METHOD FOR SOLUTION HEAT TREATED ALLOY COMPONENTS

Abstract

A method of estimating an unknown solvus for a phase of a given alloy includes providing empirical data of a plurality of alloys from an alloy class, the empirical data at least including chemical compositions, heating rates, cooling rates and alloy solvus temperatures of the plurality of alloys, providing an alloy chemical composition, a selected heating rate and a selected cooling rate of another alloy from the alloy class that has an unknown solvus temperature, estimating the unknown solvus temperature based upon the empirical data to provide an estimated solvus temperature of the alloy, and establishing a solution heat treatment temperature corresponding to the estimated solvus temperature at which to treat a component that includes the alloy.

Description

BACKGROUND

This disclosure relates to alloy components that are solution heat treated and, more particularly, relates to selecting a solution heat treatment temperature for the components.

Alloy components may be solution heat treated at a pre-selected temperature. The heat treatment is used to control the microstructure of the alloy and obtain desired mechanical properties within the components.

SUMMARY

A method of estimating an unknown solvus for a phase of a given alloy according to an exemplary aspect of the present disclosure includes providing empirical data of a plurality of alloys from an alloy class, where the empirical data at least includes chemical compositions, heating rates, cooling rates and alloy solvus temperatures of the plurality of alloys. An alloy chemical composition, a selected heating rate and a selected cooling rate of another alloy from the alloy class that has an unknown solvus temperature is provided. The unknown solvus temperature is estimated based upon the empirical data to provide an estimated solvus temperature of the alloy. A solution heat treatment temperature is established corresponding to the estimated solvus temperature at which to treat a component that includes the alloy.

In a further non-limiting embodiment of any of the foregoing examples, the estimating of the unknown solvus temperature includes determining an influence of the chemical compositions on the solvus temperatures of the plurality of alloys.

In a further non-limiting embodiment of any of the foregoing examples, the estimating of the unknown solvus temperature includes determining an influence of the heating rates on the solvus temperatures of the plurality of alloys.

In a further non-limiting embodiment of any of the foregoing examples, the estimating of the unknown solvus temperature includes determining an influence of the cooling rates on the solvus temperatures of the plurality of alloys.

In a further non-limiting embodiment of any of the foregoing examples, the estimating of the unknown solvus temperature includes determining an influence of each of the chemical compositions, the heating rates and the cooling rates on the solvus temperatures of the plurality of alloys.

In a further non-limiting embodiment of any of the foregoing examples, the estimating of the unknown solvus temperature includes determining an influence of the chemical compositions, heating rates and cooling rates on the solvus temperatures of the plurality of alloys and the estimating of the unknown solvus temperature includes comparing the alloy chemical composition, the selected heating rate and the selected cooling rate of the alloy that has the unknown solvus temperature to the chemical compositions, the heating rates and the cooling rates of the plurality of alloys to provide the estimated solvus temperature of the alloy.

In a further non-limiting embodiment of any of the foregoing examples, the alloy class is a nickel-based alloy.

In a further non-limiting embodiment of any of the foregoing examples, the nickel-based alloy has gamma double prime phase, gamma prime phase and a delta phase present after a solution heat treatment and a precipitation heat treatment.

In a further non-limiting embodiment of any of the foregoing examples, the nickel-based alloy has a gamma prime phase and a delta phase present after a solution heat treatment and a precipitation heat treatment.

In a further non-limiting embodiment of any of the foregoing examples, the nickel-based alloy has gamma prime phase present after a solution heat treatment and a precipitation heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

FIG. 1 shows an example method for adjusting properties of components made of an alloy.

FIG. 2 shows an example Time-Temperature-Transformation diagram of a legacy alloy and a more recently-produced alloy.

FIG. 3 shows a table of empirical data trend for solution heat treating temperature, cooling rate and heating rate.

FIG. 4 shows a heat treatment temperature capability curve that can be used as part of the method for adjusting properties of the components.

FIG. 5 shows a method of estimating an unknown solvus for a given alloy.

DETAILED DESCRIPTION

FIG. 1 schematically shows a method 20 for adjusting properties of components made of an alloy. For example, the components can be diffuser cases or structural components for gas turbine engines, but are not necessarily limited to such components. As will be described in more detail, the response of a nominal chemistry alloy to a pre-established solution heat treatment condition (i.e. a baseline condition) may vary over time such that one or more properties of the alloy change over that time. While random changes in the properties taken from time-to-time may be expected, a trending change is undesired and thus the pre-established solution heat treatment condition can be adjusted according to the method 20 to ensure that performance criteria are met.

