Materials Science. Non-Equilibrium Phase Transformations.
Vol. 1 (2015), Issue 2

Table of Contents

  • NANOSTATE PHENOMENON IN MATERIALS SCIENCE OF METAL-POLYMERIC SYSTEMS

    pg(s) 3-7

    There were considered the physical, structural and morphological prerequisites for the realization of the nanostate phenomenon of dispersed particles of condensed matter of different composition, nature and technology for production. It was shown the role of the size factor in the occurrence of the nanostate phenomenon due to the change of the energy parameters of the surface layers of particles that contribute to their effective modifying effect on the high-molecular matrix. Physical models of the formation of a particular energy state of dispersed particles and metallic and non-metallic materials substrates, characterized by the presence of local areas ("charge-mosaic") with a long relaxation time are proposed.It was considered practical application of the nanostate phenomenon when creating high-strength and wear-resistant materials based on thermoplastic matrices (PA6, PTFE, PET), consistent lubricant and lubricating oils, tribological and protective coatings for friction units and metalwares used in mechanical engineering, automotive and mining engineering. It was made the examples of the effective use of developed nanocomposite materials in practice.

  • SIZE FACTOR SELECTION MODIFIERS FOR FUNCTIONAL NANOCOMPOSITE MATERIALS BASED ON POLYMER MATRICES

    pg(s) 8-12

    On the basis of modern concepts of condensed matter physics and quantum physics considered the criteria for inclusion ofdispersed particles of different composition, structure, and technological background to nanomodifiers of polymeric, oligomeric and combined matrices. There were proposed an analytical expression for the evaluation of limiting size of the dispersed particles L0, which characterizes the manifestation of a particular energy state – nanostate.There was implemented the analysis of experimental and literature data confirming the adequacy of the calculated value of the size of particles in nanostate obtained using relation L0=230•θD-1/2, where θD – Debye temperature. It is shown that the provision of effective modification of macromolecular matrices necessary and sufficient condition is the presence of dispersed particles of different composition and structure of nanoscale structural fragments of the surface layer, which ensure the implementation of synergies through a combination of energy and mechanical factors in the formation of boundary layers of the optimal structure.

  • NANOCOMPOSITE ENGINEERING MATERIALS BASED ON RECYCLED THERMOPLASTICS

    pg(s) 13-16

    There were studied features of the structure of composite materials on the basis of recycled thermoplastic (HDPE, LDPE, PP) modified by components of different composition and dispersion. It was established the hardening effect of the matrix of the composite with the introduction of the highly oriented fragments that preserve the structure after the completion of the technological cycle of manufacturing products by injection molding or extrusion. It was proposed the technology of thermo-mechanical combining of thermoplastic components while simultaneous modifying by components of different composition and structure. When modification of fluorinated nanoparticles ablation products is provided the effect of increasing the rate of extrusion and formation of hydrophobized surface layer of products. Nanoscale silicate modifiers (clay, tripoli, metals phosphates and oxides,) contribute to the thermodynamic compatibility of the matrix and the modifier polymer due to formation of a spatial network of physical binds in the volume of the composite. The obtaining technologies for products based on recycled composites that the parameters of deformation strength and tribological characteristics are not inferior to raw materials, but have a significantly lower cost of production.

  • METALLOGRAPHIC INVESTIGATION OF INDUCTION HARDENED PART TWO-SIDE LEVER

    pg(s) 17-21

    Basic idea in this metallographic investigation is checking the effect of induction (surface) quenching of produced part, two-side lever made of 42CrMo4 steel. This part is build in railway wagon. According its production assignation it has to be surface hardened just in some positions. Formerly surface hardness of this part was realized by chemical-heat treatment i.e. case hardening of 16MnCr5 steel. But because of specific form of the part and increased britlness which appear in the thinnest parts of lever (between the rounded opening and the surface) and idea was obtained to change the case hardening with induction quenching. Efficiency of performed induction quenching i.e. hardness values and depth of quenched layer was controlled by optical microscopy and hardness measurement.

