DE1919487B2 - PROCESS TO INCREASE LIFE STRENGTH IN THE EVENT OF HIGH TEMPERATURE STRESS OF NICKEL-BASED SUPER ALLOYS OF NICKEL-BASED SUPER ALLOYS PRODUCED AS SINGLE CRYSTALS OR WITH A COLUMN-SHAPED JOINT - Google Patents

Description

Alloy designation

Composition in% by weight

This invention relates to a method for increasing the fatigue strength under high temperature stress of cast parts made of nickel-based superalloys, consisting of 6 to 25% chromium, 0.5, which are produced as a single crystal or with a columnar structure up to 20% aluminum, titanium and / or niobium, up to 25% cobalt, up to 20% molybdenum, tantalum and / or tungsten, 0.005 to 03% boron and / or zirconium, furthermore Carbon, the remainder nickel.

A nickel-based superalloy usually consists of nickel / chrono mixed crystals, which through Addition of aluminum, titanium and / or niobium for precipitation hardening by intermetallic compounds with the formula Nii (M) are capable. M in the Formula stands for aluminum, titanium, niobium, individually or mixtures thereof. Commercially available superalloys also contain cobalt to increase the solution annealing temperature of the precipitates, heat-resistant soluble metal additives for hardening ies Solid solution and carbon, boron and zirconium to improve the time fracture elongation.

Carbon is traditionally a necessary additional alloy component in the polycrystalline Nickel base superalloys have been used. Most of the carbon occurs with others Alloy components such as titanium, chromium, zirconium, MarM-200 9Cr, 10 Co, 2Ti, 5Al ₁ 12.5 W, INb, 0.015 B, 0.05 Zr, 0.15 C, balance Ni

Udimet700 14.6Cr, 15.3Co, 3.4Ti, 4.3 Al, 4.4 Mo,

(Sigma free) 0.016 B, 0.07 C, remainder Ni IN 100 10 Cr, 15 Co, 4.5 Ti, 5.5 Al, 3 Mo, 0.75 V,

0.015 B ₁ 0.075 Zr, 0.17 C ₁ balance Ni

B-1900 8 Cr, 10 Co, 1 Ti, 6 AI, 6 Mo, 4.3 Ta, 0.15 B,

0.07Zr, 0.11c, balance Ni

The aim of the invention is to provide a method for increasing the fatigue strength of as a single crystal or to create solidified cast parts made of nickel-based superalloys with a columnar structure, as well as the required casting alloys are available

place.

The invention relates to a method for increasing the fatigue strength under high temperature stress of as a single crystal or with a columnar shape Structural castings made from superalloys

(, 0 based on nickel, consisting of 6 to 25% chromium, 0.5 to 20% aluminum, titanium and / or niobium, up to 25% cobalt, up to 20% molybdenum, tantalum and / or tungsten, from 0.005 to 0.5% boron and / or zirconium, furthermore carbon, the remainder nickel, which is characterized in that the formation

(15 a separate monocarbide phase in the cast parts by limiting the carbon content in the superalloy to be cast to a maximum of 0.01% is suppressed.

A special embodiment of the method is characterized in that the to be cast Superalloy of 6 to 25% chromium, 0.5 to 7% aluminum, 0.5 to 5% titanium, up to 25% cobalt up to 20% Niobium, molybdenum, tantalum and / or tungsten, 0.005 to 0.5% boron and / or zirconium, up to 0.01% carbon, Remainder nickel, preferably 9% chromium, 5% aluminum, 1.7% titanium, 10% cobalt, 0.6% niobium, 12.1% Tungsten, 0.015% boron, 0.04% zirconium, 0.01% carbon, the remainder nickel

A modified embodiment of the method is characterized in that the to be potted Superalloy of 6 to 25% chromium, 03 to 7% aluminum, 0.5 to 5% titanium, up to 0.01% carbon, The remainder consists of nickel

Another modified embodiment of the method is characterized in that the to cast & de superalloy of 14.1% chromium, 4.3% aluminum, 3.2% titanium, 15.3% cobalt, 4.2% molybdenum, 0.01% carbon, the remainder nickel

It was found in connection with the development work which led to the invention that the physical properties of the directionally solidified nickel-based superalloys, especially theirs Fatigue resistance is considerable due to the presence of a large proportion of MC-type carbide phase is changed to a marked extent.

