In-situ fabrication of Al(Zn)-Al_2O_3 graded composite using the aluminothermic reaction during hot pressing

In this study, the fabrication of multilayer Al(Zn)–Al2 O3 with different volume fractions of Al2 O3 was investigated. Al and Zn O powders were milled by a planetary ball mill, after which five-layer functionally graded samples were produced through hot pressing at 580°C and 90 MPa pressure for 30 min. Formation of reinforcing Al2 O3 particles occurred in the aluminum matrix via the aluminothermic reaction. Determination of the ignition temperature of the aluminothermic reaction was accomplished using differential thermal and thermogravimetric analyses. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometery analyses were utilized to characterize the specimens. The thermal analysis results showed that the ignition temperatures for the aluminothermic reaction of layers with the highest and lowest Zn O contents were 667 and 670°C, respectively. Microstructural observation and chemical analysis confirmed the fabrication of Al(Zn)–Al2 O3 functionally graded materials composites with precipitation of additional Zn in the matrix. Moreover, nearly dense functionally graded samples demonstrated minimum and maximum hardness values of HV 75 and HV 130, respectively.     

In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700℃ under flowing N2

The Al-Al₂O₃-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M₁, M₂, and M₃, respectively, were prepared at 1700℃ for 5 h under a flowing N₂ atmosphere using the reaction sintering method. After sintering, the Al-Al₂O₃-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M₁ was composed of MgO and MgAl₂O₄. Compared with specimen M₁, specimens M₂ and M₃ possessed MgAlON, and its production increased with increasing aluminum addition. Under an N₂ atmosphere, MgO, Al₂O₃, and Al in the matrix of specimens M₂ and M₃ reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al₂O₃-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N₂ atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al₂O₃-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al₂O₃ diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al₂O₃ to form MgAl₂O₄. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al₂O₃ and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl₂O₄ at high temperatures because of their similar spinel structures.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3sf</Subscript> addition on the friction and wear properties of (SiC<Subscript>p</Subscript>+Al<Subscript>2</Subscript>O<Subscript>3sf</Subscript>)/Al2024 composites fabricated by pressure infiltration

Aluminum (Al) 2024 matrix composites reinforced with alumina short fibers (Al₂O_3sf) and silicon carbide particles (SiC_p) as wear-resistant materials were prepared by pressure infiltration in this study. Further, the effect of Al₂O_3sf on the friction and wear properties of the as-synthesized composites was systematically investigated, and the relationship between volume fraction and wear mechanism was discussed. The results showed that the addition of Al₂O_3sf, characterized by the ratio of Al₂O_3sf to SiC_p, significantly affected the properties of the composites and resulted in changes in wear mechanisms. When the volume ratio of Al₂O_3sf to SiC_p was increased from 0 to 1, the rate of wear mass loss (K_m) and coefficients of friction (COFs) of the composites decreased, and the wear mechanisms were abrasive wear and furrow wear. When the volume ratio was increased from 1 to 3, the COF decreased continuously; however, the K_m increased rapidly and the wear mechanism became adhesive wear.     

Sintering Behavior and Microstructure of diphasic β-Sialon/Al2O3 Composites

Six compositions with different ratio of β-Sialon/Al₂O₃ were synthesized from Al₂O₃, Si₃N₄ and SiO₂ by sintering with 3%Y₂O₃(mass fraction) as addition under the cover with powders of SiC+C and at nitrogen atmosphere. Theeffects of atmosphere, sintering temperature and composition on the sintering behavior were studied. The results showedthat the composites reached the best sintering behavior with the highest density about 92% at 1 650℃ under the weakreduction atmosphere. Finally the relative density of diphasic β-Sialon and β-Sialon/Al₂O₃ composites were studied andpredicted using ANN (Artificial Neural Networks) method and the results were experimental examined by fore randomsamples.     

