Powder Metallurgy and Metal Ceramics最新文献

The effect of plasma spraying parameters on the adhesion and porosity of metal ceramic coatings from clad (Ti, Cr)C–Ni composite powders was studied. The coatings were produced by atmospheric plasma spraying (APS) using a mixture of argon and hydrogen as plasma gases. The arc voltage and current were chosen as variable parameters for controlling the spraying distance and argon flow rate. The 40–80 μm (Ti, Cr)C-based composite powders clad with 17, 25, and 33 wt.% Ni were used to produce the plasma coatings. The microstructure, porosity, and adhesion of the coatings were studied to assess their quality. Optimal plasma spraying modes were determined for each powder. Plasma spraying should be conducted at an electric arc power of 27–29 kW. An increase in the power caused the nickel layer on the (Ti, Cr)C particles to evaporate and degrade, resulting in reduced coating uniformity, increased porosity, and decreased adhesion. The density and adhesive strength of the coatings improved as nickel content of the (Ti, Cr)C–Ni composite power increased from 17 to 33 wt.%. It was found that 17 wt.% Ni in the (Ti, Cr)C–Ni composite powders was not sufficient for producing high-quality plasma coatings. The (Ti, Cr)C–33 wt.% Ni coating had the highest adhesion (38 ± 1.5 MPa) and lowest porosity (7–8%).

The evolution of stress-strain state and the distribution of temperature and relative density throughout a porous workpiece subjected to hot extrusion forging to produce axisymmetric parts with an axial hole was studied by computer simulation. The hot forging process was modeled using the finite element method employing the DEFORM 2D/3D software package. Analysis of the simulation results showed that the region of strains, stresses, and relative densities formed under the conical protrusions of the punches in the initial stages of the process, and these parameters decreased radially from the center of the workpiece to its periphery. As the axial strain increased with further deformation, the region of elevated stresses and densities extended deeper into the material, spreading from the center of the workpiece to its periphery. In the final stage, after the die cavity was filled with the forged material, the relative densities and stress intensities averaged over the workpiece, while the strain intensity noticeably decreased in the radial direction from the center to the periphery following additional compaction. This was explained by the deformation that occurred in the final stage when the forged material filled the pore volume in the additional compaction process after the die cavity was filled. The forging force increased sharply when the die cavity was filled fully and the material underwent additional compaction but increased monotonically in the initial stages of the process.

Simulation modeling results for powder mixtures comprised of saponite and stainless steel powders are presented. A literature review focusing on methods for modeling the filling and production of powder materials in technological processes was conducted. Computer modeling employed to examine the behavior of particulate mixtures in two-dimensional and three-dimensional planes, considering their volumetric characteristics, was studied theoretically. The properties of AISI430 steel and saponite powders, such as grain-size composition and sphericity factors, were studied experimentally. The density of workpieces made from steel and saponite powders for modified and unmodified powder particles was calculated as percentage. A method for calculating the distribution of particles and determining the density of workpiece layers using the ImageJ2x software was proposed. Image stacks were generated and image series were analyzed using object mask functions and threshold and image inverter brightness threshold functions. The processed microscopy data enabled the determination of void percentage within the visible areas of the samples. A simulation model was proposed to describe the formation of powder materials with varying geometries and sphericity. The process of filling a cylindrical container with the powder mixture was simulated. A 3D computer model was developed to visualize the formation of a two-component powder mixture using the Blender 3D application software. Maps depicting the distribution of powder particles in selected planes were constructed.

Hydrated γ-, γ’-, θ-, and κ-Al₂O₃ powders were precipitated with nitric acid, HNO₃, from Na[Al(OH)₄] alkaline solutions at pH = 5.0–5.5. Waste materials from α-B₁₂Al and B₁₂(C–Al–C) laboratory production were used. The precipitates were rinsed and dried at 420 → 570 K (S_{specific BET} = 213 m² ⋅ g^–1, d_{CSD crystallites} ≈ 10 nm, and d_{SEM agglomerates} ≈ 200 nm). The samples were characterized by X-ray diffraction, X-ray diffractometry in the coherent scattering domain (CSD), fluorescence analysis, scanning electron microscopy (SEM), chemical elemental and phase analyses, and thermal desorption of nitrogen calculated by the BET method (S_{specific BET}) for interpreting surface measurements of nonporous bodies. The concentrations of gas-forming elements (hydrogen, nitrogen, oxygen, and carbon) were determined by reductive and oxidative extraction in helium and oxygen flow, gas chromatography, and coulometry. The multiphase γ-, γ’-, θ-, and κ-Al₂O₃ samples treated at 1370–1470 K in air exhibited an α-Al₂O₃ structure. According to X-ray diffraction in hkl₀₁₂ CSD, the α-Al₂O₃ crystallites had d_CSD ≈ 48 nm. Based on SEM analysis, the sizes of the α-Al₂O₃ powder agglomerates did not exceed d_SEM = 200–300 nm. The specific surface area of the powder, S_{specific BET}, determined by thermal desorption of nitrogen calculated with the BET method, was equal to 8.6 m² ⋅ g^–1. The weight content of α-Al₂O₃ was 99.69%, while SiO₂ impurities accounted to 0.31%, according to X-ray fluorescence analysis. The crystallites, as components of the alkaline γ-, γ'-, θ-, κ-Al₂O₃, and α-Al₂O₃ powder agglomerates, showed a lamellar shape. The thickness of the lamellas was close to the calculated d_CSD values for crystallites. The submicron γ-, γ’-, θ-, and κ-Al₂O₃ particles had a ‘sandglass’ shape, determined by the dynamics of precipitating flat crystallites of the Al(OH)₃ solid phase (nanosized thickness) as pH decreased. The α-Al₂O₃ agglomerates consisted of fused local particles connected by bridges.

