JPH0469814A - magnetic disk board - Google Patents

Abstract

PURPOSE:To obtain excellent thermal resistance and wear resistance and to reduce the thickness by using titanium as the material of a substrate and adding specific components. CONSTITUTION:Titanium is used as the material of a magnetic disk substrate to improve the thermal resistance of the substrate. Al and O are added to the titanium matrix. In the case of <=1.0wt.% (5/2)+ O + (1/3)Al, the hardness cannot obtained, and the wear resistance cannot be obtained. For the purpose of preventing degradation the cold workability, quantities of O and Al are set to <=0.6% and <=4.0% respectively. Further, V,Fe,Cr,Ni, and Co are added in 1/13:1/20:1/17:1/31:1/23 for the purpose of preventing the occurrence of pits. Thus, excellent thermal resistance and wear resistance are realized and the thickness is reduced, and the substrate is produced where interpositions, pits, or the like to cause the magnetic error are less generated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic disk substrate, and in particular to a magnetic disk substrate that has excellent heat resistance, can be made thin, and is suitable for manufacturing magnetic disks with high recording density. Regarding the board.

[Prior Art] A magnetic disk used as a recording medium for computers includes a substrate and a magnetic film formed on the substrate. Among these, the magnetic disk substrate is required to have the following characteristics.

(a) The surface quality after precision polishing or precision grinding must be good so that the magnetic head can run stably on the disk, or so that stable magnetic characteristics with few magnetic errors can be obtained. .

(b) There are no protrusions or holes on the substrate surface that would cause defects in the magnetic medium formed on the substrate surface.

(c) It has strength and rigidity that can withstand machining during substrate manufacturing and high-speed rotation when used as a disk.

(d) Must be able to withstand heating during formation of the magnetic medium.

(e) It should be lightweight and non-magnetic.

(f) It has a certain degree of corrosion resistance.

Conventionally, Al-
Aluminum alloys such as Mg-based alloys are used.

On the other hand, in recent years, there has been a trend towards higher recording densities and smaller sizes of magnetic disks, which has led to the following requirements.

(A) Improving the magnetic properties of the magnetic film. For example, forming a magnetic film with high coercive force.

(B) Making the thickness of the magnetic film thinner.

(C) Decreasing the flying height of the magnetic head.

(D) Decreasing the gap length of the magnetic head.

(E) Improving magnetic head positioning control technology.

(F) Making the substrate smaller and thinner.

In order to satisfy these demands, the following actions have been taken in the past.

That is, a magnetic film with high recording density is formed by sputtering (Kyuzo Nakamura, Kinzoku November 1986 issue), or heat resistance is imparted to the substrate against heating during sputtering.

Additionally, in order to reduce the flying height of the magnetic head, N1-P plating is applied to the aluminum alloy disk to cover inclusions and obtain a high level of surface cleanliness in terms of surface roughness and waviness. (Masahiro Saito et al. Practical Surface Technology vol. 1.35. No. 6゜1.988).

Furthermore, the alloy composition of the substrate is reduced in inclusions that cause electrical and magnetic errors (Japanese Patent Laid-Open No. 63-21695).
3) Attempts have also been made to make the substrate itself thinner.

On the other hand, new materials are being developed to replace aluminum alloys as substrate materials that satisfy the conditions (a) to (f) above. For example, glass (Hiroyoshi Ishizaki Industrial Materials No. 3)
5, No. 5), ceramics (Takeshi Matsumoto, Magnetic Materials Research Group, Electronic Materials Surface Treatment Technology, July 1986), titanium (JP-A-52-105804, JP-A-59-1513)
35, Japanese Unexamined Patent Publication No. 1-112521) has been developed.

[Problems to be Solved by the Invention] By the way, aluminum alloys such as Al-Mg series, which have been commonly used as magnetic disk substrates, are used for forming magnetic thin films with high coercive force necessary for high-density recording, and for There is a disadvantage that it does not have enough heat resistance to withstand the rise in substrate temperature that occurs during sputtering to reduce the thickness of the magnetic film. In addition, even if the composition of this material is adjusted, it is not possible to obtain a high level of surface texture because it inherently contains many inclusions, and the reduction in head flying height that is required to increase recording density. and electrical errors cannot be sufficiently reduced.

In order to obtain a high level of surface quality, the surface is plated with N1-P as described above, but there is a drawback that the yield of this plating is quite low.

Further, N1-P plating has disadvantages such as crystallization at a relatively low temperature of about 350° C., retaining magnetism, and peeling.

