Liquid-solid Doping Research Articles

Effects of Al2O3 and Cr2O3 on the microstructure and properties of Mo alloys prepared via vacuum sintering

The dilemma of strength and ductility of Mo alloy at ultra-high temperature (above 1300 °C) limits its application in space reactors and other high-temperature environments. Single oxide enhancement has been unable to meet these use requirements. In this research, a strategy of synergistic reinforcement of Mo alloys with nanosized Al2O3 and Cr2O3 ceramic particles was proposed. A 300−400 nm Mo alloy powder was prepared by liquid‒solid doping, and in situ self-generated nanosized oxides were obtained. The grain size of vacuum sintered Mo alloy was very fine, at only 5.3 μm, which was one tenth of the particle size of commercial Mo alloy. Al2O3 and Cr2O3 particles were distributed in the grains of the Mo matrix, which effectively prevented the growth of Mo grains during vacuum sintering and reinforced the Mo alloy. The maximum flow stress of the Mo–Al2O3–Cr2O3 alloy reached 367 MPa at 1000 °C/1 s−1, which was better than that of the single-oxide reinforcement. The ultimate tensile strength (UTS) of the Mo–Al2O3–Cr2O3 alloy was 862 MPa, which was twice that of pure Mo. The preparation process is simple and available for industrial production. Synergistic strengthening of multiple oxides will be the best strategy for strengthening refractory alloys in the future.

Microstructures and properties of Al2O3 dispersion-strengthened Cu10Sn oil bearings prepared by solid-liquid doping and reactive synthesis method

To modify the shortcomings of Cu10Sn oil bearing in mechanical performance, this work proposes to prepare the Al2O3 oxide dispersion strengthened (ODS) Cu10Sn oil bearings by reactive synthesis using elemental Sn and Al2O3 ODS-Cu powder, among which the uniformly doped Al2O3 ODS-Cu powder was synthesized through a solid-liquid doping of Al(NO3)3 in CuO powders followed with hydrogen reduction. The effects of Al2O3 content on the microstructure and properties of ODS-Cu powder and ODS-Cu10Sn oil bearings were investigated in details. The results showed that an increase in Al2O3 amount from 0 to 1.5 wt% leads to a decrease in the average particle size of the reduced ODS-Cu powders, and contributes to the significant improvement of radial compressive strength, and Vickers microhardness. The appropriate sintering temperature is approximately 800 °C, which can result in the evenly distributed Al2O3 and well-developed porosity in oil bearing sample after sintering. The corresponding compressive strength and microhardness of ODS1.5-Cu10Sn oil bearing can reach 305 MPa and 208 HV respectively.

Microstructure and high-temperature deformation performance of liquid-dispersed evaporated Nano-ZrTiO4 doping molybdenum alloy

To enhance the low-temperature plasticity and high-temperature strength of molybdenum alloys, we introduce a method of uniformly dispersing nano-ZrTiO4 particles within and between molybdenum grains. This approach effectively eliminates the formation of hard agglomerations between particles and leads to a further refinement of molybdenum grains. The research employs molecular level solid-liquid doping and subsequent liquid dispersion evaporation techniques to successfully synthesize Mo-ZrTiO4 nano-composite powder following H2 reduction. Subsequently, a novel fine-grained Mo-ZrTiO4 alloy sintered billet is successfully fabricated through cold isostatic pressing and high-temperature sintering. To assess the efficacy of the process, three sets of comparative experiments are designed, each employing different methods. The comparative studies have revealed compelling advantages of the liquid dispersed evaporated fine-grained samples of Mo-ZrTiO4. The key advantages identified are as follows:the samples demonstrate a refined grain size, ranging from 2 μm to 4 μm. Within the samples, the nano ZrTiO4 particles have an average size of approximately 200 nm. The density and Vickers hardness of the samples is measured at 10.21 g/cm3 and 268.5 ± 17HV0.2, respectively. The samples exhibit impressive toughness even at room temperature, notably, the high-temperature compressive strength of these samples surpasses that of the deformed samples reported in previous literature concerning this system. The mechanism of liquid dispersion evaporation method in grain nucleation, growth, and powder drying, reduction, and sintering processes was systematically elaborated. Simultaneously, a detailed analysis was conducted on two high-temperature strengthening mechanisms that impact the mechanical properties. The results indicate that this excellent performance can be attributed to the synergistic effect of both fine grain strengthening and uniform dispersion strengthening of second-phase nanoparticles.

