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.