JPH01119682A - Pure titanium for titanium alloy member - Google Patents

Abstract

PURPOSE:To form a cured layer having excellent wear resistance by forming engine parts for automobiles of Ti or Ti alloy and heating the surface to the melting temp. or above in an oxidative atmosphere to absorb and solutionize the Ti in O2. CONSTITUTION:The valve or connecting rod or the like of an engine for automobiles is made of the Ti or Ti alloy. A gaseous mixture composed of oxidative gas such as O2 or CO2 and inert gas for dilution such as Ar of He is supplied from a nozzle 6 to a part 1 where wear resistance is required while an arc 5 is generated between a W electrode 3 as a positive electrode and the Ti part 1 as a negative electrode by using a TIG device which has internally the W electrode 3 and is formed wit the gas nozzle 6 on the outside thereof and by impressing voltage to the above-mentioned two electrodes. The Ti part 1 is partly melted by the arc 5 by which the molten part 1a is formed. The O2 is absorbed and solutionized therein. This molten part is solidified by cooling, by which the relatively thick O2-solutionized layer having the high hardness and excellent wear resistance is formed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to surface-hardened pure titanium or titanium alloy members, particularly valves and connections made of pure titanium or titanium alloy that constitute automobile engine parts. It relates to rods etc. that have been subjected to surface hardening treatment.

(Conventional technology) Pure titanium and titanium alloys are used for various mechanical parts, structural parts, etc. because they are lightweight, have high strength, and have good corrosion resistance. However, on the other hand, they have inferior wear resistance compared to steel. There is a drawback. Therefore, the advantages of titanium or titanium alloys, such as light weight, high strength, and good corrosion resistance, are utilized by surface hardening using various surface hardening treatment methods described below.

In the gas nitriding method, a hardened layer made of TiN is formed on the outermost layer by heating and holding at 800° C. or higher for several hours to several tens of hours in a nitrogen gas or ammonia gas atmosphere. In the TiN ion blating method, cationized particles are deposited on Ti placed on a cathode to form a hardened layer made of TiN. The chrome plating method is a method in which Cr is electrolytically deposited on Ti in a Sargent bath to form a stable passive film made of Cr on the surface layer of Ti. The thermal spraying method uses Ti droplets of WC or ceramics that have been molten or semi-molten by plasma heat, arc heat, etc.
It is sprayed onto the surface to form a coating of WC, ceramics, etc. on the Ti surface.

(Problems to be Solved by the Invention) However, the conventional surface hardening treatment method described above has the following drawbacks.

That is, according to the gas nitriding method, the hardened layer made of TiN is a thin layer of several micrometers, and thermal deformation of the material occurs due to high temperature heating. Furthermore, according to the TiN ion blating method, the TiN layer becomes thin with a thickness of about 1 to 3 μm,
If an attempt is made to make this a thick film, there is a drawback that the TiN layer is likely to peel off. Furthermore, the chrome plating method has the disadvantage that pretreatment before plating is difficult, and after plating, the adhesion of the plating film is insufficient and it is easy to peel off. Furthermore, according to the thermal spraying method, the coating to be treated is rapidly cooled, so there is a drawback that the coating is easily damaged or peeled off.

The present invention was conceived in view of these problems, and it is an object of the present invention to provide a pure titanium or titanium alloy member that has a relatively thick surface hardened layer and has been subjected to surface hardening treatment without the risk of the hardened layer peeling off. purpose.

(Means for Solving the Problems) For this purpose, in the pure titanium or titanium alloy member of the present invention, the surface layer of pure titanium or titanium alloy is heated to a temperature higher than the melting temperature in an inert gas atmosphere containing oxygen or an oxygen compound. It is characterized in that it is heated to a temperature of 100%, and oxygen is absorbed and dissolved in the molten part to form a hardened surface layer.

In an embodiment of the present invention, the hardened surface layer is formed on the metal surface layer of a member made of pure titanium or a titanium alloy, such as an engine valve. in this case.

The surface hardening layer may be formed on each metal surface layer of the face, shaft, or shaft end of the engine valve.

Furthermore, the surface hardening layer may be formed on the large end and small end of the connecting rod made of a titanium alloy of the engine.

(Effects of the Invention) According to the present invention, a hardened layer is formed by once melting the surface layer of a pure titanium or titanium alloy member and absorbing oxygen into the melted surface layer to form a solid solution, thereby forming a relatively thick hardened layer. Moreover, there is no fear that this cured layer will peel off, and there is an effect that a surface cured layer with good adhesion can be formed.

(Example) Examples of the present invention will be described.

First, the surface of a pure titanium or titanium alloy member was heated above its melting temperature in an inert gas atmosphere containing oxygen or an oxygen compound to absorb oxygen, and then cooled to room temperature.

Table 1 shows test examples, in which pure titanium or titanium alloy members of various compositions were subjected to arc heating, plasma heating, burner heating, or laser heating in a gas atmosphere containing a predetermined oxygen element. The shape of the target material was a flat plate with a height of 8 mm, a width of 25 mm, and a length of 50 mm.

As for the test pieces in Table 1, as shown in Test No. 1 to 7, pure T
i and Ti-6, two typical types of Ti alloys (α+β) two-phase type
Aβ-4■ and β-phase Ti-13V-1lC
r-3AI2. was used. As shown in Table 1, the inert gas atmosphere consists of 02 or CO2 gas and Ar or He gas.
A solution diluted with gas to a predetermined volume of 1% was used. Exam No.
, 1 to 6 show test examples of the present invention, and test No. 007 shows a comparative example to be compared with the present invention. That is, in the comparative example, the inert gas atmosphere is an Ar gas atmosphere that does not contain oxygen or oxygen compounds.

