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United States Patent Application 20160102392
Kind Code A1
Trumble; Kevin Paul ;   et al. April 14, 2016

METHODS OF MAKING AND TREATING COPPER-BASED ALLOY COMPOSITIONS AND PRODUCTS FORMED THEREFROM

Abstract

A ternary alloy wherein copper, manganese, and a ternary element are melted together and cast into an article and the article is subjected to an age-hardening treatment. A process for producing an age-hardened copper-manganese-nickel alloy, the process including melting a composition comprising copper, manganese and nickel; pouring the molten composition comprising copper, manganese, and nickel to form a casting with a composition comprising copper, manganese, and nickel, and aging the casting so produced. An article containing copper, manganese, and a ternary element, in a cast form and the cast form has subsequently undergone age-hardening treatment. A ternary alloy comprising copper, manganese, and a ternary element melted together and solidified into a casting, wherein the microstructure of the casting produced shows substantially low microporosity attributable to dendritic solidification.


Inventors: Trumble; Kevin Paul; (West Lafayette, IN) ; Chaput; Kevin Joseph; (Merritt Island, FL)
Applicant:
Name City State Country Type

PURDUE RESEARCH FOUNDATION

West Lafayette

IN

US
Assignee: PURDUE RESEARCH FOUNDATION
West Lafayette
IN

Family ID: 1000001603237
Appl. No.: 14/880217
Filed: October 10, 2015


Related U.S. Patent Documents

Application NumberFiling DatePatent Number
62062518Oct 10, 2014

Current U.S. Class: 148/553 ; 148/414; 148/419; 148/538
Current CPC Class: C22F 1/16 20130101; C22F 1/08 20130101; C22C 22/00 20130101; C22C 30/02 20130101; C22C 9/00 20130101
International Class: C22F 1/16 20060101 C22F001/16; C22C 22/00 20060101 C22C022/00; C22C 30/02 20060101 C22C030/02; C22F 1/08 20060101 C22F001/08; C22C 9/00 20060101 C22C009/00

Claims



1. A ternary alloy comprising: copper; manganese; and a ternary element, wherein copper, manganese, and the ternary element are melted together and cast into an article and the article is subjected to an age-hardening treatment.

2. The ternary alloy of claim 1, the ternary element is nickel.

3. The ternary alloy of claim 2, weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55.

4. The ternary alloy of claim 3, the age-hardening in the range of 300.degree. C. to 600.degree. C. for a time period.

5. The ternary alloy of claim 4, wherein the time period is in the range of 1 hour to 100 hours.

6. A process for producing an age-hardened copper-manganese-nickel alloy comprising: melting a composition comprising copper, manganese and nickel; pouring the molten composition comprising copper, manganese, and nickel to form a casting with a composition comprising copper, manganese, and nickel; and aging the casting produced at a temperature in the range of 300.degree. C. to 600.degree. C. for a time period.

7. The process of claim 6, wherein the time period is in the range of 1 hour to 100 hours.

8. The process of claim 6, weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55.

9. The process of claim 8, wherein the time period is in the range of 1 and 100 hours.

10. An article comprising: copper; manganese; and a ternary element, wherein copper, manganese and the ternary element are in a cast form and the cast form has subsequently undergone age-hardening treatment and contains a precipitated phase.

11. The article of claim 10, the ternary element is nickel.

12. The article of claim 11, weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55.

13. The article of claim 12, the age-hardening treatment includes aging in the temperature range of 300.degree. C. to 600.degree. C. for a time period in the range of 1 hour to 100 hours.

14. The article of claim 11, the article is a plumbing valve or fitting.

15. The article of claim 12, the article is a plumbing valve or fitting.

16. The article of claim 13, the article is a plumbing valve or fitting.

17. A ternary alloy comprising copper, manganese, and a ternary element melted together and solidified into a casting, wherein the microstructure of the casting produced exhibits substantially low microporosity attributable to dendritic solidification.

18. The ternary alloy of claim 17, the ternary element is nickel.

19. The ternary alloy of claim 18, weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55.

20. The ternary alloy of claim 1, the ternary element is one of cobalt, zinc, chromium, and iron.

21. The article of claim 10, the ternary the ternary element is one of cobalt, zinc, chromium, and iron.

22. The ternary alloy of claim 17, the ternary element is one of cobalt, zinc, chromium, and iron.

23. The ternary alloy of claim 1, wherein the age-hardening treatment is preceded by a solution treatment.

24. The process of claim 10, wherein the aging of the casting is preceded by a solution treatment.

25. The ternary alloy of claim 23, wherein the solution treatment temperature is in the range of 700.degree. C. to 850.degree. C.