Effects of composite oxide addition on the microstructure and properties of ODS copper

Oxide dispersion strengthened copper-based material is widely used in electrical contact materials due to its excellent mechanical and electrical properties. However, researchers have found that large Y2O3 particles have poor interfacial bonding with the copper matrix in the study of oxide dispersion strengthened copper. In this work, Y4Zr3O12 nanoparticles were successfully prepared through solid–liquid doping and directly added into oxide dispersion-strengthened copper by mechanical alloying. A scanning electron microscope, a transmission electron microscope, an X-ray diffractometer, and electrical and mechanical tests were used to characterize the microstructure and performance of composite materials. The interfaces between the Y2O3/Y4Zr3O12 nanoparticles and Cu were systematically studied. The interface bonding between Y4Zr3O12 and Cu was better than that of Y2O3 and Cu. The effect of different Y4Zr3O12 contents (1, 3, and 5 wt%) on the microstructure and mechanical properties of the composites was studied. Results showed that the Cu-3 wt% Y4Zr3O12 composites exhibited the best comprehensive properties. The Vickers hardness, yield strength, ultimate tensile strength, maximum engineering strain, and electrical conductivity of the Cu-3 wt% Y4Zr3O12 composites were 132HV, 203.5 MPa, 284.7 MPa, 15.8 %, and 90.3 % International Annealed Copper Standard, respectively.

Study on Morphology and Chemical States of Surface Active Layer of Th-W Cathode.

The surface morphology and chemical states of W-2%ThO2 thermionic cathode during vacuum high-temperature treatment were investigated in this research. The W-2%ThO2 thermionic cathode was prepared by a solid-liquid doping method combined with high-temperature sintering. The morphology and distribution of thorium oxide were observed using a transmission electron microscope and scanning electron microscope. The chemical states of elements at different temperatures were analyzed by X-ray photoelectron spectroscopy. Results indicate that the surface morphology and chemical form of the alloy evolve with the increase of temperature. The matrix had a lamellar structure at low temperatures, and the surface was relatively flat. The samples were heated to 500 °C, 1100 °C, and 1300 °C for 1 h. During the heating process, thorium oxide changed from granular to spherical, and the matrix was recrystallized. As the heating temperature rises, diffusion channels appear inside the cathode. As the temperature increases, the high-priced tungsten gradually decreases, and the zero-valent tungsten content increases. The adsorbed oxygen left the cathode surface, and the lattice oxygen increased. The surface oxygen content decreased, and the thorium and tungsten content increased.

The formation mechanism of micro-nano secondary phase in solid-liquid doped TZM alloy

Among the various secondary phases distributed in the TZM (Titanium-Zirconium-Molybdenum) alloy matrix, the ones that can play a strengthening role are often those with a particle size smaller than 1 μm. In this study, titanium sulfate, zirconium nitrate, and fructose were used as raw materials. The TZM alloy with uniform distribution and an average secondary phase particle size of 940 nm (hereinafter referred to as MN-TZM alloy) was prepared through a solid-liquid doping preparation process. The thermodynamic calculation reveals the formation mechanism of the micro-nano-level secondary phase in the MN-TZM alloy. Thermogravimetric analysis (TG-DSC, TG-MS) and transmission electron microscope (TEM) confirmed the calculation results. The generation process of the micro-nano secondary phase evolution can be divided into four parts. The first stage is the process of solute dissolution at room temperature. In the second stage, doping and drying process take place below 100 °C. Third, reduction and secondary phase precursor incubation processes occur from 100 to 700 °C. Fructose decomposes (100 °C) to obtain organic carbon and water. The decomposition of zirconium nitrate (100 °C) yields NH 3 , H 2 O, ZrO 2 and Zr, while the titanium sulfate decomposes directly at 200– 242 °C to obtain SO 2 , H 2 O, TiO 2 and Ti. In the last stage, the secondary phase nucleates and grows up (700– 1800 °C). A large variety of micro-nano-scale and even nano-scale secondary phase particles have been discovered, including TiO 2 , ZrO 2 , ZrC and TiC. These observations provide necessary information for tracing back the secondary phase precipitation mechanism in the manufacturing process of high-performance molybdenum alloys. • The average grain size of MN-TZM alloy is 940 nm. • The micro-nano secondary phase reduces the average grain size of TZM alloy by 26%. • TZM alloy was prepared from titanium sulfate, zirconium nitrate, fructose and molybdenum powder for the first time. • The formation mechanism of micro-nano secondary phase in TZM alloy was clarified.

