SS Phases Research Articles

Two Mechanisms Generating Intraplate Volcanism in Southeast Asia: Insights From Mantle Transition Zone Discontinuities

AbstractDetermining the mechanisms responsible for intraplate volcanism ‐ such as slab devolatilization melting versus active mantle plumes ‐ remains a challenge. The greater South China Sea (SCS) region has experienced extensive intraplate Cenozoic volcanism across areas including Hainan, Southeast Indochina, northern Borneo, the northern SCS, and the post‐spreading SCS basin. The prevalence of volcanism distributed widely across this region prompts fundamental questions about the key geodynamic processes driving such diverse magmatic activities. In this study, we elucidate the mantle transition zone (MTZ) discontinuities in this region using SS precursors, which helps to overcome the sparse seismic coverage due to its predominantly oceanic setting. We collected over 16,000 high‐quality seismograms that sample the upper mantle and MTZ beneath this region from global earthquakes and stations. After correcting for the effects of shallow crustal variations and upper mantle heterogeneity on traveltimes of SS phases and their precursors, we unveil lateral variations in the MTZ boundaries (d410 and d660) and intricate features of the mid‐MTZ reflectors (S520S). Significant MTZ thinning and normal S520S waveforms beneath Hainan provide compelling evidence for mantle upwelling through the MTZ. Conversely, the evident splitting of S520S beneath the northern SCS, Southeast Indochina, and northern Borneo, all characterized by stagnant subducted slabs, indicates that the volcanism in these regions likely originated from a mechanism distinct from the active upwelling beneath Hainan. Dehydration melting attributed to devolatilizing stagnant slabs in the MTZ is a potential cause for Cenozoic volcanism in these regions.

High strength diffusion bonding of Ti2AlNb to GH4169 with (TiZrHfNb)95Al5 high entropy interlayer

A high entropy interlayer (TiZrHfNb)95Al5 was designed for vacuum diffusion bonding of Ti2AlNb to GH4169. The influence of bonding temperature on the interfacial microstructure morphology, mechanical properties and fracture behaviour of the resultant joints was investigated. The evolution of microstructure and fracture mechanism were revealed. The typical interface microstructure of Ti2AlNb/B2/Solid solution/(Ti, Zr, Hf)2(Ni, Nb)+(Ti, Zr, Hf)(Ni, Nb)+(Ti, Zr, Hf)(Ni, Nb)2+Solid solution/(Ti, Zr, Hf)(Ni, Nb)+(Cr, Ni, Fe)ss/(Cr, Ni, Fe)ss/Cr-rich(Cr, Ni, Fe)ss/Ni-rich(Cr, Ni, Fe)ss/GH4169 was formed. As the bonding temperature increased, the thickness of interfacial reaction layer gradually increased, and the shear strength gradually increased until 980 °C, then decreased sharply. The highest shear strength reached 376 MPa at 980 °C for 90 min. The highest microhardness region of 11.79 GPa existed on the GH4169 side, which was mainly composed of (Ti, Zr, Hf)(Ni, Nb) and (Cr, Ni, Fe)ss phases. Meanwhile, the elastic modulus dramatically changed interface formed near this region. The fracture surface morphology indicated typical brittle fracture characteristics such as cleavage steps, transgranular fracture and intergranular fracture. According to the fracture analyses, major cracks initiated in the (Ti, Zr, Hf)(Ni, Nb) phase+(Ti, Zr, Hf)2(Ni, Nb) phase and gradually extended to the (Cr, Ni, Fe)ss phase. Thus, the major crack emerged region was located at the elastic modulus dramatically changed interface.

