In this study, the laser metal deposition (LMD) of the Inconel 625–tungsten carbide (WC) metal matrix composite was investigated. The composite coating was deposited on Inconel 625 substrate by powder method. A powder mixture containing 10 wt% of WC (5 µm) was prepared by wet mixing with dextrin binder. Coating samples obtained by low-power LMD were pore- and crack-free. Ceramic reinforcement was distributed homogenously in the whole volume of the material. Topologically close-packed (TCP) phases were formed at grain boundaries between WC and Inconel 625 matrix as a result of partial dissolution of WC in a nickel-based alloy. Line analysis of the elements revealed very small interference of the coating in the substrate material when compared to conventional coating methods. The average Vickers hardness of the coating was about 25% higher than the hardness of pure Inconel 625 reference samples.
In this study, the influence of the addition of rare earth oxides on the phase composition and density of KNN piezoelectric ceramics was investigated. The initial powders of Na 2 CO 3 and K 2 CO 3 were dried at 150 • C for 2 h. Then, a powder mixture for synthesis was prepared by adding a stoichiometric amount of Nb 2 O 5 and 5 and 10 wt % overabundance of Na 2 CO 3 . All powders were mixed by ball-milling for 24 h and synthesized at 950 • C. The phase composition of the reaction bed was checked by means of X-ray diffraction (XRD). It had an appearance of tetragonal and monoclinic K 0.5 Na 0.5 NbO 3 (KNN) phases. Then, 1 and 2 wt % of Er 2 O 3 and Yb 2 O 3 , were added to the mixture. Green samples of 25 mm diameter and 3 mm thickness were prepared and sintered by hot pressing at 1000 • C for 2 h under 25 MPa pressure. The final samples were investigated via scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDS), XRD, Rietveld, and ultrasonic methods. Phase analysis showed tetragonal and orthorhombic KNN phases, and a contamination of (K 2 CO 3 ·1.5H 2 O) was present. The obtained KNN polycrystals had a relative density above 95%. Texturing of the material was confirmed as a result of hot pressing.Materials 2019, 12, 4171 2 of 12 lead-based piezoelectrics. Due to the significant piezoelectric response obtained by numerous teams [5,[7][8][9], KNN-based materials have been widely researched, including in this study.In a perovskite-type ABO 3 structure, A-site cations are either alkaline earth elements or rare-earth elements, with B-site cations being transition metals. Theoretical structure consists of A cations occupying cuboctahedral coordination positions in the middle of eight corner-sharing BO 6 octahedrons. Due to the specific structure and composition, perovskites have plenty of conductive properties used in material sciences, including significant piezoelectricity. The piezoelectric effect is directly derived from the noncentrosymmetric structure of materials. Such structures are electrically neutral, but lack symmetrical arrangement. Therefore, when mechanical stress is applied, and such structure shifts, it does not maintain a neutral charge [4]. The high magnitude of electromechanical effects obtained in perovskites is derived from the ordering tendency present in those materials, mainly the shift of B cations [4]. K 0.5 Na 0.5 NbO 3 has a similar structure to BaTiO 3 , which consists of two phases, ferroelectric K 1-x NbO 3 and antiferroelectric Na x NbO 3 . Both phases have different ferroelectric transitions, crystallizing in a perovskite structure, with different symmetries. The phase transitions of KNN depend on the K/Na ratio [10]. To synthesize the basic structure of KNN, K, and Na carbonates are used in conjunction with Nb 2 O 5 [5]: K 2 CO 3 + Na 2 CO 3 + 2Nb 2 O 5 → 4K 0.5 Na 0.5 NbO 3 + 2CO ↑ 2 .
This study focuses on the investigation of fine (~0.54 μm) tungsten carbide particles effect on structural and mechanical properties of laser cladded Inconel 625-WC composite. Three powder mixtures with different Inconel 625 -WC weight ratio (10, 20 and 30 weight % of WC) were prepared. Coatings were made using following process parameters: laser beam diameter ø ≈ 500 μm, powder feeder rotation speed -7 m/min, scanning velocity -10 m/min, laser power -220 W changed to 320 W, distance between tracks -1 mm changed to 0.8 mm. Microstructure and hardness were investigated. Coatings produced by laser cladding were crack and pore free, chemically and structurally homogenous. High cooling rate during cladding process resulted in fine microstructure of material. Hardness improved with addition of WC from 396.3 ±10.5 HV for pure Inconel 625, to 469.9 ±24.9 HV for 30 weight % of WC. Tungsten carbide dissolved in Inconel 625 which allowed formation of intergranular eutectic that contains TCP phases.
Energy harvesting from mechanical vibration of buildings is usually realized by the use of devices, in which the main element is a prismatic beam with a rectangular cross-section. The beam has been the subject of scientific research; it is usually constructed with a carrying substrate that does not have piezoelectric characteristics and from piezoelectric material. In contrast, this investigation sought to create a beam structure with a piezoelectric composite only. The entire beam structure was made of a prototype piezoelectric particulate composite. Based on courses of voltage obtained in laboratory experiments and known geometry of the specimens, a series of finite element method (FEM) simulations was performed, aiming to estimate the piezoelectric coefficient d31 value at which the mentioned voltage could be achieved. In each specimen, sedimentation caused the formation of two distinct layers: top and bottom. The experiments revealed that the presented prototype piezoelectric particulate composite converts mechanical stress to electric energy in bending mode, which is used in energy harvesting from mechanical vibration. It is self-supporting and thus a carrying substrate is not required in the harvester structure.
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