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Tungsten and its alloys are widely recognized as key components in high-temperature environments. In this study, self-passivating W-Si-xY alloys with varying Y content were prepared using mechanical alloying (MA) and spark plasma sintering (SPS). The synergistic effects of Y content and milling time on the microstructures and oxidation resistance of the alloys were revealed. This study found that the oxidation resistance of the alloys increased as the Y content increased. However, the effect of milling time on oxidation resistance was complex. For W-Si-xY alloys with low Y content (0Y and 2Y), the oxidation resistance decreased with increasing milling time. In contrast, for W-Si-xY alloys with high Y content (4Y and 6Y), the oxidation resistance increased with increasing milling time. This enhanced oxidation resistance is due to the microstructural changes in the protective composite layer, including the size and distribution of W5Si3, Y2Si2O7 aggregates, and W-Y-O melt. The thickness of the oxide layer on the W-Si-6Y alloy after being oxidized at 1000 °C for 2 h was only 70.7 μm, demonstrating its superior oxidation resistance. [ABSTRACT FROM AUTHOR]

Mo–Si–B alloys have attracted considerable research interest during the last several decades due to their high melting points, excellent high-temperature strength and relatively good oxidation resistance. However, insufficient room-temperature fracture toughness and high-temperature oxidation resistance restrain their further application. Generally, a sufficient volume fraction of BCC-Mo solid-solution phase, providing the ductility, and a high Si content, responsible for the formation of passive oxide scales, is difficult to achieve simultaneously in this ternary system. Recently, macroalloying of Ti has been proposed to establish a novel phase equilibrium with a combination of enough BCC phase and intermetallic compounds that contain a large amount of Si. In this article, the development history from the ternary Mo–Si–B to the quaternary Mo–Ti–Si–B system was reviewed. It was found that the constitution phases could be easily tailored by changing the Ti content. In this regard, better performance of mechanical properties and oxidation resistance can be obtained through proper alloy design. In-depth understanding of the advantages of the quaternary alloys over their ternary ancestors may contribute to bringing about a new concept in designing novel ultra-high-temperature structural materials. [ABSTRACT FROM AUTHOR]

Solution combustion synthesis (SCS) is an effective and rapid method for synthesizing nanocrystalline materials. However, the control over size, morphology, and microstructure are rather limited in SCS. Here, we develop a novel ultrasonic-assisted solution combustion route to synthesize the porous and nano-sized NaV(PO)/C composites, and reveal the effects of ultrasound on the structural evolution of NVP/C. Due to the cavitation effects generated from ultrasonic irradiation, the ultrasonic-assisted SCS can produce honeycomb precursor, which can be further transformed into porous NaV(PO)/C with reticular and hollow structures after thermal treatment. When used as cathode material for Na-ion batteries, the porous NaV(PO)/C delivers an initial discharge capacity of 118 mAh g at 0.1 C and an initial coulombic efficiency of 85%. It can retain 93.8% of the initial capacity after 120 cycles at 0.2 C. The results demonstrate that ultrasonic-assisted SCS can be a new strategy to design crystalline nanomaterials with tunable microstructures. [ABSTRACT FROM AUTHOR]

Molybdenum disilicide (MoSi) was in situ synthesized by spark plasma sintering into fully dense bulk material. Electron backscatter diffraction revealed that over the range from the center to periphery of the cylindrical sample, the microstructure is heterogeneously constituted by gradually refined MoSi grains and increasing amounts of MoSi impurity phase. The diversified strengthening mechanisms are primarily attributed to the Peierls-Nabarro stress in MoSi matrix, the Hall-Petch strengthening effect, and thermal mismatch stress between MoSi and MoSi. [ABSTRACT FROM AUTHOR]

