Materials Science. Non-Equilibrium Phase Transformations.
Vol. 3 (2017), Issue 5

Table of Contents

  • CORROSION BEHAVIOR OF COMMERCIALLY-PURE TITAMIUM WITH DIFFERENT MICROSTRUCTURES

    pg(s) 167-171

    This paper reports on the results of corrosion tests, using alternative methods, of Grade 4 CP Ti samples with coarse-grained (annealed) and ultrafine-grained structures after severe plastic deformation processing. The effect of microstructure on the corrosion of the material under study is demonstrated. It is revealed that the material with a UFG structure has a higher corrosion resistance, as compared to the samples with a CG structure.

  • EFFECT OF Ni ADDITION ON STRUCTURE FORMATION AT IN-SITU SYNTHESIS OF TiC HARDENED Fe-BASED POWDERED ALLOY

    pg(s) 172-175

    The feachures of structure and phase formation of TiC hardened Fe-based alloy at in-situ thermal synthesis from mixtures of TiH2, Fe, graphite and Ni powders had been investigated. It was shown that after synthesis at 1200 0С the structure of the alloy is a skeleton of titanium carbide grains of various shapes and sizes from 1 to 20 µm cemented with Fe-based binding substance mostly located around the titanium carbide grains. The phase composition of the obtained alloy includes mainly phases of titanium carbide and α-Fe. In the case of using the initial mixture with the Ni in the composition of the alloy along with the titanium carbide solid solution of Ni in alpha-iron and Ni-based compounds were identified. When Ni is used instead of Fe in initial powder mixture it leads to a noticeable refinement of the alloy grain structure: the size of the carbide grains is generally not more than 5-7 microns. With the decrease in Ni content in the mixture and respectively increase of iron content at the same Ti and graphite content, the particle size increases markedly and approaches with 5 % of Ni to the particle size of the alloy obtained from the mixture containing no Ni.

  • STRUCTURE, MECHANICAL PROPERTIES AND CORROSION RESISTANCE OF MAGNESIUM ALLOY WE43 AFTER EQUAL-CHANNEL ANGULAR PRESSING

    pg(s) 176-179

    ECAP was conducted using route Bc with an angle of 120° between the die channels and a stepwise decrease of temperature from the initial 425 °C to 300 °C at the final, 12th pass. The cumulative equivalent strain the ECAP billets underwent was about 7.8. The structure examination showed that ultrafine-grained structure with the grain size of 0.69 – 1 μm was formed during ECAP process. In addition, particles of the phase Mg12Nd with an average size of 0.45 μm were formed. The refinement of the microstructure resulted in an improvement of the mechanical properties of the alloy. After ECAP, the strength characteristics of the alloy increased to the levels of ultimate tensile strength of 300 and yield strength of 260 MPa to be compared to those for the initial state (220 MPa and150 MPa, respectively). At the same time, the ductility increased to 13.2 %, which compares favourably with the initial value of 10.5 %. The ECAP process does not affect the resistance to electrochemical corrosion. The rate of chemical corrosion was found to be reduced owing to the ECAP processing.

  • INFLUENCE OF STRUCRURAL AND PHASE TRANSFOEMARION ON PROPERTIES OF SEVERELY DEFORMED DISPERSION-HARDENING ALLOYS

    pg(s) 180-183

    The effect of severe plastic deformation on the kinetics of second phases in a dispersion-strengthening Cu-Cr-Zr alloy is investigated. The observed set of phenomena indicates that during SPD processing there occurs a complex interaction between deformation mechanisms and the processes of dissolution and precipitation of second-phase particles in the copper matrix, influencing structure refinement and resulting in a change of the particle sizes and their distribution, and consequently, the material’s strength.

  • EVALUATION OF THE RESIDUAL STRESSES IN ADVANCED COMPOSITE CERAMIC COATINGS USING X-RAY DIFFRACTION AND FINITE ELEMENT TECHNIQUES

    pg(s) 184-187

    The aim of this work is to evaluate the residual stresses in advanced composite ceramic coatings (60wt% Al2O3 – 40wt% SiO2) was produced by thermal spraying coating (flame spraying) on the mild steel substrate (AISI 1050) steel. The bond coat used in this work was AlNi alloy between metallic substrate and advanced composite ceramic coatings which was implemented by flame spraying technique. The thickness of bond coating was (150ϻm) and for composite ceramic coating was (450 ϻm). the residual stresses evaluated by X-Ray diffraction technique were compressive residual stresses ( -62.6099), while by finite element method were compressive residual stresses (-68.491). The percentage of agreement between the residual stresses evaluated by X-Ray diffraction technique and finite element technique was (91.509%).

