Solid State Phenomena Vol. 227

Abstract: This work presents an investigation of tribocorrosion properties of titanium matrix composites (TMCs) reinforced with non-oxide ceramic nanoparticles. The evaluated materials were manufactured by selective laser melting technique (SLM). As a matrix titanium and as a reinforcing phase TiC nanoparticles were used. For SLM process the mixtures of the powders composed of 0, 1, 5, 10, and 20 vol % of nanocrysalline titanium carbide (nc-TiC) were prepared. The influence of the reinforcements on the tribocorrosion properties of TMCs manufactured by SLM process was examined. Tribocorrosion “ball on disc” tests in Ringer's solution and under ambient dry conditions were carried out. It was shown that nanocomposite consisted of 20 vol.% of nc-TiC characterized by the best wear and tribocorrosion resistance.

Abstract: The carbide coatings are widely used for wear and erosion protection of different materials. In present paper the WC/Co coatings were deposited by a single-cathode Sulzer Metco F-4 plasma gun. The microstructure and thickness measurements were conducted. The erosion test was conducted using a Koechler Air Jet Errosion tester at the temperature of up to 500^oC. The procedure was similar to ASTM G76 standard. Changes in erosion resistance of coating into different temperature were observed.

Abstract: The researches have concerned cavitation erosion of AlSi7Mg and AlSi11Mg aluminium casting alloys. The alloys have been investigated in the as-cast condition and after the precipitation hardening. The cavitation erosion tests were performed using vibratory cavitation erosion equipment in 5 minutes. Resistance to cavitation of tested materials was estimated by means of MDE (mean depth of erosion) parameter according to ASTM G32. After the cavitation tests eroded surface of the specimens has been observed by means of scanning electron microscopy. The roughness of the surface was measured on profile contact tester. The best resistance for cavitation erosion exhibited AlSi7Mg alloy after heat treatment, the weakest AlSi11Mg alloy in as-cast condition.

Abstract: The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1 to 3.5.10^-7 cm².s^-1) were observed during the first build up transient; the value of 3.5.10^-7 cm².s^-1 corresponded to 10% tensile deformation. During the 2^nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1^st and 2^nd build up transients. In all studied states, a rather high sub-surface hydrogen concentration was observed during the 1^st build up transient rising to 12.6 ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

Abstract: Effect of small addition of tin (1.7 at.%) into LaNi_4.5Co_0.5 alloy on gas phase and cathodically charged hydrogen absorption ability as well as its corrosion resistance in 6M KOH solution is discussed. To reveal the effect of Sn doping three alloys have been selected: LaNi_4.5Co_0.5 (precursor), LaNi_4.5Co_0.5Sn_0.1 and LaNi₅ - as a parent compound. The room temperature p-C isotherms indicate to beneficial effect of Sn addition which causes decrease of H₂ equilibrium pressure and does not limit atomic hydrogen solubility. Discharge capacities (Q_disch), exchange current densities of H₂O/H₂ system () as well as corrosion rates () have been determined for the tested alloys on the basis of cyclic galvanostatic measurements (at –0.5C/+0.5C rates). It has been shown that for N > 3 cycle the discharge capacity of LaNi_4.5Co_0.5 is ca twofold greater than that for LaNi₅ reference. Addition of 1.7 at.% Sn into Co-containing alloy expands the discharge capacity by 30-40%. The Co containing alloys reveal twice as great exchange current densities of H₂O/H₂ system compared to LaNi₅, however, Sn addition slightly decreases the , especially for latest cycles. The partial cobalt substitution for Ni accelerates alloy corrosion in alkaline solution, however, tin addition fully eliminates this effect.

Abstract: The paper presents results of research undertaken to determine the influence of hydrogen on passivity and corrosion resistance of 2507 super duplex stainless steel welded joints. Butt welded joints were made with low heat input using flux corded arc welding (FCAW) method. Coupons of 5.0 x 5.0 mm were cut from the welded joints containing weld metal (WM), heat affected zone (HAZ) and parent metal (PM). Hydrogen was introduced into the samples by cathodic current method under galvanostatic condition at room temperature. Corrosion resistance was qualified with the polarization curves registered in synthetic sea water. Electrochemical hydrogen charging affected the native passive layer. The internal hydrogen shifted corrosion potential to the more active direction and cause an increase in corrosion current density. The corrosion sensitivity increases for higher current density applied during hydrogen charging. Weld metal area has been revealed as the most sensitive to corrosion attack.

Abstract: The present paper aims at explanation of the advantageous role of partial substitution of iron by cobalt in Nd-Fe-B magnet for distinct inhibition of mechanically assisted corrosion phenomena. The hydrogen uptake by Nd₁₆Fe₇₆B₈ and Nd₁₆Fe₅₆Co₂₀B₈ sintered materials have been compared with the use of charge/discharge method in terms of the alloys corrosion behavior in strong alkaline solution. For initial cycles, the hydrogen discharge capacity of Co-containing alloy is 5-10 times lower than that for the Nd₁₆Fe₇₆B₈ reference alloy. After 6-7 cycles both alloys reveal comparable hydrogen capacity. Also the plots of polarization curves testify to comparable corrosion resistance for both materials. The unusual resistance of Nd₁₆Fe₅₆Co₂₀B₈ sinter to pulverization should be ascribed to strong inhibition of hydrogen absorption at initial steps of corrosion process.

Abstract: The presented paper discusses a possibility of developing and modifying surface of nickel substrate by applying of Ni, Pt, Pt/Ni porous metallic layers by zol-gel method using EDTA as a complexing agent. Then gel containing Pt or Ni or Ni/Pt was decomposed during pyrolysis process and then transformed into the porous metal during oxidation/reduction process at 600°C respectively in air or H₂ atmosphere. The thermal decomposition of gels were studied by TG/DTA method. Compositions of oxidized as well as metallic layers were determined by EDX and XRD method. The morphology of Pt, Ni and Pt/Ni layers were studied by SEM method.

Abstract: This paper studies inhibition of steel-rebar corrosion in concrete immersed in 0.5 M H₂SO₄, simulating industrial/microbial environment by the leaf extract of Morinda lucida. Electrochemical monitoring methods were employed for testing different concentrations of the leaf extract admixed in duplicated specimens of steel-reinforced concrete slabs immersed in the acidic test-system. Statistical analyses as per ASTM G16-95 R04 of the experimental results showed that effectiveness of Morinda lucida at inhibiting concrete steel-rebar corrosion increased with the concentration of the admixture. 0.4167% Morinda lucida, per weight of cement, was identified with optimum inhibition efficiency η = 98.78±0.34% followed in effectiveness by 0.3333% Morinda lucida with η = 93.20±1.76% at inhibiting steel-rebar corrosion in the corrosive test-environment.

Abstract: Biofilms formed by various microorganisms are often responsible for microbiologically induced corrosion of materials exposed to moisture. Many bacteria strains may form biofilms on different mineral materials including concrete and stoneware. Among them, the sulfur-oxidizing bacteria of Acidithiobacillus genus, especially of A. thiooxidans species play an essential role in these materials' destruction. In the present study we observed comparable intensity of A. thiooxidans growth on concrete and glass, and slower biofilm formation on stoneware. Prolongation of incubation time caused an increase in biomass of A. thiooxidans biofilm formed on glass and stoneware. Amongst the investigated mineral materials, the concrete proved to be the most susceptible to deterioration by A. thiooxidans bacteria.