It is thought that protoplanets formed in protoplanetary disks excite the orbital motion of the surrounding planetesimals, and the bow shocks caused by the highly excited planetesimals heat their icy component evaporating into gas. We have performed model calculations to study the evolution of molecular abundances of the evaporated icy component, which suggests sulfur-bearing molecules can be good tracers of icy planetesimal evaporation. Here we report the result of our ALMA observations of sulfur-bearing molecules towards protoplanetary disks. The lines were undetected but the obtained upper limits of the line fluxes and our model calculations give upper limits of the fractional abundances of x(H2S) < 10−11 and x(SO) < 10−10 in the outer disk. These results are consistent with the molecular abundances in comets in our Solar system.

A new target design is presented to model high-energy radiative accretion shocks in polars. In this paper, we present the experimental results obtained on the GEKKO XII laser facility for the POLAR project. The experimental results are compared with 2D FCI2 simulations to characterize the dynamics and the structure of plasma flow before and after the collision. The good agreement between simulations and experimental data confirms the formation of a reverse shock where cooling losses start modifying the post-shock region. With the multi-material structure of the target, a hydrodynamic collimation is exhibited and a radiative structure coupled with the reverse shock is highlighted in both experimental data and simulations. The flexibility of the laser energy produced on GEKKO XII allowed us to produce high-velocity flows and study new and interesting radiation hydrodynamic regimes between those obtained on the LULI2000 and Orion laser facilities.

For the improvement of oxidation resistance of Nb-based alloys, PdAl-B2 is expected as Al reservoir for Al2O3 surface layer because it is in equilibrium with Nbss (bcc) phase. However, PdAl forms cracks during casting caused by B2 -> β’ transformation. To suppress B2 -> β’ transformation, Rh, Ru and Ir were chosen as additive elements. It is found that bcc / B2 two-phase field in Nb-Pd-Ir-Al system is limited to be small fraction of Ir, while (Pd,Rh)Al-B2 is in equilibrium with bcc solid solution in a wide composition range and addition of Rh prevents occurrence of B2 -> β’ transformation. Composition range of (Pd,Ru)Al-B2 in equilibrium with bcc phase is wider than (Pd,Ir)Al-B2 but narrower than (Pd,Rh)Al-B2. Rh and Ru addition are also beneficial for improving eutectic temperature of Nb-bcc / B2 aluminide two-phase alloys.

The effect of Ti addition on the density and microstructure development of MoSiBTiC alloy was investigated. Two kinds of MoSiBTiC alloys with the composition of Mo-5Si-10B-10Ti-10C (10Ti alloy) and Mo-5Si-10B-15Ti-10C (15Ti alloy) (at. %) were prepared by conventional arc-melting. The primary phase of as-cast 10Ti and 15Ti alloys was (Ti,Mo)C, and there were two eutectic phases of Moss + (Ti,Mo)C and Moss + T2 + (Ti,Mo)C in the alloys. In addition, 10Ti alloy had a Moss + T2 + (Mo,Ti)2C eutectic. There was no Moss + T2 + (Mo,Ti)2C eutectic in the 15Ti alloy, and thus it is apparent that the (Mo,Ti)2C formation was suppressed by 5 at. % Ti addition. The volume fraction of (Ti,Mo)C increased and thus the density reduced from 8.78 to 8.43 g/cm3 with the Ti addition. In all constituent phases, Ti concentration increased while Mo concentration decreased. In spite of the changes, hardness, Young’s modulus and shear modulus were hardly changed. Therefore, Ti addition seems to be effective to further lower the density without deteriorating mechanical properties of the MoSiBTiC alloy.

Oxidation tests of Cr containing Co-based superalloys with compositions of Co-20at.%Ni-9at.%Al-9at.%W-x at.%Cr (x = 2, 4, 6, 8 and 10) have been carried out at 1173 and 1273 K in air. Oxidation resistance is improved upon alloying with Cr not only at 1173 K but also at 1273 K. The weight gain of the 10at.%Cr alloy oxidized at 1173 K is similar to that of the 5th generation Ni-based superalloy of TMS-173. Alloying with Cr is efficient to improve oxidation resistance, however, the shape of γ’ precipitates is rounded and the alignment of the precipitates along the <100> direction becomes less pronounced upon alloying with Cr.

Deformation behavior of MoSi2 has been studied by micropillar compressions of single crystalline specimens prepared by focused ion beam (FIB) technique as a function of crystal orientation at room temperature. Activation of the {011}<100> and {01 $\overline 3$ }<331> slip systems were observed in the micropillars compressed along [ $\overline 1$ 10] and [0 15 1], respectively. The CRSS values for each slip system exhibit an approximate power law relationship with the edge length of micropillar. The {01 $\overline 3$ }<331> slip exhibit much stronger size-dependence than the {011}<100> slip system.