  • KINETICS OF FRONTS OF THE DEFORMATION PHASE TRANSFORMATION IN NITINOL

    pg(s) 188-190

    In this study, we investigated the localization of the macroscopic deformation during tensile test of nitinol at room temperature. The specimens were fully austenitic and therefore, the martensitic phase transition under deformation had place. It is established that the deformation phase transformation is realized by the formation and motion of fronts of localized deformation. Fronts moves at constant velocities and annihilated at the meeting. The velocities of their movement are determined by crosshead velocity and the duration of stress plateau. In this respect, the behavior of the phase-transition fronts is completely similar to the kinetics of the Lüders bands fronts observed in mild steel, but distinctive feature of this phenomenon is that the level of localization of the deformation at the phase transition front is an order of magnitude smaller than at the front of the Lüders band. In addition, the phase transition front has a more complex structure than the front of the Lüders band. These features of the kinetics and morphology of the transformation front lead to the fact that its motion takes place under hardening conditions, and inclined strain plateau is observed on the deformation curve.

  • ONE-STEP SYNTHESIS OF NANOCRYSTALLINE OXIDES WITH UNUSUAL PHYSICAL PROPERTIES. MULLITE-TYPE SOLID SOLUTIONS SYNTHESIZED VIA MECHANOCHEMICAL/THERMAL TREATMENT

    pg(s) 191-193

    The one-step synthesis using high energy ball milling can be used in preparation of many complex/doped oxides. In this work we report, as an example, on synthesis and characterization of mullite-type solid solutions. Mullite type Bi2(FexGa1-x)4O9 solid solutions with 0.1 ≤ x ≤ 1.0, were synthesized by combination of mechanochemical and thermal treatments of the Bi2O3/α-Fe2O3/Ga2O3 stoichiometric mixture. The microstructure of the as-prepared materials on the long-range and local atomic scales was investigated by X-ray diffraction and 57Fe Mössbauer spectroscopy, respectively.

  • INFLUENCE OF THE BEAM DEFLECTION ON PROPERTIES OF THE ELECTRON BEAM HARDENED LAYER

    pg(s) 194-197

    The usage of the high-energetic source of the electron beam enables a repeated surface quenching of the chosen areas of an engineering part surface. Different techniques of the electron beam deflections allow the creation of hardened layers of different shapes and above all the thicknesses. The deflection was tested at one point, six points, a line and a field on the material 42CrMo4 (1.7225). The effect of the process speed and defocusing of the electron beam was studied. The electron beam surface quenching resulted in a very fine martensitic microstructure with the hardness over 700 HV0.5. The thickness of the hardened layers depends on the type of deflection and depends directly on the process speed. The maximum observed depth was 1.49 mm. The electron beam defocusing affects the width of the hardened track and can cause an extension of the trace up to 40%. The hardness values continuously decrease from the surface to the material volume.

  • CUTTING TOOL COMPLEX COOL SYSTEM BASED ON PHASE CHANGED MATERIALS FOR DRY MACHINING

    pg(s) 198-199

    The paper presents a cutting tool complex cooling system (CCS) based on the use of the first-order phase transitions for cutting process thermal stabilization by prolongation of the fusible material melting (e.g., Rose’s metal) with the help of the heat pipes.Combined cutting tools and mills with indexable inserts are designed and manufactured. The time of temperature stabilization, depending on the amount of consumable substance is calculated. It is shown that the size of the container with fusible substance can provide a melting time equal to or multiple of the execution time of technological operations.

  • MATHEMATICAL MODELLING OF HOT PLASTIC DEFORMATION OF MICROALLOYED STEELS

    pg(s) 200-203

    The article concerns the possibility to optimize the parameters of forging process with the method of thermo-mechanical treatment of microalloyed steels by means of mathematical modelling of yield stress obtained from conducted plastometric hot compression tests. To describe the yield stress, rheological model proposed by C.M. Sellars was used. Based on this model, the course of experimental and theoretical stress-strain curves has been verified using a minimum of goal function, for the most accurate matching of analyzed curves of investigated steels. Numerical calculations with the method of finite element method (FEM) were performed taking into consideration test results of compression of specimens in Gleeble 3800 simulator, in a temperature range of 900÷1100°C and at the strain rate of 1, 10 and 50s-1. Obtained results allow to conclude that assumed rheological model along with coefficients, determined with the method of inverse analysis, describe satisfactorily the values of yield stress steels of studied steels.