Solid State Phenomena Vol. 331

Abstract: The aim of the work is a comparative analysis of structural features and mechanical characteristics of spot welded joints of thin-sheet stainless steels 03Х11Н10М2T and 12Х18Н10Т, produced by laser welding in different welding positions. The change in the welding position from vertical to flat allowed extend the ranges of variation of welding modes from about ±5% to about ±10%, at which it is possible to produce a welded joint with satisfactory shape and mechanical characteristics. Higher strength is typical for welded joints obtained in a flat position. It also concerns the maximum value of the shear stress, which for the flat position is higher by approximately 10%, and the average value, which is higher by approximately 24%. In addition, the results of mechanical shear tests of these joints have a significantly lower dispersion.

Abstract: In physics and mechanics, plasticity is defined as the ability of a material to undergo irreversible (plastic) deformation. Conventionally, the plastic strain at fracture in tensile tests, δ, has been used as a quantitative measure of plasticity. However, δ does not follow the scientific definition of plasticity. The influence of structural factors, temperature and strain rate on the value of δ were not elaborated over many decades. This lack of well-founded quantitative characteristic hindered efforts to control and to increase plasticity of materials. The plasticity characteristic that corresponds to the scientific definition of this quantity, δ* = plastic strain ε_р/ total strain ε_t, has been successfully used by many scientists to determine plasticity δ* by indentation. In the present work, the technique for the determination of the plasticity characteristic δ* during mechanical compression and tensile tests of metallic alloys has been introduced for the first time. In this case, δ* is determined more precisely than by indentation, and the second deformation curve δ*=f*(ε_t) is constructed. A theory of the influence of structural factors (grain size, dislocation density, disperse particles of the second phase) on the plasticity characteristic δ* has now been developed, making it possible to estimate the influence of the indicated factors on δ* and to design alloys with an optimal combination of strength and plasticity. The discovered correlation of the values of δ* and δ for steels and for aluminum alloys allows us to use the developed theory to calculate the influence of the structural factors on d for these materials as well.

Abstract: Seven multiphase YNi₃ and YN₄ based alloys have been prepared by arc-melting. Based on X-ray phase and structural analysis synthesized alloys depending on its composition contain intermetallics with PuNi₃, Gd₂Co₇ and CaCu₅ structure types. The influence of Y/La and Ni/Co/Mn/Al substitution on the discharge characteristics of the AB₃ and AB₄ electrodes was studied. Substitution Y by La and further Ni by Mn and Al lead to increasing discharge capacity from 40 to 341 mAh/g. Positive effect of Ni/Co/Al or Ni/Mn/Al substitution was also observed for the AB₃ electrodes. The high discharge capacities of 318 mAh/g and 340 mAh/g were seen for the YNi_2.65Co_0.2Al_0.15 and YNi_2.65Mn_0.2Al_0.15 electrodes.

Abstract: We report on experimental and theoretical studies of the electronic structure of ternary Tl₄CdI₆ alloy. Our XPS results indicate low hygroscopicity of its surface. The first-principle calculations indicate that the valence-band region of Tl₄CdI₆ is dominated by contributions of I 5p states (mainly at the top and the central portion), while its bottom is prevailed by contributions of Tl 6s states. The theoretical data indicate that the Tl₄CdI₆ compound is a direct gap semiconductor with the band gap value of Eg = 2.03 eV. The calculations reveal that the significant covalent component (in addition to ionic component) is characteristic for the chemical Tl–I and Cd–I bonds of Tl₄CdI₆.

