Metal Science and Heat Treatment最新文献

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.

The effect of laser cladding process technological parameters, as well as of the addition of nickel (5 – 15 wt.%) on the structure and mechanical properties of WC – 10Co – 4Cr laser cladding on mild steel, has been studied. The most effective laser cladding process parameters were determined when applying single-pass clad tracks and tracks with 50% overlap. The microstructure and the phase composition of the coatings were determined using EDS and XRD. The microhardness of the coatings and their erosion wear resistance were measured. The maximum microhardness (3.6 times higher than that of the substrate material) was exhibited by the WC – 10Co – 4Cr coating (without Ni). The WC – 10Co – 4Cr – 5Ni coating (with 5% Ni) exhibited the highest erosion wear resistance as compared to the coatings with 10 and 15% Ni.

Cross sections prepared using a focused ion beam are used for a transmission electron microscopy study of the microstructure and elemental composition of the intermetallic phases formed after long-term holding a 900 and 1150°C at the boundaries of dispersed particles of niobium carbide in a heat-resistant alloy of type HP40NbTi. Formation of a well-known G-phase is detected at 900°C. When the temperature is raised to 1150°C, an fcc intermetallic phase with parameter a = 1.084 nm (space group Fd3m) is detected. The elemental composition of the high-temperature intermetallic compound and participation of atmospheric nitrogen in its formation are established.

The effect of tempering temperature on the mechanical and corrosion properties of modified martensitic steel CA6NM is studied. Mechanical characteristics are determined in tensile and hardness tests, and corrosion properties are investigated using potentiodynamic and cyclic polarization in an artificial brine solution. The relationship between the microstructure and the mechanical and corrosion properties of the steel in the heat-treated state is revealed. It is shown that the best combination of mechanical and corrosion properties is achieved by tempering at a temperature of 600°C.