JP2013023707A - Mixed powder for powder metallurgy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide Cu-Sn-Ni based raw material powder for powder metallurgy which uniformizes the structure of a sintered compact and can obtain a green compact having high compacting property and a sintered compact having high strength as raw material powder dealing with higher strength and downsizing and more complicated shaping in sintered parts used for a Cu based bearing, sliding parts or the like.SOLUTION: The powdery mixture for powder metallurgy includes, by weight, 3 to 12% Sn, 5 to 15% Ni and 0.05 to 1.0% P, and the balance Cu with inevitable impurities.

Description

  The present invention relates to a Cu-Sn-Ni-based high-strength material utilizing spinodal decomposition, and relates to a powder for sintering a sliding member.

  Many of the copper-based sintered parts produced by blending copper powder or copper alloy powder are used as oil-impregnated bearings, sliding materials, brushes, and the like. However, in recent years, demands for properties such as higher strength, corrosion resistance, and wear resistance have increased, and new material development has been required. One way to increase the strength of copper-based alloys is to use spinodal decomposition, which is in practical use in the casting field. Spinodal decomposition generally does not require nucleation, and the concentration fluctuations continuously increase, so the decomposition product phases maintain perfect consistency with each other. Shows a significant concentration fluctuation.

  For this reason, an alloy having such a structure exhibits extremely high strength. Cu-Si-Ni and Cu-Sn-Ni systems are known as alloy systems that cause spinodal decomposition, but Si-containing alloy systems are a factor that inhibits sintering in a hydrogen reducing atmosphere. It has not been put to practical use in the field of powder metallurgy. On the other hand, Cu-Sn-Ni system is easy to sinter and subsequent aging treatment, and is expected to be put to practical use.

  Generally, an alloy powder for sintering is manufactured by a water atomization method in which an irregularly shaped powder is obtained. However, even if the Cu—Sn—Ni-based alloy powder is produced by the water atomization method, since the high melting point Ni is contained, the surface tension of the molten metal is large and it is difficult to form an irregular shape. Moreover, since Ni is contained, there exists a problem that it is inferior to a moldability because the powder itself is hard compared with the bronze type powder generally used.

  For example, Patent Document 1 proposes a Cu—Sn—Ni alloy powder having excellent formability manufactured by devising water atomization conditions. However, with sintered parts, there is an increasing demand for miniaturization and thinning of products, and it still cannot be said that it has sufficient formability.

  On the other hand, in the case of mixed powder, high formability can be imparted by using, for example, electrolytic Cu powder or heat-treated granulated powder having excellent formability as part of the constituent powder. However, in this alloy, since the diffusion rate of the Sn and Ni alloy components into the substrate is slow, long time sintering or high temperature sintering is required to obtain a uniform structure. Further, when the sintered structure becomes non-uniform, it becomes a cause of insufficient strength or variation of the sintered body (Patent Document 2).

Japanese Patent Application No. 2010-245901 JP 11-256206 A

  It is an object of the present invention to provide a Cu—Sn—Ni-based raw material powder for powder metallurgy that provides a green compact with high moldability and provides a stable high strength.

  The Cu-Sn-Ni mixed powder has a low diffusion rate of Sn and Ni alloy components into the substrate, and it is difficult to obtain a uniform sintered body structure. However, in the present invention, it has been found that a sintered body having a uniform structure can be easily obtained by mixing P in the form of Cu-P alloy powder with the above alloy-based mixed powder. The reason for this is not fully clarified, but it is generally considered as follows.

  That is, the Cu-P alloy powder having the composition range used in the present invention generates a liquid phase by heating to 714 ° C. or higher. This liquid phase is a Cu powder and a Cu—Ni alloy powder constituting the mixed powder of the present invention. And wettability is very good. In addition, Ni is likely to diffuse and dissolve in the Cu-P liquid phase. Therefore, it is assumed that the addition of Cu-P alloy powder promotes the diffusion of Ni and Sn through the liquid phase of Cu-P alloy during sintering, and a sintered body with a uniform structure can be obtained. Is done. Incidentally, a Cu-P alloy liquid phase can be obtained even if P is added in the form of a simple substance such as red phosphorus. However, since the chemical potential of P is too high, the consumption of P becomes severe, which is not preferable.