As shown in FIG. 1, the method 20 includes, at step 22, providing historical data for one or more properties of a plurality of components that are made of an alloy and that are produced at different times over a time period. For example, the time period may be over a course of weeks, a year or multiple years. The components are solution heat treated at a pre-established solution heat treatment condition. That is, the pre-established solution heat treatment condition is constant over the time period. In theory, the historical data should not change much over the time period. However, due to slight variations in the chemical composition of the alloy that can occur over the time period, the historical data can change such that one or more properties approach pre-determined performance criteria. In this regard, step 24 includes identifying a trending change in the one or more properties over the time period. For example, the properties can include ultimate tensile strength, 0.2% yield strength, tensile percent elongation and tensile reduction an area. In a further example, the properties can include, or can also include, stress rupture life, percent elongation and percent reduction in area, at given test conditions, such as 1200° F./649° C. and 90 kilo-pounds per square inch/620.5 megapascals; 1500° F./815.6° C. and 45 kilo-pounds per square inch/310 megapascals; or 1300° F./704° C. and 65 kilo-pounds per square inch/448 megapascals. The test conditions may vary depending upon the alloy class. Fatigue or other properties can also be used.

Once the trending change in one or more of the properties is identified, a series of steps as follows can be used to adjust the pre-established solution heat treatment condition and thereby improve the one or more properties that have trended in an undesired direction over the time period. Step 26 includes providing test specimens made of the alloy and that differ in shape from the plurality of locations and components. That is, the components have a shape that is designed for the intended end use, while the test specimens have a standardized shape that is appropriate for mechanical testing, such as a “dog-bone” or “dumb-bell” shape. The test specimens are untreated, at least with regard to the solution heat treatment.

The test specimens are then divided at step 28 into a plurality of groups. The groups are solution heat treated and precipitation heat treated at a different one of a plurality of heat treatment conditions. Each of the plurality of heat treatment conditions includes a set of at least a solution heat treatment temperature, a heating rate and a cooling rate. After the solution heat treatment and precipitation heat treatment, the test specimens are mechanically tested at step 30 to provide empirical data. As discussed above, the one or more properties can include certain mechanical properties of the plurality of components. In this regard, the empirical data that is collected in step 30 by mechanically testing the test specimens and the performance criteria include the same properties. The empirical data is then compared at step 32 to pre-determined performance criteria. For example, the pre-determined performance criteria can correspond to minimum or desired mechanical properties of the components for proper operation of the components in the intended end use.

Step 34 then includes identifying a solution heat treatment condition from the plurality of heat treatment conditions over which the empirical data meets the predetermined performance criteria. Once the solution heat treatment condition is identified, step 36 then includes adjusting the pre-established solution heat treatment condition for future ones of the plurality of components according to the identified solution heat treatment condition. The adjustment to the pre-established solution heat treatment condition can include changing the solution heat treatment temperature, the heating rate, the cooling rate or any combination thereof. The testing and verification of the properties of the test specimens and then adjusting the pre-established solution heat treatment condition ensures that the one or more properties of the components meet the pre-determined performance criteria.

Although the method 20 can be applied to many different types or classes of alloys, an alloy of interest for diffuser cases and other gas turbine engine components is nickel-based alloy, one example of which can be found in U.S. Pat. No. 4,888,253, incorporated herein by reference, which has gamma double prime phase, gamma prime phase and delta phase. In another example, the alloy is a nickel-based alloy that has gamma prime phase and delta phase, examples of which can include alloys found in U.S. Pat. No. 6,730,264, incorporated herein by reference, and Alloy 718Plus). In another example, the alloy is a nickel-based alloy that has gamma prime phase, one example of which includes Waspaloy.

Additionally, the method 20 can be used to non-destructively qualify that the components meet the pre-determined performance criteria. For example, by mechanically testing the test specimens and comparing the empirical data to the pre-determined performance criteria, a user can conclude that the plurality of components that are solution heat treated at the adjusted pre-established solution heat treatment condition also meet the pre-determined performance criteria.

The following example is based upon a nickel-based alloy that has a gamma double prime phase, a gamma prime phase and a delta phase after solution heat treating and precipitation heat treatment. Historical data were collected for one or more properties of components made of the alloy over a period of years. A trending change in one or more of the properties was identified over the time period and it was determined, as represented in FIG. 2, that the response of the alloy to the pre-established solution heat treatment condition had changed over the time period. FIG. 2 shows a Time-Temperature-Transformation diagram for the precipitation of the delta phase, gamma double prime phase and the gamma prime phase for a legacy alloy from several years prior to the study versus the same for a more recent batch of the alloy. As shown in the diagram, the lines L₁ and L₂ represent, respectively, the Time-Temperature-Transformation curves for delta phase precipitation start (interdendritic grain boundaries) and finish (dendritic grain core), for the legacy alloy. The lines L₃ and L₄ represent, respectively, Time-Temperature-Transformation curves for the delta phase precipitation start (interdendritic grain boundaries) and finish (dendritic grain core) for the more recent alloy. The T-T-T curve for the start of gamma prime and gamma double prime phase precipitation is shown in relation to the delta phase curves. The curves L₃ and L₄ for the more recent alloy differ from the curves L₁ and L₂ of the legacy alloy and thus indicate that the response of the more recent alloy to solution heat treatment has changed over time in comparison to the legacy alloy. The change was further evidenced in microstructural analysis, which showed a greater amount of delta phase precipitation in the more recent alloy than in the legacy alloy. The increased amount of the delta phase consumes more niobium in the microstructure, which debits the precipitation of the gamma double prime and gamma prime phases and thus changes the alloy properties.

