Ni_1−xZn_xFe₂O₄ (x = 0.5, 0.6, 0.7) nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by X-ray diffraction analysis, and they were calculated to be 46–51 nm in diameter by the Scherrer equation, depending on the composition. In the FE-SEM image, the ferrite nanoparticles have spherical shapes with slight agglomeration, and the particle size is about 50 nm, which was consistent with the value obtained by the Scherrer equation. The lattice parameter of the ferrite nanoparticles monotonically increased from 8.34 to 8.358 Å as the Zn concentration increased from 0.5 to 0.7. Initially, the saturation magnetization value slowly decreases from 81.44 to 83.97 emu/g, then quickly decreases to 71.84 emu/g as the zinc content increases from x = 0.5, through 0.6, to 0.7. Ni_1−xZn_xFe₂O₄ toroidal samples were prepared by sintering ferrite nanoparticles at 1250 °C and exhibited faceted grain morphologies in the FE-SEM images with their grain sizes being around 5 µm regardless of the Zinc content. The real magnetic permeability (μ′) of the toroidal samples measured at 5 MHz was monotonically increased from 106, through 150, to 217 with increasing the Zinc content from x = 0.5, through 0.6, to 0.7. The cutoff frequency of the ferrite toroidal samples was estimated to be about 20 MHz from the broad maximum point in the plot of imaginary magnetic permeability (μ″) vs. frequencies, which seemed to be associated with domain wall resonance.

In the selective laser melting (SLM) additive manufacturing process of Inconel 718, the emergence of Laves and δ precipitate phases in the γ matrix during or after heat treatment is a critical consideration. This study comprehensively assesses the microstructures and mechanical properties of Inconel 718 alloy produced through SLM under varied conditions: as-built (AB), homogenization + solution + aging (HSA), homogenization + aging (HA), and solution + aging (SA). Additionally, the impact of building orientation, whether horizontal (H) or vertical (V), is investigated. The AB specimens oriented horizontally display a columnar melt pool structure, with dimensions roughly between 300 and 400 μm. In contrast, the AB specimens aligned vertically show an elongated river-like structure of melt pools, with their sizes approximately at 250 μm. From the detailed microstructural analysis, the findings reveal that the as-built specimens lack γ′ and γ″ precipitates in their microstructure. Conversely, in heat-treated specimens, both the γ′ and γ″ phases are evident. Notably, Inconel 718 alloy specimens subjected to SLM fabrication and SA heat treatment demonstrate optimal mechanical performance. Notably, SA exhibits an average hardness of 476 HV for the horizontal specimen, which is 51.1% higher than that of AB specimens. The morphology and distribution of the δ phase in the γ matrix emerge as decisive factors influencing high-temperature performance. In SA specimens, the dissolution of brittle Laves phases occurs, and the presence of the δ phase at the grain boundary imparts superior properties during high-temperature tensile testing, including excellent yield and ultimate tensile strength. The presence of the granular-δ phase in the SA specimens resulted in a tensile strength of 1422 MPa and a yield strength of 1236 MPa, which are the highest values among all the specimens. SA has a tensile strength of 1120 MPa and a yield strength of 974 MPa at 650 °C.

The wear behavior of AISI304 stainless steel was investigated under dry, water-, and oil-lubricated conditions. A block-on-disk wear test was conducted in this work, since the test conditions could be controlled easily. For oil-lubricated contact, a significant amount of thin and elongated cutting chip-like debris was observed. This is attributed to the high lubricating effect of oil. Strain-induced martensitic (SIM) transformation was observed for all AISI304 blocks after the wear test, while AISI304 consisted of a single γ-austenite phase prior to the wear test. The Stribeck curve and the corresponding lubrication regimes were also considered to explain the wear behaviors and lubrication effect of AISI304. In comparison to the dry or water-lubricated conditions, which fall in the boundary lubrication regime at a low rotation speed, it is considered that the high viscosity of the oil-based lubricant causes the lubrication condition to enter the mixed lubrication regime early at a lower speed, thus reducing the specific wear rate over the 100–300 rpm range.