Abstract: Nucleation and growth conditions of single-crystallinity control are convincingly elaborated by multi-scale mathematical modeling of heat and mass transport to totally abate undesirable weld defects, e.g. disoriented crystal and hot cracking inside molten pool of nonequilibrium crystallization, in order to illustrate the usefulness of predictive capability through theory and experiment procedures. Crystal growth is complicated by crystallinity-dependent thermal and chemical driving forces in front of dendrite tip during viable laser surface modification of Ni-based single-crystal superalloy. These two thermal metallurgical determinants play crucial role in crack-insusceptible columnar crystal growth, which is favorably oriented throughout weld depth. There is particular challenge in complete elimination of disoriented crystal, i.e. stray grain formation, for acceptable surface quality. Conservative (001)/[100] crystalline orientation is desired to diminish Al concentration and supersaturation, and morphologically satisfy epitaxial growth kinetics to successfully lessen central cracking with satisfactory variability of laser power and welding speed. Comparatively, (001)/[110] crystalline orientation is disadvantageous to asymmetrically augment Al concentration and supersaturation and aggressively increase interface instability, microstructure heterogeneity and hot cracking vulnerability along disoriented crystal boundaries. Disoriented crystal is increasingly withstood if the Al concentration and supersaturation in front of dendrite tip are low enough and crack-unsusceptible part is relatively large enough in case of attractive (001)/[100] crystalline orientation with optimal range of heat input to ameliorate microstructure homogeneity. Crystalline orientation region varies with diverse welding configurations, and epitaxy across solid/liquid interface is also sensitive to heat input of laser processing, which necessitate high efficient welding conditions optimization. Considerable effort is made to distinguish diffusion-driven crystal growth between a series of combinations of multiple welding conditions, such as critical welding configuration and heat input. Metallographically, the morphologies of crystal growth and hot cracking are experimentally observed to consistently support kinetics calculation result and well explain correlation between solidification behavior and crystal growth.

Abstract: The purpose of this paper is to investigate the effect of solution temperature on the microstructure and properties of Mg-2Zn-0.5Zr-1.5Dy alloy was studied by optical microscopy (OM), immersion experiment and electrochemical experiment. The results show that the alloy has the best comprehensive properties when the solution temperature is 470°C. The minimum average grain size was 97 μm. The I_corr and E_b of as-cast alloy are-3.55 μA/cm² and-1.27 V, respectively, according to polarization curve fitting. With the increase of solution temperature, the value of I_corr first decreases and then increases, and E_b first increases and then decreases. After solution treatment at 470°C, I_corr and E_b are 1.41 μA/cm² and-1.14 V, respectively.

Abstract: In surface roughness prediction modelling, it is crucial to do away with insignificant variables. Retaining variables that are not statistically significant can lower the formulated model’s accuracy. This paper is a presentation of the Bayesian Linear Regression Model (BLRM) in assessing the impact of predictors in surface roughness prediction of single point diamond turned RSA 443 with the assistance of acquired acoustic emission signal parameter (AErms) and primary cutting parameters. The principles behind the BLRM are presented in this paper. It has been observed that the order of decreasing impact of the parameters is as follows: cutting speed, feed rate, depth of cut and AErms. Furthermore, it has been discovered that the regression model containing cutting speed and feed rate has the best prediction power. Depth of cut and AErms have high probabilities of being rejected as linear regression predictors (0.642 and 0.754, respectively). Validation of the variable responses using p-values at 0.05 significance level has produced the same order of variable significance as that produced by the BLRM. Hence, the BLRM can be reliably utilized as a parameter significance assessment prediction tool.

Abstract: Induction-heated carbon steel is used in various mechanical parts and the fracture mechanism from internal cracks is still being investigated. In order to explain the fracture mechanism of an induction-heated SUJ2 steel bar specimen, we investigated Vickers hardness distributions around the fracture surface after a rotating bending fatigue test. We found an area which is defined as the transition area near the fracture surface whose HV values decreased about 150 HV and this area was formed by the fatigue crack during the rotating bending fatigue test.

Abstract: The bulge deformation of slab narrow face can cause surface defects of hot rolled steel plate. A three-dimensional bulging model, was proposed to simulate the evolution of deformation behavior of the continuous casting slab during heavy reduction (HR). The model was taken to investigate the non-uniform deformation of slab during HR process. The bulging deformation behavior of the slab was then calculated in one segment included seven pairs of rollers. To improve the edge defect on hot-rolled steel plates, the relationship between the reduction amount and bulge deformation of slab narrow face has been investigated.