Abstract: Taking the use of Nb and Si elemental powders as raw materials, Nb/Nb5Si3 composites were successfully fabricated by a spark plasma sintering (SPS) technology. The influence of sintering temperatures on microstructures of the synthesized composites was mainly investigated. The results show that there exists a critical sintering temperature T c (1400°C) in the synthesis of Nb/Nb5Si3 composites by SPS technology. When sintering temperature is lower than T c, an intermediate Nb3Si phase is produced in the fabricated samples. Moreover, the relative density of the samples is lower. Only if the sintering temperature is higher than T c, the intermediate Nb3Si phase is thoroughly eliminated, Nb particles become a finer size and desirable Nb/Nb5Si3 composites up to 99.59% theoretic density are achieved. [Copyright &y& Elsevier]

Transparent Pr3+ doped Ca 1-x Gd x F 2+x (x = 0, 0.01, 0.03, 0.06, 0.10, 0.15) polycrystalline ceramics with fine-grained microstructures were prepared by the hot-pressing method. The dependence of microstructure, optical transmittance, luminescence performances and mechanical properties on the Gd3+ concentrations for Pr3+:Ca 1-x Gd x F 2+x transparent ceramics were investigated. The Gd3+ ions show positive effects on the microhardness of Pr3+:Ca 1-x Gd x F 2+x transparent ceramics as a result of the decrease in the grain sizes. Excited by the Xenon lamp of 444 nm, typical visible emissions located at 484 nm, 598 nm and 642 nm were observed. Furthermore, the incorporation of Gd3+ ions can greatly enhance the photoluminescence performance owing to the improvement in the concentration quenching effect. The quenching concentration of Pr3+ ions in CaF 2 transparent ceramics increased to 1 at.% as a result of the positive effect of Gd3+ codoping. The energy transfer mechanism of Pr3+ in the Pr3+:Ca 1-x Gd x F 2+x transparent ceramics has been investigated and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Field activated sintering (FAS) was employed to fabricate dense bulk MoSi2 from Mo and Si powders. During the FAS process, Si was melted first, and then Mo was dissolved leading to a precipitation of MoSi2. A eutectic reaction of MoSi2–Mo5Si3 resulted from a combined effect of Mo–Si exothermic reactions and field induced Joule heating. With hyper-stoichiometric amount of Si (Mo/Si=1:2.06), the FAS MoSi2 is free of Mo5Si3 phase. Subsequently, an un-lubricated sliding wear test of MoSi2 against carbon steel was conducted. Both normal load and temperature have crucial points related to a transition from mild to severe wear. Sliding speed and relative density have a negative effect on wear rate. In addition, at room temperature the wear is with a protective layer composed of oxide and transferred substance, whereas poor oxidation resistance leads to spalling of the layer and brittle fracture at an elevated temperature up to 500°C. [Copyright &y& Elsevier]

Abstract: Using Mo, Si, and C element powders as starting materials, a field-activated and pressure-assisted combustion synthesis (FAPACS) was employed to synthesize high-density bulk MoSi2–SiC composite in one step. Effects of sintering temperatures (1100, 1200, 1400 and 1600°C) on microstructures and densification were investigated. With the exception of 1100°C, at which synthesis was incomplete, the FAPACS was characterized by the four stages, i.e. initial expansion, slight shrinkage, abrupt shrinkage and slight expansion. The study shows that the sintering ability at the higher temperature is better than that at the relatively lower temperature. When the sintering temperature reaches 1400 or 1600°C with holding time of 10min, the high-temperature transitional phases, i.e. Mo4.8Si3C0.6, were presented and the produced SiC particles are agglomerate. The relative density of the products (holding time: 10min) was improved tremendously from 59% to 96.0% over the range 1100–1400°C, and a smaller enhancement in densification up to 98.5% was achieved between 1400 and 1600°C. Moreover, an extended holding time (up to 20min) at 1600°C resulted in nearly Mo4.8Si3C0.6-free and dense MoSi2–SiC products with the relative density of 99.0%. Simultaneously, a locally uniform distribution of SiC in the synthesized MoSi2 matrix was achieved. And the interfaces between the synthesized phases are clean without impurities (e.g. SiO2) and porosities. Thereby, in order to pursue an equilibrium among densification, microstructural uniformity and formation of transitional phases, the most suitable sintering temperature and holding time for fabrication of MoSi2–SiC by FAPACS are recommended to be 1600°C and 20min in the present work. [Copyright &y& Elsevier]

