Powder Metallurgy and Metal Ceramics最新文献

At the beginning of the 21st century, the classical yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) reached their maximum operating temperature (1200°C). A further increase in the operating temperature and associated gain in the efficiency of gas turbine engines became possible through the complex stabilization of ZrO₂; the use of other compounds (oxides with fluorite (La₂Ce₂O₇), pyrochlore (La₂Zr₂O₇, La₂Hf₂O₇), magnetoplumbite (LaMgAl₁₁O₁₉), perovskite (SrZO₃), and other structures); and the design of functionally graded and two-layer TBCs. In the latter case, the bottom layer is mainly YSZ, whose coefficient of thermal expansion (CTE) matches that of the bound coat. Various materials with low thermal conductivity are proposed as the topcoat (an overview of the efforts focusing on the development of La₂Zr₂O₇ (LZ₂)/YSZ TBCs is presented in the first paper of the series). Two-layer LZ₂/YSZ TBCs can be successfully produced by all available application methods: atmospheric plasma spraying (APS), electron-beam physical vapor deposition (EB-PVD), spark plasma sintering (SPS), etc. The LZ₂ and YSZ phases exhibit good chemical compatibility even after sintering at 1400°C for 24 h. The mismatch in the CTEs of the layers remains a serious problem. The LZ₂/YSZ coatings demonstrate better thermal shock resistance compared to nanostructured and conventional YSZ TBCs. To produce high-quality two-layer coatings with the LZ₂ topcoat, APS parameters should be lowered to avoid lanthanum losses. Reducing the elastic modulus of two-layer TBCs is useful for decreasing the crack propagation tendency. The LZ₂ phase reduces the oxygen permeability of the ceramic coat in two-layer TBCs, thus preventing the bond coat oxidation and the rapid growth of thermally grown oxides. The twolayer LZ₂/YSZ TBCs show higher resistance to hot corrosion caused by Ca–Mg–Al silicates (CMAS) and V₂O₅+Na₂SO₄ compared to their single-layer counterparts. The doping of LZ₂ with CeO₂ increases the CTE of two-layer APS coatings, improving their efficiency. The overview of two-layer La₂Zr₂O₇(LZ₂)/YSZ TBCs confirms their advantages over single-layer ones, because each layer contributes to improving the properties and mitigating the weaknesses of the coatings, ultimately enabling higher operating temperatures and longer service lives of power equipment.

The effect of the fabrication process on the structure and tribological properties of a new antifriction composite produced from grinding waste of brass L63 with CaF₂ solid lubricant was studied. The material is intended to operate under loads up to 3.0 MPa and sliding speeds up to 2.0 m/sec in friction assemblies of screen printing machines. The fabrication process ensured the formation of a two-phase antifriction composite structure: a metallic α-brass matrix with uniformly distributed CaF₂ solid lubricant particles. Comparative tests of the new composite produced from brass L63 grinding waste with (6.0–9.0)% CaF₂ demonstrated its advantageous antifriction properties over cast brass L63. The latter corresponds to CuZn37/CW508L (EN standard) or C27200 (ASTM standard, USA) brasses, which are conventionally used in the friction assemblies of Sakurai MS-80AII, Sakurai MS-80/102SD, and Sakurai SC-72AII/102AII/112AII/142AII screen printing machines. The composite from regenerated brass L63 grinding waste containing CaF₂ solid lubricant forms an antiseizure protective film on the contact surfaces at sliding speeds up to 2.0 m/sec and loads up to 3.0 MPa through the mass transfer mechanism. The film uniformly covers the surfaces. It is smooth and continuous, and its wear and regeneration rates balance under defined speed–load conditions. This minimizes friction, resulting in the lowest friction coefficient and wear rate compared to cast brass. Analysis of the functional properties allows the antifriction composite produced from industrial grinding waste of brass L63 with CaF₂ solid lubricant admixtures to be recommended for parts of screen printing equipment assemblies operating at sliding speeds up to 2.0 m/sec and loads up to 3.0 MPa.

