JPS581187B2 - Kikaibuhinno Shiyorihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating mechanical parts containing titanium at least on the surface thereof.

Such mechanical parts are parts made of titanium itself (solid titanium), parts made of titanium alloy, or parts made of any material but whose surface is coated with titanium or titanium alloy. I'm talking about parts.

Titanium is generally known as a metal with the advantageous characteristics of being particularly light and resistant to corrosion, as well as having good mechanical properties.

On the other hand, titanium has very poor frictional properties and has major drawbacks such as seizure when rubbed against other materials such as steel, or against titanium itself.

Since titanium is indispensable for technologically advanced industries that perform processing while moving spatially, we are trying to take advantage of its excellent customization by forming a protective layer based on titanium. Much more effort has been put into this than before.

In particular, promising results have been obtained with oxidation methods, and indeed some anti-friction properties have been obtained by coating titanium or titanium alloy parts with oxide films, most often based on titanium oxide. It is known that various methods such as anodic oxidation are used to form such oxide coatings, but the results obtained indicate that the coating peels off when friction is applied. However, the results were never satisfactory as scales were formed on the surfaces of the parts.

In order to eliminate such defects, several step treatment methods are used, for example to create a scale coating on the surface of the machine part to be treated by oxidation in oxygen and then to diffuse this scale coating into the titanium part. Treatment methods have been attempted in which the coated parts are heated in argon.

However, such a method is difficult to implement on an industrial scale, and has the additional drawbacks of requiring a treatment temperature of about 900°C, which is considerably higher than the temperature typically appropriate for annealing titanium, and a long treatment time of more than 24 hours. There are drawbacks.

The present invention provides a new method for oxidizing titanium and its alloys, which is suitable for economical use, and has been made in view of the drawbacks of the prior art as mentioned above, which have not been available hitherto. In order to provide mechanical parts having such characteristics over time, it is possible to obtain a coating with extremely good durability.

The roots of this new oxidation treatment method are based on the following scientific discoveries.

The surface area S made of titanium is determined by heating a test piece in an airtight furnace into which a weight Q of oxygen is introduced under predetermined temperature, pressure, and other conditions described below. was formed on the surface of this test piece.

This test is repeated several times while changing the amount of oxygen per unit area Q/S applied to the entire surface of the treated part(s).

For all of the parts treated in this way, the hardness δ and thickness ε of the layer formed within a unit time, and the coefficient of friction f when the test piece treated in this way is rubbed against steel, are respectively calculated. Carefully measure each test.

As shown in the graph of Figure 2, Q/S is plotted on the horizontal axis, and δ,
If we take ε and f appropriately on the vertical axes, the three curves obtained match one curve c, and the characteristic is that curve c represents a very high peak and a very narrow base. .

The applicant believes that it is useful to point out this phenomenon here, since this chemical phenomenon based on the applicant's knowledge is related to the gist of the titanium oxidation treatment method according to the present invention.

That is, the problem is to at least partially replace the native oxide layer covering some titanium part with the oxide layer obtained when oxidation occurs according to the peak of curve c in FIG.

If the processing method also satisfies the following necessary conditions,
The method of the invention will provide significant benefits.

(1) The natural oxide layer covering the outer surface of any part containing titanium must be at least partially removed, and the thickness of the removed layer is preferably 2 microns or more.

(2) The part to be treated is placed in a gas-tight furnace and evacuated before an amount Q of oxygen, strictly determined as the area of the total surface area S of the part to be treated, is introduced into the furnace.

Preferably, the pressure within the furnace is between 1 and 10<-8> Torr.

If Q and S are respectively expressed in cm and cm, it is desirable that Q/S according to the process of the present invention be 10-3 to 2.55 cm/cm3.

(3) Processing temperature is 450 to 880°C.

According to another feature of the invention, the order of operations is as follows.

(a) Partially removing the native oxide layer covering the treated part.

