METHOD OF MAKING IRON MATRIX COMPOSITE

Abstract

The disclosure provides a method of making an iron matrix composite. A FeNiP composite powder having a particle size of one to two micrometers and a FeN powder having a particle size of 100 to 250 nanometers are used as the raw material. The size and axial displacement of pressing heads of a graphite mold are controlled to realize the control of the porosity of porous iron. The composite produced comprises two surface layers of a FeNiP alloy and an intermediate layer of porous iron having a porosity of 14 to 39%. The method enables a reduced weight of the FeNiP alloy and enables shock absorption and damping properties to be imparted to the composite. In addition, an optional subsequent deep cryogenic treatment allows the FeNiP alloy to be subjected to phase transition from a metastable gamma-phase to an alpha-phase, thereby substantially improving the hardness and strength thereof.

Claims

1. A method of making an iron matrix composite, comprising: weighing two parts of a FeNiP composite powder with a particle size of about 1 micrometer to about 2 micrometers and one part of a FeN powder with a particle size of about 100 nanometers to about 250 nanometers, wherein each part of the FeNiP composite powder is about 15% to about 20% by weight of the total amount of the powder, and wherein the FeN powder is about 60% to about 70% by weight of the total amount of the powder; placing one of the two parts of the FeNiP composite powder, the one part of the FeN powder, and the other one of the two parts of the FeNiP 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 FeNiP composite powder and a middle section therebetween formed by the FeN 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 FeNiP 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%.

2. (canceled)

3. The method of claim 1, wherein the graphite mold (2) is in the form of a hollow cylinder.

4. The method of claim 1, wherein each of the upper and lower pressing heads (1, 6) is T-shaped and in the form of a cylinder with a stop shoulder.

5. The method of claim 1, wherein the FeNiP composite powder used has a particle size of about 1 micrometer to about 2 micrometers, and has Ni and P contents of about 28% to about 30% and about 1.5% to about 2% by weight, respectively; and wherein the FeN powder used has an N content of about 8% to about 10% by weight.

6. (canceled)

7. The method of claim 1, wherein the sintering process is performed through heating the furnace up to a temperature of about 800 C. to about 875 C. at a temperature rising rate of about 100 C./min to about 200 C./min and holding at that temperature for about 1 minute to about 5 minutes.

8. The method of claim 1, wherein the composite comprises an intermediate layer of porous iron, which has an average pore size of around one micrometer and provides shock absorbing and damping properties, and wherein a FeNiP alloy is disposed on either side of the intermediate layer and has high Ni and P contents.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a flow chart of a method of one embodiment of the invention;

[0022] FIG. 2 shows a macroscopic topography of a composite comprising two surface layers of a FeNiP alloy and an intermediate layer of porous iron therebetween, produced according to the disclosed method, and a microscopic topography of a composite interface, as well as a compression stress-strain curve; and

[0023] FIG. 3 is a schematic illustrating formation of the porous iron layer having a controllable porosity.

DETAILED DESCRIPTION

Example 1

[0024] With reference to FIG. 3-a, two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 9 g, wherein the powder had an average particle size of one micrometer and had Ni and P contents of 28% and 1.5% by weight, respectively. 27 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 100 nanometers and had N content of 8% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 20%*2 and 60% of their total amount, respectively. 9 g of the FeNiP composite powder 5, 27 g of the FeN powder 4, and 9 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 3 centimeters, respectively, to perform a pre-press forming process so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 875 C. at a rate of 100 C./min and was held at that temperature for 5 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. The resulting sample had an intermediate layer 8 of porous iron with a porosity of about 14% and a hardness of 170 HV0.1, and two surface layers 7, 9 of a FeNiP alloy with a porosity of close to 0% and a hardness of 250 HV0.1.

Example 2

[0025] Two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 8.68 g, wherein the powder had an average particle size of 1.17 micrometers and had Ni and P contents of 28.33% and 1.57% by weight, respectively. 27.9 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 125 nanometers and had N content of 8.33% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 19.16%*2 and 61.68% of their total amount, respectively. 8.68 g of the FeNiP composite powder 5, 27.9 g of the FeN powder 4, and 8.68 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2.83 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then furnace chamber was vacuumized. The furnace was heated to 862.5 C. at a rate of 117 C./min and was held at that temperature for 4.34 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. The resulting sample had an intermediate layer 8 of porous iron with a porosity of about 18%, and two surface layers 7, 9 of a FeNiP alloy with a porosity of close to 0%.

Example 3

[0026] Two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 8.2 g, wherein the powder had an average particle size of 1.34 micrometers and had Ni and P contents of 28.66% and 1.64% by weight, respectively. 28.3 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 150 nanometers and had N content of 8.66% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 18.33%*2 and 63.34% of their total amount, respectively. 8.2 g of the FeNiP composite powder 5, 28.3 g of the FeN powder 4, and 8.2 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2.66 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 850 C. at a rate of 134 C./min and was held at that temperature for 3.67 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. The resulting sample had an intermediate layer 10 of porous iron with a porosity of about 20%, and two surface layers 7, 9 of a FeNiP alloy with a porosity of about 10%.

Example 4

[0027] With reference to FIG. 3-b, two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 8.75 g, wherein the powder had an average particle size of 1.51 micrometers and had Ni and P contents of 29% and 1.71% by weight, respectively. 32.5 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 175 nanometers and had N content of 9% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 17.5%*2 and 65% of their total amount, respectively. 8.75 g of the FeNiP composite powder 5, 32.5 g of the FeN powder 4, and 8.75 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2.5 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 837.5 C. at a rate of 150 C./min and was held at that temperature for 3 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. The resulting sample had an intermediate layer 10 of porous iron with a porosity of about 23%, and two surface layers 7, 9 of a FeNiP alloy with a porosity of about 10%.

