JPH0573826A - Magnetic core and production thereof - Google Patents

Abstract

PURPOSE:To provide the magnetic core which has an oxide film possessing good wear resistance and excellent adhesion. CONSTITUTION:The magnetic core 1 is constituted by forming a substrate oxide layer 2 consisting of NiO and FeO, an intermediate oxide layer 3 consisting of F3O4 and a surface oxide layer 4 of Fe2O3 on the surface of a core consisting of a magnetic alloy of an Fe-Ni system. The properties relating to the wear resistance and the adhesion of the oxide films which are heretofore inferior to the conventional cores consisting of the magnetic alloy of the Fe-Ni system are improved according to the magnetic core of this invention and the magnetic core more excellent as the magnetic head core required to deal with the increasingly high coercive force of magnetic recording media is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides improved wear resistance and adhesion by defining the structure of an oxide film of a core made of a Fe--Ni magnetic alloy and the conditions of oxidation treatment when forming the oxide film. Provide a magnetic core having a good oxide film.

[0002]

2. Description of the Related Art Permalloy as a core material of a magnetic head,
Magnetic materials such as sendust, ferrite, and amorphous are used. Among these, permalloy (Fe-Ni
Magnetic alloys) have good magnetic properties, but have the disadvantage of poor wear resistance. Therefore, as one means for improving the wear resistance of the core made of a Fe-Ni-based magnetic alloy, it is heat-treated in oxygen or in the air or in steam to form an oxide film on the surface of the core. Has improved wear resistance.

Further, as one means for improving the wear resistance of a core made of a Fe--Ni magnetic alloy, heat treatment is carried out in oxygen, air or steam to form an oxide film on the surface of the core. Therefore, wear resistance is improved.

However, this oxidation treatment does not have the effect of abrasion resistance depending on the conditions, and the peeling of the oxide film also occurs, which becomes a problem in the performance and quality of the magnetic core and in manufacturing.

The permalloy is a Fe-Ni type alloy, contains 75 to 85 wt% of Ni and 10 to 15 wt% of Fe, and N in addition to improve magnetic characteristics and workability.
Elements such as b, W, Mn, Al, and Cr are added.
However, the metal oxide of permalloy is mainly Fe or N.
It may be considered to be an oxide of i. FIG. 2 shows an example of the analysis result of the metal oxide of permalloy.

[Problems to be Solved by the Invention]

Further, in this type of oxide film, at 570 ° C. or lower, as shown in FIG. 4, a NiO phase underlying oxide layer 6 is formed at a portion closest to the surface of the core 5 of permalloy, and is formed thereon. Fe ₃ O ₄ intermediate oxide layer 7 and Fe
_The surface oxide layer 8 composed of the ₂ O ₃ phase is formed, and a porous film having a small film thickness is formed.

By the way, generally, when a metal or an alloy is heated in oxygen and an oxidizing atmosphere in the air, the metal and oxygen act to generate a metal oxide (scale). In the case of an alloy, it forms a metal oxide of its constituent elements. On the principle of this oxidation, in order to further promote the oxidation,
Oxygen must be diffused inward through the metal oxide formed on the surface to reach the underlying metal or alloy. However, since the radius of metal ions is generally smaller than the radius of oxygen ions, it can be said that the diffusion of metal ions toward the outside is faster than the diffusion of oxygen ions toward the inside.

The characteristics of each layer component described above will be shown below. FeO (wustite phase); metal-deficient P-type semiconductor Fe ₃ O ₄ (magnetite phase); oxygen-deficient n-type semiconductor Fe ₂ O ₃ (hematite phase); oxygen-deficient n-type semiconductor where the P-type semiconductor is Although it depends on the oxygen partial pressure, the n-type semiconductor does not depend on the oxygen partial pressure. In FeO, the defects in the phase have a much higher mobility, so that they become very thick as compared with the other layers (intermediate oxide phase 3, surface oxide phase 4). The relative ratio of the thickness of each oxide _{coating, FeO: Fe 3 O 4:} Fe 2 O 3 =
It is 95: 4: 1. When a dense oxide film is formed by isothermal oxidation, the oxide film increases in thickness with the passage of oxidation time, and if the stress generated in the film exceeds the rupture stress of the oxide, the film tends to crack or peel. is there.