Effects of solid–liquid doping and spark plasma sintering on the microstructure and mechanical properties of Y2O3-doped copper matrix composites

High-strength and high-conductivity copper alloys have a wide range of applications, such as an important electrical contact material. In this work, Cu–Y2O3 composite material was prepared through solid–liquid doping, calcination reduction, and spark plasma sintering. The effect of different yttrium oxide content (1, 3, and 5 wt%) on the microstructure and mechanical properties of the composite was studied. Results showed that the surface of the calcined and reduced copper powder was uniformly covered with yttrium oxide particles. After spark plasma sintering, the relative density of the blocks almost reached 100%. With the increase in yttrium oxide content, the distribution of yttrium oxide transformed from dispersion to agglomeration, and the grain size gradually decreased. There is a good bond between the copper matrix and yttrium oxide, and the particle size of yttrium oxide particles is approximately 150 nm. In terms of mechanical properties, the Cu-3wt.% Y2O3 sample obtained the best comprehensive mechanical properties with strength of 290.1 MPa, hardness of 125.7 HV, and conductivity maintained at a high level of 95% International Annealed Copper Standard (hereinafter called IACS).

Effect of Y2O3 on microstructure and mechanical properties of WC-Co-cemented carbides prepared via solid-liquid doping method and spark plasma sintering

The effect of Y2O3 on the microstructure and mechanical properties of tungsten carbide with 12 wt.% cobalt prepared using a solid-liquid doping method and spark plasma sintering (SPS) was investigated. The novelty of this study is the use of solid-liquid method for addition of Y2O3 into WC-Co material. Composition, microstructures, densities, hardness, and fracture toughness of WC-Co-Y2O3-cemented carbides were analyzed using XRD, SEM, TEM and measuring equipment. Results show that, the existence of Y2O3 hindered the growth of WC grains, and the WC grain size decreased to 0.98 μm. The coherent relationship between Y2O3 phase and WC phase is considered as semi-coherent. Furthermore, Y2O3 did not increase the porosity of WC-based sample, and the sample with Y2O3 added possessed almost full relative density. And the sample with 1.3 wt.% Y2O3 possessed maximum hardness and fracture toughness measured at 1446.9 HV and 11.9 MPa·m1/2, respectively. Therefore, we improved the mechanical properties of WC-Co-cemented carbides with 1.3 wt.% Y2O3 doped via solid-liquid doping method and compared with the Y2O3-undoped WC-Co alloy.

Effect of water addition into the precursor powders on microstructure and tensile mechanical properties of a Mo-0.5La alloy

