The study of the effect of spherical stress waves on the phase state,
structure, and mechanical properties of metals and alloys is of great
interest nowadays because this method of pulsed loading allows to
obtain extremely high pressures and temperatures in rather large
volume of material and to preserve specimens unbroken after such
loading. The aim of this investigation was to study the structure and
phase state of the Zr-Nb alloys loaded by spherical converging stress
waves of the different intensity.
Two balls of the Zr-1wt% Nb alloy 35 and 32 mm in radii and two balls
of the Zr-2.5wt% Nb alloy of the same sizes were subjected to the
loading by spherical converging detonation waves of the different
intensity. The initial pressure on the external surface of the balls
was over 30 GPa. In the central areas of the balls, the pressures and
temperatures, sufficient for the melting of the alloys directly at the
shock-wave front, were reached at converging waves. The detailed
analysis of the structure was performed using the X-ray diffraction
analysis, the optical and transmission electron microscopy. The
specimens that were saved unbroken after the shock loading with
spherical converging stress waves have the shape of a thick-wall
spherical shell. A hollow, whose size was different in different
balls, appeared in the central part of the initially continuous balls.
In the case of high-intense loading, the area of instable plastic flow
is observed near the hollow. The boundaries of instable plastic flow
area are
"protuberance-like" In the initial state, the alloys have a two-phase
structure composed of the
a-phase and b-phase of zirconium enriched niobium. The phase state of
the loaded specimens strongly depends on the loading conditions and
the layer depth. In the case of low-intense loading, the alloys have a
two-phase structure composed of the a- and w-phases. The amount of the
w-phase is maximal in the layers near the external surface of the
specimens and
decreases until it completely disappears as the center of the ball is
approached. In addition to the a- and w-phases, the traces of the
b-phase of zirconium enriched niobium are observed on X-ray
diffraction patterns of both alloys. In the case of high-intense
loading, the w-phase disappears in the alloys because of high
remaining temperatures. The martensite structure is observed in the
area of instable plastic flow near the hollow.
X-ray diffraction analysis shows that the alloys in these regions
consistof hexagonal a?-phase. The lattice parameters of the a?-phase
correspond tothose of the a?-phase in these alloys quenched from
b-field. This indicatesthat the conditions required for martensite
bRa? transformation were realized in this case. It is shown that
dislocation structure strongly depends on the layer depth.
The a- and w-phases contain a great amount of dislocations. In
addition to
dislocations, microtwins are present in subsurface layers of the
balls. In
contrast to pure zirconium, the formation of coarse twins in the
zirconium-niobium alloys is not observed.

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