Vol 2016, No 4 (2016)

The grain-size dependence of flow stress upon transition from a micro- to a nanostructured state is analyzed. Characteristic regions with qualitatively different influences of a structure on flow stress are found. Generalized equations have been obtained for the grain-size dependences of yield strength and hardness normalized to Young’s modulus for a wide range of grain sizes using S functions and averaging integrals.

The thermal stability of the microstructure of a heat-resistant cobalt alloy, which consists of a γ solid solution strengthened with γ'-phase precipitates, has been studied. The temperature behavior of the dissolution of the hardening γ' phase and the kinetics of its coarsening at 700 and 800°C have been determined. It is found that, during prolonged annealing at 800°C, the γ' → β phase transformation occurs.

The physicomechanical behavior of a cylindrical spring made of titanium nickelide is experimentally studied during thermal cycling through the martensitic transformation ranges at a constant tensile force. The spring exhibits a reversible change in the length and the diameter, the relative change in the length reaches 1476%, and the relative change in the diameter is 33%. The alternation of reciprocating rotary motion and translational motion of the spring is observed during deformation. A method is proposed to estimate the stresses and the strains that appear in the material at large spring elongations. Thermal cycling at a constant axial force is shown to be accompanied by a reversible hysteretic change in the tangential and normal stresses and the shear strains and by a reversible hysteretic reversible change in the axial strains.

The structure, the bending strength, and the fracture mechanism of an artificial niobium-based composite material, which is fabricated by high-pressure diffusion welding of multilayer stacks assembled from niobium foils with a two-sided carbon coating, are studied. The microstructure of the composite material is found to consist of alternating relatively plastic layers of the solid solution of carbon in niobium and hardening niobium carbide layers. The room-temperature proportional limit of the developed composite material is threefold that of the composite material fabricated from coating-free niobium foils using the proposed technology. The proportional limit of the developed composite material and the stress corresponding to the maximum load at 1100°C are 500 and 560 MPa, respectively. The developed material is considered as an alternative to Ni–Al superalloys.

The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al–Cu–Li and Al–Mg–Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S₁ (Al₂MgLi), T₁ (Al₂CuLi), and δ' (Al₃Li) phases. The fraction of the δ' phase in Al–Cu–Li alloys is shown to be significantly higher than in Al–Mg–Li alloys. Therefore, the role of the T₁ phase in the hardening of Al–Cu–Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al–Cu–Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al–Cu–Li and Al–Mg–Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.

The possibilities of a one-crystal X-ray diffraction analysis of coarse-grained polycrystalline materials are demonstrated for cast 20L steel specimens in order to determine the elastic lattice strains and the residual stresses calculated from them.

The static and cyclic mechanical properties of cold-rolled corrosion-resistant VNS 9-Sh (23Kh15N5AM3-Sh) TRIP sheet steel from two batches having different deformation martensite contents in the surface layer are studied. An increase in the deformation martensite content is shown to cause an increase in the strength properties, a certain decrease in the plasticity, and an increase in the fatigue limit at 10⁷ cycles.

The structure and the internal stress fields in R65 rails withdrawn from operation because of side wear after long-term operation are studied and estimated. A high scalar dislocation density (higher by a factor of 1.5–2), the fragmentation of cementite lamellae, and the precipitation of carbide particles are detected in the layers adjacent to the roll surface. The stresses at the boundaries of the particles with the ferrite matrix can exceed the ultimate strength of the steel.

The effect of the rolling temperature and strain on the structure and the properties of corrosionresistant austenitic–martensitic 14Kh15AN4M steel is studied. The steel is shown to exhibit high ductility: upon rolling in the temperature range 700–1100°C at a reduction per pass up to 80%, wedge steel specimens are uniformly deformed along and across the rolling direction without cracking and other surface defects. Subsequent cold treatment and low-temperature tempering ensure a high hardness of the steel (50–56 HRC). Austenite mainly contributes to the hardening upon rolling in the temperature range 700–800°C at a reduction of 50–70%, and martensite makes the main contribution at higher temperatures and lower strains. Texture does not form under the chosen deformation conditions, which indicates dynamic recrystallization with the nucleation and growth of grains having no preferential orientation.

The structure and the mechanical properties of high-nitrogen austenitic 05Kh21G9N7AMF (0.56% N) and 04Kh22G12N4AMF (0.49% N) steels have been studied after hot rolling. It is found that the temperatures of the onset and end of hot deformation influence the structure and the mechanical properties of these steels. The higher set of mechanical properties of steel 05Kh21G9N7AMF after rolling in the temperature range 1100–900°C is due to the formation of a lamellar and equiaxed fragmented structure.