Full-density nanocrystalline Fe–29Al–2Cr intermetallic consolidated from mechanically milled powders

1996 ◽  
Vol 11 (1) ◽  
pp. 72-80 ◽  
Author(s):  
L. He ◽  
E. Ma
Keyword(s):  
Grain Size ◽  
Mechanical Milling ◽  
Hot Forging ◽  
Full Density ◽  
Strengthening Effect ◽  
Practical Applications ◽  
Size Refinement ◽  
Sinter Forging ◽  
Average Grain Size ◽  
Milled Powders

Fe–29Al–2Cr powders with nanoscale grain sizes were produced by mechanical milling of prealloyed intermetallic powders. A consolidation procedure employing high-pressure, low strain rate hot forging (sinter-forging) has been developed to consolidate the powders into full-density compacts. The relative density and average grain size of the compact have been studied as a function of consolidation temperature at constant pressure. Fully dense compacts (>99.5% theoretical density) were produced at a relatively low temperature of 545°C with a pressure of 1.25 GPa. Transmission electron microscopy and x-ray diffraction analysis indicate that the average grain size has been maintained to the order of 30 nm in samples consolidated under these conditions. By using protective Ar atmosphere during mechanical milling and consolidation, contamination of oxygen and carbon in consolidated samples has been controlled to below a small fraction of an atomic percent. Microhardness tests of nanocrystalline Fe–29Al–2Cr samples indicate a significant strengthening effect due to grain size refinement and a monotonic hardness increase with decreasing residual porosity. Our work demonstrates the feasibility of using mechanically milled powders as the source of nanocrystalline materials for the production of fully dense, low-impurity, nanocrystalline bulk samples needed for reliable mechanical property measurements and practical applications.

Microhardness Enhancement in Fully Dense Fe-Based Nanophase Metallic Alloys

1995 ◽  
Vol 400 ◽  
Author(s):  
L. He ◽  
E. Ma
Keyword(s):  
Grain Size ◽  
High Energy ◽  
Metallic Alloys ◽  
Full Density ◽  
Strengthening Effect ◽  
Two Phase ◽  
Grain Sizes ◽  
Sinter Forging ◽  
Interphase Boundaries ◽  
Energy Ball

AbstractNano-grained Fe-29Al-2Cr intermetallic and Fe-Cu two-phase composites have been consolidated to full density from powders produced by high-energy ball milling, using a sinter forging procedure developed recently in our laboratory. Grain sizes remained within nanophase range (<100 nm) after consolidation. Microhardness tests of Fe-29Al-2Cr samples consolidated to different density levels indicate a significant strengthening effect due to nanoscale grain size and a monotonic microhardness increase with decreasing residual porosity. Fully dense Fe-Cu composites exhibit enhanced microhardness as compared with rule-of-mixtures predictions, which may be attributable to interface strengthening at fcc-bcc interphase boundaries.

scholarly journals ODS EUROFER Steel Strengthened by Y-(Ce, Hf, La, Sc, and Zr) Complex Oxides

Metals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1148 ◽  
Author(s):  
Roman Husák ◽  
Hynek Hadraba ◽  
Zdeněk Chlup ◽  
Milan Heczko ◽  
Tomáš Kruml ◽  
...  
Keyword(s):  
Grain Size ◽  
Yield Strength ◽  
Complex Oxides ◽  
Oxide Dispersion Strengthened ◽  
Interparticle Spacing ◽  
Oxide Dispersion ◽  
Strengthening Effect ◽  
Dispersion Strengthening ◽  
Doping Element ◽  
Average Grain Size

Oxide dispersion-strengthened (ODS) materials contain homogeneous dispersions of temperature-stable nano-oxides serving as obstacles for dislocations and further pinning of grain boundaries. The strategy for dispersion strengthening based on complex oxides (Y-Hf, -Zr, -Ce, -La) was developed in order to refine oxide dispersion to enhance the dispersion strengthening effect. In this work, the strengthening of EUROFER steel by complex oxides based on Y and elements of the IIIB group (lanthanum, scandium) and IVB group (cerium, hafnium, zirconium) was explored. Interparticle spacing as a dispersoid characteristic appeared to be an important factor in controlling the dispersion strengthening contribution to the yield strength of ODS EUROFER steels. The dispersoid size and average grain size of ODS EUROFER steel were altered in the ranges of 5–13 nm and 0.6–1.7 µm, respectively. Using this strategy, the yield strength of the prepared alloys varied between 550 MPa and 950 MPa depending on the doping element.

