This paper investigates the effect of diffusion alloying from a medium of low melting liquid metal solutions (DALMMS) of 30KhGSN2A steel with Ni-Cu and Ni-Cr elemental compositions on the structure, elemental composition of surface layers and corrosion resistance in hydrogen sulphide containing media. When DALMMS of 30KhGSN2A steel with Ni-Cu is used, coatings consisting of 3 layers are formed on the surface of the steel: a surface layer, a transition layer saturated with copper, a transition layer of a base layer. The coatings have a low microhardness (133 HV), the maximum concentration of nickel is 44 %, of copper - 80 %. The total thickness of the coatings is up to 30 mu m. When DALMMS of 30KhGSN2A steel with Ni-Cr is used, coatings consisting of 2 layers are formed on the steel surface: a surface carbide layer, a transition layer of a base coating. The coatings are characterized by high surface microhardness (2000 HV). The total thickness of the coatings is up to 20 mu m. The maximum concentration of chromium was 75 %, of nickel - 20 %. When tested for hydrogen cracking resistance, samples with both types of coatings showed no corrosion. The average value of total (continuous) corrosion for the Ni-Cu coating was 0.031 mm/year and for the Ni-Cr coating 0.048 mm/year. When tested for stress-sulfide cracking test, the maximum time to fracture for a Ni-Cr coated sample was 313 hours, while the Ni-Cu coated samples withstood the test completely (720 hours) without destruction or coating failure. It was revealed that diffusion Ni-Cu coatings were found to be effective in protecting the base metal from general hydrogen sulphide corrosion at the temperatures up to 150 degrees C, with a protection rate of over 98 % (tested according to the standard NACE MR0175/ISO 15156).

Abstract—The influence of diffusion saturation of steel 20 in the medium of low-melting liquid metal melts of Pb–Bi–Li–Ni–Cu composition on its elemental composition and corrosion resistance is considered in this article. As a result of diffusion saturation, a coating is formed structurally consisting of two zones: surface and transition ones. The surface zone contains 53

This paper describes the technology for manufacturing diffusion titanium coatings on cemented carbides, WC-Co and TiC-WC-Co (VK8 and T15K6 hard alloys respectively). The purpose of the work is to elucidate the mechanism and kinetics of the formation of diffusion coatings on cemented carbides in isothermal mass transfer of titanium in the Pb-Bi-Li eutectic. It has been demonstrated that in isothermal Pb-Bi-Li exposure of cemented carbides with powdered titanium added at 950 to 1100 degrees C temperatures, mass transfer of titanium to the cemented carbide surface occurs. Meanwhile, an 8 to 32 mu m coating is formed, depending on the cemented carbide composition, process temperature, and time. The greatest thickness of the coating has been obtained at 1100 degrees C and exposure to the processing medium for 120 minutes. The coatings are formed from the TiC titanium carbide, with alpha-Ti, the Ti2Co intermetallic compound, and the WC tungsten carbide present, too. For the T15K6 hard alloy, concentration of titanium reaches 93 % in surface layers and remains so at the depth of up to 15 mu m. For the VK8 hard alloy, the surface concentration of titanium was 87.6 %, remaining the same at the depth of up to 20 mu m.

Introduction. The main methods of increasing the efficiency of products made from structural steels are considered. A description of diffusion saturation from liquid metal media solutions (DSLMMS) is given. Also, complex diffusion saturation technology (CDS), including DSLMMS and carburization is shown. The purpose of the work is to reveal the effect of steel composition on the process of formation and elemental composition of diffusion-saturated surface layers (coatings) based on chromium, as well as to establish differences and regularities in the processes of formation of diffusion-saturated coatings after DSLMMS and CDS. The methods of investigation. Cylindrical specimens 20 mm in diameter and 30 mm long were subjected to DSLMMS. The specimens were made of carbon and alloyed steels: St3, 20-Cr13, 40-Cr, 40-Cr13, 12-Cr18-Ni10-Ti. At the same time, some of the specimens were previously subjected to vacuum cementation. An eutectic Pb-Bi with the specified content of Cr was used as a transport medium when executing DSLMMS. Metallographic studies were carried out on microsection prepared according to the standard method. Studies to determine the thickness of coatings and its structure were carried out on the Dura Scan Falcon 500 Microhardness Tester. The elemental composition of the coatings was determined by the method of electron microprobe analysis on a Tescan Lyra 3 scanning electron microscope with the Oxford Ultim MAX PCMA system. Results and discussion. As a result of the research, it was revealed that the formation of saturated coatings occurs with DSLMMS and CDS. At the same time, the thickness of the coatings and its elemental composition depend on the steel grade and the technology used. After DSLMMS concentration of Cr varies from 96.9% to 91.1%. At the same time, the maximum concentration of 96.9% is observed on steel St3. After CDS, on the surfaces of all steel samples, the concentration of Cr decreases in comparison with the coatings obtained by the DSLMMS technology on steels: St3 from 96.9% to 66.8%; 40-Cr from 91.1% to 63.18%; 20-Cr13 from 93.18% to 62.54%; 12-Cr18-Ni10-Ti from 92.92% to 64.77%. The total thickness of diffusion-saturated coatings formed on all the alloys studied ranges from 17 to 17.5 µm.