The effect of water addition into the precursor powders consisting of ultrafine La(OH)3 particles and MoO2 powders on the microstructure and tensile mechanical properties of a Mo-0.5La (wt%) alloy has been studied. The results showed that the water addition improved the homogeneity of the La(OH)3 particles in the precursor powders after mechanical blending. The average powder size of the hydrogen-reduced Mo–La powders was nearly unchanged regardless of the water addition, while the apparent density was remarkably increased with the increase in the amount of water addition. A polycrystalline phase that has a chemical formula of La5Mo4O16 and a subgrain size of 0.2∼1 μm was discovered in the hydrogen-reduced powders. This means that a small portion of the powders were transformed into composite powders during the hydrogen reduction process. Particularly, this La-containing polycrystalline phase can decompose during sintering, and the decomposition may activate and promote the grain growth kinetics. A similar effect also occurred due to the doping form of La(OH)3 which underwent decomposition during sintering as well. After sintering, the grain size of the alloy was found to depend on the quantity of the water addition. As the water addition was increased from 0 to 0.15 L/Kg, the grain size was increased from a typical size of 60–80 μm up to an extraordinarily large size of 1000–3000 μm. Interestingly, this drastic grain coarsening did not deteriorate the mechanical properties of the alloy, but improved the ultimate tensile strength from 367 to 457 MPa which is a value comparable to that of the Mo-0.5La alloy fabricated with the more conventional solid-liquid doping route, on condition that the relative sintering density can reach above 98%. The improved ultimate tensile strength can be attributed to the change in the fracture mechanism from a nearly fully intergranular mode to a mixed transgranular and intergranular mode.

Preparation and Existing States of La/Al Co-Doped Quartz Powders

The La/Al co-doped quartz powders were prepared by solid-liquid doping method. The structure, morphology and existing states of La/Al co-doped quartz powders were measured and characterized by DSC-TG, XRD, ESEM-EDX and so on. The results show that the solid-liquid doping method can effectively ensure the uniform distribution of dopant elements for La/Al. The doped salt compounds for preparing La/Al co-doped quartz powders can be completely decomposed when calcined at 650 °C. There is a certain degree of fusion between the oxides of La/Al prepared by doping and quartz powders particles, which helps improve the inherent quality of doped quartz glass.

Investigations of the nickel promotional effect on the reduction and sintering of tungsten compounds

In this article, Ni-coated W powders were firstly prepared by a liquid-solid doping method combined with air calcination and hydrogen reduction. X-ray diffraction analysis, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and temperature programmed reduction analysis were carried out to investigate the nickel doping process in WO3 and its influence on the reduction behaviors of tungsten oxides. It reveals that after calcinations most Ni ions would occupy the lattice sites of host W ions and decrease the interplanar spacing of WO3. The latter is due to the promotion of oxygen vacancy generation within WO3 rather than the changes in ionic radius. After hydrogen reduction, the doped Ni atoms precipitate onto the surface of W particles as thin metallic coatings, whereby the size and morphology of reduced W particles are varied greatly with increasing Ni addition. The presence of Ni has also been found to lower the reduction barriers for WO3 by using first-principles calculation. Finally, W-Ni compacts were sintered at 1500 °C in hydrogen atmosphere and the accelerated densification phenomenon of W alloy upon Ni doping is discussed.

A systematic study of the effect of calcium on the production and properties of WC precursor powders and alloys

Effect of calcium on tungsten oxide, tungsten, tungsten carbide and WC-Co cemented carbides, and the evolution of Ca during the preparation of cemented carbides were investigated studied by the liquid-solid doping method. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to analyze the phase compositions, particle sizes and morphologies of them, respectively. The results showed that 1% Ca-doped tungsten oxide consisted of WO3 and CaWO4 phases. After hydrogen reduction, the size of Ca-doped tungsten decreased slightly. During carbonization, most of the CaWO4 and Ca4.26W10O30 transformed to CaC2. After that, the majority rest of the CaWO4 and Ca4.26W10O30 both reduced to CaO in the sintering process. The microhardness, flexural strength and fracture toughness of 1%Ca-doped WC-6wt.%Co cemented carbide were 14.83 GPa, 1456 MPa and 9.98 MPa m1/2, decrement of 10.12%, 29.53%, and 10.57%, respectively. A refining mechanism for tungsten and a weakening mechanism for WC-Co cemented carbides were proposed.

