Well-defined SiO2-coated Fe nanoparticles with various SiO2 thickness from 1.2 to 27.8 nm have been successfully prepared by controlling the amount of tetraethyl orthosilicate and by the subsequent reduction of SiO2-coated Fe3O4 nanoparticles with CaH2. The saturated magnetization of the SiO2-coated Fe nanoparticles increased with decreasing SiO2 thickness. The saturated magnetization of the SiO2-coated Fe nanoparticles with SiO2 thickness of 2.7 nm or more have slightly decreased by 192 hr and did not change above 192 hr throughout atmospheric exposure, whereas that with SiO2 thickness of 1.2 nm steeply decreased in 24 hr and continued to decrease above 24 hr.
Molecular dynamics simulations were performed to study six grain boundaries of α-alumina (Al2O3) with a glassy phase of anorthite (CaAl2Si2O8) composition. We calculated excess energy, diffusion constant and ratio of excess volume with different thickness of the glassy film. It was found that excess energy for some grain boundaries exhibited a minimum. When the thickness of the glassy film was thick adequately, excess energy corresponded to the energy of alumina-glass interface and they were different for each interface. Diffusion constants depended on the thickness of the glassy film. The diffusion constant of thin film was smaller than that of thick film. Excess volume was the maximum when the thickness of the glassy film was 0.2~0.3 nm. When the atomic arrangement of the crystals didn’t fit each either, the excess volume of the grain boundary with the glassy film was smaller than that of the pure grain boundary. When the glassy film width was nm order, the atomic arrangement of the glassy phase was regular and the atomic diffusion behavior was approached that of a solid (crystalline) phase. We need to consider not only solid-liquid interface but also solid-solid (crystalline) interface for the structure of ceramics made by liquid phase sintering.
Solid solution strengthening effect by oxygen (O) and nitrogen (N) atoms of α-titanium (Ti) materials was quantitatively evaluated using Labusch model by consideration of the experimental data. When using Labusch model to predict solid solution strengthening improvement, an application of the isotropic strains by solute elements is generally assumed to estimate Fm value, which is the maximum interaction force between the solute atoms and dislocations. It is, however, difficult to exactly calculate Fm value for α-Ti materials with O and N solute atoms because the anisotropic strains are induced in α-Ti crystal with hcp structure by these elements. In this study, Fm value was experimentally derived from the relationship between 0.2% yield stress and solute elements (O and N atoms) content of Ti sintered materials. As a result, the strengthening improvement was proportional to c2/3/Sf (c: soluted atom content, Sf: Schmid factor), and its factor of proportionality of Ti-O and Ti-N materials was 4.17 × 103 and 3.29 × 103, respectively. According to this analysis, it was clarified that Fm value of Ti-O and Ti-N materials was 6.22 × 10−10 and 5.21 × 10−10, respectively, and then the estimated strengthening improvement by using these values was significantly agreed with the experimental results of Ti sintered materials with O and N solution atoms.
The influence of strain in the Nd-Fe-B was investigated by using the structural phase transition of BaTiO3 in films consisting of a Mo top layer (10 nm), Nd-Fe-B (30 nm), and a Mo bottom layer (20 nm) deposited onto BaTiO3 (001) substrates by sputtering. As a result, it was found that the magnetization along the easy axis jumps up in magnitude by 3% at around 280 K. This significant effect is certainly due to the lattice strain accompanying the structural phase transition of BaTiO3 from orthorhombic to tetragonal. First-principles calculations were applied to simulate the relationship between magnetization, magnetocrystalline anisotropy and the strain in the Nd-Fe-B main phase. It was also found that the magnetization along the easy axis increases as the lattice constant of the a-axis expands, which shows mostly good agreement with the experimental results under some assumptions.