Abstract: Dense TiC–Al2O3–Al composite was prepared with Al, C and TiO2 powders by means of electric field-activated combustion synthesis and infiltration of the molten metal (here Al) into the synthesized TiC–Al2O3 ceramic. An external electric field can effectively improve the adiabatic combustion temperature of the reactive system and overcome the thermodynamic limitation of reaction with x <10mol. Thereby, it can induce a self-sustaining combustion synthesis process. During the formation of Al2O3–TiC–Al composite, Al is molten first, and reacted with TiO2 to form Al2O3, followed by the formation of TiC through the reaction between the displaced Ti and C. Highly dense TiC–Al2O3–Al with relative density of up to 92.5% was directly fabricated with the application of a 14mol excess Al content and a 25Vcm−1 field strength, in which TiC and Al2O3 particles possess fine-structured sizes of 0.2–1.0μm, with uniform distribution in metal Al. The hardness, bending strength and fracture toughness of the synthesized TiC–Al2O3–Al composite are 56.5GPa, 531MPa and 10.96MPam1/2, respectively. [Copyright &y& Elsevier]

Abstract: Spark plasma sintering was employed to synthesize high-density bulk MoSi2 in one step, using Mo and Si element powders as starting materials. Influence of sintering temperature on sintering behavior and microstructures of MoSi2 were investigated. The sintering behavior at whatever temperature (1473, 1673 and 1873K) is characterized by four stages, i.e., initial expansion, slight shrinkage, abrupt shrinkage and slight expansion. The maximum shrinkage displacement increased with increasing sintering temperature. When the sintering temperature reaches 1673K or 1873K, the second phases, i.e., SiO2 and Mo5Si3/Mo4.8Si3C0.6, were uniformly distributed in the synthesized MoSi2 matrix accompanied with a small amount of porosity. Most of SiO2 and Mo5Si3/Mo4.8Si3C0.6 particles were concentrated at grain boundaries. The relative density of the products (atomic ratio: Mo/2.00Si) was improved tremendously from 89% to 98.2% over the range 1473–1673K, and much smaller enhancement up to 99.0% was achieved from 1673 to 1873K. At the same time, the grain size and amount of second phase particles (mainly Mo5Si3/Mo4.8Si3C0.6) consistently increased with increasing temperature over 1473–1873K. However, the use of a slight excess of Si (e.g., atomic ratio: Mo/2.06Si) at 1673K resulted in dense products of MoSi2 nearly free of Mo5Si3/Mo4.8Si3C0.6, with the relative density of 99.2% and the average grain size of 5–10μm. Thereby, in order to pursue an equilibrium among densification, microstructural refinement and formation of second phases, the most suitable sintering temperature and stoichiometry for fabrication of MoSi2 by SPS are recommended to be 1673K and a hyperstoichiometry of Mo/2.06Si in the present work. [Copyright &y& Elsevier]

Abstract: In order to achieve combustion synthesis (CS) of high-density and fine-structured TiC–Al2O3–Al composites, the activation of combustion reactions of 3TiO2–3C–(4+ x) Al system with x ≥10mol was conducted by means of external electric field. During the field-activated combustion synthesis (FACS), liquid Al in excess stoichiometric amount was generated and it infiltrated into the synthesized TiC–Al2O3 ceramic matrix with porosities, which directly results in a dense TiC–Al2O3–Al composites. The influence of electric field on CS process of the reactive system and the resulting microstructures of TiC–Al2O3–Al composites was investigated. The results show that an external electric field can effectively improve the adiabatic combustion temperature of the reactive system. Therefore a self-sustaining combustion of the system can be induced thermodynamically. In the experiments, both practical combustion temperature and propagation velocity of combustion wave were obviously enhanced with increasing field strength, whereas sizes of the synthesized TiC and Al2O3 particles were significantly decreased at the same time. Under an electric field of 25Vcm−1, TiC–Al2O3–Al composites with a relative density of 92.5% was successfully fabricated through the combustion reaction in the system with x =14mol, in which TiC and Al2O3 particles possess fine-structured sizes of 0.2–1.0μm, with uniform distribution in metal Al. [Copyright &y& Elsevier]

