Materials Science Forum Vols. 706-709

Abstract: Tool damages including plastic deformation and wear are affected by forging load, thermal load and frictional slide applied to tool surface. Plastic deformation of forging tools proceeds in the tool corer owing to elevated temperature, high contact pressure and severe frictional slide. Hard layers on the tool surface increase plastic deformation resistance and thermal resistance. The optimal design of hard layer structure reduces the tool damage and improves tool life. Temperature and equivalent strain of forging tools are influenced by friction shear factor, contact thermal conductance and contact time between the tool and the workpiece. At the friction shear factor of less than 0.4, equivalent strain of the tool is reduced. At the friction shear factor of approximately 0.4 or greater, equivalent strain increases sharply and concentrates in the vicinity of the surface hard layer. This tendency becomes more significant when the contact time between the tool and the workpiece increases. Equivalent strain is reduced by low workpiece temperature.

Abstract: A superhydrophobic surface was elaborated using two inexpensive industrial processes: surface anodization in phosphoric acid and spin coating of the anodized surface by RTV silicone rubber. Scanning electron microscopy (SEM), atomic force microscopic (AFM) and water contact angle measurements have been performed to characterize the morphological features, and wettability of the surfaces. The water static contact angle of the elaborated surface reached 157 ° at room temperature. At supercool temperature (-10°C) the superhydrophobic coating showed an important delayed freezing time.

Abstract: There is a need in different industry sectors to improve the performance of material surface under corrosive environments, which cannot be fulfilled by conventional surface modifications and coatings. NiCrMoNb alloy is nickel alloy commonly used as coating in corrosive media at high temperatures. The aim of this work is to produce nickel alloy nanocomposite coatings on steel by laser cladding. They are obtained by laser melting blown powder on the steel surface. The powder precursor is obtained by mechanical milling of a NiCrMoNb alloy micropowder (20-63 μm) with yttria nanopowder (10-30 nm). A comparison between conventional nickel alloy laser cladded coating and nickel alloy with nanoparticles laser cladded coatings, regarding their microstructure, mechanical properties (hardness, wear resistance) and corrosion behavior, is established.

Abstract: CrAlN/BN nanocomposite coatings were deposited on mirror-polished silicon wafer and high-speed steel (HSS) substrates using reactive cosputtering, i.e., pulsed dc and rf sputtering of CrAl and h-BN targets, respectively. Further, the oxidation resistance of the obtained coatings was investigated. The CrAlN/BN coating exhibited superior oxidation resistance properties when compared with those of the CrAlN coatings; after annealing the sample at 800 °C in air for 1 h, the plastic hardness value of the CrAlN coatings decreased to 50% of the as-deposited hardness value; in contrast, the CrAlN/BN coatings exhibited self-hardening phenomena from 700 to 800 °C in the range of 5 to 30%. In particular, the CrAlN/18 vol% BN coatings showed an increase of approximately 30% in hardness values, and a maximum hardness value of approximately 50 GPa was reached after annealing the sample at 800 °C in air. The plastic hardness value hardly changed when the sample was annealed up to 800 ^°C in nitrogen and argon; this result was contrary to the result obtained for the sample that was annealed in air. The radiofrequency glow discharge optical emission spectroscopy (rf-GD-OES) analysis of the CrAlN/18 vol% BN coating annealed in air revealed that the coating has an oxide layer deposited on the surface to a depth of ~200 nm. Conventional transmission electron microscopy (TEM) observations of the same coating indicate that the columnar structure was disrupted by a thin layer (30–40 nm) of the coating annealed in air. The indentation hardness value of the annealed coating was measured using Ar ion sputtering before and after etching of the annealed surface. Subsequently, when the oxide layer was etched to a depth of 200 nm from the surface, the hardness value decreased from approximately 48 GPa to 43 GPa; this result was similar to the results obtained for the as-deposited coating.

