Friction stir tool

Abstract

A friction stir tool excellent in productivity, high temperature strength, and wear resistance at high temperatures. The friction stir tool is formed of a Co-based alloy comprising crystal grains containing a γ′ precipitate phase dispersed and precipitated therein, and a crystal grain boundary region and a precipitate phase between adjacent crystal grains, in which the precipitate phase is at least one phase selected from a μ phase, a Laves phase and a carbide phase.

What is claimed is: 
     
         1 . A friction stir tool formed of a Co-based alloy having a γ phase with an A1 structure and a γ′ phase with an L1 2  structure precipitated in the γ phase, the γ′ phase comprising (Co, X) 3 (Al, W, Z), and the γ′ phase being contained in the γ phase in an amount of 10% to 80% in terms of volume fraction, the Co-based alloy including 30-50 at. % of Ni, and the γ′ phase thereof having a solid solution forming temperature higher than 1,000° C., wherein the Co-based alloy contains a precipitate selected from a μ phase, a Laves phase and a carbide, where X includes mainly Ni, and Z includes mainly Cr and Ta. 
     
     
         2 . The friction stir tool according to  claim 1 , being formed by precision casting. 
     
     
         3 . The friction stir tool according to  claim 1 , wherein the Co-based alloy contains Co in an amount of 25 at. % or more. 
     
     
         4 . The friction stir tool according to  claim 1 , comprising a cylindrical shank, a shoulder formed in an end portion of the shank, and a pin formed in an end portion of the shoulder. 
     
     
         5 . The friction stir tool according to  claim 4 , being an integrally formed article of the Co-based alloy produced by the precision casting. 
     
     
         6 . The friction stir tool according to  claim 5 , being a machined product of the Co-based alloy made of the integrally formed article. 
     
     
         7 . A friction stir welding apparatus comprising the friction stir tool according to  claim 1 . 
     
     
         8 . The friction stir tool according to  claim 1 , wherein the Co-based alloy includes about 10 at. % of Al, about 7.5 at. % of W, about 3 at. % of Ta, about 10 at. % of Cr, about 0.06 at. % of B, about 0.6 at. % of C, and at least 25 at. % of Co. 
     
     
         9 . The friction stir tool according to  claim 1 , having a property of being capable of joining, by friction stir welding, high-melting point materials selected from the group consisting of steel materials, titanium and alloys thereof, and zirconium and alloys thereof. 
     
     
         10 . The friction stir tool according to  claim 1 , being heat-treated and air-cooled after the precision casting. 
     
     
         11 . The friction stir tool according to  claim 1 , wherein the cobalt-based alloy contains precipitates that include each of the μ phase, the Laves phase and the carbide.