(b) placing the part in an enclosure connected to a vacuum system;

(C) Create a vacuum inside this enclosure and reduce the pressure to 1
~10-8 Torr.

(d) Disconnect the enclosure from the vacuum system.

(e) introducing into the enclosure an amount of oxygen determined as a function of the total external surface area of the processing parts contained within the enclosure;

(f) Heat the enclosure containing the parts to 450-880°C.

According to yet another feature of the invention, the vacuum treatment is carried out at any time after the temperature within the enclosure has risen above ambient temperature, in which case the sequence of operations is as follows.

(a) At least partially removing the native oxide layer.

(b) Place the parts to be processed into the enclosure.

(c) Start heating.

(d) creating a vacuum within the enclosure and then disconnecting the enclosure from the vacuum system;

(e) Introducing oxygen.

According to yet another feature of the invention, the oxygen required for the oxidation process may be supplied in any suitable manner, such as the non-limiting example below.

- As a gas injected directly into the enclosure.

Through substances, such as oxides, that can release oxygen under the influence of temperature.

- by removing gas from an object with previously absorbed oxygen.

According to yet another feature of the invention, oxygen is generally not introduced at the beginning of the process, but is introduced continuously or intermittently throughout the process after evacuating the enclosure.

According to a further feature of the invention, inside the enclosure, the processing parts are gradually cooled simply by stopping the heating.

According to yet another feature of the invention, the processing parts are rapidly cooled either inside or outside the enclosure.

A mechanical component according to the invention whose outer surface initially contains titanium consists primarily of titanium oxide after treatment and
It is characterized in that it is coated with one expression having a thickness of 0 microns or more.

The amount of oxygen, suitably determined as a function of the total surface area of the processing parts, is the only gas present in the enclosure during processing, but if a fill gas is present, a rare gas in air should be selected as desired. Argon is particularly suitable as this rare gas, and after expansion the gas pressure in the enclosure is substantially equal to that of the atmosphere. It is convenient to calculate the amount of said filling gas so that:

Even if the ratio Q/S changes over time during the process and exceeds the predetermined range of the peak of curve C, that process is still within the scope of the invention.

According to yet another feature of the invention, the processing temperature and time of the part are such that the processing time is on the one hand and the processing temperature is on the other hand;
Determined from a graph that corresponds to a point inside the shaded area between the two limit curves, the shaded area between the two curves is thick enough that the titanium will not seize even if rubbed. The purpose of this study is to determine the necessary conditions for obtaining a surface layer with a

The layers formed by the process according to the invention have unique and excellent properties.

(1) As a result of the unique shape of the connecting portion, the layer has excellent adhesion to the support and is durable.

The transition from the oxide-based part to the titanium-based lower layer takes place in a uniform gradient due to interdiffusion between the two layers.

(2) Unlike all other known oxide layers, no residual tensile stresses appear, so that the treatment according to the invention has the advantageous property that it has very little influence on the anti-strain properties of the component.

This characteristic arises from the fact that the total hardness δ of the layer has a minimum value at the apex of the curve C.

(3) The most surprising fact is that the coefficient of friction can drop to extremely low values of 0.07 in steel parts without adding any lubricant.

(4) The sensitivity of titanium to seizure, which is extremely feared in the mechanical industry, has disappeared even under extremely severe loading conditions.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics of the invention will be better understood by means of the accompanying drawings, which are given as non-limiting examples.

A part to be processed 2 is placed inside the enclosure 1.

The component may be made of solid titanium or a titanium alloy or may be coated with titanium or a titanium alloy.

The enclosure 1 is equipped with heating means constituted by an electrical resistor 3, which makes it possible to precisely change the temperature inside the enclosure during implementation of the method of the invention.

A vacuum system 6 (pump or equivalent) is connected to the inner space of the enclosure 1.

Finally, line 4 supplies oxygen and line 5 supplies an inert gas such as argon in the direction of arrow 7.

