A. A. Ashmarin

Influence of the deformation mechanism on the anisotropy of the mechanical properties and workability of magnesium alloys

An experimental calculation method for the estimation of anisotropy is developed for semifinished sheet and pressed products made from magnesium alloys. The method makes it possible to calculate the anisotropy parameters from quantitative data on the texture and the relative values of the reduced critical shear stresses for the slip and twinning mechanisms operating in these alloys. The optimal alloying of magnesium alloys is shown to provide two methods for enhancing the deep drawing characteristics, namely, decreasing the intensity of the basal texture due to the formation of dispersed intermetallic compounds and increasing the compressive-strain resistance compared to tension due to a change in the deformation mechanism. Yttrium and neodymium are found to be most efficient in this respect, because they favor such a deformation mechanism that increases the Lankford coefficient by two to four times at the same texture in sheets. In addition, neodymium alloying weakens the intensity of the basal texture, which also favors an increase in the Lankford coefficient.

X-ray Technique for the Estimation of Residual Stresses after Shot-Blasting Metal Forming

A technique is developed for the correction of the depth distribution of residual stresses measured by an X-ray method with allowance for their relaxation upon the removal of surface layers. This technique is applied to the study of a D16 aluminum alloy strip subjected to shot-blasting metal forming. This technique can be used to estimate the distribution of residual stresses across massive parts after various types of treatment.

Behavior of an Austenitic–Martensitic VNS9-Sh Sheet TRIP Steel during Static and Cyclic Deformation

The properties of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) sheet TRIP steel during static and cyclic loading are studied. The specific features of the mechanical behavior of the steel during static tension that are related to shearing, twinning, and martensite formation processes are detected. The static stress–strain curve of the steel has a developed microyield stage, a long yield plateau, and a serrated stage of strain hardening (Portevin–Le Chatelier effect). The shear mechanisms at the initial stages of cyclic deformation and fatigue crack propagation mechanisms are investigated.

Effect of the Removal of a Surface Layer on the Mechanical Properties and the Static Stress–Strain Curves of an Austenitic–Martensitic Sheet TRIP Steel

The influence of the removal of a surface layer with a high strain-induced martensite content on the mechanical properties and the shape of stress–strain curves of austenitic–martensitic VNS9-Sh TRIP steel is studied by room-temperature tests. The removal of a surface layer 5–20 μm thick by electropolishing is shown not to decrease the mechanical properties of this steel and not to change the shape of its stress–strain curves, which have a developed yield plateau. This effect can be related to the presence of a long (up to 1%) stage of microyield in this steel. The existence of a yield plateau in the stress–strain curves of VNS9-Sh steel in the initial state and after the removal of a surface layer can also be explained by the simultaneous operation of three plastic deformation mechanisms, namely, slip, twinning, and martensitic transformation, during deformation.

Structural heat-resistant β-NiAl + γ′-Ni 3 Al alloys of the Ni–Al–Co system: I. Solidification and structure

When analyzing the ternary Ni–Al–M phase diagrams, where M is a group VI–VIII transition metal, we chose the Ni–Al–Co system, where the γ′ and γ phases are in equilibrium with the β phase, as a base for designing alloys with the following physicochemical properties: a moderate density (≤7.2 g/cm3) and satisfactory heat resistance at temperatures up to 1300°C. The structure formation in heterophase β + γ′ alloys during directional solidification is studied. It is found that, in contrast to cobalt-free β + γ′ alloys (where the γ′-Ni3Al aluminide forms according to the peritectic reaction L + β ⇄ γ′), the alloys with 8–10 at % Co studied in this work during directional solidification at 1370°C contain the degenerate eutectic L ⇄ β + γ. The transition from the β + γ field to the β + γ′ + γ field occurs in the temperature range 1323–1334°C, and the γ′ phase then forms according to the reaction β + γ ⇄ γ′.

Effect of the phase composition of the surface layer on the mechanical properties of 23Kh15N5AM3-Sh TRIP steel sheets

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.

Influence of the tensile strain rate on the mechanical properties and phase composition of VNS 9-Sh TRIP steel

The influence of the strain rate on the mechanical properties and the phase composition of a sheet VNS 9-Sh (23Kh15N5AM3-Sh) TRIP steel is studied during static tension. The strain rate is changed in the range from 8.3 × 10–5 to 25 × 10–3 s–1. The dependence of the mechanical properties on the strain rate is found to be nonlinear. The TRIP effect is most pronounced at a strain rate of (8.3–17) × 10–5 s–1. In this strain rate, the deformation martensite content increases significantly, from 50 to 87%, as is detected by X-ray diffraction.

Effect of the removal of the surface layer of a TRIP steel sheet on its phase composition after static tension at various strain rates

The effect of the removal of the surface layer of a thin strip made of austenitic–martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel on the phase composition of the strip surface is studied after static tension at various strain rates. An increase in the strain rate is shown to increase the austenite content in the surface layer of the metal. The removal of a 10-μm-thick surface layer by electropolishing results in an increase in the austenite content due to the initial nonuniform phase composition of the thin TRIP steel strip across its thickness after cold rolling.

Phase composition and residual stresses in thermal barrier coatings

X-ray study of the phase composition and residual stresses distribution in two-layer APS coatings showed that the ceramic layer consists of t-ZrO2 phase with tetragonal lattice and the metal underlayer γ-solid solution based on nickel. In the transition zone thickness of ~ 100 pm as the distance from the surface was revealed a gradual transition from t-ZrO2 to γ-solid solution. Increase in the specific volume of the metal underlayer resulting TGO growing leads to the formation of this layer high compressive stresses up to 600 MPa. In this case, the ceramic layer contains tensile stress up to 200 MPa.