COMPOSITE MAGNETIC MATERIALS AND METHOD OF MANUFACTURING THE SAME

Abstract

 Disclosed herein is a magnetic material comprising at least one metallic phase and at least one magnetic phase, each metallic phase comprising one of:
- a transition metal or alloys thereof,
- a post-transition metal or alloys thereof, and
- an alkali earth metal or alloys thereof,
each magnetic phase comprising one of:
- a magnetic alloy having the formula RE₂TM₁₄B,
- a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y with 0<=x<=3 and 0<=y<=3, preferably x=3 and y=0,
- a magnetic alloy having the formula SmFe₇N_xC_y with 0<=x<=1 and 0<=y<=1, preferably x=1 and y=0,
- a magnetic alloy having the formula RE'₂TM'_1-7
- a magnetic alloy having the formula RE'TM'₅
wherein RE is a first rare earth element, RE' is a second rare earth element, TM is a first transition metal, TM' is a second transition metal, B is Boron, N is nitrogen, C is carbon, Sm is Samarium, Fe is Iron,
wherein the total amount of the at least one metallic phase is comprised between 25% and 95% in volume of the magnetic material.

Description

Field of the invention

[0001] The present invention relates to magnetic materials. The invention has been developed with particular reference to sintered magnetic materials.

Prior art

[0002] Magnetic materials available in the art cover an extremely wide range of compounds and applications, ranging from the most basic iron oxide Fe₃O₄ up to the most modern Nd₂Fe₁₄B rare earth intermetallic compounds, developed only in 1982, with the highest magnetic properties.

[0003] The use of known magnetic materials ranges from the most technical, such as in electric motors and sensors, to the most ludicrous such as fridge magnets to hang notes or creative games based on the attractive forces of the magnetic fields generated by magnets. Beside the iron oxide based materials (the so-called ferrites), which due to the low costs and simplicity in production take a large share of the current market, intermetallic magnetic materials are the second most used and the most interesting as far as magnetic properties are concerned.

[0004] The most common intermetallic hard magnetic materials known in the art belong to the following families: Nd₂Fe₁₄B, Sm₂Fe₁₇N₂, Sm₂Co₅, Sm₂Co₁₇ and Al-Ni-Co magnets, based on the composition 8-12% Al, 15-26% Ni, 5-24% Co, up to 6% Cu, up to 1% Ti and the balance Fe.

[0005] The most powerful magnets are those belonging to the family of Nd₂Fe₁₄B with values of magnetic properties as high as Br=1.5T (Residual magnetic flux density), Hci=2500 kA/m (intrinsic magnetic coercitivity) and (BH)_max=440 kJ/m³ (maximum energy product).

[0006] Within this family, through the years, magnets manufacturers have worked on variations of the composition mainly to reduce cost due to shortage or limited availability of the chemical elements involved: Nd, but most of all Tb, Pr and Dy used to stabilize the coercivity of the Nd₂Fe₁₄B-based magnets.

[0007] The main technical issue with Nd₂Fe₁₄B, Sm₂Fe₁₇N₂, Sm₂Co₅ and Sm₂Co₁₇ magnets is the lack of acceptable mechanical properties due to the intermetallic nature of the chemical bonds in the crystal lattice, which prevents conventional machining with cutting tools made of steel, hard metals and cermets.

[0008] These magnets are accordingly manufactured according to either of the following methods:

• sintering: the magnetic material is subject to - in sequence - smelting, casting, grinding/mechanical reduction to powder, pressing in magnetic field, sintering, deburring and grinding to reach tight mechanical tolerances.
• bonding: the magnetic material is subject - in sequence - to smelting, ribbon casting, reduction of ribbons to flakes, heat treatment to optimize the microstructure, mixing with polymeric agents, injection molding or compression molding. An exemplary document in this field is US 4,832,891.
• hot pressing: the magnetic material is subject - in sequence - to smelting, ribbon casting, reduction of ribbons to flakes (reference is made, for instance, to US 6,478,890 B2), heat treatment to optimize the microstructure, hot pressing.
• hot forming: the magnetic material is subject - in sequence - to smelting, ribbon casting, reduction of ribbons to flakes (reference is made, for instance, to US 6,478,890 B2), heat treatment to optimize the microstructure, hot pressing, hot forging.

[0009] Sintering is generally resorted to for manufacturing magnets with the highest performances, usually named "sintered magnets".

[0010] Bonding is generally resorted to for manufacturing magnets, called bonded magnets, with much lower magnetic properties than sintered magnets, but with tight mechanical tolerances without the need for successive machining operations.

[0011] Bonded magnets can be manufactured with any hard magnetic phase but, due to the lower resulting magnetic properties, they are mainly manufactured from Nd₂Fe₁₄B type flakes.

