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The effect of cooling condition on the intergranular corrosion resistance of UNS S32506 duplex stainless steel was investigated by means of Huey test and microstructural observation. It was found that quenching at a temperature below 800 °C after air cooling at a fixed rate from solutionization temperature enhances the intergranular corrosion rate. No precipitation has been found at all cooling conditions. Formation of Cr-depletion zone on the γ phase side of the α/γ interface due to local chemical change accompanying α-γ phase transformation during air cooling is responsible for the intergranular corrosion degradation of the UNS S32506 duplex stainless steel.

The Kissinger’s formula has been analyzed theoretically and numerically to be applicable in simulation of not only the detrapping-controlled thermal desorption but also the diffusion-controlled thermal desorption provided that a sufficient pre-exposure before thermal desorption is carried out in the diffusion-controlled desorption. The desorption activation energy or the binding energy can be evaluated by a single thermal desorption spectrum from a single type of trap site. In the case of detrapping-controlled desorption the constant parameter A in the Kissinger’s formula approaches the pre-exponential factor of detrap parameter, p0, in the McNabb–Foster model as specimen size becomes smaller. In the case of diffusion-controlled desorption where local equilibrium may be maintained and an effective diffusivity can be expressed, the A value changes according to A = α2D0 where D0 is the pre-exponential factor of effective diffusivity and α is a geometrical parameter of specimen.

Development of primary recrystallization was studied in a steel containing 0.4 vol.% of fine TiC precipitations with an average size of 12 nm. After sufficiently large cold strains, the recrystallization developed readily upon annealing at temperatures above 600 °C. An increase in the cold strain as well as the annealing temperature resulted in the acceleration of recrystallization kinetics. However, a certain amount of cold worked microstructures of about 15 vol.% remained unrecrystallized even after annealing at a rather high temperature of 700 °C. The unrecrystallized portions were composed of grains with the 〈0 0 1〉 crystallographic direction parallel to the compression axis. Both the low stored energies in these grains and the pinning of recrystallizing grain boundaries by the dispersed carbides were discussed as crucial factors that resulted in the incomplete recrystallization.

The (Nb)/Nb3Si eutectic alloys in the Nb–Si binary and Nb–Ti–Si ternary systems were unidirectionally solidified in an optical floating zone melting furnace. The effect of solidification rates on microstructures of the alloys is investigated. The coupled growth of (Nb) and Nb3Si is observed in the binary alloy solidified at 10 mm/h. The ternary alloys exhibit the development of discontinuous (Nb) particles within the Nb3Si matrix. The unidirectionally solidified alloys show improved fracture toughness and enhanced high temperature compressive strength as compared with the arc-melted counterparts. The role of an aligned eutectic microstructure in toughening is discussed from the existing models based on the crack bridging and the crack deflection.

Phase equilibria in Co–Al–C ternary and Co–Ni–Al–C quaternary systems were investigated to establish the basis for designing new class of α(Co) based heat resistant alloys strengthened by the E2 1 type intermetallic compound Co 3 AlC. Phase stability of E2 1 (Co, Ni) 3 AlC was examined from the viewpoint of magnetic properties such as Curie temperature and saturation magnetization. The possibility of two-phase separation is indicated between E2 1 (E2 1 ′) (Co,Ni) 3 AlC and E2 1 (L1 2 ) (Ni,Co) 3 Al(C) in the Co–Ni–Al–C quaternary system, where we denote E2 1 ′ as standing for the ordered crystal structure of (Co,Ni) 3 AlC 0.5 formed by the extra ordering of carbon atoms. Phase diagrams information was determined by means of electron probe microanalysis and microstructural observation for the T–Al–C (T: Co, Ni, Rh, Ir) and T–Al–B (T: Rh, Ir) systems to examine the phase equilibria in each alloy system focusing on the existence of E2 1 T 3 AlC and T 3 AlB. The existence of E2 1 Ir 3 AlB (E2 1 ′ Ir 3 AlB 0.5 ) phase has been revealed in the Ir–Al–B system by diffraction analysis of transmission electron microscopy and electron probe microanalysis.