26. The process of claim 24, wherein the solution treatment temperature is in the range of 700.degree. C. to 850.degree. C.
Description



CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present U.S. patent application is related to and claims the priority benefit of U.S. Provisional Patent Application Ser. No. 62/062,518, filed Oct. 10, 2014, the contents of which are hereby incorporated by reference in their entirety into the present disclosure. Further, this application is related to co-pending U.S. patent application Ser. No. 13/441,611, filed Apr. 6, 2012, the contents of which are incorporated by herein by reference in their entirety.

TECHNICAL FIELD

[0002] This disclosure relates to metals and alloys suitable for use in the production of castings and potential other forms (for example rolling, forging, drawing etc.) for use in various industrial applications, such as, but not limited to plumbing and valve fittings.

BACKGROUND

[0003] This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.

[0004] The present invention generally relates to copper-based alloys that are suitable for use in the production of castings (for example, plumbing castings), wrought forms (for example, produced by rolling, drawing, forging, etc.), and potentially other forms. The invention also relates to the production and processing of such alloys, and particularly processes that are capable of enhancing the mechanical properties of such alloys.

[0005] Alloys based on Cu and Mn in wrought form are well known for special characteristics, such as mechanical damping capacity, resiliency and magnetic behavior. With the exception of these specialty alloys, Mn is usually a minor alloying element in Cu. The most common example is the high-strength yellow brasses, also known as manganese bronzes, which typically contain only about 2 weight percent Mn.

[0006] Cu--Mn alloy compositions that undergo cellular and dendritic growth during directional solidification as a result of their compositions containing manganese contents that are intentionally above or below the congruent point or minimum in the liquidus/solidus of the Cu--Mn phase diagram, shown in FIG. 1, have been studied. (N. A. Goken, "Journal of Alloy Phase Equilibria," 14 [1] p. 76-83 (1993)). Though there is uncertainty regarding the exact composition at the congruent point of the Cu--Mn system, Goken placed the congruent point at 34.6.+-.1.4 weight percent (about 38.+-.2 atomic percent) manganese.

[0007] Copper-manganese alloys having relatively large amounts of manganese have conventionally been produced in wrought form, for example, products in the form of wires, thin plates/sheets, rods, foils, etc. Microporosity is not a concern in such products as they may be hot- and/or cold-worked to remove the microporosity, unlike cast products. However, it is desirable if methods were available for casting copper-manganese alloys that were free of microporosity and dendritic growth. Compositions that lend themselves to eliminating or reducing microporosity and dendritic growth have been described in U.S. patent application Ser. No. 13/441,611 (Publication No. US2013/0094989 A1), the contents of which are incorporated by reference herein in their entirety. FIG. 2 is an optical image of a polished and etched low-carbon Cu-35 weight percent Mn alloy prepared in a SiC crucible. The alloy exhibits a cellular solidification microstructure and was free of microporosity typical of most alloys, which solidify in a dendritic structure that inhibits the feeding of shrinkage during solidification and tends to form interdendritic microporosity.

[0008] For many applications, including but not limited to plumbing and valve fittings, it is desirable to procure the objects in cast form of Cu--Mn alloys. It is further desirable and advantageous if the strength and other mechanical properties of such cast Cu--Mn alloys can be further controlled and enhanced through compositional changes and/or heat treatments. Due to the very narrow freezing range of alloys near the Cu--Mn congruent point, cellular solidification occurs instead of the common dendritic morphology found in most cast alloys. The cellular growth morphology leads to a microporosity-free structure. Even though the alloy was initially developed as an alternative to leaded casting bronzes for piping and plumbing, its lack of porosity shows potential for more demanding structural applications where fatigue is a primary concern. While the as-cast strength was found to be higher than that of comparable cast brasses and bronzes, it is still not high enough for these applications where stronger alloys like stainless steel are the primary choices.

[0009] Thus there is unmet need for cast Cu--Mn alloys that have higher strength than currently available for use in demanding structural applications where high mechanical strength and fatigue resistance are desired.

SUMMARY

[0010] A ternary alloy is disclosed. The ternary alloy comprises copper, manganese, and a ternary element, wherein copper, manganese, and the ternary element are capable of being melted together and cast into an article and the article is subjected to an age-hardening treatment.

