JPH07829B2 - Titanium sliding material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a sliding material, and more specifically, proposes material requirements to be satisfied when titanium (Ti) is used as a sliding material. To do.

[Conventional technology]

Titanium is used as a structural material for various structures, particularly as a structural material for aircraft, by utilizing its high specific strength. Literatures that outline the applications and properties of titanium materials include the Japan Institute of Metals, Vol. 19, No. 7, pp. 220-228, pp. 16, 16
No. 12, 829-834.

As a field in which titanium is industrially used as a material other than the structural material, there is a technology of using TiC, TiN or the like as a coating material for a super hard material or high speed steel. This technique is mainly aimed at coating TiC and the like by the CVD method without impairing the toughness of the superhard material and extending the tool life by the wear resistance of the formed TiC film. Technological improvements in this field have been remarkable, and methods using TiN and Ti (CN), vapor deposition, PVD, ion plating, etc. have been industrialized one after another.

Contrary to the above-mentioned progress of the prior art, the use of titanium as a sliding material has hardly been realized. This point is in contrast to industrial materials such as aluminum, copper, and steel, which are widely used as sliding materials, because they have wear resistance and seizure properties suitable for the mating material by adjusting the composition.

In Japanese Patent Publication No. 50-1686, about 50 at% Ti, the balance Ni is Ti-
An alloy in which a part of Ni in the Ni alloy is replaced with at least one of Fe, Mo, Co, Cr, Ta, Nb, and W is a crankshaft, connecting rod,
It is stated that when it is used for cylinders, liners, clutch plates, valves, seal rings, pump sleeves, etc., it has excellent performance in seizure resistance, wear resistance, conformability and non-aggressiveness against mating materials. There is. In this publication, titanium easily transitions from oxidative wear to melt wear.
It is recognized that the addition of Fe or the like can provide excellent sliding characteristics. The alloys known from the above publication are
It was established based on the technology of improving sliding characteristics by adding a large amount of alloying elements to Ti.

[Problems to be solved by the invention]

The basic properties required of sliding materials are wear resistance, seizure resistance, and low friction. Since these properties are greatly influenced by the mating material and the used member, the mating material and the used member will be specifically described below.

The counterpart material of the piston ring sliding material of an internal combustion engine is a cylinder made of cast iron or aluminum alloy. As is well known, chrome-plated cast iron is mainly used for piston rings. In this technical field as well, there is a strong demand for improvement in the sliding performance of the piston ring with the trend of high-speed engine rotation and high load. The development of sliding materials that are used as mating materials has become a serious issue.

The mating material of the sliding material for the vanes of the rotary compressor is steel or aluminum alloy on the cylinder side. High-Si-aluminum alloys currently exhibit the best sliding properties for vanes that slide against steel cylinders. On the other hand, regarding vanes that slide against an aluminum alloy cylinder, hardened carbon steel or alloy steel presently exhibits the best sliding characteristics. In recent years, aluminum composite materials containing Al ₂ O ₃ fibers have been used in the cylinders of rotary compressors, but the problem of insufficient wear resistance of sliding materials is emerging.

The above combination of the sliding material and the mating material is the best one obtained through many years of technical experience, but if the mating material can be an aluminum alloy and the sliding material can be titanium, the high specific strength characteristics of titanium A lightweight device that takes advantage of In addition, as the weight of the sliding material is reduced, it is possible to expect an effect of suppressing vibration, hammering, and abnormal noise during sliding. Further, if titanium can be used as a substitute for the conventional aluminum sliding material whose counterpart material is steel or cast iron, the weight can be similarly reduced because the titanium has a higher specific strength than aluminum.

However, since pure titanium and titanium alloy have a large amount of wear and seize against the mating material in a short time under a low load, conventional sliding materials cannot be substituted.

[Means for solving problems]

Thus, the present invention is realized by the combination of the following constituents.

Material composition Titanium material with nitrided surface treatment. The nitriding surface treatment refers to heat treatment of the surface of the titanium material in a nitrogen-containing medium. By such treatment, nitrogen penetrates into the surface of the titanium material, and the surface is converted into a nitrogen-containing substance having high hardness. The titanium material refers to a rolled material, a forged material, a cast material, an extruded material, a sintered material, a clad material, or any other solid material whose main component or all components except impurities are titanium.

The material composition was limited as described above, by using Ti as the main component or all components of the titanium material, the advantages of light weight and high specific strength of Ti were utilized, and the surface of the solid material was converted to the nitrogen-containing region. This is to form a strong hard layer and an excellent sliding surface.

As a nitriding surface treatment method, N at atmospheric pressure at a temperature of 900 to 1000 ° C is used.
A method of heating the titanium material in ₂ gases for 30 minutes or more, preferably 10 hours or less can be adopted. Such temperature, pressure and atmospheric gas may be changed appropriately, and in particular, the atmospheric gas is within a range that does not prevent the formation of a desired hard surface layer.
It may contain a gas other than N ₂ . Hard layer thickness is 10 to 10
It is preferably 0 μm, particularly preferably 40 to 70 μm. In addition,
No reduction in strength was observed by heating Ti at the above temperature.

