Key Engineering Materials Vol. 641

Abstract: The hereby work presents the influence of microstructure on the tribological properties of medium carbon heat-treatable steel. These steel is used for various elements of which in addition to high wear resistance a high plasticity is required. For tested steel there different heat treatments were performed in order to obtain the different microstructure and properties. Each sample was hardened from the same temperature, which has been selected on the basis of standards for these steel and it was equal 890 °C. Two samples were quenched after austenitising in water. After quenching one of the samples was cooled in liquid nitrogen for 30 minutes (sub-zero treatment). After that these two samples were tempered in the preheated furnace at 200 °C for 2 hours. The third sample immediately after austenitising was quenched in mixture of molten salts heated to 200 °C (fused salt quenching). After these three carried out heat treatments the various microstructures were obtained with preserved high hardness. After heat treatment samples for the tribological test were prepared. The test was performed using the T-05 type roll-block test machine. This type of test machine is used to obtain the resistance to friction wear of metals and others. Thanks to these tribological tests and mass loss measurements the best heat treatment, which significantly increase of the wear resistance for tested steels was indicated.

Abstract: The subject of investigations constituted the G200CrNiMo4-3-3 cast steel applied for metallurgical rolls. This is the material, which microstructure can be modified by the heat treatment. The presented hereby work concerns the initial state (as cast condition) of the investigated cast steel. This cast steel constitutes the initial material for the heat treatment. The morphology of carbide precipitates, including the cementite precipitated on grain boundaries of the primary austenite, hypereutectoid cementite precipitated in the Widmannstӓtten system and lederburitic cementite, were characterised in the study. The results of investigations of mechanical and fractographic properties of the G200CrNiMo4-3-3 cast steel, were also presented. Among others, the values of fracture work in the impact test, fracture toughness (K_Ic) and wear resistance were given. The crack pathway together with the hypereutectoid cementite fraction role in its development, was presented. The obtained investigation results, presented in the hereby paper, will constitute the comparison base for the assessment of the heat treatment influence on the microstructure and properties of the tested G200CrNiMo4-3-3 cast steel.

Abstract: Attempts have been made to describe the influence of copper infiltration on properties of HSS based composites with different iron additions. Iron powder were used to reduce price of composites. The powder compositions used to produce skeletons for further infiltration were M3/2, M3/2 + 7,5%Cu, M3/2+20%Fe and M3/2+50%Fe. The powders were cold pressed at 800 MPa. These as-pressed specimens were used for direct copper infiltration.

Abstract: Ni-Sn alloys show excellent properties having considerable technological interest. Commercial codeposition of nickel with tin is usually carried out from acidic fluoride-chloride electrolytes, but these are intended to replace by less aggressive baths. In this work codeposition of Ni-Sn alloys from acidic solutions containing sodium gluconate as a cheap and nontoxic complexing agent was carried out. The electrodeposition process was studied using various electrochemical techniques. Cathodic polarization curves have shown that tin (II) ions were reduced under limiting current. Chronoamperometric studies indicated nucleation of the alloys according to the instantaneous mechanism. Equilibrium speciation of the baths was also calculated. Chemical and phase composition as well as morphology of the coatings were investigated. Corrosion resistance of the alloys was also studied.

Abstract: Alloy electrodeposition with superimposed uniform magnetic field leads to Lorentz force generation. The Lorentz force is a factor which is able to modify the deposit structure, its texture, morphology and magnetic properties. The objective of the presented research was to show the composition, morphology and the surface roughness development of Fe-Ni binary alloys electrodeposited under the influence of the uniform magnetic field. The applied magnetic field caused increase of the paramagnetic element content in the alloys. The surface roughness decrease with an external magnetic field application was observed.

Abstract: The surface tension of the liquid ternary Cu-Pb-Fe alloys at the constant content of copper (X_Cu=0.9)-refractory material Al₂O₃-gaseous phase was determined. The experiments were performed in the range of temperature between 1100 and 1350 °C at the different content of lead and iron (X_Fe/X_Pb+X_Fe). The surface tension was determined by sessile drop method. The composition of the investigated alloys corresponds to the composition of the Cu-Pb-Fe alloys obtained via the reduction of the slag obtained during the direct-to-blister flash smelting process in an electric furnace. Images of the liquid drops were made using the X-ray technique and the surface tension values were calculated using the corresponding software programs.

