COBALT-BASED ALLOY, WEARABLE ARTICLE AND PREPARATION METHOD FOR METAL PRODUCT

Abstract

 A cobalt-based alloy, a wearable article, and a preparation method for a metal product. The cobalt-based alloy consists of the following chemical components in percentage by weight: at least about 50% cobalt, at least about 20% chromium, at least about 0.1% molybdenum, and the remainder being one or more of the groups consisting of the following chemical components: manganese, vanadium, tungsten, nickel, titanium, iron, aluminum, lanthanum, tantalum, iridium, cerium, phosphorus, carbon and inevitable impurities. The cobalt-based alloy has the properties of high ductility, deformability and hardness, and is therefore particular suitable for being made into the wearable article.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a cobalt-based alloy, a wearable object, and a method for preparing a metal product, and in particular to a wearable object made of the cobalt-based alloy and a preparation method thereof.

BACKGROUND

[0002] Cobalt-chromium alloys have excellent corrosion resistance and high-temperature resistance. Due to these properties and their biocompatibility, cobalt-chromium alloys are commonly used in applications (such as gas turbines) in harsh environments, and in medical and dental applications (such as implants for dental and orthopedic departments). However, traditional cobalt-chromium alloys generally have poor deformability and are prone to cracking, making them difficult to produce delicate and complex items (such as inlaid jewelry).

SUMMARY

[0003] In a first aspect, the present disclosure provides a cobalt-based alloy, consisting essentially of the following chemical components by weight percentage: at least about 50% of cobalt, at least about 20% of chromium, at least about 0.1% of molybdenum, and a balance being one or more selected from the group consisting of manganese, vanadium, tungsten, nickel, titanium, iron, aluminum, lanthanum, tantalum, iridium, cerium, phosphorus, and carbon, and inevitable impurities.

[0004] In some embodiments, a weight percentage of the cobalt is in a range of about 50% to about 70%.

[0005] In some embodiments, a weight percentage of the cobalt is greater than about 67%.

[0006] In some embodiments, a weight percentage of the chromium is in a range of about 20% to about 40%.

[0007] In some embodiments, a weight percentage of the molybdenum is in a range of about 0.1% to about 5%.

[0008] In some embodiments, a weight percentage of the molybdenum is about 2%.

[0009] In some embodiments, a weight percentage of the balance is less than about 5%.

[0010] In some embodiments, a weight percentage of the nickel is less than about 0.4%.

[0011] In some embodiments, the cobalt-based alloy has a Vickers hardness of at least about 270.

[0012] In some embodiments, the cobalt-based alloy is a duplex cobalt-based alloy.

[0013] In some embodiments, the duplex cobalt-based alloy has a hexagonal close-packed (HCP) phase and a face-centered cubic (FCC) phase.

[0014] In some embodiments, a ratio of the HCP phase to the FCC phase is about 1: 1.

[0015] In a second aspect, the present disclosure provides a wearable object, including a cobalt-based alloy. The cobalt-based alloy may be the cobalt-based alloy in the first aspect.

[0016] In some embodiments, the wearable object includes one selected from the group consisting of a timepiece and a jewel.

[0017] In some embodiments, the jewel includes one selected from the group consisting of a bracelet and a ring.

[0018] In a third aspect, the present disclosure provides a method for preparing a metal product, including: forming a casting from a cobalt-based alloy, where the cobalt-based alloy consists essentially of the following chemical components by weight percentage: at least about 50% of cobalt, at least about 20% of chromium, at least about 0.1% of molybdenum, and a balance being one or more selected from the group consisting of manganese, vanadium, tungsten, nickel, titanium, iron, aluminum, lanthanum, tantalum, iridium, cerium, phosphorus, and carbon, and inevitable impurities; and subjecting the casting to processing, where the processing includes: subjecting the casting to a heat treatment and then a cold treatment repeatedly by quenching. The cobalt-based alloy may be the cobalt-based alloy in the first aspect.

[0019] In some embodiments, subjecting the casting to processing includes the following steps in sequence: subjecting the casting to a heat treatment at a temperature of 1,100°C to 1,400°C for about 1 h to obtain a heated casting; quenching and cooling the heated casting to obtain a cooled casting; subjecting the cooled casting to a heat treatment at a temperature of 800°C to 1,000°C for about 4 h to obtain a heated casting; and quenching and cooling the heated casting.

[0020] In some embodiments, a temperature of the casting after the forming is in a range of 1,450°C to 1,700°C, and the subjecting the casting to processing comprises the following steps in sequence: cooling the casting at 1,100°C to 1,400°C until a temperature of the casting is in a range of 1,100°C to 1,400°C to obtain a cooled casting, and holding the cooled casting at 1,100°C to 1,400°C for about 1 h to obtain a held casting; cooling the held casting at 800°C to 1,000°C until a temperature of the held casting is in a range of 800°C to 1,000°C to obtain a cooled casting, and holding the cooled casting at 800°C to 1,000°C for about 1 h to obtain a held casting; and cooling the held casting at 400°C to 600°C until a temperature of the held casting is in a range of 400°C to 600°C to obtain a cooled casting, and holding the cooled casting at 400°C to 600°C for about 1 h.

