Shotaro Morozumi

Joining of silicon carbide

Abstract Referring to the recent experimental results on active metal joining of various kinds of SiC, the author noted the following: 1. (1) Even though the active metal itself has an important role for the joining, the reaction concerned in the bonding is different between the solid metal foil and molten braze alloys containing the same metal. 2. (2) As the additives to and/or fabrication processes of SiC to be joined have very important effects on the bonding strength up to a high temperature, these factors should be taken into account for the materials design of SiC joints.

Structure and mechanical properties of internally hydrided Mg-IIIa transition metal alloys

Magnesium alloys containing IIIa transition metals, such as Sc, Y and Ho, respectively, were hydrogenated at 773 K and examined for microstructure, X-ray diffraction pattern, micro-Vickers hardness, and tensile properties at room and high temperatures. Results obtained are as follows:1.The alloys, respectively, have been internally hydrided and have precipitated hydrides of the IIIa transition metals as small flake-like particles in the matrix and at grain boundaries, as well as twin boundaries.2.The dispersed hydride particles do not necessarily contribute to further hardening of the alloys at room temperature and up to near 673 K.3.However, the dispersed particles are very stable and seem to improve mechanical properties of the alloys above 673 K.4.Presumed relationships of crystallographic coincidence between the matrix and hydrides have been obtained.

Fusion-fission-light ion correlation of mechanical property change in a TZM alloy

In order to study the correlation of damage among fusion neutron-fission neutron-light ion irradiation at low fluence levels, mechanical properties and microstructures in a molybdenum alloy, stress-relieved TZM, were studied. Miniature tensile specimens and TEM disks were irradiated to fluences of 10−4−10−2 dpa by 14 MeV neutrons at RTNS-II, by fission neutrons at Kyoto University Reactor and by 16 MeV Deuterons at Tohoku University Cyclotron. Irradiation hardening was observed at all irradiation conditions. The ratio of the increase in yield stress at the fluence of 1 × 1022/m2 was 4:3:2 for 16 MeV deuterons, fusion neutron and fission neutron, respectively. The magnitude of irradiation hardening was not expressed by the same curve even in the dpa scale. Small defect clusters were observed uniformly in specimens irradiated with any particles.

Electric field-assisted and field-depressed segregation of reactive metals to the bonding interface in braze alloy joining

Segregation of reactive metals at the bonding interface has been observed in various ceramic and/or metal joints bonded with reactive metal-bearing braze alloys. When a d.c. of 20 mAcm−2 is applied to the ceramic/braze/ceramic system at a brazing temperature of, say, 1373 K, the electric field assists the segregation at the braze-ceramic interface on the cathode side and suppresses the segregation at the interface on the anode side. This may imply that reactive metal atoms in the braze can migrate as a cation. E.m.f. measurement on the ceramic (AIN or ZrB2)-metal foil systems with increasing temperature shows that a negative e.m.f. to the ceramic pole appears from about 900 K for AIN and from 500 K for ZrB2, as does the thermally stimulated current in polymers. These temperatures coincide well with those where the electrical conductivity of AIN and ZrB2, respectively, begins to increase with increasing temperature. Therefore, it is considered that the polarization of the ceramics may take place and assist the migration, and consequently segregation, of reactive metals in braze alloys to the braze-ceramic interface during brazing.