Influence of microstructural inhomogeneities on the fracture toughness of modified 9Cr–1Mo steel at 298–823K

B4C-Al Composites Fabricated by the Powder Metallurgy Process

“…Addition of the B4C reinforced particles reduces the macroscopic ductility, which can be verified from the formation of smaller dimples compared to those without addition of B4C. The particle-matrix de-cohesion resulting dimples are observed, indicating that the tensile fracture of the composites is controlled by void nucleation and growth [1,25]. Figure 10 shows the SEM and the concomitant BSE images (BSTL) of the typical fracture surface of the specimens.…”

“…On the contrary, although the stress-strain curves of the B 4 C-Al composites indicates apparent brittle fracture in a macroscopic scale without apparent necking (see Figure 7), the fracture surface morphology observed from SEM shows a ductile nature in microscopic scale with fine dimples of 0.5 µm (Figure 10b-e). Addition of the B 4 C reinforced particles reduces the macroscopic ductility, which can be verified from the formation of smaller dimples compared to those without addition of B 4 C. The particle-matrix de-cohesion resulting dimples are observed, indicating that the tensile fracture of the composites is controlled by void nucleation and growth [1,25]. As shown in Figure 9, the tensile strength of the composites prepared by the low-energy ball milling process (191 MPa and 194 MPa for 15 wt % and 20 wt % B4C-Al composites, respectively) was almost the same as those of the pure Al samples (191 MPa) prepared using the same process.…”

“…Addition of the B4C reinforced particles reduces the macroscopic ductility, which can be verified from the formation of smaller dimples compared to those without addition of B4C. The particle-matrix de-cohesion resulting dimples are observed, indicating that the tensile fracture of the composites is controlled by void nucleation and growth [1,25]. For the composites reinforced with 15 and 20 wt % B 4 C particles prepared by the low-energy ball milling process, and BSTL images reveal an inhomogeneous, stripe-like distribution of the B 4 C particles (with a length of 15 µm~30 µm and a width of 4 µm~10 µm) in the Al matrix (Figure 10b,c).…”

“…For the composites reinforced with 15 and 20 wt % B 4 C particles prepared by the low-energy ball milling process, and BSTL images reveal an inhomogeneous, stripe-like distribution of the B 4 C particles (with a length of 15 µm~30 µm and a width of 4 µm~10 µm) in the Al matrix (Figure 10b,c). The agglomeration of the B 4 C particles inside the Al matrix failed to transfer the shear and tensile stresses during tensile tests, blocked the movement of the slip bands, and thus lead to a de-cohesion failure of particle-matrix interfaces and fast initiation and propagation of cracks [3,25]. Consequently, the poor interfacial bonding between the Al matrix and the B 4 C particles facilitates the easy crack propagation, which deteriorates the mechanical properties of the composites.…”