The effect of nonequilibrium structure state on the creep and superplastic behaviour of materials

Mechanical behaviour at creep and superplasticity of large-grain and monocrystalline aluminum under torsion, large-grain molybdenum, fine-grain zinc alloy and amorphous cobalt alloy under tension are discussed from unified positions. It is shown that realization of their superplasticity requires fulfilment of structure-kinetic principle

EBSD анализ микроструктуры аустенитной стали после прокатки в криогенных условиях

This work is based on the use of electron backscatter diffraction (EBSD) methods to investigate the microstructure of metastable austeniticsteel 12X18H10T (321) after cryogenic rolling. Cryogenic deformation was accompanied by martensitic transformations, and the martensitic phase nucleation mainly in deformation bands. It is assumed that the proceeding of the martensitic transformation in the most deformed parts of the microstructure should prevent the evolution of deformation-induced boundaries in the austenite and, thus, inhibit the process of fragmentation of this phase. Mechanical twinning was the primary (or even sole) mechanism providing HAB formation in the austenite

A two-step approach for producing an ultrafine-grain structure in Cu-30Zn brass

A two-step approach involving cryogenic rolling and subsequent recrystallization annealing was developed to produce an ultrafine-grain structure in Cu-30Zn brass. The material so processed was characterized by a mean grain size of 0.5 μm, fraction of high-angle boundaries of 90 pct., a weak crystallographic texture, and strength twice that of initial material

Annealing behavior of cryogenically-rolled Cu-30Zn brass

The static-annealing behavior of cryogenically-rolled Cu-30Zn brass over a wide range of temperature (100-900 °C) was established. Between 300 and 400 °C, microstructure and texture evolution were dominated by discontinuous recrystallization. At temperatures of 500 °C and higher, annealing was interpreted in terms of normal grain growth. The recrystallized microstructure developed at 400 °C was ultrafine with a mean grain size of 0.8 μm, fraction of high-angle boundaries of 90 pct., and a weak crystallographic texture

Effect of electric-current pulses on grain-structure evolution in cryogenically rolled copper

The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the recrystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens

Grain growth during annealing of cryogenically-rolled Cu-30Zn brass

The grain-growth behavior of cryogenically-rolled Cu-30Zn brass during isothermal annealing at 900 °C was examined. The observed microstructure coarsening was interpreted in terms of normal grain growth with a grain-growth exponent of ∼4. The relatively slow grain-growth kinetics was attributed to the formation of precipitates at the grain boundaries and the interaction of texture and grain growth. The development of a moderate-strength {110} α fiber texture (∼4 times random) as well as the presence of a limited number of twin variants within the grains suggested the occurrence of variant selection during annealing

EBSD investigation of microstructure evolution during cryogenic rolling of type 321 metastable austenitic steel

Electron backscatter diffraction (EBSD) was employed to establish microstructure evolution in type 321 metastable austenitic stainless steel during rolling at a near-liquid-nitrogen temperature. A particular emphasis was given to evaluation of microstructure-strength relationship.As expected, cryogenic rolling promoted strain-induced martensite transformation. The transformation was dominated by the γ→α′ sequence but clear evidence of the γ→ε→α′ transformation path was also found. The martensitic reactions were found to occur almost exclusively within deformation bands, i.e., the most-highly strained areas in the austenite. This prevented a progressive development of deformation-induced boundaries and thus suppressed the normal grain-subdivision process in this phase. On the other hand, the preferential nucleation of martensite within the deformation bands implied a close relationship between the transformation process and slip activity in parent austenite grains. Indeed, the martensite reactions were found to occur preferentially in austenite grains with crystallographic orientations close to Goss {110} and Brass {110}. Moreover, the martensitic transformations were governed by preferential variant selection which was most noticeable in ε-martensite. The sensitivity of the martensitic reactions to the crystallographic orientation of the austenite grains resulted in re-activation of the transformation process after development of a deformation-induced texture in the austenitic phase at high strains. Both martensitic phases were concluded to experience plastic strain which resulted in measurable changes in misorientation distributions. Cryogenic rolling imparted dramatic strengthening resulting in a more-than-sixfold increase in yield strength. The main source of hardening was the martensitic transformation with lesser contributions from dislocations and subboundary strengthening of the austenite

Microstructure response of cryogenically-rolled Cu-30Zn brass to electric-current pulsing

The effect of transient electric-current pulses (ECP) on the evolution of microstructure and texture of cryogenically-rolled Cu-30Zn brass was determined. The pulsing was shown to lead to recrystallization followed by grain growth. The mean grain size in the recrystallized material was 0.5 μm, thus indicating that cryogenic rolling coupled with ECP is suitable for the production of an ultrafine-grain microstructure in Cu-30Zn brass. The differences in the recrystallization texture in pulsed versus statically-annealed conditions suggested a distinct recrystallization mechanism during ECP

Анализ спектра разориентировок на основе удельной поверхности границ

The described method for analysis of misorientation distribution in terms of a specific grain-boundary surface has been used. It was found that this approach was effective for study of grain structure evolution during deformation, recrystallization and grain growth

Рекристаллизация криогенно деформированной меди

In recent years, deformation at very low (cryogenic) temperatures has been considered as a promising approach for radical grinding of the grain structure. In this connection, it is of interest to estimate the thermal stability of cryogenically deformed materials. In this work, the evolution of the structure during low-temperature (50-250 ° C) annealing of copper subjected to preliminary cryogenic rolling to 90% reduction was investigated. It was found that recrystallization in the material begins at room temperature and ends after annealing at 150 ° C. The recrystallization process is accompanied by intense formation of annealing twins