In the transportation, maritime and aviation industries, aluminum alloys — particularly those in the 2xxx series (Al–Cu type) — are frequently used because they offer an ideal combination of properties, including toughness, a high strength-to-weight ratio and fatigue resistance. Graphene, a two-dimensional material with a single-atom thickness composed of carbon atoms arranged in a hexagonal lattice, attracts interest due to its remarkable properties and is commonly utilized as a reinforcement in composite materials. Few-layered graphene (FLG) reinforced Al–4 wt.% Cu matrix composites were prepared via mechanical alloying (MA, 500 rpm, ball-to-powder ratio 7 : 1), uniaxial pressing (300 MPa), and conventional sintering (59°C, 3 hours, argon gas flow). The present work investigates corrosion behaviors of FLG (0.25 and 0.5 wt.%) reinforced Al–4 wt.% Cu composites with different MA durations. Open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements were carried out in a 3.5% NaCl solution to determine the corrosion behavior. Following the corrosion test, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis were performed on the specimen that exhibited the optimum results. The data obtained before and after the test were compared to investigate the structural changes that occurred as a result of the corrosion test. The analysis demonstrated that the sample reinforced with 0.5 wt.% FLG and subjected to 7 hours of MA had the highest corrosion resistance.

The paper examines the effect of spraying parameters and production features of the nickel-clad NPG-75 graphite powder on the structure and chemical composition of plasma coatings. The starting NPG-75 powder consisted of graphite (25 wt.%) and a nickel shell (75 wt.%). During plasma spraying of the NPG-75 powder, the graphite content of the resulting coatings significantly reduced and did not exceed 4 wt.%. Several possible reasons for the reduction in graphite content of the coatings were considered. The influence of spraying parameters was studied using powder produced by the rolling process. This powder consisted of conglomerated graphite particles coated with nickel. In the spraying of coatings from the clad conglomerated powder, variations in plasma torch power from 20 to 29 kW and spraying distance from 80 to 300 mm did not have a significant effect and did not increase the graphite content of the coating. At powers below 20.4 kW, NPG-75KP coatings could not be formed. The optimal spraying parameters were found to be a plasma torch power of 24–25 kW and a spraying distance of 160 mm. Under these parameters, the graphite content of the coating reached a maximum of 5.3 wt.%, which was still much lower than in the starting powder (25 wt.%). The best results were shown by plasma coatings from the NPG-75 composite powder material produced without rolling but by direct cladding of solid graphite grains. Even though the quality of the nickel shell produced via autoclave cladding was lower, the graphite content of the resulting coating reached approximately 24 wt.%. The optimal spraying parameters remained the same as for the conglomerated NPG-75 powder. The research confirmed the critical importance of the methods employed to prepare the starting material for preserving the graphite content of plasma-sprayed Ni–C composite coatings.

The first part presented a comprehensive review of experimental studies on various types of impregnated WBa and ScBa cathodes (WBa-ICs and ScBa-ICs), used to develop thermionic emission models intended to clarify the mechanisms whereby CaO and Sc₂O₃ oxides and platinum-group metals influence cathode emission. The second part analyzes the proposed polarization WBa-IC and ScBa-IC thermionic emission model for the first time from the standpoint of G.V. Samsonov’s configurational model. The new polarization model differs from existing ones in that it incorporates donor–acceptor interactions between valence orbitals of adatoms within the emission–adsorption layer and between these adatoms and adsorbent atoms, initiated by changes in the energy stability of valence orbital configurations. According to the proposed polarization WBa-IC and ScBa-IC thermionic emission model, the electron work function is determined by the potential barriers of polarized dipole complexes of two types. These complexes result from donor–acceptor interactions between adatoms themselves and between adatoms and adsorbent atoms, Ba(Ca, Sc)⁺–O^––A⁺, and from those between adsorbed oxide molecules and adsorbent atoms, Ba⁺O^– (Ca⁺O^–)–A⁺, (Ba⁺O^––Sc^–₂O^–₃–Al⁺₂O^–₃)–A⁺, and (Ba⁺O^––Sc^–₂O^–₃–W⁺O^–₃)–A⁺. In both types, the bond between the adsorbate and the adsorbent is mediated by oxygen, acting as the electron acceptor. The characteristics of these interactions are defined by the energy stability of valence orbital configurations, d⁰, d⁵, and d¹⁰ for d-metals and s², sp³, and s²p⁶ for sp-elements, and their donor–acceptor capability. The new polarization WBa–IC and ScBa–IC thermionic emission model explains the effects of doping with CaO and Sc₂O₃ oxides and with platinum-group d-transition metals on cathode emission. Although the results are only qualitative, they are mutually consistent and correlate with emission characteristics. The simplicity of interpretation makes G.V. Samsonov’s configurational model suitable for examining charge-transfer interactions in adsorbate–adsorbent systems.