Abstract: In this work the electrical conductivity of molten sodium cryolite solutions (Na₃AlF₆) and potassium cryolite solutions (K₃AlF₆) containing different contents of aluminum fluoride were investigated. Experiments were carried out in a temperature range including the liquid phase, using electrochemical impedance spectroscopy (EIS). Based on the conducted studies, it was found that the electrical conductivity of the studied electrolytes decreases with decreasing temperature and increasing content of aluminum fluoride. It was also found that in the temperature range in which the studied salts are in the liquid state, the solutions of potassium cryolite have lower electrical conductivity than the solutions of sodium cryolite.

Abstract: The modern high voltage power overhead lines operate with high temperature low sag (HTLS) conductors due to possibility of the current capacity increase. HTLS conductors are material and technological advanced solutions. The main advantage of HTLS conductors is a special designed operation conditions which cause the transformation of tensile stresses from the external aluminium base layers to the core. The conditions of this transformation are called “knee point” because a rapid change of the conductor sag - temperature relationship is observed. Prediction of conditions of the “knee point” temperature (KPT) is a key problem during overhead line design. The KPT is a function of different factors like conductor materials properties, conductor design, span parameters, sagging procedures and overhead line exploitation conditions. The paper presents an original theoretical model for HTLS conductors KPT calculations and shows some examples and comparisons of the different conductor designs and parameters.

Abstract: The study relates to a process of continuous rotary extrusion (CRE), also known under the name of a Conform Process. This method is used more and more extensively for the plastic working of metals and alloys. In CRE, the feedstock is fed into a profiled groove on the rotating extrusion wheel and is pressed by the pressing wheel. The friction of the extruded material against the rotating wheel generates a force that is pushing the material into the deformation chamber followed by extrusion through the die orifice. The extrusion by CRE was performed on an MC-260 device supplied by Meltech-Confex and installed at IMN - OML for processing of the 6063 aluminium alloy. The feedstock was composed of annealed rods. Two parameters were controlled during extrusion: the temperature of the shoe (element of the housing pressing the extruded material to the wheel) and the speed of the driving wheel. The 6063 alloy was extruded using the wheel speed of 2, 5, 10 and 15 rpm and the shoe temperature of 90°C and 105°C. The extruded flat sections were examined visually for continuity and quality of the resulting surface. In the feedstock rod and in the extruded flat sections (before and after heat treatment), the microstructure and grains were examined by light microscopy. Mechanical properties were also determined (static tensile test and hardness measurement). The study shows how the structure and the mechanical properties of the extruded flat sections are changing depending on the extrusion parameters applied. From the 6063 alloy rods extruded by CRE, flat sections of satisfactory quality were obtained. It was found that CRE yields the highest mechanical properties combined with the correct structure and high surface quality when the feedstock is extruded with the wheel rotational speed of 10 rpm and the shoe temperature of 105°C.

Abstract: The paper presents the results of a complex study of the Ti-6Al-4V alloy, conducted with the application of the dynamic material modelling (DMM) method, in a wide range of temperatures, strain rates and strains. A compression test was carried out in a wide range of temperatures (800 – 1100°C) and strain rates (0.01 – 100 s^-1), up to the constant final true strain value of 0.9. The obtained stress-strain curves were a basis for determining deformation activation energy with the use of an Arrhenius plot and a correlation between the Zener-Hollomon parameter and flow stress, for which the constitutive equation proposed by Sellars was used. The power dissipation efficiency parameter was calculated. The maps of power dissipation as the function of temperature and strain rate were plotted in the form of the isoclines of the power dissipation efficiency parameter expressed in %. The processing maps exhibited the range of occurrence and recrystallization of the primary α phase, the degree of the β phase recrystallization progress against the background of the process deformation windows and instability flow domain. An analysis of the influence of process parameters up on the microstructure and hardness changes was conducted.