Introduction. The main ways to increase steel parts properties are considered. The rationale for choosing Ni and Cr as the main components of the coating is given. The technology of diffusion alloying from low-melting liquid metal solutions (DALMMS) is given. The purpose of this work is to identify the features of the coatings formation with simultaneous diffusion saturation of nickel and chromium structural steels using the DALMMS technology. Methodology. Cylindrical specimens with a diameter of 20 mm and a length of 30 mm were subjected to DALMMS. The specimens were manufactured of the following structural steels: carbon steel St3, alloyed carbon steels 40Cr, 40Cr13, and extrafine steel 30CrMnSiNi2. As a technological medium with DALLMS (transport melt), a Pb-Li eutectic melt with the specified content of Ni and Cr was used. Metallographic studies were carried out on microsections prepared according to the standard methodology. Studies to determine the thickness of coatings and its structure were carried out on the Dura Scan Falcon 500 microhardness tester. The elemental composition of the coatings was determined by the method of X-ray microanalysis on a Tescan Lyra 3 scanning electron microscope with the Oxford Ultim MAX PCMA system. Results and discuss. It is revealed that the formation of diffusive Ni-Cr coatings occurs with DALMMS. With DALMMS of structural steels contained carbon in cementite form two-layers coatings are formed: surface carbide layer and transition solid-soluble one. At the same time, the chromium content in the surface layers reaches 80 % with a nickel content of 1.5 %. The maximum Ni concentration is observed in the transition layer and amounts to 21 % at a depth of 5 µm on steel 30CrMnSiNi2 and 13 % at a depth of 4.5 µm for steel 40Cr. Carrying out the DALMMS on steels containing carbon in the form of chromium carbides, or containing carbon in small amounts, leads to the formation of single-layer coatings based on solid solutions. The Ni content in the coating reaches 40 %, the chromium content for steel St3 is 14.5 %; for steel 40Cr13 it was 9 %.

The technology of application of multicomponent diffusion coatings from the medium of low-melting liquid-metal solutions on hard alloys of the WC-6% Co type is described. The thickness of the coating varies depending on temperature and exposure time, and ranges from 5 to 10 microns. The results of elemental and metallographic analyzes are presented. It was found that during the formation of coatings, active diffusion of iron to the surface of hard alloys occurs with the formation of the FeNi intermetallic compound. The functional coating of the TiC-NiCu system on WC-6% Co hard alloys obtained by diffusion saturation in the medium of low-melting liquid metal melts is a solid solution of variable concentration with inclusions of TiC and WC. The phase composition on the surface of the hard alloy after diffusion saturation is: FeNi 44%, Cu 41%, TiC 12.5%, WC 2.3%, Co 0.2%.

The paper shows the mechanism of formation of functional diffusion coatings deposited in the medium of low-melting liquid metal melts. The parameters of the mechanism depend on the nature of the interaction of the elements forming the coating with the elements of the coated steel. The paper describes the characteristic features inherent in the process of forming diffusion coatings on steels. The first feature is that the formation of coatings based on carbide-forming elements is characterized by intense diffusion of carbon from steel to the surface layers of the coating and blocking the diffusion of coating elements deep into the coated material. The second feature of the mechanism of formation of coatings based on carbide-forming elements is that the blocking effect of carbon depends on the amount of carbon in the steel, the thermal stability of the carbides of the coating elements, the temperature and duration of the process. The structure of the formed coating is characterized by the presence of an adsorbed layer, a carbide layer, a transition zone and a decarbonized zone. The paper presents a scheme for the formation of diffusion coatings based on carbide-forming elements.