[0012] Hot pressing is generally resorted to for manufacturing isotropic hot pressed magnets (generally referred to as MQ2-type magnets from the company Magnequench, that first used this method).

[0013] Hot pressing and forging (hot forming) can induce anisotropy through mechanical deformation and it produces anisotropic Nd-Fe-B magnets (called MQ3 magnets). In order to improve the magnetic properties of hot deformed anisotropic magnets other elements have been added in materials of the prior art as disclosed, for example, in KR 100446453 B1: Al or Zn from 0.2 up to 2% in weight have been added in order, through chemical alloying, to further enhance the anisotropy of the grains, thereby obtaining a high residual magnetic field.

[0014] Due to their relative instability all intermetallic magnets tend to corrode quite easily and require coatings such as, for example, epoxy resins or nickel plating. Al-Ni-Co magnets, on the other hand, are better suited for machining, but have lower magnetic properties, which only allow them to be used as sensors.

[0015] Sm-Co magnets are interesting for high temperature applications due to the high Curie temperature thereof, while Sm-Fe-N based magnets are a known system, which is under industrial and scientific exploration for its relatively high Curie temperature of 470°C and low cost elements, but still under development.

[0016] A way to improve the mechanical properties of hard magnetic materials is the addition of a second non-magnetic, but strong metallic phase as disclosed in WO 2012/63407 A1. In this document, lightweight magnesium powders are mixed with ferrite (iron oxide) powders to form a mechanically robust magnet which can also be anisotropic by processing the same in a magnetic field. This was possible because of the high thermal stability of the iron oxide and the low melting point of the metal used. However, the material remains non-machinable with conventional carbide or steel tools and the magnetic properties are essentially low (Hci max 16 kA/m) and poor, since the iron oxide has been diluted with a second, non-magnetic, phase.

Object of the invention

[0017] The object of the present invention is to solve the technical problems mentioned in the foregoing. More specifically, the object of the invention is to provide a magnetic material that features, at the same time, high magnetic properties and high mechanical properties and machining capabilities.

Summary of the invention

[0018] The object of the present invention is achieved by a magnetic material and a method forming the subject of the appended claims, which form an integral part of the technical disclosure herein provided in relation to the invention.

Brief description of the figures

[0019] The invention will now be described with reference to the attached figures, provided purely by way of nonlimiting example, and wherein:

• Figure 1 is a plot of maximum energy product (BH)_max as a function of volume fraction of the magnetic phase in magnetic materials according to the invention
• Figure 2 is a plot of magnetic coercitivity H_cB as a function of volume fraction of the magnetic phase in magnetic materials according to the invention,
• Figure 3 is a plot of intrinsic magnetic coercitivity H_ci as a function of volume fraction of the magnetic phase in magnetic materials according to the invention, and
• Figure 4 is a plot of residual magnetic flux density Br as a as a function of volume fraction of the magnetic phase in magnetic materials according to the invention,
• Figures 5 to 7 are representative of stems in a method according to the invention, and
• Figure 8 are representatives of examples desired shapes for the magnetic material according to the invention.

Detailed description

[0020] Various embodiments of the invention consist of a magnetic material comprising at least one metallic phase and at least one magnetic phase, with the metallic phase(s) providing good machine processing capabilities (i.e. the material can be processed by way of machining operations, such as turning, milling, etc.), and the magnetic phase(s) achieving "hard" magnetic properties, i.e. the capability of retaining magnetic field and operating as permanent magnets.

[0021] According to the invention, each metallic phase of the magnetic material comprises one of a transition metal, a post-transition metal, and an alkali earth metal. Accordingly, a magnetic material according to the invention may feature, for instance, a first metallic phase comprising a transition metal, and a second metallic phase comprising a post-transition metal. Each group of metals concerned is intended to encompass both the metal per se, and alloys thereof, so that the invention contemplates metallic phase(s) comprising at least one of a transition metal or alloys thereof, a post-transition metal or alloys thereof, and an alkali earth metal or alloys thereof.

[0022] Each magnetic phase, on its hand, comprises one of the following:

each magnetic phase comprising one of:

• a magnetic alloy having the formula RE₂TM₁₄B,
• a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y with 0<=x<=3 and 0<=y<=3, preferably x=3 and y=0,
• a magnetic alloy having the formula SmFe₇N_xC_y with 0<=x<=1 and 0<=y<=1, preferably x=1 and y=0,
• a magnetic alloy having the formula RE'₂TM'₁₇
• a magnetic alloy having the formula RE'TM'₅

wherein RE is a first rare earth element, RE' is a second rare earth element, TM is a first transition metal, TM' is a second transition metal, B is Boron, N is nitrogen, C is carbon, Sm is Samarium, Fe is Iron. "First" and "second" may not necessarily imply different elements. Both options (different elements or identical elements) may be contemplated depending on the circumstances.