The causes of the internal stress include electrostrictive stress metal of the surface tension coating, hydration of different volume of oxides, dehydration inclusions and the like. The internal stress of the coating is shown by the following equation. _{P-P 0 = {ε (} ε-1) / 8π} (E 2 -r) / x ( the first term electrostrictive effect, the second term surface tension effects) P: vertical coating surface stress P _0: External pressure ε: Dielectric constant of coating (= 2 to 15) r: Surface tension x: Thickness of coating E: Strength of electric field

Therefore, although FeO scale has a relatively high plastic performance, it has a drawback that the adhesion with the core material metal is lost. The rapid generation of such scales induces physical defects and gas molecule penetration into the outer scale due to the associated stress.

With respect to Ni, an oxide of NiO can be obtained irrespective of temperature rise and oxygen partial pressure. NiO; P-type semiconductor with metal deficiency

Further, as shown in FIG.
Has a large difference in thermal expansion coefficient from that of permalloy, and has high thermal stress in the layered structure. This also causes the state of the oxide film to become unstable, which causes the loss of adhesion between the underlying oxide layer 2 and the core 1 between the NiO phase and the FeO phase.

Further, cracking or peeling of the oxide film is particularly likely to occur under severe conditions such as a thermal cycle, that is, repeated heating and cooling, rapid heating and rapid cooling. This process is caused by stress caused by a difference in thermal expansion coefficient between the oxide and the alloy, that is, thermal stress due to thermal contraction during cooling at a high temperature after oxidation.

For example, when both surfaces of the plate-shaped alloy are covered with a uniform oxide film, the stress σ ₀ generated in the oxide due to the temperature difference ΔT is expressed by the following equation. σ ₀ = {E ₀ (α ₀ −α _M ) ΔT} / {1 + 2 (E ₀ / E _M ) (τ ₀ / τ _M )} α ₀ : Average thermal expansion coefficient between the difference ΔT between the oxidation temperature and the cooling temperature. E: Elastic modulus τ: Thickness (The subscripts ₀ and _M represent an oxide film and an alloy, respectively.) Considering τ ₀ << τ _M , σ ₀ = E (α ₀ −α _M ) ΔT

Therefore, the difference between the temperature difference and the coefficient of thermal expansion is important for cracking and peeling of the oxide film under the thermal cycle. Thus, the thermal stress generated by the temperature difference ΔT when the alloy is cooled at a high temperature during oxidation increases with the increase in ΔT, and when the fracture strength of the oxide is exceeded, the coating film breaks and peels.

Therefore, the present invention solves the above-mentioned drawbacks of the prior art and, at the same time, makes the adhesion of the oxide film more excellent and provides a better magnetic core.

[0017]

In order to solve the above-mentioned problems, the invention according to claim 1 forms a base oxide layer made of NiO and FeO on the surface of a core made of a Fe--Ni magnetic alloy. An intermediate oxide layer made of Fe ₃ O ₄ and a surface oxide layer made of Fe ₂ O ₃ are formed.

In order to solve the above-mentioned problems, the invention described in claim 2 heat-treats a core made of a Fe--Ni magnetic alloy in oxygen, air, or steam at a temperature of 570 ° C. or higher and then removes it. After cooling, a base oxide layer made of NiO and FeO, an intermediate oxide layer made of Fe ₃ O _4, and a surface oxide layer made of Fe ₂ O ₃ are formed in order from the portion closest to the core.

[0019]

According to the magnetic core of the present invention, when the oxide film is formed, the oxide film structure as shown in FIG. Further, it is possible to suppress the generation of film stress and form an oxide film having excellent adhesion. Therefore, it is possible to form a magnetic core having excellent magnetic properties and abrasion resistance.

[0020]

Embodiments Embodiments will be described below with reference to the drawings. In FIG. 1, 1 is a core made of a Fe—Ni magnetic alloy, 2 is a base made of NiO and FeO formed by heat-treating the core 1 at 570 ° C. or higher in oxygen, air or steam. Oxide layer, 3 is Fe ₃ O ₄
Intermediate oxide layer composed of (magnetite phase), 4 is Fe ₂ O ₃
A surface oxide layer composed of (α-hematite phase). Here, the temperature at the time of forming the oxide film is defined as 570 ° C. or higher because FeO (wustite phase) is generated and a film having a large film thickness and a high hardness is formed. When the coating is formed at 570 ° C. or lower, a magnetic core having a structure as shown in FIG. 4 is formed.

In FIG. 4, 5 is a core made of a Fe--Ni magnetic alloy, 6 is the core 5 in oxygen or air,
Alternatively, a base oxide layer made of NiO formed by heat treatment at 570 ° C. or lower in steam, 7 an intermediate oxide layer made of a Fe ₃ O ₄ phase (magnetite phase), 8
Is a surface oxide layer made of Fe ₂ O ₃ (hematite phase).