An oxide-dispersion-strengthened (ODS) 13Cr-1W steel has been fabricated through mechanical alloying (MA) and spark plasma sintering (SPS) using pre-alloyed Fe-Cr-W-Y powder and TiO 2 powder. Sufficient MA effects, indicated by homogeneous distribution of alloying elements and high level of lattice strain inside the powder, have been obtained within 20 h of high-energy ball-milling. Grain refinement of the bulk materials is successfully achieved by optimizing the sintering temperature and pressure during SPS. A fine-grained ODS steel with average grain size of 626.75 nm is prepared when sintered at 950 °C/80 MPa. Ultrafine oxide dispersoids, identified as Y 2 O 3 , Y 2 TiO 5 and Y 2 Ti 2 O 7 , are observed homogeneously distributed in the steel matrix after annealing. They have a number density of 4.5 × 1022 m−3 and an average size of 11.15 nm. Tensile tests from room temperature to 700 °C are conducted to this ODS steel. It exhibits an ultimate tensile strength and a yield strength of 1559.60 MPa and 1352.82 MPa at room temperature, respectively. Due to a good combination of dislocation strengthening, grain boundary strengthening and precipitation strengthening, this alloy wins superior tensile properties over most of the commercial ODS steels and those reported in some previous studies. • A nano-Y-Ti-O dispersion strengthened 13Cr-1W steel was prepared by MA and SPS. • MA process has been finished within 20 h using Y-containing pre-alloyed powder and TiO 2 powder. • Grain refinement was achieved by optimizing sintering temperature and pressure. • High number density of Y-Ti-O nanoparticles in-situ precipitated during annealing. • The steel possesses excellent tensile properties from room temperature to high temperature. [ABSTRACT FROM AUTHOR]

Abstract The influence of titanium sources on the microstructures and properties of Li 2 TiO 3 were investigated. The results show the hydrothermal synthesized α-Li 2 TiO 3 is a metastable phase and would transform into β-Li 2 TiO 3 phase during sintering. Compared with TiO 2 -hydrothermal synthesized powder, the TBT synthesized powder has better sintering activity. The relative density of ceramic pebbles can reach 84% when it was sintered at 800 °C for 3 h. The grain size and crush load are 0.62 μm and 35 N, respectively. The formation mechanisms during hydrothermal process are also discussed. Combined results of XRD and TEM, it is concluded that for TiO 2 as titanium source, TiO 2 particles first dissolve into the LiOH solution and then the dissolved TiO x − groups react with Li+ to form Li 2 TiO 3 precipitates. While for TBT source, α-Li 2 TiO 3 nucleus immediately form as soon as TBT is added into the LiOH solution at room temperature. [ABSTRACT FROM AUTHOR]

Microstructure and oxidation behaviour of multi-phase Mo-Ti-Si-B alloys with 0.2–1.0 at% Y addition were investigated in this study. In addition to Mo ss , Ti 5 Si 3 , and Mo 5 SiB 2 , a Y-rich intermetallic compound, YTiSi, was found to generate in Y-added alloys. With increasing Y-content, microstructure coarsening and increase in Mo ss volume fraction took place. Y-addition significantly improved the oxidation resistance of the alloys at 800 °C due to the formation of a thermally stabilized Y 2 Mo 3 O 12 layer. However, the positive effect of Y-addition cannot be maintained at 1100 °C because of the decomposition of yttrium molybdates during long-term oxidation. • Microstructure and oxidation behaviour of Y-added Mo-Ti-Si-B alloys were studied. • Y-addition increased volume fraction of Mo ss and led to microstructural coarsening. • Formation of Y 2 Mo 3 O 12 layer enhanced the oxidation resistance at 800 °C. • Positive effect of Y on oxidation resistance cannot be maintained at 1100 °C. [ABSTRACT FROM AUTHOR]