Diffusion Welding for TC4 Titanium Alloy/T2 Copper with Vanadium Foil

TC4 titanium alloy (TC4) was vacuum diffusion welded to T2 copper (T2) with vanadium (V) foil as an interlayer. The influence of process parameters on elemental diffusion behavior, microstructure evolution, and shear performance of welded joints was explored. An obvious solid-solution diffusion zone appeared in the welded interface between TC4 and V, but no distinct diffusion zone formed in the joint interface of V/T2. The solid-solution phases of (Ti6, V)ss, (Ti3, V)ss, and (Ti, V7)ss appeared in the interface of TC4/V. The crystallographic orientations of (Ti6, V)ss, (Ti3, V)ss, and (Ti, V7)ss phases in high-resolution transmission electron microscope images were (002), (201), and (121), respectively. The lattice mismatch between (Ti6, V)ss and (Ti3, V)ss was calculated to be 11.9%. The activation energy to form a stable solid solution between titanium and vanadium was 226.6 kJ/mol. The highest shear strength of the welded joint reached 160 MPa, obtained at 860°C (1580°F) for 60 min. The joint fractured along the interface of V/T2, illustrating that the solid-solution structure between Ti and V was stronger than the metallurgical bonding between V and Cu. The fracture surface of the welded joints revealed a river pattern and ladder topography, representing a cleavage fracture mode. FCC-Cu, BCC-V, and β-Ti were detected on both fracture surfaces of the TC4 titanium alloy and T2 pure copper sides. The influence of welding temperature on the diffusion of V in Ti was greater than on Ti in V, and Ti and Cu diffused faster than V in the joint.

Phase diagram of a generalized Penson–Kolb–Hubbard chain with the occupation-dependent hopping

At half filling, we study analytically a one-dimensional correlated electronic system modeled by an extended Penson–Kolb–Hubbard (PKH) chain with the occupation-dependent hopping. The modification of the electron hopping amplitude is exhibited to induce the additional correlated-hopping interactions. At weak coupling, we use the field theory to obtain ground-state phase diagram, including the SDW, BCDW, BSDW, SS and TS phases for U>0. The induced three-body attractive interaction accounts for the superconductivity absent in the usual PKH model.

Phytocenological Structure and Biological Reserves of Helichrysum aurantiacum Boiss. & A. Huet in Gazakh-Tovuz Economic Region (Azerbaijan)

The article presents the phytocenological and bioecological analyzes of Helichrysum aurantiacum Boiss. et Huet., an endemic species of the Asteraceae family and assessments in plant coenopopulations of the plant. The studies were carried out in 3 districts of Gazakh-Tovuz Economic Region of Azerbaijan. Ten natural populations where H. aurantiacum species are distributed were selected. In the selected populations, the integral characteristics of the demographic structure of the plant, age and efficiency indices were studied. The formations and associations were determined, the project cover of the areas was calculated, and the abundance was determined. In the H. aurantiacum species, the highest indicator is observed in the generative development stages (225-243 individuals were counted in the g1-g3 period). The efficiency coefficient of H. aurantiacum species in mature populations was ω=0.52-0.76. The high value of the efficiency coefficient in CP 7, 6 and 10 is related to the high number dynamics of plants belonging to the juvenile and immature phases before the generative development phases, and the small number of individuals belonging to the aging (s, ss) phases. The resource potential of the plant was determined and the biological reserve in the districts was 1241.1 centners, and the annual supply was 498.6 centners. This allows the supply of H. aurantiacum species in Tovuz, Agstafa and Gazakh districts located in the north-east of the Lesser

The Effects of External Vibration on Coordination Strategies of Multi-Muscles during Voluntary Isometric Torque Production

PURPOSE: To investigate the effect of muscle vibration on performance accuracy and multi-muscle coordination pattern during voluntary isometric knee extension torque production.METHODS: The subjects were tested under two conditions of external vibration frequencies (90 Hz vibration (VIB)&no-vibration (NVIB)) with three levels of torque magnitudes of 20% (MVT20), 40% (MVT40), and 60% of maximal voluntary torque (MVT60). The subjects were instructed to perform a submaximal isometric ramp task and matched the produced torque with the torque template shown in the screen as accurately as possible. External vibration was applied to the rectus femoris (RF).RESULTS: The performance error (RMSENORM) was reduced in 60% of MVT (MVT60) in both ramp and SS phases, and the iEMGAGO was significantly reduced by vibration under the same torque conditions in the SS phase. In addition, the muscle-mode (M-mode) composition was found to be different in the VIB and NVIB in the SS phase. We found that the VIB condition showed co-contraction M-modes and mixed M-modes. However, there was no significant difference in the ramp phase under all conditions.CONCLUSIONS: The neurophysiological changes due to muscle vibration may positively affect the task characteristics and steps that require accurate torque generation and provide information for the quantitative understanding of multi-muscle coordination of vibration.