Phase equilibria among the β-Ti, α-Ti and γ-TiAl phases were examined at 1473 K, in order to reveal the M/Nb ratio dependence of the relative phase stability of β phase in the Ti-Al-Nb-M (M: V, Cr, Mo) quaternary systems. In all of the quaternary systems, the expansion of β phase region toward the lower (Nb+M) content side is observed due to the existence of negative interaction to stabilize the β phase between the third and fourth elements (i.e. Nb-V, Nb-Cr and Nb-Mo). Composition dependence of the interaction is quantified as a function of the M/(Nb+M) ratio at 42 at.% Al. The strong interaction energy existing between the different group elements should be taken into account to design the multi-component TiAl alloys.

The reverse martensitic (austenite) transformation temperatures (A s) were investigated using a diffusion couple of PtTi and CoTi with a continuous compositional gradient. It was found that PtTi and CoTi form a complete solid solution of (Pt, Co)Ti at 1373K. Surface relief was formed by heating due to the austenite transformation. Judging from the formation of the surface patterns and the corresponding chemical compositions, A s monotonously decreases with increasing Co content at a rate of -70K/at%Co, and A s is estimated to be close to room temperature (RT) when the Co concentration is 15at%Co. Besides, micro Vickers hardness values measured at RT are minimized around 15at%Co.

The formation frequency of habit plane variant (HPV) clusters in Ni-25Pd-50Ti shape memory alloy was analyzed using electron backscattering diffraction (EBSD) on the basis of the geometrically nonlinear theory of martensite. Two types of cluster, diamond and wedge, were most commonly observed. The ratio of the formation frequency of the diamond to wedge clusters was approximately 1 : 3, whereas the rotation to keep the kinematic compatibility (KC) condition, θ *, was 3.9° and 0.0032°, respectively. The ratio of the formation frequency is quantified by the value of θ * which is an indicator of the incompatibility of the cluster. The origin of the diamond cluster is discussed based on the degree of incompatibility.

Periodically arrayed rows of fine Fe2Hf Laves phase particles were found to form in 9Cr ferritic steel. Microstructural observation demonstrates that the particles were formed on cooling through the interphase precipitation on the phase transformation from the δ ferrite to the γ austenite along the eutectoid transformation route of δ → γ+Fe2Hf and subsequently a phase transformation from the austenite to the α ferrite took place. This eutectoid route is expected to be effectively used for improving the long term creep strength of ferritic steels with Laves phase.

In the present study, the crystallographic features of bcc/T1/T2 three-phase microstructure in a directionally solidified Mo–32.2Nb–19.5Si–4.7B (at.%) alloy have been examined by electron back-scattering diffraction (EBSD) analysis. The alloy was directionally solidified using an optical floating zone (OFZ) furnace in a flowing Ar gas atmosphere at a constant growth rate of 10 mm/hour. The microstructure of the directionally solidified alloy is characterized by an elongated T2 phase surrounded by inclusions of bcc and T1 phases with an interwoven morphology. The T2 grains are faceted on the (001) planes and elongated along the [110] direction. The T2 phase has an orientation relationship of (001)T2 // (011)bcc and [130]T2 // [2 ${\rm{\bar 1}}$ 1]bcc with the bcc phase, whereas any particular orientation relationships of T1 phase with bcc and T2 phases have not been found. These crystallographic features of bcc/T1/T2 three-phase microstructure suggest that the primary T2 phase crystallizes and grows along the [110] direction in liquid phase, followed by nucleation of the bcc phase on the interface between T2 and liquid phases, resulting in bcc/T1 two-phase eutectic reaction surrounding the elongated T2 phase.

The temperature dependence of yield stress and the associated dislocation dissociation in L12 intermetallic compounds are investigated in order to check the feasibility of the classification of L12 intermetallic compounds so far made in terms of the planarity of core structures of partial dislocations with b = 1/2<110> and 1/3<112> on {111} and {001} glide planes. In contrast to what is believed from the classification, the motion of APB-coupled dislocations is evidenced to give rise to the rapid decrease in yield stress at low temperatures for Pt3Al. In view of the fact that rapid decrease in yield stress at low temperatures is also observed in Co3(Al,W) and Co3Ti in which APB-coupled dislocations are responsible for deformation, the SISF-type dissociation is not a prerequisite for the rapidly decreasing CRSS for slip on (111) and the relative magnitudes of the APB energy on (111) and the SISF energy on (111) cannot be a primary factor that determines the type of the temperature dependence of CRSS for L12 compounds. The importance of the CSF energy as a factor determining the type of the temperature dependence of yield stress for L12 compounds through the changes in the planarity of the core structure of the APB-coupled partial dislocation with b p = ½[1 $\overline 1$ 0] is discussed in the light of experimental evidence obtained from Pt3Al.

