JP2632688B2 - Surface treatment method for titanium member and coil spring using the surface treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for improving the wear resistance and fatigue strength of a titanium member.

Problems to be Solved by Conventional Techniques and Inventions Titanium is light, hard to rust, and has a high specific strength, and has recently been used in various fields. There is a drawback that the part that slides or collides with the mating member has a large wear. Therefore, various PVD (Physical
Vapor Depo-sition treatment or CVD (Chemical Vapor
Although a method of forming a coating layer having excellent wear resistance on the surface by a por deposition process has been attempted, not only cannot a uniform thickness be applied when the component shape is complicated, but also in particular. For members that require fatigue strength as well as wear resistance, such as springs, the conventional PVD
Alternatively, the coating layer formed by the CVD process has a weak bonding force to the base material, and has a disadvantage that it is easily peeled off by shot peening.

Means for Solving the Problems The present invention provides electroless Ni plating on the surface of the titanium member as a means for solving such problems,
After annealing at 50 ° C., shot peening was performed.

Action and Effect of the Invention The present invention has the above-described structure, and has an electroless surface on a titanium member.
Since Ni plating is applied, there is no danger of hydrogen embrittlement unlike the case of electrolytic plating, and conventional PVD, C
Even for members with complicated shapes compared to VD processing, evenly and
The Ni coating layer can be formed firmly, and the Ni coating can be formed at low cost without the need for expensive vacuum equipment such as PVD processing, and then annealing at 250 to 450 ° C. As a result, P and B are precipitated from the Ni coating layer as compounds such as Ni ₃ P and Ni ₃ B, and the height is increased to about Hv 1000, and the wear resistance is improved, and further, the hardness and the wear resistance are increased. Compressed residual stress is given by shot peening to the Ni coating layer that has been given, acting as if a hammer was fitted with a hard shell around the titanium member,
This has the effect of increasing the hardness of the surface of the titanium member and suppressing the occurrence and growth of fatigue cracks, thereby improving the fatigue strength.

It is to be noted that mixing a hard atomizer such as Al ₂ O ₃ into an aqueous solution for electroless Ni plating and performing composite dispersion plating has an effect of further improving wear resistance.

In addition, the coil springs that have been subjected to these treatment methods have the effects of reducing the loss of wear due to line contact and extending the fatigue life.

Example 1 First, as a test piece, a round bar (φ20 × 5 mm) of an α-β type Ti alloy generally known as Ti-6A1-4V was polished, then degreased, alkali-washed, and treated with a hydrofluoric acid / nitric acid solution. after, Ni-4% P (Al 2 O 3 dispersion), Ni-8% P and Ni-1
% B solution, each electroless plating with a film thickness of 20 μm,
After that, it is annealed by heating at 200-500 ° C for 1 hour, φ0.7m
Measure the hardness, residual stress and abrasion loss when rubbing with a hard slab for a shot wire shot with a hardness of m, Hv600 projected at a speed of 68 m / s and shot peened. The results obtained are shown in Tables 1, 2, and 3, respectively. FIG. 1 shows a micrograph of a cross section of a test piece having a Ni-8% P electroless plating having a film thickness of 20 μm, and the progress of crystallization due to a change in the annealing temperature of the plating layer of the test piece. FIG. 2 shows the results of the X-ray diffraction test.

From the results of Example 1 described above, the electroless Ni plating layer hardly diffused and penetrated into the titanium base material, became a state in which the surface of the base material was covered with a shell, and crystallization was rapidly performed by annealing at 350 ° C. or more. It was found that the hardness and compressive residual stress were maximum at around 300 to 400 ° C., and the wear loss was minimum.

Example 2 β-type precipitation hardening type having a structure of Ti-13v-11Cr-3A1
After coiling the Ti alloy wire, precipitating and hardening by aging at 425 ° C for 20 hours, polishing the surface by shot peening, further degreasing, alkali washing, hydrofluoric acid-nitric acid solution treatment, Ni Electroless Ni plating was performed at −8% P to produce coil springs having specifications shown in Table 4. The thickness of the plating layer is 10
There were three levels of μm, 20 μm, and 30 μm. After that, 300
After hardening treatment at 1 ° C. for 1 hour, shot peening was performed at a projection speed of 54 m / s with a cut wire shot of φ0.7 mm, and the hardness and abrasion loss of the test material were measured. . Here, the wear loss is 1800 rpm, 50
This is the amount of reduction in wire diameter due to line-to-line contact when a durability test is repeated 2 × 10 ⁷ times with a low repetitive stress of ± 25 kgf / mm ² .

Next, Table 6 shows the results of a durability test performed using the test spring having a film thickness of 20 μm. This exam is
The average fatigue life (MTTF) was determined using a star type fatigue tester under a stress condition of 55 ± 40 kgf / mm ² . (N = 8) From the results of Example 2 above, it was found that the titanium alloy coil springs to which electroless Ni plating had been applied had significantly improved hardness, reduced wear loss due to line-to-line contact, and significantly improved fatigue life. did.

[Brief description of the drawings]

FIG. 1 is a micrograph showing a metal structure of a cross section of a test piece in which an electroless Ni plating is applied to a titanium base material, and FIG. 2 shows a progress of crystallization due to a change in an annealing temperature of the electroless Ni plating layer. It is an X-ray diffraction test result shown.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshio Osone 43, Miyashita, Fukuda-shi, Miyoshi-cho, Nishikamo-gun, Aichi Pref. 43, Miyashita, Fukuda, Chuo-cho, Japan

Claims (3)

(57) [Claims] 1. A method for surface treating a titanium member, comprising applying an electroless Ni plating to the surface of the titanium member, annealing at 250 to 450 ° C., and then subjecting the titanium member to shot peening. 2. The method according to claim 1, wherein Al ₂ O ₃ is mixed into an aqueous solution for electroless Ni plating to perform composite dispersion plating. 3. A coil spring to which the processing method according to claim 1 or 2 is applied.