• Two 20 kg scale components with inner channeled structure made of 9Cr-RAFMs were fabricated by WAAM. • A refined F/M microstructure was formed in as-built 9Cr-RAFMs-0.5Ti due to inoculation effect and constitutional supercooling. • The as-built 9Cr-RAFMs-0.5Ti has good mechanical properties at both room temperature and high temperatures. Wire and arc additive manufacturing (WAAM) is promising for rapid fabricating the blanket component of fusion reactor in large scale with a complex structure, due to its high forming efficiency and low cost. In this work, two blanket components with inner-channeled structure were fabricated with 9Cr reduced activation ferritic/martensitic steel by WAAM. It was found that Ti reacted with oxygen to form TiO 2 particles is situ in the melt pool of 9Cr-RAFMs with 0.5% addition of Ti. These high melting point particles refined the grain size by heterogeneous nucleation. The microstructures of 9Cr-RAFMs and 9Cr-RAFMs-0.5Ti were studied by SEM, EBSD and TEM. In addition, their mechanical properties at different temperatures were obtained. An increase in the mechanical strength of as-built9Cr-RAFMs-0.5Ti was observed due to the fine grain structure, high dislocation density and high number density of oxide dispersions. [ABSTRACT FROM AUTHOR]

A Y–Ti–O oxide-dispersion-strengthened (ODS) Cu alloy has been successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Excessive cold-welding during high energy ball-milling was effectively suppressed by mixing TiO 2 and pre-alloyed Cu(Y) powders as the raw powders. Microstructural evolutions during the MA and SPS processes and the subsequent annealing were investigated with a focus on the Y–Ti–O nano-oxides. The 12 h ball-milling failed to achieve super-saturations of Y, Ti, and O in Cu, which led to the in-situ formation of various types of oversized Y/Ti-rich oxides with very irregular morphologies during the SPS. With a prolonged ball-milling of 48 h, the subsequent SPS + annealing processes can promote a high density precipitation of ultra-fine Y–Ti–O nano-oxides. These nano-oxides were further identified as Y 2 Ti 2 O 7 mostly, with a high degree of coherency in Cu. Fabricating Y–Ti–O ODS-Cu alloys via MA was thus confirmed to be technically feasible, although the dispersion of nano-oxides desires further improvement. • A Y–Ti–O ODS-Cu alloy was fabricated via mechanical alloying. • Using pre-alloyed Cu(Y) powders reduced cold-welding risks during ball-milling. • A high number of Y–Ti–O nano-oxides (mostly Y 2 Ti 2 O 7) were produced in Cu matrix. [ABSTRACT FROM AUTHOR]

• ODS-Cu alloy containing a high number density (2.16×1024 m−3) of uniformly dispersed nanoscale Y 4 Al 2 O 9 particles (mean particle size: 4.8 nm) was fabricated. • Coherent interface between Y 4 Al 2 O 9 nanoparticles and Cu(Al) solid solution matrix was formed with an orientation relationship of (3 1 ¯ 2) Y 4 A l 2 O 9 ∥ (1 1 ¯ 1) Cu (Al) and a small lattice mismatch of 0.337%. • The microhardness of the ODS-Cu alloy was enhanced to 228.6 HV. A relatively high thermal conductivity of 269 W m−1 K−1 at 600 °C for the ODS-Cu alloy was maintained. The softening temperature of the ODS-Cu alloy was more than 1000 °C. Oxide dispersion-strengthened copper (ODS-Cu) alloys with yttrium oxide nanoparticles are promising heat sink materials in fusion reactor due to their high strength, thermal conductivity and thermodynamic stability. The particle size and number density of oxide nanoparticles can be improved via addition of microalloying element. In this study, the atomized Cu-Y alloy, Al and Cu 2 O were used as the Y source, the microalloying element and the oxidant material, respectively, to fabricate ODS-Cu alloy by mechanical alloying method. After spark plasma sintering and annealing, a ODS-Cu alloy with a microstructure containing Y 4 Al 2 O 9 nanoparticles homogeneously distributed in Cu(Al) solid solution matrix was successfully fabricated. It is found that a crystallographic orientation relationship of (3 1 ¯ 2) Y 4 A l 2 O 9 ∥ (1 1 ¯ 1) C u (A l) was formed between Y 4 Al 2 O 9 nanoparticles and Cu(Al) matrix and the lattice mismatch was 0.337%. The small lattice mismatch reduced the nucleation barrier for Y 4 Al 2 O 9 nanoparticles so a mean particle size of 4.8 nm and a number density of 2.16×1024 m−3 were obtained in the alloy. Consequently, the microhardness was enhanced via Hall-Petch strengthening, dislocation strengthening and dispersion strengthening. The softening temperature of ODS-Cu alloy was improved to higher than 1000 °C due to the thermodynamic stability and the pinning effect of Y 4 Al 2 O 9 nanoparticles. In addition, the thermal conductivity of Cu-1Y-9Al-0.3Cu 2 O alloy is close to other copper alloys as the volume fraction of Y 4 Al 2 O 9 nanoparticles is limited. Cu-1Y-9Al-0.3Cu 2 O alloy provides a good overall performance, which may be used as heat sink materials under severe conditions. [ABSTRACT FROM AUTHOR]

