Keiichi Hirao

Diffusion of cobalt, chromium, and titanium in Ni3Al

Diffusion studies of cobalt, chromium, and titanium in Ni3Al (γ′) at temperatures between 1298 and 1573 K have been performed using diffusion couples of (Ni-24.2 at. pct Al/Ni-24.4 at. pct Al-2.91 at. pct Co), (Ni-24.2 at. pct Al/Ni-23.1 at. pct Al-2.84 at. pct Cr), and (Ni-24.2 at. pct Al/Ni-20.9 at. pct Al-3.17 at. pct Ti). The diffusion profiles were measured by an electron probe microanalyzer, and the diffusion coefficients of cobalt, chromium, and tita-nium in γ′ containing 24.2 at. pct Al were determined from those diffusion profiles by Hall’s method. The temperature dependencies of their diffusion coefficients (m[su2]/s) are as follows: ~D(Co)= (4.2 ± 1.2) × 1O-3exp {-325 ± 4 (kJ/mol)/RT} ~D(Cr) = (1.1 ± 0.3) × 10-1 exp {-366 ± 3 (kJ/mol)/RT} and D(Ti)= (5.6 ± 3.1) × 101 exp {-468 ± 6 (kJ/mol)/RT} The values of activation energy increase in this order: cobalt, chromium, and titanium. These activation energies are closely related to the substitution behavior of cobalt, chromium, and titanium atoms in the Ll2 lattice sites of γ′; the cobalt atoms occupying the face-centered sites in the Ll2 structure diffuse with the normal activation energy, whereas the titanium atoms oc-cupying the cubic corner sites diffuse with a larger activation energy that includes the energy due to local disordering caused by the atomic jumps. The chromium atoms which can occupy both sites diffuse with an activation energy similar to that of cobalt atoms.

Bonding of partially-stabilized zirconia and nickel with nickel oxide layer

Bonding of partially-stabilized zirconia (PSZ) and nickel has been investigated. The couples of PSZ and nickel were bonded at 1073 to 1273 K for 300 to 3600 sec under a pressure of 0.75 to 262 MPa in air. PSZ was bonded to nickel with a nickel oxide layer. The nickel oxide layer filled the interstices between PSZ and nickel. The maximum shear strength (about 90 MPa) was obtained in the couple bonded at 1173 K for 900 sec under pressure above 18 MPa. The stresses generated by the differential thermal contraction and the oxide growth stresses are discussed.

Influence of thermal histories on intermediate temperature embrittlement of an Fe-17Cr alloy

Intermediate temperature embrittlement is found in an Fe-17Cr alloy. The embrittlement is due to void formation on and near grain boundaries during tensile deformation. On the other hand, the segregation of phosphorus and sulphur impurity atoms to grain boundaries enhances intermediate temperature embrittlement.

Microstructures and Vickers hardness of rapidly solidified Al-Cu alloys near the Al-Al2Cu equilibrium eutectic composition

Al-Cu alloys near the Al-Al2Cu equilibrium eutectic composition were rapidly solidified by the single-roller method. Two-zone structures were observed in transverse sections of Al-24.8, 30.0, 32.7, 33.2, 37.0 and 40.3 mass % Cu alloy ribbons, which were interpreted on the basis of the difference in cooling rates and of the temperature gradients between the chilled and free-surface sides of the ribbons. Non-equilibrium eutectic structures, cellular and irregular lamellar, were seen at the chilled side because the alloy liquids were directionally solidified with coupled eutectic growth. The coupled zone of the Al-Cu alloy expanded over the composition range 24.8–40.3 mass % Cu by rapid solidification. Dendritic structures were formed at the unchilled side of Al-24.8, 30.0, 37.0 and 40.3 mass % Cu alloys. Vickers hardness values at the chilled side differed from those at the unchilled side due to the difference in the microstructure.

Diffusion of zinc in commercial Al-Zn alloys under high pressure

The effective interdiffusion coefficients of zinc in commercial Al-Zn alloys are obtained within the temperature range 773 to 883 K under pressures from 0 to 0.41 GPa. From the temperature dependence of the effective interdiffusion coefficients, the activation energies for the 701, 703 and 705 alloys are evaluated to be 125, 124 and 127 kJ/mol respectively, and their pre-exponential factors are 3.0 × 10−5, 4.0 × 10−5, and 3.9 × 10−5 m2/s respectively. The activation volumes, ΔV, for diffusion of zinc in the commercial Al-Zn alloy are 8.30 × 10−6, and 8.60× 10−6 m3/mol at 823 and 883 K, respectively. The ratios of the activation volume to the molar volume of aluminum, ΔV/V0, are 0.83 at 823 K and 0.86 at 883 K. This means that the diffusion of zinc in the commercial Al-Zn alloys occurs predominantly by the monovacancy mechanism at 823 and 883 K.

Diffusion of platinum, vanadium and manganese in Ni3Al phase under high pressure

AbstractDiffusion of platinum, vanadium, and manganese in the Ni3Al phase is investigated under high pressure. Platinum atoms occupy cubic face centred sites (α) in the L12 ordering structure. Vanadium atoms occupy cubic corner sites (β). Manganese atoms occupy both sites. Activation volumes ΔV for diffusion of these diffusing atoms to the molar volume of the Ni3Al phase V0 are as follows:

Repetition bend properties of Cu-Cr and Cu-Cr-Sn alloys

\Delta V/V_0 {\text{ for Pt:}}{\kern 1pt} {\text{ 0}}{\text{.75, }}V{\kern 1pt} :\;\,0.97 - 1.08,{\text{ Mn: 1}}{\text{.01}} - {\text{1}}{\text{.03}}

resolution of carbon atoms in neutron-irradiated fe-0.21wt%c-0.2wt%cu alloy

These values mean that the diffusion of platinum is mediated by single vacancies, that of vanadium is done by divacancies or other complex mechanisms, and that of manganese via single vacancies plus other mechanisms.