[0021] In some embodiments, subjecting the casting to processing further comprises milling or polishing the casting.

[0022] In some embodiments, forming the casting includes forming the casting by lost wax casting.

[0023] In some embodiments, the metal product includes a duplex cobalt-based alloy.

[0024] In some embodiments, the duplex cobalt-based alloy has a hexagonal close-packed (HCP) phase and a face-centered cubic (FCC) phase.

[0025] In some embodiments, a ratio of the HCP phase to the FCC phase is about 1: 1.

[0026] In some embodiments, the metal product is a wearable object. The wearable object may be the wearable object in the second aspect.

[0027] In some embodiments, the wearable object includes one selected from the group consisting of a timepiece and a jewel.

[0028] In some embodiments, the jewel includes one selected from the group consisting of a bracelet and a ring.

[0029] Compared with traditional cobalt-chromium alloys, the properties of the cobalt-based alloy, such as ductility and deformability, are effectively improved by optimizing the contents of various elements in the present disclosure, so that the cobalt-based alloy can be used in lost wax casting molding and precious stone setting processes. Moreover, the cobalt-based alloy according to the present disclosure has a gloss similar to white gold and platinum, but is much cheaper than white gold and platinum. Furthermore, the cobalt-based alloy according to the present disclosure is hypoallergenic to the human body, has desirable stability, is not easily oxidized and easy to clean and maintain, making it very suitable for use in wearable objects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present disclosure will now be described by way of examples with reference to the drawings, in which:

FIG. 1 shows a phase diagram of the cobalt-chromium alloy according to an embodiment of the present disclosure.

FIG. 2 shows a microscopic image of the polished surface of the cobalt-chromium alloy in FIG. 1.

FIG. 3 shows a curve of the porosity of the polished surface of the cobalt-chromium alloy in FIG. 1.

FIG. 4A shows a scanning electron microscopy (SEM) image of the polished surface of the cobalt-chromium alloy in FIG. 1.

FIG. 4B shows another SEM image of the polished surface of the cobalt-chromium alloy in FIG. 1.

FIG. 5A shows a microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 1.

FIG. 5B shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 1.

FIG. 6A shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 1.

FIG. 6B shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 1.

FIG. 7 shows a scanning electron microscopy (TEM) image of the etched surface of the cobalt-chromium alloy in FIG. 1.

FIG. 8 shows an X-ray diffraction (XRD) pattern of the cobalt-chromium alloy in FIG. 1.

FIG. 9A shows the traditional 316 stainless steel material after the surface friction test.

FIG. 9B shows the cobalt-chromium alloy in FIG. 1 after the surface friction test.

FIG. 10 shows a phase diagram of the cobalt-chromium alloy according to an another embodiment of the present disclosure.

FIG. 11A shows a microscopic image of the polished surface of the cobalt-chromium alloy in FIG. 10.

FIG. 11B shows another microscopic image of the polished surface of the cobalt-chromium alloy in FIG. 10.

FIG. 11C shows another microscopic image of the polished surface of the cobalt-chromium alloy in FIG. 10.

FIG. 11D shows another microscopic image of the polished surface of the cobalt-chromium alloy in FIG. 10.

FIG. 12A shows a microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 12B shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 13A shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 13B shows another microscopic image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 14A shows an SEM image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 14B shows another SEM image of the etched surface of the cobalt-chromium alloy in FIG. 10.

FIG. 15 shows an XRD pattern of the cobalt-chromium alloy in FIG. 10.

FIG. 16A shows the cobalt-chromium alloy according to a further another embodiment of the present disclosure after the surface friction test.

FIG. 16B shows the cobalt-chromium alloy according to a yet another embodiment of the present disclosure after the surface friction test.

FIG. 17A shows the cobalt-chromium alloy in FIG. 16A after the bending test.

FIG. 17B shows the cobalt-chromium alloy in FIG. 16B after the bending test.

FIG. 17C shows the cobalt-chromium alloy in FIG. 16A after the ductility test.

FIG. 17D shows the cobalt-chromium alloy in FIG. 16B after the ductility test.

FIG. 18A shows two rings made of the traditional 316 stainless steel material.

FIG. 18B shows the ring in FIG. 18A after the bending test.

FIG. 18C shows two rings made of the cobalt-chromium alloy in FIG. 1.

FIG. 18D shows the ring in FIG. 18C after the bending test.

FIG. 19A shows the watch case made of the cobalt-chromium alloy in FIG. 16A.

FIG. 19B shows the watch case made of the cobalt-chromium alloy in FIG. 16B.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Unless otherwise specified, all tests herein are conducted under standard conditions (including test temperature at room temperature (about 25°C), sea level pressure (1 atm), pH=7), and all measurements are in metric units. Furthermore, it should be understood that all percentages, ratios, etc. herein are by weight unless otherwise specifically stated. Also, the material compounds, chemicals, etc. described herein are generally commercial and/or industry standard items available from various suppliers around the world.

