Bulk Al-Al3Zr composite prepared by mechanical alloying and hot extrusion for high-temperature applications

Bulk Al/Al₃Zr composite was prepared by a combination of mechanical alloying (MA) and hot extrusion processes. Elemental Al and Zr powders were milled for up to 10 h and heat treated at 600℃ for 1 h to form stable Al₃Zr. The prepared Al₃Zr powder was then mixed with the pure Al powder to produce an Al-Al₃Zr composite. The composite powder was finally consolidated by hot extrusion at 550℃. The mechanical properties of consolidated samples were evaluated by hardness and tension tests at room and elevated temperatures. The results show that annealing of the 10-h-milled powder at 600℃ for 1 h led to the formation of a stable Al₃Zr phase. Differential scanning calorimetry (DSC) results confirmed that the formation of Al₃Zr began with the nucleation of a metastable phase, which subsequently transformed to the stable tetragonal Al₃Zr structure. The tension yield strength of the Al-10wt%Al₃Zr composite was determined to be 103 MPa, which is approximately twice that for pure Al (53 MPa). The yield stress of the Al/Al₃Zr composite at 300℃ is just 10% lower than that at room temperature, which demonstrates the strong potential for the prepared composite to be used in high-temperature structural applications.     

Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al_3Ti

An Al-based composite reinforced with core–shell-structured Ti/Al_3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core–shell-structured reinforcement, which is mainly composed of Al_3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al_3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al–Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.     

Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti

An Al-based composite reinforced with core-shell-structured Ti/Al₃Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620℃ for 5h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al₃Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al₃Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.     

利用回收磷青铜片经热挤压法制备的磷青铜/铝两相材料及其组织和力学性能的研究

Despite the existence of conventional methods for recycling chips, solid-state techniques have become popular, whereby waste metals are directly recycled into consolidated products with the desired shapes and designs. We investigated the feasibility of recycling phosphor bronze chips through a hot extrusion process using aluminum powder as a metal binder for the fabrication of a metal-fiber-reinforced aluminum matrix composite. To do so, mixtures containing 20vol%–50vol% of chips were prepared, cold-compacted, and extruded. The quality of the consolidated samples was evaluated by determining the density of the fabricated composites and studying their microstructures. In addition, we performed tensile and hardness tests to evaluate the mechanical properties of the fabricated composites. We also analyzed the fracture surfaces of the samples to study the fracture mechanism as a function of the volume fraction of phosphor bronze chips in the fabricated composite. The results indicated that the most effective consolidation occurred in the sample containing 20vol% of chips extruded at 465°C in which the chips serve as ideal fibers for improving the mechanical properties, especially the ultimate tensile strength, in comparison with those of Al matrixes that contain no chips but are produced under the same conditions.     

Fabrication of phosphor bronze/Al two-phase material by recycling phosphor bronze chips using hot extrusion process and investigation of their microstructural and mechanical properties

Despite the existence of conventional methods for recycling chips, solid-state techniques have become popular, whereby waste metals are directly recycled into consolidated products with the desired shapes and designs. We investigated the feasibility of recycling phosphor bronze chips through a hot extrusion process using aluminum powder as a metal binder for the fabrication of a metal-fiber-reinforced aluminum matrix composite. To do so, mixtures containing 20 vol%–50 vol% of chips were prepared, cold-compacted, and extruded. The quality of the consolidated samples was evaluated by determining the density of the fabricated composites and studying their microstructures. In addition, we performed tensile and hardness tests to evaluate the mechanical properties of the fabricated composites. We also analyzed the fracture surfaces of the samples to study the fracture mechanism as a function of the volume fraction of phosphor bronze chips in the fabricated composite. The results indicated that the most effective consolidation occurred in the sample containing 20 vol% of chips extruded at 465°C in which the chips serve as ideal fibers for improving the mechanical properties, especially the ultimate tensile strength, in comparison with those of Al matrixes that contain no chips but are produced under the same conditions.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Effect of sintering temperature on the preparation of Cu–Ti3SiC2 metal matrix composite

Ti3SiC2 has the potential to replace graphite as reinforcing particles in Cu matrix composites for applications in brush,electrical contacts and electrode materials.In this paper the fabrication of Cu-Ti3SiC2 metal matrix composites prepared by warm compaction powder metallurgy forming and spark plasma sintering(SPS) was studied.The stability of Ti3SiC2 at different sintering temperatures was also studied.The present experimental results indicate that the reinforcing particles in Cu-Ti3SiC2 composites are not stable at and above 800℃.The decomposition of Ti3SiC2 will lead to the formation of TiC and/or other carbides and TiSi2.If purity is the major concern,the processing and servicing temperatures of the Cu-Ti3SiC2 composite should be limited to 750℃ or lower.The composites prepared by warm compaction forming and SPS sintering at 750℃ have lower density when compared with the composites prepared by SPS sintering at 950℃,but their electrical resistivity values are very close to each other and even lower.     