The crystallographic structures of the [0 1 1]/54.7° lath boundary and the intralath and interlath cementite precipitates in a 0.2C steel tempered at 400 °C have been observed by high resolution transmission electron microscopy and discussed in terms of the O-lattice model. The [0 1 1]/54.7° lath boundary which is composed of one Kurdjumov–Sachs variant ( α 1) and one Nishiyama–Wasserman variant ( α 2) is likely to facet on the (0 12 7) α 1 //(5 19 14) α 2 irrational plane. The O-lattice analysis indicated that the facet coincides with a plane with a high density of O-points. Intralath cementite obeys the Isaichev orientation relationship (OR) with ferrite and has a habit plane of (1 0 1) θ //(1 2 1) α . Interlath cementite precipitating on the [0 1 1]/54.7° boundary maintains a strict Bagaryatskii OR with the ferrite on one side of the boundary and has a (1 0 0) θ habit plane.

Thermal desorption spectrometry study of the hydrogen trapping capability of a tempered Fe–0.2C martensite indicated that dislocations in the martensitic substructure are the primary traps and new grain boundaries resulting from recovery and recrystallization of the ferrite matrix are the secondary traps for hydrogen. Cementite has a negligible effect on hydrogen trapping.

A new class of heat resisting ferritic steels is investigated in the Fe–Cr–Nb and Fe–Cr–Nb–Ni systems, in which the major strengthener is the Fe2Nb Laves phase. Ferritic steels strengthened by Laves phase are expected to show excellent high temperature strength, while the brittleness of Laves phase may lower the toughness of the alloy. The α-Fe/Fe2Nb two-phase microstructure is selected to improve mechanical properties through changing volume fraction and morphology of Laves phase. Effects of Nb and Ni contents on the microstructure and mechanical properties of the alloys, fixed at 10 at.% Cr, have been systematically investigated. Mechanical properties were evaluated by tensile tests conducted at room temperature, 873 and 973 K. The tensile test revealed that the room temperature ductility decreases with increasing Nb content. The alloys with 1.0–1.5 at.% Nb are found to exhibit a good balance between room temperature ductility and high temperature strength.

Plastic deformation features of Co3AlC0.5 and a Co3AlC0.5-strengthened cobalt-based alloy were studied by means of transmission electron microscopy. It was found that {111} slip system is activated and dissociation of superlattice dislocations occurs in Co3AlC0.5 in a manner similar to the L12 structure. However, in contrast to the L12 structure, motion of dislocations is hindered by the pre-existing thermally grown-in anti-phase boundaries formed by wrong site occupation of carbon atoms, a unique type of crystal defects in Co3AlC0.5. On the other hand, deformation of the α(Co) alloy containing fine Co3AlC0.5 precipitates is characterized by localized slip of 1/6 Shockley partial dislocations cutting through the fine Co3AlC0.5 particles, leaving behind a highly disordered band region.

The crystallography of the lamellar structure composed of the tetragonal C11b phase and the hexagonal C40 phase which is similar to the well-known TiAl/Ti3Al lamellae was investigated by means of transmission electron microscopy in a MoSi2–15mol%TaSi2 pseudo-binary alloy after homogenized at 1400 °C for 168 h. It was found that the orientation relationship between C11b and C40 phases obeys the coincidence of the equivalent hexagonal atomic planes for the two phases. Three distinct variants of this orientation relationship were identified by electron diffraction. 1 3 1 1 0 Dislocations prevail in the C11b/C40 interfaces to accommodate the lattice misfit between the two phases. On the other hand, networks of 1 3 1 1 0 and 1 3 1 1 3 dislocations are frequently observed in C40 phase. Significance of the 1 3 1 1 3 c-component dislocations for improvement of the plasticity of C40 phase has been discussed.