JPH03170649A - Method for forming polished specular surface in ti alloy member - Google Patents

Abstract

PURPOSE:To manufacture the Ti alloy parts free from surface flaws, excellent in appearance and having high strength by heating parts made of a Ti alloy essentially consisting of a beta phase and having a specified compsn. at a specified temp. in a nonoxidizing atmosphere, rapidly cooling the alloy, subjecting it to soln. treatment and thereafter executing aging treatment in a specified temp. range. CONSTITUTION:A slab of a Ti-Al series alloy essentially consisting of a beta phase and having a compsn. constituted of, by weight, 5.1% Al, 2.1% Sn, 1.9% Zr, 4.3% Mo, 3.8% Cr and the balance Ti is held under heating to the temp. in a beta phase range of the transformation point of the alloy +100 deg.C to the transformation point +25 deg.C in a nonoxidizing atmosphere and is subjected to soln. treatment by rapid cooling such as water cooling to transform its structure into an acicular or planar primary alphaphase. After that, the alloy is held under heating in the temp. range of 550 to 400 deg.C in the same nonoxidizing atmosphere and is subjected to aging treatment to improve its hardness. The alloy is subjected to surface polishing, by which the decorative parts made of a Ti-Al alloy such as a spectacle frame free from the generation of the flaw of a pear-skin pattern and having an extremely beautiful specular surface can be obtd.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides surface improvement to a Tl-AN alloy member having a structure mainly composed of β phase, which has conventionally been impossible to form a mirror surface without surface defects. The present invention relates to a method for forming a polished mirror surface without defects.

[Conventional technology]

Generally, pure Ti is used to manufacture eyeglass frames, watch cases, and various decorative items that require mirror surfaces.

[Problem to be solved by the invention]

On the other hand, for the above-mentioned various parts, it is desired that they be lighter, smaller, and more scratch resistant. Therefore, the application of Ti alloys with high strength and high hardness is being considered, and Ti alloys that have these properties are being considered. In particular, Ti alloy having a structure mainly composed of β phase, i.e., in weight% (hereinafter % indicates weight%), Ti-5%AII-2%S
n-2%Zr-4%Mo-4%Cr, Ti-10%V
-2%Fe-3%Al, and Ti-9%V-2%Mo
-TiAfi alloys with typical compositions such as 3% AJ are attracting attention, but when mirror polishing is applied to these TiAD alloy members, a satin pattern appears on the polished surface, which significantly impairs commercial value. Therefore, the current situation is that it cannot be put to practical use.

[Means to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors found that although the material has high strength and high hardness, a pear-like pattern appears when polished to a mirror surface, and it cannot be applied to the production of members that require a mirror surface. T having a structure mainly composed of the above β phase
Focusing on i-AN alloys, we conducted research to create a clean polished mirror surface free from surface defects such as satin-like patterns on the surface of these alloys. As a result, we found that T! First, the Ap-based alloy member is heated in a non-oxidizing atmosphere to the transformation point of the Ti-Al-based alloy +100°C (hereinafter referred to as upper limit temperature) to the transformation point +2
After maintaining the temperature at a predetermined temperature within the β phase region of 5°C (hereinafter referred to as the lower limit temperature), a rapid cooling solution treatment is performed by means such as water cooling or forced air cooling to produce an acicular or plate-shaped primary α phase. Then, in the same non-oxidizing atmosphere, an aging treatment is performed to maintain the hardness at a predetermined temperature within the range of 550 to 400°C, and in this state, when a mirror polishing treatment is performed, the surface is free from defects.
The research results showed that it was possible to obtain a beautiful mirror surface.

This invention was made based on the above-mentioned research results, and the heating temperature range in solution treatment is set to be above the transformation point.
The reason for setting the temperature range from 100'C to the transformation point +25°C is that if the heating temperature exceeds the above upper limit temperature, the crystal grains will become coarser and the strength will decrease, whereas if the heating temperature is below the above lower limit temperature, transformation will not occur. If it is not possible to fully form the β phase, even if it is rapidly cooled in this state, the formation of the needle-like or plate-like primary α phase will be insufficient, and it is difficult to avoid the formation of a pear pattern on the mirror surface. This is because the heating temperature in the aging treatment was set at 550 to 400°C.If the heating temperature exceeds 550°C, the desired high hardness, that is, the Vickers hardness (Hv) of 350 to 450 This is based on the reason that a high hardness of 0.degree. C. cannot be obtained, and on the other hand, even if the heating temperature is less than 400.degree. C., aging becomes insufficient and the desired high hardness cannot be obtained.

