| Properties of high temperature and high strength-ductility are two kinds of requirements for alloy materials in current engineering field.High temperature near-? Ti alloys with BCC structure,which are characterized by good stability in high temperature,oxidation resistance and comprehensive mechanics performance,and high strength-ductility near-? Ti alloys with FCC structure,which possess excellent tensile strength and good fracture toughness,are both applied as structural materials in different parts of aircraft.Nevertheless,the diversification of component makes the design of solid solution alloys more complicated.The method of Al equivalent and BP nepal network were applied to design near-? Ti alloys,and the method of Mo equivalent is applied to design near-? Ti alloys,while methods of d-electron theory and electron concentration criterion are applied to design both near-? Ti alloys and near-(3 Ti alloys.Atoms in solid solution alloys arrange by a rule of chemical short-range-order,showing a certain extent of structure principle,so we can describe this rule as a simplified way due to different mixing enthalpies of each element base on Ti.Work of this paper is to explore the component principle of near-? Ti alloys and near-? Ti alloys using our structure model of a cluster-plus-glue-atom,which distribute atoms into two parts,cluster part and glue atom part.Analyzed near-? Ti IMI834 and set it as a reference alloy through our model,then we got a component formula showing as[Al-(Ti13.7Zr0.3)](Al0.65Sn0.2Si0.1(Mo/Nb/Ta/W)0.15),and then analyzed near-? Ti Ti-55531 and set it as a reference alloy though model too,then we get a component formula showing as[Al-(Ti13.9/13.7Zr0.1/0.3)](Al/Mo/V/Cr/Fe)2/2.2.Two different series of alloy rods with 6mm diamenter were made by copper-mould suction-casting method.?-Ti alloys are solid-solution treated at 990? for 2 hours followed by water quench,then aged at 665? for 2 hours follow by water quench,?-Ti alloys are solid-solution treated at 800? for 2 hours followed by air cooling and then aged at 600? for 8 hours follow by air cooling too.XRD and OM were carried out to identify structures of phases and observe their microstructure,then durometer was used to test their hardness and muffle furnace was used to test their oxidation resistance.Results of experiments showed that,for high temperature near-? Ti alloys,the adding of Ta and W improves the hardness of this set of alloys,up to 380-394HV,but after aging heat treatment,their hardness can be change with a range of 366-406HV.Bimodal microstructure,consisting of equiaxed a and lamellar a,can be yielded after aging heat treatment,and alloys with higher Ta or with W have a fine-grained matrix of transformed ?.The distribution and morphology of equiaxed a in alloys with W or Ta substitutes for Nb are fine.When contents of Ta and Nb are similar,antioxidant capacity of alloys can been improved,their weight just increase 180?g/cm2 after 100h's heating at 650?,with a stable oxide,then adding W into this series of alloys by substituting for Mo can enhance antioxidant capacity ulteriorly too.When decrease amount of Nb or substituted by other elements can make antioxidant capacity more low.After heated at 800?,alloys with W element showing a higher antioxidant capacity,and one of them which has a higher Ta content has the best antioxidant capacity with an oxidation weigh gain of 1.1mg/cm-2.For high strength-ductility near-? Ti alloys,when Fe substituting for Cr,or increasing content of Mo,V and Cr,? phase is more stable after aging treatment.On the other hand,Zr substituting for Ti or Fe substituting for Cr can improve hardness. |
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