Effects of La2O3 Content and Rolling on Microstructure and Mechanical Properties of ODS Molybdenum Alloys

In order to study the effects of La2O3 content and rolling on microstructure and mechanical properties of Mo-La2O3 alloys, Mo-0.5% (1%) La2O3 alloys were prepared by liquid-solid doping technique, subsequently rolled either by a single-direction rolling or a cross-rolling. As a result, three different materials were prepared for this study. After being annealed at 1800 °C, the single-directionally rolled Mo-1% La2O3 alloy shows the best mechanical properties in terms of strength, hardness, and sagging deformation among the three materials. This is attributed to the observation that the alloy is only recovered with a microstructure of subgrains and dislocations. The single-directionally rolled Mo-0.5% La2O3 exhibits the worst mechanical property among the three materials. In this material, coarse grains, but no subgrains and dislocations, can be observed after annealing, indicating that it is fully recrystallized. For the cross-rolled Mo-1% La2O3 alloy, grains of dispersed sizes, but no dislocations, are visible after annealing, implying that this alloy is partially recrystallized. Accordingly, the mechanical property of this material is in between the other two materials. Thus, the mechanical properties of the three materials can be well understood based on OM, SEM, and TEM results. Overall, the single-directionally rolled Mo-1% La2O3 alloy possesses good mechanical properties and is more suitable for high-temperature applications.

Effects of doping technologies on mechanical properties and microstructures of RExOy doped molybdenum alloys

Mo-La alloy powders were all prepared by a novel nanoparticle spray doping technology and a conventional solid–liquid spraying technology respectively. Mo-La alloy powders were fabricated into 1.8 mm-diameter wires by powder metallurgy and thermomechanical processing. The mechanical properties of these wires were determined at room temperature and 1773 K, their microstructures observed by transmission electron microscope (TEM). The results show that with the same addition of doped elements, the comprehensive mechanical properties of Mo-La alloy synthesized by the nanosized powder spray doping technology were about 50% higher than those of the conventional solid–liquid doping process. The results attribute to the reason that the nanoparticle spray doping technology is liable to provide much more La2O3 particles compared with the conventional solid–liquid doping process, and that the particles, whose sizes are three orders smaller than that of the solid–liquid doping process, are much more homogeneously distributed in the intragranular and intergranular molybdenum substrates. The excellent dispersion strengthening effects of the novel doping technology were quantitatively analyzed by Fisher theory.

Effects of the lanthanum content on the microstructure and properties of the molybdenum alloy

The effects of the lanthanum content on the microstructure and properties of molybdenum alloy were investigated. The molybdenum powders with various lanthanum contents were prepared by a solid-liquid doping method and reduction under hydrogen atmosphere, which could be processed into sintered molybdenum and rotary swaged molybdenum. The results indicated that the grain sizes of the alloys became finer and the tensile strength increased with increasing La content. The La2O3 particles could adsorb impurity elements that existed on the grain boundary and generate the amorphous structure around the particle. The rotary swaged Mo with 0.1wt.% La was the highest tensile strength, and the rotary swaged Mo with 0.03wt.% La possessed the highest elongation to failure of 42%. In addition, the electrical resistivity of the rotary swaged Mo increased at first and later decreased with increasing La content.

Effect of rare earth element cerium on preparation of tungsten powders

Tungsten powders and Ce doped powders were prepared by hydrogen reduction combined with the liquid-solid doping method. The phase composition, particle size and powder morphology of Ce doped tungsten powders were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively. The results indicated that 10000 ppm Ce doped tungsten oxide powders were consisted of WO3 phase and Ce4W9O33 phase. The hydrogen reduction of Ce doped tungsten powders was basically accomplished at 800 °C for 3 h. The size of Ce doped W powders was remarkably decreased compared to the undoped W powders. The phase of Ce4W9O33 was reduced to Ce2 (WO4)3 phase and Ce2W2O9 phase during the process of hydrogen reduction. Moreover, Ce2 (WO4)3 phase and Ce2W2O9 phase were observed form their morphologies, where the doping content of Ce was more than 100 ppm. The ternary phase embedding into W particles was assigned to Ce2 (WO4)3, while the ternary phase distributing among W particles corresponded to Ce2W2O9. The phase of Ce2 (WO4)3 might be the nucleus of W particles and increase the number of the nucleus. And the particles of Ce2W2O9 covered WO2 particles and might inhibit the growth of W particles. These two reasons resulted in the decrease of the size of Ce doped W particles. Uniform fine W powders were fabricated with the doping content of Ce more than 100 ppm.