After completion of the treatment, the surface of the component 2 is coated with a layer based on titanium oxide, a feature of which is illustrated graphically in FIG. 2 for a non-limiting example.

This graph shows the variation of the coefficient of friction f expressed in Pickers units, the hardness δ and the thickness ε of the surface layer formed after processing of a part made of a titanium alloy as a function of Q/S.

Numbers vary depending on the nature of the underlying components.

However, if the method of the invention is followed correctly, the relative nature of the changes described above will be the same for parts exhibiting any titanium content, and the curves ε, f and δ will correspond to the curve C.

The novelty of the results obtained by the process of the invention is indicated by the operating figures reached.

Some non-limiting examples of this are given below.

-Example 1 of "Fabile" type test 1 This type of test is performed by Fabille-
Implemented at Levelly.

Diameter 6.5mm, height 40mm, surface area S9.35cm
The cylinder No. 2 is rotated between V-shaped jaws at an angle of 90°.

Apply a linearly increasing load to the jaws as a function of time.

Carry out the test in air.

Test parts made of titanium or titanium alloys and oxidized in a conventional manner, for example by immersion in a sulfuric acid bath at a current density of 0.3 A/dm2 for 20 minutes at ambient temperature in a furnace, actually seize between the steel jaws instantly. However, the test part treated by the method of the present invention was first sandblasted to a depth of 2.5 microns to remove the native oxide layer, then evacuated and then reduced to a Q/S ratio of 2 using argon as an auxiliary gas. .29 (Figure 2, point 31) oxygen 12
A titanium oxide film was formed by heating to 650° C. for 8 hours in a furnace containing 500 mg of titanium oxide (Fig. 3, point 30).The test part did not show any seizure even when rubbed under a load of 600 daN.

In this case, the coefficient of friction during the test is less than 0.12.

Example 2 "
The test was carried out on "Faville" type test parts.

Under the above conditions, the initial Q/S ratio was 3.42 mg/cm.
It is 2.

Due to leakage in the furnace, 650
The Q/S ratio at ℃ was 0.07 mg/cm2.

This is shown by curve C in FIG.

Therefore, during the treatment, the Q/S ratio passed through a predetermined range of peak P of curve C in FIG.

Results consistent with the present invention were obtained from test parts treated in this manner.

In fact, these results reduce the Q/S ratio to 0 over the entire processing time.
．． Although the results are not quite as good as those maintained at 11-2.55 mg/cm2, they are clearly better than those obtained by known methods.

In fact, no seizure occurred even when a load of 600 daN was applied with a friction coefficient of 0.15.

- Test using a cylindrical friction machine acting on a flat surface - Example 3 A titanium or titanium alloy ring with a diameter of 35 mm and a height of 20 mm was rotated at a rotation speed of 1200 r. p. m. So, the dimension is 30
It is rubbed on a parallelepiped steel plate measuring 8 mm x 8 mm.

A load increasing from 0 to 600 daN is applied to the plate within 3 minutes and 20 seconds.

After reaching the maximum load of 600 daN, a test is conducted with this maximum load.

Test in pure neutral petrolatum oil.

Titanium rings or titanium alloy rings treated with conventional methods such as anodization as described above seize as soon as the load reaches 80 daN, but as in Example 1 (650 °C, 8
Time, 1. 29 mg/cm2) After reaching a load of 600 daN, the ring treated according to the method of the invention can be rotated for 2 hours under this load without any seizure phenomenon occurring.

- Durability Test - Example 4 In this test, a titanium ring or a titanium alloy ring with an outer diameter of 60 mm was rotated at a rotation speed of 100 r. p. m. So, 100C
6 by rubbing against the hemispherical end of a steel ball.

The radius of curvature of the end portion is 6 mm.

A constant load of 5 daN is applied to the ball.