[0032] Additionally, it is to be understood that the wording and terminology used herein are for the purpose of description and should not be regarded as limiting. Degree terms such as "essentially" or "about" will be understood by those skilled in the art to refer to a reasonable range outside the given value, such as typical tolerances associated with the manufacture, assembly, and use of the described embodiments.

[0033] The present disclosure provides a cobalt-based alloy, consisting essentially of the following chemical components by weight percentage: at least about 50% of cobalt (Co), at least about 20% of chromium (Cr), at least about 0.1% of molybdenum (Mo), and a balance being one or more selected from the group consisting of manganese (Mn), vanadium (V), tungsten (W), nickel (Ni), titanium (Ti), iron (Fe), aluminum (Al), lanthanum (La), tantalum (Ta), iridium (Ir), cerium (Ce), phosphorus (P), and carbon (C), and inevitable impurities.

[0034] The characteristics and functions of each of the chemical components are as follows:
Co is hard, brittle, and ferromagnetic, and loses its magnetism at a high temperature (about 1,150°C). In the present disclosure, a content of the Co is limited to about 50% to about 70%. In some embodiments, the content of the Co is greater than about 67%. In other embodiments, the content of the Co is less than about 60%.

[0035] Cr can effectively improve the oxidation resistance and corrosion resistance of the cobalt-based alloy, as well as its hardness and strength, and can reduce the expansion coefficient of the alloy. However, an excessive Cr content may reduce the castability of the alloy and increase manufacturing costs. In the present disclosure, a content of the Cr is thus limited to about 20% to about 40%. In some embodiments, the content of the Cr is in a range of about 26% to about 35%, and preferably about 27% to about 30%. In other embodiments, the content of the Cr is in a range of about 21% to about 26%, and preferably about 23% to about 25%.

[0036] Mo has a solid solution strengthening effect due to its large atomic radius and can be used to increase the hardness of the alloy. Meanwhile, the addition of Mo alloy can also prevent grain growth and improve the fatigue performance and corrosion resistance of the alloy. However, excessive addition of Mo may precipitate the brittle phase of the solid solution and thus reduce the toughness of the alloy. In the present disclosure, a content of the Mo is thus limited to about 0.1% to about 5%. In some embodiments, the content of the Mo is in a range of about 1% to about 4%, preferably about 1.5% to about 3%, and more preferably about 2%. In other embodiments, the content of the Mo is in a range of about 0.2% to about 1%.

[0037] In some embodiments, a content of remaining elements is less than about 5%.

[0038] Mn can improve strength and toughness. However, an excessive content of the Mn may produce retained austenite in the alloy, resulting in an uneven distribution of the organization and thus affecting the hardness of the alloy. In addition, the high content of the Mn may cause segregation, toughness deterioration, and weldability reduction. Therefore, in some embodiments, a content of the Mn is in a range of 0% to 2%.

[0039] V can work with C and other metal elements to form MC-type carbides with an FCC structure (M: V and/or other metal elements), which have small size and high thermal stability. The carbides can effectively inhibit grain growth, leading to grain refinement and precipitation strengthening. In some embodiments of the present disclosure, a content of the V is in a range of 0% to 1%.

[0040] W has high hardness and a high melting point. However, excessive addition of W may precipitate the brittle phase of the solid solution and thus reduce the toughness of the alloy. Therefore, in some embodiments, a content of the W content is in a range of 0% to 5%.

[0041] Ni has medium hardness and desirable ductility. However, Ni is one of the most common allergenic metals and may be released through long-term skin contact, causing severe allergic and dermatitis symptoms. A content of the Ni should comply with the corresponding international or local nickel release test standards (for example, test standards for nickel release in various jewelry metals and electroplating). Therefore, in some embodiments, a content of the Ni is in a range of 0% to 4%, and preferably less than 0.4%.

[0042] Ti improves the tensile strength and ductility of the alloy. In some embodiments of the present disclosure, a content of the Ti is in a range of 0% to 3%, and preferably less than 0.35%.

[0043] Fe increases the elasticity and hardness of the alloy and reduces the expansion coefficient. In some embodiments of the present disclosure, a content of the Fe is in a range of 0% to 2%.

[0044] Al is ductile, but an excessive content of the Al may make casting difficult. Therefore, in some embodiments, a content of the Al is in a range of 0% to 2%.

[0045] La helps improve antioxidant properties. In some embodiments of the present disclosure, a content of the La is in a range of 0% to 5%.

[0046] Ta has desirable ductility and corrosion resistance, but low hardness. Therefore, in some embodiments, a content of the Ta is in a range of 0% to 2%.

[0047] Ir is extremely corrosion resistant. In some embodiments of the present disclosure, a content of the Ir is in a range of 0% to 0.5%.

[0048] Ce is ductile but highly susceptible to self-ignition (especially when being slightly oxidized or alloyed with iron). Therefore, in some embodiments, a content of the Ce is in a range of 0% to 1%.

[0049] P increases the wear resistance and stiffness of the alloy. However, an excessive content of the P may cause P to form brittle compounds with other metals, making the alloy brittle. Therefore, in some embodiments, a content of the P is in a range of 0% to 0.5%.