[0011] A process for producing an age-hardened copper-manganese-nickel alloys is disclosed. The process includes melting a composition comprising copper, manganese and nickel; pouring the molten composition comprising copper, manganese, and nickel to form a casting with a composition comprising copper, manganese, and nickel; and aging the casting produced at a temperature in the range of 300.degree. C. to 600.degree. C. for a time period.

[0012] An article made of an alloy is disclosed. The article contains copper, manganese, and a ternary element, wherein copper, manganese and the ternary element are in a cast form and the cast form has subsequently undergone age-hardening treatment and contains a precipitated phase.

[0013] A ternary alloy containing copper, manganese and a ternary element is disclosed. The alloy includes copper, manganese, and a ternary element melted together and solidified into a casting, wherein the microstructure of the solidified casting produced exhibits substantially low microporosity attributable to dendritic solidification.

BRIEF DESCRIPTION OF DRAWINGS

[0014] While some of the figures shown herein may have been generated from scaled drawings or from photographs that are scalable, it is understood that such relative scaling within a figure are by way of example, and are not to be construed as limiting.

[0015] FIG. 1 is a representation of Cu--Mn binary phase diagram.

[0016] FIG. 2 is a typical etched micrograph of the cellular solidification morphology of a near-congruent Cu--Mn alloy.

[0017] FIG. 3 is a representation of typical hardness values and the corresponding compositions plotted on a redrawn schematic of the Cu--Mn--Ni composition diagram.

[0018] FIG. 4 is a representation of target compositions of the alloys to be evaluated in this study overlaid on a schematic of the Cu--Mn--Ni composition diagram.

[0019] FIG. 5 is a micrograph of the Cu-40Mn-10Ni alloy showing a cellular-to-dendritic breakdown typical of several of the alloys of this disclosure.

[0020] FIG. 6 is a plot of hardness vs. aging time for alloys of this disclosure.

[0021] FIG. 7 is a plot of hardness vs. aging Time for Cu-35 weight percent Mn alloy of this disclosure and 2 weight percent Ni alloy of this disclosure.

[0022] FIG. 8(a) is an optical micrograph of the 2 weight-percent Ni alloy of this disclosure after 100 h aging at 450.degree. C.

[0023] FIG. 8(b) and FIG. 8(c) are SEM images at higher magnifications (than optical micrograph of FIG. 8(a)) of the 2-weight percent Ni alloy of this disclosure after 100 h aging at 450.degree. C.

[0024] FIG. 8(d) and FIG. 8(e) are X-Ray Diffraction results (patterns) comparing the phases present in the as-cast and 100 h-aged alloys.

[0025] FIG. 9 is a comparison of the 450.degree. C. age-hardening response between some alloys of this disclosure and the near-congruent Cu--Mn binary alloy.

DETAILED DESCRIPTION

[0026] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

[0027] As mentioned in the Back-ground section, the goal of this disclosure is to increase the strength of Cu--Mn alloys. It is also important that the freezing range be kept minimal so that the benefits of the cellular structure found in the near-congruent Cu--Mn alloy are not all sacrificed. In this disclosure, a primary strengthening approach adopted is utilization of ternary alloying elements, in particular, Nickel (Ni). Although Ni has a small solid solution strengthening effect, previous studies showed that additions of Ni can make alloys that are precipitation-hardenable through the formation of the NiMn phase or .alpha.(Mn) phase. FIG. 3 shows typical hardness values and the corresponding compositions of selected Cu--Mn--Ni alloys in wrought form after aging for 12 h at 450.degree. C. While the NiMn phase is a more potent precipitation hardener, it requires larger amount of nickel, so the focus of the present disclosure is to utilize the precipitation of the .alpha.(Mn) phase in alloys smaller amount of nickel. The binary Cu--Mn system is precipitation-hardenable not only by the .alpha.(Mn) phase, but also by a transitional fcc .gamma.' (Mn) phase, before forming coarser equiaxed .alpha.(Mn) precipitates after aging for .about.150-300 h.

[0028] The Cu--Ni binary system is well known to be an isomorphous system and the Ni--Mn system displays a congruent minimum in the liquidus-solidus very similar to that of the Cu--Mn system. While work on the Cu--Mn--Ni ternary liquidus temperature surface is rather limited, it suggests a trough in the liquidus that runs from the Ni--Mn congruent point (60 wt pct Mn, 1020.degree. C.) to the Cu--Mn congruent point (35 wt pct Mn, 873.degree. C., as shown in FIG. 1). Compositions in this trough are of great interest since they display the lower liquidus temperatures and narrow freezing ranges.

