JPH0426792A - Laminated material for machine structural use excellent in rolling fatigue life and its production - Google Patents

Abstract

PURPOSE:To provide a laminated material for machine structural use excellent in rolling fatigue life by using a lightweight and high strength titanium alloy or aluminum alloy as a base material and subjecting this base material to surface hardening treatment by the use of Ni-P plating, etc., as a coating material. CONSTITUTION:The surface of a titanium alloy or an aluminum alloy is subjected to surface roughening treatment by means of a solution containing hydrofluoric acid salt. The surface of the titanium alloy or the aluminum alloy roughened to >=0.57mum Ra and >=130 PPI50 is directly coated with Ni-P plating layer of >=HV500 hardness to >=100mum thickness. The Ni-P plating layer has P concentration difference in the layer thickness direction, and preferred P content is 2-7wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mechanical structural composite material with excellent rolling fatigue life used for wear parts of various machines and transportation equipment, and a method for manufacturing the same. be.

(Prior technology) For the wear parts of various molds and machines, carbon steel for mechanical structures, nickel chromium molybdenum steel, chromium molybdenum steel, etc., have traditionally been treated with carburizing, quenching and tempering, nitriding, or soft nitriding. This steel material is widely used and exhibits good wear resistance. However, these steel materials have a high specific gravity and are difficult to respond to the trend toward weight reduction.

Titanium alloys and aluminum alloys are beginning to attract attention as materials that can respond to the trend toward weight reduction. Due to their excellent corrosion resistance and high specific strength at high temperatures, titanium alloys and aluminum alloys have been widely used for various chemical industries and as various components for aviation and space transport aircraft.

In recent years, as the demand for higher-grade automobiles and other types of transportation equipment has increased, it has become necessary to install various functional parts in order to improve functions such as comfortable driving and safe driving.

As a result, the problem of increased vehicle weight has arisen.

On the other hand, there is still a strong demand for reduced fuel consumption, and in order to solve these problems at the same time, consideration has begun to be given to the use of titanium alloys and aluminum alloys in place of conventional steel materials.

However, it is known that titanium alloys and aluminum alloys have extremely poor seizure resistance and wear resistance as they are.
Until now, surface treatments such as electroplating, electroless plating, vapor phase plating, gas nitriding, and thermal spraying have been attempted for use as sliding members or shaft members of machines.

Among these, if a plating method such as electroplating or electroless plating can be adopted, members can be provided most simply and at low cost.

(Problem to be solved by the invention) However, in electroplating and electroless plating using an aqueous solution, titanium alloys and aluminum alloys form a strong oxide film on the surface, so it is difficult to obtain good adhesion of the plating layer. I can't.

In addition, in vapor phase plating and gas nitriding treatment, the thickness is usually 5 μm.
Only a moderately hard coating can be obtained, and it is impossible to withstand sliding wear and rolling wear under high surface pressure.

Furthermore, since thermal spray coatings are subject to high surface pressure due to rolling wear, it is difficult to obtain coatings with sufficient strength to withstand this, so neither surface treatment method is suitable for titanium alloys and aluminum alloys. It is only possible to impart wear resistance.

For example, taking the shaft material shown in Figure 6 as an example, the contact area between the ball bearing and the roll bearing of the shaft material requires not only general wear resistance, but also sliding wear and rolling wear characteristics. Ru. In other words, at the point contact part of this shaft material,
In particular, rolling wear resistance is required, several 100 kgf/mtn
Maximum contact stress of two types = high surface pressure is applied, and the maximum shear stress occurs at several 10 to several 100 μm from the surface of the material, and because this stress is repeatedly applied, fatigue cracks occur in the material and flaking occurs. This is the most important feature of this type of rolling wear. Therefore, for such applications, hard ceramic materials such as WC and TiN, which are commonly known and widely used as highly wear-resistant materials, have excellent sliding wear resistance but lack toughness and poor rolling wear resistance. It is inferior.

Therefore, in order to respond to the trend toward weight reduction, the present inventors propose a composite material using a titanium alloy and an aluminum alloy as base materials, which are lightweight and have excellent wear resistance. (Means for Solving the Problems) The present invention was developed in view of the above-mentioned problems in wear resistance of surface-treated titanium alloys and aluminum alloys. The first invention was completed by coating the surface with RaO, PP with a thickness of 5 μm or more.
This is a mechanical structural composite material with excellent rolling fatigue life, in which the surface of a titanium alloy or aluminum alloy roughened to an Iao of 130 or more is directly coated with a 1-P plating layer of 100 μm or more with a hardness of HV500 or more.