Reaction Sintering of Fe-Al Powder Mechanically Activated

The mixture of Fe and Al powder was mechanically activated and sintered to study a non-melting method of producing the intermetallics Fe₃Al. High-energy ball milling was used as an activation method, X-ray diffraction and SEM were chosen to analyze the materials variation before and after activation and sintering, and hot press of Fe-Al powder was inveshgated to compare mechanical activation with sintering. The results show that combining mechanical activation with reaction sintering can complete the transformation from pure Fe and Al powder to intermetallics. It is difficult to do the transformation by either mechanical activation or hot press.     

Fabrication and characterization of laminated Ti-(TiB+La2O3)/Ti composite

The incorporation of ceramic particulate reinforcements into titanium alloys can improve the specific strength and specific stiffness,while inevitably reduce the plasticity and ductility.In this study,in situ synthesized multilayer Ti-(TiB +La_2O_3)/Ti composite was designed by learning from the microstructure of nature biological materials with excellent mechanical properties.The Ti-(TiB + La_2O_3)/Ti composite with unique characteristic of laminated structure was prepared by combined powder metallurgy and hot rolling.The method has the synthesize advantages with in-situ reaction of Ti and LaB_6 at high temperature and controllability of reinforcements size and constituent phases in composites.The result shows that the pores in the as sintered laminated structure composite completely disappeared after hot rolling at 1050℃.The agglomerated reinforcement particles were well dispersed and distributed uniformly along the rolling direction.The thickness of pure Ti layer and(TiB+La_2O_3)/Ti composite layer decreased from 1 mm to about 200 μm.Meanwhile,the grains size was refined obviously after rolling deformation.The room temperature tensile test indicates that the elongation of the laminated Ti-(TiB + La_2O_3)/Ti composite improved from 13%to 17%in comparison with the uniform(TiB + La_2O_3)/Ti composite,while the tensile strength had little change.It provides theoretical and experimental basis for fabricating the novel high performance laminated Ti-(TiB + La_2O_3)/Ti composites.     

Novel approaches to produce Al2O3– TiC/TiCN– Fecomposite powders directly from ilmenite

Al2O3 –TiC/TiCN–Fe composite powders were successfully prepared directly from ilmenite at 1300–1400℃.The effects of Al/C ratio,sintering atmosphere,and reaction temperature and time on the reaction products were investigated.Results showed that the nitrogen atmosphere was bene cial to the reduction of ilmenite and the formation of Al2O3 –TiC/TiCN–Fe composite powders.When the reaction temperature was between 600 and 1100℃,the intermediate products,TiO2,Ti3O5 and Ti4O7 were found,which changed to TiC or TiCN at higher temperature.Al/C ratio was found to affect the reaction process and synthesis products.When Al addition was 0.5 mol,the Al2O3 phase did not appear.The content of carbon in TiCN rose when the reaction temperature was increased.     

La2O3–Al2O3 –SiO2 glass-infiltrated 3Y-TZP all-ceramic composite for the dental restora tive application

The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) powder had three particle size distributions, while the fine one was lower than 100 nm. The 3Y-TZP compact was prepared by dry-pressing under pressures ranged from 10 to 30 MPa and then presintered at 1250°C for 2 h. The matrix dry-pressed under the pressure of 20 MPa had a porosity of 16.7% and could be easily processed by computer aided design and computer aided manufacturing (CAD/CAM), and which had been infiltrated by the La2O3–Al2O3–SiO2 glass at 1200°C for 4 h. The flexural strength and fracture toughness of the composite were 710.7 MPa and 6.51 MPa m^1/2, respectively. The low shrinkage (0.3%) of the composite can satisfy the net-shape fabrication standard. XRD results illustrated that zirconia in the La2O3–Al2O3–SiO2 glass-infiltrated 3Y-TZP all-ceramic composite was mainly in the tetragonal phase. SEM and EDS results indicated that the pores of the matrix were almost filled by the La2O3–Al2O3 –SiO2 glass     

