JPH04248123A - Ti substrate blank and its production - Google Patents

Abstract

PURPOSE:To offer a Ti substrate blank having good flatness with <=5mumRa in average with little variation. CONSTITUTION:The substrate blank consists of pure Ti containing 0.15-0.4wt.% oxygen, impurities of <=0.010wt.% hydrogen, <=0.05wt.% nitrogen, <=0.05wt.% Fe, and other inevitable impurities and has >=0.07mumRa surface roughness. This Ti substrate blank for a magnetic disk has good peeling property after vacuum annealing or Ar atmosphere annealing and has excellent flatness. This blank is produced by grinding the surface of the pure Ti substrate having the above compsn. with a grindstone comprising rough grinding particles of <800 grain size and then annealing the substrate in vacuum or Ar atmosphere. Annealing is performed at 600-700o under 200-2000kg/dm<2> pressure, and for vacuum annealing, in a higher vacuum degree than 10<-5> Torr.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ti-based blank with excellent flatness, and more particularly to a Ti-based blank suitable for use in high-density magnetic disks and a method for manufacturing the same.

0002

2. Description of the Related Art The recording density of magnetic disks is increasing year by year. Along with this, the recording method is changing from the conventional coating type to the sputtering type, and miniaturization is progressing toward small diameter and thin disk substrates.

[0003] In response to these demands for higher recording density, an Al alloy with excellent plating properties has been proposed in Japanese Patent Publication No. 62-2018, for example, as opposed to the conventionally used 5086 series aluminum alloy. However, as mentioned above, in recent years, there has been a remarkable progress in thinning the walls, and problems have arisen that cannot be solved using the conventional manufacturing process of such materials.

[0004] That is, in a small disk substrate,
The plate thickness is 1.905 mm (5.25 inch diameter) to 1
．． 27mm thickness, 1.0mm thickness, 0.8mm thickness and 0.6
mm thickness etc. have been devised. Furthermore, in parallel with this, the ratio of [outer diameter]/[plate thickness] has also increased, and the problem of deformation due to handling during the magnetic disk manufacturing process has become apparent. To improve this, efforts have been made to increase the strength of Al alloys, but no matter how high the strength of Al materials, the hardness remains at Hv.
(Vickers hardness) is about 90 at most, and the elastic modulus is not improved by alloying, so no significant effect has been obtained.

[0005]

[Problems to be Solved by the Invention] In order to solve this problem, the use of a Ti alloy was proposed in JP-A-59-151335 and other publications as a metal that satisfies the following conditions: (1) high hardness, (2) light weight, and (3) non-magnetic properties. However, these Ti alloys also have various problems and have not been put into practical use.

[0006] In other words, these Ti alloys have extremely poor workability, and it is difficult to obtain good flatness.
This is because errors occur frequently when a magnetic film is formed by direct sputtering (a method of forming a magnetic film without Ni--P underplating, which is very advantageous in terms of cost reduction).

[0007] In order to solve this problem, the present inventors
Previously, in Japanese Patent Application No. 2-57494, we proposed a method for annealing a Ti-based blank that causes fewer errors and has good flatness in high-density magnetic disks. This annealing method is
Impurities: hydrogen 0.010% or less, oxygen 0.40%
Hereinafter, pure Ti consisting of 0.05% or less nitrogen, 0.1% or less iron, and other unavoidable impurities was cast, homogenized, heated, hot rolled, cold rolled, intermediate annealed, and cold rolled according to the conventional methods. For the Ti base blank manufactured in the process, the annealing temperature was 500°C or more and 640°C or less, and the pressing force was 50 to 1000°C.
This is an annealing method characterized by performing press annealing under conditions of kg/dm2.

However, with this annealing method, the average value of the obtained flatness is at most 6 to 10 μmRa, and when variations are taken into account, it has been found that the flatness of the entire substrate cannot be guaranteed.

[0009] The present invention eliminates the drawbacks of the above-mentioned prior art and provides a Ti substrate blank that can obtain good flatness of about 5 μm Ra or less on average with little variation.
The object of the present invention is to provide a method for producing the same.

0010

[Means for Solving the Problems] In order to solve the above problems, the present inventor conducted various tests on measures to improve the flatness of Ti substrate blanks, and found that by controlling the surface condition, the flatness of Ti substrate blanks could be improved by vacuum annealing. We have discovered that it is possible to minimize the adhesion of the base.

