Influence of grain size distribution on mechanical properties and HDI strengthening and work-hardening of gradient-structured materials

Enhancing mechanical properties of metallic materials by architecting gradient structures

“…The refinement of ferrite grain size results in the gradual increase in yield strength with decreasing the annealing temperature (see Figure 2(b) and Figure 3(a)). As reported in our previous paper [15], the ferrite grain size at a certain location can be also refined by using pre-torsion with a larger twist angle, as shown in Figures 8 and 10(b), which indicates that the grain size distribution of the linear GGS can be also effectively manipulated by tailoring the twist angle with the identical annealing parameters. As an example, a grain size distribution from 3.4 ± 1.6 μm at the surface to 8.0 ± 3.5 μm at the centre is achieved in the 1440-600 sample (see Figure 10(b)).…”

“…Before any processing, the dog-bone-shaped samples were thermally annealed at 700°C for 1 h to remove the effect of previous processes and gain a coarse-grained (CG) microstructure with an average grain size of some 25 µm (see Figure 1(a)). Subsequently, the CG samples were subjected to pre-torsion deformation at room temperature (RT) by a torsion machine [15,16]. The torsion was conducted at a constant rate of 60° per min and assigned to twist from 180–1440°, as indicated by ● in the torque-twist angle curve in Figure 1(b).…”

“…Heterogeneous structures, currently gaining extensive attention of materials scientists, endow metallic materials with incomparable mechanical or physical properties [1][2][3][4][5][6][7][8][9], which are far better than those of conventional monolithic materials. As an important member of heterogeneous structures family, the gradient structure (GS) has been successfully engineered in many metals and alloys, such as Cu [10,11], Al [12], steel [13][14][15][16] and high-entropy alloy [17], using surface mechanical deformation or pre-torsion, and an outstanding strength-ductility synergy is achieved [10][11][12][13][14][15][16][17]. The advanced integrated mechanical properties by the GS are determined by the unique deformation mechanism, i.e.…”

“…hetero-deformation induced (HDI) strengthening and work-hardening resulting from the accumulation of geometrical necessary dislocations (GNDs) at the hetero-boundaries to accommodate the strain gradient [2,7,13,[18][19][20][21]. So far, multiple types of GS have been designed and produced in different materials, including gradient grain structure (GGS) [2,[10][11][12][13][14][15], gradient twining structure (GTS) [16,17,22] and gradient dislocation structure (GDS) [23,24], etc. Previous studies have demonstrated that better strength-ductility-toughness combinations are achieved by the GGS than those by the GDS.…”

“…However, the difference in the efficiency of enhancing integrated mechanical properties between different GS has not been well researched yet. Furthermore, the GS can be treated as a ‘composite structure’ composed of ‘hard domain’ and ‘soft domain’ [2,7,19], and the volume fraction [11], degree [22,25], domain misorientation [26], residual stress [27] and grain size distribution [15,28,29] of the GS have been shown to have a profound influence on the mechanical properties. However, exploring other factors, e.g.…”