[0029] FIG. 4 shows several compositions studied in experiments leading to this disclosure plotted on a ternary composition diagram. For reference, the congruent compositions of the binary Cu--Mn and Ni--Mn systems are shown with filled circles. It should be noted that studies earlier to the present studies did not focus on the aging of these systems, and they did not focus on the compositions of interest in this disclosure and have only considered homogenized, wrought alloys. An important aspect of the present disclosure is aging of as-cast structures, where microsegregation and the as-cast grain morphology can play a role.

[0030] In this disclosure we use the term ternary element to mean a metallic element added to a Cu--Mn binary alloy. Thus nickel is an example of a ternary element of this disclosure. Further, the term "about" may be used in describing the weight percent of an element or a constituent of a ternary alloy or a binary alloy. For example the phrase "about 35 weight percent" means 35 weight percent with in a tolerance of +/-1 percent. When a constituent is about 1 percent, however, it must be understood, that zero weight percent is not included.

[0031] In experiments leading to this disclosure, alloys were prepared by melting in an open-air induction furnace in approximately 1-kg charges of the compositions (in weight percent, sometimes abbreviated as wt. percent or wt. % or wt pct) listed in FIG. 4. Fire clay (Al.sub.2O.sub.3--SiO.sub.2) crucibles were utilized to limit reaction with the melt. The charge was placed in the crucible with all of the elements together from the beginning. The copper that was utilized was C110 (99.9 wt pct, 0.04 wt pct oxygen max), the nickel source was 99.9 wt pct pure nickel shot, and the manganese was electrolytic plate manganese (99.9 wt pct, metallic). The alloys were melted and poured at 1423 to 1473 K (1150 to 1200.degree. C.) into a steel mold, producing slugs 2.5 cm in diameter and 10 cm tall. It should be noted that FIG. 4 contains a ternary composition diagram, which is typically used to indicate compositions of ternary alloys and its form and usage is very familiar to those of ordinary skill in the art and has been well described in literature.

[0032] Samples for optical microscopy of the alloys made as described above were sectioned by an abrasive saw, then ground on silicon carbide paper from 320 to 600 grit. Polishing was done with 6- and 9-.mu.m diamond paste with the final polish being done with a 0.05 .mu.m alumina slurry on napped cloths. To evaluate the solidification structure a micro etchant containing 25 g iron (III) chloride, 25 ml concentrated hydrochloric acid and 100 ml deionized water was used to reveal the morphology. Evaluation of the microstructure was done through the use of optical microscopy and scanning electron microscopy (SEM). The SEM used was an FEI.RTM. XL40 SEM with an acceleration voltage of 15 keV. Evaluation of the composition was done through Energy Dispersive X-ray Spectroscopy (EDS) in an SEM using a thin window detector (EDAX.RTM. ESEM 2020). Measurements were done using an accelerating voltage of 15 keV with an area analysis to evaluate the overall composition. Analysis was done through the EDAX program with standardless EDS through the use of the calibrated Standard Element Coefficients (SEC). X-Ray diffraction (XRD) was performed on the ingots using a Bruker.RTM. D-8 diffractometer with a copper source at a scan rate of 8 deg/min with measurements taken at increments of 0.02 deg from 2.theta. between 20 to 90 deg.

[0033] Alloy compositions made as described above were subjected to aging treatments in a box furnace in air at 723 K (450.degree. C.) for 1, 10, 20, 50 and 100 h. The temperature was measured/monitored through the use of a K-type thermocouple attached to an Omega.RTM. HH806AU reader. Temperature was observed to fluctuate by less than 15.degree. C. during the aging process. The specimens were .about.1 cm thick slices cut transversely from the as-cast slugs. After aging these samples were prepared for metallography by the same technique as described above. Vickers hardness testing was conducted using a LECO.RTM., LV-100 hardness testing apparatus. Each sample was tested 5 times with a load of 30 kgf.

[0034] It is to be recognized that the alloys were aged directly in the as-cast condition. As inferred from the Cu--Mn binary phase diagram and metallographic observations, the alloys .alpha. solidify to a single solid phase. In the Cu--Mn binary system, precipitation below the .alpha.(Mn) solvus temperature is known to be so sluggish that solution treatment prior to aging is not necessary. Hence we do not need to solution treat (namely, as in typical solution treatments, reheating from room temperature to a temperature higher than solvus temperature, hold and then quickly cool to room temperature). Such solution treatment is a normal step in age-hardening processes. But in the experiments leading to this disclosure no solution treatment was given to the alloys in the age-hardening treatments of this disclosure. A special feature of these alloys that we can age the cast structure directly without solution treatment, which is an advantage. However one can design age-hardening processes for the alloys of this disclosure that can include a solution treatment at a temperature higher than the solvus temperature. Thus the age-hardening process of this disclosure can include a solution treatment step. If a solution treatment is used in the Cu--Mn--Ni system, it can be done in the temperature range of 700-850.degree. C. Solution treatment step, when employed, precedes the aging step in a typical age-hardening process.