The influences of La doping method on the microstructure and mechanical properties of Mo alloys

In this paper, the effects of the La doping method on the microstructure and mechanical properties of Mo alloys were investigated. The powders were fabricated by the industrial produced pure Mo powder, solid–solid doping method (S–S), solid–liquid doping method (S–L) and liquid–liquid doping method (L–L), respectively. In addition, the powders were processed into sintered Mo, rotary swaged Mo and Mo wire. The results indicated that the powders became finer and the grain boundaries of the Mo prepared by S–L(S–L Mo) and L–L (L–L Mo) had the ability to migrate and wrap the La2O3 particles into the grain interior during sintering with the addition of La. The tensile strength and elongation of the rotary swaged L–L Mo were the highest and the tensile elongation was raised to 42% at room temperature. Moreover, the L–L Mo wire had the highest tensile strength after the treatment at all the annealing temperatures and the S–L and L–L Mo wire possessed higher recrystallization temperature than the Mo prepared by S–S (S–S Mo) and pure Mo wire obtained.

Scandate Dispenser Cathodes With Sharp Transition and Their Application in Microwave Tubes

We report on a new cathode which is based on die-pressed matrices made from scandia-doped tungsten powder using the liquid-solid doping technique. Transition temperatures from space charge to temperature limited emission are as low as 840 °C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> (W) for emission of 5 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Transitions are sharper than previously published scandate cathodes and compare favorably with M and ternary alloy cathodes. We present emission curves on several cathodes, show comparisons with other types of cathodes, and offer tentative explanations for the improvement. We discuss their suitability in microwave tubes at loadings of 5-10 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Microstructure and tensile properties of Mo alloy synthetically strengthened by nano-Y2O3 and nano-CeO2

Nano-Y2O3 and nano-CeO2 of different weight ratio mixed with deionizing water were doped into MoO2 powder by liquid–solid doping method. The diameter 1.80 and 0.18 mm alloy wires of Mo–0.3Y, Mo–0.3Ce, and Mo–0.15Y–0.15Ce were prepared through reduction, isostatic pressing, sintering, and drawing. Tensile properties, second phase microstructure and fracture surface appearance of wires were analyzed. The better refining effect for Mo alloy powder can be gotten after two kinds of nanoparticle oxide doped into MoO2 than only one doped. Nano-Y2O3 and nano-CeO2 have different influences on sintering process. For nano-CeO2, the constraining effect of grain growth focuses on the initial sintering stage, nano-Y2O3 plays refining grains roles in the later densification stage. Nano-Y2O3 is undistorted and keeps intact in the process of drawing; and nano-CeO2 is elongated and broken into parts in the drawing direction. The strengthening effect of nano-Y2O3 and nano-CeO2 keeps the finer grains and superior tensile properties for Mo–0.15Y–0.15Ce wire.

Effect of scandia doping method on the emission uniformity of scandate cathode with Sc2O3–W matrix

Scandia doped tungsten matrix dispenser cathodes were manufactured using scandia doped tungsten powder prepared by mechanical mixing, liquid–solid doping and a spray drying method. It is found the macrostructure of the cathode depended on the powder preparation method. The cathode prepared using the powder prepared by spray drying method had a homogenous and porous matrix characterized with grains with a diameter of less than 1μm and with many nanoparticles distributing uniformly around these grains. The cathode with submicron structure and uniform distribution of scandia exhibited good emission uniformity. The emission uniformity ΔJ/J of the cathode prepared by spray drying method was 0.17, about 6 times lower than that of the cathode prepared by mechanical mixing method. The calculation results showed that the nanoparticles led to electric field enhancement. A Ba–Sc–O multilayer on the cathode surface and nanoparticles distributing mainly on W grains contributed to the emission property of the cathode.