High strength low-alloyed (HSLA) Cr-Mn-Si steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Those properties depend both on the temperature and time of tempering. Knowing the tempering parameters, it is possible to reach the desired properties of the treated steel. Some results on investigating the Hollomon-Jaffe equation (in parametric form) application for tempering of HSLA steel, are shown in this paper. The experiments were performed in real production conditions, using a standard material. The quenching was performed at 870 °C, the heating period was always 30 min, with subsequent cooling into the oil bath. The tempering was carried out in temperature range from 480 to 680 °C, while tempering time varied from 15 min to 24 h. The degree of tempering is referred through the hardness values changing. The experimental results have shown a pretty well agreement to tempering parameters, included in Hollomon--Jaffe equation, for this kind of HSLA steel.Quenched steels, from a group of heat-treatable steels, always have high values of both hardness and strength, but pretty low values of impact properties. The residual stresses are also on a high level. So, any kind of tempering has to be done -depending of the steel type. However, the tempering [1-4] is provided in a wide temperature range (even up to Ac 1 point), and then a wide diapason of structures will appear: from the untransformed martensite (with differrent amounts of retained austenite) to the structure, which contains carbide globules into ferrite matrix.Although the tempering temperature shows a dominant influence on the structure changes, the tempering time also has a strong influence but is usually less investigated. One more reason for investigating the tempering time is a fully diffusion character of all processes which are involved in tempering processes [1,4]. In relation with the processes mentioned, many efforts are still made to find out one proper parameter, which will include both the temperature and time of tempering. Only in that way, i.e., on the equivalency of a simultaneous influence of tempering temperature

Hydroxyapatite is a widely used bioceramic material in implant coatings research because of its bioactive behavior when being deposited onto the metallic implant and compatibility with the human bones composition. The coating of nanosized hydroxyapatite was electrophoretically deposited on a blasted surface of stainless steel 316LVM samples at constant voltage, for different deposition times and subsequently sintered in both, vacuum and argon atmosphere, at 1040 and 1000 °C, respectively. Although sintering temperatures needed to achieve highly dense coatings can cause HAp coating phase changes, the possibility to obtain a bioactive coating on 316LVM substrate, without the coatings phase changes due to the nature of the used stoichiometric nanostructured hydroxyapatite is presented in this work. The thermal stability of the used HAp powder was assessed by DTA-TG analyses over the temperature range of 23-1000 °C, i.e., at the or nearby experimental sintering temperature. The microstructure characterization was accomplished using SEM, while phase composition was determined using XRD.

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Polygonal Pt nanoparticles were synthesized using ultrasonic spray pyrolysis (USP) at different precursor concentrations. Physicochemical analysis of the synthesized Pt particles involved thermogravimetric, microscopic, electron diffractive, and light absorptive/refractive characteristics. Electrochemical properties and activity in the oxygen reduction reaction (ORR) of the prepared material were compared to commercial Pt black. Registered electrochemical behavior is correlated to the structural properties of synthesized powders by impedance characteristics in ORR. The reported results confirmed that Pt nanoparticles of a characteristic and uniform size and shape, suitable for incorporation on the surfaces of interactive hosts as catalyst supports, were synthesized. It is found that USP-synthesized Pt involves larger particles than Pt black, with the size being slightly dependent on precursor concentration. Among ORR-active planes, the least active (111) structurally defined the synthesized particles. These two morphological and structural characteristics caused the USP-Pt to be made of lower Pt-intrinsic capacitive and redox currents, as well as of lower ORR activity. Although being of lower activity, USP-Pt is less sensitive to the rate of ORR current perturbations at higher overpotentials. This issue is assigned to less-compact catalyst layers and uniform particle size distribution, and consequently, of activity throughout the catalyst layer with respect to Pt black. These features are considered to positively affect catalyst stability and thus promote USP synthesis for improved properties of host-supported Pt catalysts.

Hybrid nanomaterials based on manganese, cobalt, and lanthanum oxides of different morphology and phase compositions were prepared using a facile single-step ultrasonic spray pyrolysis (USP) process and tested as electrocatalysts for oxygen reduction reaction (ORR). The structural and morphological characterizations were completed by XRD and SEM-EDS. Electrochemical performance was characterized by cyclic voltammetry and linear sweep voltammetry in a rotating disk electrode assembly. All synthesized materials were found electrocatalytically active for ORR in alkaline media. Two different manganese oxide states were incorporated into a Co3O4 matrix, δ-MnO2 at 500 and 600 °C and manganese (II,III) oxide-Mn3O4 at 800 °C. The difference in crystalline structure revealed flower-like nanosheets for birnessite-MnO2 and well-defined spherical nanoparticles for material based on Mn3O4. Electrochemical responses indicate that the ORR mechanism follows a preceding step of MnO2 reduction to MnOOH. The calculated number of electrons exchanged for the hybrid materials demonstrate a four-electron oxygen reduction pathway and high electrocatalytic activity towards ORR. The comparison of molar catalytic activities points out the importance of the composition and that the synergy of Co and Mn is superior to Co3O4/La2O3 and pristine Mn oxide. The results reveal that synthesized hybrid materials are promising electrocatalysts for ORR.