[0023] Accordingly, a magnetic material according to the invention may feature, for instance, a first metallic phase comprising a transition metal, and a second metallic phase comprising a post-transition metal, as well as a first magnetic phase comprising a RE₂TM₁₄B alloy and a Sm₂Fe₁₇N₃ alloy, or else a single metallic phase and a single magnetic phase.

[0024] According to the invention, whatever the constituents and the number of phases involved, the total amount of the metallic phase(s) corresponds is comprised between 25% to 95% in volume of the magnetic material overall. For instance, in a magnetic material according to the invention that features two metallic phases and one magnetic phase, the two metallic phases together amount of 25%-95% in volume of the magnetic material overall (i.e. all of the three phases, two metallic, and one magnetic).

[0025] More in detail, the volume fraction of the magnetic phase (s) f_v,m is determined as f_v,m = v_m/(v_m+v_h) wherein v_m is the volume of the metallic phases altogether and v_h is the volume of the hard magnetic phases altogether. More in general, f_v,m = ∑_iv_m,i/(∑_iv_m,i+∑_jv_h,j), wherein ∑_i and ∑_j are sum operators, v_m,i is the volume of the i-th metallic phase, and v_h,j is the volume of the j-th magnetic phase. Indexes i and j may have an identical range (equal number of metallic and magnetic phases) or different ranges (different number of metallic and magnetic phases).

[0026] To determine how much powders to weight in order to prepare the composite magnetic material, the starting point is the definition of density as: δ_m=v_m/m_m and δ_h=v_h/m_h were δ is the density in units of g/m³ or more frequently g/cm³ from which the value m, the amount of powder in weight, can be calculated.

[0027] The density of the composite material (δ_c), since there is little or no chemical interaction to form other phases, results from the application of the law of phases to the two powders, namely: δ_c = f_mδ_m + f_hδ_h (fm and fh being the volume fractions of, respectively, the metallic phase and the magnetic phase) and this value is used to evaluate the residual porosity in the materials produced.

[0028] In the broadest possible terms, the density of a composite magnetic material according to the invention can also be defined as: δ_c = ∑_if_m,iδ_m,i + ∑_jf_h,jδ_h,j, wherein f_m,i is the volume fraction of each metallic phase, f_h,j is the volume fraction of each magnetic phase, δ_m,i is the density of each metallic phase, δ_h,j is the density of each magnetic phase in the composite magnetic material.

[0029] As the magnetic material is obtained, according to the invention, starting from the metallic phase(s) and the magnetic phase(s), both provided in powdered form, the metallic phase(s) constitutes 25% to 95% in volume of the total volume of a mixture PWMX of the metallic phase(s) and the magnetic phase(s).

[0030] According to preferred embodiments of the invention, the transition metal (again, meaning the metal per se or an alloy thereof) of the metallic phase is selected from the following group: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Copper (Cu), Zinc (Zn), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Palladium (Pd), Silver (Ag), Hafnium (HF), Iridium (Ir), Platinum (Pt), or Gold (Au), paramagnetic alloys of iron (Fe), Nickel (Ni) or Cobalt (Co), diamagnetic alloys of iron (Fe), Nickel (Ni) and Cobalt (Co).

[0031] Examples of iron alloys providing a metallic phase in a material according to the invention comprise the following (all alloys in austenitic grade only):

• EN 1.4310, X10CrNi18-8, AISI 301
• EN 1.4301, X5CrNi18-10, AISI 304
• EN 1.4541, X6CrNiTi18-10, AISI 321
• EN 1.4401, X5CrNiMo17-2-2, AISI 316
• EN 1.4841, AISI314
• EN 1.4886, AISI 330

[0032] Examples of aluminium alloys providing a metallic phase in a material according to the invention comprise the following (nomenclature following the International Alloy Designation System):

• A16061
• A17075
• A12024
• A17178
• A18006

[0033] Examples of Copper alloys providing a metallic phase in a material according to the invention comprise the following:

• Zinc based series (UNS numbers) C1XXXX-C4XXXX, C66400-C69800
• Aluminium bronzes (UNS numbers) C60600-C64200
• Silicon bronzes (UNS numbers) C64700-C66100
• Molybdenum alloys:
• TZM (Titanium Zirconium Molybdenum), titanium and zirconium carbide reinforced molybdenum, Type 363 and Type 364
• ML (Molybdenum Lanthanum) - oxide reinforced alloy

