Mössbauer Analysis of Deformation–Induced Acceleration of Short-Range Concentration Separation in Fe-Cr Alloys—Effect of the Substitution Impurity: Sb and Au

Abstract

The effect of doping the ferrite alloy Fe-16Cr by the oversized impurities Sb and Au on the mechanism of the short-range ordering induced by “warm” severe plastic deformation was studied using the method of Mössbauer spectroscopy. A comparison between the results obtained and the positron annihilation data on the evolution of the defects of vacancy type stabilized by the impurities Sb and Au was performed. It has been established that the impurities Sb and Au entail a shift of the temperature region of short-range ordering realization in conditions of applying pressure torsion towards greater temperatures by 250 and 100 K, respectively.

Inversion of Nitrogen Redistribution in Austenitic Steel by Severe Plastic Deformation

“…The formation of vacancy complexes in high concentrations close to the concentrations achieved at premelting temperatures was experimentally confirmed when studying the SPD of copper by ECAP and HPT [29,30]. In [26], a direct relationship between the strain-induced short-range ordering and the mobility of vacancy complexes was shown for a ferritic Fe-Cr alloy. According to the Mössbauer spectroscopy and TEM data, the dynamic decomposition during warm deformation of the FeMn 22 Cr 18 N 0.83 steel proceeds along the path of formation of segregations of alloying elements and highly dispersed secondary nitrides in a developed network of grain boundaries in the nanocrystalline matrix.…”

“…However, it should be specially noted that the main condition for the acceleration of dynamic aging processes is the continuous generation of mobile point defects during plastic deformation. It is the continuous saturation of the structure with mobile point defects, such as the vacancy complexes, that is responsible for an increase in the mobility of substitutional elements (in this case, Cr) [26,27] and, as a result, a decrease in the temperature of decomposition of austenite supersaturated with nitrogen with the formation of secondary nitrides [14,28]. The increased diffusion mobility of nitrogen at lowered temperatures obviously promotes relaxation along the path of decomposition of the solid solution.…”

Structure-Phase Transformations in the Course of Solid-State Mechanical Alloying of High-Nitrogen Chromium-Manganese Steels

“…Synergetic nature of deformation-induced processes, which manifests itself in the decomposition of supersaturated solid solutions in the course of concurrent mechanical alloying, was demonstrated in the works on the short-range order investigations into the Fe-Ni and Fe-Cr alloys [44,45]. The influence of the diffusion mobility of the alloying elements of substitution on this process was shown in the works on the dynamic aging in the Fe-Ni-Me alloys where Me = Ti, Al, Si, Zr [44,46,47].…”

“…According to the data from [48], the nitride Mn 2 N undergoes decomposition at 900 • C, while the nitride CrN decomposes at sufficiently higher temperatures (>1000 • C). The effect of the thermal stability and chemical activity of the constituents of would-be MA products on the kinetics of the dynamic aging and formation of secondary phases was demonstrated in the example of deformation-induced dissolution of nitrides, as well as intermetallics in [44,46,47].…”

Critical Redistribution of Nitrogen in the Austenitic Cr-Mn Steel under Severe Plastic Deformation

“…During “warm” deformation, the factors affecting (i) the accelerated dissolution of primary perlite-like cellular decomposition products and (ii) the formation of secondary nano-scale nitrides are the formation of a developed network of intergranular boundaries and the saturation of the structure with linear and point defects [ 11 , 16 , 33 ]. The lowering of the nitrogen content in the metal matrix is caused by its release to the boundaries of nanoparticles in the form of segregations [ 34 ] and extremely disperse secondary nitrides [ 8 , 9 , 10 ].…”