JPH02277762A - Surface hardening method for titanium or titanium alloy - Google Patents

Abstract

PURPOSE:To provide a hardened layer having sufficient hardness with high adhesive strength by carrying out hard facing by the use of a hard facing material selected from a mixture consisting of Ni or Ni alloy and Ti or Ti alloy and an Ni-containing Ti alloy so that this hard facing material is mixed with a base material. CONSTITUTION:A hard facing material 2 selected from a mixture of Ni or Ni alloy and Ti or Ti alloy and an Ni-containing Ti alloy is fused in the surface of a base material 1 consisting of Ti or Ti alloy so that the hard facing material 1 is mixed with the base material to carry out hard facing. The above hard fasing is performed under the atmosphere containing oxygen and nitrogen, and hardening caused by the entering into solid solution of the above gas components is simultaneously exerted. The resulting product is applicable to valve face made of Ti alloy. By this method, lightweight parts having required wear resistance can be provided.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for surface hardening mechanical parts made of titanium or titanium alloys.

[Conventional technology]

For example, in order to impart wear resistance to the faces of valves in internal combustion engines, it has been conventional practice to weld and harden Co alloys such as "Stellite" for domestic use. On the other hand, in recent years, as engines have improved in performance, attempts have been made to reduce the weight of valves by using Ti alloys. However, even when a commonly used Co alloy is made thicker than a Ti or T1 alloy, it tends to crack and peel from the interface between the base material and the built-up metal layer, resulting in a lack of durability and reliability. Ta. Other surface hardening techniques for Ti and Ti alloys include nitriding. In this method, parts made of Ti or T1 alloy are heated to high temperatures in an N2 gas atmosphere to form a TiN phase on the surface layer and harden the parts. However, the difficulty of the nitriding method is that the thickness of the hardened layer that can be formed is extremely large, several micrometers, and when this hardened layer is worn away or peeled off, the wear resistance is lost all at once. The applicant has conducted research with the aim of breaking through the current state of technology, and has developed a base metal of Ti or T1 alloy with Co (or Go alloy) and Ti (or T1 alloy) as overlay materials. Establish a technique for effectively surface hardening by using a mixture of or using a Co-containing Ti alloy and melting it so that the base material and the overlay material are mixed, Already proposed (Patent Application Hei 1-
29258). As a result of extensive research, the above method was confirmed to be effective when Ni (or Ni alloy) and Ti (or T1
It has been found that the present invention can also be applied to a mixture with a Ti alloy containing Ni or a Ti alloy containing Ni, giving good results. rProblem to be Solved by the Invention 1 The purpose of the present invention is to utilize the above-mentioned new findings to provide a hardened overlay layer with sufficient thickness and high adhesion on the surface of a mechanical component made of T1 or Ji gold alloy. The object of the present invention is to provide a surface hardening method for forming a durable wear-resistant surface. [Means for Solving the Problems] The method for surface hardening titanium or titanium alloy of the present invention has T1
Or, on the surface of a base material made of T1 alloy, a) a mixture of Nr or Ni alloy and Ti or Ti alloy, or b) a filler material selected from Ti alloy containing Ni is mixed with the base material. It consists of melting and hardening overlay so that The Ti alloy to which the present invention can be applied has Ti-
Typical products such as 6Afl-4V include Ti as the main component and a relatively small amount of alloying components are added to it. It also includes those to which relatively large amounts of alloy components are added. Also, Ti -13V -11Cr-3
Alloys such as AJ2, Ti-5A, and ff-2,5Sn are also targets. The Ti or Ti alloy mixed with Ni or Ni alloy and used for overlay is preferably the same type as the base material, but even if the base material is a Ti alloy, pure T1 may be used; There is no problem even if it is a Ti alloy different from the material. Conventional commercially available N1 alloys can be conveniently used as the material for the overlay. For example, “Hastelloy Cl (Ni
-16Mo-15Cr -5Fe -4W>, [Inconel 625J (Ni -21Cr-9MO-4N
Materials such as b> are available in powder and bar form. N
Although Ti alloy containing i is not found on the market, it may be alloyed with T1 or Ti alloy so that Ni accounts for 10 to 50% by weight, and prepared in the form of powder or rod. Ni (or Ni alloy) and Ti (
Similarly to the composition of the T1 alloy containing Ni, the composition of the mixture with the T1 alloy (or T1 alloy) may be selected so that Ni is in the range of 10 to 50%. Melting must be accomplished by supplying sufficient heat so that mixing of the overlay material and base material occurs. For this purpose, means such as plasma arc welding and TIG welding are suitable. For the melting atmosphere, it is easy to work if an inert gas such as Ar is used, but CO2, 02
It is also advantageous to use an atmosphere containing a controlled amount of ,N2. [Function 1 When overlaying a CO alloy on the surface of a 1i or Ti-based alloy, the adhesion of the overlay metal layer is not good because a layer of intermetallic compounds T1Co and Ti2CO is formed at the interface. This was discovered during the process of Zaki's invention. Although such an intermetallic compound is hard in itself, it is brittle, so when it is formed in a layer, it is easily peeled off from the layer. According to the invention, as seen in FIG.
Ni (or Ni alloy) and Ti are added to the base material (1) of the alloy.
(or T1 alloy), the molten gold B (3) is more compatible with the base material due to the presence of the Ti component than when simply welding the Go alloy. Furthermore, since this melting is carried out in such a way that the base metal and the refinished material are mixed, the content of the Ti component is high in the portion of the molten metal that is close to the base metal. If this is shown schematically, it will look like the graph in Figure 2. In other words, when using conventional build-up welding using Stellite as the build-up material, the hardness distribution from the surface to the inside is as shown by the thin line, where the hardness of Stellite itself is maintained from the surface to a certain depth; There, the hardness increases rapidly and then suddenly decreases to the hardness of the base material. This rapid increase in hardness is due to the above-mentioned intermetallic compounds TiCo, T
This is due to the production of + 2 Co. In contrast, according to the present invention, for example, Hastelloy has T
When a mixture of two alloys is used, as shown by the thick line in Figure 2, the hardness is maintained over a considerable thickness and then the distribution decreases continuously from the molten part toward the base metal. I'll show you. Since a brittle layer is not formed between the built-up metal layer and the base metal, there is no need to worry about peeling. Of course, even in this case,
Although T1Ni and Ti 2 Ni are generated, T in the melted zone
Due to the high concentration of the i component, these intermetallic compounds do not exist in a layered form, but exist in a finely dispersed form in the molten metal layer, which helps to improve its hardness. As can be easily understood, the higher the hard alloy mainly composed of Ni, the higher the wear resistance of the built-up hardened layer, while the higher the proportion of T1 or Ti alloy The adhesion with the material becomes even better. The thickness of the molten metal layer (3) can be varied within a fairly wide range by adjusting the amount of filler material (2) used and the amount of heat given to the welded area, and can be made considerably thicker if desired. Therefore, even if the surface is polished after overlay welding and scraped off to the position shown by the broken line in FIG. 1, a sufficient hardened layer can still remain. [Example 1] Using a Ti or Ti alloy flat plate as the base material, Ni (or Ni alloy) and Ti (
The hardness of the hardened surface and the thickness of the built-up part are shown in the table. The contents are as follows. The weight percentage in parentheses is A-1: Hastelloy C.
Powder (15) + Ti-6Af! -4V powder (85) A-2 = Hastelloy powder (25) + Ti -6Aj-4V powder (75) B: Inconel 625 powder (25) + Ti -6Al-4V powder (75) C: Ni powder (15) 10Ti-6A, l! -4V powder (85) D: Ni powder (
150) + Ti powder (85) E: Ni rod (diameter 2 m) 10 Ti rod (diameter 3.5 Jlll) F: Ti -6Aj-4V-1ONi powder For comparison,
The surface hardness of pure T1 and T1 alloy without surface hardening treatment, and the surface hardness and hardened layer thickness of gas nitrided Ti alloy are listed in the table. [Example 2] A mixture of the same Ti alloy powder and Ni or Ni alloy powder was overlay welded onto the face of an engine valve made of T:-6AfJ-4V alloy using a plasma arc. The graph in FIG. 3 shows the relationship between the hardness of the surface after finishing the face and the composition of the overlay material.
The composition and atmosphere of the overlay material are as shown in the graph.