Counterpart material composition Al-Si alloy, fiber reinforced Al alloy and cast iron. The Al-Si alloy is a wear resistant Al alloy containing a large amount of Si, and the general Si content is 13% or more, and the typical Si content is 15 to 20%. This Al alloy may contain second and third additive elements. Fiber reinforced Al alloys are fibers such as Al ₂ O ₃ , SiO ₂ and SiC (yarn form,
It is an Al alloy strengthened by chop form and whisker form. Matrix Al alloy is JIS-H4000, H520
2, the publicly known one described in H5302 and the like. Typical contents of fibers are 3 to 30 vol%, typical contents are 5 to 15 vol%. The structural shape of the mating member is the same as described in the related art, but is not necessarily limited to this. How to configure the sliding structure is not the subject of the present invention and will not be described in more detail. Cast iron refers to gray cast iron, white cast iron, spheroidal graphite cast iron, alloy cast iron, malleable cast iron, etc.

As described above, the reason for limiting the mating material structure is that the sliding characteristics are meaningless unless the mating material is specified, and other than the mating material for which excellent sliding characteristics have been obtained by experiments by the present inventors. This is because I thought it should be outside the invention.

Properties Composition High abrasion resistance and low friction (hereinafter collectively referred to as "sliding property")
That). There was a fate that titanium materials did not have excellent slidability even if a considerable amount of alloying elements were added. However, if Ti is not a main component of titanium material and a large amount of alloying elements are added, good sliding property may be obtained to some extent, but the advantage of Ti cannot be utilized. Since the present invention intends to improve slidability while taking advantage of Ti, slidability is limited as a constitution of the invention. Since the slidability cannot be quantitatively and generally expressed, instead of this expression, if the slidability is described by a method that is generally expressed in comparison with various sliding materials, the slidability of the present invention is described. Is equal to or higher than hardened bearing steel. The point to be noted is that the slidability of the present invention exhibits a much better performance under sliding conditions in which there is little oil and boundary lubrication is performed. This has particularly advantageous results in sliding parts whose oil consumption is being severely limited, such as car cooler compressors and piston rings.

[Action]

The operation of combining the above configurations is as follows.

By combining titanium material with Al-Si alloy or FRM-Al alloy, the weight of rotary compressor etc. can be reduced, and by using titanium material with nitrided surface treatment, it is superior to hardened bearing steel sliding material. Sliding property is also realized. By substituting the titanium alloy for the alloy cast iron sliding material that has been generally used as the counterpart material of cast iron, the weight reduction is achieved and the excellent sliding property is also realized.

〔Example〕

The outline of the experiment performed until the present invention is completed will be described. The properties of various sliding materials were measured under the following conditions.

(1) Testing machine-Pin disk type testing machine (2) Load-15kgf (constant) (3) Lubrication method-Fluid oil (1 volume part) to light oil (9 volume parts) mixed oil: Pad lubrication (4) Opponent material -Al-17% Si-5% Cu-0.5% Mg (T 6 treatment material); gray cast iron (Hv230); Al-based FRM (Al ₂ O ₃ -SiO ₂ fiber 15 volume% and the balance Al-3% Cu-0.5% Mg Al alloy) (5) Test time-60 minutes The test materials and the measurement characteristics are as shown in Tables 1 to 3 below.

The present inventor devised the results shown in Table 1 as follows.

Titanium (without surface treatment) has a high wear coefficient and low wear resistance for Si-containing Al alloys. It is considered that this is because the primary crystal Si particles in the Si-containing Al alloy are hard and the titanium is scraped off.

The properties of nitrided and hardened bearing steels are superior to those of titanium (without surface treatment). In other words, titanium does not have the performance to replace nitrided steel or hardened bearing steel. It is considered that the excellent properties of these steel materials are due to the tendency of the primary crystal Si particles to scrape off the steel material due to their hardness.

Comparing nitriding steel and hardened bearing steel, the latter characteristic is clearly superior.The cause is not only the hardness value of the sliding material but also how the hard part exists in the sliding member. It is believed that there is.

TiC (CVD) coated steel is the material with the highest hardness in the table, and the wear resistance of TiC (CVD) coated steel is one of the highest in the table. The friction coefficient of TiC (CVD) coated steel is between that of nitrided steel and hardened bearing steel. Such TiC (CV
D) The properties of the coated steel can be inferred only for wear resistance due to the magnitude of the tendency of the sliding material surface to be abraded by primary Si particles as described above. However, regarding the friction coefficient, even though the sliding surface hardness is much higher than that of nitrided steel and hardened bearing steel, the result is inferior to these results.
Obtained with C (CVD) coated steel. Therefore, it is considered that the quality of the friction characteristics is influenced by the surface composition of the sliding material. Comprehensively evaluating the above properties, it should be said that CVD-TiC is not attractive enough to be industrially adopted as a substitute for hardened bearing steel.