The Far Side of Mars: Two Distant Marsquakes Detected by InSight

Abstract For over three Earth years the Marsquake Service has been analyzing the data sent back from the Seismic Experiment for Interior Structure—the seismometer placed on the surface of Mars by NASA’s InSight lander. Although by October 2021, the Mars seismic catalog included 951 events, until recently all these events have been assessed as lying within a radius of 100° of InSight. Here we report two distant events that occurred within days of each other, located on the far side of Mars, giving us our first glimpse into Mars’ core shadow zone. The first event, recorded on 25 August 2021 (InSight sol 976), shows clear polarized arrivals that we interpret to be PP and SS phases at low frequencies and locates to Valles Marineris, 146° ± 7° from InSight. The second event, occurring on 18 September 2021 (sol 1000), has significantly more broadband energy with emergent PP and SS arrivals, and a weak phase arriving before PP that we interpret as Pdiff. Considering uncertain pick times and poorly constrained travel times for Pdiff, we estimate this event is at a distance between 107° and 147° from InSight. With magnitudes of MwMa 4.2 and 4.1, respectively, these are the largest seismic events recorded so far on Mars.

PHYTOSENOLOGICAL STUDY OF ZOSIMA ABSINTHIFOLIA (VENT.) LINK. IN AZERBAIJAN

Describes the study of the habitats, populations and phytocenology of the Zosima absinthifolia (Vent.) Link. Zosima absinthifolia belongs to the Apiaceae family and the only species of the genus distributed in the Nakhchivan Autonomous Republic and Absheron Peninsula in the steppe landscapes. The results showed that in 6.7,10th senopopulations the coefficient of efficiency was higher (ω = 0.59-0.67). This is due to the fact that, in these populations, the dynamics of the number of plants belonging to the juvenile and immature phases before the generative developmental phases is high, and individuals with aging (s, ss) phases were few. In favorable conditions seed reproduction increases the number of seedling senopopulation (35.48%). In such cases, the post-generation fraction level decreases (25.87%). As the environment deteriorates, the role of vegetative reproduction increases. As a result, sprouts in the age spectrum are minimized (3.97%). The maximum share of j + im + v (47.4%) in the III senopopulation decreased accordingly (7.77-35.38%). Number of individuals in populations VI, VII and X is increasing. In other populations, a decrease in the number of individuals was observed.

A Possible Roll-Over Slab Geometry Under the Caroline Plate Imaged by Monte Carlo Finite-Frequency Traveltime Inversion of Teleseismic SS Phases

The shape of a subducting slab varies as a function of trench motion. Two end-members of subduction modes are geodynamically possible: roll-back mode underneath neighboring plates and roll-over mode underneath the plate itself. Whereas most of major slabs seem to roll back while the Pacific plate shows a slab piling behavior down to ∼1,000 km depth under the Mariana trench, no clear evidence of slab roll-over in nature has been reported so far. Here we show a possible roll-over slab beneath the Caroline microplate, revealed from its three-dimensional seismic velocity structure derived by analyzing teleseismic reverberating SS phases. We suggest that slab roll-over is driven by at least two factors: 1) the overall buoyancy and fragility of the Caroline microplate at the surface, induced by a thin hot mantle plume that rises from depths ≥800 km; and 2) the pushing force of the Pacific plate acting on the trailing edge of the Caroline plate.

