The influence of the joining pressure and surface roughness on the flexural strength of boron carbide (B_4C) joined by an Al sheet was investigated. The joining surface of B_4C was ground or polished to a surface roughness ranging from 0.1 to 6.1 μm. B_4C was joined by Al under a pressure of 0.5-12 kPa or stabilized with a carbon jig at 1000 °C for 2 h in vacuum (10~(-1)-10~(-4) Pa). The fracture surfaces were observed by an optical microscope and the microstructures in the B4C joining layer were observed by scanning electron microscopy. The flexural strength of B_4C joined at 12 kPa and stabilized with a carbon jig was similar to that of the B4C base material. However, the flexural strength of B_4C joined at less than 6 kPa was lower than that of the B_4C base material because of the presence of voids in the joining interlayer. When the surface roughness was 6.1 μm, the flexural strength was slightly lower than that of the B_4C base material. However, when the joining surface roughness ranged from 0.1 to 1.7 μm, the flexural strength of joined B4C was similar to that of the B4C base material. boron carbide, joining, aluminum, pressure, surface roughness
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