Method of making iron matrix composite

A method of making an iron matrix composite, comprising:

• weighing two parts of a Fe—Ni—P composite powder with a particle size of about 1 micrometer to about 2 micrometers and one part of a Fe—N powder with a particle size of about 100 nanometers to about 250 nanometers, wherein each part of the Fe—Ni—P composite powder is about 15% to about 20% by weight of the total amount of the powder, and wherein the Fe—N powder is about 60% to about 70% by weight of the total amount of the powder;
• placing one of the two parts of the Fe—Ni—P composite powder, the one part of the Fe—N powder, and the other one of the two parts of the Fe—Ni—P composite powder in a graphite mold (2) in sequence to be subjected to a pre-press forming process under an axial pressure of 20 MPa, so as to form a composite cylinder with two ends formed by the Fe—Ni—P composite powder and a middle section therebetween formed by the Fe—N powder;
• and
• placing the preformed cylinder along with the mold (2) in a spark plasma sintering furnace to be sintered in a vacuum environment, wherein the sintering process produces a Fe—Ni—P alloy having a metastable gamma-phase structure, i.e., a face-centered cubic structure;
• and
• wherein the axial pressure is applied from two opposing directions, and wherein an upper pressing head (1) has an advance length of about 2 centimeters to about 3 centimeters inside the mold, and a lower pressing head (6) has an advance length of about one centimeter thereinside, and wherein during the sintering process, the upper and lower pressing heads (1, 6) positioned at either end of the mold (2) move toward each other in an axial direction until stop shoulders on the upper and lower pressing heads (1, 6) abut end surfaces of the two ends of the mold (2), such that a space of about 6.28 cubic centimeters to about 9.42 cubic centimeters is left in a cavity of the mold (2) for free sintering and final forming of the powder and the resulting composite has an intermediate layer with a porosity of about 14% to about 39%.