How hard metal becomes soft: crystallographic analysis on the mechanical behavior of ultra-coarse cemented carbide

Abstract

Investigation into the temperature dependence of the mechanical behavior of ultra‐coarse grained cemented carbide materials is highly demanded due to its service conditions of concurrent applied stress and high temperature. In the present study, based on the designed experiments and microstructural characterization combined with crystallographic analysis, the evolution of slip systems, motion and interaction of dislocations with temperature are quantified for the WC hard phase. Mechanisms are proposed for the formation of the sessile dislocations in the main slip systems at the room temperature and the glissile dislocations in the new slip systems activated at high temperatures. Furthermore, the correlation of the plastic strain and fracture toughness with the temperature‐dependent slip activation, dislocation reaction and transformation is explained quantitatively. Enlightened by the present findings, potential approach to enhance the high‐temperature strength of ultra‐coarse cemented carbides based on WC strengthening was suggested.

Nanomechanical Behaviour of Individual Phases in WC-Co Cemented Carbides, from Ambient to High Temperature.

“…In addition to the cracks, plastic deformation was observed within the entire cross-section of the grain at 600 ˚C. Whilst plastic deformation intensifies in both WC grains with temperature, leading to higher densities of slip bands as observed in previous work [22], the anisotropic plastic flow in WC crystals, and more especially, the difference in the plastic index measured for basal and prismatic grains, can therefore be explained by the preferential accommodation of stress via the initiation of different slip system and cracking. Stresses were found to be released through cracking, probably on the prismatic plane, when indenting the basal plane of WC.…”

“…Therefore, understanding the deformation mechanisms in WC grains at the nanoscale is of great importance. While a lot of effort has been made to improve the performance of WC-Co though microstructural design, gathering mechanical properties from the different phases and WC crystal orientation at room temperature, very little information has been collected at high temperature [14,22]. Vickers hardness measurements, at temperatures ranging from ambient to 1000 ˚C, have been conducted on several WC-Co grades with varying Co binder phase proportions and WC grain sizes, revealing significant decrease in hardness of the overall material, especially at temperature higher than 600 ˚C [23].…”

Effect of Grain Refinement on the Comprehensive Mechanical Performance of W–Cu Composites

“…According to the previous study [ 30 ], the high strength of UFG W–Cu composites at room temperature was attributed to the load-bearing effect of tungsten and the dislocation strengthening induced by the grain boundaries and phase boundaries. As the temperature was raised, the motion of atoms and dislocations was intensified [ 37 , 38 ], and the critical shear stress required for dislocation slip was reduced [ 39 ], so the strength of both copper and tungsten decreased with temperature. Comparatively, however, tungsten remained in a hard phase at high temperatures, making it the dominant load-bearing phase.…”

Could an amorphous binder Co phase improve the mechanical properties of WC–Co? A study of molecular dynamics simulation

“…Moreover, with WC–Co as the tool/chip, the service conditions of applied intensive stress and high temperature need to be investigated. 33–37…”

“…Moreover, with WC-Co as the tool/chip, the service conditions of applied intensive stress and high temperature need to be investigated. [33][34][35][36][37] With this background, the effects of the amorphous binder phase on the mechanical properties of WC-Co at room and high temperatures were studied. The structural transformations and mechanical behavior during the deformation of each case have been systematically analyzed and reported in the following sections.…”