Further, when a conventional aluminum alloy substrate is made thinner as required, it is not possible to maintain sufficient strength and rigidity to withstand high-speed rotation of the disk (for example, 3600 rpm) for shortening access time.

Further, when glass or ceramics is used as the substrate material, it has sufficient heat resistance and strength, but since both are brittle materials, there is a drawback that reliability is low. Furthermore, glass substrates emit gas when heated to high temperatures during sputtering, and impurity elements in the glass diffuse into the magnetic film, which adversely affects the magnetic properties of the magnetic film.

Ceramic substrates have many pores, making it impossible to obtain sufficient surface texture. Thus, glass and ceramics are still insufficient as magnetic disk substrates.

As mentioned above, various proposals have been made regarding titanium substrates. For example, Japanese Patent Laid-Open No. 52-105804 proposes a magnetic disk substrate made of titanium or a titanium alloy with an oxide film or nitride film formed on the surface. This is intended to increase the hardness of the substrate surface by oxidizing or nitriding the surface to form an oxide film or a nitride film, thereby improving the grindability and thereby obtaining good surface quality. In addition, in JP-A-59-151335, h
Contains at least 80% cp phase by volume and has a strength of 60 kg/
We have proposed a magnetic disk substrate made of an α-type titanium alloy with a particle diameter of ms2 or higher. Furthermore, JP-A-1-11252
No. 1 proposes a magnetic disk substrate made of a titanium alloy whose surface is mirror-polished to have a surface roughness Ra of 0.03 μm and a cross-sectional hardness HV of 250 or more.

However, in ordinary pure titanium and α-type titanium alloy, Fe,
β-type stabilizing elements such as V are unavoidably contained at 0.1% by weight, and these β-type stabilizing elements tend to segregate during the melting, blooming and finish rolling stages, and are caused by segregation during polishing. Easy to cause pitting. For this reason, when trying to obtain a high level of surface quality, the yield will decrease. Also,
Since α-decade-β type and β-type alloys also contain different phases, the yield decreases for the same reason. In addition, the oxidation and nitridation rates of the α phase and β phase (segregation area) are different, making it difficult to oxidize or nitride uniformly. The yield is low and the manufacturing cost is high. In addition, the total content of impurity elements in ordinary pure titanium and α-type titanium alloys is specified to be 0.3% by weight or less, which is significantly lower than that in aluminum alloys. It is still insufficient to completely eliminate errors caused by objects, and it cannot be said to be sufficient to obtain a high level of surface quality.

As described above, at present, good magnetic disk substrates mainly made of titanium have not been obtained.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a magnetic disk substrate that has excellent heat resistance and abrasion resistance, can be made thinner, and does not generate inclusions or bits that cause magnetic errors.

[Means and effects for solving the problem] As a result of various studies on magnetic disk substrates by the inventors of the present application, it has been found that the heat resistance and strength of magnetic disk substrates mainly depend on the substrate material and its composition. It has been found that wear resistance, processability, and the occurrence of inclusions and bits that cause magnetic errors and deterioration of surface quality are mainly related to the component composition of the substrate material. This invention was made based on such knowledge.

That is, in weight percent, 0 is 0.6% or less, Aj) is 4.
0% or less, (5/2) O+ (4/3.) Ajl is 1
．． 0% or more, (V / 13) + (F e / 2
0 ) + (Cr/17) + (N, i/3
1) + (Co/23) is 0.020% or less, Rem+S i +B+W is 0.015% or less (However, Rem represents a rare earth metal element), and the remainder is substantially composed of Ti. The above object is achieved by the disk substrate.

This invention will be explained in detail below.

In the following description, for the sake of brevity, the above (
5/2) 0. + (1/3)Ajl! EQI, (V/
13)+(Fe/20)+(Cr/17)+(N i
/ 31 ) + (Co / 23 ) with EQ2,
R<em>S i +B+W is expressed as EQ3.

Titanium has a high melting point of about 1650°C, so by using titanium as a magnetic disk substrate material, the heat resistance of the substrate can be improved, and the temperature of the substrate when forming a magnetic thin film by sputtering is 300°C. 40
There is no change in shape even at 0°C. In addition, titanium has a tensile strength of about 30 kgf'/■2 and a longitudinal elastic modulus of 100.
Since it has high strength and rigidity of about 10000/intestine 2, even if it is thin, it can sufficiently withstand the centrifugal force generated during high speed rotation of 3600 rpm or more. Furthermore, since the substrate is made of titanium alone, it is easy to reduce the thickness, and N1-P plating type A
Unlike fi alloy substrates, peeling does not occur at the interface between different layers. Thus, it is preferable to use titanium as the substrate material.