That is, in order to improve the flatness, vacuum annealing should be performed at as high a temperature, under high pressure, and for a long time as possible, but on the other hand, peeling becomes difficult, and even if good flatness is obtained, deformation occurs due to peeling. This can lead to a situation that makes no sense at all. When we tried to elucidate the cause of this phenomenon, we found that because titanium is a very active metal, during vacuum annealing, the oxide film on the surface dissolves and diffuses into the matrix, leaving the surface bare. It was determined that the titanium particles were bonded together in a solid state. To prevent this, it is desirable to coat the surface with an elemental component phase that does not diffuse into titanium. However, this method was found to be undesirable in terms of cost and environment, as it required removal of the compound phase adhering to the surface in a subsequent step and also contaminated the vacuum furnace.

[0012] Therefore, the inventor of the present invention conducted further research and development on other measures and found that by roughening the surface, the contact area between the bases can be reduced, and even if they are partially joined, the joining force will be reduced. The present invention has now been completed by finding out that it can be made into a small and easily removable state.

That is, in the present invention, oxygen: 0.15 to 0
．． Contains 4wt%, hydrogen: 0.010w as an impurity
t% or less, nitrogen: 0.05wt% or less, Fe: 0.05
Peeling after vacuum annealing or Ar atmosphere annealing in a substrate blank made of pure Ti containing Ti containing wt% or less and other unavoidable impurities, characterized in that the surface roughness is 0.07 μm Ra or more The purpose of this invention is to provide a Ti-based blank for magnetic disks that has good properties and flatness.

[0014] Furthermore, the manufacturing method includes processing the surface of a substrate blank made of pure Ti having the above composition with a grinding wheel made of abrasive grains coarser than No. 800, and then vacuum annealing or It is characterized by performing Ar atmosphere annealing.

The present invention will be explained in more detail below.

[0016]

[Operation] First, in the present invention, pure Ti is used as the base material in order to eliminate intermetallic compounds that cause pits after polishing.

There are several types of alloying elements in Ti, including Al and V, but all of them form intermetallic compounds and fall off during polishing, forming pits and causing recording errors. The addition of alloying elements must be avoided. Therefore, in the present invention, it is essential to use pure Ti. However, pure Ti needs to have a specific composition as explained below.

Since oxygen acts as a reinforcing element for the Ti matrix, it is desirable to have a large amount of oxygen, and the content is preferably 0.15 wt % or more. However, if it is more than 0.4 wt%, it tends to cause grain boundary erosion during polishing, so it is set to 0.4 wt% or less.

[0019] Since Fe also combines with Ti to form an intermetallic compound, it is necessary to have a small amount as an impurity, and 0.05w
It should be less than t%.

Other impurities such as hydrogen and nitrogen move to the grain boundaries during annealing and during cooling after annealing, and are preferentially eroded during polishing to form grooves, so they must be kept in small amounts. 010wt% or less, nitrogen is 0.05wt
% or less.

[0021] The pure Ti base blank having the above composition can be produced by casting,
A blank is produced by the conventional manufacturing process of homogenization heating, hot rolling, cold rolling, intermediate annealing and final cold rolling, and this blank is subjected to grinding and annealing as explained below. Ru.

The surface roughness of the blank needs to be 0.07 μmRa or more in order to improve releasability. Although methods such as lapping can be used to form this surface roughness, grinding using a so-called fixed grindstone is preferable from the viewpoint of ease of post-processing. In order to obtain the surface roughness by grinding with a fixed grindstone, it is necessary to use a grinding wheel composed of abrasive grains coarser than No. 800. Although there is no upper limit to the surface roughness, in order for the rough surface to be easily polished in the grinding or polishing step after the process of the present invention,
It is desirable that Ra is substantially 0.5 μm or less.

During annealing, if the oxygen partial pressure is too high, T
Since oxidation of the i surface progresses easily, vacuum annealing or Ar atmosphere annealing is used. In the case of vacuum annealing, a degree of vacuum higher than 10 −5 Torr is preferred. If the degree of vacuum is lower than this, oxidation of the Ti surface may proceed. Note that among the inert gases, it is also possible to use only Ar, which does not react with Ti, and perform annealing in this inert gas atmosphere.

