Effect Of Precipitate Size Research Articles

Effect of precipitate size distribution on hardness of aluminium 6063 alloy

In this study, the effects of precipitate size and size distribution on the hardness of Aluminium 6063 alloy were examined. Al 6063 samples were subjected to a solution treatment at 530oC for 4 hours and quenched in water followed by storing in freezer (-18oC) to prevent natural aging. Aging treatment was done at 1900C for 135, 180, 225, 270 and 315 minutes. Precipitates distributed in the matrix were identified as Fe-Si-rich and Fe-Si-Mg-rich precipitates by performing Scanning Electron Microscope (SEM)/ Energy Dispersive Spectroscopy (EDS) analysis. Number of precipitates, average size and area covered by precipitates were calculated by image J software based on the precipitates observed in SEM images. For all heating profiles, precipitate size was less than 3.2 µm. The maximum hardness of 143.90 HV was achieved for 270 minutes aging time. A significant decrease in hardness was evident when the particles are coarsening above 1.5 µm, possibly due to overaging, for aging time beyond 270 min.

The Effects of Precipitate Size on the Hardness and Wear Behaviors of Aged 7075 Aluminum Alloys Produced by Powder Metallurgy Route

In this study, the effects of precipitate size, which occurred on the microstructure by applying T6 heat treatment at different temperatures and different time intervals, were investigated on hardness and wear behaviors of 7075 Aluminum alloys produced by powder metallurgy route. Aging heat treatments were performed at three different temperatures (110–130 °C) and four different times (16–28 h). The results show that MgZn2 precipitates were formed in the microstructure by aging heat treatments and their sizes were changed depending on aging temperature and time. The precipitate size was increased by increasing aging temperature and time. The largest size of the precipitate was measured from SEM images of the samples aged at 130 °C for 24 h. The highest hardness values were measured at 120 °C for 24-h aged samples. The wear test results revealed that the weight loss was increased with increase in sliding distance and the minimum weight loss was observed at 120 °C for 24-h aged samples.

Effect of precipitate state on the stress corrosion behavior of 7050 aluminum alloy

The effect of precipitate size and state on stress corrosion property of 7050 aluminum alloy has been investigated for the first time. The results suggest that 7050 aluminum alloy with fine precipitates in matrix and discontinuous copper-rich precipitates at grain boundary exhibits excellent stress corrosion resistance. The different precipitates in matrix lead to electrochemical heterogeneity and different corrosion susceptibility, due to the different coherence with matrix and alloy element matrix solute content. The discontinuous grain boundary precipitates can hinder corrosion cavities connecting into a continuous crack, and copper-rich grain boundary precipitates can retard hydrogen embrittlement, during the stress corrosion process. Furthermore, the in-situ electrochemical impedance spectroscopy (EIS) in real time suggests that precipitate state has obvious influence on passivation during the stress corrosion process. Fine nanoscale precipitates in matrix are beneficial to maintaining continuous passivation, and the copper-rich grain boundary precipitate is beneficial to repassivation.

Microstructural behaviour of hot deformed AA 6015 alloy

The hot workability of AA 6015 alloy has been studied by means of torsion tests over the temperature range 300–500°C and strain rate of 0.1 s−1. The ductility was very low at 300–350°C but attained large values at higher temperatures. Optical microscopy showed original grains partially elongated up to 350°C and recrystallized grains at higher temperatures. Electron metallography revealed a distribution of fine Mg2Si precipitates with unrecovered structures at lower temperatures and well defined subgrain with the presence of large Mg2Si particles at temperatures higher than 400°C. The effect of precipitate size on dynamic restoration was analysed.

