Proposed mechanism of HCP → FCC phase transition in titianium through first principles calculation and experiments

Abstract

Abstract By means of first principles calculation and experiments, a detailed mechanism is proposed to include the stages of slip, adjustment, and expansion for the HCP → FCC phase transformation with the prismatic relation of $${{\{}{10}\bar{{1}}{0}{\}}}_{{hcp}}{\parallel }{\{}{1}\bar{{1}}{0}{{\}}}_{{fcc}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mo>{</mml:mo> <mml:mn>10</mml:mn> <mml:mover> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> <mml:mo>}</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>hcp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∥</mml:mo> <mml:mo>{</mml:mo> <mml:mn>1</mml:mn> <mml:mover> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> <mml:msub> <mml:mrow> <mml:mo>}</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>fcc</mml:mi> </mml:mrow> </mml:msub> </mml:math> and $${{[}{0001}{]}}_{{hcp}}{\parallel }{[}{001}{{]}}_{{fcc}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mo>[</mml:mo> <mml:mn>0001</mml:mn> <mml:mo>]</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>hcp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∥</mml:mo> <mml:mo>[</mml:mo> <mml:mn>001</mml:mn> <mml:msub> <mml:mrow> <mml:mo>]</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>fcc</mml:mi> </mml:mrow> </mml:msub> </mml:math> in titanium. It is revealed that the formation of four FCC layers is preferable after the slip of Shockley partial dislocations of 1/6 $$\langle {1}\bar{{2}}{10}\rangle $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>〈</mml:mo> <mml:mn>1</mml:mn> <mml:mover> <mml:mn>2</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>10</mml:mn> <mml:mo>〉</mml:mo> </mml:math> on $${\{}{10}\bar{{1}}{0}{\}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>{</mml:mo> <mml:mn>10</mml:mn> <mml:mover> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> <mml:mo>}</mml:mo> </mml:math> planes, and that the adjustment of interplanar spacing and the volume expansion are energetically favorable and could happen spontaneously without any energy barrier. It is also found that the transformed FCC lattice first follows the c / a ratio (1.583) of HCP and then becomes an ideal FCC stru c ture ( c / a = √2). The proposed mechanism could not only provide a deep understanding to the process of HCP → FCC prismatic transformation in titanium, but also clarify the controversy regarding volume expansion of HCP-FCC phase transition of titanium in the literature.