[0035] The results of EDS analysis have shown little loss of the alloying elements during melting, except for the first heat of the 5 wt pct Ni alloy which had a nickel content measuring closer to 2 wt pct Ni. The full composition is shown in FIG. 4. Therefore, another heat of the 5 wt pct Ni (target) alloy was made which showed minimal losses like all the other heats. Even though the 2 wt pct alloy was not a target composition, it was evaluated in the study. The as-cast alloy was shown to be single-phase with no appearance of .alpha.(Mn) phase. Observation of the unetched structure showed no formation of microshrinkage porosity, with some natural centerline macro shrinkage (pipe). After etching the as-cast morphology was then characterized to look for degree of cellular morphology and for the presence of microshrinkage porosity. A qualitative evaluation of the degree of cellularity is summarized below (The appearance of secondary arms was used as the criteria for setting the transition from cellular to dendritic solidification.):

TABLE-US-00001 Alloy Cu--Mn--Ni (wt pct) Percent Cellular 55-43-2 <1% 55-40--5 80% 50-40-10 40% 45-45-10 10% 3-50-20 5%

[0036] FIG. 5 shows an image of Cu-40Mn-10Ni alloy showing a cellular-to-dendritic breakdown typical of these alloys.

[0037] Compared to the Cu--Mn binary it appears that the freezing range for all these ternary alloys is too large for complete cellular solidification in conventional casting. It should be noted that during this study, however, even in the alloys with little to no cellular solidification (i.e., mostly or completely dendritic), the presence of microshrinkage porosity was not observed. This is unquestionably beneficial to as-cast mechanical properties, especially for fatigue resistance. Potentially, altering the casting parameters, such as increasing the superheat, may promote the desired solidification morphology. But since no microporosity was observed during this study, which was the goal for the as-cast structures, the freezing ranges appear to be sufficiently narrow to hinder fluid flow defects, even without the formation of a completely cellular (non-dendritic) structure.

[0038] The hardness of alloys as-cast is listed in Table I below (In Table 1, in the alloy designations represent weight percent of the corresponding element.)

TABLE-US-00002 TABLE I Hardness of the alloys in this study in the as-cast condition Alloy Composition Cu--Mn--Ni (wt pct) As-Cast Vickers Hardness (kg/mm.sup.2) 65-35-0 93 .+-. 4.0 55-43-2 99 .+-. 4.0 55-40-5 94 .+-. 1.7 50-40-10 98 .+-. 4.0 45-45-10 99 .+-. 3.4 30-50-20 106 .+-. 3.4

[0039] From Table I, it can be seen that the increase in Ni and Mn in these alloys from the Cu--Mn congruent composition (Cu-35 wt pct Mn) does increase the hardness (strength) by up to .about.20%, through solid solution strengthening alone, when compared to the congruent Cu--Mn binary alloy.

[0040] FIG. 6 shows a plot of hardness vs. aging time for the alloys studied in experiments leading to this disclosure. After aging, most of the alloys displayed a minimal aging response. Even the 5 wt pct Ni alloy, which is shown to exist in the .alpha.(Mn)+.gamma.(Cu,Mn) two-phase region at 450.degree. C., does not display a significant aging response to 100 h. Any increase in strength is likely due to the formation of the very small, .gamma.'(Mn) transitional phase that strengthened the binary Cu-35Mn wt pct alloy.

[0041] FIG. 7 shows a plot of hardness vs. aging time for the 2 wt pct Ni alloy and Cu-35Mn binary alloy. Referring to FIG. 7, the 2 wt pct Ni alloy, shows a marked aging response, when compared to the binary Cu-35Mn wt pct alloy. The aging response of this 2 wt pct Ni alloy when compared to the binary congruent alloy is much larger, leading to a hardness comparable to that of austenitic stainless steels.

