Russian Metallurgy (Metally)最新文献

A study was performed of the effect of the operating temperature (~550°C) simulation in a new design of the cylinder head for internal combustion engines (ICE) of cars on the thermal stability of the structure and the hardness of castings of exhaust valve seat inserts made of phosphorus bainitic gray iron (in the cast state and tempered) of specially selected chemical composition for the production of bainite metal base under continuous cooling without austempering. The effects of the single and double tempering on changes in the cast iron structure and hardness are shown. The performance of the bainitic structure for valve seats was found to be unsatisfactory since it fails to maintain the required hardness level.

High-temperature KhN45MVTYuBR alloy is often used in the aerospace industry. This material is hard to process due to its high strength and corrosion resistance. In this work, the effect of various cutting parameters on the tool wear of the tool on machining a high-temperature KhN45MVTYuBR alloy is analyzed. The effects of two various tool path strategies on the cutting tool wear have been studied. To determine the optimal values of the cutting parameters, the change in the wear zone width at the milling tool back surface and the resulting cutting force on machining are analyzed.

A method for strengthening heavily loaded machine parts using volume–surface quenching (VSQ) of carbon steels of reduced (RH) or controlled (CH) hardenability is considered. The properties of these steels, their microstructure, and hardenability are described. Various technological processes for manufacturing steel parts are discussed. The simplification of preliminary heat treatment without decreasing quality by utilizing the heat from previous hot metal forming operations is considered; in some cases, this allows for complete elimination of preliminary heat treatment. The possibility of using preliminary and, in some cases, final heat treatment to entirely prevent flake formation is also discussed.

The article presents the results of static modeling of determining the influence of the geometric parameters of a cylindrical workpiece on the stress–strain state during straightening of a local area with smooth plates. It was found that the straightening quality on a local area of a cylindrical workpiece depends on the magnitude of the initial deflection and the diameter of the cylindrical workpiece at the initial stage of straightening.

Studies were conducted on gold extraction from ore of a deposit in Tajikistan using cyanide and thiourea. Thiourea leaching was found to involve decomposition of the solvent, which increased its consumption and caused passivation of the gold surface by elemental sulfur, leading to a low extraction rate. The decrease in gold extraction with increasing thiourea leaching time was attributed to resorption of the gold complex by sorption-active minerals. Cyanidation achieved 98.1% gold recovery, whereas thiourea leaching gave 78.1%.

We have studied the effect of a deformed surface layer on the quality of articles made of brittle materials, exemplified by beryllium as the most brittle and abrasive material. The smallest depth of the deformed (cold-worked) surface layer in the case of edge cutting machining of beryllium, a brittle material, has been determined as a function of processing conditions and cutting tool geometry. We have proposed processing conditions and cutting tool geometry for processing beryllium workpieces to ensure high quality of the processed surface, without microcracking, with the smallest depth of the deformed (cold-worked) layer, and described a sequence of studies and approaches for improving the quality of articles made of brittle materials, exemplified by beryllium as the most brittle and abrasive material.

A technique for manufacturing a star-shaped elastic-clutch element using the FDM (fused deposition modeling)/FFF (fused filament fabrication) additive manufacturing technology is discussed. The investigation of properties and the choice of engineering plastics, specifically TPU (thermoplastic polyurethane), are described. When an appropriate material is chosen, additive manufacturing is shown to successfully produce parts capable of withstanding mechanical loads and long-term operation, which results in extremely rapid production, a high accuracy, and even lower costs compared to other traditional technologies.

A number of electrolytes to obtain nickel coatings on a graphite substrate of resistive elements that offer good adhesion, strong shine, sufficient wear resistance, and thickness uniformity have been tested. The operating conditions of electrolytes have been determined, the appearance of coatings have been examined, and internal stresses have been estimated. It has been found that if a product to be coated has a cylindrical form, it is necessary to apply coatings with internal compressive stresses σ = 0–70 MPa. The throwing power and current efficiency of test electrolytes have been studied. It has turned out that the coating thickness uniformity can be achieved if the throwing power of the electrolyte falls into the interval 70–90%. The throwing power of sulfuric acid electrolyte is in the range 20–30%. Because of this, it is suggested that the cylindrical shape of the anode copy that of the resistor (cathode). Such a method is known as the artificial technique for increasing the throwing power, which proved to be very efficient in plating from sulfuric acid electrolytes. Based on a laboratory setup, an industrial technology of bright nickel plating on resistive elements of different rating values has been developed.

The effect of a combined chemical heat treatment process with the saturation of small-size drills made of high-speed steels R6M5 and R6M5K5 with tungsten and nitrogen on the structure of the surface layer and the tool life was studied. Spectral analysis showed that the simultaneous saturation of iron-based drill alloys with tungsten and nitrogen in a pulsed mode produces diffusion layers of different thicknesses containing dispersed inclusions identified as tungsten nitrides. The treatment increases the surface layer hardness. The microhardness at the surface can increase up to 15 GPa, depending on the volume fractions of strengthening nitrides. Surface hardening leads to a substantial increase in the drill life when machining holes in various structural materials.

TiC/Ti cermet coatings were produced on VT3-1 titanium alloy by electrical discharge treatment in a mixture of titanium granules with the addition of 2, 6, and 10 vol % titanium carbide powder. The titanium carbide concentration in the coating increased with increasing TiC powder content in the anode mixture. At the same time, the coating microhardness increased from 6.82 to 8.69 GPa, and the friction coefficient decreased from 0.65 to 0.42. The use of TiC/Ti coatings makes it possible to increase the wear resistance of the VT3-1 titanium alloy surface by up to 17 times.