Effects of HfB2 and HfN Additions on the Microstructures and Mechanical Properties of TiB2-Based Ceramic Tool Materials
The effects of HfB2 and HfN additions on the microstructures and mechanical properties of TiB2-based ceramic tool materials were investigated. The results showed that the HfB2 additive not only can inhibit the TiB2 grain growth but can also change the morphology of some TiB2 grains from bigger polygons to smaller polygons or longer ovals that are advantageous for forming a relatively fine microstructure, and that the HfN additive had a tendency toward agglomeration. The improvement of flexural strength and Vickers hardness of the TiB2-HfB2 ceramics was due to the relatively fine microstructure; the decrease of fracture toughness was ascribed to the formation of a weaker grain boundary strength due to the brittle rim phase and the poor wettability between HfB2 and Ni. The decrease of the flexural strength and Vickers hardness of the TiB2-HfN ceramics was due to the increase of defects such as TiB2 coarse grains and HfN agglomeration; the enhancement of fracture toughness was mainly attributed to the decrease of the pore number and the increase of the rim phase and TiB2 coarse grains. The toughening mechanisms of TiB2-HfB2 ceramics mainly included crack bridging and transgranular fracture, while the toughening mechanisms of TiB2-HfN ceramics mainly included crack deflection, crack bridging, transgranular fracture, and the core-rim structure.
Microstructure and Mechanical Properties of TiB2-HfC Ceramic Tool Materials
AbstractEffects of different metallic additives and sintering parameters on microstructure and mechanical properties of TiB2-HfC ceramics were investigated. The results showed that the core-rim structure and HfC particle dispersion were discovered in these ceramics. Only Co as the metallic additive could more easily promote the formation of the strip-shaped TiB2 than the others; TiB2-HfC-Ni-Mo ceramic had more serious agglomeration of HfC particles than the others; for TiB2-HfC ceramic, using Ni-Co as the metallic additive could obtain better mechanical properties than using the others. In addition, with sintering temperature increasing from 1500°C to 1650°C, grains grew gradually and the core-rim structures became fewer and unobvious. Extending the holding time from 15 min to 60 min, grain size just had a slight increase, and the influence of holding time on mechanical properties was not significant. The increase of sintering temperature (1500–1650°C) could lead to more obvious grain growth and change of core-rim structure than the increase of holding time (15–60 min). The better sintering parameters for TiB2-HfC-Ni-Co ceramic were 1600°C and 30 min. Besides, better mechanical properties of TiB2-HfC-Ni-Co ceramic sintered at 1600°C with 30 min holding time were that Vickers hardness was 21.2 ± 0.3 GPa, flexural strength was 1169 ± 16 MPa, and fracture toughness was 6.7 ± 0.3 MPa m1/2. Meanwhile, its toughening mechanisms included core-rim structure, particle dispersion, crack deflection and crack bridging. The mixed intergranular/transgranular fracture could also improve fracture toughness.

The Categorical Stability of Gambling Motives Among Community-Recruited Gamblers: A Longitudinal Assessment
Over the past decade, several motivational models have been proposed to explain the role of motives in gambling disorder. In the model captured by the four-factor Gambling Motives Questionnaire Financial (GMQ-F), gamblers are described as being primarily motivated to gamble for ‘coping’, ‘enhancement’, ‘social’, and ‘financial’ reasons. Although this model has received significant empirical support; to date, research assessing the role of motives in gambling disorder has been primarily cross-sectional in nature. Thus, the extent to which gambling motives remain stable over time has yet to be explored. In the current study, the stability versus fluidity of self-assessed gambling motives was investigated using the Quinte Longitudinal Study, a longitudinal dataset of gambling behaviour collected over 5 years. Gambling motives of 2795 gamblers were examined over all five annual assessments. The total proportion of gamblers who stayed in the same primary motive category across each of the 5 consecutive assessments was 22%, indicating substantial fluidity in category membership. Substantial movement between categories was seen for each GMQ-F group, as well as an additional group of non-classified motives. Logistic regression analyses suggest that greater resistance to gambling fallacies significantly predicted stability between the baseline assessment and a follow-up 1 year later, but gambling severity did not. Potential limitations in the study design and opportunities for future research are discussed.