Том 60, № 5-6 (2018)

Theoretical and statistical evaluation is provided for the dependence of mechanical properties for bars, plates, and forgings on chemical composition for different modifications of alloy Ti – 6% Al – 4% V. The proportion of mechanical property variation is determined due to variations in grade composition. Recommendations are developed for improving property stability and excluding rejects by adjusting the content of the main components and impurities taking account of production scatter.

The effect of bulk porosity on the kinetics of hydrogen thermal diffusion impregnation and on the structure of specimens prepared from different semiproducts, i.e., bars, wires, and fibers of commercially pure titanium, is studied. It is established that the rate of hydrogen absorption by porous titanium is at a maximum at 650°C and it increases with an increase in bulk porosity, pore size and a reduction in typical size of original semiproduct. Simultaneous thermal diffusion impregnation of monolithic and porous material leads to nonuniform distribution of hydrogen between them and correspondingly a change in structure.

We study the effect of the content of oxygen (carbon) impurities on the temperature of complete polymorphic α + β→β transformation (T_pt) and a set of properties of Ti – 10% V – 2% Fe – 3% Al and VST5553 (Ti – 5% Al – 5% V – 5% Mo – 3% Cr) titanium alloys in the thermally hardened state. We determine the microstructure of the alloys by metallographic analysis and test them for tension and fracture toughness. The dependence of T_pt on the content of impurities in the analyzed alloys is determined. It is shown that the value of T_pt can be found by the method of differential scanning calorimetry whose accuracy is comparable with the accuracy of the method of test quenching. The dependences of the strength and ductile properties of the alloys in tension on the aging temperature are constructed. We also establish the relationship between the fracture toughness of the alloys and the morphology of the primary α-phase.

A structure, phase composition and properties of Ti – 19.6Al – 12.4Nb – 1.5V – 0.9Zr – 0.6Mo alloy after quenching in water from 650 – 1050°C depending on the initial condition have been studied. Two variants of the initial structure were studied: β-state obtained by quenching from the β-range, and initial hot-rolled O + β + (α₂)-state. A significant difference in structure and properties was determined in the lower range of the quenching temperatures (up to 850°C), and a mild effect of the initial structure was established after quenching from the higher temperature range. It was found that in order to obtain a structure, favorable for cold deformation, quenching in the temperature range from 850 to 900°C should be used, which would allow balancing the effect of the initial structure.

The method of orientation microscopy (EBSD) is used to study the special features of recrystallization texture in drawn copper wire. It is shown that the strict crystallographic relationships between deformation and recrystallization orientations are consequences of the dominant role in structural transformations of special misorientations, i.e. special boundaries. Mechanisms of the appearance and “growth” of annealing twins are proposed.

The effect of small additions of Mn, Ni, and Cr on a set of mechanical properties at room and elevated temperatures and electrical conductivity of alloys based on the Al – Fe – Si system is studied. It is shown that nickel increases electrical conductivity by 3% for alloys based on the Al – Fe – Si system, and chromium and manganese reduce it by 5 – 10%, which is connected with formation of a more alloyed solid solution. It is established that as a result of cold deformation treatment a dispersed structure forms within the alloy with an average excess phase size up to 0.7 μm. Excess phases of this size are effective recrystallization barriers, and therefore a cold-worked structure is retained in all alloys up to 300°C, which points to good thermal stability of the experimental alloys.

Results are provided for a study of the effect of different forms of ultrasonic treatment on properties of powder corrosion-resistant steel PH-1 prepared layer-by-layer with selective laser melting. Specimens are studied after ultrasonic cavitation-erosion and cavitation-abrasion treatment, and also ultrasonic surface-plastic deformation. After treatment microhardness and parameters of the micro- and sub-microgeometry of a surface layer are measured. Fields of application for this form of treatment are considered.

An argon TIG welded joint of the Al – Zn –Mg – Cu alloy was studied. Based on the hardness and differential scanning calorimetry studies, a post-weld alloy heat treatment regimen has been proposed to ensure a welded joint strength of 622 MPa versus the strength of the base metal of 676 MPa. The post-weld heat treatment provides for a two-stage solid solution treatment (470°C, 90 min + 500°C, 20 min) and artificial aging at 120°C for 24 h.

The method of orientation microscopy (EBSD) is used to study the structure and texture over the thickness of hot-rolled plate of aluminum alloy of the Al – Si – Mg system. In the surface layers of plates there are mainly shear components of the texture, and in the central layers a rolled texture is observed. With use of fast hot rolling rates alloy surface layers undergo recrystallization that substantially changes structure homogeneity over the plate thickness.

We study special features of the transformation of supercooled austenite under the continuous cooling of Si – Mn steels with reduced contents of nickel as compared with traditionally used machine steels. The temperature ranges of the phase and structural transformations running under the conditions of heating and cooling of steels are determined by the dilatometric method. We plot the thermokinetic diagrams of transformations of supercooled austenite. The microstructural components formed in the investigated steels are analyzed both qualitatively and quantitatively. We also propose the chemical compositions of promising steels characterized by a high stability of supercooled austenite and high hardenability.

The effect of homogenizing regime is studied for continuously cast ingots of alloy of the Al – Zn – Mg – Sc – Zr system on the structure and properties of extruded strips and cold-rolled sheets prepared from them. It is established that the properties of these semiproducts in a thermally strengthened condition depend little on homogenizing regime as a result of constancy of their grain structure, which remains unrecrystallized (polygonized) after heating for hardening. Breakdown of transition metal solid solution present in the alloy, occurring during ingot homogenization affects the recrystallization temperature and kinetics, and also the stability of zinc and magnesium solid solution in aluminum in the semiproducts obtained from ingots.

Surface strengthening of structural steels with carbon nanomaterials using laser and electron-beam heating is studied. It is shown that during laser treatment the maximum microhardness of a modified layer is achieved in a strengthened zone up to 70 μm thick with q = 9 × 10⁴ W/cm², and with electron beam treatment in a strengthened zone up to 300 μm thick with q = 4.6 × 10⁴ W/cm². It is established that in both cases with optimum treatment regimes strengthening is due to forming martensite, a cellular structure, and grain disintegration.

The properties of the welded joints of 6082-T6 alloy produced by friction stir welding (FSW) and laser welding (LW) were studied. The maximum temperature and microhardness fields in the friction stir-welded joints were shown to be asymmetrical. The concentrated energy input during laser welding yields a narrow heat-affected zone (HAZ) with sharp changes in mechanical properties. The strength of the FSW joint constitutes 72% and that of the LWjoint—67% of the base metal strength. In case of LW, the minimum hardness of the joint corresponds to the metal of the welded joint, while in case of FSW, it corresponds to the heat-affected zone. At the same maximum heating temperature, the hardness of the heat-affected zone of the friction stir-welded joint is lower compared to laser welding due to substantially lower rates of heating and cooling.

Ageing of supersaturated solid solution in Pb – 3.2% Cd – 0.08% Sr alloy is studied at 20 and 80°C by measuring hardness, and light and scanning electron microscopy. Structural changes are established corresponding to stages of ageing and supersaturation.