Gürgenç, Turan; Macit, Cevher Kürşat; Sömer, Medeni; Aksakal, Bünyamin; Ayık, Merve; Say, Yakup

High-velocity oxy-fuel (HVOF)-sprayed NiCrBSi coatings containing 0, 10, 30, and 50 wt.% WC-Co were evaluated on AZ91D magnesium alloy to determine how the discrete reinforcement level affects surface topography, phase constitution, Vickers microhardness, dry-sliding friction, mass loss, and wear-track microchemistry. As-sprayed surfaces were characterized by three-dimensional profilometry; coating cross-sections and worn surfaces by optical microscopy and SEM/EDS; phase constitution by XRD; and mechanical response by HV0.1 indentation. Dry-sliding tests were performed at 10, 30, and 50 N over 100–1000 m. Increasing WC-Co content raised Sa from 8.8 ± 0.3 to 13.0 ± 0.5 µm and Vickers microhardness from 776 ± 4 to 959 ± 5 HV0.1. XRD indicated a γ-Ni-based matrix containing boride/carbide constituents, while WC, W2C, and Co became increasingly prominent in the reinforced coatings. Boride assignments are based on diffraction evidence, whereas B and C EDS signals were treated semi-quantitatively. The 50 wt.% WC-Co coating exhibited the lowest mass loss and mean coefficient of friction at every load. Its mean friction coefficients were 0.31, 0.35, and 0.41 at 10, 30, and 50 N, corresponding to reductions of 40.1%, 38.9%, and 36.2% relative to AZ91D. At 1000 m, its mass-normalized wear rate indices were 9.0 × 10−4, 4.0 × 10−4, and 5.3 × 10−4 mg N−1 m−1, respectively. Post-wear mapping showed the largest field-scale W-Co-rich fraction in the 50 wt.% coating; however, isolated spectra containing more than 94 wt.% Mg are compatible with local coating penetration/substrate exposure and/or Mg-rich debris. The 50 wt.% composition therefore provided the best combined response among the four tested levels, while intermediate compositions are required to identify a continuous-composition optimum.

İncele

Güner, Melek; Özkan, Betül Çiçek; Gürgenç, Ezgi; Macit, Cevher Kürşat; Aslan, Naim; Gurgenc, Turan

Rare-earth oxide nanoparticles offer a strategy to tune dielectric films via interfacial polarization while maintaining low-loss insulating behavior. Here, polystyrene/samarium oxide (PS/Sm2O3) nanocomposite films containing 0, 1, 3, 5, and 10 wt.% Sm2O3 were fabricated by solvent casting and evaluated as a low-loss dielectric for frequency-sensitive electronic applications. FTIR, XRD, SEM/EDX, and XPS confirmed successful Sm2O3 incorporation, preservation of the PS structure, formation of PS/Sm2O3 interfacial regions, and Sm3+/Sm–O species. XRD revealed amorphous PS with increasingly intense crystalline Sm2O3 reflections, whereas SEM/EDX showed relatively uniform filler distribution at low and moderate loadings and partial agglomeration at 10 wt.%. Dielectric spectroscopy at room temperature from 1 kHz to 1 MHz showed a frequency-dependent response governed by interfacial polarization and limited charge transport. At 1 kHz, the dielectric constant increased from 8.67241 ± 0.00280 for pure PS to 10.13061 ± 0.00641 for PS-10, while the loss tangent remained low (∼ 0.068). The dielectric loss increased moderately from 0.59535 ± 0.00236–0.69194 ± 0.00710, and AC conductivity rose from (3.31202 ± 0.01314) × 10−10 to (3.84935 ± 0.03948) × 10−10 S cm−1. These results indicate interface-controlled dielectric enhancement without conductive percolation, highlighting PS/Sm2O3 films for capacitor dielectric layers, insulating films, flexible electronics, and frequency-sensitive dielectric technologies.

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