Masuo Okada

Ti-V-Cr b.c.c. alloys with high protium content

Abstract The effects of composition and heat-treatment on the protium absorption–desorption properties of Ti–V–Cr alloys were investigated. It was found that the Ti–35V–40Cr alloy shows a 2.6 mass% protium capacity. The plateau pressure of the Ti–35V–xCr alloys increased with decreasing lattice constants associated with increasing Cr content. The main phase of the as-cast Ti–xV–Cr (Cr/Ti=40/25) alloys containing more than 15%V was a b.c.c. phase. These b.c.c. alloys exhibited a 2.4 mass% protium capacity. Heat-treatment over 1673 K was effective on stabilizing the b.c.c. structure for the Ti–xV–Cr (Cr/Ti=2/3) alloys with low V content. The Ti–5V–57.5Cr alloy heat-treated at 1673 K for 1 h yields a high capacity of 2.8 mass% protium, which is the highest value at 313 K reported so far. The alloy is economically promising since it contains low amounts of expensive V metal.

New V-based alloys with high protium absorption and desorption capacity

Abstract The hydrogen absorption properties of V–Zr–Ti–M(M=Fe, Mn, Ni) alloys were examined in order to develop the alloys with high hydrogen capacity. It was found that the best composition among the studied alloys is the V–Zr–Ti–Ni system. A suitable amount of the vanadium in the V–Zr–Ti–Ni system was studied in correlation with its hydrogen absorption properties, and turned out to be around 75 at.%V. Substitution with Zr improved the hydrogen absorption properties in forming the grain boundary network phases of C14 Laves phase. Heat treating the alloys (homogenize and quench) drastically improves the plateau region of PCT curves. Zr addition also improves the properties for V–Zr–Ti–Cr alloys.

Protium absorption properties and protide formations of Ti–Cr–V alloys

Abstract Ti–Cr–V alloys are known to absorb about 3.8 mass% (H/M=2) of protium (hydrogen atom), but to desorb about 2.4 mass%. This paper aims to clarify protium absorption properties and protide formations of Ti–Cr–V alloys. It was found that higher protium desorption capacity was achieved by increasing Cr content and controlling measurement temperature in order to control the desorption plateau pressure near atmospheric pressure for the alloys with less than 40 at% V content. However, Cr-rich alloys were found to absorb up to H/M=1 because of the formation of the mono-protides. The region with higher protium desorption capacity was obtained. The lattice parameters of the alloys and the enthalpy changes for di-protide formation were estimated from the compositions of the alloys. Moreover, estimated enthalpy changes for di-protide formation and the lattice parameters of the alloys were found to be generally constant on the limited line between appearance of regions of mono- and di-protides.

Fe-Cr-Co permanent magnet alloys containing Nb and Al

The vertical section of the Fe-Cr-Co system at 15 wt%Co, 1 wt%Nb and 1 wt%Al was constructed. The extention of the α phase region of the system was sufficient enough to allow for the solution treatment of the alloys at 25∼30 wt%Cr content at any temperature above the α 1 +α 2 miscibility gap. After step-tempering, their magnetic properties were given as Br = 11.5∼13 KG, Hc = 500∼600 Oe and (BH)max = 4∼5 MGOe. These values were also achieved by continuous cooling from α phase region. The addition of Nb and Al to Fe-Cr-Co system will facilitate a practical manufacturing for producing Fe-Cr-Co permanent magnets.

Phase diagram of Fe-Cr-Co permanent magnet system

The miscibility gap of the α phase in Fe-Cr-Co permanent magnet alloys is constructed using mechanical hardness and Curie temperature measurements. It is found that the miscibility gap of the Fe-Cr binary system develops into Fe-Cr-Co ternary system, and that the addition of cobalt raises the decomposition temperature, and extends the difference in concentrations between the iron rich phase (α 1 ) and the chromium rich phase (α 2 ). For instance, the α phase of an Fe-31%Cr-23%Co alloy exhibits a miscibility gap below 670°C, and decomposes into the (α 1 ) phase of 65%Fe-32%Co-3%Cr and the (α 2 ) phase of 69%Cr-21%Fe-10%Co at 600°C.