  • HARDENING OF AUSTENITIC STEELS WITH HIGH Mn AND Al CONTENT

    pg(s) 22-24

    Estimates and experimental study of aluminum, carbon and nitrogen content effect for thermally and mechanically stable austenitic alloys based on Fe-(20–25)%Mn-(5–10)%Al-(0–10)%Ni-C-N, and hardening efficiency of these alloys by nitrogen addition are conducted. It is shown that the alloys based on the investigated system with C content of >1.2% for nickel-free system and ≥1.4 % for 5% and 10% of Ni can be proposed as high-strength non-magnetic cryogenic both in heat-treated and aged states. Nitrogen addition in the alloy containing 5% Al can be considered as micro-alloying, enhances dispersion of the cast structure. Ni enhances the dispersion hardening effect due to increase in carbide release rate resulted from the reduction of C solubility in austenite. Rational content of nickel equals to ~5%.

  • EFFECT OF ALLOYING ELEMENTS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF NiAl-Cr(Mo) EUTECTIC ALLOY

    pg(s) 25-29

    Microstructure and mechanical properties of NiAl-Cr(Mo) eutectic alloy and the effect of 0.1Fe,1Nb,4Ti additions are investigated at room temperature (RT) and high temperature (1000°C). The alloys are prepared by arc melting method and then homogenized at 1300°C in Ar atmosphere for 24 h. In addition to the room temperature and high temperature compression tests and X-ray diffraction measurements, hardness measurements and microscopic analyses at room temperature are performed. NiAl-Cr(Mo) alloy exhibit fine cellular eutectic structure with coarse eutectic at interdendiric regions. However, the Nb and Ti addition reduced the formation of eutectic structure. Cr2Nb-type Laves and Ni2AlTi-type Heusler phases are observed in the XRD patterns of the Nb and Ti containing alloys respectively. Addition of Fe does not have important effect on the room and high temperature yield strength of the alloy, while the Nb and Ti increase the yield strength of the alloys at both temperatures.

  • INVESTIGATIONS ON MAGNETRON SPUTTERED TANTALUM OXYNITRIDE THIN FILMS

    pg(s) 30-33

    Tantalum oxynitride thin solid films have been deposited by reactive magnetron sputtering, using a fixed proportion reactive gas mixture (85% N2 + 15% O2) but with varying partial pressures, onto silicon (100) wafer substrates. The physical integrity was observed after vacuum thermal annealing at temperatures from 100 °C to 800 °C. The structural evolution on the as deposited and annealed samples was obtained by X-ray Diffraction. For the lowest partial pressure, the crystalline structure is that of tetragonal β-Ta. Increasing the reactive gas partial pressure leads to the formation of fcc-Ta(O,N) crystals, with various orientations (111, 200, 220).The higher partial pressure films are amorphous. The thermal annealing induces a phase transformation, from tetragonal β-Ta to hexagonal TaNx (x<1). AFM measurements resulted in low RMS roughness values, regardless of the partial pressure or the annealing temperature.

  • INVESTIGATION OF PLASTIC DEFORMATIONS OF CARBURIZED ALLOY STEEL DURING HEAT TREATMENT

    pg(s) 34-37

    The article deals with the investigation of plastic deformations of carburized medium carbon stainless steel after quenching and tempering. After carburization the specimens were heated at 1020 °C temperature and then air quenched. At the process of air quenching the specimens were bent within the temperature dropping interval approximately from 550 °C to room temperature. The bending caused tension or compression in different parts of the specimen, so interstitial distortion was formed. As the bending stress was much lower than the yield stress, the specimen didn’t bend during the first minutes of experiment, and then started bending during the martensitic transformation (transformation plasticity effect). The curved quenched specimens then were tempered at temperatures 200, 300, 400, 500, 600 and 700 °C for 1 hour and the deflection of specimen after each tempering was measured.

    The results showed different influence of tension and compression on transformations occurring in steel during quenching and tempering. The tempering temperature effect on self-deformation of curved specimen was revealed.

  • MECHANICAL PROPERTIES OF NANOSTRUCTURED B4C/C60 AND c-BN/C60 COMPOSITES PREPARED BY HPHT METHOD

    pg(s) 38-41

    Nanostructured boron carbide/C60 (B4C/C60) and cubic boron nitride/C60 (c-BN/C60) carbon-ceramic composites were prepared by a high-energy ball milled pre-treatment of the parent materials with the addition of a CS2 solvent followed by a high-pressure/high-temperature (HPHT) treatment. Tthe elastic moduli were calculated based on the experimentally measured density and velocity values of the longitudinal and transverse bulk acoustic waves (BAW) in the specimens. The BAW velocities were measured with a pulse-echo method by laser optoacoustic excitation of ultrasonic pulses. Acoustic microscopy was used to visualize the bulk microstructure and internal defects and to measure the local values of BAW velocities of specimens on which the elastic moduli had been calculated and compared with the data defined by the pulse-echo method. The microhardness and flexural strength of the samples were measured also.