On the other hand, at 570 ° C. or higher, as shown in FIG. 1, NiO is formed at the portion closest to the surface of the core 1 of permalloy.
Phase and FeO phase underlying oxide layer 2 is formed, and F is formed on the underlying oxide layer 2.
The intermediate oxide layer 3 made of the e ₃ O ₄ phase and the surface oxide layer 4 made of the Fe ₂ O ₃ phase are formed, and the film thickness becomes large and a dense and highly hard coating film is produced. This is also apparent from the Fe-O phase diagram shown in FIG.

By the way, in order to improve the adhesion, it is necessary to remove internal stress and thermal stress. Oxidation treatment temperature is 5
If the temperature is lower than 70 ° C, FeO is not generated and the adhesion is excellent. To do. As this pretreatment,
Ultrasonic cleaning of the core surface, sufficient annealing in H ₂ , and the like are effective means.

Further, it is particularly important to remove the thermal stress, and it is necessary to carry out a heat treatment at a predetermined temperature of 570 ° C. or higher and then a cooling treatment instead of a rapid cooling. At least 59
In order to obtain the same adhesion as that of an oxide film that does not generate FeO at 0 ° C. or lower, a predetermined temperature of 570 ° C. or higher to 100
That is, the temperature is cooled to 0 ° C. in 20 minutes or more.

As described above, by heat-treating the core 1 at a temperature of 570 ° C. or higher, NiO + is formed on the upper surface of the core 1.
The underlying oxide layer 2 composed of the FeO phase is generated. When Ni is oxidized, it does not depend on oxygen and Ni oxide easily mixes with metal ions.
The underlying oxide layer 2 containing the iO phase is easily formed, and this underlying oxide layer 2 forms a dense and hard coating, and the abrasion resistance can be improved. However, as shown in FIG. 6, since the NiO phase has a large difference in thermal expansion coefficient from the core 1, it is likely to be peeled due to a large amount of internal strain. Adhesion to the core 1 is improved and a stable oxide film is obtained.

When permalloy is used as the core material of the magnetic head and is oxidized to form an oxide film on its surface, the relationship between the oxidation temperature and the amount of core wear of the magnetic head is shown in FIG. Show. As is clear from this, 5
It was clarified that the amount of wear of the core portion decreased at a temperature of 70 ° C. or higher, and the effect of abrasion resistance was brought out.

[0027]

According to the magnetic core of the present invention, the conventional Fe
-Provided that the properties relating to wear resistance and oxide film adhesion, which were inferior to the core made of a Ni-based magnetic alloy, were good,
As a magnetic head core compatible with a high coercive force of a magnetic recording medium, there is an effect that a more excellent magnetic core can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of a magnetic core when a processing temperature is set to 570 ° C. or higher in an embodiment of the present invention.

FIG. 2 is a graph showing the components and their ratios of conventional Fe—Ni alloy permalloy and oxide film in weight percent.

FIG. 3 is a graph showing the relationship between the oxidation treatment temperature and the wear amount of the core when the Fe—Ni magnetic alloy permalloy core is subjected to the oxidation treatment.

FIG. 4 is a cross-sectional view of a conventional magnetic core using a Fe—Ni based magnetic alloy as a core material.

FIG. 5 is a phase diagram of the Fe—O system.

FIG. 6 is a table showing an average thermal expansion coefficient of a metal / permalloy alloy and main oxides formed on the surface thereof.

[Explanation of symbols]

 1 core 2 underlying oxide layer 3 intermediate oxide layer 4 surface oxide layer 5 core 6 underlying oxide layer 7 intermediate oxide layer 8 surface oxide layer

Claims (2)

[Claims] 1. An underlying oxide layer made of NiO and FeO and Fe ₃ O on the surface of a core made of a Fe—Ni magnetic alloy.
A magnetic core comprising an intermediate oxide layer of ₄ and a surface oxide layer of Fe ₂ O ₃ . 2. A core made of a Fe—Ni magnetic alloy is heat-treated at a temperature of 570 ° C. or higher in oxygen, air, or steam to form NiO and FeO in order from the portion closest to the core. Underlayer oxide layer and Fe
_A method of manufacturing a magnetic core, comprising forming an intermediate oxide layer made of ₃ O ₄ and a surface oxide layer made of Fe ₂ O ₃ .