The technology of application of multicomponent functional diffusion coatings from the medium of low-melting liquid-metal solutions on a carbide cutting tool of the WC-TiC-Co and WC-Co type is described in detail. It was found that the thickness varies with the exposure time and temperature and ranges from 8 to 27 microns on alloys of the WC-Co type; and from 9 to 29 microns on alloys of the WC-TiC-Co type. As a result of X-ray spectral analysis, it was revealed that the elemental composition of the coating depends on the composition of the base on which it is applied. The maximum concentration of elements in the surface layer of the coating is: Ni 1.23%, Cu 4.14%. The Ti content in the coating is in the transition layer and is 23.96%. Diffusion coatings obtained on hard alloys are characterized by a smooth change in the concentration of elements along the thickness.

A current way of increasing cutting efficiency in the turning operation is applying functional coatings based on carbides, nitrides, carbonitrides, etc. on the cutting tool surface. Most technologies for applying functional coatings are supposed to use technically sophisticated, expensive equipment. In addition, the coatings have a sharp change in properties at the coating-coated material boundary. The technology of diffusion saturation from the medium of low-melting liquid metal melts lacks these disadvantages. The aim of the work was to study the effect of the formation of a coating based on titanium carbide on the surface of a cutting tool made of hard TiC-WC-Co and WC-Co alloys on its wear resistance and the quality of the product surface after turning. The research methods included field tests, micro-x-ray spectral analysis, optical microscopy, and microdurametric tests. The paper presents the results of research of turning of materials of various cutting group using a carbide tool with a functional diffusion coating obtained due to saturation in the melt containing Pb, Bi, Li, Ti. The resulting coatings had a thickness of 3-6 microns, and contributed to an increase in tool life up to 7.4 times compared to the tools with PVD coating and tools without coatings as well as a decrease of the roughness parameter Ra of the treated surface up to 2 times.

This paper investigated the overlap of carburization and diffusion saturation from liquid metal medium solutions technologies. The carburization of austhenic steel able to increase of its wear resistance and microhardness to 700HV. But this kind of treatment provided to reduction of corrosion resistance. This effect conditioned by formation of chromium carbides, herewith austenite of steel impoverished of chromium. This paper proposes the new technology lets increase the durability of asthenic steels, using carburization and diffusion saturation in eutectic Pb-Bi-Li medium with adding of nickel and chromium. The most effective technology consisted of previous carburization, diffusion saturation and final carburization. First carburization provided to increase of surface layers microhardness to 2800 MPa, diffusion saturation to 7500 MPa, the final carburization to 19500 MPa. The properties of coating depended of combination of technological impact and technological modes of every stage of technological process: temperature and duration. The temperature influenced to microhardness of coating: when the temperature increased microhardness decreased. The duration of diffusion saturation influenced to thickness of diffusion layer: when the duration increased the thickness increased too

Introduction. One of the most popular ways to increase operational properties of cutting carbide-tipped tool is applying functional coatings on its surface. At the same time, coatings based on titanium carbide TiC are widely used. A sufficiently high scientific and practical interest, from the point of view of the formation of functional coatings, is the technology of diffusion metallization of cutting tools made of hard alloys in Pb-Bi-Li-Ti melts, which can significantly increase its resistance. However, the effect of functional coatings based on titanium carbide TiC on the mechanical properties of hard alloys is described insufficiently. The purpose of the work is to analyze the effect of diffusion saturation of a carbide cutting tool in a Pb-Bi-Li-Ti medium on its mechanical characteristics. The methods of investigation are the following: tests for macro- and microhardness, studies of flexural strength, impact strength and fracture toughness. Results and Discussion. It is revealed that the formed functional diffusion layers affect the mechanical characteristics of coated instruments. In this case, the main influence on the mechanical properties of the coated products is exerted by the temperature of diffusion saturation and its duration. When forming diffusion layers with a thickness of up to 5 mu m for VK alloys, the flexural strength, impact strength and fracture toughness gradually increase, with a further increase in thickness, the above characteristics decrease, for TK alloys the thickness is 4 mu m. It is found that the application of diffusion titanium coatings can increase such mechanical characteristics of carbide tools as hardness (up to 91 HRA), tensile strength in bending (for 9%WC-15%TiC-6%Co - 1380 MPa, for 92%WC-8%Co - 1875 MPa), impact strength (for 79%WC-15%TiC-6%Co-2.99 kJ/m(2), for 92%WC-8%Co - 5.97 kJ/m(2)) and fracture toughness (for 79%WC-15%TiC-6%Co - 7.65 MPa, for 92%WC-8%Co - 11.9 MPa).

