P.P. Pal-Val

Bio: P.P. Pal-Val is an academic researcher from National Academy of Sciences of Ukraine. The author has contributed to research in topics: Atmospheric temperature range & Dislocation. The author has an hindex of 3, co-authored 8 publications receiving 54 citations.

Unusual Young׳s modulus behavior in ultrafine-grained and microcrystalline copper wires caused by texture changes during processing and annealing

Abstract: Effect of annealing on the dynamic Young׳s modulus E of ultrafine-grained (UFG) and microcrystalline (MC) copper obtained by combined severe plastic deformation (SPD) including repeated hydrostatic extrusion and drawing (UFG copper) or only repeated drawing (MC copper) is investigated. It is established that the Young׳s modulus in the SPD-prepared UFG and MC samples exceeds that in the coarse-grained fully annealed (CGFA) samples by 10% to 20%. Subsequent isothermal annealing at elevated temperatures between 90 and 470 °С leads to a sharp decrease of the Young׳s modulus for annealing temperatures above 210 °С. After annealing at 410 °С, the value of E reaches its minimal value that is 35% lower than E in CGFA samples (total change in E is about 50% of the initial value). Further annealing at higher temperatures leads to some increase in the Young׳s modulus. It is shown that the unusual behavior of the Young׳s modulus is caused by the formation of the 〈111〉 axial drawing texture in the SPD-treated samples which is replaced by the 〈001〉 annealing texture during the post-SPD heat treatments.

Slip in a {112} bicrystal with asymmetrical orientations of the loading axis

Abstract: The observations of slip patterns in the vicinity of symmetrical grain boundaries loaded asymmetrically, reported in this paper, can be explained to a large extent by the compatibility stresses arising due to elastic anisotropy of the component single crystals. Depending on the choice of the loading axis the compatibility stresses can suppress the slip activity or, on the contrary, initiate new slip systems at the grain boundary.

Low-temperature dislocation internal friction in crystals

Abstract: An analysis of the experimental and theoretical results related to studies of the low-temperature dislocation mobility by the internal friction method is given. It is shown that a number of unusual experimental results obtained at low and very low temperatures might be explained in the framework of the existing theories modified by taking into account the influence of quantum effects and viscous drag on the overcoming by dislocations of various potential barriers in crystals.

Effect of superconducting transition on temperature dependence of elastic moduli in niobium: Superposition of quasistatic and dynamic effects

Abstract: Low-temperature elastic properties of niobium crystals of different purity and orientation are investigated in normal (N) and superconducting (S) states. Experiments are carried out using the composite vibrator technique at frequencies ∼90 kHz. Temperature dependences of the Young's modulus E(T) and the shear modulus G(T) in the N- and S-states are measured in the temperature range 2K

Ultrasonic and related experiments in high-Tc superconductors

Abstract: The results of ultrasonic, sonic and infrasonic experiments in high-Tc superconductors (HTSC) are reviewed. Some other related fields of investigation are also mentioned.

Elastic behavior of a YBaCuO sample prepared by the MPMG method

Abstract: Ultrasonic velocity measurements have been undertaken by the pulse transmission technique using YBaCuO samples prepared by the melt-powder-melt-growth (MPMG) process over a temperature range of 80–300 K. It has been observed that the sample exhibits a very high value of Young's and rigidity moduli, thereby indicating that the material is an excellent one from the point of view of its mechanical strength. Further, the Young's modulus apart from exhibiting a hump at around 120 K, is found to increase continuously with decreasing temperature. In the superconducting phase, however, the modulus is found to remain almost constant. It has been concluded that the observed elastic behavior, to a large extent, is analogous to that of normal oxide materials. In order to understand how far the experimentally observed behavior deviates at 120 K, the elastic moduli of the sample were also estimated theoretically and compared with the empirical values.

Cathodoluminescence and microRaman analysis of oxygen loss in electron irradiated YBa2Cu3O7−x

Abstract: The effect of oxygen loss on the luminescence of YBa_2Cu_3O_(7-x) has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM) and by Raman microprobe measurements. The results herein indicate that a CL band at 530 nm is related to oxygen loss rather than to impurity phases such as Y_2O_3 formed in the material by electron irradiation in the SEM.

One-step consolidation and precipitation hardening of an ultrafine-grained Al-Zn-Mg alloy powder by Spark Plasma Sintering

Abstract: In the present work, ultra ne-grained Al-Zn-Mg alloy produced by high energy ball milling and Spark Plasma Sintering was synthesized. The Hall-Petch strengthening due to grain re nement (about 150 nm) is preserved and the Orowan's e ect attributed to the presence of the hardening phase ' is obtained in a single-step during the sintering. Maximum compression stresses as high as 736 MPa and 830 MPa were reached in quasistatic and dynamic conditions respectively. Hardness was increased from 124 HV5 for a consolidated coarse grained material to 196 HV for a consolidated ultra ne-grained (UFG) material. The mechanical properties obtained in this study were all superior to the ones of the reference AA7020-T651.