Solution and aging behavior of precipitates in laser melting deposited V-5Cr-5Ti alloys

V-5Cr-5Ti alloys have been fabricated using a laser melting deposition(LMD)additive manufacturing process,showing precipitates aggregated near the grain/dendrite boundaries.Since the mechanical properties of vanadium alloys considerably depend on the precipitates,solution and aging treatments have been applied to eliminating the aggregations of the precipitates.The results show that as the solution temperature increases from 800 to 1560℃,the densities and the lengths of the precipitates are reduced,while the widths of the precipitates are increased.When the solution temperature reaches 1560℃,most impurity elements diffuse into the matrix and form into a nearly uniform supersaturated solid solution.Aging treatments have been applied to the 1560℃solution treated samples.It shows that as the aging temperature increases from 800 to 1200℃,the precipitate length increases,and the shapes of precipitates change from near-spherical to lath-like.Compared to 800 and 1200℃,aging at 1000℃results in the highest precipitate density.Compared to the LMD and solution-treated samples,the aged samples have the highest micro-hardness,due to the precipitation strengthening.

Effect of heat treatment on microstructure and properties of semi-solid squeeze casting AZ91D

Semi-solid AZ91D magnesium alloy billets were prepared by near-liquidus heat holding.Semi-solid squeeze casting was conducted at 575,585 and 595℃,respectively,with 1 mm·s^-1 squeeze speed.The semisolid squeeze casting AZ91D samples were heat treated by T4(solution at 415℃for 24 h)and T6(solution at 415℃for 24 h+220℃for 8 h)processes,respectively.The microstructure and mechanical properties of the alloy in different states were investigated by means of OM,SEM and tensile testing machine.The results show that compared to as-cast alloy,the grain size of the semi-solid squeezed AZ91D decreased significantly,and with the increase of semi-solid squeeze temperature,the grain size of AZ91D increased.The grains of the alloy were refined by T4 treatment,and further refined by T6 treatment.T6 treatment greatly improved the tensile strength,elongation,and hardness,but did not significantly improve yield strength.After 575℃squeeze casting and T6 treatment,the ultimate tensile strength(UTS)reached 285 MPa,the elongation reached 13.36%,and the hardness also reached the maximum(106.8 HV),but the yield strength(YS)was only 180 MPa.During the process of semi-solid squeeze casting and heat treatment,the matrix grain was refined and a large number of precipitated and secondary precipitated phases of Mg17Al12 appeared.Both the average size of matrix grain and secondary precipitated phase decreased,while the volume fraction of secondary precipitated phase increased.All these resulted in high tensile strength,elongation and hardness.

Effect of Heat Treatment on the Microstructure of Multiphase NiAl-based Alloy

The alloy Ni-Al26.6-Cr13.4-Co8.1-Ti4.3-W1.3-Mo0.9 （at. pct） was fabricated from superalloy K44 and Al element using vacuum induction and casting technique. Investigations to this alloy reveal that a new phase Cr3Ni2 possessing low melting point and poor ductility is formed, which is distributed as a network along NiAI matrix grain boundaries. Subsequent different solution and aging treatments are carried out and lead to microstructural changes to various extents. Rapid cooling after solution at 1250℃ for 20 h gives rise to macrocracks in the specimen while slow cooling after the same treatment results in the formation of spheric α-Cr solid solution and needle-like Ni3Al phase, which are embedded in NiAl matrix. It is comfirmed that aging treatments initiate lath-shaped Ni3Al phase and pearl-shaped α-Cr phase to precipitate from the NiAl matrix, which own orientation relationships with these precipitates.

T6处理对Mg-10Gd-3Y-0.6Zr合金组织及拉伸性能的影响(英文)

The effects of solution and ageing treatment (T6) on microstructure and tensile properties of as-extruded Mg-10Gd-3Y-0.6Zr (mass fraction. %) alloy were investigated. The results show that after T6 treatment, the diameter of grain increases to 20 μm. As the second phases dissolve into the matrix, the smaller and denser β′ phases precipitate inside the grains. After T6-treatment, both yield strength (TYS) and ultimate tensile strength (UTS) are increased. Comparing with that in only ageing condition (T5), the UTS and TYS increased from 365 MPa,285 MPa to 400 MPa,310 MPa, respectively, but the elongation decreased from 7.0% to 3.5%. It has been found that the effects of precipitates on the strength are stronger than that of the growth of grain size.

Optimized Mechanical Properties,Corrosion Resistance and Bactericidal Ability of Ti-15Zr-xCu Biomedical Alloys During Aging Treatment

The effects of different aging conditions on the microstructure,strength,corrosion resistance,cytotoxicity and antibacterial ability of Ti-15Zr-xCu(3≤x≤7,wt%)(TZC)alloys were systematically investigated.Microstructural evolution and behavior were analyzed by X-ray diffraction(XRD)patterns and scanning electron microscopy with energy-dispersive spectroscopy(SEM-EDS),while potentiodynamic polarization technique was employed to characterize the corrosion response of the alloys after solution-treatment and aging(STA).High-temperature aging at 660℃ for 4 h(660-4)gave the best combination of properties by enabling significant precipitation of the Cu-rich Ti_(2)Cu and Zr_(2)Cu compounds,and mild formation of the Zr_(7)Cu_(10) secondary phase.The high kinetics at this condition was beneficial to the complete precipitation and more homogeneous distribution of the intermetallic particles.These led to the inhibition of dislocation movements and allowed for significantly improved mechanical strengths with added ductility,availability of more Cu ions for the desired oligodynamic activity without evoking cytotoxicity,better corrosion resistance and very high antibacterial ability(over 99.5%),thus improving the overall properties of the TZC alloys for biomedical applications.

Microstructure and property of laser additive manufactured alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si after aged at different temperatures

The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures.In this study,the influence of aging temperatures(600,700 and 800°C)on microstructure and mechanical properties of titanium alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si was investigated.The results indicate that after solid solution treatment at 970°C followed by water quenching,the alloy mainly consists of coarsening lamellar a phase in martensite α' matrix.Aging at 600°C will not change the size of primary lamellar α phase but lead to huge amount of secondary a phases(α_(s))generating with very fine microstructure.By increasing the aging temperature,the number of α_(s) decreases but with coarsened microstructures.When aged at 800°C,the width of the asphase reaches 350 nm,almost 7 times wider than that aged at 600°C.The changing size of α_(s) obviously influences the property of the alloy.The fine α_(s) leads to high strength and microhardness but low plasticity,and specimen aged at 700°C with suitable assize has the best comprehensive properties.

Microstructure and tensile properties of A356 alloy with different Sc/Zr additions

Addition of rare earth elements for improving the tensile properties of aluminum alloys has attracted great attention. In this study, a systematic analysis on the microstructure and tensile properties of A356–0.13 Ti alloys with different contents of scandium(Sc) and scandium/zirconium(Sc/Zr) after solution and aging treatment process was carried out. The addition of Sc/Zr into A356–0.13 Ti alloys can greatly refine the grain size and modify the deleterious coarse eutectic Si structure and harmful acicular iron-containing phase morphology. As a result, the maximum value of strength(298 MPa) and ductility(elongation of 8.4%) are acquired by co-addition of Sc/Zr after solution and aging treatment process, which indicates that the tensile properties of A356 alloy are greatly enhanced by the synergistic effect of co-addition of Sc/Zr.