A novel ultra-high temperature Pt–Rh alloy with balanced tensile strength and creep resistance achieved by rare-earth intermetallics

A novel ultra-high temperature Pt–25Rh (wt.%) alloy with a minor addition of rare-earth (RE) elements (0.2 wt% La and 0.2 wt% Ce) was developed for the first time which exhibits the capability to withstand aggressive environment with a high operating temperature of >1500 °C. Tensile creep tests of the alloy were carried out at 1500 °C under a load of 5 MPa, the high tensile strength (σb) was up to 47.8 MPa, the creep rate (ε) as low as 0.008%/h and a rupture time (τ) more than 53 h, respectively. Detailed microstructure characterization revealed that there exist two balanced phases in the alloy, a ductile (Pt, Rh) solid solution phase with a face-centered cubic structure and a strengthening Pt5RE (RE = La, Ce) intermetallic phase with a hexagonal structure. The Pt5RE phases present three types of forms in the alloy, precipitates in the (Pt, Rh)ss matrix, an intergranular phase along the grain boundaries and a eutectic mixture in the matrix. Composition analysis showed that RE elements almost completely exist in the Pt5RE intermetallic phase but rarely in the (Pt, Rh)ss phase. It is interesting to note that the Pt5RE intermetallic phase is a RE-poor phase in which the content of RE elements is less than 5 wt%, much lower than the stoichiometric ratio (12.46 wt%). Compared with the reported Pt–Rh binary alloys, a minor additions of La and Ce in the new alloy effectively improves its high-temperature mechanical properties, which can be attributed to the formation of the strengthening Pt5RE intermetallic phase. By the way, an orientation relationship was identified between the Pt5RE and (Pt, Rh)ss phases in the eutectic structure for the first time.

Studies on Creep and Wear Behavior of Mo-40Ti-10Si Alloy Prepared by Hot Pressing

The present study deals with the development and characterization of a Mo-Ti-Si alloy by pressure-assisted sintering for high-temperature applications. The three-phase alloy was found to be consisted of (Mo,Ti)3Si-type silicide and discontinuous Mo-rich and Ti-rich α-(Mo, Ti)ss phases. The alloy was characterized for mechanical properties, creep, and wear behavior. Elastic modulus and hardness of all the constituent phases were determined using nanoindentation technique. Creep properties of the alloy determined from the compression creep tests in vacuum were found to be better than the single-phase Mo5Si3 and Ti5Si3 at the tested temperature of 1000 °C. The coefficient of friction values were found to be 0.59, 0.55 and 0.4 at the testing loads of 10, 15 and 20 N, respectively, at 10 Hz frequency in reciprocal testing mode at room temperature, while 0.42 at 500 °C with a load of 15 N. The dominant wear mechanism was proposed based on the wear scar analysis.

Microstructural evolution and mechanical properties of Ni–45Ti–5Al–2Nb–1Mo alloy subjected to different heat treatments

The effects of solution and aging heat treatment on microstructural evolution and room temperature tensile properties for as-forged Ni–45Ti–5Al–2Nb–1Mo alloy were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile tests. The results show that the microstructure of solution-treated alloy comprises NiTi matrix, Ti2Ni and (Nb,Ti)SS phases. After aging treatment at 700 °C for 6 and 100 h, the distribution of Ti2Ni and (Nb,Ti)SS precipitates increases in uniformity. No new type of precipitate is observed in the specimen aged at 700 °C. After aging at 800 °C for 100 h, numerous nanosized Ni2TiAl phases are precipitated within the grains. Solution and aging treatments improve the tensile properties at room temperature. Tensile strength and ductility are improved after solution treatment at 1100 °C plus aging treatment at 800 °C for 6 h or 700 °C for 100 h. With aging time prolonging to 100 h at 800 °C, the precipitation of fine Ni2TiAl particles leads to the improvement in tensile strength and deterioration of elongation.

On the Microstructure and Isothermal Oxidation of Silica and Alumina Scale Forming Si-23Fe-15Cr-15Ti-1Nb and Si-25Nb-5Al-5Cr-5Ti (at.%) Silicide Alloys.

