Microstructure of modified Inconel 706 superalloys-3 dimensional atom-probe and HRTEM investigations
The Ni-base superalloy Inconel 706 was initially developed for gas-turbine components in the aeroengine. However, it has been successively adopted to substitute steels in larger forged parts of stationary gas turbines. Several challenging requirements are in fact introduced, outpacing significantly the aeroengine needs. In particular, two aspects are of importance: the capability of manufacturing very large forgings (up to 50 tons) and an exceptional long term stability of the microstructure in the temperature range of 700 ℃, to ensure stable mechanical performance over the entire operating life of the power plant (～ 200,000h). Among the commercial wrought nickel-iron-base superalloys, Inconel 706 stands out for this application because it combines high mechanical strength with good fabricability and machinability. These properties directly relate to the precipitation hardening system of alloy 706, which provides the desirable characteristic of delaying the hardening response during exposure to precipitation temperatures. The austenitic Ni-Fe-Cr matrix of Inconel 706 is mainly strengthened by the precipitation of two kinds of coherent A3B-type compounds: the tetragonal Ni3Nb γ phase and the cubic Ni3Al,Ti γ phase. The major source of strengthening in Inconel 706 is γ, resulting from coherency strain and caused by a relatively large lattice misfit between the tetragonal cell of γ and the cubic cell of the γ matrix. Further, precipitation of intergranular Ni3Ti η platelets can occur under some heat treatment conditions. The η precipitation stabilizes the grain boundaries against environmental embrittlement and enhances the creep crack growth resistance of Inconel 706 up to three orders of magnitude compared to the unstabilized material.
N. Wanderka V. Kindrachuk
Hahn-Meitner-Institut Berlin, Glienicker Str. 100, D-14109 Berlin, Germany
国际会议
桂林
英文
149-150
2006-07-17（万方平台首次上网日期，不代表论文的发表时间）