[0042] To evaluate the aged microstructure, the 2 wt pct Ni alloy was etched and evaluated through SEM and optical microscopy. FIG. 8(a) is an optical image of the 2 wt pct Ni alloy after 100 h aging at 450.degree. C. After etching it can be seen that this alloy has retained the dendritic appearance (FIG. 8(a)), meaning that it did not completely homogenize during the aging treatment. FIGS. 8(b) and 8(c) are higher magnification (SEM) images of an area of the etched 2 wt pct Ni alloy. Referring to FIGS. 8(b) and 8(c), it can be seen that there is a plate-like phase that is only found in the intradendritic regions of the aged structure. The appearance of this phase in only the intradendritic regions can likely be explained by microsegregation that occurred during solidification. Due to the sluggish kinetics in this system, solidification most likely occurred in a manner close to Scheil conditions (no diffusion in the solid, complete mixing in liquid). This would allow for the intradendritic region to be richer in Mn and thus in the hardenable region, while the interdendritic region would be near or at the congruent point in the Cu--Mn binary, which is outside the hardenable region.

[0043] Through XRD analysis, the formation of .alpha.(Mn) after aging was confirmed by comparing the as-cast spectra to the spectra of samples aged for 100 h at 450.degree. C. FIG. 8(d) shows the XRD spectrum for as-cast structure of the 2 wt pct Ni alloy and FIG. 8 (e) shows the XRD spectrum for the 2 wt pct Ni alloy aged for 100 h at 450.degree. C. The XRD results also show the formation of a second FCC phase when comparing the as-cast and aged samples. This most likely corresponds to the .gamma.' phase. Due to the difference in composition between the interdendritic and intradendritic regions it is possible that the different phases precipitated in each region. That is, the intradendritic regions precipitated the .alpha.(Mn) like an alloy in the hardenable region, while the interdendritic regions acted more like the near-congruent Cu--Mn binary alloy.

[0044] Homogenization may lead to an increase in strength with the whole microstructure being aged or it may move the composition away from a hardenable composition all together. Manipulation of the as-cast structure and the microsegregation present may be a way to get age-hardenable alloys that have average compositions outside of the hardenable region and closer to the narrow freezing range trough in the Cu--Mn--Ni system to minimize the freezing range and promote a more cellular or less dendritic structure. It is also important to note that the freezing range, although not narrow enough for completely cellular growth, was not wide enough to yield shrinkage porosity in any of the Cu--Mn--Ni alloys of this disclosure, which is the primary benefit of the near-congruent Cu--Mn alloys. That is, the onset of microporosity formation occurs at a wider freezing range than the onset of transition from cellular to dendritic solidification. Therefore if the criterion for selecting alloy compositions is to obtain a defect free structure, instead of a cellular structure, there is increased freedom for creating an alloy with a better aging response.

[0045] As mentioned previously, a solution treatment step that also serves as homogenizing treatment step can be set up. The terms homogenization and solution treatment are sometimes used synonymously. Such a homogenization/solution treatment step before aging is most generally conducted between the solvus and the solidus (which depend on composition). The temperature range for such a step before aging can be 700-850.degree. C. for alloys of this disclosure, depending on the composition.

[0046] In this disclosure, the effect of Ni on the mechanical properties was evaluated in parallel with the resulting cast morphology to gauge Ni as a potential ternary alloying addition to increase the strength without sacrificing the benefits of the cast morphology found in the near-congruent Cu--Mn binary alloys. Evaluation of the as-cast morphology showed varying degree of cellular solidification, with the 2 weight percent Ni alloy showing the least and the 5 weight percent alloy the most, 1% and 80% cellular morphology, respectively. Even though the amount of cellular solidification varied from alloy to alloy, no microshrinkage porosity was observed in any of the Cu--Mn--Ni alloys of this study. As for the aging response, the 2 weight percent Ni alloy was shown to increase the hardness by more than 100 percent after 100 h aging heat treatment through the precipitation of .alpha.(Mn) phase in the intradendritic regions. Aging responses in the other alloys showed very little hardness increase with aging treatment. Important factors were identified that could optimize the aging response of these alloys including evaluation of the effect of the as-cast microstructure on aging response and possible compositions that can be conventionally cast free of microshrinkage porosity.

[0047] As described above, precipitation-hardenable casting alloys have been demonstrated in the Cu--Mn--Ni ternary system, along a line of compositions between the congruent points in the Cu--Mn and Ni--Mn binary systems. As mentioned earlier, this disclosure is related to U.S. patent application Ser. No. 13/441,611, filed Apr. 6, 2012 which covers near-congruent Cu--Mn alloys. The Ni--Mn system also has a congruent freezing point (minimum) and the available thermodynamic data indicate that the Cu--Mn--Ni ternary system exhibits a trough of narrow freezing range compositions between the two binary congruent points, making these ideal compositions for castability, as taught in the above applications for the Cu--Mn system. In this disclosure, compositions near the narrow freezing range trough in the Cu--Mn--Ni system with up to 25 wt pct Ni were utilized to take advantage of the narrow freezing range for high castability.

