Effect of annealing on the structure and properties of hot-pressed boron carbide base cermets
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During the annealing of a hot-pressed boron carbide-aluminum materials at a temperature exceeding the melting point of aluminum intense formation ofα-AlB12 takes place. This has a deleterious effect on the strength properties (transverse rupture strengthσtr, fracture toughness kIc, and impact strengtha) of the material and increases its hardness and electrical resistivity. It follows therefore that, to obtain boron car-bide-aluminum materials of maximum strength, it is necessary to perform their liquid-phase pressing under high pressures (above 0.5 GPa) and dispense with subsequent annealing. Annealing at a temperature below the melting point of aluminum brings about only very small changes in the structure of the material, and the resultant fall in hardness is less than the increase in hardness. Consequently, when it is necessary to increase the hardness of the material and a slight loss of strength is acceptable, recourse may be had to low-temperature annealing (below 660°C).
KeywordsCarbide Boron Melting Point Fracture Toughness Electrical Resistivity
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