An Nb-silicide based alloy will require some kind of coating system. Alumina and/or SiO2 forming alloys that are chemically compatible with the substrate could be components of such systems. In this work, the microstructures, and isothermal oxidation at 800 °C and 1200 °C of the alloys (at.%) Si-23Fe-15Cr-15Ti-1Nb (OHC1) and Si-25Nb-5Al-5Cr-5Ti (OHC5) were studied. The cast microstructures consisted of the (TM)6Si5, FeSi2Ti and (Fe,Cr)Si (OHC1), and the (Nb,Ti)(Si,Al)2, (Nb,Cr,Ti)6Si5, (Cr,Ti,Nb)(Si,Al)2 (Si)ss and (Al)ss (OHC5) phases. The same compounds were present in OHC1 at 1200 °C and the (Nb,Ti)(Si,Al)2 and (Nb,Cr,Ti)6Si5 in OHC5 at 1400 °C. In OHC1 the (TM)6Si5 was the primary phase, and the FeSi and FeSi2Ti formed a binary eutectic. In OHC5 the (Nb,Ti)(Si,Al)2 was the primary phase. At 800 °C both alloys did not pest. The scale of OHC1 was composed of SiO2, TiO2 and (Cr,Fe)2O3. The OHC5 formed a very thin and adherent scale composed of Al2O3, SiO2 and (Ti(1−x−y),Crx,Nby)O2. The scale on (Cr,Ti,Nb)(Si,Al)2 had an outer layer of SiO2 and Al2O3 and an inner layer of Al2O3. The scale on the (Nb,Cr,Ti)6Si5 was thin, and consisted of (Ti(1−x−y),Crx,Nby)O2 and SiO2 and some Al2O3 near the edges. In (Nb,Ti)(Si,Al)2 the critical Al concentration for the formation of Al2O3 scale was 3 at.%. For Al < 3 at.% there was internal oxidation. At 1200 °C the scale of OHC1 was composed of a SiO2 inner layer and outer layers of Cr2O3 and TiO2, and there was internal oxidation. It is most likely that a eutectic reaction had occurred in the scale. The scale of OHC5 was α-Al2O3. Both alloys exhibited good correlations with alumina forming Nb-Ti-Si-Al-Hf alloys and with non-pesting and oxidation resistant B containing Nb-silicide based alloys in maps of the parameters δ, Δχ and VEC.

Microstructural Characteristics and Mechanical Properties of a Nb/Nb5Si3 based Composite with and without Directional Solidification

The Nb/Nb5Si3 based composites were fabricated by conventional casting (CC) and directional solidification (DS) methods. Micro structural characteristics, compressive properties and fracture toughness of the CC and DS composites were investigated by SEM, XRD, TEM, bending and compression tests. The results demonstrate that in the CC Nb/Nb5Si3 based composite, the intergrowth of fine (Nb,Ti)ss and α-(Nb,Ti)5Si3 phases leads to the formation of eutectic structure and the coarse α-(Nb,Ti)5Si3 dendritic phase prefers to grow along eutectic cell boundary. The (Nb,Ti)3Si, (Ti,Nb)5Si3 and Dy2O3 phases mainly segregate along the eutectic cell boundary and moreover there is an orientation relationship between the (Nb,Ti)3Si and (Nb,Ti)ss phases: [001] (Nb,Ti)3Si//[112](Nb,Ti)ss and (110)(Nb,Ti)3Si//(110)(Nb,Ti)ss. The DS processing promotes the formation of coarse primary α-(Nb,Ti)5Si3 phase, (Ti,Nb)5Si3/(Nb,Ti)ss eutectic and α-(Nb,Ti)5Si3/(Nb,Ti)ss eutectic in the DS Nb/Nb5Si3 based composite. Moreover, the (Nb,Ti)ss and α-(Nb,Ti)5Si3 phases are aligned paralleling to the DS direction and exhibits strong crystal orientation preference. In addition, an orientation relationship between the (Nb,Ti) ss and α-(Nb,Ti)5Si3 phases is observed: [310]α(Nb,Ti)5Si3//[110](Nb,Ti)ss. Compared with the CC Nb/Nb5Si3 based composite, the DS Nb/Nb5Si3 based composite possesses the higher yield strength and fracture toughness, which should be ascribed to the microstructure optimization.