[0034] Examples of Gold alloys providing a metallic phase in a material according to the invention comprise the following:

• Au 999.9 24kt Gold
• 18kt3N Yellow Gold
• 18kt2N Yellow gold
• 18kt5N Red gold
• Au917 AgCu44 (Yellow 22kt)
• Au917 Cu83 (Rose gold 22kt)
• Au925 Pd75 (White gold 22kt)

[0035] Examples of Silver alloys providing a metallic phase in a material according to the invention comprise the following:

• Ag 925 Cu (Sterling silver)
• Ag 800 Cu

[0036] Examples of Titanium alloys providing a metallic phase in a material according to the invention comprise the following:

• Ti6A14V grade 5
• CP Titanium or commercially pure grades 1 to grade 3
• Ti5A12.5Sn, grade 6
• Ti6A17Nb

[0037] Examples of Nickel alloys providing a metallic phase in a material according to the invention comprise the following Nickel alloy (non magnetic):

• Alloy 600, ASTM B166 - Ni 76%, Cr 15.5% and Fe 8%
• Monel alloy K-500, ASTM B 865, UNS N05500.

[0038] Yet according to preferred embodiments of the invention, the post-transition metal (again, meaning the metal per se or an alloy thereof) of the metallic phase is selected from the following group: Aluminum (Al), Tin (Sn).

[0039] Yet according to preferred embodiments of the invention, the alkali earth metal (again, meaning the metal per se or an alloy thereof) of the metallic phase is selected from the following group: Beryllium (Be), Magnesium (Mg).

[0040] Turning now to the magnetic phase, when the latter is embodied by a magnetic alloy having the general composition RE₂TM₁₄B, the rare earth element RE comprises Neodimium (Nd), and the transition metal TM comprises iron (Fe). In one embodiment, the rare earth element RE consists of Neodimium (Nd), and the transition metal TM consists of iron (Fe).

[0041] When a magnetic phase is embodied by a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y, the alloy may comprise Sm₂Fe₁₇N₂, Sm₂Fe₁₇N₃, or Sm₂Fe₁₇C_1.1N.

[0042] When a magnetic phase is embodied by a magnetic alloy having the formula RE'₂TM'_1.7 or RE'TM'₅, the rare earth element RE' may comprise (or consist of) samarium (Sm) or Gadolinium (Gd), and the transition metal TM' may comprise or consist of Iron (Fe) or Cobalt (Co). Examples may consist of Sm₂Co₁₇ and Sm₂Co₅.

[0043] With reference to figures 5 to 8 as a further support, the magnetic material according to the invention is manufactured by means of a method which envisages the application of pressure and voltage through a mixture PWMX of at least one magnetic phase in powdered form and at least one the metallic phase in powdered form, the mixture being placed in a forming die 1. More in detail, the method comprises at least the following steps:

• providing at least one metallic phase in a powdered form; as disclosed in the foregoing, each metallic phase comprises at least one of a transition metal or alloys thereof, a post-transition metal or alloys thereof, and an alkali earth metal or alloys thereof as the species detailed above,
  • providing at least one magnetic phase in a powdered form; as disclosed in the foregoing, the magnetic phase comprising one of:

    a magnetic alloy having the formula RE₂TM₁₄B,

    a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y with 0<=x<=3 and 0<=y<=3, preferably x=3 and y=0,

    a magnetic alloy having the formula SmFe₇N_xC_y with 0<=x<=1 and 0<=y<=1, preferably x=1 and y=0,

    a magnetic alloy having the formula RE'₂TM'₁₇

    a magnetic alloy having the formula RE'TM'₅

    wherein RE is a rare earth element, RE' is a rare earth element, TM is a transition metal, TM' is a transition metal, B is Boron, N is nitrogen, C is carbon, Sm is Samarium, Fe is Iron,

• mixing the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form to obtain a mixture of the at least one metallic phase and the at least one magnetic phase indicated by reference PWMX in figures 5, 6; mixing of the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form to obtain the mixture PWMX of the at least one metallic phase and the at least one magnetic phase PWMX is provided preferably by means of one of a Turbula-type mixer, an attritor mill, and a planetary ball mill,
• placing the mixture PWMX of the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form into a forming die 1, particularly into a forming cavity 2 thereof, the total amount of the at least one metallic phase in powdered form being comprised between 25% and 95% in volume of the mixture PWMX of the at least one metallic phase and the at least one magnetic phase;
• applying to the mixture PWMX into the forming die a pressure from 10 to 350 MPa, and a voltage of 5 to 150V for a time interval up to 500 ms, to form the mixture into a defined shape (and into a magnetic material according to the invention, designated by reference CMM). A preferred time interval ranges from 1 ms to 300 ms, and an even more preferred time interval ranges from 1 ms to 100 ms.