The second invention provides P in at least the surface layer of the Ni-P plating layer.
The composite material for mechanical structures having excellent rolling fatigue life according to claim (1), wherein the content is 2 to 7% by weight. The third invention is N
The composite material for mechanical structures having excellent rolling contact fatigue life according to claim 1 or 2, wherein the i-P plating layer has a difference in P concentration in the thickness direction of the layer.

A fourth invention is a composite for mechanical structures having excellent rolling fatigue life according to claim (1), wherein the surface of the titanium alloy or aluminum alloy to be coated is subjected to surface roughening treatment with a solution containing a fluoride salt. This is a method of manufacturing the material.

(effect) Hereinafter, the effects of the present invention will be explained.

In order to withstand fatigue fracture due to rolling wear, HV500 or higher is required.
It is necessary to form the second hard layer with a thickness of at least 100 μm or more. In order to firmly adhere the hard layer to the surface of the titanium alloy or aluminum alloy, a strong anchor effect is required, but the surface condition can be improved by etching or shot blasting to Ra of 0.5 μm or more.
) A strong anchor effect can be obtained by adjusting PP[5G to 130 or higher. Here, PPI (Peak
s Per Inch) is a constant reference level H set in both positive and negative directions from the average line of the extraction curve (measured value) of the contact type surface roughness meter, and when the negative reference level is exceeded and the positive reference level is exceeded. , ■ Mountains and displays the number of mountains per inch. In other words, PP15.130 has a standard level of 50 μm, and the number of ridges per inch is 1.
30 is shown. This makes it possible to suppress peeling of the hard plating layer from the titanium alloy or aluminum alloy interface. In addition, as a type of hard plating, electroless N
Possible options include i-P plating, hard Cr plating, and electrolytic Ni-P plating, but electrolytic Ni
-P plating is considered to be the most advantageous.

As mentioned above, rolling wear is characterized by high surface pressure, contact stress of several 100 kgf/mm2, and maximum shear stress occurring at a depth of several 10 to several 100 μm from the contact surface. Furthermore, when the shaft and bearings are subjected to repeated rolling stress, the raceway may peel off, making it impossible to operate. This phenomenon is called flaking, and is a type of fatigue failure of the shaft and bearing materials, which determines the lifespan of the shafts and bearings.

Therefore, the inventors conducted a rolling wear test to select a covering material. The results will be explained below.

FIG. 1 is a schematic diagram of the rolling wear test method, in which 1 is a test piece, 2 is an evaluation surface, 3 is a ball bearing, 4 is a bearing race, and 5 is a rotating shaft. There is an evaluation surface 2 at the tip of the test piece 1, and the evaluation surface 2 is tapered so as to come into contact with the ball bearing 3. A required number of ball bearings 3 are arranged within a bearing race 4. The bearing race 4 is attached to the rotating shaft 5 and rotates together with the rotating shaft 5. The rotating shaft 5 is connected to a rotating device (not shown). In the test, a load P is applied to the test piece 1, and the rotating shaft 5
This is done by rotating.

The sample material was Ti-6AI-4V as a base material, and W was used as the base material.
There are three types: one with carbon sprayed, one with electrolytic Ni-P plating applied to the base material, and one with the base material as is. These test pieces
The shape was finished and subjected to a rolling wear test. Second test result
As shown in FIG.

Figure 2 shows the rolling contact fatigue life of the test materials.
The figure summarizes the relationship between electrolytic Ni-P plating thickness and rolling fatigue life.

As shown in FIG. 2, the lifespan of each sample material is approximately 5 hours for those coated with WC. The reason for this is thought to be that although the WC film exhibits good wear resistance during sliding wear, the WC film breaks and falls off due to high surface pressure during rolling wear. Of course, T16Al-4V as the base material has a lifespan of 5 hours or less.

FIG. 3 shows the relationship between electrolytic Ni-P plating thickness and rolling fatigue life in rolling wear tests. It is clear that the rolling fatigue life of electrolytic Ni--P plating is rapidly extended as the plating thickness increases JtD.

From this result, the thickness of the coating material to improve the rolling contact fatigue resistance of electrolytic Ni-P plating is determined in order to keep the area where the maximum shear stress occurs inside the coating material, and to improve the rolling contact fatigue resistance of the coating material. In order to make the wear resistance possible and effective, it is preferably 0.1 mm or more, and from the viewpoint of wear resistance, 1 mm is sufficient. Further, increasing the thickness of the covering material is not preferable from the viewpoint of weight reduction, which is the objective of the present invention.

The hardness of the coating material is adjusted to the required hardness depending on the plating conditions, but from the viewpoint of providing wear resistance and rolling fatigue life, it is recommended to use HV50.
Limited to 0 or more.

