Duplex eutectic silicon alloy, manufacturing method thereof, and manufacturing method of sintered compact using silicon alloy powder
A duplex eutectic silicon alloy including 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, and 1-40 weight % oxygen has a eutectic structure comprising a β′-sialon phase and an ο′-sialon phase. The alloy is produced by controlling cooling at a rate of 50° C. or less per minute in combustion synthesis. A ductile sintered product capable of replacing steel in various applications can be produced by placing a compact composed of a powder of the alloy in a sintering furnace which can supply a heat quantity at least ten times the heat capacity of the compact; and sintering the compact at a pressure at least as great as atmospheric pressure, within a nitrogen atmosphere in which the silicon gas mole fraction is 10% or more, and at a temperature within the range from 1400° C. to 1700° C.
1. A duplex eutectic silicon alloy including 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, 1-40 weight % oxygen, and elemental boron in an amount up to 1 weight %, sufficient to produce a measurable improvement in the ductile fracture surface rate of the alloy, characterized by a eutectic structure comprising a β′-sialon phase and an ο′-sialon phase.
2. A duplex eutectic silicon alloy according to claim 1 , in which the eutectic structure occupies an area ratio of at least 60%.
3. A duplex eutectic silicon alloy according to claim 1 , in which the eutectic structure occupies an area ratio of at least 40%.
4. A duplex eutectic silicon alloy according to claim 1 , in which said elemental boron is present in an amount in the range from 0.1 weight % to 1 weight %.
5. A method for manufacturing a sintered compact of a duplex eutectic silicon alloy characterized by:
shaping a compact using as a raw material a duplex eutectic silicon alloy powder which includes 30-70 weight % silicon, 10-45 weight % nitrogen, 1-40 weight % aluminum, 1-40 weight % oxygen, and elemental boron in an amount up to 1 weight %, said amount being sufficient to produce a measurable improvement in the ductile fracture surface rate of the alloy, and characterized by a eutectic structure comprising a β′- sialon phase and an ο′-sialon phase is obtained;
retaining the compact in a sintering furnace which can supply a heat quantity at least ten times the heat capacity of the compact; and
sintering said compact at a pressure at least as great as atmospheric pressure, within a nitrogen atmosphere that includes a silicon gas mole fraction of 10% or more, and at a temperature within the range from 1400° C. to 1700° C.
6. A method for manufacturing a sintered compact according to claim 5 , in which the eutectic structure occupies an area ratio of at least 60%.
7. A method for manufacturing a sintered compact according to claim 5 , in which the eutectic structure occupies an area ratio of at least 40%.