A successful backward step correlates with hip flexion moment of supporting limb in elderly people.

PurposeThe objective of this study was to determine the positional relationship between the center of mass (COM) and the center of pressure (COP) at the time of step landing, and to examine their relationship with the joint moments exerted by the supporting limb, with regard to factors of the successful backward step response.MethodsThe study population comprised 8 community-dwelling elderly people that were observed to take successive multi steps after the landing of a backward stepping. Using a motion capture system and force plate, we measured the COM, COP and COM-COP deviation distance on landing during backward stepping. In addition, we measured the moment of the supporting limb joint during backward stepping. The multi-step data were compared with data from instances when only one step was taken (single-step). Variables that differed significantly between the single- and multi-step data were used as objective variables and the joint moments of the supporting limb were used as explanatory variables in single regression analyses.ResultsThe COM-COP deviation in the anteroposterior was significantly larger in the single-step. A regression analysis with COM-COP deviation as the objective variable obtained a significant regression equation in the hip flexion moment (R2 = 0.74).ConclusionsThe hip flexion moment of supporting limb was shown to be a significant explanatory variable in both the PS and SS phases for the relationship with COM-COP distance. This study found that to create an appropriate backward step response after an external disturbance (i.e. the ability to stop after 1 step), posterior braking of the COM by a hip flexion moment are important during the single-limbed standing phase.

Microstructure Evolution and Mechanical Properties of a Directionally Solidified Nb-Ti-Si-Cr-Al-Hf-Dy Alloy

The Nb-Ti-Si-Cr-Al-Hf-Dy alloy was prepared by conventionally casting and then directionally solidified (DS) with the optical floating zone melting technology. Microstructural evolution and mechanical properties of the as cast (AC) and DS alloys were studied by XRD, SEM, TEM, compression and bending tests. The results exhibit that α-(Nb, Ti) 5 Si 3 , (Ti, Nb) 5 Si 3 and (Nb, Ti)ss phases formed the microstructure of the AC alloy, with precipitates of Cr 2 Nb, Dy 2 O 3 and (Nb, Ti) 3 Si along phase or grain boundaries. The DS alignes (Nb, Ti)ss and α-(Nb, Ti) 5 Si 3 lamellae parallel to the growth direction and refines the eutectic cell, but coarsens the primary α-(Nb, Ti) 5 Si 3 phase. The DS alloy exhibits strong orientation of (310) (Nb, Ti)5Si3 and (110) (Nb, Ti)ss along the growth direction. TEM observation reveals that (Nb, Ti)ss and α-(Nb, Ti) 5 Si 3 phases have an orientation relationship of [110] (Nb, Ti)ss // [310] α-(Nb, Ti)5Si3 and (002) (Nb, Ti)ss // (002) α-(Nb, Ti)5Si3 . Compared with the AC alloy, the DS increases the mechanical properties of the alloy obviously and the alloy DS at 8 mm/h exhibits the best mechanical properties.

Contribution of gallium oxide content to the crystallization characteristics and chemical stability of sodium phlogopite glasses

The effect of gallium oxide content on the crystallization characteristics and chemical durability of a sodium phlogopite based glass-ceramic of the stoichiometric phase formula NaMg3(Si3[Al1−X,Gax]O10)F2 where X=0.0, 0.25, 0.5, 0.75 and 1.0 was investigated. The Ga2O3/Al2O3 replacement and heat treatment have an effect on the crystalline phases developed and their microstructure. Forsterite ss, enstatite, and sodium phlogopite phases were mostly detected in the crystallized glasses. There is a preferential tendency for forsterite to accommodate sodium phlogopite ions in its structure forming olivine solid solution of forsterite type. At low Ga2O3/Al2O3 replacement an increase in the crystallization temperature led to the decomposition of the sodium phlogopite phase to form forsterite ss phase, while at high Ga2O3 replacement increasing the heat-treatment temperature led to the development of forsterite ss at the expense of enstatite phase. The chemical stability of the crystallized materials was better in acidic than in alkaline media. The present data provides valuable information about the role played by the glass oxide constituent in determining the nature of the crystalline phases and solid solution formed in the materials especially in the field of preparation of glass-ceramic substrate used for magnetic information storage.