添加Co3O4纳米颗粒引起的残余结构应变对粉末冶金制备的Al/Co3O4纳米复合材料的结构、硬度和磁性能的影响

Al composites are of interest due to their appropriate ratio of strength to weight. In our research, an Al/Co₃O₄ nanocomposite was generated using a sintering technique. The powders of Al with various Co₃O₄ nanoparticle contents (0wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, and 2.5wt%) were first blended using planetary milling for 30 min, and compressed in a cylindrical steel mold with a diameter of 1 cm and a height of 5 cm at a pressure of 80 MPa. The samples were evaluated with X-ray diffractometry (XRD), scanning electron microscopy (SEM), Vickers hardness, and a vibrating sample magnetometer (VSM). Although the crystallite size of the Al particles remained constant at 7–10 nm, the accumulation of nanoparticles in the Al particle interspace increased the structural tensile strain from 0.0045 to 0.0063, the hardness from HV 28 to HV 52 and the magnetic saturation from 0.044 to 0.404 emu/g with an increase in Co₃O₄ nanoparticle content from 0wt% to 2.5wt%.     

Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Using coal fly ash slurry samples supplemented with different amounts of Al₂O₃, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al₂O₃. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al₂O₃ content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.     

功能梯度Ni?W/Er2O3稀土纳米颗粒复合膜的电沉积

Multi-layered functionally graded (FG) structure Ni?W/Er₂O₃ nanocomposite films were prepared by continuously changing the deposition parameters, in which the Er₂O₃ and W contents varied with thickness. The microstructure and chemical composition of the electrodeposited Ni?W/Er₂O₃ films were determined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The anti-corrosion and wear properties of the electrodeposition films were investigated by electrochemical measurement and ball-on-disk friction test. The microhardness distribution of the cross section of nanocomposites was measured by nanoindentation. The results showed that with decreasing agitation rate or increasing average current density, the contents of Er₂O₃ nanoparticles and tungsten were distributed in a gradient along the thickness, and the contents on the surface were larger. By comparison, FG Ni?W/Er₂O₃ films had better anti-corrosion and wear properties than the uniform Ni?W/Er₂O₃ films. Atomic force microscopy (AFM) and profilometry measurements indicated that Er₂O₃ nanoparticles had an effect on the surface roughness.     

Effect of interaction of refractories with Ni-based superalloy on inclusions during vacuum induction melting

This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories. Three different crucibles were tested—MgO, Al₂O₃, and MgO–spinel. We studied the variations in the compositions of the inclusions and the alloy–crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed that the MgO and MgO–spinel crucibles form MgO-containing inclusions (Al–Mg oxides and Al–Mg–Ti oxides), whereas the inclusions formed when using the Al₂O₃ crucible are Al₂O₃ and Al–Ti oxides. We observed a new MgAl₂O₄ phase at the inner wall of the MgO crucible, with the alloy melted in the MgO crucible exhibiting fewer inclusions. No new phase occurred at the inner wall of the Al₂O₃ crucible. We discuss the mechanism of interaction between the refractories and the Ni-based superalloy. Physical erosion was found to predominate in the Al₂O₃ crucible, whereas dissolution and chemical reactions dominated in the MgO crucible. No reaction was observed between three crucibles and the Ti of the melt although the Ti content (3.8wt%) was higher than that of Al (2.1wt%).     

Fabrication and densification enhancement of SiC-particulate-reinforced copper matrix composites prepared via the sinter-forging process

The fabrication of copper (Cu) and copper matrix silicon carbide (Cu/SiC_p) particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiC_p composite samples were observed to decrease with the increase in SiC content.     

Formation mechanism of calcium hexaluminate

To investigate the formation mechanism of calcium hexaluminate (CaAl₁₂O₁₉, CA₆), the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al₂O₃ ratio of 12.57:137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300–1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al₂O₃, a small amount of CA₆ forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows: CaO·2Al₂O₃ (CA₂) + 4Al₂O₃ → CA₆. The diffusions of Ca2+ in CA₂ towards Al₂O₃ and Al3+ in Al₂O₃ towards CA₂ change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca2+ in CA₂ towards Al₂O₃.     

