RU2542199C1 - Method for preparing composite coatings of powder materials - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: processed surface is prepared by cleaning, washing and abrasive flow machining. That is followed by laser clad deposit of a powder material in an inert gas medium. The powder material is presented by titanium and silicon carbide particles 20-100 mcm in size in mass ratio 6:4 or 6:5. The deposit process is performed at laser power 4÷5 kWt, laser beam travel speed 500÷700 mm/min and power consumption 9.6÷11.9 g/min.

EFFECT: invention enables the defect-free wear-resistance coating with high adhesion to the substrate and minimum effect thereon.

2 tbl, 1 dwg

Description

The invention relates to a technology for laser surfacing of coatings, mainly on a metal substrate, and can be used in machine building in the manufacture and repair of parts of industrial equipment and tools.

The prior art method of laser surfacing on a metal base. In the process of its implementation, the multicomponent filler material is melted (for example, carbon + chromium + manganese, with a particle size of the powder 1-100 microns) and, partially, the base. Surfacing is carried out by short-term targeted exposure to a laser beam at a laser power of 1-20 kW, a scanning speed of 127-12700 mm / min on the deposited surface, followed by cooling (US 4015100 A 03/29/1977, B23K 26/34).

However, when powder is deposited by this method, it is difficult to obtain a defect-free coating. On the surface of the coating made by the described method, cracks are observed associated with the formation of borides and chromium carbides in the transition zone that embrittle it.

As a solution that is closest in technical essence and the problem to be solved, a method for producing functionally gradient wear-resistant coatings from powder materials was selected, including cleaning, washing and blast-abrasive treatment of the weld surface of the part and blowing the prepared surface with compressed air, preparing powder material, supplying powder material from at least one dispenser and transporting it to the surfacing zone using a gas stream from an inert argon gas to the surface of the part and bench powder pulsed laser beam in an argon atmosphere. Additionally, cleaning and washing of the surfaces of the part adjacent to the weld zone are carried out. In the process of jet-abrasive surface treatment give roughness. The supply of powder materials is carried out from two dispensers. Surfacing is carried out in several layers, while reinforcing non-metallic dispersed particles of agglomerated tungsten carbide with a fraction of 80.0-150.0 μm are introduced from one of the dispensers into the flow of the transporting gas, and metal particles of cobalt B3K with a fraction of 53-106 μm are introduced from another dispenser use a laser beam with a power of 2 kW and move it during the deposition process at a speed of 2 m / min, the first layer is deposited with the supply of reinforcing non-metallic dispersed particles of agglomerated tungsten carbide and metal particles of cobalt in the ratio of 1: 4, after applying the first layer, the ratio of the supply of powders from the dispensers is changed to 1: 5 and the next layer is applied (RU 2011141951 A 04/27/2013, C23C 4/12, B23K 26/34).

The disadvantage of the described technical solution is the uneven distribution of hardness on the surface of the coating, as a result of which defects in the coating appear, namely cracks. These coating defects lead to poor adhesion of the resulting coating to the substrate.

The technical result, to which the claimed invention is directed, is to provide, during the welding process, the possibility of forming a reinforcing base of the coating from particles of titanium carbide (TiC) with a high hardness in the form of small inclusions uniformly distributed over the coating, which ultimately allows defect-free wear-resistant coating with high adhesion to the substrate with minimal impact on it.

The specified technical result is achieved through the implementation of a method for producing composite coatings from powder materials, including the preparation of the treated surface by cleaning, washing and blast-abrasive treatment, followed by laser surfacing of the powder material in an inert gas environment. Moreover, according to the claimed invention, as a powder material, a mixture of particles of titanium and silicon carbide with a size of -20-100 microns in a mass ratio of 6: 4 or 6: 5 is used, and the surfacing process is carried out at a laser power of 4 ÷ 5 kW, speeds scanning a laser beam of 500 ÷ 700 mm / min and a powder flow rate of 9.6 ÷ 11.9 g / min.

The claimed invention is illustrated by graphical images, in which Fig. 1 (a-e) shows the microstructure of the deposited layers depending on the deposition modes with different ratios of components in a mixture of titanium / silicon carbide (Ti / SiC).