[0044] According to the invention, good magnetic materials are obtained when each metallic phase and each magnetic phase have a particle size in the range 0.1 µm to 500 µm. Exceptionally good magnetic materials are obtained when each metallic phase has a particle size of 0.1 to 50 µm, and at least part of each magnetic phase, preferably at least 60% in volume of each magnetic phase, has a particle size of 50 to 500 µm.

[0045] In a preferred embodiment, the magnetic materials are formed into a desired shape by means of electro sinter forging, a sintering method disclosed in European Patent no. EP 2 198 993 B1 in the name of the same Applicant. This sintering method is also known, and referred to accordingly in the following, as electro-sinter-forging.

[0046] The forming cavity 2 of the forming die 1 is, accordingly, delimited by the inner walls of the forming die 1 and a pair of sintering electrodes 3, 4 movable into and out of the cavity along an axis X1. The forming die 1 is received in a forming machine globally designated by reference M. Pressure is therefore applied to the mixture PWMX into the forming die by means of the sintering electrodes 3, 4, and so is voltage, which is applied across the sintering electrodes 3, 4 themselves. The combination of pressure and voltage applied across the electrodes 3, 4 sinter the mixture PWMX into the desired shape. Exemplary shapes are depicted in figures 8A through 8I. In each case, the cross section of the forming cavity 2 matched that of the sintered material CMM: circular for figure 8A, round annular for figure 8B, rounded rectangle/flattened oval for figure 8C, square for figure 8D, rectangular for figure 8E, flattened round annular for figure 8F, triangular for figure 8G, square/rectangular with circular through opening for figure 8H, and circular with square/rectangular through opening for figure 8I. For annular shapes, as well as shapes featuring through openings, the void (opening) is provided through the use of inserts or, preferably through the use of fixed or mobile core rods and properly designed plungers.

[0047] Such a shape might be - depending on the conditions, a final shape (already formed to tolerances) or a "green" shape ready for subsequent processing.

[0048] According to a preferred embodiment of the invention, manufacturing a composite magnetic material with even better magnetic properties involves the following steps, which are configured as an evolution of the last two steps of the method.

[0049] The powdered mixture PWMX is inserted in the forming die 1 configured for accommodating an overlap of an electrical current I in the direction of a mechanical deformation, which is parallel to the force F applied to the plunger electrodes 3, 4 and which generates - through . In other words, the forming die 1 features inlet openings intended for receiving axially movable plunger electrodes 3, 4 configured for applying mechanical pressure and voltage to the mixture PWMX in the forming cavity.

[0050] Prior to the application of pressure and voltage to the powdered mixture in the forming cavity, a constant magnetic field B is applied to the powdered mixture PWMX itself in order to align the magnetic domains of the powders during the rest of the procedure. In order to avoid interactions between the to-be-applied electrical currents and the magnetic field B required to align the domains, either the magnetic field has to be parallel to the direction of the currents, or it should be kept exclusively during the pressing stage and should be turned off or shielded during the flow of currents. Figure 7 is representative of a processing step wherein the magnetic field B overlaps a current I having a direction essentially parallel to the axis X1. Clearly, the magnetic field lines of field B might not be exactly as straight as the axis X1, but for the purposes of sintering the mixture PWMX into a (composite) magnetic material CMM it is sufficient for the field lines to come as close as possible to a parallel condition to the current I.

[0051] The higher the magnetic field, the more aligned the domains, and the higher the residual field of the magnets after production and magnetization.

[0052] Then a nominal pressure is applied through the plunger electrodes (calculated as the force applied on/by the cross section of the plungers 3, 4 perpendicular to the current flow) between 10 to 350 MPa. A voltage is also applied across the plunger electrodes 3, 4 ranging between 5 and 150 V for a time interval of 0 to 500 ms in order to develop, on the tool and powder ensemble, a specific energy input (SEI) - defined as the integral in time of the product of the real part of the voltage and real part of the current, normalized by the weight of the powders concerned - between 0.5 and 2.4 kJ/g. As the voltage increases from 0 V to the desired value, the plungers 3, 4 follow up and/or exert pressure on the powders PWMX while the current I is flowing, thereby consolidating the powders to a dense sintered material CMM. EP 2 198 993 B1 is, again, exemplary of such procedures. If the time interval of the voltage/current is increased further, the thermodynamics of the system will prevail and the magnetic phase will transform in chemical composition because of long range atomic diffusion, thereby loosing its magnetic properties. This preferred embodiment of the method according to the invention results in anisotropic composite machinable magnets with pre-aligned domains and a preferential direction of magnetization given by the direction of the magnetic field during manufacturing.

