Metal Science and Heat Treatment最新文献

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.

The efficiency of replacing traditional quenching in a bath by spray quenching to manufacture grinding balls ∅120 mm made of 70SiMnCr steel to reduce stresses and control the phase composition is investigated. A process of forging grinding balls with the use of water spray cooling is suggested, which ensures bainite transformation under isothermal conditions and formation of the specified structure. The W70A45W20 process, implemented at 200°C for 4.5 h, yields balls with a final volume hardness of 56 HRC and a toughness of 73 J. After this mode of heat treatment, the steel balls have a high wear resistance, and the main mechanism of their surface wear is plastic deformation and micro-cutting.

The effect of complex alloying with iron, nickel, aluminum, zinc, zirconium and titanium in an amount of 0.5 – 1.2% each on the damping capacity of binary alloys Mn – 50% Cu and Mn – 40% Cu in the range of amplitude-independent damping is studied after aging at 643 K for 0.5 – 40 h and natural aging for 7 months. It is shown that alloying of the Mn – Cu alloys in cast condition may either raise their damping capacity or leave it invariable. With increase of the aging time, the values of the frequency of resonance vibrations of specimens of the Mn – Cu alloys fall to a minimum and then grow to a maximum level. The high damping capacity of the multicomponent Mn – 45.6% Cu – 1% Fe – 1% Ni – 1% Zn – 0.9% Zr – 0.5% Ti alloy (ψ = 2.9%) and of the Mn – 35.8% Cu – 1%Fe – 1%Ni – 1%Al – 1.2% Zr alloy (ψ = 3.5%) cast and aged for 40 h at 643 K does not decrease after 7 months of natural aging at 293 K.

Special features of structural and phase transformations, position of critical points, quantitative parameters of the structure, and hardness under continuous transformation of supercooled austenite in steels 30KhNMFRA, 30KhGNMFRA and 30KhN3MFRA are determined. Thermokinetic diagrams of decomposition of supercooled austenite in the steels are plotted using a Gleeble 3500 research complex. Recommendations are developed for selection of chemical composition and cooling rate for billets in order to provide a high strength and enough impact toughness of the steels after quenching and low tempering. The results may be used for development of high-strength cold-resistant steels and modes of their heat hardening.