In this invention, AI,0 is added to the titanium matrix. These elements improve the hardness of the substrate and provide good wear resistance. However, these amounts are E
It is necessary to satisfy the relationship QI≧1.0%. This is because, outside this range, sufficient hardness will not be obtained and good abrasion resistance will not be obtained. In addition, these elements cause an increase in hardness and worsen cold workability, so 0 is 0.6.
%, if All is added in excess of 4.0%, there is a risk of cracking during cold working even if the above relationship is satisfied, and it is difficult to produce a blank material before mirror finishing with a high yield. It is difficult to do so. Therefore, the amount of 0 and Afi is 0
≦0.6%, Aρ≦4.0%, and EQI≧1.0%.

In titanium, V, Fe, Cr, Ni.

Co is an element that is stable at high temperatures and stabilizes the β phase having a cc structure. If a certain amount or more of these elements is present in the titanium matrix of the magnetic disk substrate, these elements will become concentrated or segregated during processes in which the titanium matrix is exposed to high temperatures, such as melting, blooming, or finish rolling. and,
The concentration and segregation of these elements is carried over even to the blank material, which is a circular plate before the mirror finishing process. As described above, when a blank material in which β-stabilizing elements are concentrated or segregated is polished or ground for mirror finishing, pitting occurs due to the difference in characteristics between the concentrated or segregated portion and the matrix. Therefore, V, Fe, Cr, N in the Ti matrix
It is necessary to minimize the amount of β-stabilizing elements such as i and Co. The present invention contains O and/or Al that stabilizes the α phase that is the matrix in the substrate material, so even if some β stabilizing elements are included, concentration and segregation will not occur, but ■ Concentrations higher than 0.26%, F
Concentrations higher than 0.40% for e, higher than 0.34% for Cr, 0.62% for Nl
If the concentration of CO is higher than 0.46%, blemishes will occur. For this reason, ■≦0
．． 26%, Fe≦0.40%, Cr≦0.34%, Ni
It is desirable that CO≦0.62% and CO≦0.46%. However, since each of these elements has similar effects,
It is necessary to specify the total. And the ratio of these effects is V:Fe:Cr:Ni:Co-1/13+1/2
0:1/17:1/31:1/23. Therefore, the content of these components is set to EQ2≦0.02%.

Rem, St, B in the titanium matrix.

When W is present at a certain concentration or higher, these elements combine with O and N dissolved in titanium to form oxides and nitrides, or combine with titanium to form intermetallic compounds. It causes the formation of inclusions.

Therefore, by reducing Rem, Si, B, and W, the generation of inclusions is suppressed. Each of these elements is 0.015
% or less, but since each has the same effect, it is necessary to specify the total. Therefore, the total amount of these components is set to EQ3≦0.15%. Note that Rem is Sc, Y.

La, Ce, Pr, Nd, Pm, Eu, Gd.

Represents rare earth elements such as Tb, Dy, and Lu.

In this way, by specifying the composition of the magnetic disk substrate, we can create a substrate that has excellent heat resistance and wear resistance, can be made thinner, and has fewer inclusions and bits that can cause magnetic errors. It can be manufactured with good yield.

[Example〕 Examples of the present invention will be described below.

Ingots having the composition shown in Table 1 (composition numbers AOI~A20.BOI~B25) were melted by VAR melting, and then bloomed at 1000°C to a thickness of 2.
05m slab. 870℃ for these slabs
A final hot rolling process was performed to obtain a hot rolled sheet with a thickness of 6 cm. After that, the oxide film of this hot-rolled plate was removed, and it was cut into a plate with a thickness of 5 cm, and then cold rolled to a thickness of 0.6 cm.
It was made into a cold-rolled sheet. Evaluation of the cracking test described below was performed on this cold rolled sheet.

A ring shape (outer diameter 95m5, inner diameter 25mm) is made from this cold-rolled plate.
+, thickness Q, 6m5), and after hot straightening at 600℃ for 6 hours, the surface of these disk substrate materials was #400.
, #800, #1500, and #4000 grindstones, and finally alumina finish polishing was performed to produce 100 magnetic disk substrates for each composition. Each sample produced in this manner was evaluated for hardness, abrasion resistance, bits, and inclusions.

