Evidence for phase transitions in mineral inclusions in superdeep diamonds of alluvial placers in the São Luiz River deposits (Brazil) is obtained by the electron backscatter diffraction technique. It has been shown that the crystal structure of superdeep diamonds is significantly deformed around inclusions of MgSi-, CaSi-, and CaTiSi-perovskites, SiO2 (stishovite?), and Mg2SiO4 (ringwoodite?). On the contrary, significant deformations around inclusions of olivine, ferropericlase, and majoritic garnet are not detected. The absence of deformation near these minerals reveals the lack of phase transitions with dramatic volume changes. The present study suggests that the formation of superdeep diamonds proceeds at different levels of the sublithospheric mantle, transition zone, and lower mantle.

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Methods of transmission electron microscopy were used to investigate the mechanisms of plastic deformation of TiNi(Fe, Mo) [001] crystals on compression in the interval of stress-induced martensitic transformations. It has been revealed that the formation of {113} and {114} twins of the В2-phase by the В19′→В2 reverse martensitic transformation over another path is, alongside with mechanical (100) twinning of В19 ′ martensite, an important deformation mechanism in this interval.It has been shown [1] that twinning in austenite over the {112} В2 and {114} В2 planes is one of the basic mechanisms of plastic deformation on compression of TiNi(Fe, Mo) [001] crystals in the temperature region Т >> М d (temperature of the onset of plastic flow of the В 2 -phase). The twinning develops at early stages of plastic deformation and is accompanied by the formation of macroscopic localized strain bands that contain martensite plates. Simultaneous observation of В2-phase and В19′ martensite twins in the deformed specimen testifies to their interrelation and competition. In addition, for the same crystals as in the experiment described in Ref. 1, whose deformation axis was orientated parallel to the [035] direction (near the [011] pole), rolled in the temperature region of the "stress-induced" В2→В19′ transformation, the formation of low-angle localized strain bands (LSB) with habits close to the habit planes of В19′ martensite and of В2-phase twins has been revealed [2, 3]. A new mechanism of the formation of twins and LSB in austenite by local recoverable В2→В19′→В2 martensitic transformations in stress fields was proposed [2][3][4][5][6]. In this connection, the goal of the present work was to investigate the mechanisms of deformation on compression of TiNi(Fe, Mo) [001] crystals in the interval of temperatures from М on to М d and to find out, for this interval, the role of the mechanical twinning in the В2-phase and its relation to the martensitic transformations that occur under load.Experimental investigations were performed on monocrystals of the TiNi (Fe, Mo) alloy, which has many medical uses [7]. The monocrystals were grown up in helium by the Bridgeman method without seed crystals. Growth blanks were prepared by melting with the use of spongy titan and type HI nickel. The grown crystals were homogenized at Т = 1233 K for 20 h and then quenched in ice water. After quenching, the monocrystals had В2 structure with a type СsCl crystal lattice and a small content of coarse particles based on titanium carbides and oxides. The temperatures of the onset and of the completion of direct and reverse martensitic transformations determined from the plotted temperature dependence of resistance were, respectively, М on = 266 K, М com = 249 K, А on = 271 K, and А com = 299 K. The orientation of the test monocrystals was determined by a special technique on a DRON-3 x-ray apparatus using CuK α copper radiation and standard stereographic projections. The axis of compression of the specimen was ∼7° off the pole [001].Specimens for me...

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