Fine gas-atomized powders of R6M5K5 tool steel were studied. The spherical powders were produced with two distinct melting procedures, each involving spraying under different modes: at a conventional pressure of 0.6 MPa used to make powders of this steel and a calculated pressure of 2 MPa. To obtain a fine-sized fraction, the powders were sieved through a wire mesh with 50 μm square openings, and the content of this fraction was calculated for each of the two powders. The powders with particle sizes greater than 50 μm were subsequently ground and additionally sieved through a 50 μm mesh. Four types of powders with particle sizes below 50 μm were produced using this method. They varied in particle size distribution and particle shape. Mechanical tests were performed with the powders of this size fraction. The equivalent particle diameter distribution, morphology, and changes in elemental composition of the powders were studied. Distribution characteristics, including d₁₀, d₅₀, and d₉₀, were calculated. The arithmetic mean of flat particle projections was slightly higher for the powder atomized employing the conventional mode (0.6 MPa), measuring 0.914 compared to 0.901 for the powder particles atomized under the calculated mode. The yield of the <50 μm fraction was lower (6 and 55 wt.%, respectively). After grinding, the roundness of both powders decreased, resulting in more complex shapes. The relative bulk density, relative tapped density, and flowability of the powders decreased as the roundness factor reduced. An attempt to classify the tool steel powders using the Hausner ratio and Carr index, commonly applied to pharmaceuticals and some metal powders to evaluate their flowability, indicated that the potential application of this classification required further verification. The flowability of the studied powders correlated well with the magnitude of the repose angle.

A new technique for producing powders from the electron-beam CoCrAlYSi alloy (MZP-11 grade) is proposed. The method includes step-by-step grinding of the alloy employing a press and a two-roll vertical mill. The energy consumed to produce these powders is almost one-seventh the energy consumed in conventional methods (crushers, mills) and within one-twentieth that in spraying methods. The chemical and phase composition and structure of the CoCrAlYSi powders were studied. The proposed grinding method allowed the production of powders that corresponded to the starting alloy in terms of chemical composition and structure. The powder particles had polyhedral shape, being close to round, were quite uniform in size, and almost completely preserved the microstructure of the starting CoCrAlYSi alloy. Grinding the alloy led to a slight increase in the content of some impurities in the 40–100 μm powders; in particular, the amount of oxygen increased from 0.05 to 0.08–0.09 wt.% and that of carbon from 0.06 to 0.08–0.1 wt.%. According to the chemical composition and technical characteristics, the powders comply with technical specifications for plasma deposition of two-layer thermal-barrier metal/ceramic coatings. The outer ceramic topcoat is formed with the participation of yttria-stabilized zirconia of at least 99.5 wt.% purity. The coating thickness is controlled by technical documents and is 135–225 μm for the metal layer and 80–120 μm for the ceramic layer. The developed metal powders are used to deposit thermal-barrier coatings on various types of gas turbine blades. The structure and composition of a two-layer thermal-barrier coating produced by plasma spraying of the CoCrAlYSi alloy and ZrO₂– Y₂O₃ ceramic powders were studied.