【Effect of the invention】

By performing overlay hardening by the method of the present invention, a sufficiently thick hardened layer with high adhesion can be provided on the surface of the Ti or Ti alloy base material. Therefore, the surface hardening method of the present invention is useful for manufacturing parts that are required to be lightweight and wear resistant, such as internal combustion engine valves, rocker arms, connecting rods, or piston pins.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a base material and build-up weld metal showing surface hardening performed by the method of the present invention. FIG. 2 is a graph schematically showing differences in hardness depending on surface hardening materials. FIG. 3 is a graph showing the relationship between the composition of the build-up material and the hardness of the build-up part in an example of the present invention. 1... Base material 2... Welding material 3... Weld metal patent applicant Daido Steel Co., Ltd. agent Patent attorney Souo Suga Figure 3 Section 1 Korekin Se (Kurat%)

Claims (3)

[Claims] (1) On the surface of the base material made of Ti or Ti alloy, a fill-up material selected from a) a mixture of Ni or Ni alloy and Ti or Ti alloy, or b) Ti alloy containing Ni is applied to the base material. A method for surface hardening Ti or Ti alloys, which consists of melting and overlay hardening so that mixing occurs. (2) The surface hardening method according to claim 1, which is carried out in an atmosphere containing oxygen and/or nitrogen, and hardening is also carried out by solid solution of these gas components. (3) The surface hardening method according to claim 1 or 2, which is applied to a Ti alloy valve face.