Thermal conductivity and other thermoelectric properties were investigated on β-Zn4Sb3 and CoSb3 thin films. They are prepared by co-deposition of the specific sets of Zn, Sb and Co targets by RF magnetron sputtering. Thermal conductivity measurement was performed based on an AC calorimetry method using LaserPIT. The Zn4Sb3 thin films investigated are Zn-rich with respect to the stoichiometric composition. Their thermal conductivity decrement is proportional to the reciprocal film thickness. A nano-scale grain size in a ∼350 nm-thick film specimen gives arise to an almost 50% reduction in its thermal conductivity (∼0.5W/mK) at room temperature. Low electrical resistivity and high Seebeck coefficient can be achieved simultaneously in the film specimen with properly controlled thickness and microstructure. A ZT of 1.2 at ∼460K has been obtained for the ∼350nm thick Zn4Sb3 film specimen. The minimum thermal conductivity of about 1.1 W/mK was obtained in a ∼325 nm-thick CoSb3 film specimen at room temperature.

Direct access to a T2-Moss eutectic microstructure with a nominal composition of Mo-9Si-18B (at.%) was obtained using an optical floating zone method at a growth rate of less than 5mm/h. The Mo-9Si-18B two-phase alloy has relatively high 0.2% proof stress at 1500°C of about 700 MPa and fracture toughness at room temperature (RT) of ∼11 MPaVm. The (Mo,Nb)-19.5Si-B alloys with (Mo,Nb)ss-T1-T2 three-phase eutectic microstructure have lower yield stress at 1500°C and fracture toughness at RT lower than the Mo-9Si-18B two-phase alloy. The dense short rod-type morphology of Moss in the Mo-9Si-18B alloy may be pulled out of T2 matrix and crack bridging may play a crucial role in toughening. Due to the limited ductility of Mo at RT, its morphology is more important rather than its volume fraction in improving the fracture toughness of multi-phase alloys.

Silicide coating on the Mo-9Si-18B alloys with the T2-Moss two-phase microstructure using a halide-activated pack cementation was also examined. The B-doped Mo5Si3 layer with the D8m structure was formed on the substrate after oxidation at 1500°C for 24 hours. The substrate is the source of B atoms. A steady-state weight gain was observed at 1300–1500°C and their steady-state constants are almost equal to those of MoSi2. The weight loss was saturated in 16–26 cycles at 1500°C. It was about -0.4mg/cm2, suggesting thermal stress resistance of the coated Mo-9Si-18B two-phase alloys is sufficient in the present condition.

The relationship between microstructures and hydrogen absorption-desorption properties described in terms of pressure-composition (P-C) isotherms has been investigated for binary and Co- and Al-added LaNi5-based alloys as a function of the number of hydrogen sorption cycles. From microstructure observations, factors determining absorption pressures are deduced and variations of P-C isotherms with cycle number for these three LaNi5-based alloys are discussed.

Mo5X3+α (X=Si, B, C) intermetallic compounds such as Mo5SiB2 (D8l), Mo5Si3 (D8m) and Mo5Si3C (D88) have a great potential for ultra-high temperature applications. The present study was undertaken putting greater emphasis on clarifying how their physical and mechanical properties are similar or different in terms of a structure type. Some interesting features are summarized in this paper.

The resistivity of Mo5SiB2, Mo5Si3 and Mo5Si3C single crystals exhibited a negative curvature (d2ρ(T)/dT2<0), with a tendency towards saturation. In the Mo5Si3C with large ρ0 due to impurity carbon atoms, resistivity saturation is pronounced. In contrast, a much higher temperature is required to reach saturation in the Mo5SiB2. The anisotropy ratio of CTE (αc/αa) for the Mo5SiB2 is about 1.2–1.6 and is significantly reduced from about 2 of the Mo5Si3 and Mo5Si3C. On the other hand, the Young's modulus of the Mo5SiB2 is more anisotropic than those of the Mo5Si3 and Mo5Si3C. Plastic anisotropy was observed in the Mo5SiB2, because only slip on [001] {100} is operative at 1500°C. On the contrary, plastic deformation was observed at temperatures above 1300°C for the Mo5Si3C and Mo5Si3. Anisotropy of their plastic deformation was much less than that of the Mo5SiB2, presumably because more than two slip systems can be activated. Creep resistance of the Mo5SiB2 is much better than that of the Mo5Si3 as well as the most advanced materials such as MoSi2 and Si3N4 based structural ceramics.