Example 5

[0028] Two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 8.55 g, wherein the powder had an average particle size of 1.68 micrometers and had Ni and P contents of 29.33% and 1.78% by weight, respectively. 34.2 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 200 nanometers and had N content of 9.33% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 16.66%*2 and 66.68% of their total amount, respectively. 8.55 g of the FeNiP composite powder 5, 34.2 g of the FeN powder 4, and 8.55 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2.33 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 825 C. at a rate of 167 C./min and was held at that temperature for 2.34 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. The resulting sample had an intermediate layer 10 of porous iron with a porosity of about 27%, and two surface layers 7, 9 of a FeNiP alloy with a porosity of about 10%.

Example 6

[0029] Two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 8 g, wherein the powder had an average particle size of 1.85 micrometers and had Ni and P contents of 29.66% and 1.85% by weight, respectively. 34.17 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 225 nanometers and had N content of 9.66% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 15.83%*2 and 68.34% of their total amount, respectively. 8 g of the FeNiP composite powder 5, 34.17 g of the FeN powder 4, and 8 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2.16 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 812.5 C. at a rate of 184 C./min and was held at that temperature for 1.67 minutes. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. Thereafter, an appropriate amount of liquid nitrogen was taken and its temperature was adjusted to minus 50 C. (50 C.) with ethyl alcohol. The sample was put into the liquid nitrogen at 50 C. for 15 minutes, and was then removed therefrom to be allowed to return to room temperature. During this, the sample was subjected to a phase transition from -[Fe, Ni] to -[Fe, Ni]. The resulting sample had an intermediate layer 11 of porous iron with a porosity of about 35% and two dense surface layers 7, 9 of a FeNiP alloy with a porosity of about 10%, and had been reinforced through deep cryogenic treatment. Upon examination, no crack was found in the sample subjected to the deep cryogenic treatment. It was also found that about 90% of the -[Fe, Ni] had been transformed to the -[Fe, Ni] and the hardness of the surface layers had been increased to 370 HV0.1 from 250 HV0.1.

Example 7

[0030] With reference to FIG. 3-c, two parts of a FeNiP composite powder 3, 5 were weighed and each part weighed 7.5 g, wherein the powder had an average particle size of 2 micrometers and had Ni and P contents of 30% and 2% by weight, respectively. 35 g of a FeN powder 4 was weighed, wherein the FeN powder 4 had an average particle size of 250 nanometers and had N content of 10% by weight. That is, the amounts of the FeNiP composite powder 3, 5 and the FeN powder 4 were 15%*2 and 70% of their total amount, respectively. 7.5 g of the FeNiP composite powder 5, 35 g of the FeN powder 4, and 7.5 g of the FeNiP composite powder 3 were placed in sequence in a graphite mold 2 with a diameter of 2 centimeters and a height of 6 centimeters. Lower and upper pressing heads 6, 1 were advanced by a distance of 1 centimeter and 2 centimeters, respectively, to perform a pre-press forming process under an axial pressure of 20 MPa so as to attain adequate contact between the powder particles. The powder along with the mold 2 was then placed in a furnace cavity to be sintered by using a spark plasma sintering (SPS) technique. An axial pressure of 20 MPa was applied to the powder inside the mold to fix it and then the furnace chamber was vacuumized. The furnace was heated to 800 C. at a rate of 200 C./min and was held at that temperature for 1 minute. During this, the upper and lower pressing heads 1, 6 gradually moved toward each other with the proceeding of densifying the powder until inner sides of stop shoulders on the pressing heads 1, 6 abutted end surfaces of the mold. Thereafter, the powder was not subjected to the 20 MPa fixed pressure any more, but rather was subjected to free sintering and final forming in a fixed space. After the hold period, the heating was stopped, and the sintered powder was cooled to room temperature in a vacuum environment with circulating water along with the furnace. Then, the sample was removed from the furnace, and the graphite remaining thereon was removed to produce smooth surfaces. Thereafter, an appropriate amount of liquid nitrogen was taken and its temperature was adjusted to minus 20 C. (20 C.) with ethyl alcohol. The sample was put into the liquid nitrogen at 20 C. for 15 minutes, and was then removed therefrom to be allowed to return to room temperature. During this, the sample was subjected to a phase transition from -[Fe, Ni] to -[Fe, Ni]. The resulting sample had an intermediate layer 11 of porous iron with a porosity of about 39% and two dense surface layers 7, 9 of a FeNiP alloy with a porosity of about 10%, and had been reinforced through deep cryogenic treatment. Upon examination, no crack was found in the sample subjected to the deep cryogenic treatment. It was also found that about 30% of the -[Fe, Ni] had been transformed to the -[Fe, Ni] and the hardness of the surface layers had been increased to 310 HV0.1 from 250 HV0.1.

REFERENCE NUMERAL LIST

[0031] 1 Upper pressing head [0032] 2 Graphite mold [0033] 3 FeNiP composite powder [0034] 4 FeN powder [0035] 5 FeNiP composite powder [0036] 6 Lower pressing head [0037] 7 FeNiP alloy [0038] 8 Porous iron (with a low porosity) [0039] 9 FeNiP alloy [0040] 10 Porous iron (with a medium porosity) [0041] 11 Porous iron (with a high porosity)