[0053] Provided below is an overview of exemplary magnetic materials representative of embodiments of the invention. The examples below also provide an overview of exemplary embodiments of the manufacturing method herein.

Example 1

[0054] 

Powders: AlSi10 powder (pre-alloyed 10% in weight Si, the remainder Al, particle size <160 µm, theoretical density of 2,67 g/cm³) as powdered metallic phase, Nd₂Fe₁₄B isotropic flakes type MQP-16-7-11277-070 (Residual magnetic flux density B_r=960-1000 mT, intrinsic coercitivity H_ci = 530-600 kA/m, maximum Energy product (BH)_max = 124-140 kJ/m³, theoretical density 7,61 g/ cm³, particle size < 400 µm) as powdered magnetic phase

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 50% magnetic, 50% metallic

Procedure: after weighing and mixing of the powders, they are inserted in a 15 mm diameter die 1 (meaning the diameter of the forming cavity 2) and electro-sinter-forged to theoretical density (5,23 g/ cm³) with a height of 10,579 mm with the following processing parameters: specific energy input (SEI)=780 kJ/g, initial pressure P_start = maximum pressure P_max = 300 MPa and voltage V_max = 21,24 V. After densification, the part is extracted and magnetized in a commercial magnetizing system. The magnetic properties are then checked with a commercial hysteresisgraph with the following results: B_r=326 mT, Hci=644 kA/m, H_cB=199 kA/m and (BH)_max=16, 7 kJ/m³. Another sample produced in the identical conditions, without magnetization, was instead taken to a lathe, held on the fixtures and machined with a coated tungsten carbide tool to reduce the diameter. The axel turned at 775 rpm and the depth of cut was 1 mm. Another sample produced in the identical conditions was fixed on a lathe to drill a central bore with a steel, TiC coated tip.

Example 2

[0055] 

Powders: AlSi10 powder as powdered metallic phase, Nd₂Fe₁₄B isotropic flakes as powdered magnetic phase,

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 25% volume of AlSi10 powder ( prealloyed powder with Al 90% in weight, Si 10% in weight) 75% NdFeB isotropic flake as in Example 1.

Procedure: after weighing and mixing of 1,987 g of powders they are inserted in a diameter 10 mm die 1 (meaning the diameter of the forming cavity 2) and sintered to a theoretical density of 99,73% corresponding to a density of 6,501 g/cm³, using a SEI of 1,05 kJ/g, initial pressure P_start of 260 MPa, maximum pressure P_max of 260 MPa, maximum voltage V_max of 6,36 V. After densification, the part is extracted and magnetized in a commercial magnetizing system. The magnetic properties are then measured with a commercial hysteresisgraph with the following results: B_r=610 mT, Hci=745 kA/m, H_cB=399 kA/m and (BH)_max=63 kJ/m³.

Example 3

[0056] 

Powders: AlSi10 powder as powdered metallic phase, Nd₂Fe₁₄B isotropic flakes as powdered magnetic phase

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 75% volume of AlSi10 powder, 75% NdFeB isotropic flake as in Example 1.

Procedure: after weighting and mixing of the powders they are inserted in a diameter 10 mm die 1 (meaning the diameter of the forming cavity 2) and sintered to theoretical density (3,953 g/ cm³) with a SEI of 1,454 kJ/g, starting and maximum pressure P_start = P_max of 260 MPa, maximum voltage V_max of 4,96 V to produce a sample with a height of 4 mm. After densification, the part is extracted and magnetized in a commercial magnetizing system. The magnetic properties are then measured with a commercial hysteresisgraph with the following results: B_r=205 mT, Hci=853 kA/m, H_cB=153 kA/m and (BH)_max=7,8 kJ/m³.

Example 4

[0057] 

Powders: sterling silver (92,5% Ag - 6,5%Cu) as the powdered metallic phase, Nd₂Fe₁₄B isotropic flakes as in Example 1 as powdered magnetic phase

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 50% magnetic, 50% metallic

Procedure: after weighing and mixing of the powders, 2,528 g of the composite powders are inserted in a diameter 10 mm die and sintered to a density of 98,66% (8,183 g/cm³) with a SEI of 0,853 kJ/g, starting and maximum pressure P_start = P_max of 255 MPa, maximum voltage V_max of 7,32 V to produce a sample with a height of 4 mm. After densification, the part is extracted and magnetized in a commercial magnetizing system. The magnetic properties are then measured with a commercial hysteresisgraph with the following results: B_r=409 mT, Hci=793 kA/m, H_cB=279 kA/m and (BH)_max=28 kJ/m³.

