Mamoru Kawakami

New method for the evaluation of brittleness in ceramics

Using Vickers indentation method, plastic deformation (Ef) is suggested to be a convenient measurement to determine the ductility (brittleness) of brittle new materials. It was found that Ef is related empirically to KIC and GIC through a logarithmic linear relationship.

Effects of peening on resistance to plastic deformation in a metallic glass

Abstract The change in microhardness with peening is studied for metallic glasses. The peened glass shows small Hv. If the driving force of the peening is the collision energy, a rate process may be applied for the glass. The parameter X = (Hv − Hv0)/(Hvm − Hv0), where Hvm and Hv0 are the Hv of the peened glass after an extremely long period of time and the minimum value of Hv, respectively. Based on the rate process, X is expressed by a following equation. log 10 {−1 n (1 − X)} = n log t + log k Hv approaches Hvm with peening. Hvm is 425 when the correlation coefficient is maximum. The value of Hvm agrees with the hardness value of the extremely fast liquid-quenched glass. We conclude that a given value of Hv can be obtained by controlling the cooling rate and peening time.

Kinetics of oxidation of pure iron near the eutectoid temperature of Wüstite

Kinetics of oxidation of pure iron near the eutectoid temperature of wüstite was investigated in atmospheric oxygen, and the reduction in the temperature dependence of the growth rate of iron oxides layer was examined. The results show a good agreement with those obtained from the linear theory of reaction rates in irreversible thermodynamics and the theory of absolute reaction rates.

Effect of chromium content on remarkably rapid nitriding in austenitic Fe-Ni-Cr alloys

Remarkably rapid nitriding which is independent of diffusion theory based on the thermal activation process, was observed during nitriding of austenitic Fe-Ni-Cr steels containing 16 and 19 mass% chromium. Increase of the chromium content in the alloys yielded increasing thickness of the nitrided layer, i.e. the internal nitriding theory did not hold in the nitriding. No rapid nitriding was observed in steels containing less than 13 mass% chromium. Hence the limiting concentration of chromium for the rapid nitriding will lie between 13 and 16 mass% chromium. A solution to the problem of abnormalities arising during nitriding of practical austenitic stainless steels which have been investigated since 1972, has been presented experimentally by nitriding various chromium-containing steels. Based on the experimental results, the origin of the rapid nitriding is discussed in connection with the free-energy function of Cr2N and CrN to temperature. In particular, a plateau of nitrogen concentration measured in the nitrided layers leads to the conclusion that a forced nitrogen diffusion in the layer resulted in the rapid nitriding.

Effect of a plated Fe-Cr-Ni alloy layer for rapid nitriding of invar

The nitriding rate in a plated invar with an Fe-Ni-Cr alloy (face-centred cubic) layer were compared by optical microscopy with the rate in an unplated invar. In the plated invar rapid nitrogen diffusion was discovered. The plated layer plays a role in enhancing the nitriding rate. The result gives a solution for an abnormal enhancement nitriding rate in austenitic stainless steels. The enhancement is explained from the viewpoint of non-equilibrium thermodynamics.

Isothermal crystallization on the surface of Te-15 at % Ge alloy glass

Isothermal surface crystallization is investigated for Te-15 at % Ge alloy glass. This surface-crystalline pure tellurium nucleates by ageing at low temperature below 451 K. Since germanium-rich phases and GeTe chemical compound prevent this growth, the maximum thickness of the surface layer is below 0.005 mm.

HighT c of YBa2Cu3O x coated film on a nickel plate annealed for a short period

Direct coating of YBa 2 Cu 3 O x on nickel plate was done. A short period of annealing increases T c . The highest T co f f  is obtained by annealing for 600 sec at 1213 K. Excess annealing decreases T c is obtained by annealing for 600 sec at 1213 K. Excess annealing decreases T c because of nickel diffusion in YBa 2 Cu 3 O x . The change in T c is consistent with the results of lattice constants

Dependence of Tcc on the cooling conditions for liquid-quenched A15 chemical compounds☆

Abstract The change in T c with cooling conditions is investigated for the liquid-quenched A15 chemical compounds Nb 3 Al, Nb 3 Si, Nb 3 (Al, Si), Nb 3 (Ge, Al) and Nb 3 (Ge, Si). T c generally decreases with increase in cooling rate; however, abnormal increases in T c with increase in cooling rate are often found for NbSi binary alloys.

X-ray Studies on the Mechanical Properties of Boronized Steel

ABSTRACT The X-ray method was successfully applied to measure the residual stress distribution in a boronized steel. The X-ray elastic constants were determined separately for the FeB and Fe2 B phases of the boronized layer, and compared with the mechanically measured values. Tensile tests were conducted on mechanical and structural steel specimens of different diameters, which contained various amounts of carbon and had differing thicknesses of the boronized layer. One of the characteristics in boronized steels is the formation of redistributed carbon below the boronized layer. When this carbon-redistributed layer became thicker than the tensile residual stress distributed layer, both the tensile and yield strengths improved. Plane and rotating bending fatigue tests on boronized steels with various thicknesses of the boronized layers were conducted. The effects of the thickness and compressive residual stress of the bronized layer on the fatigue strength were investigated. A compressive residual stress was effective to increase the fatigue strength when crack initiation occurred at the surface. The maximum fatigue strength was obtained when the boronized area was controlled to be about 1.5% of the total area. An Amsler type of wear test was carried out, the wear loss being unaffected by the compressive residual surface stress value that was dependent on the thickness and type of the boronized layer. As the wear distance increased, the half-value breadth of the X-ray parameter increased.

Evaluation of Brittleness of HTSC

We have suggested a new method to evaluate brittleness KIC by use of a standerd hardness tester. We found the KIC value is controlled by the process. This method is useful to evaluate brittleness of small high Tc superconductor specimens.