The WC-Co cemented carbides with the addition of Ti(C,N) base particles with different sizes were fabricated by liquid phase sintering and their microstructures were mainly investigated in detail comparing the microstructure of the alloys with VC and Cr3C2 addition. It was found that the WC grain growth was more strongly inhibited with increasing Ti(C,N) content and with decreasing Ti(C,N) particle size. The degree of inhibition by the addition of Ti(C,N) particle with about 0.1 μm size was lower than that of VC addition and was almost same as that of Cr3C2 addition. Considering the results about the relationship between WC grain size and Ti(C,N) particle size and the analysis of Co phase composition, it was seen that the mechanism of grain growth inhibition by the addition of Ti(C,N) particles was the pinning (Zener) effect by the second phase particle, which was different from the mechanism for the addition of VC and Cr3C2 reported previously. The case that one Ti(C,N) particle contacts plural WC grains was often observed, so that the pinning effect was considered to work by many Ti(C,N) particles neighboring one WC grain. The very important result that the pinning effect by Ti(C,N) addition enable to develop the new type of ultra-fine cemented carbide was obtained in this study.
The recrystallization behavior of pure iron powder cores during the annealing process core is visualized with the Grain Orientation Spread (GOS) map from an SEM/EBSD analysis, and found to be significantly inhomogeneous, leading to an inhomogeneous dislocation density distribution. Nevertheless, a conventional dislocation pinning model well describes the coercive force behavior if the average dislocation density is applied. The pinning model is modified to separate the influence of the grain boundary pinning, and the relationship between the coercive force and the microstructure is discussed comprehensively.
Wire drawing dies and specimens of WC-Co cemented carbides containing TaNbC or Cr3C2 were fabricated by hot isostatic press (HIP) treatment at 1633 K in 40 MPa Ar and by anneal treatment 1593 K in vacuum. The lifetime of steel code wire drawing were evaluated for the dies and mechanical properties such as hardness, transverse-rupture strength and fracture toughness were examined for the specimens. It is noted that the lifetime of drawing die was remarkably improved by the anneal treatment for both of TaNbC and Cr3C2 containing WC-Co cemented carbides. The TaNbC containing alloys showed longer lifetime than the Cr3C2 containing alloys. The lifetime of drawing die had weak relationship to hardness, but seemed to have no correlation with strength and toughness. The remarkable improvement of drawing die lifetime by the annealing treatment after HIP and the longer lifetime for TaNbC containing alloys can be understood from the viewpoint of adhesion strength between WC and Co phase affected by alloy content and heat treatment of cemented carbides.
Titanium carbonitrides containing transition metal ((Ti, Me)(C, N), Me: transition metal) have been studied for applying them to cutting tools and wear- resistant tools. Thermal shock resistance is an important property of tool materials used in severer thermal environment. Therefore, the thermal conductivity of such materials is important to improve the thermal shock resistance of tool materials. The present work is aimed to clarify the effects of the composition of carbonitrides on thermal conductivity and electrical conductivity of carbonitrides. The experimental results showed that the thermal conductivity and electrical conductivity of carbonitrides decreased with increasing solid solution of transition metal.
The microstructures of Ca-La-Co M-type sintered ferrite magnets were analyzed by Spherical Aberration Corrected Scanning Transmission Electron Microscopy (Cs-STEM) to devise guidelines for improving performance. It was confirmed that there were Ca-Si-based oxides, which consists of Si, Ca, La and Fe, at multiple-junction phases of the sintered body, after adding only SiO2 instead of both CaCO3 and SiO2, which are sintering aids for ferrite magnets. It was also confirmed that the ratio of Si, Ca, La and Fe at multiple-junction phases was 30:60:2:5. Moreover, we found that a step-terrace structure of Ca-Si-based oxides formed at the boundary of the M-type ferrite grain, and that the maximum width of the intergranular grain boundary was about half (1.15 nm) the edge length of the c-axis of the M phase. This suggested that ferrite grains were magnetically isolated by the presence of Ca-Si-based oxide phases at the intergranular grain boundary, whereby improving coercivity.
Low-cost, high-strength titanium alloy plates were prepared using a prealloyed titanium powder (Ti-6Al-4V) as a starting material. Ti-6Al-4V was prepared via a hydrogenation/dehydrogenation process from Ti-6Al-4V alloy machine turnings. Prealloyed Ti-6Al-4V and iron (3 %–3.5 %) powders were mixed and subsequently consolidated by a vacuum hot pressing (VHP) process. Densification of the prealloyed powder to the theoretical density level was confirmed by VHP process. The combination of VHP, hot rolling, and mill annealing processes led to the production of titanium alloy plates with a 1200 MPa tensile strength and a 5 % elongation. Remarkably, the Ti-6Al-4V alloy exhibited enhanced tensile strength and lower elongation values upon iron addition.