Didymium‐Fe‐B sintered permanent magnets

Present works describe the developments the low cost R‐Fe‐B sintered permanent magnets. Three different didymiums are chosen for the low cost mixtures of rare‐earth elements. The studied alloy compositions are Fe‐(32.5–34.5)wt. %R‐(1–1.6)wt. %B, where R elements are didymium (Nd‐10wt. %Pr), 5Ce‐didymium (Nd‐15%Pr‐5%Ce), and 40 Ce‐didymium (Nd‐10%Pr‐40%Ce). The specimens were prepared by the conventional powder metallurgical techniques. The best magnetic properties obtained in this studies are Br=13.2 kG, iHc=10.2 kOe, and (BH)max=40 MGOe with the Fe‐33.5% (5Ce‐didymium)‐1%B alloy. Temperature dependence of iHc of this alloy is almost comparable to that of the Nd‐Fe‐B alloys.

Protium absorption properties of Ti–V–Cr–Mn alloys with a b.c.c. structure

The protium absorption–desorption properties of Ti–V–Cr–Mn alloys were studied by varying the contents of Mn, Ti and V in the alloys. It was found that Mn addition of <10 at% was effective in improving the slope of the plateau region without any reduction of the protium absorption–desorption capacity. For Ti–V–Cr–Mn alloys, the α-Ti phase, which does not contribute to the protium storage capacity, appeared along grain boundaries during heat treatment. The formation of the α-Ti phase was found to be suppressed by reducing the Ti content and increasing the V content. By inhibiting the appearance of the α-Ti phase along the grain boundary, the protium absorption–desorption capacity of Ti–xV–Cr–Mn (x=45, 55; Ti/Cr/Mn=24:31:10) heat-treated alloys exhibited 2.7 mass% H, the highest value reported so far.

Effects of HDDR treatment conditions on magnetic properties of Nd‐Fe‐B anisotropic powders

It is reported that Nd‐Fe‐B magnetic powders prepared by utilizing the HDDR (hydrogenation, disproportionation, desorption, and recombination) phenomena exhibit high coercivity, and the addition of Co, Ga, and Zr induces magnetic anisotropy in these powders. HDDR phenomena are caused by the heat treatment in hydrogen (H treatment) and subsequently in vacuum (V treatment). Present works describe the effects of V‐treatment conditions on magnetic properties of Nd12.6Febal.CoxB6.0 (x=0–17.4) alloys. The powders V‐treated at lower temperature show lower remanence and no noticeable magnetic anisotropy. V treatment at higher temperature enhances remanence and increases the differences of remanence between the powders aligned with and without magnetic field. Higher values are obtained in Co added alloys. This result suggests that a selective grain growth of Nd2Fe14B grains during V treatment plays an important role for the inducement of magnetic anisotropy in HDDR‐treated powders. The temperature for complete rec...

Role of intermetallics in hydrogen storage materials

Abstract Many intermetallics such as AB5, AB2, A2B show the excellent hydrogen absorbing properties. Specially, LaNi5 compound has been extensively studied for the negative electrode of Ni–MH batteries. In todays use for the negative electrode of Ni–MH batteries, alloys must be single phase. But it is well known that it is difficult to make non-stoichiometric LaNi5 alloys as single phase because of its limited solid-solution range. The present study describes the rapid quenching effects on the solid-solution range of La(Ni, M)x (x=3–5) alloys prepared by melt spinning in discussing their hydrogen absorption properties. It is found that the single phase with CaCu5 crystal structure extends to LaNi4.65 compositional alloys. For fuel cell automobile, the alloys with high content of hydrogen must be developed. Strong candidates for this will be Vanadium based BCC alloys, which would be hard to be activated. Since it is well known that the Laves phases undergo easy activation treatment, it may be possible that the BCC phases will be easily activated if the alloys contain such Laves phases. The present study also found that Zr addition is effective on forming Laves phase as grain boundary phases in BCC phases in V–Ti–Zr–Ni alloys, and on improving the hydrogen absorbing properties. The study will be also extended to future hydrogen absorbing alloys with high capacity.

Ti−V−Cr BCC alloys system with high protium content

This paper aims to study the relationship between the protium absorption properties and alloy composition of Ti−V−Cr alloys. We studied the effects of composition of the alloys and the heat-treatment on the protium absorption-desorption properties of Ti−V−Cr alloys, and found that Ti−35V−40Cr alloys show 2.6 mass% protium capacity. The plateau pressure of the alloys increased with decreasing lattice constants, resulting from increasing Cr content. The main phase of the samples containing more than 15%V was a BCC phase in the cast state. These BCC phase alloys exhibited 2.4 mass% protium. It was also found that the heat-treatment was effective in stabilizing a BCC structure in Ti−V−Cr alloys with low V content. The alloy yields the high capacity of 3.0 mass% protium capacity, which will be the highest value at 313 K reported so far. The alloy will be promising since it contains a low amount of the expensive V element.