Although the anodizing ring can only rotate for 2 hours and regularly loses 12 mg every 30 minutes, the effect is multiplied by a factor of 100 for the test parts treated according to the invention as described above.

The part under test can be rotated for more than 10 hours, and the wear after 10 hours is minimal, only about 2.5 mg.

The new method of oxidation treatment of titanium and titanium alloys is carried out by a number of techniques adapted to the individual case.

Any processing technique is consistent with the present invention if it precisely adheres to any of the four characteristics of the process of the present invention.

Examples thereof will be described.

UTA6 containing 6% aluminum and 4% panadium
One part of V titanium alloy was taken out.

This has a diameter of 6.5 cm, a height of 40 mm, and a surface area of 9.35
The test part is of the “Fabile” type with cm.

The above parts are manufactured under the trade name “Vapor Blast Vapor”.
Sandblasted for 2 minutes at a jet pressure of 5 bar in an apparatus known as ``Blast''.

The particle size of the abrasive was 4 microns.

Immediately after sandblasting, this part is
The sample was placed inside a stainless steel vacuum furnace enclosure with a length of 965 mm and a volume of 8.275 dm3.

This vacuum furnace is impermeable to fluids.

Next, start the vacuum system and increase the pressure in the furnace to 10-10-
I made it to 6 torr.

The pump enclosure was isolated, then the heating system was started and the parts were heated to 600° C. in the oven.

While the temperature was rising, 16.8 mg of oxygen was introduced (treated area: 1.8 mg/cm3).

Argon was then introduced as an auxiliary gas to bring the total pressure within the enclosure to 400 Torr.

The parts were held in the enclosure at 600°C for 10 hours (Figure 3, point 28, line 24), then the enclosure was cooled to about 100°C and the parts were removed.

The layer obtained by this treatment is essentially titanium oxide TiO2
The layer thickness was approximately 24 microns.

Its average hardness is 500 Pickers hardness under 15g.

If the Fabille-type test described above is carried out with jaws of carbon steel (XC35) with a carbon content of 0.35%, the following results are obtained.

Initially, the coefficient of friction is extremely small, about 0.05.

Next, as the load increases, the friction coefficient increases slightly to a value of 0.0.
Stabilizes at 75.

At the end of the test, ie after 40 seconds of operation, the part under test is observed to creep under a load of 540 daN.

After the test, the friction parts are completely smooth.

Weighing the tested parts before and after the test shows that the wear is 1m.
It was less than g.

This can be considered virtually zero. For comparison, an untreated test part was tested and seizure occurred immediately.

It is noted that the method used in the above examples is fully consistent with the present invention by including four novel features that constitute the present invention.

In practice, (1) a part of the natural oxide layer covering the part before treatment is appropriately removed by sand blasting;

(2) According to the present invention, oxygen Q is appropriately introduced into the airtight furnace.

The amount of oxygen at this time is Q/S ratio of 0.11 to 2.55 mg
/cm2 is desirable.

(3) The oxidation step is suitably carried out in the presence of only the required total amount of oxygen and a rare gas in the air (argon in this example).

(4) A suitable temperature is 450 to 880°C.

However, this example illustrating the practice of the present invention is provided in a non-limiting manner, and any titanium oxidation or titanium alloy oxidation process that complies with the four features of the process according to the present invention is contemplated by the present invention. This is considered to be the implementation method.

Therefore, the treatment range of titanium parts during the introduction of oxygen according to the predetermined limit amounts is shown in FIG.
1 and 22.

A first example is given by parts processed at a temperature of 600°C.

The line 24, which corresponds to the processing temperature and is drawn at the coordinate 600° C. in the graph of FIG. It passes through the shaded area A.

It is therefore desirable that the parts be processed within said time range.

If the part is kept at 600°C for longer than 121/2 hours, a finely ground layer will form; if the part is kept at 600°C for less than 31/2 hours,
Otherwise, the thickness of the cambium will be too low to allow accurate friction.