In the process of implementing the inventive method for producing composite coatings of powder materials, the surface is initially prepared. To do this, the mentioned surface is cleaned, washed, and jet-abrasive treatment is performed.

Next, the powder is fed through the nozzle directly into the molten bath created on the working surface of the substrate. Coaxial surfacing head is mainly used, this allows surfacing in any direction, with better protection from the surrounding atmosphere and relatively small heat-affected zone, with the possibility of forming protective coatings exactly in the required area, for example, for wear conditions or for the restoration of locally damaged / worn surfaces .

Then carry out laser surfacing of the powder material in an inert gas, such as argon. In order to more reliably protect the powder from oxidation and, consequently, improve the quality of the deposited layer, a structure consisting, for example, of fiberglass, preventing the access of oxygen to the surfacing region, can be used.

Particles of titanium (Ti) and silicon carbide (SiC) with a size of 20-100 microns in a mass ratio of 6: 4 or 6: 5 are used as a powder material. In the process of laser surfacing in the deposited layers, reactions occur and new phases form. In this case, the formation of reinforcing particles of titanium carbide (TiC) with a high hardness occurs as a result of its synthesis during laser remelting of Ti and SiC powders directly during processing. The synthesis of titanium carbide occurs according to the scheme Ti + SiC → TiC + Si.

A necessary condition for obtaining TiC in the process of surfacing is also the determination of specific modes that ensure the melting of Ti and SiC, determining the type of phases formed, morphology, and the nature of the distribution in the matrix. The surfacing process is carried out at a laser power of 4 ÷ 5 kW, a scanning speed of the laser beam of 500 ÷ 700 mm / min and a powder flow rate of 9.6 ÷ 11.9 g / min. Under these conditions, as a result of the reaction between Ti and SiC in the deposited layer, TiC uniformly distributed over the coating is formed.

In the claimed invention, a powder particle size of 20-100 μm is selected, based on the following: with a decrease in the size of the powder (for example, ultra-fine powder) less than 20 μm, its mobility decreases, in addition, transportation of the powder becomes problematic; the use of a powder with a particle size of more than 100 μm does not allow sufficient focus of the flow and leads to loss of material.

Due to the fact that spherical particles, as a rule, have better technological properties, particles of titanium powder in the form of spheres can be used in the process of manufacturing the mixture.

Laser surfacing can be carried out on an industrial Trumpf DMD 505 installation. The following powders can be used in the process: titanium TLS GD2, silicon carbide SiC - 135.

As a substrate, in particular, low carbon steel with the following composition in volume percent can be used: 0.17-0.22 C; 0.40-0.60 Mn; Si <0.5; Ni <0.03; Cr <0.03; P <0.04; Cu <0.03; Fe is the rest.

The ratios of titanium and silicon carbide in a powder mixture given in the claims in conjunction with other essential features set forth in the claims are necessary and sufficient to achieve the indicated technical result, which is confirmed by the examples presented in the table below.

Table 1 No. Ti, parts by weight SiC, parts by weight Coating properties Example 1 four 7 Upon completion of laser cladding, unmelted SiC particles remain on the coating surface, which leads to the formation of cracks and pores. Example 2 6 four In the deposited layers, reinforcing particles of finely dispersed uniformly distributed TiC are formed. Received high-quality coating. Example 3 6 5 During laser surfacing, TiC is released in the form of dendrites uniformly distributed over the coating volume. Received high-quality coating. Example 4 7 3 Insufficiently hard coating.