Example 5

[0058] 

Powders: irregular bronze 85% Cu-15% Sn as powdered metallic phase, Nd₂Fe₁₄B isotropic flakes as powdered magnetic phase

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 50% magnetic and 50% metallic

Mixing: Turbula-type mixing for 20 minutes

Volume percentages: 50% magnetic, 50% metallic

Procedure: after weighting and mixing of the powders, 2,771 g of the composite powders are inserted in a diameter 10 mm die and sintered to a density of 96,8% (8,8 g/cc) with a SEI of 2,02 kJ/g, starting pressure of 200 MPa and maximum pressure of 220 MPa, maximum voltage of 9,38 V to produce a sample with a height of 4 mm. After densification, the part is extracted and magnetized in a commercial magnetizing system. The magnetic properties are then measured with a commercial hysteresisgraph with the following results: B_r=415 mT, Hci=788 kA/m, H_cB=275 kA/m and (BH)_max=28,5 kJ/m³

[0059] As can be seen from figures 1 through 4, relevant magnetic properties increase when the volume percentage of the magnetic phase increases (H_cB, BH_max, B_r), or remain within performance-wise satisfactory values (Hci) .

[0060] The experimental data plotted in figures 1 to 4 correspond to the following experimental data, all obtained from electro-sinter-forging of 10mm samples (the reference "NdFeB" designates Nd₂Fe₁₄B magnets)

[0061] According to the invention, forming the mixture of the metallic phase(s) and the magnetic phase(s) in powdered form by means of the application of pressure and voltage therethrough achieves multiple benefits and technical advantages. In the first place, owing to the speed of the forming process and the nature of the process itself, wherein electrical currents will flow preferentially through the metallic phase(s) travelling for the most part around the hard magnetic semiconducting phases, the hard magnetic phase(s) will not degrade or only degrade marginally, thereby allowing to manufacture a fully dense metal-(hard) magnetic intermetallic composite. This composite, thanks to the enhanced mechanical properties provided by the metallic phase, is machinable with hard tools such as tool steels, hard metals and cermets in conventional lathes and mills without the need of abrasives machining or electro-discharge machining which are sensibly costlier and less popular machining methods.

[0062] A second important effect of the invention is the possibility to manufacture precious metal magnets such as, but not limited to, 22 carat, 18 carat and 14 carat gold magnets. These find interesting and useful applications in jewelry and in the fashion industry. For example, unlike conventional magnetic buckles for bags which feature a precious metal (typically gold) main body wherein a magnet is nestled in a position that is not visible from the outside, and another magnet is nestled in the receiving area at which the buckle is intended to magnetically couple, magnetic materials according to the present invention can be formed (e.g. electro-sinter-forged) into the shape of the buckle main body thereby providing a one piece, aesthetically appealing, golden magnetic buckle.

[0063] Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.

Claims

1. A magnetic material (CMM) comprising at least one metallic phase and at least one magnetic phase, each metallic phase comprising one of:

- a transition metal or alloys thereof,

- a post-transition metal or alloys thereof, and

- an alkali earth metal or alloys thereof,

each magnetic phase comprising one of:

- a magnetic alloy having the formula RE₂TM₁₄B,

- a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y with 0<=x<=3 and 0<=y<=3, preferably x=3 and y=0,

- a magnetic alloy having the formula SmFe₇N_xC_y with 0<=x<=1 and 0<=y<=1, preferably x=1 and y=0,

- a magnetic alloy having the formula RE'₂TM'₁₇

- a magnetic alloy having the formula RE'TM'₅

wherein RE is a first rare earth element, RE' is a second rare earth element, TM is a first transition metal, TM' is a second transition metal, B is Boron, N is nitrogen, C is carbon, Sm is Samarium, Fe is Iron,
wherein the total amount of the at least one metallic phase is comprised between 25% and 95% in volume of the magnetic material.

2. The magnetic material of Claim 1, wherein the transition metal of the metallic phase is selected from the following group: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Copper (Cu), Zinc (Zn), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Palladium (Pd), Silver (Ag), Hafnium (HF), Iridium (Ir), Platinum (Pt), Gold (Au), paramagnetic alloys of iron (Fe), Nickel (Ni) or Cobalt (Co), diamagnetic alloys of iron (Fe), Nickel (Ni) and Cobalt (Co).

3. The magnetic material of Claim 1, wherein the post-transition metal of the metallic phase is selected from the following group: Aluminum (Al), Tin (Sn).

4. The magnetic material of Claim 1, wherein the alkali earth metal of the metallic phase is selected from the following group: Beryllium (Be), Magnesium (Mg).

5. The magnetic material of Claim 1 or Claim 2, wherein said rare earth element RE consists of Neodimium (Nd), said transition metal TM consists of iron (Fe), said .

