MECHANICAL PROPERTIES OF FORGED TUNGSTEN HEAVY ALLOYS

Tungsten heavy alloys are composite materials containing spherical tungsten particles embedded in binder matrix. Their excellent mechanical properties can be further improved by rotary forging. This paper aims to gain deeper understanding of the forging process by investigating the local elastic modulus, hardness, and residual stress of individual phases in W6Ni3Co pseudo-alloy. The resulting global properties of the composite material such as stress-strain behavior, fracture toughness and fatigue crack growth rate behavior are also studied. The results show that sintered and quenched material consists of highly textured matrix containing nearly perfect single crystal spheres of pure W. The rotary forging leads to significant lattice deformations destroying the texture and significantly increasing the hardness of both WNiCo matrix and W particles and making residual stresses in W particles anisotropic with increased compression along the longitudinal axis of the forged part.

Production Of High-Purity Cadmium Single Crystals By Vertical Directed Crystallization Method

The process of producing high-purity Cd crystals by the vertical directed crystallization (VDC) from a melt according to the Bridgman method is investigated. Single crystals with the preferred growth direction and were produced. The angles of deviation of the growth direction relative to the axis of the samples are α = 27.2° and α = 0.5°. The crystal perfection, microstructure and microhardness of the grown crystals are determined. As shown by x-ray diffraction analysis, in this VDC variant of high-purity cadmium, a perfect single-crystal structure is not reached. In the start section there are separate grains with different orientations, the amount of which decreases in the end section of the single crystal. This results in the formation of a more perfect single-crystal structure with a preferred orientation, which occupies the entire cross section of the crystal. The microhardness of the upper and lower sections of single crystals was determined. The more contaminated end sections of the crystals have lower microhardness than the initial parts. The impurity composition of the start and end sections of single crystals produced from cadmium of various grades purity was studied. The efficiency of impurity elements redistribution along single crystals is the same for different grades of cadmium. The developed VDC process can be used for growing single crystals of low-melting metals, such as Zn, Pb, Te, In, Bi, Sn, etc.

Neutron spin rotation effect at Laue diffraction in a weakly deformed and nonabsorbing crystal with no center of symmetry

The effect of the neutron spin rotation at Laue diffraction in a weakly deformed noncentrosymmetric and transparent for the neutrons crystal has been theoretically described and experimentally investigated. This effect arises in the deformed crystal because of the curvature of the neutron trajectory in the crystal. A certain type of deformation leads to the escape outside the crystal of one of the two neutron waves excited at Laue diffraction. This two waves propagate in the crystal without a center of symmetry in electric fields with the opposite sign. In this case the spin of the remaining neutron wave will be rotating relative to the original direction due to the interaction of the magnetic moment of the moving neutron with the crystal's intracrystalline electric field. In a perfect undeformed crystal such spin rotation effect is absent. There is only a depolarization of the beam since both waves in opposite electric fields are present with the same amplitudes. A technique for controlled deformation of a perfect single crystal by creating a temperature gradient has been developed. Thus a new possibility to measure the electric fields which act on the neutron in noncentrosymmetric crystals has been realized. There also appeared a way to control these fields in experiments on the study of the neutron fundamental properties.

Applied Stress on Silicon Perfect Single Crystal for Controlling the Extinction Layer

The extinct layer of Si(311) perfect single crystal has been investigated by neutron diffraction method with the residual stress diffractometer DN1-M installed at the experimental hall of Indonesian multipurpose reactor RSG-GAS, in Serpong, which provides micro beam and point detector arrangement. A Si(311) perfect single crystal with thickness of 5mm was used in this experiment. The crystal was finely polished at one side and roughly polished at the opposite one. It was measured that diffracted beam from the finely polished side shows very low intensity with narrow peak profile, while for the roughly polished surface, shows stronger and broaden peak. The diffraction layer of rough surface was determined to be 0.36mm, while the smooth one was 0.28mm. It was also found that in the direction of crystal thickness in between layers no diffraction peak was detected. By these experiments it was confirmed that the applied stress on Si(311) perfect single crystal produced thicker diffraction layer. This technique is one that can be used in order to enhance the total diffracted neutron, which is desired to produce a good monochromator system.

First-Principles Calculations of Grain Boundary-Surface for Various Grain Boundaries with Different Energies in Aluminum

The grain boundary surface is the excess energy of the grain boundary as the lattice on one side of the grain is translated relative to the lattice on the other side of the grain. The maximum in the slope of the grain boundary surface determines the ideal shear strength for the grain boundary sliding. We presented the ideal shear strength for the grain boundary sliding in aluminum Σ3(11 2)[110] tilt grain boundary from the first-principles calculations. The ideal shear strength for the grain boundary sliding was much smaller than the ideal shear strength of a perfect single crystal.

SCATTERING OF PIONS AND CHANNELED MUONS BY IMPURITIES IN SINGLE CRYSTALS

The possibility of pions and muons being used as probe particles for defects studies in materials research has been investigated for the past thirty years or so. We discuss here the similarities of π+ and µ+ with positrons and tritons so that they can be treated as light hydrogen isotopes. Incident pions occupy a lattice site (substitutional or interstitial) and then decay into muons of energy 4.12 MeV which undergo channeling effects. The scattering cross-section of pions in tantalum single crystal with oxygen impurities has been evaluated applying Born approximation and using a double screened potential. The same calculation is applicable for muons after making some relativistic corrections. This model should also be applicable in various other situations where dechanneling by heavy ion impurities existing in multiple charge states takes place in an otherwise perfect single crystal.

Investigation On Subsurface Damage In Silicon Wafers

Micro-Raman spectroscopy and chemical etching were applied to determine the depth of subsurface damage in silicon wafers undergoing different machining processes: cutting, grinding, polishing and lapping. In comparison with the Raman spectrum of perfect single crystal silicon, both the shape and intensity at the shoulder (500 cm−1) and the subpeak (300 cm−1) spectral regions were changed in all the machined wafers. The intensities at shoulder and subpeak gradually decreased and finally resumed to normal, as the depth of the investigated layer increased. According to the chemical etch rate, the depth of the subsurface damage was thus evaluated for the different wafers. TEM observations further confirmed the obtained results.