La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> TBCs toughened by Pt particles prepared by cathode plasma electrolytic deposition

La₂Zr₂O₇ thermal barrier coatings (TBCs) with dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED) with ceramic balls added to the cathode region. Compared with the conventional CPED, when ceramic balls are used in the cathode region, the plasma discharge ignition current density decreases approximately 62-fold and the stable plasma discharges occur at the whole cathode surface. Such TBCs with a thickness of 100 μm exhibit a crack-free surface and are composed of pyrochlore-structured La₂Zr₂O₇. Cyclic oxidation, scratching, and thermal insulation capability tests show that such TBCs not only exhibit high resistance to oxidation and spallation but also provide good thermal insulation. These beneficial effects are attributed to the excellent properties of TBCs, such as good thermal insulation because of low thermal conductivity, high-temperature oxidation resistance because of low-oxygen diffusion rate, and good mechanical properties because of the toughening effect of Pt particles.     

Microstructures and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dispersion-strengthened copper alloys prepared through different methods

Al₂O₃ dispersion copper alloy powder was prepared by internal oxidation, and three consolidation methods—high-velocity compaction (HVC), hot pressing (HP), and hot extrusion (HE)—were used to prepare Al₂O₃ dispersion-strengthened copper (Cu–Al₂O₃) alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density (98.3% vs. 99.5% for HP and 100% for HE), which resulted in the lowest electrical conductivity (81% IACS vs. 86% IACS for HP and 87% IACS for HE). However, this alloy also exhibited the highest hardness (77 HRB vs. 69 HRB for HP and 70 HRB for HE), the highest compressive strength (443 MPa vs. 386 MPa for HP and 378 MPa for HE), and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.     

Effect of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O on gasification dissolution and deep reaction of coke

To more comprehensively analyze the effect of CO₂ and H₂O on the gasification dissolution reaction and deep reaction of coke, the reactions of coke with CO₂ and H₂O using high temperature gas-solid reaction apparatus over the range of 950-1250℃ were studied, and the thermodynamic and kinetic analyses were also performed. The results show that the average reaction rate of coke with H₂O is about 1.3-6.5 times that with CO₂ in the experimental temperature range. At the same temperature, the endothermic effect of coke with H₂O is less than that with CO₂. As the pressure increases, the gasification dissolution reaction of coke shifts to the high-temperature zone. The use of hydrogen-rich fuels is conducive to decreasing the energy consumed inside the blast furnace, and a corresponding high-pressure operation will help to suppress the gasification dissolution reaction of coke and reduce its deterioration. The interfacial chemical reaction is the main rate-limiting step over the experimental temperature range. The activation energies of the reaction of coke with CO₂ and H₂O are 169.23 kJ·mol-1 and 87.13 kJ·mol-1, respectively. Additionally, water vapor is more likely to diffuse into the coke interior at a lower temperature and thus aggravates the deterioration of coke in the middle upper part of blast furnace.     

Evaluation of precipitation hardening in TiC-reinforced Ti<Subscript>2</Subscript>AlNb-based alloys

Ti₂AlNb-based alloys with 0.0wt%, 0.6wt%, and 2.0wt% carbon nanotube (CNT) addition were fabricated from spherical Ti-22Al-25Nb powder by sintering in the B2 single-phase region. Phase identification and microstructural examination were performed to evaluate the effect of carbon addition on the hardness of the alloys. Carbon was either in a soluble state or in carbide form depending on its concentration. The acicular carbides formed around 1050℃ were identified as TiC and facilitated the transformation of α₂+B2 → O. The TiC was located within the acicular O phase. The surrounding O phase was distributed in certain orientations with angles of 65° or 90° O phase particles. The obtained alloy was composed of acicular O, Widmanstatten B2+O, and acicular TiC. As a result of the precipitation of carbides as well as the O phase, the hardness of the alloy with 2.0wt% CNT addition increased to HV 429±9.     

