The results of the influence of preliminary thermal-cyclic deformation and subsequent hardening heat treatment on the microstructure and mechanical properties of hot-rolled sheet steel 10 are presented. It is shown that the use of preliminary thermal-cyclic deformation of the steel 10 stock material results in a fine-grained structure of a hot-rolled sheet (3 mm thick) produced by an industrial technology. Deformation occurred at a temperature above AC3 (1250 °C), with cooling to 200-300 °C during 10 cycles and the deformation ratio per cycle being 6-8 %. The magnitude of the overall reduction ratio was 1.90 and the total amount of deformation was 65÷68 %. Such a treatment before sheet hot-rolling allows increasing the strength characteristics (tensile strength, yield strength) by almost 30 %. It has been established that the use of subsequent heat treatment (quenching, 900 °C, water and tempering 1 h, 600 °C) leads to a further increase in strength characteristics by 15-20 % while maintaining a sufficient level of ductility of sheet steel.
Materials Science. Non-Equilibrium Phase Transformations.
Vol. 2 (2016), Issue 4
Table of Contents
With 65 wt% solid content, Polymer/YSZ composites have been produced via extruder by using of PP, PMMA and TPU. With pyrolysis process, physical stability conditions of continuous YSZ free form fibres have been investigated according to type of polymer and pre-sintering temperature. In addition to this, melt flow rate values and thermal analysis investigations of PP, PMMA, TPU, PP/YSZ, PMMA/YSZ, TPU/YSZ were determined by melt flow rate analysis and TGA. Compared to unreinforced polymers (PMMA, PP and TPU) the melt flow rate of the composites containing YSZ powder has decreased approximately 15 %. From TGA results it was also found that the contribution of the yttria stabilized zirconia changed the decomposition temperature of the polymer part.
Amorphous microwire in a glass shell has low thermal inertia and can be rapidly heated to the crystallization temperature. We observed the transition process of the microwire from amorphous to microcrystalline state during its heating by pulse current of different amplitudes and durations. The crystallization of amorphous state proceeded in two ways depending on a pulse parameters: “slow” and explosive. In the second case electromagnetic waves emission (light flash) and burst of resistance were observed. The propagation velocity of the crystallization front in our experiments was 1 m/s.
RESEARCH OF PHASE TRANSFORMATION PRODUCTS IN HIGH STRENGTH STEELS BY ELECTRON BACKSCATTER DIFFRACTION (EBSD)pg(s) 22-25
In the present work, in order to evaluate the metastable structural state of high-strength steel immediately after the phase transformation as well as during the following tempering, the SEM-based EBSD is employed. The lattice orientation gradient in the alfa-phase of steel is mapped by a standard GAM function (“grain average misorientation”) that makes it possible to identify various types of martensite and bainite distinguishable in the dislocation density and phase stresses. The GAM sensitivity to the crystal curvature not only allows one to tell between different types of alfa-phase in the non-equilibrium quenched state but also reveals their change during tempering.
Gel matrix of the natural polymer starch has been employed as template for the preparation of ZnO nanocrystals via solution-solid technique. The template offers selective binding sites for Zn(II) under aqueous conditions. Controlled solvent-exchange, further isolation of solid product by microfiltration and drying, and subsequent removal of the template backbone enable the synthesis of spatially separated ZnO nanocrystals. The crystalline character and near narrow particle size distribution pattern have been confirmed through powder XRD measurements and TEM with SAED observation. The morphology, surface and optical properties of ZnO sample were characterized by SEM observation, BET-surface area, UV–Vis and PL spectra. The UV photocatalytic activity of ZnO nanocrystals was studied by analyzing the degradation of methylene blue in aqueous solution. The nanosized ZnO sample showed greater photocatalytic activity than commercial TiO2 (P25) photocatalysts. The size and shape factor seems to be of great importance in the observed photocatalytic performance.
THE INFLUENCE OF THE HEATING RATE IN THE PROCESS OF SPARK-PLASMA SINTERING ON THE KINETICS OF COMPACTION, STRUCTURE FORMATION AND PROPERTIES OF THE MATERIALS OF Fe – Ti – C – B SYSTEMpg(s) 3-5
Regularities of the influence of spark plasma sintering heating rate on the structure and properties of dispersion-strengthened materials based on Fe – Ti – C – (B) system are studied. Increasing heating rate of the samples from 10 °C/s to 20 °C/s induced by increasing current rise rate leads to decrease the average grain size in the material matrix of the Fe – Ti – C – B system from 2.5 to 1.5 microns. This allows to increase hardness from 48 HRC up to 70 HRC and wear resistance 7 times compared to R6M5 (full analog of HSS M2) steel during SPS consolidation in the mode with a heating rate of 20 °C/s and isothermal exposure 1100 °C for 180 s.
ANALYSIS OF THE EUTECTOID TRANSFORMATION INTO CARBON STEEL ON THE BASIS OF POSITIONS OF NON-EQUILIBRIUM THERMODYNAMICSpg(s) 30-33
The non-equilibrium thermodynamics analysis of the eutectoid transformation is executed into carbon steel. Onsager’s equations of motion are built for the model thermodynamics system describing eutectoid transformation. Dependences of basic kinetic pa-rameters of process are expected are speeds of height of pearlite and inter-plates distance from the size of subcooling became for the sta-tionary process of eutectoid transformation.
