Metal Science and Heat Treatment最新文献

The effect of hot forging and heat treatment parameters (austenitization temperature, quenching medium and tempering temperature) on the microstructure and mechanical properties (hardness, impact strength and wear resistance) of AISI D2 steel has been studied. It has been established that during hot forging, the primary M₇C₃ carbides in the steel structure are transformed into secondary M₂₃C₆ carbides. This leads to hardening of the steel, since the secondary M₂₃C₆ carbides are the main factors in its increased strength and wear resistance. Carrying out of quenching after forging contributes to an increase in the number of secondary carbides and their more uniform distribution in the steel structure, which leads to an increase in its hardness, toughness, and wear resistance.

The results of a study of structural-phase transformations and kinetics of decomposition of supersaturated solid solution that occur during heat treatment (aging) of a new-generation magnesium alloy with an elevated ignition temperature are presented. The microstructure of the alloy in cast, quenched and aged states is studied. The physical and mechanical properties of magnesium alloy VML26 after aging at different temperatures and time parameters are determined. Dependence of the mechanical properties and hardness of alloy VML26 on the aging modes is established.

The effect of powder feed rate (PFR) on the structure, phase composition, and mechanical properties of Stellite 6 coating deposited on SS316L steel substrate by plasma welding is studied. It is shown that a high powder feed rate leads to delamination of the coating, and a low PFR leads to an extreme melting depth of the substrate due to the high thermal energy. It is shown that a cobalt-rich fcc phase is formed at low PFR, while the M₂₃C₆, M₆C, MC, and M₇C₃ phases (M is W, Cr, Co, and Mo) are metastable. At high PFRs, a cobalt-rich hcp phase is formed in the coating structure. The cobalt-based hcp phase is more resistant to sliding wear than the other phases. The coatings deposited at higher PFRs increase the hardness and the wear resistance due to formation of an hcp cobalt phase in the structure, but the bond between the substrate and the coating is worse than when using low PFRs. Therefore, for critical components used in the petrochemical industry, Stellite 6 coatings deposited on stainless steel at lower powder feed rates are recommended.

Coatings on a titanium alloy are prepared by electrospark deposition with a non-localized anode consisting of titanium and aluminum granules with addition of chromium diboride powder. With increase of the CrB₂ concentration from 2 to 10 vol.%, the gain in the weight of the cathode increases monotonically from 4.10 to 9.56 mg/cm². According to the data of polarization tests and electrochemical impedance spectroscopy, the Ti – Al – Cr – B coatings reduce the corrosion rate of the VT3-1 alloy. The highest oxidation resistance of the coatings is observed for a CrB₂ concentration of 2 vol.%. Deposition of Ti – Al – Cr – B coatings makes it possible to increase the surface hardness of the VT3-1 alloy by a factor of 2.7 – 4. The deposited Ti – Al – Cr – B coatings increase the wear resistance of the surface of titanium alloy VT3-1 by up to a factor of 6.

Analysis of published data on the effect of the exposure algorithms, energy, and scanning speed on the geometric characteristics of the molten pool and its fine structure, on the texture and grain structure of metallic materials synthesized by selective laser melting (SLM) is presented. A regression model describing the correlation between the required laser energy density and the powder composition characteristic temperatures during SLM of heat-resistant nickel- and cobalt-based alloys is obtained.

The effect of aluminum, copper and manganese on the structure, mechanical and tribotechnical properties of cast irons is studied. Cast irons of three types (aluminum-alloyed, aluminum- and copper-alloyed, and aluminum-, copper- and manganese-alloyed ones) are obtained by casting into sand-liquid-glass molds. The structure of the iron containing aluminum and copper acquires nanosize particles of phase ε-Cu promoting increase in the hardness and strength of the material. Alloying with aluminum, copper and manganese yields a structure where pearlite is accompanied by microvolumes of martensite and retained austenite. Particles of ε-Cu are detectable both within the colonies of lamellar pearlite and inside martensite crystals. The presence of martensite in the structure of the cast iron raises its wear resistance.

Multilayer composites formed by explosion welding from alternated plates of niobium and aluminum are studied. The samples are subjected to annealing at 700, 800 and 900°C under a load and without load. The structure, the ultimate tensile strength, the impact toughness and the Vickers microhardness of the composites are determined. It is shown that mixed zones represented by nonequilibrium phases, intermetallic particles of NbAl₃ and Nb₂ Al, and undissolved niobium volumes are formed near “local melting/rapid solidification” interfaces. Increase of the annealing temperature from 700 to 900°C causes growth of the intermetallic inclusions, appearance of cracks in the reaction layer, and considerable worsening of the mechanical properties. The highest ultimate strength (700 MPa) and impact toughness (86 J/cm² ) are obtained in the samples annealed under pressure at 900 and 800°C, respectively. Annealing at 700°C at a pressure of 30 MPa is shown to be an optimum treatment producing a favorable effect on the strength characteristics and providing a defect-free structure.