Precipitation and growth study of intermetallics and their effect on oxidation behavior in Zr–Sn–Fe–Cr alloy

Microstructural evolution of the second phase precipitates and their microchemistry in Zr–Sn–Fe–Cr alloy during various alpha annealing heat treatments have been investigated by transmission electron microscopy and energy dispersive spectrometer attached with scanning transmission microscopy. Two types of precipitates, namely, Zr – rich Zr2(FeCr) with aspect ratio one and Zr lean Zr(FeCr)2 with parallelepiped morphology were identified. Size distribution of the precipitates was estimated from small angle neutron scattering. The effect of precipitate size, its distribution and matrix microstructure on the oxidation behavior of the alloy was studied during accelerated autoclaving. The shorter duration annealing at 700°C does not improve the oxidation resistance of the alloy as it would lead to formation of non uniform distribution of alloying elements and precipitates in the matrix. It is revealed that alpha annealing at 700°C for 10h imparts a significant resistance to oxidation as well as substantial formation of Zr(FeCr)2 precipitates.

The effect of precipitate size on the yield strength-pitting corrosion correlation in Al–Cu–Mg alloys

The effect of precipitate size and state on the combinations of yield strength and corrosion pit susceptibility exhibited by a model aluminum alloy Al–2.5Cu–1.5 Mg (wt.%) has been measured for the first time. For aging times less than 2 h at 200 °C, it is shown that the fine nanoscale precipitates that form strongly affect the yield stress of the alloy but do not contribute to electrochemical heterogeneity that leads to corrosion susceptibility. This illustrates that a precipitate size range exists where the usually observed inverse correlation between strength and corrosion resistance can be broken. At longer aging times, when the precipitates become larger, a three orders of magnitude increase in the pitting rate is observed between aging times of 2 h and 9 h. The step change in pitting rate corresponds with a critical precipitate size lying between ∼3 nm and 8 nm and it is hypothesized that this size corresponds to a critical size above which it is not possible for the formation of a continuous protective passive oxide film to occur.

The effect of precipitate size on magnetic domain behavior in grain-oriented electrical steels

Precipitates in the form of grain growth inhibitors play an essential role in the production of grain-oriented electrical steels, as they promote the development of Goss texture during secondary recrystallization. However, the presence of precipitates in the final material can have a detrimental effect on loss and permeability, as they impede domain wall motion during the magnetization process. In previous work [K. Jenkins and M. Lindenmo, J. Magn. Magn. Mater. 320, 2423 (2008)], a conventional grain-oriented electrical steel was presented that contained very fine precipitates, which did not damage the bulk magnetic properties. In this article the influence of precipitate size is investigated by comparing local Barkhausen noise measurements and electron backscatter diffraction analysis for a number of grain-oriented electrical steels, which are metallurgically similar except for the size and abundance of precipitates.

A computational method for dislocation–precipitate interaction

A new computational method for the elastic interaction between dislocations and precipitates is developed and applied to the solution of problems involving dislocation cutting and looping around precipitates. Based on the superposition principle, the solution to the dislocation–precipitate interaction problem is obtained as the sum of two solutions: (1) a dislocation problem with image stresses from interfaces between the dislocation and the precipitate, and (2) a correction solution for the elastic problem of a precipitate with an initial strain distribution. The current development is based on a combination of the parametric dislocation dynamics (PDD) and the boundary element method (BEM) with volume integrals.The method allows us to calculate the stress field both inside and outside precipitates of elastic moduli different from the matrix, and that may have initial coherency strain fields. The numerical results of the present method show good convergence and high accuracy when compared to a known analytical solution, and they are also in good agreement with molecular dynamics (MD) simulations. Sheared copper precipitates (2.5 nm in diameter) are shown to lose some of their resistance to dislocation motion after they are cut by leading dislocations in a pileup. Successive cutting of precipitates by the passage of a dislocation pileup reduces the resistance to about half its original value, when the number of dislocations in the pileup exceeds about 10. The transition from the shearable precipitate regime to the Orowan looping regime occurs for precipitate-to-matrix elastic modulus ratios above approximately 3–4, with some dependence on the precipitate size. The effects of precipitate size, spacing, and elastic modulus mismatch with the host matrix on the critical shear stress (CSS) to dislocation motion are presented.