The technology of applying diffusion titanium coatings from the medium of low-melting liquid-metal melts to hard alloys of the TiC-WC-Co and WC-Co types is described. It is shown that in the case of diffusion saturation of the surface layers of a hard alloy tool of the TiC-WC-Co and WC-Co types with titanium from the Pb-Bi-Li-Ti melt, preliminary carburization is an obligatory stage in the process of coating formation, and allows avoiding the formation of a decarburized zone under the diffusion layer. The effect of preliminary carburization on the phase composition of the coated hard alloy is shown. As a result of the phase analysis, it was revealed that the surface layer contains such phases as WC, TiC, Co2C, Co-C. In this case, titanium carbide TiC is formed due to the destruction of cobalt carbide upon further diffusion saturation with titanium. In the absence of carburization, the formation of a decarbidized layer was revealed, which differs from the coating and the base in lower microhardness, the drop in microhardness is about 1000 MPa. After carburization, there was a slight increase in the hardness of the coated parts from 89 to 91 HRA. Characteristics such as the microhardness of the carburization zone and its length depend on the temperature and duration of the preliminary carburization, as well as on the elemental composition of the material to be coated. Carburization was carried out in the temperature range from 950°C to 1150°C from 30 to 120 minutes. After saturation with carbon, the thickness of the carburization zone was from 2 to 25 μm, the microhardness from 16700 to 17150 MPa for the WC-Co alloy and from 18750 to 19200 MPa for the TiC-WC-Co alloy. The hardness of the layer under the coating ranged from 27000 to 28500 MPa for the TiC-WC-Co alloy and from 19300 to 23500 MPa for the WC-Co-type alloy.

The technology of the increase of wear resistance of austenitic steel products by combining the technologies of carburization and diffusion alloying in the medium of fusible liquid metal solutions has been described. The preliminary and subsequent carburization led to increase of surface layers microhardness of coated material to 5600 MPa. At the same time, the depth of the doped layer can reach 420 microns.

The application of diffusion nicke-copper coatings on hard alloys leads to an increase in the durability of carbide-tipped cutting tools when machining even hard carbide-containing steels at the high cutting speeds, which improves the productivity of the machining process. The analysis of the influence of deposition of nicke-copper coating by the diffusion metallization from environment of the fusible liquid metal solutions at the resistance of alloy carbide inserts of type WC-Co and TiC-WC-Co, and to the quality of the processing of hard alloy high viscosity has been performed.

The technology of diffusion titanium coating from the liquid metal media to the carbide-tipped tolls 15%Ti-WC-6%Co and WC-8%Co have described. The thickness of the coating varies depending on the temperature and holding time of diffusion saturation, and ranges from 2,6 to 5,6 mu m on alloys of the 15%Ti-WC-6%Co type, from 2 to 5,4 microns on WC-8%Co alloys. It is revealed, that the elemental composition depended of composition of hard alloy. The microhardness of coating on hard alloy 15%Ti-WC-6%Co is 30000 MPa, and for hard alloy WC-8%Co is 24750 MPa. The high microhardness of the coating is provides by its formation on the basis of titanium carbide TiC. It was found that the elemental composition of the coating depends of the composition of the hard alloy to which it is applied. It was found that the surface layers consist of titanium carbide TiC, alpha-Ti like bind, intermatallide Ti2Co for 15%Ti-WC-6%Co alloy. The WC-8%Co alloy also include tungsten carbide WC.

The technology of applying titanium diffusion coatings on cutting tools of medium of fusible liquid-metal solutions has been describe. The results of research of process of heat treatment of carbide inserts of type WC-8% Co and TC after diffusion tianation from medium of fusible liquid-metal solutions has been describe. The results of influence of heat treatment of the cutting tool with diffusion titanium coating to its durability has been describe. It founded that the wear resistance of the tool and the microhardness of the coating influenced by the temperature of heat treatment and its duration, and the composition of the coated material. It is established that thermal treatment of carbide tools, the diffusion of titanium has a coating, allows to increase its durability in 1,5-2 times compared to the coated tool, but without heat treatment, relative to the tool without coating, durability is increased 7 times.

