Metal Science and Heat Treatment最新文献

The effect of quenching and aging on the microstructure and mechanical properties of welded joints obtained by laser welding of titanium alloy Grade 2 and aluminum alloy 2024 is studied. Microstructural analysis of the welded joints is carried out using light and scanning electron microscopes. The samples are tested on a slice. It is shown that during heat treatment, the columnar heat-affected zone of aluminum undergoes a significant change, in which the grain width increases from 5 – 7 to 20 – 40 μm, and the length from 30 – 100 to 100 – 200 μm. The shear strength of the welded joint after a heat treatment increases from 120 to 195 MPa, and the microhardness of the columnar heat-affected zone changes from 100 – 111 HV to 145 – 161 HV. The effect of the heat treatment on the distribution of chemical elements in the weld metal is not revealed, whereas the columnar heat-affected zone contains presumably a hardening Al₂Cu phase.

Features of formation of surface layers in steel VKS-10 (13Kh3N3M2VFB-Sh) under thermal and thermochemical treatments, i.e., laser processing with and without surface fusion and subsequent vacuum nitriding, are considered. The effect of preliminary laser treatment on the kinetics of saturation of the surface with nitrogen is studied. It is shown that the preliminary laser treatment without fusion of the surface followed by nitriding provides a higher effective thickness of the layer on steel VKS-10 and higher wear resistance of the surface than the treatment with fusion.

Special features of the process of synthesis of oxide dispersion-strengthened (ODS) ferritic/martensitic steels by powder metallurgy and laser technologies are considered. The process of production of ODS steels is described. The properties of the steels and the possibilities of their additive manufacturing are analyzed.

The results of studies of hot cracks formed in cast shapes from low-alloy steel G21Mn5 are presented. Macroand microstructural analyses are carried out. Fractography studies of samples cut from castings used in the production of railway freight cars are performed. The criteria used to assess the susceptibility of alloys to hot brittleness are considered. It is shown that the orientation of dendritic crystals affects significantly the formation of hot cracks, and the direction of the dendrite growth is determined by the conditions of heat dissipation, which are influenced in their turn by the geometry of the casting. The phenomenon of coalescence under the conditions of misorientation of neighbor dendrites and its effect on the formation of hot cracks is studied. A modified RDG criterion is suggested, which allows for the influence of the geometry of the cast product on the formation of hot cracks through the angle of misorientation of neighbor crystals.

The method of chemical cleaning of the surface of blades of gas turbine units in a solution of orthophosphoric and sulfuric acids using a purpose-designed closed-type autoclave microwave system “Mars 5” and ultrasonic exposure in distilled water is described. The two-stage cleaning involves the chemical action of the acid solution in the autoclave and ultrasonic cleaning in the stage of washing. The effect of acid solutions of various concentrations on the degree of surface cleaning from metal oxides and microcracks in the gas turbine blades is studied. It is shown that when the samples of gas turbine blades are treated in the “Mars 5” autoclave with a solution of acids and with ultrasound in the washing stage, the residual oxygen content reflecting the presence of oxides on the surface of the samples is less than 1%.

A method for obtaining composite surface-alloyed castings from gray cast iron SCh25 by cavityless casting with the use of master alloys containing chromium and ferroboron deposited as a paste layer on the surfaces of the casting molds is considered. The microstructure and the phase composition of the surface layer and the microhardness of the structural components are determined. Mechanical tests of the cast samples for compression and wear are carried out. Self-propagating high-temperature synthesis is shown to occur between the components of the master alloys deposited on the surfaces the molds during the production of the castings. The types and compositions of the borides and carboborides formed in the alloyed layer are determined. The effect of the parameters of the alloyed layer on the properties of the composite castings is analyzed.

The possibility of four-layer (Ni – Cu – Ni – Sn) electroplating and epoxy paint coating of a NdFeB magnet from a hard magnetic alloy used in wind generators is considered. The corrosion-protective effect of various paint coatings on the magnet in aggressive environments is determined. It is shown that the electroplate layuer should have a thickness of at least 20 µm and the epoxy paint coating should be no thinner than 15 µm.

The boundary conditions for describing the mass transfer of carbon from oxygen-free low-pressure atmospheres into steel during vacuum carburizing are analyzed. The effect of the content of carbide-forming alloying elements on the values of the carbon potential of low-pressure acetylene atmospheres is determined depending on the temperature of the process of vacuum carburizing. Temperature dependences of the carbon mass transfer coefficient are derived.

The possibility of production of metal powder of grade “EOS Stainless Steel PH 1” by electrolyte-plasma spraying of finished products manufactured by selective laser melting is considered. The sample is sprayed by gas-discharge plasma at atmospheric pressure in an electrode configuration, where the metal cathode is the sprayed product and the electrolytic anode is a 3% NaCl solution in purified tap water. The current-voltage characteristics of the discharge, the surface temperature of the electrodes, the topography and the elemental composition of the powder are determined.

The effect of heat treatment (quenching and aging) on the structure and mechanical characteristics of maraging steel Cr12Ni9Mo2Si (EP659A) obtained using a hybrid CMT surfacing technology consisting in multilayer cold metal transfer and layer-by-layer deformation hardening is investigated. Metallographic analysis of the samples is carried out using light and scanning electron microscopes. The local elemental composition of the surfacing is determined. Tensile tests at 20°C and impact tests at 20 and –100°C are performed. The micromechanisms of crack growth and their special features are investigated. The effect of structural segregation of the material during the CMT with deformation without heat treatment is detected. It is shown that the structural segregation in the surfaced layer disappears after the heat treatment; the strength characteristics and the impact toughness increase, and the elongation decreases slightly. The micromechanism of crack growth after the surfacing followed by heat treatment changes from a mixed viscous-quasi-brittle one to a viscous one. To obtain a set of high mechanical characteristics at room and negative temperatures in the material synthesized by CMT surfacing with interlayer forging, it is recommended to carry out a heat treatment involving water quenching from 940°C for 45 min and aging at 520°C for 240 min.