ABSTRACT:

The influence of the titanium-to-aluminum proportion on the structure and properties of Ni – 15% Cr–15% Co – 8% (Al + Ti) (Ti/Al = n = 0,3 – 4,0) superalloys is studied. Is showed that high-temperature nickel alloys with Ti / Al = 1…2 can have a satisfactory resistance to high-temperature corrosion (HTC) and high high-temperature mechanical properties.

INTRODUCTION

Aluminum and titanium with nickel form the major ?/ -phase on the Ni 3 (Al, Ti) basis with an face centered cubic (FCC) lattice, which strengthen the nickel superalloys.1 Thus usually, the their effect especially on the mechanical properties was studied simultaneously. It universally recognized, that aluminum (like chromium) increases the resistance to oxidation. However, chromium oxide scales are much more resistant to high-temperature corrosion than are Al 2O 3 scale. 1, 2 Titanium substitutes for aluminum in the ?/ -phase on the Ni 3(Al,Ti) basis, forms the carbides (TiC), which contribute to grain boundary strengthening, and also forms the carbonitrides M(C,N) that embrittle the alloys. Titanium increases the high-temperature corrosion resistance. It is known, that the increase (to a limit) of the summary content of the aluminum and titanium rises the creep resistance of nickel superalloys. However, the effect of the proportion of titanium and aluminum is not accepted obviously or widely. It turned out that the resistance to HTC could be satisfactory at a moderate (13 – 16%) content of chromium. At a high service temperature these alloys become dynamic systems from the physicochemical standpoint. For this reason, the structural changes in them frequently cause worsening of the properties. In particular, excess titanium alloying can lead to the formation of a Ni 3 Ti ?-phase with a flake morphology or to the variation of the rate of the processes of coagulation of the hardening phase.

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