The brazing of dissimilar materials, despite significant progress in the field, still requires fundamental physical, chemical, and technological research and necessitates improvements to existing brazing processes and filler alloys and the development of new multicomponent alloys, metallization coatings, and methods for their application. An option for improving the wetting of nonmetallic materials by filler melts that do not wet ceramic surfaces includes their metallization with adhesion promoters deposited by friction-induced rubbing. Three new types of titanium tools for rubbing nonmetallic surfaces, using a porous sponge-like structure or foil of VT1-0 titanium with a thickness of 0.07–0.10 mm, were proposed and fabricated. This approach is intended to reduce both the force separating the metallizing particles from the tool and the rigidity of the contact interaction. A device was developed for argon purging of the ceramic surface during air metallization. The purging operation in the metallization process significantly improves brazing by lowering the wetting onset temperature and reducing the amount of titanium oxides in the brazed joint. Samples of high-alumina A995 and VK94-1 ceramics were metallized by the proposed method. The wetting of these ceramics with PSr72 filler alloy (copper–silver eutectic) was studied, brazed joints were produced, and the microstructure of the metal–oxide interface was analyzed. Microstructural analysis revealed that the PSr72 melt permeated the titanium coating, became saturated with titanium, and wetted the ceramic surface. This indicates that this metallization method does not require a dense coating and accelerates the saturation of the melt with titanium. The surface roughness of nonmetals was found to influence the composition and microstructure of the coating deposited in air. As surface roughness decreased, both the coating density and oxidation increased. The primary role of friction-induced metallization is to deliver titanium into the filler melt. The advantages of rubbing nonmetallic materials with a porous titanium sponge or foil, compared to tools made from compact titanium, were indicated. The best results were showed by the porous titanium tool.

Aramid fibers, with their excellent mechanical properties and thermal stability, face limitations in tribological applications due to surface inertness. In this study, aramid fibers were modified with the silane coupling agent KH550. Subsequently, composites containing different amounts of nano-BN (ranging from 0 to 2.5%) were prepared using an epoxy resin matrix and an aramid fiber via the vacuum infusion process. FTIR confirmed successful fiber modification, showing new peaks at 2925, 2852, and 3310 cm^–1 from methylene, methoxy, and amino groups, respectively. The incorporation of nano-BN was confirmed by SEM-EDS through the detection of B and N elements. Tribological tests on an MFT-3000 tester under 100 N load, 10 Hz frequency, 1 mm wear distance, and 15 min duration revealed optimal performance at 0.5 wt.% nano-BN. SEM results showed the COF of ~0.4 and wear rate of 6.2∙10^–10 m³∙(N∙m)^–1, attributed to a stable transfer film reducing direct contact. However, as the BN content increased, the agglomeration of nano-BN became more severe. This agglomeration led to an elevation in both the wear rate and the COF. Besides, the load and friction speed had a significant impact on the friction and wear performance of the composites, with higher speeds increasing the rate of wear and the volatility of the coefficient. The primary wear mechanism was identified as adhesive wear. Nano-BN played a crucial role in facilitating the formation of a transfer film by enhancing the wear resistance of the composites and effectively decreasing the COF.

The corrosion resistance of compact materials and composite coatings in the (TiB₂–SiC)–(Ni–20% Cr) system was studied in a 3% NaCl solution simulating seawater using potentiodynamic polarization curves. Both the compact materials and the composite coatings in the (TiB₂–SiC)–(Ni–20% Cr) system exhibited high corrosion resistance in aggressive environments. It was established that the corrosion resistance of the coatings in a 3% NaCl solution could be significantly increased by adjusting its composition: specifically, by reducing the nickel content and increasing the TiB₂–SiC content. The starting materials for spraying were (TiB₂–SiC)–x(Ni–20% Cr) powders with x = = 20, 30, and 40 wt.%. Coatings were deposited onto Steel 3 substrates by detonation and plasma spraying. For detonation spraying (Dnipro-5M installation), composite powders with a particle size fraction of −63+40 μm were used. Plasma spraying (UPU-3D installation) employed powders with a size fraction of −120+63 μm. The spraying process proceeded with a mixture of argon and hydrogen as plasma-generating gases in an open atmosphere. The results demonstrate the feasibility of using detonation- and plasma-sprayed coatings in the (TiB₂–SiC)–(Ni–20% Cr) system with enhanced properties in mechanical engineering and aerospace applications.