As shown in FIG. 3, test specimens of the more recent alloy were mechanically tested as described herein and the influence of the solution heat treatment temperature, cooling rate and heating rate on the properties were determined. In the table shown in FIG. 3, a “zero” indicates insignificant or no influence of a condition on the given property, an “up arrow” indicates that the property increased as the given condition increased, and a “down arrow” indicates that the property decreased as the given condition decreased.

As shown in FIG. 4, each property was plotted on a graph versus the solution heat treatment condition, here shown as the solution heat treatment temperature. The property, as represented by line T, was then compared to a performance requirement, represented at line R. Thus, the graph is essentially a solution heat treatment temperature capability curve that facilitates identifying a condition range over which the empirical data meets the pre-determined performance criteria, rather than a single point condition that meets the performance criteria. As shown in the graph in FIG. 4, a temperature range TR was then be identified over which the empirical data meets the predetermined performance criteria. For example, the identified temperature range began at a temperature that is beyond the intersection of the trend line T and the performance requirement line R, to provide a margin above the performance requirement. In the example, a pre-established solution heat treatment condition of 1825-1875° F. (996.1-1024° C.) and a cooling rate of 75° F. (24° C.) per minute was adjusted to 1860-1900° F. (1016-1038° C.) and a cooling rate of 25° F. (3.9° C.) per minute.

Similarly, the heating rate and/or the cooling rate (or ranges thereof) can be identified. Once the condition was identified, components that were made of the same alloy as the test specimens that were used to identify the condition range, were solution heat treated at the identified condition to ensure that the components met the property requirements or performance criteria.

As another example, a variation of the method 20, optionally without steps 22 and 24, can be used to adjust the pre-established solution heat treatment condition on a per-batch basis of the alloy. As used herein, a “batch” differentiates the alloy by time of production of the alloy, but does not necessarily mean that the alloy was produced using batch processing techniques. For example, each batch of the alloy may vary slightly from a nominal chemical composition. Typically, chemical compositions of alloys, such as nickel-based alloys, are defined with regard to specific ranges of each element of the chemical composition. Thus, the actual amount of any given element can vary within the specified range of that element from batch-to-batch of the alloy. These slight differences in chemical compositions between batches can change the response of a batch to a given baseline or pre-established solution heat treatment condition. In this regard, the modified method 20 can be used on each batch to adjust or tailor the pre-established solution heat treatment condition for that particular batch. That is, one batch of the alloy can have a first adjusted pre-established solution heat treatment condition and another, different batch of the alloy can have a different adjusted pre-established solution heat treatment condition that differs in at least one of solution heat treatment temperature, heating rate or cooling rate. This allows the properties of the batch of the alloy, and thus the properties of the components that are to be produced from that batch of the alloy, to be tailored to the particular batch of the alloy.

FIG. 5 shows an example method 50 of estimating an unknown solvus for a phase of a given alloy. As used herein, the term “solvus” or variations thereof refer to a line, boundary or point that represents a separation between a homogenous solid solution and a multi-phase microstructure, as a function of temperature. In the solution heat treating of alloy components, the solvus can be used to select the solution heat treatment temperature at which the components are to be treated to obtain a desired microstructure and thus desired properties. However, the solvus can vary depending upon a number of factors and thus the response of a given alloy to a pre-established solution heat treatment condition can vary. Moreover, although an unknown solvus for a given alloy can be experimentally determined, such a determination can be somewhat complex, especially when trying to select from various different alloys and determine appropriate solution heat treatment conditions for those alloys. Thus, as will be described, the method 50 provides a technique for estimating an unknown solvus for a given alloy based upon empirical data of other alloys.

The method 50 includes, at step 52, providing empirical data of a plurality of alloys from an alloy class. For the purpose of this disclosure, an alloy class is determined according to the base metal (most abundant metal) of the alloy. For example, nickel-based alloys are considered to be an alloy class. Thus, the alloys from which the empirical data is provided all include the same base metal but may differ in the amounts and/or types of other elements. In a further example, the alloys from which the empirical data is provided can have all of the same elements, with multiple elements being present in different amounts in the alloys.