An examination of the structure of the nickel-based superalloys of conventional composition in both manifestations, namely with a columnar structure and in the single crystal form, has revealed that the MC-type carbides are much larger in these forms than in the conventional castings. Farther these carbides can exist as interconnected networks. These big MC-type carbides result from the slower solidification rate and the low thermal gradient the solidification front, which are used when casting parts with an antisotropic structure. It was also discovered that many of these carbides cracked parallel to their longest extent. Since the If cracks were present in the casting material immediately after casting, it is evident that they were in the Solidification of these alloys were formed. Tearing of the carbides has never been observed until then and this required extremely careful mechanical polishing or electropolishing, to watch this.

The plastic deformability and the cracking of the structure in the cast parts which are in the cast or heat-treated state existed, was proven by tensile and fatigue tests (fatigue strength) and found here that the further cracks originate from the cracks already contained in the MC-type carbides. It has been shown that the fatigue strength of these cast alloys is a very sensitive function of the Carbide size is. For example, it has been demonstrated that the swelling strength of test pieces from the Top of the ingot was degraded by a factor -on more than three hundred when the comparison was performed with samples taken from the bottom or center of the same ingot where the carbides were smaller because of a faster solidification rate and because of a steeper one thermal gradient at the solidification front.

This is clearly demonstrated by the data given in Table 1, the swelling strength as a special case of fatigue strength for an im

40

45 alternation of two changes per minute between zero and a maximum value (total deformation) increasing and decreasing load has been determined

Table 1

Influence of the position in the casting when determining the fatigue strength of Mar-M-200 in the fatigue test

Type of 'S Location in Check Total- Load cycle Cast Benefit tempe ver number to rature forming to he in% tired break _/

Directed center 2Γ 1.4 366 Stiffens Top 2V 1.4 1/4 Single crystal Lower part 2V 12th 1621 Top 2V 1/4 Single crystal Lower part 760 ^c 1.2 798 Top 760 ^c 1.2 7th ¹ C 'C ¹ C ¹ C 'C 'C

It was also found that the time elongation behavior of specimens obtained from the tops of the Cast ingots were removed, approximately half that of the test pieces is that from the lower part of the same ingot.

The carbon content required according to the invention of a maximum of 0.01% can be obtained by melting and pouring the superalloys under Vacuum with no intentional addition of carbon to the alloy. The presence of carbon goes is due to carbon impurities present in various alloying elements. Since the Carbides no longer needed or not in the alloy If required, small adjustments to the target composition of the various alloys can be made be carried out in order to take into account the fact that certain proportions of the elements are not find more use for the formation of carbides. Typical alloy compositions with low Carbon content for Mar-M-200 and Udimet 700 alloy types are listed in Table 2 with the corresponding alloys compared with their normal chemical composition.

Table 2

Ele Mar-M-200 with Udimet 700 (Sigma free) ments low normal carbon normal with salary low 0.01 carbon 12.1 salary C. 0.15 1.7 0.07 0.01 W. 12.5 0.6 - Ti 2.0 0.04 3.4 3.2 Nb 1.0 10.0 - - Zr 0.05 9.00 - - Co 10.0 5.00 15.3 15.3 Cr 9.00 0.015 14.6 14.1 Al 5.00 - 4.3 4.3 B. 0.015 rest 0.016 - Mon - 4.4 4.2 Ni rest rest rest

Single crystal castings made from the Mar-M-200 alloy are manufactured with the low carbon content, have a clearly pronounced superior fatigue strength in comparison with the corresponding articles with contents of MC-type carbides. One The test showed no MC-type carbides and therefore also no cracked carbides in the alloy with the low carbon content This finding is supported by the comparison data in Table 3.