Abstract: Bulk dense composites of Al–Fe alloys containing 2.5–10at% Fe were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Supersaturated Al(Fe) solid solutions were obtained by MA for 80h. The sintered samples are composed of nano and ultrafine needle-like Al13Fe4 phase and angular-shaped Al13Fe4 phase with a size range of 1–2μm uniformly distributed in the Al matrix. Needle-like Al13Fe4 phase originates from the precipitation of supersaturated Al(Fe) solid solutions, and angular-shaped Al13Fe4 phase originates from the reaction of undissolved Fe particles and the Al melt. The hardness of the alloys varied from 1.44 to 1.97GPa and Al–10%Fe exhibited highest specific yield strength of 391.1kNm/kg. The yield strength varied from 657 to 1130MPa, depending on the Fe content. Excellent plastic strain (>14.5%) were achieved in the alloys containing 2.5–5%Fe, but the Al–10%Fe exhibited elastic behavior only, failing without any macroscopic yielding or plastic strain. The lack of plastic performance of Al–10%Fe is attributed to large amount of undissolved Fe particles reacted with the Al melt to form angular-shaped Al13Fe4, leading to the absence of soft α-Al phase. [Copyright &y& Elsevier]

Abstract: Nb/Nb5Si3 composites were successfully fabricated by a spark plasma sintering (SPS) technology. The effects of element (Nb and Si) proportions on the microstructures of the synthesized composites were mainly investigated. The results show that element proportions strongly affect the microstructures of Nb/Nb5Si3 composites; Nb/Nb5Si3 in situ composites up to 99.59% of theoretical density were fabricated by SPS technology, and the microstructures of the fabricated composites comprise the synthesized Nb5Si3 and the uniformly distributed Nb particles. Moreover, with the increase in the Si content from 6% to 20% (atom fraction), the volume fraction of the synthesized Nb5Si3 in the composites increases, whereas the content and size of Nb particles decrease obviously. The higher shrinkage and densification for Si content (16at.% and 20at.%) close to the eutectic composition take place. When sintering temperature over 1400°C, the shrinkage obviously retards and finally stops. [Copyright &y& Elsevier]

