Abstract
Abstract In this article, the structural and nanoscale strain field of the α/β phase interface layer in Ti80 alloy were studied by using high-resolution transmission electron microscopy (HRTEM) and geometric phase analysis (GPA). The α/β interface layer was observed in forged and different annealed Ti80 alloys, which is mainly composed of lamellar face-centered cubic (FCC) phase region and α′ + β region. The FCC phases between α and β phases show a twin relationship, and the twinning plane is ( 1 1 ¯ 1 ) (1\bar{1}1) . The orientation relationship of the β phase, the α phase, and the FCC phase is (110)β//(0001)α// ( 1 1 ¯ 1 ) (1\bar{1}1) FCC and [ 1 ¯ 11 \bar{1}11 ]β//[ 2 1 ¯ 1 ¯ 0 2\bar{1}\bar{1}0 ]α//[011]FCC. The nanoscale strain field of FCC + α and β + α′ regions was analyzed by using the GPA technology. The FCC + α region shows more significant strain gradient than the α′ + β region, and ε FCC > ε α, ε α′ > ε β. The influence of element addition on the formation mechanism of the FCC phase was discussed. The addition of Zr promotes the formation of the FCC phase by inducing lattice distortion and reducing the stacking fault energy of the α phase. In addition, the Al element forms an obvious concentration gradient around the interface layer during the cooling process of the alloy, which provides a driving force for the formation of the FCC phase.
Highlights
Titanium and titanium alloys are widely used in aerospace, biomedicine, shipbuilding, and other fields due to their high specific strength, excellent corrosion resistance, and high-temperature mechanical properties [1,2,3,4]
Some regions surrounded by the primary α phase have complex structures, which may include β phase, α′ phase, interfacial layer, and so on, which cannot be clearly observed under the metallurgical microscope, as marked by the white circle
There are some complex α + β phase regions that cannot be clearly observed in Ti80 alloys with equiaxed, bimodal, and lamellar structures, which may contain the α/β interface layer, as shown by the red circle
Summary
Titanium and titanium alloys are widely used in aerospace, biomedicine, shipbuilding, and other fields due to their high specific strength, excellent corrosion resistance, and high-temperature mechanical properties [1,2,3,4]. The α/β interface layers were observed in pure titanium and titanium alloys [7], which mainly composed of the face-centered cubic (FCC) phase [8]. There is no systematic study on the interface layer and the FCC phase of near α titanium alloy. Zhu et al [12] proved that the existence of the interface layer and the FCC phase by using in situ heating based on the high-temperature instability of Ti-hydride. Hong et al [13] observed the stress-induced FCC phase in pure titanium and considered that the stress-induced phase transformation was attributed to the gliding of Shockley partial dislocations, which provides a new plastic deformation martensite transformation mode. Most stress-induced HCP → FCC phase transitions are caused by severe plastic deformation conditions, such as cryogenic channel-die compression, high energy shot peening, and cold rolling [14]
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