M. M. Perkas

Effect of the quasi-continuous equal-channel angular pressing on the structure and functional properties of Ti–Ni-based shape-memory alloys

The effect of severe plastic deformation by equal-channel angular pressing (ECAP) under normal and quasi-continuous regimes on the structure and the mechanical and functional properties of a Ti–50.2 at % Ni shape-memory alloy (SMA) has been studied. ECAP was carried out at an angle of intersection of channels of 120° in the normal regime with heating between passes at 450°C for 20 passes and in the quasi-continuous regime at the temperature of 400°C for three, five, and seven passes. The hot screw rolling with subsequent annealing at 750°C for 30 min and cooling in water was used as a control treatment (CT). A mixed submicrocrystalline and nanosubgrained structure was formed. The increase in the number of passes from three to seven led to a decrease in the average size of structural elements from 115 ± 5 to 103 ± 5 nm and to an increase in the fraction of grains/subgrains having a size less than 100 nm. After ECAP (seven passes) and post-deformation annealing at the temperature of 400°C for 1 h, a completely recoverable strain was 9.5%; after normal ECAP, 7.2%; after CT, 4.0%.

Effect of copper additions on the mechanical properties of iron

The effect of copper alloying on the mechanical properties of iron is studied. Alloying of a model material (armco-iron) with 0.2–2.0% Cu is shown to increase the strength characteristics by a factor of 1.5–2.5 and to decrease the ductility by 8–60%.

Stampability Parameters of Automotive Steel

The methods of estimating the plasticity of sheet metals subjected to standard and nonstandard tests of their mechanical and technological properties have been analyzed and compared. A strain-hardening exponent and a coefficient of normal plastic anisotropy are found to adequately characterize the stampability of metals. It is demonstrated that a plastic stability criterion can be used to estimate the energy required for metal forming at the stage of uniform deformation.

Refinement of the technique of plotting the flow curves of a metal to predict its hardening in alternating cold plastic deformation

The technique of plotting the flow curves of a metal, which describe the true strain as a function of the true principal strain intensity, is refined. The forms of analytical representation of these curves are substantiated. Using copper as an example, we show that the flow curves of a metal in a softened state can be used to predict its hardening in cold deformation. The alternating deformation of commercial-purity copper on a mangle is shown to increase its conventional yield strength substantially.

Mechanical and functional properties of commercial alloy TN-1 semiproducts fabricated by warm rotary forging and ECAP

The influence of various thermomechanical treatment schemes, which include rotary forging and severe plastic deformation by equal-channel angular pressing, on the structure and the mechanical and functional properties of TiNi alloys is studied. Treatment according to these schemes is shown to result in the formation of a mixed nano- and submicrocrystalline structure with a high dislocation density, which ensures high mechanical (σ0.2 = 760–954 MPa, σu = 917–1097 MPa, δ = 21–51%) and functional (maximum completely recoverable strain of 6.8–8%) properties.

Role of molybdenum in increasing the resistance of steel to the breaking effect of hydrogen at elevated temperatures and pressures (hydrogen corrosion)

The physicochemical nature and the mechanism of the breaking effect of hydrogen on steel at elevated temperatures and pressures (hydrogen corrosion) are studied. This phenomenon is found to be based on the chemical reaction of hydrogen with carbon on the inner surface of closed micropores in the steel volume. Methane accumulates gradually in these micopores, and they transform into microcracks at a certain critical methane pressure. As a result, the metal embrittles catastrophically and undergoes cracking. When methane accumulates in micropores (incubation period of hydrogen corrosion), the mechanical properties of the steel remain almost unchanged. Alloying of steel up to 2.0 wt % (the upper limit of the concentration range under study) is shown not to affect the thermodynamics of carbon in steel in the pearlitic temperature range. However, this alloying element strongly affects the incubation period of hydrogen corrosion. Thus, prerequisites formed for a preliminary (before steel is put into operation) determination of the conditions of the absolute and relative (within the incubation period) hydrogen resistance of steel.

The mechanism of metal corrosion passivation

The main regularities of variations in the thermodynamic properties of components of cubic vanadium carbide, depending on the composition in the region of homogeneity, are investigated experimentally. It is believed that these regularities are inherent only to metal oxides. This serves as the basis for the concept that passivation during the corrosion of metals occurs due to the formation of surface metal oxide whose composition corresponds to the maximum concentration of oxygen in the region of homogeneity. The thermodynamic stimulus of corrosion is in this case reduced to almost zero.

On the nature of metal passivation during cathode depolarization by oxygen dissolved in an electrolyte

A hypothesis is suggested and grounded according to which a metal is passivated due to the formation of an oxide whose composition corresponds to the maximum oxygen concentration in the homogeneity area of this oxide on the metal surface. In this case, the thermodynamic probability of a corrosion process becomes close to zero. Experimental data are obtained on the dependence of the thermodynamic activity of carbon on its concentration in the homogeneity areas of cubic vanadium and titanium carbides. The dependences derived from these data are assumed to be also valid for metal oxides.