Effect of Composition on the Morphology and Hardness of Nanostructured Cu Based Composite and Alloy Powders/Granules Produced by High Energy Mechanical Milling

2007 ◽  
Vol 29-30 ◽  
pp. 143-146 ◽  
Author(s):  
Aamir Mukhtar ◽  
De Liang Zhang ◽  
C. Kong ◽  
P. R. Munroe
Keyword(s):  
Grain Size ◽  
Mechanical Milling ◽  
Alloy Powder ◽  
High Energy ◽  
Al2o3 Nanoparticles ◽  
X Ray ◽  
Fine Powders ◽  
Average Grain Size ◽  
Powder Particles

Cu-(2.5 or 5.0vol.%)Al2O3 nanocomposite balls and granules and Cu-(2.5vol.% or 5.0vol.%)Pb alloy powder were prepared by high energy mechanical milling (HEMM) of mixtures of Cu and either Al2O3 or Pb powders. It was observed that with the increase of the content of Al2O3 nanoparticles from 2.5vol.% to 5vol.% in the powder mixture, the product of HEMM changed from hollow balls into granules and the average grain size and microhardness changed from approximately 130nm and 185HV to 100nm and 224HV, respectively. On the other hand, HEMM of Cu–(2.5 or 5.0vol.%) Pb powder mixtures under the same milling conditions failed to consolidate the powder in-situ. Instead, it led to formation of nanostructured fine powders with an average grain size of less than 50nm. Energy dispersive X-ray mapping showed homogenous distribution of Pb in the powder particles in Cu–5vol.%Pb alloy powder produced after 12 hours of milling. With the increase of the Pb content from 2.5 to 5.0 vol.%, the average microhardness of the Cu-Pb alloy powder particles increases from 270 to 285 HV. The mechanisms of the effects are briefly discussed.

Fully dense Al–Pb nanocomposite bulk samples consolidated from mechanically milled powders

1998 ◽  
Vol 13 (2) ◽  
pp. 249-252 ◽  
Author(s):  
F. Zhou ◽  
H. W. Sheng ◽  
K. Lu
Keyword(s):  
Melting Point ◽  
Mechanical Milling ◽  
Theoretical Density ◽  
Full Density ◽  
Consolidation Process ◽  
Grain Coarsening ◽  
Grain Sizes ◽  
Milled Powders

Powders with a nanostructured mixture of pure Al and Pb phase were produced by mechanical milling of elemental blends of Al and Pb with a composition of Al90Pb10 (wt. %). Under a pressure of 1.5 GPa at 280 °C, the as-milled powders were successfully consolidated into bulk, full-density samples (>99.5% theoretical density) while the average grain sizes of Al and Pb in the compacted samples remain unchanged with respect to those in the as-milled powders. The achievement of the full density without grain coarsening in the consolidation process could be reasonably attributed to melting of the nanometer-sized Pb particles of which the melting point is considerably depressed.

scholarly journals Effect of Milling Time on Microstructure, Crystallite Size and Dielectric Properties of Srtio3 Ceramic Synthesized via Mechanical Alloying Method

2011 ◽  
Vol 364 ◽  
pp. 388-392
Author(s):  
Yick Jeng Wong ◽  
Hassan Jumiah ◽  
Mansor Hashim ◽  
Swee Yin Wong ◽  
Leow Chun Yan
Keyword(s):  
Dielectric Constant ◽  
Grain Size ◽  
Dielectric Properties ◽  
Mechanical Alloying ◽  
Crystallite Size ◽  
Single Phase ◽  
Milling Time ◽  
Average Grain Size ◽  
Average Lattice ◽  
Milled Powders

