Microstructure evolution and mechanical properties of homogenizing treated fully lamellar Ti-46Al-0.5W-0.5Si alloy

The microstructure of as-cast Ti-46Al-0.5W-0.5Si alloy exhibits significant microinhomogenetity due to the non-equilibrium solidification and low atom diffusion rate. In order to reduce the adverse effect of this microsegregation on plasticity, the microstructure evolution of the Ti-46Al-0.5W-0.5Si alloy homogenized at different temperatures from 1,200 ℃ to 1,320 ℃ was investigated, and the optimized process of homogenizing treatment, i.e., annealing treated at 1,280 ℃ and held for 8 h, was determined. Microstructures of both the as-cast and heat treated alloys were observed by means of optical microscope and scanning electron microscopes. Tensile tests at room temperature were conducted on the homogenizing treated fully lamellar Ti-46Al-0.5W-0.5Si alloy with loading axis parallel to the lamellar interface. Results show that, at higher heat treatment temperatures, the W element diffuses sufficiently, the microstructure tends to be more homogeneous, and the profile of the silicide clusters becomes smooth. Heat treating conducted in the α+γ two phase region can keep the columnar grains and the original lamellar orientation within them. The microstructure of the alloy after heat treated in α+γ two phase region exhibits the coexisting morphology of coarse lamellar and thin lamellar. The homogenization process at 1,280 ℃ for 8 h can significantly reduce the microsegregation, and the elongation at room temperature can increase from 0.48% (as-cast) to 1.34%.

Formation and transformation of metastable LPSO building blocks clusters in Mg-Gd-Y-Zn-Zr alloys by spinodal decomposition and heterogeneous nucleation

To study the formation and transformation mechanism of long-period stacked ordered(LPSO)structures,a systematic atomic scale analysis was conducted for the structural evolution of long-period stacked ordered(LPSO)structures in the Mg-Gd-Y-Zn-Zr alloy annealed at 300℃~500℃.Various types of metastable LPSO building block clusters were found to exist in alloy structures at different temperatures,which precipitate during the solidification and homogenization process.The stability of Zn/Y clusters is explained by the first principles of density functional theory.The LPSO structure is distinguished by the arrangement of its different Zn/Y enriched LPSO structural units,which comprises local fcc stacking sequences upon a tightly packed plane.The presence of solute atoms causes local lattice distortion,thereby enabling the rearrangement of Mg atoms in the different configurations in the local lattice,and local HCP-FCC transitions occur between Mg and Zn atoms occupying the nearest neighbor positions.This finding indicates that LPSO structures can generate necessary Schockley partial dislocations on specific slip surfaces,providing direct evidence of the transition from 18R to 14H.Growth of the LPSO,devoid of any defects and non-coherent interfaces,was observed separately from other precipitated phases.As a result,the precipitation sequence of LPSO in the solidification stage was as follows:Zn/Ycluster+Mg layers→various metastable LPSO building block clusters→18R/24R LPSO;whereas the precipitation sequence of LPSO during homogenization treatment was observed to be as follows:18R LPSO→various metastable LPSO building block clusters→14H LPSO.Of these,14H LPSO was found to be the most thermodynamically stable structure.

Effect of homogenization treatment on microstructure evolution and the distributions of RE and Zr elements in various MgeLieREeZr alloys

Mge3Lie0.4Zr alloys containing RE elements(Gd,La,Nd)(Mge3LieREe0.4Zr alloys)are investigated to reveal the influence of homogenization treatment on microstructures and distributions of RE,Zr elements.It is found that 300
C24 h homogenization treatment shows better improvement on the microstructure including the refinement of grain size,the dispersion of cellular dendrite and low melting point particles.Before treatment,La and Nd segregate effectively at grain boundary and Zr segregates in the form of precipitates.Homogenization treatment induces the reduction of RE segregation.However,the segregation of Zr in precipitates cannot be abated due to the relatively low diffusion rate compared with RE elements.

