Characterization of two-phase B2–HCP alloys in the Ru–Al–Cr system

Alloys of Ru–Al–Cr produced by arc-melting and by directional solidification at 20 mm/h were heat treated at 1100 °C and 1500 °C. Partial isothermal sections at 1100 °C and 1500 °C were constructed using the results from scanning (SEM) and transmission (TEM) electron microscopy. Both isothermal sections displayed a large B2 region with a composition extending towards Ru–20Al–38Cr at%. The directionally solidified Ru–6Al–38Cr and Ru–4Al–41Cr (at%) alloys exhibited uniformly distributed B2 precipitates in an HCP matrix after heat treatment at 1100 °C for 200 h. The Burgers orientation relationship of ( ( 0001 ) HCP / / ( 011 ) B 2 , [ 2 1 ¯ 1 ¯ 0 ] HCP / / [ 1 1 ¯ 1 ] B 2 ) was found between the HCP matrix and the semicoherent B2 precipitates by TEM. A uniform Al compositional profile within the B2 precipitates was found using STEM while limited solubility was detected in the matrix.