Influence of microstructural modifications induced by ultrasonic impact treatment on hardening and corrosion behavior of wrought Co-Cr-Mo biomedical alloy.

In this work, biomedical Co-28Cr-6Mo alloy is subjected to ultrasonic impact treatment (UIT). XRD, TEM and SAED analyses show that the plastic deformation induced by the UIT process results in a complex microstructural formation in surface layer of Co-28Cr-6Mo alloy. The peculiar feature observed in the alloy structure by TEM is the formation of Lomer-Cottrell locks originated by simultaneous sliding of Shockley partial dislocations in intersecting planes. At the beginning of the UIT process (till the strain extent e ≈ 0.2), dislocation pile-ups are gathered in front of the Lomer-Cottrell locks stimulating the formation of a great number of chaotic stacking faults (SFs) packets (incompletely transformed martensite), which are predominant with regard to the occurrence of ε-martensite and micro-twins. The incompletely transformed martensite hinders the shear translation through the twin boundaries and suppresses grain subdivision in surface layer of Co-28Cr-6Mo alloy at the UIT process used. On-going deformation to e ≈ 0.4 leads to further modification of microstructure in the micron-scale γ-grains, which consists of numerous Lomer-Cottrell locks, chaotic subtraction SFs, intersected nano-twins and fine lathes of ε-martensite with average size of approx. 50-100 nm. The observed structural features (at e ≈ 0.4) allow adequately explaining noticeable increase in microhardness without any cracks/cleavages in surface layer. Enhanced corrosion resistance of Co-28Cr-6Mo alloy, which manifests itself with less negative corrosion potential and lower corrosion and passivity currents in potentiodynamic curve, is promoted by the UIT induced oxide films and the following structural features: the CSL type of γ/ε interfacial boundaries, uniformly distributed fine carbides, and high fraction of the grains oriented with close packed (111)γ and (0002)ε planes parallel to the surface of the UIT-processed specimen.

Mechanical alloying of powder materials by ultrasonic milling.

An ultrasonic grinding mill was designed. It permits to carry out simultaneously intensive ultrasonic, mechanical and cavitation treatments of powder materials that in turn leads to sharp acceleration of diffusion, mass-transfer processes and solid phase reactions due to crystallite size and structure changing. It was shown that meta-stable non-equilibrium solid solution (Cu+Ni+Fe, Fe+C), and crystalline structure transformed (Fe(4)N: fcc-hcp transformation) powders could be obtained for the much shorter time in compare with traditional mechanical alloying in planetary ball mill.

Mössbauer and X-ray studies of Fe-powder mechanically alloyed with C using power ultrasonics.

The Mössbauer and X-rays analysis of as-received Fe-powder and Fe-powder mechanically alloyed with C using high power ultrasonics were carried out. The powder blend of Fe-powder and graphite was processed in He environment during 5 to 50 h. The dissolution of carbon in iron particles and inhomogeneous distribution of C atoms in crystallites was revealed. The ultrasonic milling of the f.c.c. Fe-Ni-powder with graphite was carried out. As established, the saturation of iron particles with carbon under ultrasonic milling occurs for much shorter time as compared to the high-energy ball milling.

[Apparatus "Stimul-1" foe electric stimulation of muscles]. / Apparat dlia élektricheskoi stimuliatsii myshts "Stimul-1".

The apparatus "Stimul-1" has been designed and recommended for batch production, its purpose being broad application in the medical practice of electrical stimulation of the muscles. For stimulation is used sinusoidal a.c. current with frequency of 2 kHz, which produces and effective contraction of the muscles without causing any sensation of pain. The unit is constructed by using up-to-date components, including microminiature logic circuits, operational amplifiers and field-effect transistors.