The results of a study of the mechanism and kinetics of metallic material fracture (dual phase steels, binary Zr-2,5Nb and multicomponental Zr-1,2Sn-1Nb-0,3Fe alloys, reinforced surface layers and protective coatings, multifilamentary Nb3Sn and Nb-Ti based superconductors and HTSC-based composition wires) are given. The quantity fracture analysis is based on measurements of acoustic impulse peak (maximum) amplitudes by non-resonance sensors for linear measurement of acoustic shifts and crack parameters measurement. The developed methods of absolute calibration of AE equipment were checked by testing various types of materials and crack parameter measurements in laps and fractures. The calibration dependencies for quantity measurements are shown. The possibilities of AE for quality analysis and for characterizing of materials in the process of various mechanical tests and in the process of pressure processing with the help of a developed experimental computerized AE system are demonstrated.
The discovery of a shift martensite transformation made by G. V. Kurdyumov [I] and the many-sided electron microscopic studies of martensite in various alloys [2] have made it possible to create a morphological classification of their structures. A number of systematic studies of martensite strength (including that in 29 compositions of carbon steel with equal impurity contents [3]) have given a simple dependence of the yield strength on the carbon content and on the amount of austenite. A similar dependence exists for other concentrated interstitial solutions (of oxygen and nitrogen in Nb and "Ira) [4], which means that the high martensite strength is not an anomaly. The retainment of this strength after a low-temperature tempering is not an anomaly either; other interstitial solutions of a quite high concentration behave similarly (in them the softening due to the depletion of the solution is compensated by the hardening due to the zonal stage of the decomposition). The only "anomalous" phenomenon is the high hardening of martensite in deformation (up to 4500 MPa in 10 -30% compression [5]), but this is a natural consequence of dynamic strain aging (in Fe-C and Fe -N solutions it occurs even at 20~ Therefore, the toughness of carbon martensite is low and depends on the stage of decomposition before and during the tempering and on the initial structure of the crystals.Martensite is the main structural component of high-strength steels and has a complex self-organizing structure. The lattice deformation and the accompanying accommodation strain determine the final morphology, i.e., the shape and size of the structural components, their crystallographic orientation and the packing pattern, and hence the state of the interfaces between the structural components. Analyzing the structure and mechanisms of plastic flow of martensite, we can predict many features of the behavior of this composite structure in deformation and fracture.Out of the two basic morphological types of martensite [1,2], lath martensite formed in hardening structural lowand medium-carbon steels, maraging steels, and iron or its moderately alloyed carbon-free alloys presents the greatest 140 interest for applications. Studies of random sections of this morphologically complex structure give numerous and quite contradictory data. The origin of the structure of lath martensite became clear in quenching single crystals of austenite [6][7][8][9][10]. Their initial structure does not possess interphase and intergrain boundaries, subboundaries, and dislocation substructure, and the structure of the martensite is determined only by the martensitic transformation as such. When the length of the martensite crystals attains 100 btm or more and the width of the martensite laths is several millimeters, we can study single-lath specimens in oriented sections and directly observe the relation between the crystal geometry, the morphology, the plastic defonnation, and the fracture. Such studies made it possible to determine the general rules of formation of a m...
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