Processing and properties of PcBN composites fabricated by HPHT using PSN and Al as sintering additive

Dense polycrystalline cubic boron nitride(PcBN)composites were fabricated by high-pressure and high-temperature(HPHT)sintering using polysilazane(PSN)and Al as sintering additive.After high-energy ball milling,the cBN fine particles were uniformly coated with PSN by ultrasonic treatment.After thermocuring and pyrolysis,the cBN–SiCN particles were mixed with Al The PcBN composites were prepared after sintering a1450°C for 10 min with a pressure of 5 GPa.The refining effect of high-energy ball milling on the c BN particles was studied by scanning electron microscopy(SEM)and laser particle size analyzer.The oxidation of the cBN particles after milling was investigated by nitrogen–oxygen analyzer.The phase composition and microstructure of the sintered PcBN composites were investigated by X-ray diffractometer(XRD)and SEM.The main phases of the sintered PcBN composites are c BN,AlN,SiC and Si3N4The conversion of cBN to hBN was inhibited by the formation of AlN.The mechanical properties of the sintered PcBN composites were improved by the appearance of SiC and Si3N4.The density and mechanical properties of the PcBN composites both increased with the content of the cBN particles increasing.The sintered sample with 60 wt%cBN,30 wt%PSN and 10 wt%Al showed the best results density of 99.7%,Vickers’hardness of(25.2±0.8)GPa and flexural strength of(602±15)MPa.

Abnormal spontaneous brain activity in patients with non-arteritic anterior ischemic optic neuropathy detected using functional magnetic resonance imaging

To the Editor: Non-arteritic anterior ischemic optic neuropathy (NAION), characterized by a sudden onset of unilateral painless visual loss and a swollen optic disc, is the most common form of acute optic neuropathy in patients over 50 years of age.[1] The pathogenesis of NAION remains unclear, but most histopathological studies support the concept of vasculopathic occlusion in the region of the short posterior ciliary arteries.[2] Functional magnetic resonance imaging (fMRI) is one of the most widely used non-invasive techniques for measuring brain function over time in vivo. To the best of our knowledge, only one study has investigated the effects of stimulating the affected eye in the extra-visual areas in NAION in humans.[3]However, this previous study only examined task-state fMRI, and lacked a measure of resting-state fMRI (rs-fMRI). Thus, it remains unclear whether regional spontaneous brain changes are limited to the visual system.