SrTiO3 sample has been successfully prepared by mechanical alloying (MA) method. The effect of milling time on microstructure, crystallite size and dielectric properties of SrTiO3 were studied. The results revealed that the mean crystallite size of milled powders decreased from 84.56 to 12.87 nm with increasing milling time. However, the average lattice strain of milled powders increased from 0.2 to 0.93% with increasing milling time. A single phase SrTiO3 could not be formed with milling alone and required annealing process. A transformation of anatase-TiO2 to rutile-TiO2 was observed at 16 h of milling. After the milled powders were subjected to sintering process at 1200°C, formation of single-phase SrTiO3-type cubic (Pm-3m) perovskite structure was observed. The peak intensities of the sintered SrTiO3 samples decreased as the milling time was increased. For microstructural observations, the average grain size of the sintered SrTiO3 sample milled for 8 h showed the largest. For dielectric measurements, the dielectric constant of the sintered SrTiO3 sample milled for 8 h showed the highest among others. This could be due to the largest grain size obtained for sintered SrTiO3 sample milled for 8 h. The decrease in the grain size with increasing milling time resulted to the decrease in dielectric constant.

scholarly journals The influence of powder particle size on properties of Cu-Al2O3 composites

2009 ◽  
Vol 41 (2) ◽  
pp. 185-192 ◽  
Author(s):  
V. Rajkovic ◽  
D. Bozic ◽  
M. Popovic ◽  
M.T. Jovanovic
Keyword(s):  
Thermal Stability ◽  
Particle Size ◽  
Grain Size ◽  
Copper Powder ◽  
Average Particle Size ◽  
High Energy ◽  
Average Particle ◽  
Size Refinement ◽  
Al2o3 Particles ◽  
Milled Powders

Inert gas atomized prealloyed copper powder containing 2 wt.% Al (average particle size ? 30 ?m) and a mixture consisting of copper (average particle sizes ? 15 ?m and 30 ?m) and 4 wt.% of commercial Al2O3 powder particles (average particle size ? 0.75 ?m) were milled separately in a high-energy planetary ball mill up to 20 h in air. Milling was performed in order to strengthen the copper matrix by grain size refinement and Al2O3 particles. Milling in air of prealloyed copper powder promoted formation of finely dispersed nano-sized Al2O3 particles by internal oxidation. On the other side, composite powders with commercial micro-sized Al2O3 particles were obtained by mechanical alloying. Following milling, powders were treated in hydrogen at 400 0C for 1h in order to eliminate copper oxides formed on their surface during milling. Hot-pressing (800 0C for 3 h in argon at pressure of 35 MPa) was used for compaction of milled powders. Hot-pressed composite compacts processed from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800?C for 1 and 5h in argon) in order to examine their thermal stability. The results were discussed in terms of the effects of different size of starting powders, the grain size refinement and different size of Al2O3 particles on strengthening, thermal stability and electrical conductivity of copper-based composites.

Hydrothermal synthesis and sintering of ultrafine CeO2 powders

1993 ◽  
Vol 8 (7) ◽  
pp. 1680-1686 ◽  
Author(s):  
Y.C. Zhou ◽  
M.N. Rahaman
Keyword(s):  
Grain Size ◽  
Hydrothermal Synthesis ◽  
Oxygen Vacancies ◽  
Maximum Density ◽  
Full Density ◽  
Particle Sizes ◽  
Heating Rates ◽  
Hydrothermal Conditions ◽  
Average Grain Size ◽  
Constant Heating

Undoped CeO2 and Y2O3-doped CeO2 powders, with particle sizes of ≍10–15 nm, were prepared under hydrothermal conditions of 10 MPa at 300 °C for 4 h. The compacted powders were sintered freely in air or in O2 at constant heating rates of 1–10 °C/min up to 1350 °C. The undoped CeO2 started to sinter at ≍800–900 °C and reached a maximum density of 0.95 of the theoretical at 1200 °C, after which the density decreased slightly. Isothermal sintering at 1150 °C produced a sample with a relative density of ≍0.98 and an average grain size of ≍100 nm. The samples sintered above 1200 °C exhibited microcracking. The decrease in density and the microcracking above 1200 °C are attributed to a redox reaction leading to the formation of oxygen vacancies and the evolution of O2 gas. Doping with Y2O3 produced an increase in the temperature at which measurable sintering commenced and an increase in the sintering rate, compared with the undoped CeO2. Sintered samples of the doped CeO2 showed no microcracks. The CeO2 doped with up to 3 mol% Y2O3 was sintered to almost full density and with a grain size of ≍200 nm at 1400 °C.

