In situ studies and modeling the fracture of Zircaloy-4

The role of stress-state on the deformation and fracture mechanism of hydrided and non-hydrided Zircaloy-4

“…The deformation and fracture of Zircaloy-4 has been observed to occur by a ductile process of void nucleation, growth, and coalescence as evidenced by the formation of dimples on the fracture surface [7e28]. Void nucleation is observed to occur by slip band intersections at Laves precipitates located within grains or at grain/lath boundaries, along slip bands, at slip band intersections with grain/lath boundaries, and at slip band intersections with other slip bands [7,8]. The most common site of these four sites is slip intersections with Laves phase precipitates [7,8].…”

“…Recent work has utilized in-situ studies of the deformation and fracture of non-hydrided Zircaloy in a Scanning Electron Microscope (SEM) to show that crack extension and deformation to failure occurs by void nucleation, growth, and coalescence at positive values of triaxiality [7,8]. Triaxiality (h) is defined as the ratio of the hydrostatic (pressure) stress to the equivalent stress (also known as the von Mises Stress) [29e35].…”

“…The correlation between the principal stresses and the triaxiality and the Lode parameter values is analogous to the relationship between Cartesian (x, y) and cylindrical (r, q) coordinates, with r / h and q / x [29e35]. A micromechanical model was developed for fracture strain that consists of a void nucleation strain component for the initiation of failure that is insensitive to triaxiality, and a void growth and coalescence strain component that is highly dependent on triaxiality [7,8]. This model is an extension of the void nucleation, growth, and coalescence model of Rice and Tracey [36] by treating void nucleation and growth at multiple sites rather than at a single site.…”

“…The effective fracture strain and the void nucleation strain were observed to be lower for beta-treated Zircaloy with a Widmanst€ atten microstructure than for the same alloy with a recrystallized alpha-annealed microstructure. This was attributed to the concentration of intermetallic particles mainly along the lath boundaries in the beta-treated material, which provide a linear array of sites for void nucleation [7,8].…”

Defining recrystallization in pilgered Zircaloy-4: From preferred nucleation to growth inhibition

“…For example, a balance between plastic deformation and recrystallization annealing define the concentration of the basal pole [1,[3][4][5][15][16][17][18][20][21][22][23][24][25][26][27][28][29][30][31]. This, on the other hand, decides the Kearns factor [9,10,[32][33][34][35][36][37][38][39][40][41][42][43]; which industry often uses to 'certify' their product. It is to be noted that microstructure, in general, and crystallographic texture, in particular, has a direct role to play in determining a range of critical properties: mechanical anisotropy, creep, hydride formation, etc.…”