Oxygen amount per unit area of processed parts is 2.55mg/c
If the amount is greater than m2, a layer is formed that is thinner than the layer obtained using the amount of oxygen according to the invention, and the coefficient of friction is 0.
It is clear that it is larger than 07.

Oxygen amount per unit area of processed parts is 10-3 mg/c
Below m2, a layer of such small thickness is formed that it is impossible to rub this layer accurately.

A second example is given by parts processed at a temperature of 700°C.

The line 27, which corresponds to the treatment temperature and is drawn at the coordinate 700 DEG C. in the graph of FIG. 3, passes through the shaded area 3 according to the treatment time, which ranges from 15 minutes to 5 hours.

In this way, the oxygen content of parts is 10-3 to 2.55 mg/c.
m2 and will be processed within said time range to obtain said quality.

As explained above, according to the method of the present invention, by removing the natural oxidation layer on the surface in advance, it is possible to form a base layer with a smooth surface free from contamination. After removing nitrogen, etc. from the air from inside the container, the process of introducing and heating oxygen makes the oxide layer formed on the surface of the base layer uniform, and furthermore,
Can eliminate nitride contamination or nitrogen gas contamination,
A uniform titanium oxide layer containing no bubbles or the like can be formed.

In addition, the oxide layer spreads not only on the surface layer but also in the depth direction due to diffusion, but since the underlying surface is smooth, the oxide film formed is uniform, and the diffusion using the oxide film as a diffusion source The rate of diffusion becomes uniform, the depth of diffusion can also be made uniform, and a homogeneous film with good adhesion can be formed.

In addition, since the oxidation reaction is carried out by introducing oxygen after being placed in a vacuum, the oxygen concentration in the reaction vessel can be accurately regulated, and the reaction can be carried out at high temperatures, reducing the processing time (heating time). , is greatly reduced, thereby suppressing variations in diffusion length.

Furthermore, during the oxidation process, since no reactive gas other than oxygen is present in the container, the titanium oxide formed on the surface layer evaporates again, liberating titanium and reacting with other reactive gases. do.

- For example, it becomes possible to prevent secondary products such as titanium nitride from being mixed into the film.

The incorporation of air bubbles into the membrane deteriorates the properties of the membrane over time, that is, reduces the corrosion resistance, and also greatly contributes to the decrease in the abrasion resistance of the membrane as well as the generation of secondary products.

In this way, the transition from the surface layer mainly composed of oxide to the lower layer mainly composed of titanium is done with a uniform gradient, and the adhesion of the film is good. Since the film has a uniform distribution and no residual strain stress is generated, it is difficult to peel off and has good anti-strain properties.

For example, conventionally it took 24 hours to form an oxide film, but in the present invention, it can be significantly shortened to about 2 and a half hours, and a good titanium oxide protective film can be formed in a short time. .

Some examples of embodiments of the invention are summarized below.

(1) The purpose is to improve the frictional properties, durability, and resistance to seizure of mechanical parts by first removing, at least in part, the natural oxide layer covering the outer surface of any part containing titanium. heating the part to be processed within an enclosure that creates a vacuum for a predetermined period of time, isolating the enclosure containing the part to be processed from the vacuum system, and injecting an amount of oxygen precisely determined as a function of the outer surface of the part to be processed; was introduced into the furnace, and the temperature of the parts to be processed was raised to 450 to 8
The temperature is raised to a range of 80° C., the pressure in the enclosure is between 1 and 10 −8 Torr before the introduction of oxygen, and the amount of oxygen provided to the part inside the enclosure is determined according to the increasing relationship across the outer surface of the part to be treated. And this oxygen amount is 10-3 to 2.55 m
2. Process according to claim 1, characterized in that it complies with any of the requirements consisting of being in the range of g/cm2.

