, adhesion of the coating to the base alloy.

The coating obtained in this way satisfactorily works for friction and wear, has insufficient hardness and ductility. The introduction of chromium carbide and tungsten carbide into a mechanical powder mixture increases the hardness and wear resistance of the coating insignificantly, while the increase in their concentration leads to chipping of the coating, both during coating and its processing, uneven coating thickness, particle crumbling during operation, and the impossibility of coating with a thickness of more than 200 microns, which is a necessary condition for increasing the wear resistance of parts of the cylinder-piston group of automotive vehicles.

To increase the resistance of the coating to wear during friction, it is necessary to increase the hardness, wear resistance, ductility of the coating, to ensure uniformity of coating thickness while increasing it.

An object of the invention is to increase the wear resistance and durability of parts of the cylinder-piston group of automotive vehicles through the use of heat-protective wear-resistant coatings (TZP).

The essence of the invention lies in the fact that in the method of applying a heat-resistant wear-resistant coating to parts made of cast iron and steel, comprising plasma spraying a Co-Cr-Al-Y sublayer and then spraying a cermet composition from a mechanical powder mixture containing zirconia stabilized with yttrium oxide, nichrome, chromium carbide, tungsten carbide, before plasma spraying, abrasive blasting is carried out with silicon carbide with a particle size of 1.5 mm, and the spraying is carried out from a mechanical powder mixture, additional containing nickel aluminum and nickel titanium, in the following ratio, wt.%: nichrome 10-20, zirconia 30-20, nickel aluminum 30-40, nickel titanium 20-10, chromium carbide 5, tungsten carbide 5.

The technical result is achieved due to the new action and the new composition of the cermet composition during coating, namely, abrasive blasting of parts with silicon carbide with a particle size of 1.5 mm before plasma spraying, which increases the adhesion strength of the coating and the base alloy, introducing nickel aluminum into the cermet mixture to increase ductility and nickel titanium to increase the strength, hardness and wear resistance of the coating. The percentage of nichrome and zirconium dioxide is reduced, but sufficient to ensure thermal stability of the coating within the operating temperature range of 20-400 ° C, to exclude polymorphic transformations during temperature casting, the necessary porosity to ensure the wettability of parts with oil in the tribological conjugation zone. The introduction of nickel-aluminum into the composition of the mechanical mixture increased the ductility of the coating, ensures uniformity of coating in thickness with the possibility of spraying coatings up to 500 microns. The content of chromium carbide and tungsten carbide is reduced to 5 wt.%, Since nickel titanium is more effective for increasing the strength, hardness and wear resistance of the coating. The percentage in weight% of nickel aluminum 30-40, nickel titanium 20-10, chromium carbide 5, tungsten carbide 5 is optimal for the strength and plastic properties of the coating, which allows the coating to have both high wear resistance and workability of the product after coating (table one).

Table 1 Characteristics of the state, microhardness, coefficient of plasticity of coatings Material (coating) condition Microhardness, MPa Ductility coefficient Ductile iron source 3.0-3.5 0.880-0.890 after friction 6.0-8.1 0.820-0.870 Chrome plating source 6.0-8.0 0.700-0.705 after friction 9.0-11.3 0.670-0.680 20 wt.% NiCr - 50 wt.% ZrO ₂ -Y ₂ O ₃ - 20% wt.% CrC - 10 wt.% WC (prototype) source 2.3-2.6 0.92-1.09 after friction 4.6-4.9 0.87-0.88 10 wt.% NiCr - 30 wt.% ZrO ₂ - Y ₂ O ₃ - 30 wt.% NiAl - 20 wt.% NiTi - 5 wt.% CrC - 5 wt.% WC (inventive method) source 4.78-6.0 0.93-0.97 after friction 6.2-8.4 0.81-0.82 10 wt.% NiCr - 25 wt.% ZrO ₂ - Y ₂ O ₃ - 50 wt.% NiAl - 5 wt.% NiTi - 5 wt.% CrC - 5 wt.% WC source 2.8-2.9 0.90-0.98 after friction 4.9-5.7 0.76-0.79 10 wt.% NiCr - 30 wt.% ZrO ₂ - Y ₂ O ₃ - 20 wt.% NiAl - 30 wt.% NiTi - 5 wt.% CrC - 5 wt.% WC source 5.7-7.8 0.63-0.69 after friction 8.0-10.4 0.62-0.67 20 wt.% NiCr - 30 wt.% ZrO ₂ - Y ₂ O ₃ - 30 wt.% NiAl - 20 wt.% NiTi source 3.2-3.4 0.884-0.92 after friction 5.6-6.2 0.84-0.86

An increase in these concentrations leads to an increase in hardness of the coating, a decrease in ductility, and chips of the coating during application and processing.

The reduction in the percentage of nickel titanium, chromium carbide and tungsten carbide, the exclusion of chromium carbide and tungsten carbide from the mixture leads to a decrease in the microhardness of the coating and an increase in the wear rate.

Figure 1 shows the piston rings of automotive vehicles with heat-shielding coating.

Figure 2 shows the microstructure of a heat-protective wear-resistant coating with a Co-Cr-Al-Y sublayer.

Figure 3 shows the microstructure of a heat-protective wear-resistant coating.

Figure 4 shows the dependence of the adhesive strength of the coating with the base alloy on the composition of the sublayer.

Figure 5 shows the dependence of the wear rate on the composition of the coating.

