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.
Preparation and cutting performance of reactively hot pressed TiB2-SiC ceramic tool when machining Invar36 alloy
TiB2-10wt%SiC ceramic cutting tools were fabricated by the reactive hot pressing (RHP) technique. The mechanical properties and microstructure of the materials at room temperature were investigated. The flexural strength, fracture toughness, and hardness were 705 MPa, 6.6 MPa m1/2, and 22.5 GPa, respectively. The improved fracture toughness was ascribed to the mixed mode of intergranular fracture and transgranular fracture. The cutting performance including the tool life and surface roughness, as well as the failure mechanisms of the ceramic cutting tools when continuously wet-turning Invar36 alloy, was studied. Orthogonal test and range analysis were employed to determine the optimal cutting parameters. The optimal cutting speed, feed rate, and depth of cut were 140 m/min, 0.1 mm/rev, and 0.4 mm, respectively. The wear resistance of the TiB2-SiC ceramic cutting tool was better than that of the Al2O3-based ceramic cutting tool reinforced by TiC particles. The wear mechanisms were abrasive wear, diffusion wear, and oxidation wear. The tool life reliability when continuously wet-turning Invar36 alloy using the optimized cutting parameters was investigated. The distribution of the tool life obeyed the log-normal distribution, and the coefficient of variation was 0.085, indicating that the ceramic cutting tools had a high reliability. The study on the cutting performance and tool life reliability is useful for improving the machining efficiency, decreasing the rejection rate, and determining the tool replacement interval.
The costs of identifying undiagnosed prostate cancer in asymptomatic men in New Zealand general practice
Background. Screening for prostate cancer (PCa) using the prostate-specific antigen (PSA) test is widespread in New Zealand. 3 informed testing history in 2007–09 were NZ$8887 compared to NZ$13 870 if the men had PSA tests in 2007–09. If we assumed a PSA test involved a full 15-minute general practice consultation, the estimated costs increased to NZ$26 877 per PCa identified. Conclusions. Screening of asymptomatic men for PCa is widely practiced. Most of the costs of screening were incurred in general practice. Calls for men to receive increased information on the harms and benefits of screening will substantially increase the costs. The current costs could be reduced by better targeting of screening.