Ni-based single crystal super alloy

Abstract

The object of the present invention is to provide an Ni-based single crystal super alloy capable of improving strength by preventing precipitation of a TCP phase at high temperatures. This object is achieved by an Ni-based single crystal super alloy having a composition consisting of 5.0-7.0 wt % Al, 4.0-8.0 wt % Ta, 2.9-4.5 wt % Mo, 4.0-8.0 wt % W, 3.0-6.0 wt % Re, 0.01-0.50 wt % Hf, 2.0-5.0 wt % Cr, 0.1-15.0 wt % Co and 1.0-4.0 wt % Ru in terms of its weight ratio, with the remainder consisting of Ni and unavoidable impurities.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a Ni-based single crystal super alloy, and more particularly, to a technology employed for improving the creep characteristics of Ni-based single crystal super alloy.[0003] 2. Description of the Related Art[0004] An example of the typical composition of Ni-based single crystal super alloy developed for use as a material for moving and stationary blades subject to high temperatures such as those in aircraft and gas turbines is shown in Table 1.1TABLE 1 Alloy Elements (wt %) name Al Ti Ta Nb Mo W Re C Zr Hf Cr Co Ru Ni CMSX-2 6.0 1.0 6.0 -- 1.0 8.0 -- -- -- -- 8.0 5.0 -- Rem CMSX-4 5.6 1.0 6.5 -- 0.6 6.0 3.0 -- -- -- 6.5 9.0 -- Rem Rene'N6 6.0 -- 7.0 0.3 1.0 6.0 5.0 -- --0.2 4.0 13.0 -- Rem CMSX-10K 5.7 0.3 8.4 0.1 0.4 5.5 6.3 -- --0.03 2.3 3.3 -- Rem 3B 5.7 0.5 8.0 -- -- 5.5 6.0 0.05 -- 0.15 5.0 12.5 3.0 Rem[0005] In the above-mentioned Ni-based single crystal super alloys, after performing solution treatment at ...

AI Technical Summary

Benefits of technology

[0015] According to the above Ni-based single crystal super alloy, precipitation of the TCP phase, which causes a decrease in creep strength, during use at high temperatures is inhibited by the addition of Ru. In addition, by setting the composite ratios of other composite elements within their optimum ranges, the lattice constant of the matrix (.gamma. phase) and the lattice constant of the precipitation phase (.gamma.' phase) can be made to have optimum values. Consequently, strength at high temperatures can be enhanced.

[0039] According to the above Ni-based super crystal super alloy, precipitation of the TCP phase, which causes decreased creep strength, during use at high temperatures is inhibited by addition of Ru. In addition, by setting the composite ratios of other composite elements to their optimum ranges, the lattice constant of the matrix (y phase) and the lattice constant of the precipitation phase (.gamma.' phase) can be made to have optimum values. As a result, creep strength at high temperatures can be improved.

Problems solved by technology

Although the above-mentioned CMSX-2, which is a first-generation alloy, and CMSX-4, which is a second-generation alloy, have comparable creep strength at low temperatures, since a large amount of the eutectic .gamma.' phase remains following high-temperature solution treatment, their creep strength is inferior to third-generation alloys.

In addition, although the third-generation alloys of Rene'N6 and CMSX-10 are alloys designed to have improved creep strength at high temperatures in comparison with second-generation alloys, since the composite ratio of Re (5 wt % or more) exceeds the amount of Re that dissolves into the matrix (y phase), the excess Re compounds with other elements and as a result, a so-called TCP (topologically close packed) phase precipitates at high temperatures causing the an problem of decreased creep strength.

However, since the lattice constant of each phase fluctuates greatly fluctuated according to the composite ratios of the composite elements of the alloy, it is difficult to make fine adjustments in the lattice constant and as a result, there is the problem of considerable difficulty in improving creep strength.

If the composite ratio of Cr is less than 2.0 wt %, the desired high-temperature corrosion resistance cannot be secured, thereby making this undesirable.

If the composite ratio of Cr exceeds 5.0 wt %, in addition to precipitation of the .gamma.' phase being inhibited, harmful phases such as a C phase or .mu. phase form that cause a decrease in strength at high temperatures, thereby making this undesirable.

If the composite ratio of Mo is less than 1.0 wt %, strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of Mo exceeds 4.5 wt %, strength at high temperatures decreases, and corrosion resistance at high temperatures also decreases, thereby making this undesirable.

If the composite ratio of W is less than 4.0 wt %, strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of W exceeds 8.0 wt %, high-temperature corrosion resistance decreases, thereby making this undesirable.

If the composite ratio of Ta is less than 4.0 wt %, strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of Ta exceeds 8.0 wt %, the .sigma. phase and .mu. phase form that cause a decrease in strength at high temperatures, thereby making this undesirable.

If the composite ratio of Al is less than 5.0 wt %, the precipitated amount of the .gamma.' phase becomes insufficient, and strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of Al exceeds 7.0 wt %, a large amount of a coarse .gamma. phase referred to as the eutectic .gamma.' phase is formed, and this eutectic .gamma.' phase prevents solution treatment and makes it impossible to maintain strength at high temperatures at a high level, thereby making this undesirab

If the composite ratio of Hf is less than 0.01 wt %, the precipitated amount of the .gamma.' phase becomes insufficient and strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of Hf exceeds 0.50 wt %, local melting is induced which results in the risk of decreased strength at high temperatures, thereby making this undesirable.

If the composite ratio of Co is less than 0.1 wt %, the precipitated amount of the .gamma.' phase becomes insufficient and the strength at high temperatures cannot be maintained, thereby making this undesirable.

If the composite ratio of Co exceeds 15.0 wt %, the balance with other elements such as AL, Ta, Mo, W, Hf and Cr is disturbed resulting in the precipitation of harmful phases that cause a decrease in strength at high temperatures, thereby making this undesirable.

On the other hand, if a large amount of Re is added, the harmful TCP phase precipitates at high temperatures, resulting in the risk of decreased strength at high temperatures.

If the composite ratio of Re is less than 3.0 wt %, solution strengthening of the .gamma. phase becomes insufficient and strength at high temperatures cannot be maintained at the desired level, thereby making this undesirable.

If the composite ratio of Re exceeds 6.0 wt %, the TCP phase precipitates at high temperatures and strength at high temperatures cannot be maintained at a high level, thereby making this undesirable.

If the composite ratio of Ru is less than 1.0 wt %, the TCP phase precipitates at high temperatures and strength at high temperatures cannot be maintained at a high level, thereby making this undesirable.

If the composite ratio of Ru exceeds 4.0 wt %, the cost increases which is also undesirable.

As a result, a TCP phase was unable to be confirmed in the structure.