6. The magnetic material of Claim 1, or Claim 2 or Claim 5, wherein said rare earth element RE' consists of Samarium (Sm) or Gadolinium (Gd), and said transition metal TM' consists of Iron (Fe) or Cobalt (Co) .

7. A method of manufacturing a magnetic material (CMM), comprising:

- providing at least one metallic phase in a powdered form, each metallic phase comprising one of a transition metal or alloys thereof, a post-transition metal or alloys thereof, and an alkali earth metal or alloys thereof,

- providing at least one magnetic phase in a powdered form, each magnetic phase comprising one of:

a magnetic alloy having the formula RE₂TM₁₄B,

a magnetic alloy having the formula Sm₂Fe₁₇N_xC_y with 0<=x<=3 and 0<=y<=3, preferably x=3 and y=0,

a magnetic alloy having the formula SmFe₇N_xC_y with 0<=x<=1 and 0<=y<=1, preferably x=1 and y=0,

a magnetic alloy having the formula RE'₂TM'₁₇

a magnetic alloy having the formula RE'TM'₅

wherein RE is a rare earth element, RE' is a rare earth element, TM is a transition metal, TM' is a transition metal, B is Boron, N is nitrogen, C is carbon, Sm is Samarium, Fe is Iron,

- mixing the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form to obtain a mixture (PWMX) of the at least one metallic phase and the at least one magnetic phase,

- placing the mixture (PWMX) of the at least one metallic phase and the at least one magnetic phase in powdered form into a forming die (1), particularly in a forming cavity (2) thereof,

- applying to the mixture (PWMX) of the at least one metallic phase and the at least one magnetic phase into the forming die (1) a pressure from 10 MPa to 350 MPa, and a voltage of 5 V to 150V for a time interval up to 500 ms, preferably from 1 ms to 300 ms, and an even more preferably from 1 ms to 100 ms, to form the mixture into a defined shape,

wherein the total amount of the at least one metallic phase in powdered form is comprised between 25% and 95% in volume of the mixture (PWMX) of the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form.

8. The method of Claim 7, wherein each metallic phase and each magnetic phase have a particle size in the range 0.1 µm to 500 µm.

9. The method of Claim 8, wherein each metallic phase has a particle size of 0.1 to 50 µm, and at least part of each magnetic phase has a particle size of 50 to 500 µm, preferably at least 60% in volume.

10. The method of any of Claims 7 to 10, wherein the forming cavity (2) is delimited by inner walls of the forming die (1) and a pair of sintering electrodes (3, 4) movable into and out of the forming cavity (2), wherein pressure is applied to the mixture (PWMX) of the at least one metallic phase and the at least one magnetic phase into the forming die (1) by means of said sintering electrodes (3, 4).

11. The method of Claim 11, wherein voltage is applied to the mixture (PWMX) of the at least one metallic phase and the at least one magnetic phase into the forming die through said sintering electrodes (3, 4).

12. The method of any of Claims 10, 11, wherein prior to said applying a pressure and a voltage to the mixture of the at least one metallic phase and the at least one magnetic phase (PWMX) into the forming die (1), a magnetic field (B) is applied to the mixture of the at least one metallic phase and the at least one magnetic phase (PWMX) into the forming die (1) to align magnetic domains in the mixture of the at least one metallic phase and the at least one magnetic phase (PWMX) to a desired direction.

13. The method of any of Claims 7 to 12, wherein said mixing the at least one metallic phase in powdered form and the at least one magnetic phase in powdered form to obtain a mixture of the at least one metallic phase and the at least one magnetic phase (PWMX) is provided by means of one of:

- a Turbula-type mixer,

- an attritor mill

- a planetary ball mill.

14. The method of any of Claims 7 to 13, wherein

- the transition metal of each metallic phase is selected from the following group: Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Copper (Cu), Zinc (Zn), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Palladium (Pd), Silver (Ag), Hafnium (HF), Iridium (Ir), Platinum (Pt), Gold (Au), paramagnetic alloys of iron (Fe), Nickel (Ni) and Cobalt (Co), diamagnetic alloys of iron (Fe), Nickel (Ni) or Cobalt (Co).

- the post- transition metal of each metallic phase is selected from the following group: Aluminum (Al), Tin (Sn),

- the alkali earth metal of each metallic phase is selected from the following group: Beryllium (Be), Magnesium (Mg).

15. The method of any of Claims 7 to 14, wherein RE consists of Neodimium (Nd), RE' consists of Samarium (Sm) or Gadolinium (Gd), TM consists of Iron (Fe), TM' consists of Iron (Fe) or cobalt (Co).

Drawing