The investigation of influence of modified conditions on formation of complex materials based on tetragonal zirconia doped by d-elements of I group (Cu or Ag) was carried out, in particular the routes of synthesis and type of dopant. The kinetic parameters of separated stage of NPs formation (drying of hydrogel under MW irradiation, dehydration and crystallization of amorphous zirconia NPs) were estimated. It was shown, the dehydration of tetragonal zirconia hydrogel in conditions of MW irradiation occurs due in two stage. In contrast for Cu (or Ag) –modified hydrogels only one stage dehydration is observed. The dehydration and crystallization of unmodified and modified xerogel is studied by DSC method. It was shown that the kinetic parameters of dehydration depend as from nature of zirconium salts that were using for synthesis and type of dopant. For crystallization processes the some parameters (crystallization temperature, enthalpy) are saved features of dependence on route of synthesis for unmodified and modified systems. However, the behaviour of dependence of activation energy on route of synthesis is contrast for unmodified and modified systems.
Measurements of linear thermal expansion coefficient (TEC) of a nanoporous metal carbide based carbon material were car-ried out. The values of linear thermal expansion coefficient in the range from 20°C to 300°C were obtained. The measured value of TEC are presented for this material for the first time.
On the basis of complex metallophysical studies, surface-modified layers (electron microscopy, spectroscopy, X-ray diffraction, calorimetry, durometer analysis), we obtained new data on nanoscale composition within the surface-modified layer, on its mechanical properties, phase composition, which determines functional properties. This allows us to find ways of their purposeful formation for different operating conditions. On the basis of experimental data of X-ray analysis of the TiNiHf alloy, we calculated energy consumption, the theoretical strength. As a result of the simulation, we constructed generalized diagrams of energy intensity and theoretical strength of the ternary alloy Ti-Ni-Hf and compiled their relationship equation.
It was investigated the structure, phase and chemical composition, thickness diffusion boride layers obtained after boriding and complex saturation boron and copper with simultaneous action an external magnetic field (EMF) on solid alloy T5K10. It was established that the application of an external magnetic field allows to intensify the process of diffusion saturation hard alloys boron and by 2 hours chemical – thermal treatment with simultaneous action EMF get such thickness diffusion boride layer which is formed by 4 hours chemical – thermal treatment without EMF. It was found increase microhardness diffusion layers formed on the hard alloys on 2 – 2.5 GPa (30 – 30.5 GPa) that is associated with a decrease areas of coherent scattering and as a result increase operating parts that work in conditions of intensive wear.
The present work is devoted to analysis of relations between the physical, mechanical properties and microstructure of the material produced by spark-plasma sintering (SPS) of bimodal copper powders. The used starting powders were bimodal mixtures of nano- and micro-sized copper powders, including the pre heat treatment of these powders in a hydrogen atmosphere. As a result, it was studied the influence of sintering parameters on the final density, microstructure and mechanical properties of bimodal copper sintered compacts. It was also produced a comparison of physical and mechanical properties of sintered samples obtained by SPS and by hot pressing (HP) from these bimodal copper powders.
Structural investigations performed by the methods of X-ray diffractometry and scanning electron microscopy of electrodeposited iron-based coatings revealed common and specific features and regularities of influence of nickel and chromium on their structure formation. Significant changes in surface morphology, crystallographic texture and microhardness of the electrodeposited coatings caused by the insertion of nickel and chromium in the sulfate iron-plating electrolyte were found and compared.
Austenitic stainless steels are widely used for various industrial, construction and biomedical application because of their high resistance to uniform corrosion and suitable mechanical properties. However, they are prone to local corrosion in aggressive halides environments. In contrast of corrosion resistance research in chloride containing environments, there have been few investigations into the effect of fluorides on passivity breakdown and pitting corrosion of stainless steels. This article focuses on the effect of fluoride added to chloride solution on corrosion resistance of AISI 316L stainless steel. Evaluation is based on results of exposition immersion tests performed in 0.9 % NaCl, 0.9 % NaCl + 0.05 % NaF and 0.9 % NaCl + 0. 5 % NaF solutions (42 days) and on results of cyclic potentiodynamic polarization tests performed in the same solutions.
Depleted U3O8 was mechanically activated in suspension with tributyl phosphate (TBP), trioctylamine (TOA) and ethylenglycolmonomethylether (EGME) in planetary ball mill with stainless steel vessels and balls. X-ray diffractograms and IR spectra of the activated solid samples were taken. The radioactivities of 238U and 234Th in the leaching solutions were determined by α/β liquid scintillation spectrometry. The reduction degree of the oxide, the mean crystallite size of U3O8 and U3O7 and the leaching of 238U and 234Th as a result of the mechanoactivation were determined. Higher degree of 238U and 234Th leaching was achieved when mechanoactivation with TBP was performed. No leaching of 238U daughter product (234Th) proceeded at mechanoactivation with TOA and EGME. The role of the solvents complexation ability, milling induced increase of crystal defect concentration and UO2 – ThO2 solid solution formation is discussed. Further studies have to be made to elucidate the potential of the applied approach as a step in spent nuclear fuel processing.