Effect of precipitate size and dispersion on recrystallization behavior in Ti-added ultra low carbon steels

The effect of coiling temperature on precipitates and solid solution was investigated in P-free and P-added Ti-stabilized ultra low carbon steels. The volume fractions of the fine precipitates smaller than 60 nm were evaluated by using small-angle neutron scattering technique. The solute P was quantified from the lattice parameters obtained from neutron diffraction patterns. In the P-free steels, TiC and Ti4C2S2 with various sizes ranging from 5~60 nm were observed. In addition to these precipitates, FeTiP precipitates of a size exceeding 50 nm were also observed in the P-added steel. The amount of fine precipitates smaller than 10 nm and the concentration of solute P was higher in the samples coiled at low temperature. The recrystallization temperature increases if the coiling temperature decreases in both, P-free and P-added steels. The recrystallization temperature of P-free steels is lower than that of P-added steels. In the P-free steels, the pinning effect of fine precipitates played a key role for the retardation of the recrystallization. In the P-added steels, the retardation of recrystallization is due to both, the pinning effect of fine precipitates and the solute drag effect of P in solid solution.

Creep and Fatigue at Elevated Temperatures. Creep Behavior of Orthorhombic Ti2AlNb Based Intermetallic Alloys.

For the purpose of studying the creep behavior of orthorhombic Ti 2 AlNb (O-phase) based alloys, nine 0-based alloys modified by V, Mo, or W were prepared. These alloys were heat-treated under various conditions. The creep tests were carried out at 650 - 750°C/310 MPa in air, using a dead-weight creep-rupture machine. The activation energy of creep was calculated to be 327 to 416 kJ/mol, which showed that the creep process was controlled by a dislocation climb. The alloys modified by W exhibited lower steady-state creep rates and longer transient times than the alloys modified by Mo and V, which is thought to be due to the lower diffusion rate of W in O-based alloys. The transformation of B2 phase into O phase during creep test runs at temperatures lower than the aging temperature was responsible for the large transient creep strain in a B2+O alloy. The effect of precipitate size on creep behavior is discussed.

Investigation of the Mechanical Strength of Hydrogen‐Annealed Czochralski Silicon Wafers

The mechanical strength of hydrogen‐annealed Czochralski silicon wafers was investigated with emphasis on the generation of slip dislocations by oxide precipitates. Thermal stress, which was far larger than that generated in actual device processes, was applied to wafers after thermal simulation of a low‐temperature process (low‐temperature simulation) or a high‐temperature process (high‐temperature simulation). It was found that slip generation by oxide precipitates did not occur in the case of the low‐temperature simulation, while many slip dislocations were generated in the case of the high‐temperature simulation. The experimental results can be explained by the effect of precipitate size on slip generation. It was concluded that wafers have no mechanical strength problems during actual low‐temperature processes. © 1999 The Electrochemical Society. All rights reserved.

Effect of Precipitate Size and Dispersion on Lankford Values of Titanium Stabilized Interstitial-free Steels.

A quantitative study was undertaken to characterise the size, dispersion and microchemistry of precipitates and the texture of two hot-dip galvanised Ti stabilised interstitial free steels of comparable chemistry and grain size but with a distinct difference in Lankford values. Small angle neutron scattering technique was used complementary to electron optical techniques to resolve the ultra-fine precipitates (<5 mm). The specimen with a dense dispersion of fine precipitates exhibited a weak intensity of {111} texture and a low Lankford value. In order to clarify whether the development of {111} texture was suppressed by increased solute carbon in the matrix or by the Zener pinning force exerted by the ultra-fine precipitates during recrystallisation growth, internal friction measurements were carried out. The effect of ultrafine precipitates in retarding the grain boundary mobility is confirmed. The possible roles of solute carbon effect, and particle pinning effect on the evolution of {111} texture are discussed.