Oxidation behavior of the Fe-36Al-0.09C-0.09B-0.04Zr alloy at 1250℃

<正>To explore and study the Fe-Al system alloy presenting exceptional oxidation resistance at high temperature,the Fe-36Al-0.09C-0.09B-0.04Zr alloy was designed and developed.The microstructure and hardness of the backing at 1250℃were analyzed and measured.Thermodynamics and kinetics of the oxidation behavior were also analyzed by X-ray diffraction,scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques.The results show that the microstructure of the Fe-36Al-0.09C-0.09B-0.04Zr alloy is FeAl phase at ambient temperature and is stable at 1250℃.It displays the excellent property of oxidation resistance because the oxide film has only the Al_2O_3 layer,and its oxidation kinetics curve obeys the parabolic law at 1250℃.The oxidation mechanism at 1250℃is presumed that in the early oxidation period,the alloy oxidizes to form a large number of Al_2O_3 and a little Fe_2O_3,then,the enrichment of Al caused by Fe oxidization combines with O to form Al_2O_3.     

Fabrication of homogeneously dispersed graphene/Al composites by solution mixing and powder metallurgy

Graphene-reinforced aluminum (Al) matrix composites were successfully prepared via solution mixing and powder metallurgy in this study. The mechanical properties of the composites were studied using microhardness and tensile tests. Compared to the pure Al alloy, the graphene/Al composites showed increased strength and hardness. A tensile strength of 255 MPa was achieved for the graphene/Al composite with only 0.3wt% graphene, which has a 25% increase over the tensile strength of the pure Al matrix. Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the morphologies, chemical compositions, and microstructures of the graphene and the graphene/Al composites. On the basis of fractographic evidence, a relevant fracture mechanism is proposed.     

A TiCx reinforced Fe (Al) matrix composite using in-situ reaction

A new Fe matrix composite reinforced by the in-situ generated TiCx grains was prepared using the element Fe and Ti3AlC2 powders as the starting materials.Several hot-pressing temperatures were tried for exploring the phase transformation behavior from Ti3AlC2 to TiC x.Microstructures of the hot-pressed product were observed and analyzed.A tensile test was carried out for the new composite material,and the fracture face was analyzed.The results showed that the starting Ti3AlC2 was wholly decomposed and transformed into submicron TiC x grains at the hotpressing temperature above 1100℃.Most of the Al ions escaped from Ti3AlC2 were aggregated at the grain boundary of Fe grains,but a small amount of Al ions could be absorbed by Fe and formed Fe(Al) alloy around the surface of Fe grains.The prepared material exhibited a higher tensile strength of about 660 MPa and a uniform deformation of about 7%.     

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.     

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn–1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures: gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples’ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness (Hv = 122 MPa), compressive yield strength (382 MPa), tensile yield strength (332 MPa), ultimate tensile strength (370 MPa), and elongation (9%). This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall–Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.     

Effect of sintering temperature on phase evolution of Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.     

Effect of oxygen content and heat treatment on carbide precipitation behavior in PM Ni-base superalloys

The influence of oxygen content and heat treatment on the evolution of carbides in a powder metallurgy (PM) Ni-base superalloy was characterized. The results reveal that oxygen content has little influence on the precipitation of carbides inside the particles. However, under the consolidated state, stable Ti oxides on the particle surface act as nuclei for the precipitation of prior particle boundaries (PPB). Also, oxygen can diffuse internally along grain boundaries under compressive stress, which favors the precipitation of carbides inside the particles. Therefore, a higher amount of carbides will appear with more oxygen content in the case of consolidated alloys. It is also observed that PPB can be disrupted into discontinuous particles at 1200℃, but this carbide network is hard to be eliminated completely. The combined MC-M₂₃C₆ morphology approves the nucleation and growth mechanism of carbide evolution.     

XPS Study of CeO2/Al2O3 film

The redox capacity of CeO₂/Al₂O₃ thin film which was prepared by sol-gel method has been investigated by X-ray Photoelectron Spectrascopy (XPS). The results showed that the thin film was easier to be reduced and re-oxidized than pure CeO₂ powder. The key role played by oxygen vacancies which were created from the interaction between CeO₂ and Al,O, was also discussed.     

Fine grain tungsten produced with nanoscale powder

Nanoscale tungsten powder was prepared by reducing nanoscale tungsten trioxide in hydrogen to WO_2.90 and further to W powder. After compacted with a rubber die, the nanoscale tungsten powder was sintered in a high-temperature dilatometer to investigate its shrinkage process. The results show that the compact of the nanoscale tungsten powder starts to shrink at 1050℃ and ends at 1500℃. The shrinkage rate reaches the maximum value at 1210℃. The relative density of sintered samples is 96.4%, and its grain size is about 5.8 μm.