Relaxation effects during the densification of ultrafine powders at high hydrostatic pressure

The development of high-strength superductile hardmetals and tools based on these materials under ultrahigh isostatic pressure

“…A similar behavior is inherent in systems having a hierarchy of energy barriers; specifically, logarithmic relaxation with time is attributable to the almost uniform distribution of activation energies [14]. In the case of powder systems, the slow (logarithmic) relaxation can be explained in terms of the model of a hierarchically organized mechanical system [12]. This inference is based on the fact that nanoparticles, unlike big particles, do not undergo plastic deformation under pressure and practically retain their shape and dimensions after the pressure is released [8] due to the absence of initial dislocations and the extremely high energy of the formation of new dislocations within individual nanoparticles.…”

“…The unique strain gauge technique [10] and a "TOROID" high-pressure device [9] were used in the experiments. It was shown [11][12][13] that different powders of crystalline and amorphous nanoparticles (Fe 15, 30, 60 and 100 nm, Ni 20 nm, TiN 20 nm, Si 3 N 4 15 nm, the glasses SiO 2 and GeO 2 ) exhibit under pressure abnormally weak and anomalously slow logarithmic relaxation at a fixed pressure (Fig. 1а, b).…”

“…This inference is based on the fact that nanoparticles, unlike big particles, do not undergo plastic deformation under pressure and practically retain their shape and dimensions after the pressure is released [8] due to the absence of initial dislocations and the extremely high energy of the formation of new dislocations within individual nanoparticles. As a result, compaction of nanoparticles under ultrahigh pressure occurs only by virtue of their sliding and repacking [11,12]. Porosity of the compact remains very high after the pressure is released.…”

“…experiments [9]. Details of the experimental technique are described in earlier papers [8][9][10][11][12][13].…”

High-precisionin situinvestigation of the kinetics of the high-pressure phase transition inCaF2including the initial transformation stages

“…9 The technique has been applied with equal success to the study of compressibility and transformation kinetics of crystalline and amorphous solids, as well as of powdered compacts. [9][10][11][12] By an absolute accuracy of volume measurements, the strain-gauge technique compares well with the x-ray method ͑for crystals͒, while its relative sensitivity is several orders ͑2-4͒ of magnitude higher. The straingauge technique enables one to detect a fraction of a new phase during the transition and to study the kinetics of the phase transition in-situ under high pressures.…”