Microstructural evolution of Al-Cu-Li alloys with different Li contents by coupling of near-rapid solidification and two-stage homogenization treatment

Microstructural improvement of Al-Cu-Li alloys with high Li content plays a critical role for the acquisition of excellent mechanical properties and ultra-low density.In this regard,the Al-Cu-Li alloy castings with high Li content from 1.5 wt.%to 4.5 wt.%were prepared by near-rapid solidification,followed by two-stage homogenization treatment(490℃/16 h and 530℃/16 h).The microstructural evolution and solidification behavior of the as-cast and homogenized alloys with different Li contents were systematically studied by combining experiments with calculations by Pandat software.The results indicate that with the increase of Li content,the grain sizes decrease,the solution ability of Cu in the matrixα-Al phase increases,while the content of secondary dendrites increases and the precipitated phases change from low melting point phases to high melting point phases under the near-rapid solidification.Additionally,by the coupling of near-rapid solidification and two-stage homogenization,the metastable precipitated phases(Al7Cu4Li and AlCu3)can be dissolved effectively in the alloys with Li content of 1.5 wt.%-2.5 wt.%;moreover,the stable precipitated phases(Al6CuLi3 and Al2CuLi)uniformly distribute at the grain boundaries in the alloys with Li content of 3.5 wt.%-4.5 wt.%.As a result,the refined and homogenized microstructure can be obtained.

HOMOGENIZATION TREATMENT OF ALLOY GH169

A new point of view on the homogenization treatment has been proposed.It is supposed that a little liquid in the alloy may promote the homogenization process in some aspects and reduce the time for eliminating the Laves-phase in alloy GH169.The microprocess of the elimination of Laves-phase in the case of a little liquid existing in the alloy has also been described.

INFLUENCE OF HOMOGENIZATION TREATMENT UNDER AN ELECTRIC FIELD ON DUCTILITY OF 2091 Al－Li ALLOY DURING HOT ROLLING

For 2091 Al-Li alloy, the volume fraction of second phase particles is greatly determined by the homogenization temperature and homogenization time under an electric field and the ductility of the alloy is determined by the fraciton of second phase particles. The combined homogenization treatment shortens the homogenization time, reduces the loss ofLi content and increases the ductity of the alloy.

Effect of homogenization treatment in electric field on microstructure and properties of 1420 Al-Li alloy

In comparison with the homogenization treatment without an electric field prior to the same solid solution and aging treatment, the homogenization treatment in an electric field increases the hardness and strength of 1420 Al Li alloy, but somewhat decreases the elongation of the alloy. Moreover, the elongation of the alloy increases with the homogenization temperature in an electric field increasing. TEM observation showed that the homogenization treatment in an electric field can accelerate the dissolution of the coarse particles of second phase on the grain boundary as well as make δ′phase precipitated in subsequent aging process finer and more numerous.

EFFECT OF HOMOGENIZATION TREATMENT UNDER AN ELECTRIC FIELD ON T_1 DISTRIBUTION AND MECHANICAL PROPERTIES OF 2091 Al－Li ALLOY

Homogenization treatment under an electric field increases the distributive homogeneity of the T1 precipitation and improves the yield strength of 2091 Al-Li alloy.

Study on Low Temperature Coefficient Rare-Earth Magnets

The rare-earth hard magnets with lower temperature coefficient, including Nd_2Fe_ 14B/Fe_3B-ferrite compound bonded magnets and Sm_ 0.8RE_ 0.2 (Co_ balFe_ 0.22Cu_ 0.06Zr_ 0.03)_ 7.4(RE=Gd, Er) sintered magnets, were studied. The result shows that the addition, that dope ferrite magnetic powder to double-phase nanocomposite Nd_2Fe_ 14B/Fe_3B magnetic powder, can make β_ jH_c to be obviously decreased. Similarly, the effect of homogeneous heating treatment on magnetic properties was studied. Doping heavy rare earth elements to the 2∶17-type SmCo magnet material powders shows that the sintered magnets obtained lower temperature coefficient, and enhanced magnets temperature stability.

Homogenization heat treatment of 2099 Al–Li alloy

Abstract The microstructure evolution and composition distribution of as-cast and homogenized 2099 aluminumlithium （Al-Li） alloy were studied by optical microscopy （OM）, differential thermal analysis （DTA）, scanning electron microscopy （SEM）, energy dispersive spectrometry （EDS）, area and line scanning, X-ray diffraction （XRD）, and Vickers microhardness test methods. The results show that severe dendrite exists in the as-cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low-melting point nonequilibrium eutectic phases dis- solve into the matrix during the first-step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second-step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of A1-Cu-Fe phases. An optimized homogenization process of the 2099 A1-Li alloy is developed （515℃ - 18 h ＋ 525℃ - 16 h）, which shows a good agreement with the homogenization kinetic analysis results.

