Nanostructured Al87Ni8.5Ce3Fe1Cu0.5 alloy prepared by mechanical milling spark plasma sintering and hot extrusion (original) (raw)
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Acta Metallurgica Sinica (English Letters), 2013
The effect of sintering temperature on the densification mechanisms, microstructural evolution and mechanical properties of spark plasma sintered (SPS) compacts of a gas atomized Al-4.5 wt.%Cu alloy was investigated. The powder particles whose size varied between 10 to 500 µm was subjected to SPS at 400, 450 and 500 • C at a pressure of 30 MPa. The compact sintered at 500 • C exhibited fully dense microstructure which was characterized by a uniform distribution of the secondary phase, free of dendrites and micro-porosity. Microscopy and the SPS data reveal that the events such as particle rearrangement, localized deformation and bulk deformation appear to be the sequence of sintering mechanisms depending on the size range of powder particles used for consolidation. The compact sintered at 500 • C exhibited the highest hardness and compression strength since the microstructure was characterized by fine distribution of precipitates, large fraction of submicron grains and complete metallurgical bonding.
Materials & Design, 2015
Al-10Si-21Fe and Al-20Si-16Fe (wt.%) alloys were prepared by mechanical alloying and subsequent compaction via SPS technology. A heat-treated and artificially aged casting Al-12Si-1Cu-1Mg-1Ni (wt.%) alloy, generally considered to be thermally stable, was used as a reference material. The ultrafine-grained microstructure of compact alloys resulted in excellent mechanical properties, e.g., hardness and compressive strength. Furthermore, the Al-10Si-21Fe alloy exhibited an unexpected yield drop when compressive tested at elevated temperatures. Both tested alloys exhibited high initial hardness reaching almost 400 HV5, exceeding the hardness of the reference alloy by nearly a factor of four. Additionally, even when annealed at 400°C for 100 h, the change in hardness was negligible. Furthermore, the compact Al-10Si-21Fe and Al-20Si-16Fe alloys exhibited compressive strengths of 1033 MPa and 758 MPa, respectively. The casting alloy exhibited low mechanical properties compared to those of the investigated alloys at laboratory temperature and softened remarkably during annealing, reducing its initial compressive yield strength and compressive strength from 430 MPa and 680 MPa to 180 MPa and 498 MPa, respectively. Moreover, the initial hardness of the casting alloy decreased by 50% to a final value of 63 HV5. In contrast, the investigated compact alloys maintained high compressive strength even after annealing.
In this study, nanostructured Al 5083 powders, which were prepared via cryomilling, were consolidated using spark plasma sintering (SPS). The influence of processing conditions, e.g., the loading mode, starting microstructure (i.e., atomized vs cryomilled powders), sintering pressure, sintering temperature, and powder particle size on the consolidation response and associated mechanical properties were studied. Additionally, the mechanisms that govern densification during SPS were discussed also. The results reported herein suggest that the morphology and microstructure of the cryomilled powder resulted in an enhanced densification rate compared with that of atomized powder. The pressure-loading mode had a significant effect on the mechanical properties of the samples consolidated by SPS. The consolidated compact revealed differences in mechanical response when tested along the SPS loading axis and radial directions. Higher sintering pressures improved both the strength and ductility of the samples. The influence of grain size on diffusion was considered on the basis of available diffusion equations, and the results show that densification was attributed primarily to a plastic flow mechanism during the loading pressure period. Once the final pressure was applied, power law creep became the dominant densification mechanism. Higher sintering temperature improved the ductility of the consolidated compact at the expense of strength, whereas samples sintered at lower temperature exhibited brittle behavior. Finally, densification rate was found to be inversely proportional to the particle size.