  The mixed powder of the present invention is Sn: 3-12% by weight, Ni: 5-15% by weight, P: 0.05-1.0% by weight with the balance being Cu and inevitable impurities, and the sintered body made from the powder of the present invention is By performing an aging treatment, spinodal decomposition is caused, and a high-strength tissue can be easily obtained. Spinodal decomposition is a phase separation involving fine concentration fluctuations in an alloy of a supersaturated solid solution that has been rapidly cooled from a homogeneous solid solution region to a two-phase region. It is possible to obtain high strength in the initial to intermediate stage where the phases are separated and the consistency with the parent phase is maintained.

In order to obtain a sintered part having high strength due to the above phenomenon, it is necessary to contain at least Sn of 3% by weight or more and Ni of 5% by weight or more. However, even if Sn is contained in an amount of more than 12% by weight and Ni is contained in an amount of more than 15% by weight, a hard and brittle compound phase (eg, Ni ₃ Sn) is formed. (Strength) cannot be obtained sufficiently, so the optimum content of Sn was limited to 3 to 12% by weight, and Ni was limited to 5 to 15% by weight. In particular, Ni in the mixed powder has a slow diffusion rate into the substrate and is easily segregated in the sintered body. P forms an alloy phase with other components of the mixed powder, Cu and Ni, at a low melting point, generates a liquid phase with good wettability to the powder particles during the sintering process, and promotes sintering, as well as a Ni substrate Encourage diffusion into the inside. In order to obtain the effect of promoting sintering by adding P, at least 0.05% by weight or more is required. However, if it exceeds 1.0% by weight, the compound phase with Ni and Sn formed at the grain boundary increases, and the strength of the sintered body is reduced. Therefore, the P content is limited to 0.05 to 1.0% by weight.

Although there is no restriction | limiting in particular in Cu powder used for the mixed powder of this invention, Generally it is preferable to use the electrolytic Cu powder or heat-processed granulated powder which is excellent in a moldability. These powders are soft and irregular in shape, and have high moldability. In order to maintain high formability in the mixed powder, it is necessary to blend these Cu powders in an amount of at least 20% by weight, preferably 50% by weight.
Sn in the mixed powder of the present invention is added in the form of a simple powder and a Cu-Sn alloy powder. However, when the amount of Cu powder blended for the purpose of maintaining formability is reduced, such as when the Sn content in the alloy powder is small, the addition of a simple substance is preferable.

Ni in the mixed powder of the present invention is added in the form of Cu-Ni alloy powder produced by an atomizing method. Ni has a particularly slow diffusion rate into the substrate and tends to cause concentration segregation in the sintered body. Further, Ni powders, particularly carbonyl nickel powders that are generally used, are feared to be harmful to the human body, so it is preferable to add them in the form of alloy powders that keep the chemical potential of Ni low.
The Ni content of the Cu—Ni alloy powder is preferably 20 to 50% by weight, more preferably 20 to 35% by weight. If the Ni content is less than 20% by weight, the amount of Cu—Ni alloy powder added is increased, and the amount of Cu powder added for the purpose of improving formability is reduced, which is not preferable.
Further, if the Ni content is more than 50% by weight, it is not preferable because concentration segregation of Ni in the sintered body tends to occur.

P in the mixed powder of the present invention is added in the form of Cu-P alloy powder produced by the atomizing method. The P content in the Cu-P alloy powder is preferably 6 to 14% by weight, more preferably 8 to 10% by weight. When the P content is less than 6% by weight, the amount of Cu-P alloy powder added is increased, and the amount of copper powder added for the purpose of improving formability is decreased, which is not preferable.
In the present invention, `` inevitable impurities '' means impurities that are inevitably mixed in the manufacturing process of each raw material, although not intentionally added, and the sum of these is usually 0.1% by weight or less. is there.