Abstract: Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies and the evaluation of the corresponding induced properties as material specific volume reduction at the surface, microhardness and wear resistance. Additional remarks on the improved character of the LSP technique over the traditional “shot peening” technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

Abstract: Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl₃ was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti₂Al₅ (at 1100°C), TiAl₂ and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl₃ during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl₃ layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl₂ and Al-rich TiAl developed by solid-state diffusion from TiAl₃ layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl₂ and 292 kJ/mol for Al-rich TiAl.

Abstract: The versatile chemical spray pyrolysis was used to prepare elongated double tipped ZnO nanoparticles and microsausages on glass substrates. X-ray diffraction studies revealed several crystallographic plane orientations with the most predominant along the (002) direction. Scanning electron microscope (SEM) observations indicated double tipped nanoparticles with an aspect ratio of 4.5-8.6 which coalesced in regular patterns to form microsized sausages of width ranging up to 1.2 µm. The absorption mechanism was through direct transitions with an absorption edge corresponding to a band gap of 3.18 eV.

Abstract: For the first time it could be shown that, upon nitriding Fe-Cr-Al alloys, the thermodynamical stable cubic CrN and hexagonal AlN nitrides do not develop. Instead, a mixed Cr_xAl_1-xN nitride develops of rock-salt crystal-structure type exhibiting a Bain orientation relationship with the ferritic matrix: the Al atoms are “dragged” into the developing cubic CrN precipitates. Similar observations were made upon nitriding Fe-Cr-Ti alloys. The formation of these mixed Cr_xAl_1-xN precipitates is associated with the incorporation of large amounts of (mobile and immobile) “excess nitrogen” and the development of large residual stresses. Creep, associated with residual stress relaxation, occurs during nitriding, giving rise to complex residual stress-depth profiles.

Abstract: Arc ion plating (AIP) is one of the most attractive physical vapour deposition (PVD) method for the industrial manufacture of TiN coatings, owing to a high degree of ionization in the target material and convenient control of the process parameters. The important characteristic of hard coating is the adhesion strength between the coating layer and the substrate. The coating will be subjected to various loads, such as mechanical, thermal load, etc., in practical applications. Therefore, for more than a decade, Ti-based hard coatings have been applied to tools, dies, and mechanical parts because of the enhance lifetime and performance. It is focus on the attractive properties such as high hardness, good wear, and chemical stability. In the present study, TiN monolayer film was prepared at various N2 partial pressures and current by the AIP technique in SACM645 material. The correlation between microstructure and properties of the TiN coating was comparatively investigated by XRD, FE-SEM and AFM. These study carried steadily out improve the adhesion properties and wear resistance of Ti-based coating using pre-treatment of the substrate, insertion of an interlayer, application of multi-layers and adjustment of the process parameters. The main phase FCC TiN displayed (200) orientation in the film with the highest N₂ partial pressure. The (111) orientation was observed with decreasing N₂ partial pressure. The (200) and (111) textures in the film which was treated 80A arc current were found to be competitive orientations, however stronger arc treated the (200) texture was increased. The multilayer TiN films has possessed high hardness (up to 42Nm) and the best wear resistance among the specimens. These features were attributed to the presence of dense microstructures that were mainly composed of TiN phase around 5.16㎛ thickness, HF1 adhesion and Ra 35㎚ surface roughness

Abstract: It has been established that hardness and density of diamond-like carbon (DLC) layers can be raised by increasing ion energy during deposition, decreasing H-content and by increasing sp³-fraction. To confirm differences in hydrogen content of hydrogen containing and hydrogen free DLC films deposited at different bias voltages, layers were etched in oxygen atmosphere in a capacitively coupled plasma device. By employing real-time ellipsometry measurements, the H-content of the hydrogen containing a-C:H layers were estimated by determining the optical constants n and k (n-real part and k-imaginary part of the refractive index). In addition, DLC layers were analyzed by X-ray photoelectron spectroscopy to estimate the ratio of sp^²- and sp^³-hybridization. The mechanical and tribological properties of the coatings were evaluated by means of nanoindentation and ball-on-disc-tests. Finally correlations between these properties, H-content and sp³/sp²-ratio were obtained in an effort to explain different tribological behaviors of DLC-layers.