Papers by Keyword: Indentation Fracture Toughness

Abstract: This paper is aimed at investigating the mechanical properties of spark plasma sintered alumina (Al₂O₃) reinforced with tungsten-carbide-cobalt (WC-12wt%Co). Pure Al₂O₃ and admixed-Al₂O₃ powders were sintered using spark plasma sintering (SPS) technique at a temperature of 1800°C, heating and cooling rates of 100 °C/min and 200 °C/min, a pressure of 48 MPa in an argon atmosphere. The density, hardness (HV) and indentation fracture toughness (K_IC) of the sintered samples were measured and compared. Between 9 and 17% increase was observed in the HV values of the additives, while the K_IC value recorded an increase between 17 and 63% for all the additive as compared to pure Al. Phase analysis and identification was carried out with X-ray diffraction and microstructure was taken with scanning electron microscope. The results obtained showed the samples potential for cutting tool applications.

Abstract: The influence of 1 wt.% and 2 wt.% of graphene platelets (GPLs) addition on indentation fracture toughness (IF) of aluminium oxide (Al₂O₃) and silicon nitride (Si₃N₄) based composites has been investigated and compared to the monoliths. Ceramic composites reinforced with GPLs were prepared using hot-press processing technology. Microstructures were observed at fracture surfaces by scanning electron microscopy (SEM). Crack type identification was performed by gradually polishing of the indentation surface and mechanical properties of both systems were measured. Indentation fracture toughness was calculated by various methods and R-curves were prepared. The main activated toughening mechanisms, responsible for the increased fracture toughness are crack deflection, crack branching and crack bridging in the forms of graphene sheet pull-out or graphene necking.

Abstract: The influence of high temperature exposure on the mechanical and wear properties of selected HVOF sprayed CrC and No/Co – based alloy coatings were tested. Comparison of as-sprayed and 600°C/116 h annealed coatings’ microhardness, cohesive strength, abrasive and adhesive wear resistance showed that the Co-based Stellite 6 coating’s wear properties were deteriorated by heat exlosure despite of the increase of its hardness and cohesive strength. The heat exposure was found to be beneficial for both mechanical and wear properties of NiCrBSi self-fluxing coating. On the contrary, mechanical properties of Cr₃C₂-NiCr coating slightly decreased, while its wear resistance slightly increased as a result of high temperature exposure.

Abstract: Pin-on-disc tribological tests were performed on Si3N4/SiC/graphite ceramic composites with 5N applied load, at room temperature in dry conditions. Tests were completed with microhardness tests (F=10N), indentation fracture toughness tests (F=100N), furthermore morphological analyses of the wear tracks by SEM. Based on SEM pictures of the wear traces the main damage mechanism could be identified as an abrasive wear. The purpose of the paper is to model the abrasive wear of the given composites. For this reason lateral crack chipping model suggested by Evans and Marshall for Si3N4 ceramics was used for the assessment of the worn volume of the abrasive wear process. The model has been applied with the aim of validating it

Abstract: Micro- and macro-hardness of the individual layers of an Al2O3 / Al2O3 + ZrO2 layered composite have been investigated. The indentation load size effect has been studied in a range of indentation load of 25 mN – 100 N using depth sensing indentation technique and conventional Vickers hardness testers. Fracture toughness values of the layers have been measured using indentation fracture method. The effect of residual stresses on the KIC value has been analyzed.

Abstract: The work is devoted to the evaluation of indentation fracture toughness in ceramic materials and to the comparison of these data with the results of this characterisation obtained by the application of fracture mechanics method (chevron notched beam specimen – CVNB). The indentation fracture toughness measurement is realized using the indentation load lying in the loading extent between 50-300 N. The evaluation of basic parameters of lateral crack initiation resulting in chipping formation in the vicinity of indent is performed. This measuring is based on the finding of relationship between the indent load level and the number of loading cycles leading to chips formation. The geometry of lateral cracks and chipping morphology are described. This evaluation is complemented with the analysis of chip fracture surfaces.