Microstructure and mechanical properties of Nb- and Mo-modified NiTi–Al-based intermetallics processed by isothermal forging

A compositionally modified Ni–45Ti–5Al–2Nb–1Mo (at%) alloy was developed by simultaneously adding Nb and Mo in NiTi–Al-based alloy and processed by forging isothermally. The as-forged Ni–45Ti–5Al–2Nb–1Mo alloy consists of NiTi matrix, Ti2Ni and dispersive (Nb,Ti)SS phases. Mo addition reduces the solubility of Nb in the NiTi matrix and gives rise to the precipitation of numerous nanoscale (Nb,Ti)SS phases (bcc structure) within the grains. The (Nb,Ti)SS phase is semi-coherent to the NiTi matrix with a lattice misfit of 6.7%. The addition of Mo and Nb dramatically enhances the NiTi–Al alloy at high temperatures, which is mainly attributed to the solid solution strengthening of Nb and Mo elements as well as the precipitation strengthening of (Nb,Ti)SS phases. The Ni–45Ti–5Al–2Nb–1Mo alloy is expected to become a high-temperature structural material using at intermediate temperatures with strengths of 650MPa at 923K and 350MPa at 1073K.

The Role of GeO 2 and In 2 O 3 in the Glass-Ceramic Formation and Microstructure of Lithium Alumino-Silicate Glasses

The crystallization characteristics of the glasses based on the Li2O–Al2O3–SiO2 system have been investigated. The base glass composition was modified by partial replacement of GeO2 for SiO2 and In2O3 for Al2O3. The effect of the compositional variation on the crystallization products of the glasses and the type of the solid solution (ss) phases formed as well as the resulting microstructure were traced by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). A decrease in the endothermic and exothermic temperatures was detected by the replacement processes. β -spodumene ss, β -eucryptite ss, lithium meta- and di-silicate, lithium aluminum germanate and two forms of indium-containing phases (LiInSi2O6 & In2Si2O7 phases) were mostly developed in the crystallized glasses. The objective of the present work is to understand the role of the glass oxide constituents in determining the type of the crystalline phases formed, their solid solution formed and the microstructure of the resultant glass-ceramic materials.

Microstructure and mechanical properties of hot pressed Mo–Cr–Si–Ti in-situ composite, and oxidation behavior with silicide coatings

The present study deals with the synthesis of Mo–16Cr–4Si–0.5Ti (wt.%) alloy by means of the reactive hot pressing method. The microstructure of the synthesized alloy consisted of (Mo, Cr, Ti)3Si, and the discontinuous α-(Mo, Cr, Ti)SS phases. The isothermal oxidation behavior of the alloy was investigated in air at 1273K for 50h. The alloy exhibited superior oxidation behavior in comparison with single phase molybdenum alloys, because of the formation of SiO2 and Cr2O3 over the alloy surface. The flexural strength determined from three-point bend testing of single edge notch bend specimens was 615±15MPa. The dominant mechanism of fracture was identified as transgranular mode of crack propagation. To extend the life of the alloy under oxidizing atmosphere, silicide based oxidation resistant coatings were developed, using halide activated pack cementation process. The kinetic behavior of growth of the coating was established and the activation energy of the coating process was determined to be 52.5kJ/mol. Isothermal oxidation tests of the coated alloy at 1273K for 50h, revealed a small weight gain at the initial stages of oxidation followed by no change of weight, indicating the protective nature of the coating.