scholarly journals Grain Size-Related Strengthening and Softening of a Precompressed and Heat-Treated Mg–Zn–Ca Alloy

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 351 ◽  
Author(s):  
Patrik Dobroň ◽  
Daria Drozdenko ◽  
Klaudia Horváth Fekete ◽  
Juraj Olejňák ◽  
Jan Bohlen
Keyword(s):  
Grain Size ◽  
Thermal Treatment ◽  
Electron Backscatter Diffraction ◽  
Deformation Behaviour ◽  
Strengthening Effect ◽  
Average Grain Size ◽  
Ebsd Technique ◽  
Size Interval ◽  
Evolution Of Microstructure ◽  
The Impact

The impact of precompression, thermal treatment and its combination on the deformation behaviour of an extruded Mg–Zn–Ca (ZX10) alloy was studied with respect to a varied average grain size. The Hall–Petch plot was used to highlight the impact in a wide grain size interval. The initial texture of the wrought alloy was characterized by X-ray diffraction. Moreover, the evolution of microstructure and texture was provided by the electron backscatter diffraction (EBSD) technique. The obtained results indicate the strong contribution of deformation-thermal treatment on the resulting deformation behaviour. Particularly, after precompression and heat treatment, higher strengthening effect was observed in the reversed tensile loaded compared to compressed samples without any change in the Hall–Petch slope throughout the grain size interval. Unlike this strengthening effect, a reversed tension–compression yield asymmetry with higher strength values in compression has been obtained.

Comparison of the strengthening effects of Nb, V, and Ti on the mechanical properties of 20MnSi low-alloy steel

2020 ◽  
Vol 111 (6) ◽  
pp. 504-510
Author(s):  
Qingxiao Zhang ◽  
Qing Yuan ◽  
Wenwei Qiao ◽  
Guanghui Chen ◽  
Guang Xu
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Grain Refinement ◽  
Alloy Steel ◽  
Precipitation Strengthening ◽  
Strengthening Effect ◽  
Strengthening Mechanisms ◽  
Low Alloy Steel ◽  
Average Grain Size ◽  
Base Steel

Abstract Three alloys, containing niobium, vanadium and titanium, respectively, were refined and the strengthening effect attained after adding them individually in a 20MnSi low-alloy rebar steel was investigated. The results show that the strengthening effect attained due to the addition of niobium is the best, whereas that due to the addition of titanium is the poorest. Grain refinement and precipitation strengthening are the main strengthening mechanisms observed in niobium-steel and vanadium-steel, whereas only precipitation strengthening is observed in titanium-steel. Moreover, the average grain size of niobium-steel is the smallest among the four types of steels, while the size of ferrite and pearlite microstructures show almost no obvious change as compared to the base steel in the case of titanium-steel. Furthermore, the volume fractions of ferrite and pearlite in the four tested steels have no noticeable change.

Microstructure and Mechanical Properties of Quasicrystal Reinforced Magnesium Matrix Composites

2011 ◽  
Vol 686 ◽  
pp. 242-246
Author(s):  
Xu Dong Wang ◽  
Wen Bo Du ◽  
Chao Hui Wang ◽  
Shu Bo Li
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Maximum Yield ◽  
Icosahedral Quasicrystal ◽  
Strengthening Effect ◽  
Magnesium Matrix Composites ◽  
Fine Grain ◽  
Average Grain Size ◽  
The Matrix ◽  
Maximum Yield Strength

Magnesium-based composites reinforced with stable icosahedral quasicrystal particles have been fabricated via Repeated Plastic Working (RPW) process. The microstructure of the composites has been investigated by XRD, SEM, TEM and HREM, and its mechanical properties have also been studied. The results showed that the RPW process could reduce the matrix grain size significantly, and the average grain size of matrix was only about 500 nm after 200 cycles of RPW. A good metallurgical bond interface between the quasicrystal particles and the Mg matrix was found. The composites exhibited the maximum yield strength of 265MPa and the maximum ultimate tensile strength of 309MPa at room temperature, respectively. The enhancement of mechanical properties is attributed to the strengthening effect of the quasicrystal particles and the fine-grain size of matrix.

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