During the experiments, the parameters of laser cladding, which are presented in table 2, were adopted.

table 2 V = 500 mm / min V = 700 mm / min V = 1000 mm / min P = 3 kW 9.6 g / min 9.6 g / min 9.6 g / min 11.9 g / min 11.9 g / min 11.9 g / min 21.0 g / min 21.0 g / min 21.0 g / min P = 4 kW 9.6 g / min 9.6 g / min 9.6 g / min 11.9 g / min 11.9 g / min 11.9 g / min 21.0 g / min 21.0 g / min 21.0 g / min P = 5 kW 9.6 g / min 9.6 g / min 9.6 g / min 11.9 g / min 11.9 g / min 11.9 g / min 21.0 g / min 21.0 g / min 21.0 g / min

As a result of the experiments, it was shown that with a large value of the mass flow rate of the powder (21.0 g / min), obtaining high-quality coatings is difficult even at the maximum value of the laser radiation power, since the power is insufficient to melt the entire supplied powder. At low mass flow rates (less than 9.6 g / min) there is a strong mixing of the coating material with the substrate material, the thickness of the resulting coating is minimal. A decrease in the deposition rate leads to an improvement in the quality of the coating (the number of pores and cracks in the deposited layer is reduced). The value of the scanning speed must be chosen so that, on the one hand, reduce the number of pores and cracks, on the other hand, to limit the amount of substrate material entering the coating. The highest quality coatings are obtained with a mass powder flow rate of 9.6-11.9 g / min and high radiation power values (4-5 kW), while the thickness of the deposited layer decreases with increasing value of the surfacing speed. In this case, the best adhesion of the coating to the substrate is achieved due to the absence of defects on its surface and partial mixing of the coating materials and the substrate.

With a decrease in the deposition rate (less than 500 mm / min, with other constant parameters), the microhardness value gradually decreases. In general, the average microhardness in the coating areas obtained by the claimed method with a large number of TiC inclusions is 1300-1500 HV and 1000-1300 HV for the ratios of Ti and SiC components in the powder mixture 6: 5 and 6: 4, respectively, and in the regions with a small number of TiC inclusions - 700-850 HV.

Figure 1 shows the microstructure of the deposited layers in the following ratio of surfacing modes and various ratios of components in the Ti / SiC mixture: (a) 6: 5 vol.%, P = 5 kW, V = 700 mm / min; (b) 6: 5 vol.%, P = 4 kW, V = 700 mm / min; (c) 6: 5 vol.%, P = 4 kW, V = 500 mm / min; (g) - 6: 4 vol.%, P = 5 kW, V = 700 mm / min; (d) 6: 4 vol.%, P = 4 kW, V = 700 mm / min; (e) 6: 4 vol.%, P = 4 kW, V = 500 mm / min.

From figure 1 it is seen that in the resulting coatings there was a complete remelting of the starting components. There is an increase in the dispersion of the structure with an increase in the speed of the beam. A decrease in speed leads to the formation of branched dendritic inclusions that are fairly evenly distributed in the coating.

Thus, we can conclude that as a result of the implementation of the claimed method using Ti and SiC powders with a certain particle size in the declared range of processing conditions, TiC is released in the form of small inclusions uniformly distributed over the coating, resulting in a defect-free, wear-resistant coating with high adhesion to the substrate with minimal impact on it.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the formula are essential and interconnected with the formation of a stable population that is not known at the priority date from the prior art, the necessary features sufficient to obtain the required synergistic (over-total) technical result.

The properties regulated in the claimed compound by individual features are well known in the art and require no further explanation.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- the object embodying the claimed technical solution, in its implementation is intended for laser surfacing;

- for the claimed object in the form described in the claims, the possibility of its implementation using the above-described in the application materials known from the prior art on the priority date of the means and methods is confirmed;

- the object embodying the claimed technical solution, when implemented, is able to ensure the achievement of the technical result perceived by the applicant.

Therefore, the claimed subject matter meets the patentability conditions of “novelty”, “inventive step” and “industrial applicability” under applicable law.

Claims (1)

A method of producing composite coatings from powder materials, including preparing the surface to be treated by cleaning, washing and blast-abrasive treatment, followed by laser surfacing of the powder material in an inert gas medium, characterized in that a mixture of titanium and silicon carbide particles is used as a powder material size - 20-100 microns in a mass ratio of 6: 4 or 6: 5, and the surfacing process is carried out at a laser power of 4 ÷ 5 kW, a scanning speed of the laser beam of 500 ÷ 700 mm / min and pore consumption margin 9.6 ÷ 11.9 g / min.