〔Example〕

Next, the method of the present invention will be specifically explained using examples.

By the consumable electrode melting method, TiAD-based alloy ingots having the component compositions shown in Table 1 were formed, and after the ingots were made into slabs with a thickness of 50 mm by blooming, the transformation point was -50°C. The hot-rolled sheet was heated to a temperature of 100° C. and hot-rolled to a thickness of 5 mm, and the hot-rolled sheet was strain-removed by holding it at a predetermined temperature within the range of 650 to 750° C. for 4 hours in a vacuum. Diameter after annealing:
A test piece of 40 mrs x thickness = 5 mm was cut out, heated to a temperature of transformation point -50°C, and hot forged to give a thickness of 2 mm Tl-1! Manufacture plate material as a system alloy member,
Next, these Ti-Ail alloy members were subjected to solution treatment and aging treatment under the same conditions shown in Table 1, and then the surface was descaled by sunblasting, and subsequently, it was used as a puff liquid. Average particle size: 3.0-Ag203 powder =
Methods 1 to 3 of the present invention are performed by performing puff polishing using an aqueous solution containing 30% and 20% oxalic acid to form a mirror surface.
were carried out respectively.

Moreover, for the purpose of comparison, Comparative Methods 1 to 3 were conducted under the same conditions except that the solution treatment and aging treatment were not performed.

Next, the mirror surfaces of the various Ti-AN alloy plates obtained as a result were observed, and the Vickers hardness (Hv) was measured. These results are shown in Table 1.

Further, FIG. 1 shows a microstructure photograph (both magnified at 400 times) of the mirror surface obtained by the method 3 of the present invention, and FIG. 2 shows the structure taken by a metallurgical microscope of the mirror surface obtained by the comparative method 3.

[Effects of the Invention] As is clear from the results shown in Table 1 and Figure 1.2, in the m-planes obtained by methods 1 to 3 of the present invention, the primary α phase is precipitated in an acicular or plate shape. It has a very beautiful structure with no surface defects such as pear-like patterns, and has a high hardness compared to pure Tl, which has a hardness of H■: about 170, and is extremely scratch-resistant. While it is difficult to get marks,
Although the mirror surfaces obtained by Comparative Methods 1 to 3 have the same high hardness, they have a structure in which the primary α phase is precipitated in granular form.
This caused a pear pattern to appear on the entire surface.

As mentioned above, according to the method of the present invention, a high-quality material having a structure mainly composed of β phase, which has conventionally been unable to be put to practical use in fields where a mirror surface is required due to the appearance of surface defects such as a satin pattern on the mirror surface. A beautiful mirror surface free from surface defects can be formed on the surface of a strong and hard Ti-Al alloy member.

[Brief explanation of the drawing]

FIG. 1 is a micrograph of the structure of a mirror surface formed by method 3 of the present invention taken with a metallurgical microscope, and FIG. 2 is a micrograph of the structure of a mirror surface formed by comparative method 3 taken with a metallographic microscope. Procedural amendment 1 (Method) Indication of the April 1990 case Patent application No. 1-306887 Name of the invention Person making the amendment Method for forming a polished mirror for Ti alloy members Relationship to the case Patent applicant address Ote, Chiyoda-ku, Tokyo 1-5-2, Machi Name (626) Mitsubishi Metals Co., Ltd. Representative: Kenyo Nagano Address: 8th Floor, Jisouho Daini Building, 1-23 Kanda Nishiki-cho, Chiyoda-ku, Tokyo Date of Procedure Amendment Order Heisei 2 March 27, 2015 (shipment date) (1) In the description, No. 8, brief explanation of drawings, the 3rd line from the bottom and the 2nd line from the bottom (2 places) replace the word ``structure'' with ``metallic structure.'' I am corrected. that's all

Claims (1)

[Claims] (1) First, in a non-oxidizing atmosphere, a Ti-Al alloy member having a structure mainly composed of β phase is placed in the β phase region of the above Ti-Al alloy at a transformation point of +100°C to +25°C. After holding at a predetermined temperature, a rapid cooling solution treatment is performed to make an acicular or plate-like primary α phase appear, and then the same is held at a predetermined temperature within the range of 550 to 400°C in a non-oxidizing atmosphere. A method for forming a polished mirror surface on a Ti alloy member, characterized in that the Ti alloy member is subjected to an aging treatment to improve its hardness, and finally, a mirror polishing treatment is performed in this state.