Fig. 1 Microstructure of as-casted specimen: a OM image; TEM images of b intergranular phase, c intragranular phase, with their SAED patterns shown at the right side; as-homogenized specimen: d OM image; TEM images of e intergranular phase, f intragranular phase, with their SAED patterns shown at the right side

Fig. 2 a SEM image of as-homogenized GWZK114; b micro-hardness of different phases

Fig. 3 OM microstructure of samples compressed with a strain rate of 0.1 s-1 at different temperatures: a 350 °C; b 400 °C; c 450 °C; d 500 °C

Fig. 4 Kinking angles of 14H-LPSO phase and DRX fractions extracted from Fig. 3

Fig. 5 EBSD analysis of microstructure at the temperature of 450 °C and strain rate of 0.01 s-1 with compressive strain being a 0.4, b 0.8, c 1.2, d enlarge image of dash circle shown in a, e enlarge image of white arrows shown in b, f enlarge image of dash square shown in c. The white lines represent low-angle grain boundaries with their misorientation angle between 2° and 15°, black lines are high-angle boundary with misorientation angle larger than 15°. The black block is the non-indexed intergranular phase

Fig. 6 Ture strain-stress curves of specimens compressed at temperatures of 300-500 °C with a strain rate of a 0.01 s-1, b 0.1 s-1, c 1 s-1, d 10 s-1

Fig. 7 Relationships among stress, strain rate and temperature: a ln|σ| versus ln$\dot{\varepsilon }$; bσ versus ln$\dot{\varepsilon }$; c ln sinh(ασ) versus ln$\dot{\varepsilon }$; dln sinh(ασ) versus 1/T

Fig. 8 Strain evolution of selected points (P1-P6) in specimen compressed at 450 °C to a strain of 1.2 (compression displacement 8.4 mm). The analytical strain (hollow dot) was calculated by $\varepsilon = - \ln (1 - h/H_{0} )$, h is height of compressed cylinder and H0 is initial height of cylinder, 12 mm

Fig. 9 Microstructure of specimens deformed at 450 °C and 0.01 s-1: OM images at true strains a 0.4 (0.85); b 0.8 (2.06) and c 1.2 (2.5); DRX grains extracted from EBSD tests in Fig. 5; d true strain 0.4 (0.85); e true strain 0.8 (2.06); f true strain 1.2 (2.5). The strains in the brackets are the local true strain

Fig. 10 Fitted curves of DRX model based on experimental data at 450 °C with strain rates of 0.01 and 1 s-1

Fig. 11 Comparison between measured and predicted DRX fractions of: a various compression conditions at a local strain of 2.06 (nominal strain 0.8); b RUE without (dash lines) and with (solid line) considering non-uniform strain. The mean strain rate of RUE process is calculated through Eq. (6) in the Ref. [33]. More parameters of RUE process, such as plastic strain per pass, extrusion speed, are referred to the references [27]

Fig. 12 a Comparison between measured and predicted DRX fractions [Eqs. (9) and (10)] of 400 °C-0.01-1 s-1; b kinking angles of 14H-LPSO phase under different compression conditions (350-450 °C and 0.01-1 s-1). DRX fractions at N1-N4 were achieved by OM observation and their corresponding values of strain are determined by FEM

Fig. 13 a Relation between n and $\dot{\varepsilon }$ considering LPSO kinking and its validation by data of 400 °C, b predicted DRX fractions of RUE process by DRX model without and with LPSO kinking at 420 °C-0.108 s-1 [28]; c evolution of f values with different deformation temperatures and strain rates

Fig. 14 Evolution of DRX grain size with a deformation temperatures at 0.1 s-1; b strain rates at temperatures of 400 °C, 450 °C and 480 °C, c compression strains at 450 °C with strain rate being 0.01 s-1 and 1 s-1

Fig. 15 a Fitting curve of experimental data; b validation for model of DRX grain size