(2) partially removing a portion of the natural layer covering the part to be processed, placing the part inside an enclosure, creating a vacuum inside the enclosure for a period of time, and isolating the enclosure from the vacuum system; The amount of oxygen described above was introduced into the enclosure, and the enclosure was heated to 4.
The method according to the preceding item (1), characterized by comprising a continuous step of heating to a temperature in the range of 50 to 880°C.

(3) remove a portion of the native oxide layer, place the component inside the enclosure, heat the enclosure to a temperature above ambient temperature, apply a vacuum for a certain period of time, introduce oxygen, and bring the enclosure to the processing temperature. The preceding paragraph is characterized by consisting of an operating sequence of heating up to
The method described in 1).

(4) Using the method described in the preceding paragraph (1), wherein the outer surface initially containing titanium is coated with a layer consisting essentially of titanium and having a thickness of more than 10 microns after completion of the treatment. formed parts.

(5) The method according to item (1) above, characterized in that the entire amount of oxygen necessary for the treatment is introduced at the start of the treatment.

(6) The preceding item (which is characterized in that the oxygen necessary for the treatment is introduced continuously or in successive batches throughout the heating process)
The method described in 1).

(7) The method according to item (1) above, characterized in that oxygen is introduced in gaseous form in an amount required for the treatment.

(8) The method according to item (1) above, characterized in that the oxygen required for the treatment is introduced into the treatment enclosure through a substance, such as an oxide, that can easily separate oxygen by temperature action.

(9) The method according to item (1) above, wherein the oxygen required for the treatment is provided by degassing an object that has previously absorbed a certain amount of oxygen.

(1O) Item 1), characterized in that the amount of oxygen precisely determined as a function of the area of the part to be treated is accompanied by an auxiliary gas, for example a rare gas in air, such as argon. the method of.

(11) The amount of oxygen per unit area during processing temporarily becomes 0.
The method according to item (1) above, wherein the value is in the range of 11 to 2.55 mg/cm2.

(12) A method according to the preceding paragraph (1), characterized in that the minimum thickness removed from the native oxide layer initially covering the treated part is at least 2 microns.

(13) The processing temperature and processing time of the part are determined from the graph of FIG. Moreover, it corresponds to a point existing inside the shaded area included between the two limit curves 21 and 22 that determines the necessary conditions to be satisfied in order to form a surface layer having a thickness that allows friction without seizing. 3)) The method according to the preceding item (1).

(14) The method according to item (1) above, wherein the treatment temperature is in the range of 500°C to 750°C.

(15) The method according to item (1), wherein the temperature is maintained for 2 to 30 hours.

(16) Parts are cooled slowly inside the enclosure.
That is, the method described in the preceding item (1) is characterized in that the method is carried out only by stopping heating of the enclosure.

(17) The method according to item (1) above, wherein cooling of the processed parts is carried out rapidly inside or outside the enclosure.

(18) The component according to item (4) above, characterized by having a surface layer that is mainly composed of titanium oxide and connected to a lower layer that is mainly composed of titanium via a portion that has a uniform transfer gradient.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of an enclosure implementing the method of the invention, and FIG. 2 shows the thickness of the surface layer as a function of the amount of oxygen introduced per unit area, ε, the coefficient of friction f, and the total hardness. This is a graph showing the law of change of δ, and curves ε, f, and δ match curve C, and Figure 3 is a graph showing the law of change of δ. FIG. 2 is a graph showing processing time as a function of temperature. 1... Enclosure, 2... Parts, 3...
...Resistor, 4...Line, 5...Line, 6...Vacuum system.

Claims (1)

[Claims] 1. For a mechanical part whose outer surface is made of a titanium-containing material,
removing at least a portion of the native oxide layer covering the outer surface of the mechanical part; evacuating the processing atmosphere of the part; was introduced into the processing atmosphere and heated at 450°C to 88°C for a predetermined time to form a titanium oxide layer on the surface of the machine component.
A method for treating mechanical parts, characterized in that the parts are heated at a temperature in the range of 0°C.