Optimal Selection and Control for Precipitation of α_2 Phase in Near α High Temperature Ti Alloys during Aging Treatment

The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near α Ti alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution of α2 phase precipitated and cause the changes in growth speed of α2 phase. For various aging temperatures, the time to finish precipitation of α2 phase is different. The facts that various distribution characteristics and growth speed of α2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation of α2 ordered phase reachable. Some discussions on adoptable aging steps are presented.     

Effect of Al Content on Precipitation of α_2 Ordered Phase in Ti-Al-Sn-Zr-Mo-Si-Nd Alloys

The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered phase changed with temperature and Al content. The dislocations were the only places where the α2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of α2 ordered phase increased. When the aging temperature was relatively low (650℃), the precedent precipitation of α2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed (3) of the alloys with lower Al content. But after certain aging time (50 h), the size of α2 particles was almost equal in both the primary a and the transformed β. And no obvious growth of α2 particles could be observed after 50 h.     

A New Aging Treatment Way for Near α High Temperature Titanium Alloys

Two near α titanium alloys,Ti-5.6Al-4.8Sn-2.0Zr-1Mo-0.35Si(1#) and Ti-6.0Al-4.8Sn-2.0Zr-1Mo-0.35Si(2#),were solution-treated in the upper α+β phase fields,and the duplex mixture microstructures consisting of the less volume fraction primary α phase(αp) and the transformed β phase(βt) were obtained.The aging treatments were carried out at 700℃ for 1# alloy and 760℃ for 2# alloy under varied terms,respectively.It guaranteed α2 ordered phase to precipitate only in αp but not in βt for the two alloys.The slower...     

Growth Behavior of a Phase in Ti-5.6Al-4.8Sn-2.0Zr-1.OMo-0.35Si-0.7Nd Titanium Alloy

The thermal stability of the microstructure of a near-αtitanium alloy after aging at 750℃was investigated using optical microscope and transmission electron microscope as well as composition analysis. Aging treatment brings about significant coarsening of grain boundaryαandαplatelets within the colonies for martensitic microstructure. The observed changes are related to the growth steps or ledges of the interface and lamellar termination presented in the microstructure. The composition analysis of the coarsenedαplate is consistent with the growth kinetics. TheαWidmanstatten plates were coarsened due to the movement ofα/βinterface for Widmansta'tten microstructure, and the phase boundaries of primaryα(αp) phase directly moved into the transformedβfor bimodal microstructure.     

Precipitation of α Phase in the Massive and Feathery Structures in TiAl Alloys during Aging in the Single α Field

1.IntroductionThemechanicalpropertiesofTiAl-basealloysareverysensitivetotheirmicrostructures,which,inturn,arecontrolledbyheattreatments.Forthecomposi-tionsofengineeringimportance,the7-TiAlalloyscanbesolution-treatedinthesinglea-phasefieldandsub-jectedtothea-7transformationduxingsubsequentcooling.Dependingoncoolingrate,theadecompo-sitioncanoccurinseveralpaths,yieldingalamel-larstructureunderrelativelyslowcooling,afeath-ery7structureunderaircoolingandamassive7structureforwater-quenching.Curren…     

Influence of α Phase on Shape Memory Effect and Superelasticity of CuZnAI Alloy

The influence of a small amount of α phase inβ′ matrix on shape memory effect andsuperelasticity of CuZnAl shape memory alloy hasbeen studied systematically.It has been found thattransformation temperature can be adjusted in alarge scale by controlling the amount of α phase,meanwhile,shape memory effect and superelasticitydo not decrease obviously when there exists a smallamount of α phase.Based on the optical and trans-mission electron microscopy observation,the influ-ence of α phase on shape memory effect andsuperelasticity has been discussed.     

Growth of Carbon Nanocoils by Porous α-Fe2O3/SnO2 Catalyst and Its Buckypaper for High Efficient Adsorption

High-purity(99%)carbon nanocoils(CNCs)have been synthesized by using porousα-Fe2O3/SnO2 catalyst.The yield of CNCs reaches 9,098%after a 6 h growth.This value is much higher than the previously reported data,indicating that this method is promising to synthesize high-purity CNCs on a large scale.It is considered that an appropriate proportion of Fe and Sn,proper particle size distribution,and a loose-porous aggregate structure of the catalyst are the key points to the high-purity growth of CNCs.Benefiting from the high-purity preparation,a CNC Buckypaper was successfully prepared and the electrical,mechanical,and electrochemical properties were investigated comprehensively.Furthermore,as one of the practical applications,the CNC Buckypaper was successfully utilized as an efficient adsorbent for the removal of methylene blue dye from wastewater with an adsorption efficiency of 90.9%.This study provides a facile and economical route for preparing high-purity CNCs,which is suitable for large-quantity production.Furthermore,the fabrication of macroscopic CNC Buckypaper provides promising alternative of adsorbent or other practical applications.