The empirical data at least includes chemical compositions, heating rates, cooling rates and alloy solvus temperatures of the plurality of alloys. At step 54, an alloy chemical composition, a selected heating rate and a selected cooling rate of another alloy from the alloy class that has an unknown solvus temperature are provided. At step 56, the unknown solvus temperature is then estimated based upon the empirical data to provide an estimated solvus temperature of the alloy. A solution heat treatment temperature corresponding to the estimated solvus temperature is then established at which to heat treat a component that includes the alloy.

For example, estimation of the unknown solvus temperature can include determining an influence of one or more of the chemical compositions, the heating rates and the cooling rates on the solvus temperatures of the plurality of the alloys. For example, by comparing the chemical compositions, the influence of chemical composition with regard to one or more of the elements on a baseline solvus temperature can be determined. Similarly, the influence of the heating rates and the cooling rates on a baseline solvus temperature can be determined. By then comparing the chemical composition, the selected heating rate and the selected cooling rate of the alloy of unknown solvus temperature to the empirical data and determined influences, the unknown solvus temperature of the alloy can be estimated. Optionally, the method 50 can further include a verification of the selected solution heat treatment temperature. The verification can include experimental testing of the alloy, components formed of the alloy or a combination thereof. The selected solution heat treatment temperature can then be modified based upon the verification results.

A component that is made of the same alloy as the alloy with the unknown solvus temperature can then be solution heat treated according to the estimated solvus temperature, selected heating rate and selected cooling rate, without actual testing or determination of the unknown solvus temperature. For example, the selected solution heat treating temperature of the alloy can be a pre-determined increment above the estimated solvus temperature.

In another application of the present disclosure, variations in composition from elemental changes, such as niobium content, can be characterized by their effect on the empirical data, which may be reflected in the respective heat treatment temperature capability curve. The empirical property versus temperature may indicate changes in the resultant best-fit curve in FIG. 2, e.g., higher or lower shifts from the nominal composition curve. Comparison of such compositional effects provides quantitative correlation curves that can be used to estimate the respective changes in the solution temperature. Hence, a given heat chemistry determination at the melt stage can be compared with the database of compiled heat treatment capability curves to determine the appropriate solution heat treatment conditions that meet the performance criteria.

Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

1. A method of estimating an unknown solvus for a phase of a given alloy, the method comprising: providing empirical data of a plurality of alloys from an alloy class, the empirical data at least including chemical compositions, heating rates, cooling rates and alloy solvus temperatures of the plurality of alloys;providing an alloy chemical composition, a selected heating rate and a selected cooling rate of another alloy from the alloy class that has an unknown solvus temperature;estimating the unknown solvus temperature based upon the empirical data to provide an estimated solvus temperature of the alloy; andestablishing a solution heat treatment temperature corresponding to the estimated solvus temperature at which to treat a component that includes the alloy.

2. The method as recited in claim 1, wherein the estimating of the unknown solvus temperature includes determining an influence of the chemical compositions on the solvus temperatures of the plurality of alloys.

3. The method as recited in claim 1, wherein the estimating of the unknown solvus temperature includes determining an influence of the heating rates on the solvus temperatures of the plurality of alloys.

4. The method as recited in claim 1, wherein the estimating of the unknown solvus temperature includes determining an influence of the cooling rates on the solvus temperatures of the plurality of alloys.

5. The method as recited in claim 1, wherein the estimating of the unknown solvus temperature includes determining an influence of each of the chemical compositions, the heating rates and the cooling rates on the solvus temperatures of the plurality of alloys.

6. The method as recited in claim 1, wherein: the estimating of the unknown solvus temperature includes determining an influence of the chemical compositions, heating rates and cooling rates on the solvus temperatures of the plurality of alloys; andthe estimating of the unknown solvus temperature includes comparing the alloy chemical composition, the selected heating rate and the selected cooling rate of the alloy that has the unknown solvus temperature to the chemical compositions, the heating rates and the cooling rates of the plurality of alloys to provide the estimated solvus temperature of the alloy.

7. The method as recited in claim 1, wherein the alloy class is a nickel-based alloy.

8. The method as recited in claim 7, wherein the nickel-based alloy has gamma double prime phase, gamma prime phase and a delta phase present after a solution heat treatment and a precipitation heat treatment.

9. The method as recited in claim 7, wherein the nickel-based alloy has a gamma prime phase and a delta phase present after a solution heat treatment and a precipitation heat treatment.

10. The method as recited in claim 7, wherein the nickel-based alloy has gamma prime phase present after a solution heat treatment and a precipitation heat treatment.