[0050] C can form carbides with certain metal elements, including M23C6 and MC (M: metal). However, an excessively high content of the C may cause the alloy to continuously precipitate carbide phases at high temperatures and become brittle, affecting polishing performance. Therefore, in some embodiments, a content of the C is in a range of 0% to 0.5%, and preferably less than 0.25%.

[0051] In addition to the above components, the cobalt-based alloy in the present disclosure further includes other inevitable impurities, such as one or more of the following elements: nitrogen (N), nitrogen (O), and silicon (Si). These inevitable impurities are, for example, impurities present in the purchased raw materials themselves, or components present in the ambient air during component test. These impurities are generally undesirable and can, for example, have a negative impact on the hardness and ductility of the cobalt-based alloy. For example, excessive contents of N and O may reduce the ductility of the alloy, while excessive content of Si may increase the chance of crack formation in the alloy and reduce its wear resistance. Therefore, in the present disclosure, the contents of both N and O are less than 25 ppm, and the occurrence of Si should be avoided as much as possible.

[0052] In an embodiment, the cobalt-based alloy has a Vickers hardness (HV) of at least about 270.

[0053] In the present disclosure, the cobalt-based alloy can be prepared by methods known in the art, such as melting (for example, controlling the content of non-metals in the alloy by controlling the ratio of nitrogen and oxygen), electrodeposition, reduction, and powder metallurgy. Therefore, the preparation method of the cobalt-based alloy will not be described herein.

[0054] The above cobalt-based alloy is suitable for making a wearable object, such as a watch and a jewel (including a bracelet and a ring), especially a inlaid jewelry piece.

[0055] The present disclosure further provides a method for preparing a metal product, including: forming a casting and then subjecting the casting to processing to form the metal product. The casting may be the above cobalt-based alloy, or may be a casting formed from the cobalt-based alloy by lost wax casting.

[0056] As mentioned above, the cobalt-based alloy may have carbide particles that affect the properties of the alloy, such that the parameters of the treatment process need to be controlled to maintain the size and distribution of the carbide particles and the grain size at a desired level.

[0057] The metal product may be a duplex cobalt-based alloy having an HCP phase and an FCC phase. In some embodiments, a ratio of the HCP phase to the FCC phase is about 1:1, thus bringing high plasticity and toughness as well as relatively low brittleness to the alloy. In order to achieve a duplex (especially a duplex of about 1: 1) and to control the properties and precipitation of carbides, the processing of the casting may include (e.g. in a quenching process) subjecting the casting to a heat treatment (e.g. using a thermostatic oven) and then a cold treatment repeatedly, where the cold treatment is preferably conducted in a gradual cooling manner. Generally speaking, high-temperature (for example, 1,100°C to 1,400°C) solid solution treatment is conducted to dissolve all primary carbides (including some MC carbides) into the solid solution to ensure that the grains do not grow too much, and then an aging treatment is conducted at a lower temperature (such as 800°C to 1,000°C) to re-precipitate the carbides. The treatment process can also help improve ductility.

[0058] In an embodiment, subjecting the casting to processing includes the following steps in sequence: subjecting the casting to a heat treatment at a temperature of 1,100°C to 1,400°C for about 1 h to obtain a heated casting; quenching and cooling the heated casting (e.g. immersing in cold water (e.g. 4°C)) to obtain a cooled casting; subjecting the cooled casting to a heat treatment at a temperature of 800°C to 1,000°C for about 4 h to obtain a heated casting; and quenching and cooling the casting. The quenching may be, for example, immersing the casting in cold water (for example, 4°C water).

[0059] In an embodiment, a temperature of the casting after the forming is in a range of 1,450°C to 1,700°C, and the subjecting the casting to processing comprises the following steps in sequence: cooling the casting at 1,100°C to 1,400°C until a temperature of the casting is in a range of 1,100°C to 1,400°C to obtain a cooled casting, and holding the cooled casting at 1,100°C to 1,400°C for about 1 h to obtain a held casting; cooling the held casting at 800°C to 1,000°C until a temperature of the held casting is in a range of 800°C to 1,000°C to obtain a cooled casting, and holding the cooled casting at 800°C to 1,000°C for about 1 h to obtain a held casting; and cooling the held casting at 400°C to 600°C until a temperature of the held casting is in a range of 400°C to 600°C to obtain a cooled casting, and holding the cooled casting at 400°C to 600°C for about 1 h. Finally, the casting is allowed to stand at room temperature until its temperature cooled down to room temperature.

[0060] In another embodiment, subjecting the casting to processing includes: subjecting the casting to a heating from a low temperature (e.g., about 25°C) to 1,250°C at a constant heating rate (e.g., 10°C/s) and maintaining at 1,250°C for 1 h, and then quenching (for example, cooling to about 25°C) to obtain a heated casting; subjecting the heated casting to a heating from a low temperature (e.g., about 25°C) to 900°C at a constant heating rate (e.g., 10°C/s) and maintaining at 900°C for 4 h, and then quenching (e.g., cooling to about 25°C).

[0061] After that, the duplex cobalt-based alloy can be subjected to milling (for example, using a hanging mill at 2,500 r/min) or polishing (for example, using a plasma polisher) based on actual needs, or additional elements (for example, gemstones) can be inset to form the metal product. In some embodiments, the metal product includes a wearable object, such as a watch and a jewel (including a bracelet and a ring), and preferably a inlaid jewelry piece.

[0062] The embodiments of the present disclosure will be further described below in conjunction with examples, but the present disclosure is not limited to the scope of the described examples.

Alloy

[0063] The analysis and test of the compositions of various cobalt-based alloys of the present disclosure were conducted using an X-ray fluorescence (XRF) spectrometer, and the test results are shown in Table 1. It should be understood that due to instrument detection limits, analytical method detection limits, etc., the alloy components listed in the table below may still contain a small amount of inevitable impurities even if a sum of them without calculating impurity components is already 100%.

Table 1 Composition of cobalt-based alloy

Mater ial	Component (wt %)
	Co	Cr	Mo	Mn	V	W	Ni	Ti	Fe	A l	L a	T a	Ir	C e	C	P	Inevita ble impurit ies
Alloy 1	67.8 7	28.4 2	2.21	1.09	0.06	-	0.3 4	-	-	-	-	-	-	-	-	-	Balanc e
Alloy 2	67.7	28.0	2.0	0.9	-	-	-	0.5	0.6	-	-	-	-	-	0.3	-	Balanc e
Alloy 3	69.5 59	27.3 85	2.10 6	0.94	-	-	-	-	-	-	-	-	-	-	-	-	Balanc e
Alloy 4	63.5 42	28.5 86	6.47 8	0.22 2	0.06 8	-	0.3 7	-	0.62 5	-	-	-		- -	-	-	Balanc e
Alloy 5	67.8 2	29.0 6	2.06	0.99	0.06	-	-	-	-	-	-	-	-	-	-	-	Balanc e
Alloy 6	58	24.5	0.6	-	-	3	1.7	2.0 1	1.5	1. 5	4. 5	1. 5	0.0 4	0. 5	0.2 5	0. 4	Balanc e

Example 1 - Alloy 1

[0064] Alloy 1 contained 14 ppm of oxygen and 0.64 ppm of nitrogen as impurities and had a hardness of 311.3 HV.

[0065] FIG. 1 to FIG. 8 illustrate various physical properties of Alloy 1. As shown in FIG. 1, the HCP phase begins to appear at 928°C, while the FCC phase disappears at 896°C. Harmful phases σ and µ (which have adverse effects on the toughness and corrosion resistance of the alloy) begin to appear at 425°C and 600°C, respectively. For metallographic observation, Alloy 1 was polished and etched, and a polished surface and an etched surface of Alloy 1 are observed with a microscope and SEM (FIG. 2 to FIG. 7). Alloy 1 has many pores, most of which are small in size (1.87±0.05 µm) (FIG. 2). In addition, larger pores of 6±0.05 µm are mainly distributed in the upper and lower positions in FIG. 2. As shown in FIG. 3, the size distribution of the pores is mainly 1 µm to 3 µm, and their average size is 2.11±0.05 µm. Under secondary electrons, some irregular 7.16±0.05 µm pores are seen under the surface of Alloy 1 (FIG. 4A and FIG. 4B). As shown in FIG. 5A to FIG. 6B, Alloy 1 is in a duplex. Under 100× magnification, obvious dendrites are seen, and the gray lath-like HCP phase as well as the white dendritic FCC phase are also observed. A combined phase of the HCP and FCC is shown in the lower right position in FIG 5B. FIG. 7 shows the white lath-shaped HCP phase and the combined phase of HCP and FCC (a lower right position in FIG. 7). In order to understand the crystal structure of Alloy 1, an XRD measurement was conducted to obtain an XRD pattern (FIG. 8). From the XRD pattern and using a volume fraction calculation formula (Equation 1), it was concluded that the HCP phase of Alloy 1 has a volume content of 74.9%.

[0066] Alloy 1 was compared with a traditional 316 stainless steel material through an anti-friction test, and the test results are shown in FIG. 9A and FIG. 9B. The anti-friction test was conducted in the following manner: sample blocks of the traditional 316 stainless steel material and Alloy 1 were polished, fixed on a testing machine platform, and a vertical pressure on the surface of samples was set at 1 kilogram force (kgf). The sample blocks were wiped with steel wool for 1,000 cycles, where a surface wiping frequency was 40±2 cycles/min, and a scratching degree of each surface was checked after every 200 cycles of wiping. FIG. 9A and FIG. 9B show the excellent difference in wear resistance between the traditional 316 stainless steel material and Alloy 1. It is seen that the wear resistance of Alloy 1 is better than that of the traditional 316 stainless steel material.

Example 2 - Alloy 2

[0067] Alloy 2 contained 25 ppm of oxygen and 0.19 ppm of nitrogen as impurities.

[0068] FIG. 10 to FIG. 15 illustrate various physical properties of Alloy 2. As shown in FIG. 10, the HCP phase begins to appear at 890°C, while the FCC phase disappears at 840°C. Compared with Alloy 1, the temperature at which the HCP phase appears and the temperature at which the FCC phase disappears in Alloy 2 are significantly reduced, and an increase in the interval between these two temperatures expands the heat treatment process window. Harmful phases σ and µ begin to appear at 454°C and 518°C, respectively. Compared with Alloy 1, the temperature at which the σ phase appeared is slightly increased, while the temperature at which the µ phase appeared is significantly decreased, and the volume fractions of the two phases are significantly decreased. In addition, Alloy 2 has additional Ti, Fe, and C elements than Alloy 1, such that M23C6 and MC carbides are produced correspondingly, which begin to appear at 1,280°C and 1,335°C, respectively.

[0069] For metallographic observation, Alloy 2 was polished and etched, and a polished surface and an etched surface of Alloy 2 were observed with a microscope and SEM (FIG 11 to FIG. 14). As shown in FIG. 11A to FIG. 11D, Alloy 2 has no pores, and a typical as-cast structure is seen under 50× magnification. Due to the addition of C, carbides could be seen at 500× magnification (FIG. 11D). Compared with Alloy 1, Alloy 2 shows a lower polishing performance. As shown in FIG. 12A to FIG. 13B, Alloy 2 is in a duplex. At 50× magnification, it is seen that the dendrite structure is smaller than that of Alloy 1 (FIG. 12A). It is also clearly seen that the white strips are the FCC phase, while the gray strips are the combined phase of HCP and FCC, which generates carbides at the grain boundaries (FIG. 13B). A chromium content at point 1 in FIG. 14A is much higher than the average value. It is concluded that this substance is Cr23C6 carbide distributed on the grain boundaries of the structure. The needle-like ones seen in Figure 14A are HCP phases, and most of them are the combined phase of FCC and HCP. A titanium content at point 6 in FIG. 14B is high, and it is speculated that this substance is TiC. The size of titanium carbide is 8 µm, which is larger than expected, such that the Ti content should be reduced. Without being limited by theory, it is believed that the Ti content is preferably 0.3%. In order to understand the crystal structure of Alloy 2, an XRD measurement was conducted to obtain an XRD pattern (FIG 15). From the XRD pattern and using a volume fraction calculation formula (Equation 1), it was concluded that the HCP phase of Alloy 2 had a volume content of 14.2%, and its HCP was less than that of Alloy 1, and its FCC was more than that of Alloy 1.

Example 3 - Comparison of Alloy 3 and Alloy 4

[0070] Alloy 3 and Alloy 4 were compared through anti-friction test, bending test, and ductility test, and the test results are shown in FIG. 16A to FIG. 17D. The anti-friction test was conducted in the following manner: sample blocks of Alloy 3 and Alloy 4 were polished, fixed on a testing machine platform, and a vertical pressure on the surface of samples was set at 1 kilogram force (kgf). The sample blocks were wiped with steel wool for 1,000 cycles, where a surface wiping frequency was 40±2 cycles/min, and a scratching degree of each surface was checked after every 200 cycles of wiping. FIG. 16A and FIG. 16B show the excellent difference in the wear resistance properties of Alloy 3 and Alloy 4. It is seen that the wear resistance properties of Alloy 3 and Alloy 4 are substantially the same. The bending test was conducted as follows: the sample blocks of Alloy 3 and Alloy 4 having substantially the same size and shape were repeatedly bent with a testing machine to detect whether there was a risk of cracking and breakage. FIG. 17A and FIG. 17B show the excellent difference in bending properties between Alloy 3 and Alloy 4. It is seen that Alloy 3 has better bending properties than that of Alloy 4. The ductility test was conducted as follows: the sample blocks of Alloy 3 and Alloy 4 having the same size, diameter, and shape were fixed on a tensile machine to detect the elongation rate of the steel wire. FIG. 17C and FIG. 17D show the excellent difference in ductility between Alloy 3 and Alloy 4, indicating that Alloy 3 has better ductility than that of Alloy 4.

Metal product

[0071] The analysis and test of the composition of the castings made of various metal products according to the present disclosure were conducted with an XRF spectrometer, and the test results are shown in Table 2. It should be understood that due to instrument detection limits, analytical method detection limits, etc., the casting components listed in the table below may still have a small amount of inevitable impurities even if a sum of them without calculating impurity components is already 100%.

Table 2 Composition of castings

Material	Component (wt %)
	Co	Cr	Mo	Mn	V	Pb	Ni	Ti	Fe	Cd	Inevitable impurities
Ring plaster casting	65.53	31.10	-	1.03	-	0.02	0.19	-	0.26	0.01	Balance
Ring slurry casting	67.82	29.06	2.06	0.99	0.06	-	-	-	-	-	Balance
Bracelet casting	67.87	28.42	2.21	1.09	0.06	-	0.34	-	-	-	Balance

Example 4 - Ring plaster casting

[0072] A ring plaster casting had a hardness of 336.46 HV. The ring plaster casting was made of Alloy 5 with a hardness of 422.36 HV by the lost wax casting. Ni in the ring plaster casting was caused by the Ni element on a vessel sticking to the cobalt-based material during the casting. A wax was injected into a wax tank with an automatic wax casting machine and dissolved at high temperature, and then injected into a mold to form wax pieces, and the wax pieces were disassembled, where the wax casting was conducted at about 65°C, a pressure of about 0.5 kgf/cm, and a vacuum degree of about 7.6 mmHg. Then through high-temperature dissolution, the wax pieces were welded one by one to a wax tree (which was called loading on a wax tree) using an electric iron at about 50°C to obtain a piece. On the other hand, about 100 g of a gypsum powder and 23 mL of water were mixed into a solidifying liquid using a mixer and/or vacuum pump for shell making, and the gypsum powder was sintered in a numerically controlled high-temperature furnace and cooled to a suitable temperature for reversing mold, where the sintering was conducted at 280°C for 240 min, 500°C for 120 min, 700°C for 240 min, 780°C for 90 min, and then 680°C for 60 min in sequence. Then a reversing mold and casting were conducted by melting Alloy 5 at about 1,700°C using a gold melting machine and then the melted Alloy 5 was poured into a gypsum mold. After forming, the resulting pieces were cut off one by one (called unloading from wax tree) using a cutting machine, and a water level on the pieces was removed at 2,500 r/min using a grinding wheel to form the ring plaster casting.

Example 5 - Ring slurry casting

[0073] The ring slurry casting was also made of Alloy 5 with a hardness of 422.36 HV. A preparation method of the ring slurry casting was similar to that of Example 4, except that a slurry was used instead of the gypsum in the shell making step. The stock (i.e., ring slurry casting) had a hardness of 271.2 HV, while a finished ring had a hardness of 401.82 HV.

Example 6 - Bracelet casting

[0074] The bracelet casting was made of Alloy 1 and had a hardness of 362.14 HV. A preparation method of the bracelet casting was similar to that of Example 4, except that the mold had a different shape and size. In addition, 3 sets of data under a test tension of 5 kg and 2 sets of data under a test torque of 3 kg were obtained during a tensile and torque test of the bracelet casting (where the buckle was not welded). These data indicated that the bracelet casting had a desirable tensile torque.

Example 7 - Ring

[0075] Rings were made from Alloy 1 and a traditional 316 stainless steel material by the method of Example 4 (FIG. 18A to FIG. 18D).

[0076] Alloy 1 was compared with the traditional 316 stainless steel material by means of a bending test and a ductility test, and the test results are shown in FIG. 18A and FIG. 18B. The bending test was conducted in the following manner: two rings made of the traditional 316 stainless steel material and Alloy 1 were equipped with gemstones, respectively, in which the rings had four-sided supporting claws. The four-sided supporting claws were bent using a testing machine to fix the gemstones. The disassembly and assembly process was repeated twice to detect whether there was a risk of cracking and breakage of the supporting claws. FIG. 18A and FIG. 18B show the ring made of the traditional 316 stainless steel material before and after the bending test, respectively. As shown in FIG. 18B, two rings made of the traditional 316 stainless steel material have broken supporting claws. FIG. 18C and FIG. 18D show the ring made of Alloy 1 before and after bending test, respectively. As shown in FIG. 18D, two rings made of Alloy 1 do not have broken supporting claws, and could be used for stone setting. FIG. 18A to FIG. 18D show the excellent difference in bending properties between the traditional 316 stainless steel material and Alloy 1, indicating that the bending properties of Alloy 1 are better than those of the traditional 316 stainless steel material.

[0077] The ductility test was conducted as follows: two rings made of the traditional 316 stainless steel material and Alloy 1 were flattened with a testing machine to allow deformation, and the rounding process was repeated twice. The ring was opened and straightened with scissors, and fixed on a tensile machine to detect the elongation rate of the steel wire. FIG. 18A to FIG. 18D shows the excellent difference in ductility between the traditional 316 stainless steel material and Alloy 1, indicating that the ductility of Alloy 1 is better than that of the traditional 316 stainless steel material.

Example 8 - Watch case

[0078] Watch cases were made from Alloy 3 and Alloy 4 by the method of Example 4 (FIG. 19A and FIG. 19B), and it is seen that there is not much difference in the appearance of the watch cases. However, according to the test results in Example 3, since Alloy 3 has better bending properties and ductility than those of Alloy 4, Alloy 3 is considered to be more suitable than Alloy 4 for the preparation of watch cases with claw stones.

[0079] Those skilled in the art will appreciate that various changes and/or modifications can be made to the present disclosure shown in the detailed description without departing from the spirit or scope of the present disclosure as broadly described. For example, the cobalt-based alloy may have properties not specifically described above (as long as it has the above composition), or the preparation method of the metal product may omit some of the above steps, or include additional steps. For example, the cobalt-based alloy may be inherently in the duplex due to its composition (e.g., a ratio of the HCP phase to the FCC phase is about 1:1). Therefore, the preparation method of the metal product can omit the steps of heat treatment and cold treatment, that is, the casting can be directly milled or polished. As another example, instead of lost wax casting, the metal product may be produced using other suitable casting techniques, such as sand casting, investment casting, centrifugal casting, low-pressure casting, and die casting. Additionally, the metal product may be wearable objects other than watches and jewels (e.g., eyeglass frames), or non-wearable objects (e.g., gas turbines, and dental and orthopedic implants).

[0080] Accordingly, the examples described in the present disclosure should be considered in all respects as illustrative and not restrictive.

Claims

1. A cobalt-based alloy, consisting essentially of the following chemical components by weight percentage:

at least about 50% of cobalt,

at least about 20% of chromium,

at least about 0.1% of molybdenum, and

a balance being one or more selected from the group consisting of manganese, vanadium, tungsten, nickel, titanium, iron, aluminum, lanthanum, tantalum, iridium, cerium, phosphorus, and carbon, and inevitable impurities.

2. The cobalt-based alloy of claim 1, wherein a weight percentage of the cobalt is in a range of about 50% to about 70%.

3. The cobalt-based alloy of claim 1 or 2, wherein a weight percentage of the cobalt is greater than about 67%.

4. The cobalt-based alloy of claim 1, wherein a weight percentage of the chromium is in a range of about 20% to about 40%.

5. The cobalt-based alloy of any one of claims 1 to 4, wherein a weight percentage of the molybdenum is in a range of about 0.1% to about 5%.

6. The cobalt-based alloy of any one of claims 1 to 5, wherein a weight percentage of the molybdenum is about 2%.

7. The cobalt-based alloy of claim 1, wherein a weight percentage of the balance is less than about 5%.

8. The cobalt-based alloy of any one of claims 1 to 7, wherein a weight percentage of the nickel is less than about 0.4%.

9. The cobalt-based alloy of any one of claims 1 to 8, wherein the cobalt-based alloy has a Vickers hardness of at least about 270.

10. The cobalt-based alloy of any one of claims 1 to 9, wherein the cobalt-based alloy is a duplex cobalt-based alloy.

11. The cobalt-based alloy of claim 10, wherein the duplex cobalt-based alloy has a hexagonal close-packed (HCP) phase and a face-centered cubic (FCC) phase.

12. The cobalt-based alloy of claim 11, wherein a ratio of the HCP phase to the FCC phase is about 1:1.

13. A wearable object, comprising the cobalt-based alloy of any one of claims 1 to 12.

14. The wearable object of claim 13, wherein the wearable object comprises one selected from the group consisting of a timepiece and a jewel.

15. The wearable object of claim 14, wherein the jewel comprises one selected from the group consisting of a bracelet and a ring.

16. A method for preparing a metal product, comprising:
forming a casting from a cobalt-based alloy, wherein the cobalt-based alloy consists essentially of the following chemical components by weight percentage:

at least about 50% of cobalt,

at least about 20% of chromium,

at least about 0.1% of molybdenum, and

a balance being one or more selected from the group consisting of manganese, vanadium, tungsten, nickel, titanium, iron, aluminum, lanthanum, tantalum, iridium, cerium, phosphorus, and carbon, and inevitable impurities; and

subjecting the casting to processing, wherein the processing comprises subjecting the casting to a heat treatment and then a cold treatment repeatedly by quenching.

17. The method of claim 16, wherein subjecting the casting to processing comprises the following steps in sequence:

subjecting the casting to a heat treatment at a temperature of 1,100°C to 1,400°C for about 1 h to obtain a heated casting;

quenching and cooling the heated casting to obtain a cooled casting;

subjecting the cooled casting to a heat treatment at a temperature of 800°C to 1,000°C for about 4 h to obtain a heated casting; and

quenching and cooling the heated casting.

18. The method of claim 16, wherein a temperature of the casting after the forming is in a range of 1,450°C to 1,700°C, and the subjecting the casting to processing comprises the following steps in sequence:

cooling the casting at 1,100°C to 1,400°C until a temperature of the casting is in a range of 1,100°C to 1,400°C to obtain a cooled casting, and holding the cooled casting at 1,100°C to 1,400°C for about 1 h to obtain a held casting;

cooling the held casting at 800°C to 1,000°C until a temperature of the held casting is in a range of 800°C to 1,000°C to obtain a cooled casting, and holding the cooled casting at 800°C to 1,000°C for about 1 h to obtain a held casting; and

cooling the held casting at 400°C to 600°C until a temperature of the held casting is in a range of 400°C to 600°C to obtain a cooled casting, and holding the cooled casting at 400°C to 600°C for about 1 h.

19. The method of any one of claims 16 to 18, wherein subjecting the casting to processing further comprises milling or polishing the casting.

20. The method of any one of claims 16 to 19, wherein forming the casting comprises forming the casting by lost wax casting.

21. The method of any one of claims 16 to 20, wherein the metal product comprises a duplex cobalt-based alloy.

22. The cobalt-based alloy of claim 21, wherein the duplex cobalt-based alloy has an HCP phase and an FCC phase.

23. The method of claim 22, wherein a ratio of the HCP phase to the FCC phase is about 1:1.

24. The method of any one of claims 16 to 23, wherein the metal product is a wearable object.

25. The method of claim 24, wherein the wearable object comprises one selected from the group consisting of a timepiece and a jewel.

26. The method of claim 25, wherein the jewel comprises one selected from the group consisting of a bracelet and a ring.

Drawing