Next, TiN (PVD) coated steel has one of the lowest friction coefficients, but its wear resistance is between that of nitrided steel and hardened bearing steel. The cause of this is clarified by the above-mentioned invention, and the fact that the surface of the sliding material is TiN realizes the low friction coefficient, and the hardness is 2300 (Hv).
Since it is lower than TiC (CVD), it is considered to be the cause of the appropriate wear resistance.

Finally, the nitrided surface-treated titanium has a balance between low friction and low wear amount, and has a performance that surpasses the hardened bearing steel that is the current material in which these are balanced. The cause of this is also apparent from the above invention. Yui, TiN (PVD) and Ti
When comparing the properties of C (CVD) coated steel and nitrided surface-treated titanium and considering the differences in properties, it is necessary to pay particular attention to the properties of the surface layer (coating). In other words, the nitriding treatment has substantially the same wear resistance as the hardness of CVD-TiC, although the wear resistance is equivalent to that of the base material itself, compared to the case where a hard layer (coating) is formed on the base material. This is explained because the wear resistance is better when the surface is changed to be hard. Also,
Even if TiN is present on the surface, if the nitriding in which the surface of the substrate itself is changed to TiN has better wear resistance than PVD-TiN in which TiN is present on the substrate, Can be explained. Furthermore, it can be said that nitriding is a method that can select only the advantages of PVD-TiN and CVD-TiC.

Table 2 shows the measurement characteristics when the same test material as in Table 1 was used and the mating material was gray cast iron.

The measured characteristics in Table 2 have a difference in absolute value from those in Table 1, but show the same characteristic change as in Table 1 depending on the type of test material. However, it is noteworthy that the wear resistance of titanium nitride surface-treated titanium is the highest among the test materials as a unique tendency due to the fact that the mating material is gray cast iron.

The structure of the counterpart material, gray cast iron, was flake graphite dispersed in pearlite and ferrite matrix, and a small amount of free cementite dispersed in the matrix. Such a structure is characterized in that a large amount of primary crystal Si is dispersed in the matrix, and the proportion of hard particles is relatively small as compared with an Al-Si alloy in which the proportion of hard particles (primary crystal Si) is high. Have

The hardness of the mating material (Hv230) is titanium (no surface treatment).
It is not much different from the hardness (Hv200).

Considering the tendencies shown in Table 2 based on the characteristics of the mating material and the characteristics of hardness, it is as follows.

Titanium is a metal that has a poor compatibility with gray cast iron, which is relatively soft, in terms of sliding characteristics. That is, since the hardness of gray cast iron is macroscopically soft, titanium is abraded by the hard phase although the amount of the hard phase capable of scraping titanium is small.

Table 3 shows the measurement characteristics when the same test material as in Table 1 was used and the counterpart material was Al-based FRM.

The measured characteristics in Table 3 have a difference in absolute value from those in Table 1, but show characteristic changes with a tendency similar to that in Table 1 depending on the type of test material. However, it is noteworthy that the friction coefficient and the amount of wear are the lowest among the test materials as the peculiar effects of the counterpart material being Al-based FRM.

Since the Al-based FRM, which is the mating material, contains a large amount of hard fibers, the nitrided surface-treated titanium shows superior sliding characteristics to the mating material that has many hard phases. It is clear that the difference in sliding characteristics with the material becomes large.

The present inventor confirmed by many experiments other than the above that titanium could not be put to practical use as a sliding material by the PVD method or the CVD method, and selected the titanium nitriding method from other possible means. Is. Some of the tools we have considered
There are sintered materials such as TiN and TiN-TiC. It is considered that these materials are probably due to their low strength, but when they were used as sliding materials, the result was that abrasion resistance was poor. Another means is addition of alloying elements. It is well known that titanium has a tensile strength of 100 kg / mm ² or more when Al, V, etc. are added. However, the properties were not improved at all by the increase in strength accompanying the increase in tensile strength.

Further, using a pin disk type tester, the seizure load was measured under the following test conditions.

Test conditions Peripheral speed −15 m / SEC load −40 kgf gradually increases from 40 kgf to 40 kgf every 20 minutes Lubrication − 1 part by volume of light oil to 9 parts by volume of refrigerator oil Mating material − Al-Si alloy (18% Si-4.5% Cu-0.5% Mg) The results are shown in the table below.

[Advantages of the Invention] The present invention has found material requirements that enable titanium to be used as a sliding material, and thus expands the applications of titanium and realizes slidability superior to that of conventional sliding materials. In order to do so, it largely contributes to the development of industry.

Claims (3)

[Claims] 1. A high wear resistance, characterized in that the mating material is an Al-Si alloy, a fiber reinforced Al alloy or cast iron, and the surface of a titanium material sliding against the mating material is nitrided.
Low friction titanium sliding material. 2. The titanium sliding material according to claim 1, wherein the nitrided surface-treated depth is 10 to 100 μm. 3. The titanium sliding material according to claim 1 or 2, wherein the hardness of the nitrided surface treatment layer is Hv1300 to 2500.