Table 1 shows the composition of each sample as well as the characteristic values evaluated by each test. In addition, in Table 1, composition numbers AOI to A
20 is within the composition range of this invention, composition number B
OI-B25 are comparative examples outside of this range. In addition, in the "Crack" column in Table 1, the length 1+ that occurred during rolling is
Indicates the presence or absence of cracks of i + i or more, "bits and inclusions"
In the column 1. with a differential interference microscope and an optical microscope. The number of samples in which bits and inclusions were present is shown when 100 samples of each composition were observed in 60 fields of view at a magnification of 0x. The hardness was measured using a Vickers hardness meter under a load of IKg. Furthermore, the abrasion resistance is determined by forming a substrate surface (I think it would be better to explain it simply) and making it in the same condition as a current magnetic disk, with a disk rotation speed of 60 Orpm, a load of 100 g/C112, and a sliding time of 24 hours. The conditions were evaluated.

Further, the results in Table 1 are summarized in FIGS. 1 to 3. Figure 1 is a diagram showing the relationship between the content of A[ and O and characteristics, Figure 2 is a diagram showing the relationship between the value of EQ2 and the number of substrates on which bits are generated, and Figure 3 is a diagram showing the relationship between the value of EQ3 and the number of substrates on which bits are generated. FIG. 6 is a diagram showing the relationship between the number of substrates on which objects are generated;

First, the results of the processability and abrasion resistance of the disk substrate will be shown. As shown in Table 1 and FIG. 1, composition numbers AOI to A2 of examples in which Al and 0 amounts are within the range of the present invention
0 and Comparative Examples B] and 3 to B22, no cracking occurred, the hardness was Hv≧250, and the abrasion resistance was good. On the other hand, if Aj7≦4.0% and O
Comparative example composition numbers B01 to BO5 and 823 to B24 that satisfy ≦0.6% but do not satisfy EQI≧1.0% have good durability with no cracking or hardness of Hv<250. Abrasion resistance could not be obtained. Also, EQI≧
1.0% is satisfied, but Aj) 64.0% and O≦0.6
Composition numbers BO6 to B12 and B of comparative examples that do not satisfy %
In No. 25, Hv≧250 and abrasion resistance was good, but cracking occurred.

From these results, it was confirmed that as long as the contents of AN and O are within the range of the present invention, good workability and wear resistance can be obtained as a magnetic disk substrate.

Next, bit generation will be explained. As shown in Table 1 and FIG. 2, among the composition numbers A01 to A20 within the scope of the present invention and the comparative examples, composition numbers BO that satisfy EQ2≦0.02%
No bits occurred in 7-B15. On the other hand,
Composition numbers BOI to BO that do not satisfy EQ2≦0.02%
6 and B16 to B25, the occurrence of bits was confirmed.

From this result, it was confirmed that if EQ≦0.02% is satisfied as in the present invention, a magnetic disk substrate without bit generation can be obtained.

Next, the occurrence of inclusions will be explained. As shown in Table 1 and FIG. 3, among the composition numbers AOI to A20 within the scope of the present invention and the comparative examples, composition numbers B12.816 to B18 and 823 to B25 that satisfy EQ3≦0.015% have inclusions. There were no occurrences. On the other hand, EQ3≦0.015
801-Bll, 813-B15 and 8 that do not meet %
Generation of inclusions was confirmed in samples No. 19 to B22. From this result, it was confirmed that if EQ3≦0.015% is satisfied as in the present invention, a magnetic disk substrate without generation of inclusions can be obtained.

As mentioned above, 0 is 0.6% or less, AN is 4.0% or less, (5/2)0+(1/3)AI is 1.0% or more, (V
/13)+(Fe/20)+(Cr/17)
+ (N i / 31) + (Co / 23
) was 0.020% or less, Rem+S i +B0W was 0.015% or less, and it was confirmed that a magnetic disk substrate with excellent characteristics could be obtained with a component composition in which the remainder was substantially Ti. .

It goes without saying that the magnetic disk substrate according to the present invention can also be applied to high recording density media that require high substrate temperatures, such as Fe oxide thin films and barium ferrite thin films.

[Effects of the Invention] According to the present invention, it is possible to provide a magnetic disk substrate that has excellent heat resistance and abrasion resistance, can be made thinner, and is suitable for a high recording density magnetic disk substrate.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the content and characteristics of AN and 0,
FIG. 2 is a diagram showing the relationship between the value of EQ2 and the number of substrates where bits are generated, and FIG. 3 is a diagram showing the relationship between the value of EQ3 and the number of substrates where inclusions are generated.

Claims (1)

[Claims] (1) In weight%, O is 0.6% or less, Al is 4.0% or less, (5/2) O + (1/3) Al is 1.0% or more, (V/
13) + (Fe/20) + (Cr/17) + (Ni/3
1)+(Co/23) is 0.020% or less, Rem+Si+B+W is 0.015% or less (however, Rem represents a rare earth metal element), and the remainder is substantially composed of Ti. magnetic disk board.