Metal Science and Heat Treatment最新文献

An algorithm for determining macrohardness is suggested and tested experimentally for biocompatible titanium alloys of different classes i.e., Ti – 6Al – 4V, Ti – 14Mo, Ti – 39Nb – 5Zr, on the base of hardness measurements at low loads (1 – 24 N) by the Oliver and Pharr method. The possibility of adjustment of the hardness values for eliminating the impression effect detected during the indentation at low loads and obtaining more accurate results is demonstrated. Derivation of the Nix–Gao equation for quenched titanium alloys has made it possible to determine the hardness values at low loads(3.09 ± 0.03 GPa for Ti – 6Al – 4V, 2.58 ± 0.04 GPa for Ti – 14Mo, 1.73 ± 0.03 GPa for Ti – 39Nb – 5Zr), which correspond to the values of the macrohardness.

The structural and textural states formed in samples of stainless steel of the ferritic-martensitic class, close in composition to Cr12NiMoWoSiVNb, are studied by the method of scanning electron microscopy using orientation analysis and software for reconstruction of high-temperature austenitic grains. The samples are taken from a hot-rolled pipe that has been quenched in water and tempered at a high temperature. The samples are heat treated by holding at 950°C and cooling at different rates (in water, in air, in the furnace). At all the cooling rates, the steel structure consists of grains of δ-ferrite and martensite and contains coarse precipitates of (NbMo)(CN) carbonitrides and finer M₂₃C₆ and (VNb)C carbides. When the phase transformations occur in the sequence δ + α′ → δ + γ → δ + α′, the steel inherits structural and textural features due to nucleation of a new phase on special boundaries.

The effect of thermal and thermomechanical treatments on the structure and mechanical properties of pressed rods from aluminum alloy D16 (2024) is studied. The temperatures of phase transformations in the alloy are determined using the method of differential scanning calorimetry. It is shown that pressing of the rods with diameter 350 mm after preheating to 380 – 470°C preserves cast structure in the central part of the pressed articles. Intermediate annealing at 380 – 420°C promotes leveling of the structure and uniform precipitation of S-phase particles, while the subsequent hot pressing of the rods with diameter 76 mm provides high mechanical properties throughout the entire cross section. The chosen temperature range of thermomechanical processing makes it possible to obtain a uniform distribution of structure and mechanical properties over cross section of the pressed rods.

The effect of aging at temperatures of 550, 650 and 750°C for 30 min on the microstructure, phase composition and shape memory characteristics of the Fe17Mn6Si9Cr5Ni1Ti alloy obtained by wire laser directed energy deposition technique is studied. It is shown that with an increase in the aging temperature, the amount of cooling martensite in the alloy structure decreases, the number of TiC precipitations increases, and ferrite is gradually eliminated. In this case, the shape recovery rate of the alloy first increases and then decreases. The mechanism of the effect of aging on the shape memory characteristics of the Fe17Mn6Si9Cr5Ni-1Ti alloy is discussed.

The phase composition of laser welded joints of heat-hardenable aluminum–lithium alloys of the 3rd generation of grades V-1461 and V-1469 is studied. The phase composition of the alloys in the initial state and in laser welded condition is determined using synchrotron radiation and high-resolution transmission electron microscopy. It is shown that the weld structure is significantly affected by the thermal mode of the laser welding and by the variation of the temperature of the metal during the welding. The formation of the dendritic structure is shown to depend on the relation between the crystallization parameter G/R and the cooling rate dT/dt = GR. The energy parameters of the fiber laser welding are optimized, i.e., the welding speed, the radiation power, the location of the focal spot.

The effect of the scale factor on fatigue characteristics and failure mechanisms of drill pipes from aluminum alloy D16T and steel G-105 is studied experimentally. The endurance limit in multicycle tests of samples and the fatigue life of drill pipes in in-situ full-scale tests are determined for both materials. A significant decrease in the fatigue characteristics of the materials is detected in the full-scale tests. It is shown that the drill pipes from aluminum alloys meet the requirements on pipes from steel of strength group G-105 according to API RP 7G and have a significant advantage in the specific characteristics compared to steel pipes.

The stages of the development and application in of scandium-alloyed aluminum alloys in Russia are analyzed. The processes of production of deformed semiproducts from them are considered. It is shown that all industrial aluminum alloys with scandium can be divided into three groups according to their chemical compositions, i.e., not heat-hardenable alloys based on the Al – Mg system, heat-hardenable alloys based on the Al – Zn – Mg – (Cu) system, and heat-hardenable lithium-containing aluminum alloys. The Al – Mg – Sc alloys are used mainly in the space industry. The Al – Zn – Mg – (Cu) – Sc alloys with unique combination of physical and mechanical properties in deformed condition, are promising for manufacture of lining sheets. Aluminum-lithium alloys with scandium have a limited application due to the embrittling effect of scandium and low values of fracture toughness. In addition, the influence of scandium alloying on the weldability of semiproducts from alloys of this group awaits further study. It is inferred that aluminum-lithium alloys with scandium are not appropriate for the aircraft industry.

Heat-resistant nickel alloy Inconel 718 obtained by an additive technology employing electron beam melting is investigated. Texture analysis of the built blanks is performed using orientation microscopy (EBSD). The influence of the technological parameters of the electron beam melting on the texture characteristics of the blanks additively manufactured from Inconel 718 is determined.

A comparative analysis of the structure, properties of the surface layer and fatigue resistance of samples of steel 20Kh (20Cr4) subjected to gas carburizing, quenching and low tempering with subsequent surface treatments — grinding, diamond burnishing or nanostructuring burnishing with a PSTM DBN tool after preliminary turning is carried out. Fatigue tests of cylindrical samples are performed using a bending-twisting scheme according to the ASTM E466-07 Standard, and their fractures are examined. It is shown that the surface layer with a nanocrystalline structure suppresses the development of fatigue cracks until 1.9 × 10⁵ test cycles of treatment at a load of 1000 MPa. The surface layer formed by the nanostructuring burnishing has a thickness of 8– 10 μm, a nanocrystalline structure, and a microhardness of 1185 HV_0.05; together with the deformed carburized layer with carbon concentration 0.97% at a distance of up to 125 μm from the surface it provides a higher fatigue resistance than the processing by grinding and diamond burnishing.

The effect of chemical composition on the texture of high-permeability anisotropic (grain-oriented) electrical steel is studied using physical modeling of high-temperature annealing. Electron backscatter diffraction methods are used to investigate the formation of texture during the abnormal grain growth in secondary recrystallization. The texture sharpness is measured, and the distribution of the areas and numbers of grains with respect to the angles of misorientation from the ideal Goss texture position is determined. The misorientations differing from the Goss texture in the secondary recrystallization texture are analyzed. Hypotheses on the appearance of unabsorbed grains due to their size advantage and possible segregation of tin on grain boundaries are formulated. A possible cause of growth of the{112}<110> texture component at the expense of the {111}<112> component during secondary recrystallization is described.