Surface-treated titanium material excellent in oxidation resistance, production method thereof, and engine exhaust system

Abstract

Disclosed are a surface-treated titanium material that is excellent in oxidation resistance and allows the excellent oxidation resistance to last for a long period of time and the surface treatment itself to be applied safely at a low cost; the production method thereof; and an exhaust system thereof. A surface-treated titanium material produced by forming an oxidation-resistant baked film 5 μm or more in thickness on a substrate comprising commercially pure titanium or titanium-base alloy, and said baked film is formed by filling the gaps among particles comprising Al alloy containing Si by 10 at % or less or commercially pure aluminum with chemical compounds comprising a metallic element M (M represents one or more of Ti, Zr, Cr, Si and Al) and C and / or O.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to: a surface-treated titanium material that is excellent in oxidation resistance and thus used for a part such as an engine exhaust system requiring oxidation resistance; the production method thereof; and an exhaust system thereof. [0003] 2. Description of the Prior Art [0004] Titanium alloy has a higher specific strength in comparison with a generally used steel material and is increasingly applied to the field of transport vehicles, mostly automobiles, which are intensively directed to weight reduction. In the field, as a material for an exhaust pipe in an exhaust system around an engine, stainless steel is mainly used at present but the application of titanium to an exhaust system has been studied with the aim of weight reduction. The temperature of an exhaust system however rises up to 500° C. or higher at some sites. Hence, when a titanium alloy material which is not surface-trea...

AI Technical Summary

Benefits of technology

[0010] The present invention has been established in view of the above situation and the object thereof is to provide: a surface-treated titanium material that is excellent in oxidation resistance and allows the excellent oxidation resistance to last for a long period of time and the surface treatment itself to be applied safely at a low cost; the production method thereof; and an exhaust system thereof.

[0015] For that purpose, the present invention uses, as a sealer, a substance which, after baked, forms chemical compounds comprising a metallic element M (M represents one or more of Ti, Zr, Cr, Si and Al) and C and / or O. When the chemical compounds comprising the metallic element M and C and / or O exist among the heretofore known particles of commercially pure aluminum type or Al—Si alloy containing Si by 10 at % or less in the baked film, the high temperature oxidation resistance of the baked film improves remarkably.

[0016] In addition, the chemical compounds comprising a metallic element M and C and / or O also play the role of the binder of Al powder and thus improve the adhesiveness among Al particles in the baked film or between the baked film and the surface of a titanium material. Here, the coating of the surface of a titanium material with organometallic compounds comprising a metallic element M (M represents one or more of Ti, Zr, Cr, Si and Al) and C and / or b as the raw materials of the chemical compounds can be applied at the same time as the coating thereof with Al powder and is simple and easy to apply as indicated in the gist of the production method of a surface-treated titanium material according to the present invention. Furthermore, the chemical compounds are not poisonous unlike the chromic acid that has heretofore been used and assure safety not only in the surface treatment process but also in the application to a member.

Problems solved by technology

Hence, when a titanium alloy material which is not surface-treated is applied, oxidation progresses fast, the oxidation resistance is inferior at a high temperature, and that causes the problem of durability.

However, the problems of those proposals are that: the cladding method yields a high cost; and, in the cases of the vapor deposition method and the PVD method, not only the treatment cost is high but also, when a titanium material has a tubular shape like such an exhaust pipe as described above, an oxidation-resistant film can hardly be formed on the inner surface of the pipe.

However, gaps are inevitably formed among the Al particles after baking.

To that end, it is necessary to introduce the process of using an inorganic binder to deposit Al powder on a titanium substrate and moreover the process of using chromic acid to fill the gaps formed among Al particles after baked, namely two-step treatment is required, and thus it is not efficient.

Further, the chromic acid solution only described as the inorganic binder is extremely poisonous and hence the safety of not only the treatment processes but also the usage as a member is concerned.