Table 3

Low swelling strength of nickel-based superalloys at 760 ° C with a total deformation of 1.6%

material Kind of good Number of load cycles up to comment to fatigue fracture Mar-M-200
Mar-M-200 conventional
Single crystal .,;} large MC carbides Mar-M-200 columnar structure 360 small MC carbides Mar-M-200 low carbon Single crystal 717 no MC carbides salary Udimet 700 malleable polycrystal 165 - Udimet 700 Single crystal 551 large MC carbides Low carbon Udimet 700 Single crystal 956 no MC carbides salary

It can be seen that the formation of cracked carbides in directional solidification casting is a Function of both the carbon content of the alloy and the solidification parameters in the casting process insofar as this carbide size, type and also influence the distribution in the cast article. Under about 0.06% carbon will be an improvement in properties at normal solidification rates of the directionally solidified casting found when the carbon content of the alloy is reduced, whereby the cracks of the carbides are less frequent and more dispersed. Up to 0.01% carbon MC-type carbides are not formed.

Claims (5)

Patent claims: t. Process air increase in fatigue strength High temperature stress of manufactured as a single crystal or with a columnar structure Castings made of super alloy on a nickel basis, consisting of ^ 6 to 25% chromium, 05 to 20% Aluminum, titanium and / or niobium, up to 25% cobalt, up to 20% molybdenum, tantalum and / or tungsten, 0.005 to 0.5% boron and / or zirconium, furthermore carbon, the remainder nickel, characterized in that the formation of a separate monocarbide phase in the cast parts by limiting the carbon content in the superalloy to be cast a maximum of 0.01% is suppressed. 2. The method according to claim 1, characterized in that the superalloy to be cast from 6 to 25% chromium, 0.5 to 7% aluminum, 0.5 to 5% titanium, up to 25% cobalt, up to 20% niobium, molybdenum, Tantalum and / or tungsten, 0.005 to 0.5% boron and / or zirconium, up to 0.01% carbon, remainder Nickel 3. The method according to claim 2, characterized in that the superalloy to be cast from 9% chromium, 5% aluminum, 1.7% titanium, 10% cobalt, 0.6% niobium, 12.1% tungsten, 0.015% boron, 0.04% Zirconium, 0.01% carbon, the remainder nickel 4. Modification of the method according to claim 1, characterized in that the to be cast Superalloy of 6 to 25% chromium, 0.5 to 7% aluminum, 0.5 to 5% titanium, up to 0.01% carbon, The remainder nickel 5. Modification of the method according to claim 1, characterized in that the to be cast 14.1% chromium, 43% aluminum superalloy, 3.2% titanium, 15.3% cobalt, 4.2% molybdenum, 0.01% carbon, the remainder nickel Niobium and tungsten combine to form metal carbides in a variety of phases (MC, M ₂ SC ₆ , M ₆ C and M ₇ C ₃ ), the main phase or phases present depending on the composition S and heat treatment as the high temperature -The creep behavior of the superalloys with carbide contents is superior to those without carbide contents, in the past the carbon alloy additives were generally regarded as absolutely necessary ίο in the polycrystalline superalloys 93, pp. 96-100 (February 1968) confirmed The requirement for the presence of the carbon remains a fact to be considered, although certain studies, for example in British Patent No. 1033715, have shown that a limited number of nickel-based superalloys improved one Impact resistance at low carbon contents exhibit. Recently, certain casting technologies have been used to achieve unidirectional solidification of the Superalloys developed into cast parts with a columnar structure or in single crystal form. The mainly preferred techniques of these Art are illustrated in US Pat. No. 3,260,505 to VerSnyder Generally speaking, they are for the different Alloys of the same composition have hitherto used methods for directional solidification been like those alloys used in conventional casting techniques, and accordingly the have contained common carbon alloy additives. Representative nickel-based superalloys and their common compositions are given below: