RAPID SOLIDIFIED DUCTILE Cu-Al-Mn RIBBON FOR ELASTOCALORIC APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application No. 63/654,473, filed May 31, 2024, the entire teachings and disclosure of which are incorporated herein by reference thereto.

This invention was made with government support under DE-AC02-07CH11358 awarded by the Department of Energy. The government has certain rights in the invention.

This invention generally relates to an elastocaloric material and, in particular, to a melt-spun Cu—Al—Mn ribbon with enhanced elastocaloric and magnetic properties.

Elastocaloric cooling (EC) exploits the latent heat of the reversible martensite transformation of shape memory alloys for refrigeration and space conditioning applications. Instead of cycling between the gas and liquid phases of the refrigerant in vapor-compression technology that causes concerns on global warming, EC uses a solid crystalline material and cycles between its two different crystal structures (i.e., austenite and martensite) through mechanical loading and unloading. This gives EC the inherent advantage of being environmentally friendly. EC systems have also been identified to be more efficient than the vapor-compression systems. It is estimated that EC systems can deliver substantial energy savings to the nation with 790 TWh of energy per year and have been identified as the most promising non-vapor compression-based cooling and refrigeration technology.

Since the first discovery of EC effect more than 160 years ago, significant progress has been made in this field, including the discovery of many alloys that show prominent EC effects. The effectiveness of the EC materials can be roughly estimated by its latent heat as the associated adiabatic temperature change ΔTis proportional to L/Cp, where L is the latent heat and Cp is the heat capacity.summarizes the latent heat of various EC materials. Ni—Mn—Z are alloys where Z is Ga, In, or Sn (p-block). Ni—Mn—Ti are all-d-metal full Heusler alloys. Heusler alloys have low latent heat values, typically less than 5 J/g, except for that of Ni—Mn—Sn—Cu and Ni—Mn—Sb—Co, which have 17.3 J/g and 10.2 J/g, respectively. Copper-based alloys typically exhibit latent heat values of around 5 J/g. Ni—Ti alloys typically show a latent heat of 10-20 J/g with the highest value of 35.1 J/g seen in a NiTiHfalloy. VOhas been identified as a new candidate, and its latent heat can be as high as 51.5 J/g induced by hydrostatic stress. Due to the large latent heat from Ni—Ti, a large cooling effect of 17° C. was demonstrated on Ni—Ti via wire tensile experiments. And a recent breakthrough in adiabatic temperature change of as high as 31.5° C. was demonstrated on a Ni—Mn—Ti alloy.

In addition to latent heat, other factors such as materials cost and availability, transformation stress, hysteresis, ductility, and transformation temperature window can be equally important. Copper-based alloys (i.e., Cu—Al—Mn, Cu—Al—Ni) stand out due to their low cost, low transformation stress, and wide compositional-dependent transformation temperature window. Cu—Al—Mn alloy can also be ductile through composition tuning and processing design. The high-temperature bcc β phase of the alloy responsible for the martensitic transformation can experience an order-disorder transition, A2 (disordered bcc Cu)—B2 (CuAl)—DO—(CuAl), and embrittle the alloy. Increasing Mn content widens the β phase region and results in Heusler L2(CuAlMn) magnetic order, while increasing Al content (which strongly affects the martensitic transformation temperature) leads to a higher degree of order. The order-disorder transition may be fully bypassed if the Al content is less than 18 at. %.

The alloy's ductility and shape memory properties are also affected by grain size and orientation. Larger β grains are desirable for improving recoverable strain due to the relaxation of grain geometrical constraints. However, β alloy with coarse grains is susceptible to intergranular fracture because of its abnormally high elastic anisotropy. Therefore, the microstructure of the alloy must be appropriately controlled for a balance of ductility and shape memory properties. Recent studies show columnar or bamboo (i.e., oligocrystalline) grain is preferred for improved shape memory properties, cyclic stability, and elastocaloric effect for Cu—Al—Mn alloy. However, such improved grain structure is achieved either by directional solidification or repeated thermomechanical processing, which is cost-ineffective and energy-intensive.

Rapid solidification by melt spinning is known to bypass order-disorder transformation and promotes the formation of columnar grains. The process directly produces continuous thin ribbons (such as ribbons having a thickness of ˜20 μm and a width of ˜1 mm) that may be of interest to miniature EC systems. However, studies on melt-spun copper-based ribbons are rare and focused mainly on the transition temperatures. According to the present disclosure, the order-disorder transition, microstructure, tensile property, phase transformation characteristics, and elastocaloric potential for melt-spun Cu—Al—Mn ribbons has been systematically studied.

In a first aspect, embodiments of the present disclosure relate to a ribbon of elastocaloric material. The ribbon comprises copper alloyed with aluminum and manganese. The ribbon comprises a length, a width, and a thickness. The length is a longest dimension of the ribbon, and the width is perpendicular to the length. The thickness is perpendicular to both the length and the width, and the thickness is 0.1 mm or less. In a room temperature ambient environment, the ribbon increases in temperature by at least 4° C. upon application of 6% of tensile strain and cools by at least 4° C. when the tensile strain is unloaded.

In a second aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the first aspect in which a microstructure of the ribbon is oligocrystalline comprising columnar grains extending across a thickness of the ribbon separated by intergrain nodes. The columnar grains each comprise a width, and the width is at least twice the thickness.

In a third aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect in which the ribbon exhibits an induced magnetic moment of at least 1 emu/g in an applied magnetic field of ±30 kOe.

In a fourth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect or the third aspect in which the ribbon exhibits a latent heat of martensitic transformation of at least 5.0 J/g.

In a fifth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect to the fourth aspect, comprising an elastic modulus of at least 10 GPa.

In a sixth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect to the fifth aspect, comprising a yield strength (σ) of at least 50 MPa.

In a seventh aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect to the sixth aspect, comprising a critical transformation stress of at least 50 MPa

In an eighth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect to the seventh aspect, comprising an ultimate tensile strength of at least 200 MPa.

In a ninth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the second aspect to the eighth aspect, comprising a total strain before failure of at least 5%.

In a tenth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the first aspect in which a microstructure of the ribbon comprises columnar grains extending across a thickness of the ribbon and wherein the columnar grains each comprise a width, the width being less than the thickness.

In an eleventh aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the first aspect to the tenth aspect in which the copper alloyed with aluminum and manganese comprises a formula of CuAlMn, where x=17±5, and y=11±5.

In a twelfth aspect, embodiments of the present disclosure relate to the ribbon of elastocaloric material of the first aspect to the eleventh aspect in which the copper alloyed with aluminum and manganese further comprises up to 5 at % of a metal selected from a group consisting of Ni, Ag, Au, Zn, Sn, Ti, Cr, Fe, Co, Si, and combinations thereof.

In a thirteenth aspect, embodiments of the present disclosure relate to a cloth comprising at least one ribbon of elastocaloric material according to any of the first aspect to the twelfth aspect.

In a fourteenth aspect, embodiments of the present disclosure relate to a method of preparing a ribbon elastocaloric material. In the method, a stream of the elastocaloric material in a molten form is directed onto an outer surface of a rotating wheel. The elastocaloric material comprises copper alloyed with aluminum and manganese. The stream of elastocaloric material is cooled on the outer surface of the rotating wheel to form the ribbon. The ribbon is removed from the outer surface of the rotating wheel. The ribbon comprises a thickness as measured perpendicular to the outer surface, and the thickness is 0.1 mm or less.

In a fifteenth aspect, embodiments of the present disclosure relate to the method according to the fourteenth aspect in which the ribbon is annealed at a temperature in a range from 600° C. to 1100° C. for a time in a range from 5 minutes to 10 hours.

In a sixteenth aspect, embodiments of the present disclosure relate to the method according to the fourteenth aspect or the fifteenth aspect in which the ribbon is aged at a temperature in a range from 50° C. to 500° C. for a time in a range from 1 minutes to 2 hours.

In a seventeenth aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect in which, after aging, the ribbon comprises an oligocrystalline microstructure having columnar grains extending across the thickness of the ribbon. The columnar grains are separated by intergrain nodes, and the columnar grains each comprise a grain width that is at least twice the thickness.

In an eighteenth aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect or the seventeenth aspect in which the ribbon exhibits an induced magnetic moment of at leastemu/g in an applied magnetic field of ±30 kOe.

In a nineteenth aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the eighteenth aspect in which the ribbon exhibits a latent heat of martensitic transformation of at least 5.0 J/g.

In a twentieth aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the nineteenth aspect in which the ribbon comprises an elastic modulus of at least 10 GPa.

In a twenty-first aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the twentieth aspect in which the ribbon comprises a yield strength (σ) of at least 50 MPa.

In a twenty-second aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the twenty-first aspect in which the ribbon comprises a critical transformation stress of at least 50 MPa.

In a twenty-third aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the twenty-second aspect in which the ribbon comprises an ultimate tensile strength of at least 200 MPa.

In a twenty-fourth aspect, embodiments of the present disclosure relate to the method according to the sixteenth aspect to the twenty-third aspect in which the ribbon comprises a total strain before failure of at least 5%.

In a twenty-fifth aspect, embodiments of the present disclosure relate to the method according to any of the fourteenth aspect to the twenty-fourth aspect in which the copper alloyed with aluminum and manganese comprises a formula of CuAlMn, where x =17±5, and y=11±5.

In a twenty-sixth aspect, embodiments of the present disclosure relate to the method according to any of the fourteenth aspect to the twenty-fifth aspect in which the copper alloyed with aluminum and manganese further comprises up to 5 at % of a metal selected from a group consisting of Ni, Ag, Au, Zn, Sn, Ti, Cr, Fe, Co, Si, and combinations thereof.

Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.

Cu—Al—Mn alloys display martensitic transformation over a wide range of temperatures. In addition to low cost, this alloy is known for its low transformation stress with reasonable latent heat favoring elastocaloric applications. However, the ductility of Cu—Al—Mn can be limited owing to ordering and intergranular fracture. Through rapid solidification by melt spinning, Applicant has demonstrated that Cu—Al—Mn ribbon can be made highly ductile (greater than 8% tensile strain in the as-spun state and 10% tensile strain after heat treatment). The ductility of the melt-spun ribbon is related to the suppression of L2ordering that is characterized through magnetic property measurement. Heat treatment of the ribbon promotes “bamboo” grain formation, and the latent heat is increased to 6.4 J/g. Under tensile conditions, embodiments of the presently disclosed Cu—Al—Mn ribbon exhibited about 4° C. temperature change (4.4° C. on heating and 4.2° C. on cooling) from 6.3% strain. These and other aspects and advantages of the disclosed elastocaloric Cu—Al—Mn ribbon will be described more fully in relation to the embodiments presented below and in the figures. These embodiments are presented by way of illustration and not limitation.

Embodiments of the present disclosure relate to a ribbonof an elastocaloric material. In one or more embodiments, the elastocaloric material comprises copper (Cu), aluminum (Al), and manganese (Mn). In one or more embodiments, the elastocaloric material has the formula of CuAlMn, where x=11±5, and y=17±5. Minor alloying elements may also be added to the material system, such as Ni, Ag, Au, Zn, Sn, Ti, Cr, Fe, Co, and Si in a combined amount of up to 5 at %.

As shown in, the ribbonis produced using a melt-spinning apparatus. The apparatusincludes a cruciblethat contains an elastocaloric material feedstock. Disposed around the crucibleis a heating element, such as an inductive heating element, among other possibilities. The heating elementis configured to melt the elastocaloric material feedstock, and the molten elastocaloric material feedstockis forced through a nozzleof the crucibleas a streamof molten elastocaloric material. In one or more embodiments, the molten elastocaloric material feedstockis forced through the nozzleusing pressurized gas, such as an inert gas (e.g., argon).

The streamis directed onto a spinning wheel. As shown in, the wheel is depicted as rotating, which allows the streamto contact an uncovered surface of the wheel. In this way, the surface of the wheelimmediately cools the streamof molten elastocaloric material to produce the solidified ribbonof elastocaloric material. To facilitate cooling, in one or more embodiments, the wheelis cooled with a fluid, such as water. In one or more embodiments, the wheelis rotated at a speed of at leastm/s (tangential speed), in particular at a speed of at least 10 m/s (tangential speed). The degree of cooling is dependent, at least in part, on the length of time that the stream/ribbon/is in contact with the outer surface of the wheel. In one or more embodiments, the ribbon of elastocaloric material is in contact with the outer surface of the rotating wheelover an arcuate distance (D) of at least 25 mm. In one or more embodiments, the rotating wheel has a diameter of about 250 mm or more. In one or more embodiments, the ribbonof elastocaloric material is in contact with the rotating wheelfor at least 5° of rotation (as denoted by rotation angle θ in). Advantageously, the molten elastocaloric material cools at a rate on the order of 10° C./s, which allows the elastocaloric material to substantially or fully suppress the ordering transition A2-B2-L2and refines the microstructure to contribute to well-balanced strength and ductility.

In one or more embodiments, the melt-spun ribbonof clastocaloric material is further annealed. In one or more such embodiments, the annealing takes place at a temperature in a range from 600° C. to 1100° C. for a time of 5 minutes to 10 hours. Further, in one or more embodiments, the annealed ribbonis quenched, e.g., in brine ice water. In one or more embodiments, the melt-spun and annealed ribbonof elastocaloric material is aged. In one or more such embodiments, the aging is performed at a temperature in a range of 50° C. to 500° C. for a time of 1 minute to 2 hours. Further, in one or more embodiments, the aging may be performed in air. As will be discussed more fully below, the aging process may be used to tune certain properties of the melt-spun ribbon, such as its magnetic properties.

In one or more embodiments, the ribbonexhibits an ultimate tensile strength of at least 200 MPa, in particular at least 300 MPa, and most particularly up to about 350 MPa. In one or more embodiments, the ribbonexhibits a yield strength (60.2) of at least 50 MPa, in particular at least 100 MPa. In one or more embodiments, the ribbonexhibits a critical transformation stress of at least 50 MPa. In one or more embodiments, the ribbonexhibits an elastic modulus of at least 10 GPa, in particular at least 11 GPa. In one or more embodiments, the ribbonexhibits a tensile ductility (i.e., total tensile strain before failure) of at least 5%, in particular at least 8%, and most particularly up to about 15%. The ribbonexhibits mechanical properties far exceeding the properties reported in the literature for Cu—Al—Mn alloys (typically 100-200 MPa yield strength and less than 10% tensile strain).

In one or more embodiments, the ribbonexhibits an oligocrystalline, or “bamboo,” microstructure in which narrow crystalline nodes separate wide columnar, internodal crystal grains. Such structure can be seen and will be more fully described below in relation to. In one or more other embodiments, the ribbonexhibits a microstructure containing columnar grains in which a width of the grains (dimension extending into the depth of the ribbon) is more than the height (in the thickness direction) of the columnar crystal as can be seen and will be more fully described below in relation to.

In one or more embodiments, the ribbonsproduced via melt-spinning have a thickness (dimension of ribbonperpendicular to the outer surface of the wheel) of 0.1 mm or less, in particular in a range from 0.01 mm to 0.1 mm. The thickness of the ribboncan be controlled, e.g., based on the speed of the spinning wheeland the rate of flow of the streamof molten elastocaloric material. In one or more embodiments, the ribbonshave a width in a range from 0.1 mm to 300 mm. Commercially, melt-spun ribbonsare typically produced having widths of about 50 mm or about 250 mm. Further, in one or more embodiments, the ribbonsmay be melt-spun to lengths up to 1000 m. While not particularly limited, the ribbonstypically have a length of at least 10 m when produced via melt-spinning.

In one or more embodiments, the ribbonproduced via melt-spinning, after having been annealed, quenched, and aged, exhibits an induced magnetic moment of at least 1 emu/g, in particular at least 3 emu/g, and most particularly at least 5 emu/g, in an applied field of ±30 kOe.

In one or more embodiments, the ribbonproduced via melt-spinning exhibits a latent heat for martensitic transformation of at least 5 J/g, in particular at least 6 J/g. In one or more embodiments, the ribbonexhibits a thermal hysteresis for austenite finishing temperature (Af)-martensite finishing temperature (Mf) in a range of about 1° C. to about 100° C., in particular about 55° C. Further, in one or more embodiments, the ribbonproduced via melt-spinning exhibits a change in temperature of at least 4° C. when loaded to or unloaded from a tensile strain of about 6%.

An ingot of CuAlMn(nominal composition in at. %) was prepared by arc melting of elemental Cu, Al, Mn chunks (>99.9%) acquired from the Materials Preparation Center at Ames National Laboratory. The alloy ingot was melt spun to ribbons using a custom-built melt spinner with a vacuum chamber partially filled with ⅓ of ultra-high purity helium. The melt spinner included a quartz crucible nozzle having a diameter of 0.81 mm. Further, the melt spinner melt shot temperature was 1150° C., and the overheat pressure was 120 Torr. The copper wheel had a diameter of 25 cm, a width of 2.5 cm, and rotated at a speed of 30 m/s. The melt-spun strip was annealed in a helium-filled quartz ampule at 900° C. for 2 hours, followed by quenching in brine ice water. The melt-spun and annealed ribbon was subsequently aged at 200° C. in air.

is a photograph of a collection of ribbons after the melt-spinning process. The ribbon has a width of 1 mm and a thickness of 20-30 μm, controlled mainly by nozzle size and wheel speed. The ribbon is continuous (tens of meters long) with excellent surface quality, and as shown in the inset of, the ribbon can be wound onto a cylinder.

Cross-sectional microstructures (along the ribbon length direction) of the ribbons were analyzed using Scanning Electron Microscope (SEM) (Teneo, FEI Inc) equipped with Energy Dispersive X-ray Spectroscopy (EDS) detector. The ribbons were mounted on their side and polished and etched with% nital prior to imaging.depicts the as-spun ribbon, which exhibits a columnar grain microstructure with the grains aligned substantially parallel to the thickness direction (T). Such columnar gain microstructure is commonly observed in melt-spun ribbons as it follows the heat extraction from the wheel side to the free side of the ribbon. However, the as-spun ribbon does not show any stress-induced martensitic (SIM) transformation at room temperature, presumably because of the large quench in vacancy density and unstable martensite formation (see discussion below relative to the DSC analysis). To facilitate SIM, the ribbon was annealed and aged. The heat treatment resulted in significant recrystallization, grain growth, and the formation of oligocrystalline grains as shown in. The height of the grains extends to the ribbon's full thickness (T), while the length (L) of the grains is about 3-4 times the ribbon's thickness (T). In this way, the grains of the ribbon highly resemble the cellular structure seen in bamboo in which nodes separate internodal grains. EDS confirmed the composition of the ribbons, and it matched the nominal composition.

Tensile tests were conducted using a universal testing machine (Zwick/Roell, zwickiLine) equipped with a laser extensometer using a strain rate of 1×10son a single ribbon. Each of the samples tested was pre-loaded at 50 MPa. The as-spun ribbon exhibited a yield strength (YS) of about 400 MPa, and tensile ductility of at least 8% as in. Failure of the as-spun ribbon was likely due to defects in the ribbon.