Figure 6 shows the dependence of the adhesion of the oil to the coating on the composition of the cermet mixture.

An example of a specific implementation (optimal)

The proposed method of applying a heat-resistant wear-resistant coating is implemented as follows. The coating was applied to compression and oil scraper piston rings of automotive vehicles. The material of the piston rings is cast iron of the MF grade (gray) or HF (high strength) with a hardness of 96-112НВ for gray or 100-112НВ for high-strength cast iron with a microstructure in accordance with the scales: G1, G2 ... for graphite, П1, П2 ... for perlite ( GOST 3443-77). Oil scraper ring steel lamellar. Ring disks are made of high-carbon steel (U8A steel) tape with a size of 0.7-4.0 mm. For spraying, an UPN-40 air-plasma spraying unit was used as part of the APR-404 power source, PN-B1 plasma torch, and D-40 (M) feed batcher. Spraying was carried out in a chamber equipped with a rotator with a central displacement system and a device for moving the plasma torch. Before spraying the coatings, abrasive blasting with silicon carbide with a particle size of 1.5 mm was carried out. The Co-Cr-Al-Y sublayer was deposited with an argon plasmatron 30–40 μm thick. Used powder of zirconium dioxide granulation of 10-40 microns and powders of nichrome, nickel aluminum, nickel titanium, chromium carbide and tungsten with a particle size of 40-100 microns. Coating was sprayed according to the prototype and the proposed method with an PN-B1 air plasma torch at I = 190-200 A, U = 200 V. The coating thickness was 150-200 μm. Data on the thicknesses of the coating layers was determined using a Neo-phot-21 optical microscope.

Phase analysis of coatings: porosity - 10%, ceramic-metal ratio 34-56%, depending on the composition of the mixture.

The adhesion strength of the wear-resistant coating with the base metal was evaluated according to GOST 621-87. Wear tests were carried out on an Armsler type machine (MT-2 friction machine) at a load excluding scoring (p = 3.42 MPa; V = 2.5 m / s; t = 10 hours). The linear wear of the samples was determined on the optimometer by the difference in its readings before and after the tests. The wear rate was determined as the ratio of linear wear to the distance traveled by the samples during the test.

To determine the adhesion of the lubricant, they were based on measurements of the spreading pressure of a drop of oil over a sample. The oil-holding ability of the coatings was characterized by the work of adhesion of the lubricant obtained by summing the spreading pressure and doubled surface energy of the oil. For motor oil, its surface energy (tension) is assumed to be 30.3 · 10 ^-3 N / m.

The chemical composition was determined by the X-ray microspectral method on a Stereoscan S-600 electron microscope with a Link microanalyzer.

Conducted comparative tests of samples with coatings showed the advantage of the proposed coating on the adhesive strength of the coating with the base alloy (figure 4), its wear resistance (figure 5). Reducing the adhesion of the oil developed coating in comparison with the prototype does not occur, since 10% porosity of the coating provides sufficient oil absorption (Fig.6).

A set of coated piston rings with the geometrical dimensions of the parts in accordance with GOST, TU, after their processing at the STAPRI piston ring factory in Stavropol, were installed on a D-240 engine for bench tests.

The average compression in the cylinders with rings having the proposed ceramic-metal coating at the start of the run-in was 8.97 kgf / cm ² , and in the control cylinders with serial rings - 8.83 kgf / cm ² , in the cylinders with rings having a ceramic-metal coating according to the prototype, - 8.87 kgf / cm ² . The average drop in engine torque when you turn off the cylinder with rings having the proposed cermet coating is 47.5 nm, when you turn off the cylinder with serial rings - 90 nm, when you turn off the cylinder with rings having a ceramic coating according to the prototype, it is 56 n .m., i.e. in the first case, the moment decreases by 13.5%, in the second - by 25.7%, and in the third - by 16%.

The friction force of the piston ring was measured by a dynamometer when pulling the ring through the engine sleeve. In experiments with dry (fat-free) rings and a sleeve, the friction force was: for a serial ring with a galvanic coating - 12-17 N; for a ring with the proposed ceramic-metal coating - 7-8 N; for a ring with a ceramic-metal coating according to the prototype, 8–9 N. In experiments with rings lubricated with engine oil and a sleeve, the friction force was: for a serial ring with a galvanic coating, 10–12 N; for rings with cermet coatings - 5-6 N.

Plasma coatings reduce the frictional force between the ring and the sleeve both in a defatted condition due to a decrease in the contact area during friction, and when lubricating parts, having increased oil absorption values.

The use of the method is most effective for parts of a cylinder-piston group of engines of automotive vehicles in connection with their decisive influence on the resource.

Claims (1)

The method of applying a heat-resistant wear-resistant coating to parts made of cast iron or steel, including plasma spraying a Co-Cr-Al-Y sublayer and subsequent spraying from a powder mixture containing zirconia stabilized with yttrium oxide, nichrome, chromium carbide and tungsten carbide, characterized in that before plasma spraying, abrasive blasting is carried out with silicon carbide with a particle size of 1.5 mm, and the cermet composition is sprayed from a powder mixture additionally containing nickel aluminum and nickel tan, in the following ratio of components, wt.%: nichrome 10-20, zirconia stabilized with yttrium oxide, 30-20, nickel aluminum 30-40, nickel titanium 20-10, chromium carbide 5, tungsten carbide 5.

Images