[0048] FIG. 9 shows a comparison of the aging responses of the near-congruent Cu--Mn alloy and some Cu--Ni--Mn alloys of this disclosure. The higher hardness values (.about.200 HV) are in the realm of austenitic stainless steels and approaching precipitation-hardened Cu--Be alloy, which is the only significant commercial Cu-based alloy that is age-hardened. While the solidification structure of the age-hardening alloys was not completely cellular like the near-congruent Cu--Mn binary alloy, the narrow freezing range was still sufficient to hinder the formation of microshrinkage porosity. The increased aging response is also possible in the binary Cu--Mn system (0% Ni) with increased Mn.

[0049] The above description has established that addition of nickel followed by age-hardening is a viable technique to increase hardness of the ternary Cu--Mn--Ni alloy. It is well known to those skilled in the art that increased hardness implies increased mechanical strength. It is further known that a strong correlation exists between mechanical strength and fatigue strength. The higher the mechanical strength of a metal or alloy is, the higher is its fatigue strength. Thus the principles and methods of this disclosure clearly teach techniques to increase the fatigue resistance of Cu--Mn alloys by ternary additions such as, but not limited to, nickel.

[0050] Based on the above description, we can define a ternary alloy comprising copper, manganese and a ternary element wherein copper, manganese, and the ternary element are melted together and cast into an article and the article is subjected to an age-hardening treatment. In particular, the ternary element can be nickel. Other non-limiting examples of the ternary element include cobalt, chromium, iron and zinc. In employing nickel, it is clear from the above-described studies that nickel content can vary in a non-limiting range of 1-25 weight percent. Further, it can be inferred from the studies described above, that Cu--Mn--Ni alloys can be made advantageously such that weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55. These compositions are indicated as a parallelogram designated as 401 in FIG. 4. The alloys contained in the parallelogram 401 can be age-hardened in a temperature range of 300.degree. C. to 600.degree. C., a range based on the kinetics of precipitation and thermodynamic stability of the precipitated phases. Thus while some of the data reported in this disclosure refers to an aging temperature of 450.degree. C., a range of 300.degree. C. to 600.degree. C. can be used for aging temperature. Aging time can vary between 1 h and 100 h.

[0051] It is further clear that based on the studies conducted, a process for producing an age-hardened copper-manganese-nickel alloy can be described. The process included melting a composition comprising copper, manganese and nickel; pouring the molten composition comprising copper, manganese, and nickel to form a casting with a composition comprising copper, manganese, and nickel; and aging the casting at a temperature in the range of 300.degree. C. to 600.degree. C. The aging period in this process can vary from 1 h to 100 h and the nickel content can vary from 1 to 25 weight percent. Further, alloys that lend themselves to this process include Cu--Mn--Ni alloys which have weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55. These compositions are indicated as within the parallelogram designated as 401 in FIG. 4.

[0052] Based on the above descriptions, articles or products for various applications, such as plumbing as a non-limiting example, can be made using the method of forming a melt comprising copper, introducing manganese into the melt, and adding other elements or metals, casting the alloy in a mold to form the article. The cast-alloy can then be subjected to age-hardening processes as described in this disclosure. In a preferred embodiment, the element added is nickel. Instead of introducing manganese into the melt, metals (Cu, Mn) and/or any other elements or metallic additives can be melted together. In particular, an article, such as but not limited to a plumbing valve or fitting can be made from an alloy comprising copper; manganese; and a ternary element, wherein copper, manganese and the ternary element are in a cast form and the cast form has subsequently undergone age-hardening treatment. In particular, the ternary element can be nickel in the range of 1-25 weight percent. Further it is advantageous to have the composition of the Cu--Mn--Ni alloy of such an article be such that weight percent of nickel is in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55. These compositions are indicated as within the parallelogram designated as 401 in FIG. 4. The melting and casting temperature for the alloys shown in the region 401 of FIG. 4 is in the range of 875.degree. C. to 1200.degree. C. Again the aging temperature can vary between 300.degree. C. and 600.degree. C. and the aging time can vary between 1 h and 100 h.