Introduction. A modern approach to improving the operational properties of cutting tools is covering its surface with functional coatings based on carbides, nitrides, oxides of metals such as titanium, chromium, aluminum, silicon, etc. In spite of a number of cutting tool coating technologies, most of it has such drawbacks as the complexity of the equipment, the limited geometry of the coated products, the limited elemental composition of the coatings, and the low operating properties of the coatings formed. The above drawbacks are absent in the technology of diffusion metallization from the medium of low-melting liquid metal solutions. The purpose of the work: to analyze the effect of diffusion titanizing from low-melting liquid metal medium on the wear resistance of carbide-tipped tool and the quality of machined parts. The methods of investigation. Tests for macro-and microhardness, X-ray spectral analysis, X-ray diffraction analysis, in-situ testing on the tools durability are carried out. The quality of the processed parts is determined. Results and Discussion. It is revealed that functional diffusion titanium layers, obtained by diffusion titanizing from low-melting liquid metal solutions, are formed on the TiC-base. At the same time, the coating is characterized by the presence of two layers - surface layer with a microhardness level of about 30 000 MPa and a transitional layer with a gradual decrease in microhardness level and titanium concentration. It is found that the structure of the diffusion and the transition layers depends on the temperature of diffusion saturation, on the duration of diffusion saturation, as well as on the modes of subsequent heat treatment. The developed technology makes it possible to increase tool life as compared to a tool that does not have a coating up to 7.4 times, and also that has a PVD coating up to 1.85 times, depending on the cutting group and the speed of processing. The coating is most effective at high cutting speed - 190 m/min. At the same time, the roughness parameter Ra is reduced to 2 times, depending on the cutting group and processing conditions.

The paper describes the technology of applying titanium diffusion coating to the cutting tool from low-melting liquid metal solutions. The results of thermal treatment of the carbide cutting blades (WC and TiC type) after titanium diffusion coating from low-melting liquid metal solutions are given. The results of thermal treatment influence on the firmness of cutting tool having titanium coating are shown. It is found out that thermal treatment temperature, its duration and material composition influence affect tool durability and coating micro-hardness. It is revealed that thermal treatment of the carbide instrument with titanium diffusion coating lets to increase its persistence by 1.79 times comparing to the tool without coating. But without thermal treatment persistence of the instrument with coating increases by 9 times in comparison to the tool without coating.

A technology for the deposition of diffusion titanium coatings from liquid metal media on hard alloys of TK (WC+TiC+Co) and VK (WC+Co) systems is described. It is shown that the diffusion saturation of hard alloy tools of these types by titanium from the Pb-Bi-Li melt in a temperature range 1000-1100 degrees C and subsequent heat treatment results in a seven-fold increase of the wear resistance of the tools due to the formation of a diffusion coating. The thickness of the coatings varies depending on the temperature and deposition time and ranges from 2.6 to 6 mu m on TK alloys and from 2 to 5.4 mu m on VK alloys. The coatings consist of two layers, the surface one and transition one. The results of elemental and metallographic analyses are presented. The microhardness of a coating on hard alloy T15K6 is about 30000 MPa and on the hard alloy WC-8Co is 25000 MPa. The high microhardness of the coatings is caused by their formation on the basis of titanium carbide TiC, while other elements are driven depthward the material to coat. It has been found that the elemental composition of the coatings depends on the composition of the hard alloy under coating. The concentration of titanium in the surface layer of the tool amounts 87.6 % for VK alloys and 93 % for TK alloys. The transition layer is characterized by approximately equal concentrations of titanium and tungsten (about 20 to 25 %) and a reduced microhardness. The diffusion coatings are characterized by a smooth change of the concentration of elements with depth and good adhesion to the base material.

The analysis of the strengths and weaknesses of the existing technologies aimed at improving the performance properties of carbide-tipped tools is presented. The results of studies into the process of diffusion metallization by titanium of a carbide-tipped tool TK type from the media of fusible liquid-metal solutions is given. The influence of titanium diffusion coatings on the durability of carbide tools is investigated. A method of providing formation on hard alloys for wear-resistant titanium high-quality functional coatings is described. The thickness of the coating varies depending on the temperature and exposure time, and ranges from 4 to 6 μm. The hardness of the coatings obtained depends on the temperature of the coating and modes of pre-carburizing, and varies from 24100 to 30000 MPa. The microstructure of the coatings is investigated. The coating consists of two layers: the coating and the transition zone, the size and hardness of which depends on the conditions of pre-carburization and modes of application of the coating. The dependence of the coatings thickness on the duration of the plates exposure in the melt, the temperature of coating composition from the coated hard alloy is investigated.