FIG. 1 is a schematic diagram showing an example of a melting processing apparatus using the TIG method as an arc heating method.

In FIG. 1, 1 is an object made of pure titanium or a titanium alloy on which a hardened surface layer is to be formed, and 2 is a melting treatment device. A voltage is applied to the tungsten electrode 3 via the conductor 4, and the tungsten electrode 3 becomes, for example, a positive pole, and the object l becomes a negative pole, and the gap between the tip of the tungsten electrode 3 and the object l is arc 5
appears to be flying. At this time, an inert gas containing oxygen or an oxygen compound flows inside the gas nozzle 6 in the direction of the arrow shown in the figure, and a predetermined atmosphere is maintained in which oxygen comes into contact with the melted portion 1a of the object 1.

The melted part 1a of the object 1 contains 0,
Alternatively, upon contact with CO2 gas, the oxygen element penetrates into this molten titanium or titanium alloy, and the oxygen element becomes a solid solution in the titanium alloy as an interstitial element. As a result, when the molten part is cooled, a hardened layer containing a high concentration of oxygen as a solid solution is formed in this part.

For test Nos. 1 to 7 in which the surface hardened layers were formed in this way, the hardness of the hardened layers was tested. The graph shown in FIG. 2 shows the hardness test results. The horizontal axis represents the distance from the metal surface, and the vertical axis represents the Vickers hardness. As is clear from the graph shown in Figure 2, in Test No. 7 as a comparative example, a hardened layer was not formed on the surface layer because there was no oxygen element in the melting atmosphere even though the test piece was once melted. Therefore, the hardness of the surface layer after cooling remains almost constant regardless of the distance from the metal surface.

On the other hand, in Test Nos. 1 to 6, approximately 1
．． It can be seen that the hardness is increased within a range of 5 mm. In test No. 006, the hardness was significantly improved within 1.2 mm from the metal surface, but this was due to the high oxygen concentration in the molten gas atmosphere, and the relative concentration of oxygen that entered the surface layer during melting. This is thought to be due to the fact that it is higher than those of other test Nos.

Next, an example will be described in which the above hardened surface layer is formed on an engine valve made of a titanium alloy constituting an engine part for an automobile.

FIG. 3 shows a schematic diagram of an engine valve to be subjected to surface hardening treatment. In the figure, 7 is the valve body, 8 is the face that comes into contact with the intake and exhaust boat of the engine,
Reference numeral 9 indicates a shaft portion to which the valve body 7 is slidably guided when it reciprocates, and reference numeral 10 indicates a shaft end portion to which a driving force for opening and closing the valve is transmitted.

The material of the valve body 7 was T1-6AI2-4V. The areas on which the surface hardening layer was formed are the face, the shaft, and the shaft end. A hardened surface layer was formed on each of these parts under the treatment conditions shown in Table 2, and the hardness and depth of the hardened surface layer were measured. The depth of the hardened layer was determined to have a Vickers hardness Hv of 400 or more. The results are shown in Table 2.

Table 2 In this example, Ti-6Aj2- is used as the material of the valve.
4V was used, but in the present invention, other titanium alloys such as Ti-6Aj2-23n-42r-2Mo-0, IS
i etc. can also be used. Furthermore, although the surface hardening layer was formed at three locations, namely the face surface, the shaft portion, and the shaft end portion of the valve, the surface hardening layer may be formed at one or two of these locations depending on the case.

In general, engines installed in racing cars use titanium alloy valves instead of conventional heat-resistant steel valves to reduce the weight of the valve body and improve engine output. Often, in this case,
For example, the face of the valve is not hardened, but the shaft is treated with Mo spraying, C plating, etc., and the shaft end is brazed with stellite chips or friction welded with carburized case hardened steel. However, with these hardening methods, for example, the cost of MO raw materials is high in Mo thermal spraying, and the adhesion of the plating part is poor in Cr plating, and furthermore, it is difficult to braze Stellite chips and to reduce the friction of case hardened steel carburized materials. The pressure welding method has a problem in that the processing process is complicated.

On the other hand, according to the present invention, there are no major problems and the surface layer of the titanium alloy can be heated to high temperatures by simply melting the surface of the titanium alloy in an inert gas atmosphere containing oxygen or oxygen compounds. A hard Ti oxide or the like is formed to form a hardened layer with no fear of peeling. Therefore, the surface hardening treatment has the advantage of being low cost and having simple processing steps. If the present invention is applied to engine valves, connecting rods, etc., it is possible to provide a titanium alloy engine that is cheaper than conventional surface treatments and that can be practically mass-produced.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a melting processing apparatus using the TIG method according to an embodiment of the present invention, Figure 2 is a graph showing the relationship between the distance from the metal surface and hardness, and Figure 3 is a diagram showing the relationship between the hardness and the distance from the metal surface. It is a schematic block diagram. ! ...Target, la... Melting part, 2... Melting processing device, 3... Tungsten electrode, 6... Gas nozzle, 7... Valve body, 8... Face surface, 9... ...Shaft part, 10...Shaft end part.

Claims (4)

[Claims] (1) The surface layer of pure titanium or titanium alloy is heated above the melting temperature in an inert gas atmosphere containing oxygen or oxygen compounds, and oxygen is absorbed and dissolved in the molten part to form a hardened surface layer. A pure titanium or titanium alloy member characterized by: (2) The pure titanium or titanium alloy member according to claim 1, wherein the hardened surface layer is formed on an engine valve. (3) The hardened surface layer is applied to the face surface of the engine valve,
The pure titanium or titanium alloy member according to claim 1, characterized in that it is formed at at least one of the shaft portion or the shaft end portion. (4) The pure titanium or titanium alloy member according to claim 1, wherein the surface hardening layer is formed on a large end portion and a small end portion of a connecting rod of an engine.