Homogenization heat treatment for an additively manufactured precipitation-hardening high-entropy alloy

A precipitation-hardening high-entropy alloy(HEA),(FeCoNi)_(86)Al_(7) Ti_(7),was successfully fabricated using selective laser melting(SLM).Severe segregation of Ti occurred at the boundaries of dislocation cells.Therefore,homogenization heat treatment at 1150℃for 0.5 h was performed to alleviate the microsegregation.After homogenization,almost no dislocation cells were left in the grains,and recrystallization occurred as the average grain size increased from 37 to 54μm.Compared with the initial as-built HEA,the ductility of the HEA increases significantly from 29%to 40%,and the strength decreases slightly from 710 to 606 MPa.For further aging,pre-homogenization can decrease the precipitation of ordered L2_(1) phases.Because void has a high propensity to initiate from the matrix/L2_(1) incoherent interface,pre-homogenization reduced the number of weak points,thus considerably improving the plastic deformation ability of the aged HEA by 36%.In addition,the strengthening mechanism has also been analyzed for the aged HEA.It was revealed that the coherent L1_(2)precipitate contributed the most to the increased strength.

Stress Relaxation Behavior of a Nb-Stabilized Austenitic Stainless Steel at 550℃

Stress relaxation resistance is one of the most significant properties that are critical to the service life of the fasteners.In this study,the stress relaxation behavior of a Nb-stabilized austenitic stainless steel was investigated.It was revealed that the homogenization treatment at 1250℃could make more primary NbC particles dissolved back into the matrix and consequently get a great number of nano-sized secondary NbC carbides.Therefore,the stress relaxation resistance will be enhanced due to the effective pinning of such higher density of nano-sized secondary NbC carbides on the dislocation movement.

Microstructure and mechanical properties of Mg-Zn-Y-Nd-Zr alloys

The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr （x=0, 1 wt.%, 2 wt.%, 3 wt.%） alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W （Mg3Y2Zn3） and I （Mg3YZn6） phases. With the addition of Nd, I-phase disappeared and Mg3Y2Zn3 phase changed into Mg3（Nd,Y）2Zn3 phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg＋W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.

Effects of isothermal homogenization on microstructure evolution of Mg-7Gd-5Y-1MM-0.5Zr alloy

Optical microscopy （OM）, scanning electronic microscopy （SEM） and X-ray diffraction （XRD） were performed to inves- tigate the influence of homogenization on the microstructures of the Mg-7Gd-5Y-1MM （Ce-rich RE）-0.5Zr magnesium alloy. The results indicated that α-Mg, Mg24（GdY）5 phase, Mg5（GdY） phase and Mg12MM phase coexisted together in as-cast alloy; the micro- structures were largely characterized by α-Mg matrix and gray globular or elliptic ball Mg12MM phase, in addition to those with cubic block Mg24（GdY）5 phase after homogenization; the reasonable homogenization regime was maintained at 530 ℃ for 32 h.

Catalytic activities of ultra-small β-FeOOH nanorods in ozonation of 4-chlorophenol

We report the catalytic properties of ultra-small β-FeOOH nanorods in ozonation of4-chlorophenol（4-CP）. XRD, TEM, EDS, SAED, FTIR and BET were used to characterize the prepared material. Interaction between O3 and β-FeOOH was evident from the FTIR spectra.The removal efficiency of 4-CP was significantly enhanced in the presence of β-FeOOH compared to ozone alone. Removal efficiency of 99% and 67% was achieved after 40 min in the presence of combined ozone and catalyst and ozone only, respectively. Increasing catalyst load increased COD removal efficiency. Maximum COD removal of 97% was achieved using a catalyst load of 0.1 g/100 m L of 4-CP solution. Initial 4-CP concentration was not found to be rate limiting below 2 × 10^-3mol/L. The catalytic properties of the material during ozonation process were found to be pronounced at lower initial p H of 3.5.Two stage first order kinetics was applied to describe the kinetic behavior of the nanorods at low p H. The first stage of catalytic ozonation was attributed to the heterogeneous surface breakdown of O3 by β-FeOOH, while the second stage was attributed to homogeneous catalysis initiated by reductive dissolution of β-FeOOH at low p H.