Initiation of a plastic flow in boron carbide at nanoindentation

Does grain size have an influence on intrinsic mechanical properties and conduction mechanism of near fully-dense boron carbide ceramics?

“…To this end, an accurate analysis of hardness and elastic modulus as well as conductivity and their grain size dependence is essential for advanced applications. In this sense, previous studies have shown a relatively wide range of hardness values by Vickers indentation ~20-35 GPa [3][4][5][6][7][8][9][10][11][12][13] and nano-indentation  40GPa as well as elastic modulus 500GPa [14][15][16][17][18][19]. This large variation is mainly related to the presence of porosity in boron carbide ceramics, their grain-size effects, the composition and the indentation load.…”

Spark Plasma Sintered B4C—Structural, Thermal, Electrical and Mechanical Properties

“…Upon further loading, the mean contact pressure recovered back to above 40 GPa, where a second pop-in event was detected at a contact penetration depth of about 50 nm. The appearance of such pop-in events during loading of B4C can possibly be explained either by plastic deformation by nucleation of dislocations [55] or a high pressure structural phase transition, with an associated decrease in the volume of the high-pressure phase [99,101]. The simulated estimate of ~4% sudden volume reduction were reported in [102], however, the pressure where such a significant volume change would occur was estimated to be ~22.8 GPa.…”

“…Some of the load-displacement plots obtained during nanoindentation of B 4 C exhibited one to three discontinuities during loading ( Figure 7C). The presence of such pop-in events during nanoindentation is explained by transition from the elastic to elastoplastic deformation upon nanocontact in the imprint [55]. A second order phase transition in B 4 C was reported to occur at 32 GPa to 35 GPa due to reordering of polar atoms [99].…”

“…The hardness of B 4 C thin films measured by nanoindentation varied significantly in the range of 28 GPa to 60 GPa [53]. The indentation hardness of B 4 C single crystals or polycrystalline ceramics was reported to be around 39-55 GPa as measured using a Berkovich indenter [54][55][56]. Discontinuities in the loading and unloading deformation plots of B 4 C during nanoindentation were reported, which were either explained by cracking or by the transition from elastic to elastoplastic deformation caused by homogeneous nucleation of dislocations due to the high shear stresses below the indenter [55,56].…”

“…The indentation hardness of B 4 C single crystals or polycrystalline ceramics was reported to be around 39-55 GPa as measured using a Berkovich indenter [54][55][56]. Discontinuities in the loading and unloading deformation plots of B 4 C during nanoindentation were reported, which were either explained by cracking or by the transition from elastic to elastoplastic deformation caused by homogeneous nucleation of dislocations due to the high shear stresses below the indenter [55,56]. The flexural strength of B 4 C is not very high and is reported to be around 36,45,[57][58][59], while compressive strength is much higher and lies in the range of 6.1 ± 0.3 GPa [60].…”