Science and Technology of Advanced Materials, 2004
B 4 C-TiB 2-SiC composites were fabricated via hot pressing using ball milled B 4 C, TiB 2 , and SiC powder mixtures as the starting materials. The impact of ball milling on the densification behaviors, mechanical properties, and microstructures of the ceramic composites were investigated. The results showed that the refinement of the powder mixtures and the removal of the oxide impurities played an important role in the improvement of densification and properties. Moreover, the formation of the liquid phases during the sintering was deemed beneficial for densification. The typical values of relative density, hardness, bending strength, and fracture toughness of the composites reached 99.20%, 32.84 GPa, 858 MPa and 8.21 MPa m 1/2 , respectively. Crack deflection, crack bridging, crack branching, and microcracking were considered to be the potential toughening mechanisms in the composites. Furthermore, numerous nano-sized intergranular/intragranular phases and twin structures were observed in the B 4 C-TiB 2-SiC composite. 2. Experimental 2.1. Materials Commercially available B 4 C powder (D 50 = 2.5 μm, Jingangzuan Boron Carbide Co., Ltd., Mudanjiang, China), TiB 2 powder (D 50 = 8.0 μm, Dandong Chemical Research Institute Co., Ltd., Dandong, China) and SiC powder (D 50 = 0.5-0.7 μm Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai, China) were used as the raw materials. The characteristics of the raw material powders, including mean particle size, specific surface area, oxygen content and certain metal impurities content are shown in Table 1.
Materials Science and Engineering: A, 2016
Mechanically alloyed amorphous Al 86 Ni 8 Y 6 powders were consolidated by spark plasma sintering (SPS) and the effect of varying sintering pressure (100-400 MPa) on phase transformation and resulting mechanical property was studied. Fully amorphous Al 86 Ni 8 Y 6 powder obtained via mechanical alloying exhibited good thermal stability with a wide glass transition range of 45°C. Higher sintering pressure (400 MPa) during SPS resulted in (i) better densification (98%) with improved inter-particle bonding and moreover, (ii) retention of higher volume fraction ($ 92 vol%) of amorphous phase with lower amount of intermetallic nano-precipitates, indicating improvement in thermal stability of the amorphous phase. Vickers microhardness test showed improvement in hardness with increasing sintering pressure attributed to a larger fraction of the retained amorphous phase and better inter-particle bonding. Nanoindentation test exhibited similar trends in hardness and elastic modulus with wide variation in hardness and elastic modulus values attributed to the distribution of comparatively soft nanocrystalline Al and very hard intermetallic precipitates in the amorphous matrix.
Acta Materialia, 2013
A bulk nanostructured alloy with the nominal composition Cu-30Zn-0.8Al wt.% (commercial designation brass 260) was fabricated by cryomilling of brass powders and subsequent spark plasma sintering (SPS) of the cryomilled powders, yielding a compressive yield strength of 950 MPa, which is significantly higher than the yield strength of commercial brass 260 alloys ($200-400 MPa). Transmission electron microscopy investigations revealed that cryomilling results in an average grain diameter of 26 nm and a high density of deformation twins. Nearly fully dense bulk samples were obtained after SPS of cryomilled powders, with average grain diameter 110 nm. After SPS, 10 vol.% of twins is retained with average twin thickness 30 nm. Three-dimensional atom-probe tomography studies demonstrate that the distribution of Al is highly inhomogeneous in the sintered bulk samples, and Al-containing precipitates including Al(Cu,Zn)-ON , Al-ON and Al-N are distributed in the matrix. The precipitates have an average diameter of 1.7 nm and a volume fraction of 0.39%. Quantitative calculations were performed for different strengthening contributions in the sintered bulk samples, including grain boundary, twin boundary, precipitate, dislocation and solid-solution strengthening. Results from the analyses demonstrate that precipitate and grain boundary strengthening are the dominant strengthening mechanisms, and the calculated overall yield strength is in reasonable agreement with the experimentally determined compressive yield strength.