The (VNbTaMoW)C₅–SiC high-entropy ceramics were prepared by spark plasma sintering at 1900°C and 40 MPa. The effects of SiC content (0–30 wt.%) on the microstructure, mechanical properties, and tribological properties were examined. The results showed that the matrix phase (VNbTaMoW)C₅ exhibited a face-centered cubic structure, and the second phase (SiC) was uniformly distributed, inhibiting excessive grain growth. The relative density of (VNbTaMoW)C₅– SiC composite ceramics decreased first and then dropped as SiC content increased. The fracture mode of (VNbTaMoW)C₅–SiC composite ceramics changed from transgranular to mixed (transgranular fracture and intergranular) fracture with an increase in SiC content due to weak bonding between (VNbTaMoW)C₅ and SiC. The grains of the (VNbTaMoW)C₅ in multiphase ceramics were refined because of the grain growth-inhibiting effect of SiC. With the increase in SiC content, the hardness of (VNbTaMoW)C₅–SiC multiphase ceramics increased, and the fracture toughness first increased and then decreased. The (VNbTaMoW)C₅–20 wt.% SiC multiphase ceramics exhibited the best mechanical properties with Vickers' hardness and fracture toughness of 18.2 GPa and 5.7 MPa ∙ m^1/2, respectively. Coupled with WC, (VNbTaMoW)C₅–SiC multiphase ceramics exhibit good wear resistance with a specific wear rate of (5.7–8.1) ∙ 10^–8 mm³/N ∙ m.

The tribological properties of heterogeneous Ti–Si–Zr titanium alloys with an e(β-Ti + (Ti, Zr)₂Si) eutectic were studied in different friction conditions. Tribological tests were performed with two methods. The samples were subjected to shaft–bush (counterface–material) tests by dry friction against ShKh15 steel employing an M-22M machine at a load of 20 N and a sliding speed of 1–6 m/sec with one method. The other method involved quasistatic and dynamic sphere–plane tests with an effective load of 30 N employing a computer-assisted tribology system. The indenter materials were ShKh15 steel and Si₃N₄ ceramics. The tests were performed at a sliding speed of approximately 0.0147 m/sec in water. The linear and weight wear rate for the cast Ti–10Si–10Zr–1Sn sample with a superfine eutectic structure determined with the first method at the greatest test speed (6 m/sec) was found to be 1.4 times higher than that of the Ti–9Si–7.6Zr alloy. The Ti–10Si–10Zr– 1Sn alloy showed the lowest wear resistance under quasistatic and dynamic loads with the second method, regardless of the indenter material (ShKh15 or Si₃N₄). Contrastingly to the previous data for cast irons and steels, the eutectic Ti–Si–Zr titanium alloys for the first time showed smaller wear under dynamic loading than under quasistatic loading. Thermomechanical treatment of the hypoeutectic Ti–9Si–7.6Zr alloy was established to increase its wear resistance by more than 1.6 times.

The thermal fatigue life of zirconia-based complex composite ceramics doped with a mixture of rare earth oxides was studied. Two concentrates of rare earth oxides were chosen (wt.%): 1) cerium- subgroup concentrate of composition 62.4 CeO₂, 13.5 La₂O₃, 10.9 Nd₂O₃, 3.9 Pr₆O₁₁, 0.92 Sm₂O₃, 1.2 Gd₂O₃, 0.24 Eu₂O₃, 2.66 ZrO₂, 1.2 Al₂O₃, 1.7 SiO₂, and 1.38 other oxides (light concentrate (LC)) and 2) yttrium-subgroup concentrate of composition 13.3 Y₂O₃, 1.22 Tb₄O₇, 33.2 Dy₂O₃, 8.9 Ho₂O₃, 21.8 Er₂O₃, 1.86 Tm₂O₃, 12.5 Yb₂O₃, 0.57 Lu₂O₃, and 6.65 other oxides (heavy concentrate (HC)). Two-layer metal/ceramic thermal-barrier coatings (TBCs) were deposited on gas turbine engine blades by electron-beam physical vapor deposition (EB-PVD) in one process cycle. The properties of ZrO₂–LC and ZrO₂–HC TBC ceramic top coats were compared to those of a standard yttria-stabilized zirconia layer (ZrO₂–Y₂O₃). The thermal fatigue experiment was performed by heating the samples to 1100°C in a muffle furnace for 5 min, holding them at this temperature for 50 min, and cooling in water for 5 min. The standard ZrO₂–Y₂O₃ layer withstood 138 thermal cycles, while the ZrO₂–LC and ZrO₂–HC layers withstood 161 thermal cycles. The porous microstructure of the ceramic layers developed during thermal cycling was found to depend on laminar microstructures acquired by the layers in the EB-PVD process. The number of spherical pores in the ZrO₂–LC and ZrO₂–HC layers was much higher than in the ZrO₂–Y₂O₃ layer. This increased their thermal fatigue life by 16% compared to the standard coating. An integrated approach to the choice of the ceramic top coat composition based on ZrO₂ solid solutions doped with natural rare earth oxide concentrates and of the technique for their deposition, as well as improvement in the coating architecture, will promote cost-effective TBCs with the properties required.