DE3234264C2 - - Google Patents

Description

The development of modern gas turbine jet engines aims at ever higher working temperatures to the Improve efficiency and harmful Engine emissions as low as possible. These Demand in turn requires the development of Gußwerkstücken, these temperatures at high withstand mechanical stresses for a sufficiently long time can. So one uses for mechanically highly stressed Parts that are exposed to the highest temperatures in particular for the nozzle guide vanes and the Turbine Rotor Blades Single crystal castings made of Nickel superalloys are made. So led the developed by the patentee Einkristallgußstücken, as described in FR-PS 24 78 128 are described. For the single crystal castings will be here a nickel alloy that is relatively broad Salary ranges are defined as follows:

Chrome | 7-13% cobalt 2-15% titanium 0-2.5% aluminum 4.5 to 6.7% tungsten 7-12% niobium 0-1% molybdenum 0-1% tantalum 1.5-5% hafnium 0-2% carbon 0.015-0.05% boron 0-0.01% zirconium 0-0.05%.

It is known that the properties of Superalloys of this kind by heat treatment can be improved. For this purpose, in the FR-PS 24 78 128 a solution annealing at 1300 to 1320 ° C. suggested during one hour. One should Cool the alloy to room temperature with a Cooling rate of 70 to 100 ° C per minute be performed. After that, the temperature of the Alloy can be increased to about 870 ° C, and this Temperature should be kept for 16 hours.

Based on these experiments, the invention is the Task is to create single crystal castings, the an even better creep behavior at high Temperatures and high mechanical stresses guarantee.

The task is solved by a method, wherein the single crystal casting of an alloy with  the following composition (in weight percent):

8.5% chrome
5% cobalt
2.2% titanium
5.5% aluminum
9.5% tungsten
2.8% tantalum
0.015% carbon
Balance nickel and impurities,

taking a heat treatment with the following steps is carried out:

• a) annealing the alloy at 1260 to 1320 ° C during 4 hours,
• b) cooling the alloy to room temperature with a Cooling rate of 70 to 200 ° C per Minute,
• c) heating the alloy to 1080 to 1120 ° C during an hour and
• d) Treatment of the alloy at 870 ° C during 16 hours.

Experiments have shown that the heat treatment of special alloy leads to optimal results,  surprisingly, the creep behavior by the heating according to step c) improved considerably becomes.

The alloy according to the claim is in practice on a large scale, in particular for turbine blades, used.

In a comparative experiment, a single crystal casting was used divided into several candidates, the different Heat treatments were exposed, and it was then the service life with different tensile loads and temperatures determined:

• 1. The first sample was subjected to the following heat treatment: 1300 ° C. for 4 hours, followed by cooling in air and a final heat treatment of 870 ° C. for 16 hours (this essentially corresponds to the heat treatment as described in French Pat 78 128 is given, but not according to the invention). Service life at a load of 850 MPa at 750 ° C | 122,7 h. Service life at a load of 550 MPa at 850 ° C 72.3 hours Service life at a load of 160 MPa at 1050 ° C 67.7 hours
• 2. The second sample was subjected to the following heat treatment: 1300 ° C for 4 hours, cooling in air, heating to 1090 ° C for one hour and final treatment at 870 ° C for 16 hours (this heat treatment is in accordance with the invention). Service life at a load of 850 MPa at 750 ° C | 200.4 hrs. Service life at a load of 550 MPa at 850 ° C 130.9 hours Service life at a load of 160 MPa at 1050 ° C 96.2 hours
• 3. The third specimen was annealed at 1300 ° C for 4 hours and then cooled in air. It was heated to 1100 ° C for one hour and finally treated at 870 ° C for 16 hours. (This is within the scope of the invention.) Service life at a load of 850 MPa at 750 ° C | 167,5 hrs. Service life at a load of 550 MPa at 850 ° C 141.7 hours Service life at a load of 160 MPa at 1050 ° C 108.3 hours

The experiments show that alone by the Prior art not intended Intermediate heating stage according to para. c) of  Claim a very significant improvement of attainable service life under all load conditions Conditions and all temperature conditions achieved could be. A comparison of experiments 2 and 3 shows that the temperature of this interheater of considerable influence and by choice of temperature within the already pretty narrow range of 1080 to 1120 ° C the service life varies, but in in each case much higher than in experiment 1. It shows that the intermediate heating to 1090 ° C according to Try 2 for high loads and low Temperatures are cheaper and the only 10 ° C higher Intermediate heating according to experiment 3 at the two highest Temperatures gives the best results.

As a result, the reheat stage c) decisive for the properties of the final product, and that by selecting and adjusting the temperature of Reheat level within the specified limits an optimization to the respectively prevailing in the engine Conditions is possible.

Claims (1)

Method for improving the creep behavior of a single crystal casting at high temperatures and high mechanical stress, in which the single crystal casting consists of an alloy having the following composition in percent by weight: 8.5% chromium
5% cobalt
2.2% titanium
5.5% aluminum
9.5% tungsten
2.8% tantalum
0.015% carbon
Balance nickel and impurities, wherein a heat treatment is carried out with the following steps:

• a) annealing the alloy at 1260 to 1320 ° C for 4 hours,
• b) cooling the alloy to room temperature at a cooling rate of 70 to 200 ° C per minute,
• c) heating the alloy to 1080 to 1120 ° C for one hour and
• d) Treatment of the alloy at 870 ° C for 16 hours.