Although good flatness can be obtained by subjecting a Ti blank having the above-mentioned surface roughness to vacuum annealing or Ar atmosphere annealing, the annealing temperature must be adjusted in order to obtain a blank material with even better flatness. 600℃ or more, pressure is 2
00 kg/dm2 or more is preferable. If the temperature exceeds 700° C., the effect is saturated and the annealing jig (spring) itself becomes soft and no longer contributes to improving flatness. Also, 20
If it exceeds 00 kg/dm2, no matter how rough the surface is, the material itself will significantly diffuse, the bonding strength will increase, and peeling will become difficult. Note that the holding time is preferably 1 hour or more and 10 hours or less. Annealing for more than 10 hours is very uneconomical, especially considering the vacuum atmosphere.

The Ti base blank obtained by the above manufacturing process and conditions has an excellent surface roughness of 0.07 μmRa or more and 5 μmRa or less, and has good releasability after annealing.

This Ti base blank is excellent as a base for high-density recording magnetic disks, and even if a magnetic film is formed by direct sputtering after finishing the base by grinding and polishing, there will be very few errors.

Next, examples of the present invention will be shown.

[0028]

[Example 1]

[Table 1] Pure Ti base blank (dimensions: 0.83
mm thickness x outer diameter 95 mm x inner diameter 25 mm) by a conventional manufacturing process, and for this blank, a grinding wheel (grain size 400
After processing with a PVA grindstone (elastic grindstone),

Vacuum annealing was performed under the conditions shown in Table 2. Table 2 also shows the results of examining the releasability, flatness, etc.

From Table 2, it can be seen that all of the examples of the present invention have excellent releasability and blank flatness. On the other hand, in Comparative Example 1, the flatness was poor due to the low pressure, and in Comparative Example 2, the pressure was too high, resulting in poor releasability.

[0030]

[Example 2] For a pure Ti base blank (the dimensions are the same as in Example 1) with the chemical components shown in Table 1,

As shown in Table 3, the blanks were vacuum annealed with various surface roughness changes. In addition, the surface roughness 0.02μmRa is 3000
PVA grinding wheel of No. 800 is used for 0.08μmRa.
The A grindstone was adjusted, and the 0.15 μm Ra was adjusted using a No. 400 PVA grindstone. The results of examining the peelability, flatness, etc. are also listed in Table 3.

From Table 3, it is clear that all the examples of the present invention are excellent in releasability and flatness. On the other hand, Comparative Example 3 is inferior in releasability and flatness because the surface roughness is not appropriate.

[0032]

[Example 3] After grinding a pure Ti substrate (the dimensions are the same as in Example 1) with the chemical composition shown in Table 1 using a grinding wheel,

[Table 4] Ar atmosphere annealing was performed under the conditions shown below. The results of examining peelability, flatness, etc. are also listed in Table 4.

From Table 4, it can be seen that the releasability is excellent and the flatness of the blank is also excellent.

[0034]

[Effects of the Invention] As detailed above, according to the present invention,
Since the pure Ti substrate blank is subjected to vacuum annealing or Ar atmosphere annealing after roughening and controlling the surface, the peelability after vacuum annealing or Ar atmosphere annealing is good, and a product with excellent flatness can be obtained. In addition, there is little variation in flatness, resulting in high quality.

Claims (4)

[Claims] [Claim 1] Contains oxygen: 0.15 to 0.4 wt%, hydrogen: 0.010 wt% or less, nitrogen:
In a base blank made of pure Ti, the surface roughness is 0.0.
Vacuum annealing or A characterized by having a temperature of 7 μmRa or more
A Ti-based blank for magnetic disks with good peelability and flatness after annealing in an r atmosphere. 2. The surface of the substrate made of pure Ti having the above composition is processed with a grinding wheel made of abrasive grains with a grain size coarser than No. 800, and then subjected to vacuum annealing or Ar atmosphere annealing. Vacuum annealing or A characterized by
A method for manufacturing a Ti-based blank for magnetic disks that has good releasability and flatness after annealing in an r atmosphere. [Claim 3] Vacuum annealing is performed at a temperature of 600°C or higher and 70°C.
0℃ or less, pressure is 200kg/dm2 or more 2000k
3. The method according to claim 2, wherein the method is carried out at a vacuum level of less than g/dm2 and higher than 10@-5 Torr. 4. Ar atmosphere annealing is performed at a temperature of 600°C or more and 700°C or less, and a pressure of 200kg/dm2 or more.
3. The method according to claim 2, wherein the method is carried out at a pressure of 00 kg/dm2 or less.