A self-passivating W-Si-Y alloy was prepared by spark plasma sintering, while the microstructure evolution and oxidation mechanism at 1000 °C were analyzed. The alloy exhibits excellent oxidation resistance due to the introduction of Y. At high temperatures, Y enriches on the surface of the oxide scale, and a melt mainly containing W, Y and O is formed. The melt can close the pores on the surface of loose oxide layer to form a dense protective layer, which not only prevents oxygen from permeating into the alloy, but also alleviates the sublimation of WO 3. • A novel self-passivating W-Si-Y alloy with excellent oxidation resistance is obtained by SPS. • The specimen maintains its cubic shape oxidized for 80 h, the thickness of the oxide scale is almost the same for 20 h–80 h. • The improvement of oxidation resistance of W-Si-Y is quite related with the melt during oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Starting from powder mixture of MoO3–CuO–Al–Si system, a process of self-propagation high-temperature synthesis and casting (SHS-casting) was employed to fabricate Cu–MoSi2 composite successfully with assistance of thermit reactions of Al–CuO and Al–MoO3. DTA measurements and Gibbs energies change calculations were made to determine sequence of reactions for in situ synthesis of the composite. First, the thermit reaction between Al and CuO took place. The next was the thermit reaction between Al and MoO3, followed by a series of reactions in Mo–Si system to form MoSi2 and Mo5Si3. Enrichment of Si may aid in depression of transitional phase Mo5Si3. With an environment of high adiabatic temperatures, silicon got molten. Thus, generation of MoSi2 may result from a coverage effect of continuous liquid Si to particles of Mo. Due to melting of copper, the Cu–MoSi2 solidified directionally with an aligned composite structure by means of a steep temperature gradient. [Copyright &y& Elsevier]

• Microstructure evolution was analyzed for three Mo–Ti–Si–B alloys. • Suppressing the volume fraction of Mo 3 Si is an effective way to prevent pesting. • Site-specific microstructure of the oxide scale was observed. • Interactions between constituent phases contributed to the oxidation resistance. Three Mo–Ti–Si–B alloys with compositions of 50Mo–20Ti–20Si–10B, 40Mo–30Ti–20Si–10B and 30Mo–40Ti–20Si–10B (at.%) were designed and prepared by arc-melting. Microstructure evolution at 1600 °C and oxidation mechanism at 800 °C of these alloys were analyzed. 50Mo–20Ti–20Si–10B suffered from pesting because of a large volume fraction of Mo 3 Si, which produced porous products with severe volume expansion. Both 40Mo–30Ti–20Si–10B and 30Mo–40Ti–20Si–10B have better oxidation resistance. It can be inferred that during long-term oxidation, interactions between constituent phases contributed to the overall oxidation resistance of the alloys. [ABSTRACT FROM AUTHOR]

Three Mo–Ti–Si–B-based alloys with the compositions of 35Mo–35Ti–20Si–10B, 35Mo–35Ti–15Si–10B–5Al and 32.5Mo–32.5Ti–20Si–10B–5Cr (at.%) were designed and produced by arc-melting in argon atmosphere, and their oxidation behavior was investigated at temperature between 700 °C and 1100 °C. All the alloys were composed of three phases, i.e., Mo-rich solid-solution, Ti 5 Si 3 and Mo 5 SiB 2. Specific weight change against oxidation time was obtained at both intermediate and high temperatures. A rapid mass loss occurred in the initial period of oxidation, after which the oxidation rate gradually decreased and sometimes even stayed stable. The total mass loss within 24 h was less than 2.0 mg/cm2 at all testing temperatures for all compositions. All the alloys demonstrated a relatively good oxidation resistance at intermediate temperatures, which was attributed to the relatively low viscosity of the borosilicate glass in the TiO 2 -borosilicate duplex scale. Pest phenomenon or spalling of the oxide scale did not occur for all alloys, and Al- or Cr-addition improved the oxidation resistance at intermediate temperatures through microstructure revolution. Continuous Al- or Cr-oxide layer was not observed on the alloys even after they were oxidized at high temperature. Besides, 32.5Mo–32.5Ti–20Si–10B–5Cr (at.%) had the best oxidation resistance at 1100 °C in this study because a dense borosilicate-matrix duplex layer formed on this alloy. • Three Mo ss –Ti 5 Si 3 –T 2 composites were prepared by arc-melting. • Pest phenomenon did not occur during intermediate-temperature oxidation. • Al- or Cr-addition improves the oxidation resistance at intermediate temperature. • High-temperature oxidation resistance relies on the borosilicate-matrix scale. [ABSTRACT FROM AUTHOR]