电弧熔炼TA10钛合金中hcp/bcc结构结晶取向计算

Calculation of Crystallographic Orientation of hcp/bcc Structures in TA10 Titanium Alloy Prepared by Arc Smelting

通过电弧熔炼的方法制备了TA10钛合金铸锭,对铸锭通过光学显微镜(OM)、扫描电镜(SEM)、X射线衍射(XRD)和透射电镜(TEM)进行了一系列表征,观察了该合金铸锭的微观结构,明确了α/β两相之间的晶体学位向关系。基于合金的α/β两相的晶体常数,应用“边-边匹配”模型,确定了α/β两相的(近)密排方向及(近)密排面,计算了晶向原子间距错配度以确定可能匹配的晶向,进而计算了晶面间距错配度以确定可能匹配的晶面。最终,计算得到四种在合金α/β两相中可能存在的位向关系,对这4种可能存在的位向关系以2D不变线理论进行了进一步明确。对于明确后的位向关系,基于“边-边匹配”模型的基本原则,进行了α/β两相界面处原子模拟。铸锭中存在的位向关系属于预测计算的位向关系的一种,并且α/β两相电子衍射花样与模拟衍射斑点花样吻合较好,因而验证了“边-边匹配”模型在TA10钛合金中的适用性。

Titanium and its alloys are currently commonly used structural materials with low density in the industry.It is widely used in aerospace,chemical industry,bioengineering and other fields.TA10 titanium alloy is a kind of nearlyαtype titanium alloy,which has strong resistance to crevice corrosion in high temperature and high content chloride.Therefore,TA10 titanium alloy is widely used as the sealing surface material of container equipment to solve the problem of crevice corrosion on the sealing surface of equipment.And it is also an excellent material for heat exchangers and pipes.At present,most of the research on TA10 titanium alloy focused on corrosion performance and processing technology.The domestic prediction and calculation of orientation relationship of titanium alloys are relatively weak.Therefore,the possible orientation relationships in TA10 titanium alloy were calculated and the edge-to-edge matching model was verified on TA10 titanium alloy for its applicability.In recent decades,researchers proposed several crystallographic models to describe the orientation relationship between the two phases in the phase transition process,such as structural ledge model,near-coincidence site model,invariant line model,O-lattice model,edge-to-edge matching model and so on.Among them,the edge-to-edge matching model was a recently developed model.The basis of the theoretical calculations in this paper was the edgeto-edge matching model.Compared with other crystallographic models,the edge-to-edge matching model could predict the orientation relationship of the two phases in a phase transition,not just explain the orientation relationship of two phases.And the edge-to-edge matching model only needed the basic crystallographic information of the two phases as a basis.To acquire the basic crystallographic information of TA10 titanium alloy,TA10(Ti-0.3Mo-0.8Ni)alloy ingots were prepared by arc smelting method using titanium powder,molybdenum powder and nickel powder as raw materials.TA10 alloy ingot was smelted three times under the protection of argon to improve chemical homogeneity.The microstructure and orientation relationship of the TA10 alloy ingots were characterized by optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD)and transmission electron microscope(TEM).TA10 alloy ingot was composed ofαand_(β)phases,which belonged to a lamellar structure.αphase and_(β)phase had the following orientation relationships:[12-10]α/[11-1]_(β),(0002)_(α)(/011)_(β).The crystallographic information ofαphase and_(β)phase of TA10 titanium alloy,such as the crystal structure and lattice constants,was obtained through the above-mentioned characterization methods.Based on the crystallographic information,the close packed or nearly close packed directions of α and_(β)phases were determined and classified into the straight atom row and zigzag atom row.According the principle that the atom rows matching,the interatomic spacing mismatches along the possible matching directions inαphase and_(β)phase were calculated to determine the possible matching directions.10%was selected as the critical value for the interatomic spacing mismatches,and the possible matching directions ofαphase and_(β)phase were<112-0>α/<111>_(β),<112-3>α/<113>_(β),<101-0>α/<113>_(β).Meanwhile,the interplanar spacing mismatches between the close or nearly close packed planes inαphase and_(β)phase were determined.6%was selected as the critical value for the interplanar spacing mismatches,and the possible matching plane ofαphase and_(β)phase were{0002}α/{110}_(β),{101-1}_(α)/{110}_(β).Excluding the unmatched orientation relationship,the possible matching orientation relationship was<112-0>_(α)/<111>_(β),{0002}_(α)/{110}_(β);<112-0>α/<111>_(β),{101-1}_(α)/{110}_(β);<112-3>α/<113>_(β),{101-1}_(α)/{110}_(β)and<101-0>_(α)/<113>_(β),{0002}_(α)/{110}_(β).In this article,the above four possible orientation relations were simplified into the following four specific orientation relationships:[12-10]_(α)/[11-1]_(β),(0002)_(α)(/011)_(β);[12-10]_(α)/[11-1]_(β),(1-011)_(α)/(011)_(β);[112-3]_(α)/[31-1]_(β),(1-011)_(α)/(011)_(β)and[101-0]_(α)/[31-1]_(β),(0002)_(α)(/011)_(β).These four possible orientation relationships were further refined with the two-dimensional invariant line approach(2D invariance line approach):[12-10]_(α)/[11-1]_(β),(0002)_(α)0.63°from(011)_(β);[12-10]_(α)/[11-1]_(β),(1-011)_(α)0.67°from(011)_(β);[112-3]_(α)/[31-1]_(β),(1-011)_(α)-7.21°from(011)_(β)and[101-0]_(α)/[31-1]_(β),(0002)_(α)0.87°from(011)_(β).According the refined orientation relationships,the spot diffraction patterns of α phase and β phase were simulated.Based on the match between atom rows,the atomic simulation between the α/β two-phase interfaces was carried out.TEM image of TA10 alloy ingot showed that electron diffraction pattern of α and β phases were consistent with the simulated one,thus the edge-to-edge matching model was verified on TA10 titanium alloy for its applicability.The edge-to-edge matching model could not only predict the orientation relationship,but also calculated the habitual surface of the precipitated phase.However,the edge-to-edge matching model also had some inherent limitations.The edge-to-edge matching model was mostly applied to simple structures,and only a few complex structures could apply this model.The edge-to-edge matching model was also lacking in applicability.Not all the orientation relationships of precipitation phase transitions could be explained by this theory.In terms of applicability,the edge-to-edge matching model needed further development.