Hydrogen absorption/desorption of Ti3Al-based alloys with α2 single-phase, β0 single-phase and β/O two-phase microstructures was investigated to obtain systematic understanding microstructure effects. On exposing all the alloys to hydrogen, β (βH) and γ (γH) hydrides are formed. The βH and γH have bcc and bct (close to fcc) based structures, respectively. The hydrogen/metal ratio of the γH is larger than that of βH. Thus, solute hydrogen in Ti3Al based alloys stabilizes the bcc-based phase just like Nb, regardless of their original structure before hydrogenation. On the other hand, reversible hydrogen absorption/desorption around 100°C and related reversible βH-γH transformation was observed in β/O two-phase (Ti,Nb)3Al and α2-Ti3Al alloys, but not obviously observed in a β0-(Ti,Nb)3Al alloy. In forming the βH, the expansion of the β0 and β phases occurred isotropically keeping their structures B2 and bcc, respectively. In contrast, the O and α2 phases expanded in anisotropic manner. The lattice deformation for the βH→γH transformation can be described similarly to those for the O→βH and α2→βH transformations. Such lattice deformation in anisotropic manner most likely agrees with that observed in a martensitic displacive transformation, because of the surface relief observed on the γH after the βH→γH transformation in the β0-(Ti,Nb)3Al alloy and many twins formed during the α2→βH transformation in the α2-Ti3Al alloy. Mechanisms of the reversible βH-γH transformation in the β/O two-phase (Ti,Nb)3Al and α2-Ti3Al alloys was proposed on the basis of similarities in the lattice deformation and ordering of hydrogen atoms required for the βH-γH, O-βH and α2-βH transformations.

MoSi2 has a great potential for very high temperature structural applications. Plastic deformation of MoSi2 single crystals with the C11b structure is extremely anisotropic. It is caused by non-Schmid behavior of slip on {013}<331> with the higher CRSS values for orientations closer to [001]. In order to provide better understanding of key factors on such non-Schmid behavior in MoSi2 (c/a=2.45), we chose PdZr2 with a c/a axial ratio higher than 3 (c/a=3.30) and characterized the plastic deformation. Compression tests were conducted at various temperatures along [001], [010] and [110] axes. Slip on {013}<100> has the shortest Burgers vector and the largest interplanar spacing in PdZr2 and was observed to be activated for [110] with the lowest CRSS. While slip on {013}<331> can be activated even at -196°C for [001]. Although {013}<331> slip has the same Schmid factors for [001] and [010], the yield stress of the [010]-oriented crystals is about twice higher than that of the [001]-oriented crystals. Thus non-Schmid behavior of slip on {013}<331> is also observed in PdZr2, and the manner is opposite to that in MoSi2. Plastic anisotropy in the C11b structure will be discussed in terms of the c/a axial ratio.

Effects of ternary additions on the deformation behavior of single crystals of MoSi2 with the hard [001] and soft [0 15 1] orientations have been investigated in compression and compression creep. The alloying elements studied include V, Cr, Nb and Al that form a C40 disilicide with Si and W and Re that form a C11b disilicide with Si. The addition of Al is found to decrease the yield strength of MoSi2 at all temperatures while the additions of V, Cr and Nb are found to decrease the yield strength at low temperatures and to increase the yield strength at high temperatures. In contrast, the additions of W and Re are found to increase the yield strength at all temperatures. The creep strain rate for the [001] orientation is significantly lower than that for the [0 15 1] orientation. The creep strain rate for both orientations is significantly improved by alloying with ternary elements such as Re and Nb.

Design rules are described here for high-temperature straining stages for transmission electron microscopy. Temperatures above 1000°C can be attained by electron bombardment of the specimen grips. Thermal equilibrium can be reached in a short time by carrying off the heat by water cooling. Some applications of this stage are described. Ferroelastic deformation was observed at 1150°C in t′ and partially stabilized zirconia, which changes the microstructure for successive dislocation plasticity. In the oxide-dispersion-strengthened alloy INCOLOY MA 956, dislocations are impeded by oxide particles and move smoothly between the particles. At high temperatures, both the resting and traveling times control the average dislocation velocity. In MoSi2 single crystals of a soft orientation, dislocations with 1/2〈111〉 Burgers vectors are created in localized sources and move on {110} planes in a viscous manner. The dislocations in Al-Pd-Mn single quasicrystals are oriented in preferred crystallographic directions and move in a viscous way as well. On the basis of in situ observations, conclusions are drawn for interpreting macroscopic deformation behavior at high temperatures.

The operative slip systems in the so-called PST alloy are determined by transmission electron microscopy. Both post-mortem analyses and in situ observations are presented. It is shown that glide of ordinary dislocations and twinning are the most easily deformation modes activated at yield. The role of the interfaces on the activation of these operative slip systems is then examined and discussed.

Deformation microstructures in a 45°<321> oriented (the lamellar interface was tilted 45° from the loading axis about the <321> direction in the lamellar interface) poly synthetically twinned (PST) TiAl crystal deformed in compression at 3000 s-1 and 800 °C was studied. Deformation of this PST crystal is characterized as follows: 1) Deformation of domains [III] and [IV] is dominated by 1/6 [112] parallel twinning (twinning parallel to lamellar interfaces). Ordinary dislocations observed in these domains are found to be a complementary deformation mode. 2) Deformation of domains [II], [V] and [VI] is controlled by a 1/2<110] ordinary dislocation slip. Complementary deformation modes in these domains are ordinary dislocation slip, superdislocation slip and cross-twinning. 3) Domain [I] is not deformed after the specimen deforms up to ∼7% strain.