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The effect of addition of submicrometer-sized B 4 C (5,10 and 15 wt%) on microstructure, phase composition, hardness, fracture toughness, scratch resistance, wear resistance, and thermal behavior of hot-pressed ZrB 2 -B 4 C composites is reported. ZrB 2 -B 4 C (10 wt%) composite has V H1 of 20.81 GPa and fracture toughness of 3.93 at 1 kgf, scratch resistance coefficient of 0.40, wear resistance coefficient of 0.01, and ware rate of 0.49 9 10 À3 mm 3 /Nm at 10N. Crack deflection by homogeneously dispersed submicrometer-sized B 4 C in ZrB 2 matrix can improve the mechanical and tribological properties. Thermal conductivity of ZrB 2 -B 4 C composites varied from 70.13 to 45.30 W/m K between 100°C and 1000°C which is encouraging for making ultra-high temperature ceramics (UHTC) component.

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ZrB 2 -SiC composites were prepared by hot pressing with different sources of SiC to study the effect of SiC with different morphology on densification, microstructure, phase composition and mechanical properties like hardness, fracture toughness and tribological properties (namely, scratch resistance, wear parameters) and thermal behaviour of the composites. Three different ZrB 2 -SiC composites, i.e. ZrB 2 -SiC P (polycarbosilane derived SiC), ZrB 2 -SiC C (SiC from CUMI, India) and ZrB 2 -SiC H (SiC from H. C. Starck, Germany), were studied. It is found that ZrB 2 -SiC C composite shows highest hardness (19?13 GPa) and fracture toughness (5?30 MPa m 1/2 at 1 kgf load) in comparison with other composites. Interconnected network, better contiguity between grains of ZrB 2 -SiC composites and impurity content in starting powders can play significant roles for achieving high mechanical, tribological and thermal properties of the composites. Coefficient of friction and wear parameters of all ZrB 2 -SiC composites are very low, and thermal conductivity of ZrB 2 -SiC composites varied from 52?71 to 65?53 W (m K) 21 (ZrB 2 -SiC P ), 54?30 to 71?55 W (m K) 21 (ZrB 2 -SiC C ) and 64?25 to 88?02 W (m K) 21 (ZrB 2 -SiC H ), respectively and also calculate the interfacial resistance of all the composites.

SiC–TiB2 (10 wt. %) and SiC–TiB2 (10 wt. %)–TaC (5 wt. %) composites are consolidated using spark plasma sintering (SPS) technique at different sintering temperatures (2000 °C and 2100 °C) for 15 min soaking time under 35 MPa pressure. The effects of sintering temperature on densification and mechanical properties of composites have been investigated in detail. SiC–TiB2 and SiC–TiB2–TaC composites sintered at 2100 °C showed high Vickers hardness value, i.e., 27.20 ± 1.23 GPa and 26.40 ± 0.80 GPa, respectively, under 1 kgf (9.81 N) load. Poor fracture toughness {2.28 MPa(m)1/2 at 1 kgf (9.81 N) load} of monolithic silicon carbide (SiC) sintered at 2100 °C is improved with addition of titanium diboride (TiB2) and tantalum carbide (TaC) as secondary phases. Scratch resistance of SiC–TiB2 and SiC–TiB2–TaC composites show coefficient of friction value below 0.40 and 0.50 under 5 N and 10 N loads, respectively. SiC–TiB2 and SiC–TiB2–TaC composites show constant thermal conductivity response above 810 °C and 603 °C in the range of 48.70–47.15 W/m K and 60.35–60.41 W/m K, respectively.

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Background: Atherosclerotic coronary artery disease is rare in young adults aged 40 years or less. However, South Asia is among the top 3 of the countries with highest proportion of cases of first acute coronary syndrome events occurring at age 40 years or less. This study was to explore the extent and pattern of angiographic coronary artery disease among patients of ischemic heart disease aged 40 years or less. Methods: This cross-sectional retrospective descriptive study included 140 patients who had coronary angiography for ischemic heart disease at the Department of Cardiology of Enam Medical College between July 2012 and December 2020. Coronary angiography was analyzed with particular attention to the extent of involvement of major epicardial coronary arteries including significant branch involvement. Results: Of the 140 patients included in the study - aged 18-40 years (mean 35.90 and SD 4.05) and 59.28% in the 36-40 years age group – 85% were male. Coronary angiogram revealed Single Vessel Disease in 39.29%, Double Vessel Disease in 25.72%, Triple Vessel disease in 23.57%, normal Coronaries in 9.28%. Left Anterior descending territory was most involved - 94 (67.14%) patients having significant stenosis in the main trunk and/or one or more major branches. Overall, 23(16.43%) of the whole cohort of patients had multiple branch involvements in the three coronary artery territories. Conclusion: In patients aged up to 40 years with ischemic heart disease, significant coronary artery disease burden was seen, including a significant proportion with multi-vessel disease and a high level of branch involvement in all the principal epicardial coronary territories. This indicates a high burden of disease in a relatively young age group, with significant implications for long term management over and beyond reperfusion/revascularization efforts. Cardiovasc j 2022; 14(2): 103-110