FIG. 4 shows the relationship between the P content in the Ni-P plating layer and the hardness of the plating layer. In the present invention, it has been found that the hardness of the plating layer reaches a peak of 1 (V500 or more) when the P content in the Ni--P plating layer is 2 to 7% by weight, as shown in the figure. Of course, the hardness can be controlled by other additives and plating conditions in addition to the P content, but this result shows that in normal Ni-P plating, 10% by weight or more of P is normally used in electroless plating. This shows that the hardness increases with a lower P content than Ni-P plating. Therefore, if we try to easily achieve high hardness in the present invention, the P content in Ni-P plating It is preferable that the content is 2 to 7% by weight.

However, in the present invention, since it is difficult to control the P content with the electroless plating, electroplating is better as a metallization method.

Figure 5 shows the relationship between rolling contact fatigue life and P concentration in plating. Using Ti-6AI-4V as the base material, degreasing → washing with water →
After performing etching → water washing → surface activation treatment, electrolytic Ni-P plating was performed. The plating bath composition is NlSO4
・6H20: 200g/l SN+C12・6H20:
50g/l, H, PO3: 4-40g/l SH*PO
4:5 (Ig/l).The surface roughness is Ra 1.
32 am, PP[50283. The current density was varied depending on the thickness of the plating layer. In the diagram, ■ is 15A
/dm2, ◆ is 30A/dm2, and both are "single layer plating" in which the P concentration in the thickness direction of the plating layer is constant. The thickness of the plating layer is 700 μm.

On the other hand, ・ is lower layer 5A/dm2 (201tm thickness formation)
, middle layer +5A/dm2 (500um thickness formation), upper layer 3
The thickness of the plating layer was changed in three stages: 0 A/dm2 (200 μm thick), and the lower layer was changed in two stages: 15 A/dm2 (200 to 300 μm thick), and 30 A/dm2 (200 to 300 μm thick) for the upper layer. This is "multilayer plating" in which the P concentration in the thickness direction is changed.

The P concentration of the outermost plating layer is as follows.

■ is 5.2% by weight "single layer plating" ◆ is 4.9% by weight "single layer plating" ・ is 2.8% by weight "double layer plating" Mu is 2.8% by weight "double layer plating A 5th As shown in the figure, "multi-layer plating" in which the P concentration of the plating layer is varied is superior to the rolling contact fatigue life targeted by the present invention. Therefore, it is preferable to provide the plating layer with a difference in P concentration in the thickness direction.

The manufacturing process of the composite material for mechanical structures of the present invention is as follows. Namely, ■ Machining of base material (titanium alloy or aluminum alloy) ■ Alkaline degreasing (5% sodium orthosilicate solution, 70°C
) ■Water wash■Etching (fluoride salt) ■Water wash■Activation treatment ■Water wash■Electroplating or electroless plating.

Even in the conventional method, etching is naturally performed as a pretreatment for plating. However, the acid used for this etching is
Nitric acid, hydrofluoric acid, or a mixture of these acids, nitric and hydrofluoric acid, are the main ones.These conventionally used mineral acids cannot produce the rough surface defined in the present invention, but simply etching the surface uniformly or vice versa. It is only smoothed.

According to the findings of the inventors, in order to obtain the rough surface specified in the present invention by chemical etching, NH4F -HPNaF
- Hydrofluoric acid such as IP is required, and nitric acid and hydrofluoric acid, which are commonly used as other etching agents, are effective as brightening agents, but are not preferred agents for the roughening specified in the present invention. .

In addition, in the present invention, after etching to roughen the surface if necessary, before hard plating, phosphoric acid electrolytic treatment is performed to remove smut from the surface, and acid such as chromic acid or hydrofluoric acid is applied to expose the metal surface. It is possible to perform activation processing.

That is, the steps from forming a rough surface on the surface of the material to plating are the same as usual. This also applies to the pretreatment for surface roughening etching.

Furthermore, regarding the necessity of heat treatment after plating, conventional technology has adopted a method of mutually diffusing titanium and plating metal through heat treatment in an attempt to improve the adhesion between the plating and the titanium interface. However, in the present invention, it has been found that heat treatment tends to make the plating layer more brittle, and the plating adhesion of the present invention does not deteriorate even without heat treatment.

The base material (core material) obtained in this way is made of a light and high-strength titanium alloy or aluminum alloy, and the surface layer is made of HV5
Since a thick electrolytic Ni-P plating layer of 0.00 or more and 0.1 to 1 mm is formed, excellent wear resistance can be exhibited.

It goes without saying that a hard layer for imparting wear resistance is not required in the portion of the composite material that does not come into contact with the shaft material.