  The present invention improves the non-uniformity of the sintered body structure, which has been a problem of Cu-Sn-Ni mixed powders that can obtain high formability, by adding P to the raw material powder, and compacted powder with high formability We have developed a raw material powder that can produce sintered parts with excellent body and strength.

Cross-sectional structure of the sintered body of Example 2 Cross-sectional structure of the sintered body of Comparative Example 3

Hereinafter, the powder of the present invention will be described in more detail based on examples. The compressive strength of the green compact is 0.5% by weight of wax-based lubricant mixed in the powder, press-molded into a 30 × 12 × 6mm cuboid so that the green compact density is 6.6g / cm ^3, and ISO 3995 standard It was determined according to the measurement method. The crushing strength was determined according to the measurement method of JIS Z 2507 standard.

Examples 1-3, Comparative Examples 1-3 are electrolytic Cu powder as raw material powder, Cu-Sn alloy powder produced by gas atomization method, Cu-P alloy powder, Sn powder produced by water atomization method, Cu-Ni powder Prepared and blended so as to have the composition shown in Table 1. Add 0.3% by weight of a wax lubricant as a mold lubricant to these powders, mix with a rocking mixer, and then a bearing with a density of 6.60 ± 0.05Mg / m ³ Molded into a green compact.
Comparative Example 4 was produced by the water atomization method so as to have the composition shown in Table 1.
As sintering conditions, the samples of Examples 1 to 3 and Comparative Examples 1 to 4 were sintered at 860 ° C. under a condition of holding 1.2 ks in an atmosphere of 10 vol% hydrogen and 90 vol% nitrogen. After sintering, it was cooled to 300 ° C. within 260 s to obtain a sintered body. This was followed by an aging treatment for 3.6ks held under 350 ° C. These sintered body further N ₂ atmosphere.

  Examples 1 to 3, which are the present invention, contain 3 to 12% by weight of Sn, 5 to 15% by weight of Ni, 0.05 to 1.0% by weight of P, and Cu powder, Sn powder, Cu-Sn alloy powder, It is a mixed powder consisting of Cu-Ni alloy powder and Cu-P alloy powder, and the die strength of those green compacts is very high formability of 20MPa or more, and sintered body after aging treatment Then, a high crushing strength of 400 MPa or more can be obtained.

  On the other hand, in Comparative Example 1, since the amount of P added is as small as 0.01% by weight and sintering does not proceed, and the contents of Sn and Ni are also as small as 1% by weight, respectively, the sintered body is sufficient even after aging treatment A strong crushing strength cannot be obtained. In Comparative Example 2, Sn is 15% by weight, Ni is 18% by weight, P is 1.1% by weight, and a large amount of hard and brittle Ni-Sn-P compound phase is precipitated at the grain boundaries inside the sintered body. The strength decreased. Comparative Example 3 has the same Sn and Ni contents as Example 2, but does not contain P and has a crushing strength lower than that of Example 2. It can be seen that the cross-sectional structure of the sintered body of Comparative Example 3 shown in FIG. 2 is not uniform compared to the cross-sectional structure of the sintered body of Example 2 shown in FIG. It can be seen that Sn and Ni in the powder of the present invention are promoted to diffuse in the matrix by adding P, and the sintered body structure is made uniform. Comparative Example 4 is an atomized powder, and a high crushing strength is obtained, but the bending strength is lower than in Examples 1 to 3.

The mixed powder for sintering of the present invention can produce a sintered body having a uniform structure by adding P to Cu, Sn, and Ni, and can have high strength by aging treatment. Furthermore, because it is possible to produce green compacts with excellent moldability, it is possible to produce sintered parts with small and thin-walled parts, which may also be applied to the field of powder metallurgy that could not be applied before. There is.

Claims (1)

  Cu-Sn-Ni-based mixed powder used for powder metallurgy, the mixed powder contains 3 to 12% Sn, 5 to 15% Ni, 0.05 to 1.0% P in weight ratio The remaining powder is made of Cu and inevitable impurities, and the mixed powder is composed of Cu powder, Sn powder, Cu-Sn alloy powder, Cu-Ni alloy powder, and Cu-P alloy powder. Mixed powder for metallurgy.