The ternary system Fe - 25 at% Co - 9 at% Mo shows an age hardening behavior similar to aluminum alloys. After solution annealing followed by rapid quenching, the Fe-Co-matrix is hardened during subsequent aging through precipitation of the intermetallic µ-phase (Fe,Co)7Mo6. In aged condition the entire Mo content is present in coarse primary and fine µ-phase particles and, therefore, the matrix consists exclusively of 71 at% Fe and 29 at% Co. The binary system Fe-Co shows a transformation from the disordered bcc structure to the ordered B2 structure between 25 and 72 at% Co at a critical ordering temperature ranging from room temperature to 723°C. As a consequence, the remaining overaged matrix in the Fe - 25 at% Co - 9 at% Mo system should also show such a transition. However, an ordered phase is brittle and, thus, not wanted for many applications. Better mechanical properties in terms of ductility can be achieved with a partially or fully disordered phase. Such a state can be obtained by rapid quenching from temperatures above the critical ordering temperature. In this study such an approach was implemented on the ternary Fe - 25 at% Co - 9 at% Mo alloy. The effect of different cooling rates on the mechanical properties was investigated by means of hardness testing. The actual ordering transition of the Fe - 29 at% Co matrix was determined with differential scanning calorimetry and neutron diffraction.

In this work we examine a Ti-48Al-2Cr-2Nb alloy obtained with an additive manufacturing technique by Electron Beam Melting (EBM) by conducting monotonic and cyclic loading experiments both on tension and compression samples for investigating the influence of the microstructure in strain accumulation process by fatigue loading. The residual strain maps corresponding to different applied stress levels, number of cycles and microstructures are obtained through the use of high-resolution Digital Image Correlation (DIC). The strain maps were overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. Such experiments, conducted ex-situ at room temperature, allow to characterize the effect of different microstructures on the strain accumulation process, and to clearly identify the role of the microstructural features of this TiAl intermetallic alloy on the fatigue initiation process.

The Au-Si liquid phase was obtained by melting the Si surface via Au-Si eutectic reaction, which contributed to the formation of semiconducting iron disilicide (β-FeSi2), on Au-coated Si(100) substrates. By coating a substrate with an Au layer of 60 nm or more, the Au-Si liquid phase covered the entire Si substrate surface, and single-phase β-FeSi2 was grown on Si(100) substrates. A clear photoluminescence spectrum of β-FeSi2 indicated the formation of high-quality crystals with a low density of the non-radiative recombination center in the grains.

The effect of Si addition on microstructure and mechanical properties of dual two-phase intermetallic alloys was investigated. Si was added to the base alloy composition Ni75Al9V13Nb3 + 50 wt. ppm B by three substitution ways in which Si was substituted either for Ni, for Al and for V, respectively. The alloys added with 1 at.% Si showed a dual two-phase microstructure composed of Ni3Al (L12) and Ni3V (D022) phases, while the alloys added with over 2 at.% Si exhibited the same dual two-phase microstructure but contained third phases. The third phases were G phase (Ni16Si7Nb6) and A2 phase (the bcc solid solution consisting of Nb and V). Yield and tensile strength of the 1 at.% Si-added alloys were high in the alloy in which Si was substituted for Al but low in the alloys in which Si was substituted for Ni or for V, in comparison with those of the base alloy. Tensile elongation was lower than that of the base alloy irrespective of substitution ways. The density of the Si added alloys was close to or slightly lower than that of the base alloy. Oxidation resistance of the Si added alloy was increased. Si addition to the dual two-phase intermetallic alloys is beneficial for reducing the density and enhancing the oxidation resistance without a harmful reduction of strength properties.

B2 aluminides have a role of Al reservoir for Al2O3 surface and it is expected to increase oxidation resistance of (Nb,Mo)-bccss substrate. For the accumulation of the basic information to design the alloy composed of B2 coating on bccss matrix, bccss - B2 two-phase field was investigated in the Nb-Mo-Ni-Pd-Al system at 1273 K. It is found that Pd-rich B2-(Ni,Pd)Al phase is in equilibrium with Nb-rich bccss phase, while without Pd, the composition range of bccss coexisting with B2-NiAl phase is limited to be low Nb.

New low aluminium high niobium TiAl alloys exhibit a nano scale modulated microstructure consisting of lamellae with a tweed substructure. These tweed like appearing lamellae are a modulated arrangement of at least two phases. One constituent of the crystallographic modulation in the lamellae is an orthorhombic phase, which is closely related to both the hexagonal α2-Ti3Al phase and the cubic B2 ordered βo-TiAl phase.

In this study the nature and formation of this orthorhombic phase has been investigated by high-energy X-ray diffraction.

Measurements have shown that the newly formed orthorhombic phase is structurally comparable to the O phase (Ti2AlNb). It forms in the temperature range of 550 °C to 670 °C from the α2 phase by small atomic displacements and chemical reordering. The in situ experiments yielded information about the thermal stability of the orthorhombic phase. After dissolving at temperatures above 700 °C the phase can be re-precipitated by annealing within the temperature range of formation.

The phase equilibrium and oxidation behavior of the disilicides that form in the Nb-Cr-Si ternary system have been investigated. Although NbSi2 and CrSi2 both exhibit a C40 crystal structure, they form separate ranges of compositional homogeneity in the ternary system. Their phase boundaries at 1300 °C have been experimentally determined in this study. The binary NbSi2 exhibited poor oxidation resistance, showing pest-like behavior during oxidation at temperature above 800 °C. In contrast, the alloys containing Cr showed much better oxidation resistance up to 1200 °C.