[0053] It is also an objective of this description to disclose ternary alloys comprising copper, manganese, and a ternary element melted and solidified into a casting, wherein the microstructure of the solidified casting shows substantially low microporosity attributable to dendritic growth. In this disclosure, microporosity has the usual meaning of interdendritic porosity on the size scale of the dendrite arms or smaller, that results from insufficient liquid flow to feed solidification shrinkage; and by low microporosity, we mean microporosity less than about 1%. by volume. It is advantageous to use nickel as the ternary element. Further, in order to achieve the benefits of cellular solidification with much reduced dendritic growth, preferred embodiments include copper-manganese-nickel compositions with weight percent of nickel in the range of about 1 to about 25 and the weight percent of manganese is in the range of about 35 to about 55. These compositions are indicated as within a parallelogram designated as 401 in FIG. 4. It is further advantageous if the compositions in the region 401 are closer to the line 402 shown in FIG. 4, connecting the congruent point compositions of the Cu--Mn binary and the Ni--Mn binary. The closer the compositions of the region 401 are to the line 402, the narrower is the expected freezing range for a Cu--Mn--Ni alloy and greater the advantage in reducing microporosity attributable to dendritic solidification.

[0054] In the Cu--Mn--Ni alloys and composition, process and article embodiments described above, that include an aging treatment, and the aging treatment can be optionally preceded by a solution treatment at a temperature in the range of 700-850.degree. C.

[0055] It is to be recognized that compositions falling into the region 401 of the ternary composition diagram of FIG. 4 can be used in the as-cast condition and need not be age-hardened, and even without age-hardening can give higher strength than many previously known forms and give rise to desirable microstructure with low microporosity attributable to dendritic growth.

[0056] The articles or products that can be produced for various applications, such as plumbing as a non-limiting example, can be made using a method of: forming a melt comprising copper, introducing manganese into the melt, adding other elements or metals into the melt, and melting copper, manganese and added elements to form an alloy, and casting the resulting alloy into a mold to form the article, wherein the carbon and oxygen contents of the alloy are controlled in order to control the formation of graphite, manganese carbide, and/or manganese particles within the article. Methods of controlling the copper and oxygen contents during the melting process of such alloys are described in U.S. patent application Ser. No. 13/441,611 (Publication No. US 2013/0094989 A1), the contents of which are incorporated by reference herein in their entirety.

[0057] The cast-alloy can then be subjected to age-hardening processes as described in this disclosure. In a preferred embodiment, the element added is nickel. It should be noted that in melting the alloy for making the casting, the metals, copper and manganese and nickel can also be melted together. Further nickel can be added to molten copper before manganese is added. Nickel can also be introduced into the Cu--Mn melt. Those skilled in the art will be able to infer many other ways of achieving the desired composition for the melt before pouring into the mold for making the casting.

[0058] It should be recognized that ternary elements other than nickel can be used as the ternary element in alloys of this disclosure. Examples of such ternary elements include, but are not limited to, cobalt, zinc, chromium, and iron. It is possible to add more than one of the elements from this non-limiting group of nickel, cobalt, zinc, chromium, and iron to a copper-manganese binary system and apply the principles and methods of this disclosure. Thus it is an objective of this disclosure to teach that by employing methods and principles of this disclosure it is possible to have 4-component, 5-component systems or in general terms multi-component systems. In accordance with the principles of this disclosure these systems can be narrow freezing range and/or age-hardenable. Thus those skilled in the art will recognize that the teachings of this disclosure are not limited to binary and ternary alloy systems.

[0059] While this disclosure describes several compositions, it is to be understood that other additives are possible. While specific age-hardening treatments are described in detail in terms of time and temperature, other combinations will be apparent to those skilled in the art. This disclosure is intended to cover all compositions described, methods described, age-hardening treatments and methods of making articles using the processes described here. It is also possible to apply age-hardening treatments described here to articles made of alloys with compositions described here that have been already cast into articles.

[0060] While the present disclosure has been described with reference to certain embodiments, it will be apparent to those of ordinary skill in the art that other embodiments and implementations are possible that are within the scope of the present disclosure without departing from the spirit and scope of the present disclosure. For example, other similar compositions and variation of the aging treatment disclosed in this disclosure can be adapted by those skilled in the art. Addition of other elements and/or metals or combinations of elements or metals to achieve desired microstructures can be inferred by others skilled in the art. Further, additions of other elements or metals, or combinations of elements or metals, to enhance mechanical properties by suitable aging treatments are also possible and can be derived from this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting. Thus, this disclosure is limited only by the following claims.

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