CS199185B1 - Forming smooth surfaces from metal carbides and nitriles - Google Patents

Description

The invention relates to a process for forming smooth coatings of metal carbides and nitrides, in particular Ti, Zr, Hf, V, Nb, Ta, Si and Cr, Mo, W, respectively, intended to form guide surfaces for guiding moving parts therein.

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The frictional and guiding surfaces of the components should have a surface designed to minimize abrasion. To a small extent, it is also often desired that the counterpart is not worn by abrasion. In technical practice, these requirements are routinely solved by appropriate selection of friction pairs of unequal materials. In more complex cases, these methods are not sufficient and the solution is sought in the use of soft liners filled with harder particles or in the use of hard coatings with low surface roughness or with an amorphous structure. For this purpose, hard surface layers are relatively laboriously treated. In the case of thin surface layers, mechanical treatment is practically not feasible, since the continuity of such a layer is damaged and its wear resistance is greatly reduced. However, there is also a need in the technical practice for a high specific load on traction surfaces, that is to say where both materials have a high hardness and because of dimensional dimensions, it is not possible to increase or otherwise modify the contact surfaces.

The nitride and / or carbide coatings of Ti, Zr, Hf, V, Nb, Ta, Si, or Cr, Mo, W used to form the guide surfaces have so far been formed on steels and iron castings of these metal halides in hydrogen or inert atmosphere with an admixture capable of reacting, such as

199 185 \. .-- r ř; n 2 of nitrogen, methane, at elevated temperature. This results in the diffusion of the metal and the reaction-capable constituents into the steel and the formation of reaction products, i.e. nitrides or carbides. The reaction product is deposited under commonly known technological conditions, such as a uniform alloy layer, relatively uniformly covering the treated surface of steel or cast iron parts, the surface roughness of the coating depends on both the initial roughness of the steel or cast iron surface and the thickness of the coating. As the thickness of the cover layer is increased, the surface area of the cover layer increases. The increase in daytime adversely affects the mechanical properties of the coating, making it more brittle, brittle and less abrasion resistant. Due to its unfavorable properties, in particular the formation of an abrasive canvas, it increases the abrasion of moving counter-parts. In practice, the undesirable effects of thicker layers are limited by the fact that the cover layers are formed either with a thickness of about 10 to 20 µm or on a thin layer of decarburized material.

One known solution by which the cover layers are obtained on a thin layer of decarburized backing material to form the guide plates of the parts is that the cover layers consist of the outer part of the hard layer corresponding to up to 30 times the surface roughness of the guide. areas. The hard layer is based on the soft interlayer resulting from the decarburization of the material. The thickness of the intermediate layer is up to 50 times the surface roughness of the guide surface, and the hardness of the hard layer exceeds that of the material guided by it. !

In this solution, the technological processing of the cover layers is formed in such a way that the " component "

to which they are to be formed is placed in a reactive atmosphere at barometric pressure.

having a temperature of about 1150 ° C with an Hg content in the range of 50% to 99.5% by weight, 49% to 0.45% by weight of the Ng content, and from 0.0001% to 0.1% by weight of the halogen, Ti, Zr content,

Hf, V, Nb, Ta, Si, or Cr, Mo, W, respectively. Facilitation of the hard layer is then performed under vacuum and when the component is placed at an ionizing voltage above 250 V or the corresponding coronary discharge. The component is connected to the cathode of the device.

In practice, the use of these processes is limited by the range of applicable specific pressures and the frictional properties of the treated surfaces. Technical solutions which in certain cases would lead to a decrease in the specific wear values, increased hardness of the treated sheets.

The above-mentioned disadvantages of the present solutions and technological processes and further improvements are achieved by the method of forming smooth coatings of carbides and metal nitrides according to the invention, which is based on the fact that soothed surface of carbides and metal nitrides is further treated with a carbonitriding environment. % by weight of potassium cyanate and 50% by weight of sodium cyanide at a temperature of 750 to 950 ° C or a carbonitriding atmosphere, for example of 40% by volume of nitrogen, 10% by volume of methane f

and the residue cleaved with ammonia at a temperature of 550 to 750 ° C.

The coatings produced according to the invention are very smooth to glossy, irrespective of the layer thickness, are formed on a heat-treatable steel or cast iron substrate, are amorphous, have a mosaic structure and therefore have a high abrasion resistance. They also have low compressive stress. All of these properties are achieved by forming a lattice of metal nitrides, carbides and carbonitrides, so that the nitride and metal carbide coating on the decarburized backing material layer is re-treated with a carbonitriding salt, bath or carbonitriding atmosphere. By prolonging the action of the nitriding process, the substrate is strengthened, and the corrosion resistance of the treated surface is further increased. It is also advantageous that the process can be used to process the vast majority of steel and cast iron.

In the process, the nitrides of Ti, Zr, Hf, V, Nb, Ta, Si and Cr, Mo, W are initially coated as well as in the above-described Zhám process. The increase in surface roughness resulting from the formation of a hard layer is smoothed by mechanical pressing, for example by roller or calibrating. Smoothing the hard substances into the soft decarburized layer

- located below the nitride layer. This smoothing is accomplished by moving the calibration mandrel in one direction, thereby creating unidirectional seeds for further crystal growth. For this purpose, in order to significantly improve the technical properties, the surface treated with carbonitriding is treated either in salt melts or carbonitriding atmospheres. The temperatures for carbonitriding are suitable for carrying out the subsequent heat treatment. '

Example:

Treatment of the carbon steel surface containing 0.60% by weight of carbon at 800 to 1100 ° C in an atmosphere composed of 99.5% by weight of hydrogen and 0.5% by weight of nitrogen with 0.1% by weight of TiCl 2. After six hours, a TiN layer of 3 to 25 µm thick is formed on a decarburized 100 µιη thick steel layer. The surface dissipation of the layers thicker than 5 µm should be raised from the original 0.8 HRa according to the thickness being produced, even over 6 HRa. By pushing the unevennesses so formed into the soft carbonaceous steel backing layer, the density is gradually reduced to about 0.5 HRa. The treated surface is treated in a carbonitriding medium either in a salt melt of 30% by weight potassium cyanate and 50% by weight sodium cyanide at 750 to 950 ° C or by a carbonitriding atmosphere such as 40% by volume nitrogen, 10% by volume ether, it forms cleaved ammonia at a temperature of 700 to 950 ° C, and topo for six hours. The layers are smooth, corrosion-resistant and highly abrasion-resistant.

SUBJECT MATTER E, FROM

Claims (1)

SUBJECT MATTER E'Z U, r · '·. A method for forming smooth coatings of metal carbides and nitrides, in particular titanium, zirconium, hafnium, vanadium, niobium, tantalum, silicon or chromium, molybdenum, tungsten, formed on a decarburized steel or cast iron surface and subsequently treated, e.g. further treating the smoothed surface of carbides and metal nitrides with a carbonitriding medium, for example a salt bath of 30% by weight potassium cyanate and 50% by weight sodium cyanide at a temperature of 750 to 950 ° C, or a carbonitriding atmosphere, for example 40 % by volume of nitrogen, 10% by volume of methane and the residue cleaved by ammonia at a temperature of 550 to 750 ° C.