In order to further improve weight reduction, it is effective to apply covering material only to the minimum necessary parts.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 First, a method for manufacturing a composite material as a test material will be described. N
The base material (core material) of i-P plating is titanium alloy, Ti-6.
AI-4V, TiTi-6AI-2Sn-42r-2
, using Ti-6AI-6V2Sn, as described above.
After degreasing → washing with water → etching → washing with water → surface activation treatment, electrolytic Ni-P plating was performed. The plating bath composition was NiSO4.6H20: 200g/I, NIC
12.6H20: 50g/l, H3PO3: 4-40
g/l, H3PO4: 5 og/l, and the current density was appropriately selected within the range of 5 to 40 A/dm2. The plating thickness was appropriately selected within the range of 0.02 to 0.5 mm. The abrasion resistance and plating adhesion of these test materials were investigated using the rolling abrasion tester (Fig. 1) described above. Plating adhesion was evaluated by a tape peel test after cutting 100 1 mm crosscuts on the plated surface, bending the crosscuts to a diameter of 5 mm and 180°.

The results are shown in Tables 1-1 and 1-2 for surface roughness, It is also written together with the plating layer hardness and thickness.

Table 1 1-16 = Table 1 2 As is clear from Tables 1-1 and 1-2, the composite material in which electrolytic Ni-P plating was applied to the titanium alloy of the example of the present invention has a coating material thickness of The abrasion resistance improves as the coating thickness increases, and stable abrasion resistance is shown when the thickness of the coating material is 0.1 mm or more. Of course, uncoated titanium alloy as a base material has poor wear resistance.

Further, in the composite material in which the titanium alloy of the present invention was electrolytically plated with Ni-P, no peeling was observed in the tape peeling test, and the plating adhesion was good.

On the other hand, the comparative example had poor plating adhesion and poor wear resistance due to insufficient surface roughness.

Example 2 Ti-6AI-4V shown in Table 1-1 of Example 1, surface roughness Ra 1.32 u, m, PP[5,283
Using the base material, plating was performed under the same electrolytic Ni-P plating conditions as in Example 1, with only the current density changed, and the P content of the plating layer was changed. The thickness of the plating layer is 7
00 μm. The P content and hardness of these plated layers were measured. The results are shown in FIG.

Of course, the surface hardness of the plating layer is primarily important for the rolling contact fatigue life characteristics targeted by the composite material of the present invention, and from the results shown in Figure 4, when the P content is 2 to 7% by weight, It can be seen that the hardness increases.

In addition, if the P content exceeds 7% by weight, the Ni-P plating layer itself becomes brittle, its toughness decreases, and the plating layer may crack under load.From this point of view, the P content should be 2.
~7% by weight is preferred.

(Effects of the Invention) As explained above, the composite material for mechanical structures with excellent rolling contact fatigue life and the method for manufacturing the same according to the present invention have the above-mentioned configuration, so that lightweight and high-strength titanium alloys and aluminum alloys are used. It has the excellent effect of imparting wear resistance to titanium alloys and aluminum alloys by subjecting the base material to a surface hardening treatment using NiP plating or the like to the coating material.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic diagram of a rolling wear test method. FIG. 2 is a diagram showing the rolling fatigue life of the 1vC coating, electrolytic Ni-P plating, base material, and material. FIG. 3 is a diagram showing the relationship between electrolytic Ni--P plating thickness and rolling fatigue life. FIG. 4 is a diagram showing the relationship between the P content in the Ni--P plating layer and the hardness of the plating layer. FIG. 5 is a diagram showing the relationship between rolling fatigue life and P concentration of the plating layer. Figure 6 is a diagram showing a model of rolling wear and the concept of contact pressure and shear force. ■ Test piece evaluation surface Hall bearing bearing race rotating shaft

Claims (4)

[Claims] (1) PPI_5_0 is 1 when the surface Ra is 0.5 μm or more
Directly apply 1 Ni-P plating layer on the side of hardness HV500 to the surface of titanium alloy or aluminum alloy that has been roughened to 30 or higher.
Composite material for mechanical structures with excellent rolling fatigue life characterized by a coating of 00 μm or more. (2) The composite material for mechanical structures having excellent rolling fatigue life according to claim (1), wherein the P content of at least the surface layer of the Ni--P plating layer is 2 to 7% by weight. (3) The composite material for mechanical structures having excellent rolling contact fatigue life according to claim (1) or (2), wherein the Ni--P plating layer has a difference in P concentration in the thickness direction of the layer. (4) A machine with excellent rolling fatigue life according to claim (1), characterized in that the surface of the titanium alloy or aluminum alloy to be coated has been subjected to surface roughening treatment with a solution containing fluorate. Method of manufacturing structural composites.