  • MICROSTRUCTURE AND THERMAL STABILITY OF 0.08%C-17.0%Cr-0.8%Ti STEEL AFTER HIGH-TEMPERATURE NITRIDING AND HIGH PRESSURE TORSION

    pg(s) 42-43

    The influence of high pressure torsion (HPT) on structure, phase composition, microhardness and thermal stability of 0.08%C-17.0%Cr-0.8%Ti steel subjected to volume high-temperature nitriding were investigated. HPT results in the formation of the nanostructure with structural elements size of 55-85 nm. Microhardness of nitrided steel after HPT increases by 2.2-2.7 times. Hardening is retained when heated to 450 °C.

  • THE COMPREHENSIVE TECHNIQUE FOR QUANTITATIVE ANALYSIS OF THE STRUCTURE IN COMPOSITE SUPERCONDUCTORS BASED ON Nb3Sn

    pg(s) 44-45

    The complex technique for study of the structure in Nb3Sn-based composite superconductors is developed. Technique is based on scanning and transmission electron microscopy on different scale levels. The possibility of using the method of focused ion beam for TEM sample preparation is confirmed.

  • INCREASE WEAR RESISTANCE HARD ALLOYS T15K6 BORIDE COATINGS

    pg(s) 46-48

    The results of studies on the application of complex boron coating powder method on hard alloys. Defined phase and chemical composition, thickness and microhardness of the coating on alloys.

    It was established that after diffusion saturation of hard alloy in boron mixture for 4 hours formed coating with boride phases TiB, WB, CoB and WC, TiC, whose thickness is 50-60 microns. At complex saturation with boron and copper for 4 hours diffusion saturation formed coating with boride phases TiB, WB, CoB and WC, TiC and separate inclusions of copper with a thickness of the diffusion layer up to 70-80 microns.

    Boriding and complex saturation with boron and copper allows in 2 – 2.5 times increase the microhardness of the surface layers of hard alloys, that in turn leads to increased wear resistance.

  • MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF TIG BIMETALLIC JOINTS

    pg(s) 49-52

    Bimetallic weld techniques have progressed a great deal in the last decade. In this work, the effect of the filler metal composition on microstructure and mechanical behavior of dissimilar HSLA-X70/304L stainless steels weld joint is investigated. The dissimilar weld joints are fabricated using austenitic, duplex and low Carbone filler metal. The mechanical behavior is investigated through microhardness, charpy impact and tensile test.

    The results show that, the weld metal composition has a great influence on mechanical properties and microstructure of weldments, in particular the grain size and phases nature, changes with filler metal composition. In addition presence of martensitic slats in the FZ when using the low Carbone filler metal, detailed microstructure examination is carried out and related to the mechanical behavior of the dissimilar joints.

  • HOT FORGING OF POWDERED Fe3Al INTERMETALLIC ALLOYS

    pg(s) 53-57

    The capabilities of powder hot forging for manufacturing of Fe3Al intermetallics and effect of forging and following thermal treatment routines on their structure and properties had been investigated. Fe3Al intermetallic powders were produced by means of thermal synthesis at 1000°С in vacuum from a mixture of Fe and Al elemental powders. Hot forging of consolidated preforms had been carried out from 1000, 1050, 1100 and 1150°С and afterwards the hot forged preforms were subjected to supplementary sintering in vacuum at 1100÷1450°С. It is foud, that thermal synthesis of Fe + 14% Al powder mixture results in formation of Fe3Al phase. Sintering of hot forged specimens result in increasing of strength and crack growth resistance, which values enhance with increasing of sintering temperature. Otherwise the hardness of hot forged intermetallics decreases after their sintering. The influence of modes of treatment on the structure and properties of the materials was investigated. It has been established that the strength and fracture toughness of the intermetallics obtained from milled blend after hot forging had the higher values as compared with the alloy made from the batch without its milling.