Static synthesis of high-quality MCM-22 zeolite with high SiO2／Al2O3 ratio

We demonstrate a synthesis method to broaden the range of SiO2/Al2O3 ratio (30-100) of high-silica MCM-22 zeolites by prolonging the aging time of the gel before the crystallization. The synthesis conditions such as silica sources, chemical compositions of initial gel and aging time of gel were investigated in detail.High quality MCM-22 products with various morphologies have been synthesized by optimize their synthesis conditions.Our results show that increasing of the aging time can make the gel be homogenization and promote their nucleus formation,which may avoid the formation of impurity phase and thus broaden the range of SiO2/Al2O3 ratio.     

Novel mechanism for the modification of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based inclusions in ultra-low carbon Al-killed steel considering the effects of magnesium and calcium

Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al₂O₃-based inclusions during secondary refining. The results showed that Al₂O₃-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition,[Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO-MgO-Al₂O₃ multi-component inclusions. Thermodynamic analysis confirmed that the reaction between[Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3wt% and the temperature is higher than 1843 K.     

Adsorption and catalytic combustion of ARB on CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

CuO-Fe2O3 composite material with strong magnetism and a large surface area is prepared by the co-precipitate method. Its adsorption properties towards Acid Red B (ARB) and the regeneration by catalytic combastion of organic compounds have been studied. The results show that the prepared CuO-Fe2O3 composite is an excellent adsorbent for ARB adsorption at acid condition. The presence of Cl^- has no effect on ARB adsorption. But the SO4^2- can inhibit ARB adsorption. After being recovered by the magnetic separation method, the adsorbent can be regenerated by catalytic oxidation of absorbate at 300℃ in air atmosphere. The combustion reactions of ARB in the presence or absence of CuO-Fe2O3 are studied by in situ diffuse refieclion FTIR. The results indicate that, in the presence of CuO-Fe2O3, the degradation temperature is significantly lowered by the catalysis of CuO-Fe2O3, and ARB can be oxidized completely without volatile organic compound by-product; in comparison, in the absence of CuO-Fe2O3, the temperature needed for oxidation of ARB is higher and the reaction is incomplete with some N-containing harmful compounds produced. The reusability of CuO-Fe2O3 is also studied in successive seven adsorption-regeneration cycles.     

Synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> magnetic composite nanoparticles by a one-pot process

Fe₃O₄@SiO₂ core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe₃O₄@SiO₂ core–shell structures from prepared Fe₃O₄ nanoparticles. The properties of the Fe₃O₄ and Fe₃O₄@SiO₂ composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe₃O₄ particles were approximately 12 nm in size, and the thickness of the SiO₂ coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe₃O₄@SiO₂ powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe₃O₄ powder (79.55 A·m2·kg–1), which demonstrates that Fe₃O₄ was successfully wrapped by SiO₂. The Fe₃O₄@SiO₂ composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.     

Super-plasticity of Zr<Subscript>64.80</Subscript>Cu<Subscript>14.85</Subscript>Ni<Subscript>10.35</Subscript>Al<Subscript>10</Subscript> bulk metallic glass at room temperature

Generally, bulk metallic glasses （BMGs） exhibit a very limited plastic deformation under a compression load at room temperature, often less than 2% before fracturing. In this letter, through an appropriate choice of BMGs＇ composition, an amorphous rod of Zr64.80Cu14.85Ni10.35Al10 with a diameter of 2 mm was prepared by using copper mold suction casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability, and the uniaxial compression test was adopted to study its plastic deformation behavior at room temperature simultaneously. The results showed that the glass transition temperature and onset temperature of the exothermic reaction of the amorphous rod were 646 and 750 K, respectively, and its micro-hardness was 594.7 Hv. During compression, when the engineering strain and engineering stress arrived at 9.05% and 1732 MPa, respectively, i.e., the true strain and true stress reached 9.42% and 1560 MPa, respectively, the amorphous rod started to yield. After yielding, with the increase of load, the strain increased and the glass rod ulti- mately were compressed into flake-like form. Although the maximum engineering strain was larger than 70%, i.e., the maximum true strain exceeded by 120%, the amorphous specimen was not fractured, indicating that it has super-plasticity at room temperature. Through the appropriate choice of composition and optimization of the technological process, flexible BMG with super-plasticity at room temperature could be produced.