Materials, 2016
In this work, Al-20Si-10Fe-6Cr and Al-20Si-10Fe-6Mn (wt %) alloys were prepared by a combination of short-term mechanical alloying and spark plasma sintering. The microstructure was composed of homogeneously dispersed intermetallic particles forming composite-like structures. X-ray diffraction analysis and TEM + EDS analysis determined that the α-Al along with α-Al 15 (Fe,Cr) 3 Si 2 or α-Al 15 (Fe,Mn) 3 Si 2 phases were present, with dimensions below 130 nm. The highest hardness of 380 ± 7 HV5 was observed for the Al-20Si-10Fe-6Mn alloy, exceeding the hardness of the reference as-cast Al-12Si-1Cu-1 Mg-1Ni alloy (121 ± 2 HV5) by nearly a factor of three. Both of the prepared alloys showed exceptional thermal stability with the hardness remaining almost the same even after 100 h of annealing at 400 • C. Additionally, the compressive strengths of the Al-20Si-10Fe-6Cr and Al-20Si-10Fe-6Mn alloys reached 869 MPa and 887 MPa, respectively, and had virtually the same values of 870 MPa and 865 MPa, respectively, even after 100 h of annealing. More importantly, the alloys showed an increase in ductility at 400 • C, reaching several tens of percent. Thus, both of the investigated alloys showed better mechanical properties, including superior hardness, compressive strength and thermal stability, as compared to the reference Al-10Si-1Cu-1Mg-1Ni alloy, which softened remarkably, reducing its hardness by almost 50% to 63 ± 8 HV5.
Production of high-strength Al 85 Y 8 Ni 5 Co 2 bulk alloy by spark plasma sintering
Journal of Physics: Conference Series, 2010
Highly dense bulk samples were produced by spark plasma sintering (SPS) through combined devitrification and consolidation of partially amorphous Al 85 Y 8 Ni 5 Co 2 gas atomized powders. The microstructure of the consolidated samples shows a mixed structure containing crystalline, ultrafine-grained and amorphous/nanocrystalline particles. The sintered sample exhibits a remarkable high strength of about 1050 MPa combined with 3.7 % fracture strain. 1 2,3 1 1 2 J S Kim K B Surreddi , V C Srivastava , S Scudino , M Sakaliyska , V Uhlenwinkel ,
Materials Science and Engineering: A, 1999
The texture and microstructure of as-extruded Al-7.7Fe-4Ni and Al-8.2Fe-4.3Ni-2.8Zr (wt.%) alloys reinforced by large volume fractions ( \30 vol.%) of coherent intermetallics was studied. It is shown that the texture and microstructure developed in the as-extruded alloys is very sensitive to characteristics of the rapidly solidified powders. In particular, variations in powder microstructure and associated hardness are responsible for heterogeneous deformation which leads to the formation of a banded structure consisting of alternate coarse and fine microstructure characterised by a major B111\ fibre texture of the Al-matrix. This texture of the Al-matrix is coupled to a texture of the coherent intermetallic phase. On contrast, more homogeneous deformation results in a more homogeneous microstructure with fairly random texture for both the Al and t phases.
Journal of Materials Science, 2009
The present work is focused on the understanding of the phase and microstructural evolution during mechanical alloying of 82Cu-14Al-4Ni powder mixture. Morphology and phase evolution in the milled powder at different stages of milling were studied and a physical modeling of the mechanical alloying has been proposed. It has been demonstrated that milling process mainly consisted of four stages, i.e., flattening and cold welding of powder particles to form a porous aggregate followed by its fragmentation, plastic deformation of small aggregates to form layered particles, severe plastic deformation of layered particles to form elongated flaky particles, and fragmentation of elongated particles into smaller size flaky powder particles. It was also found that the initial period of milling resulted in rapid grain refining, whereas alloying was accomplished during the later period of milling. TEM study of the 48 h milled powder revealed that the microstructure was equiaxed nanocrystalline in nature. It was found that the grains were either randomly distributed or arranged as banded type. A possible explanation for such a behavior has been presented.