SK288686B6 - Method of microwave annealing of magnetically soft powders without sintering - Google Patents

Abstract

Powder material on the basis of Fe, Co, Ni, their alloys or the alloy of Fe, Co, Ni with Cr, Mn, Mo, Nb, Al, Si, B, P is placed into an annealing crucible with low absorption of microwave radiation. The powder material is exposed to microwave radiation within the range of 915 MHz to 8 GHz in an atmosphere of inert gas or dry air. Influence of microwave radiation results in heating of powder metal to the temperature in the range from 100 to 1500 øC during 10 seconds to 120 minutes. After finishing of annealing follows slow cooling at thespeed of 15 øC/min.

Description

Otáasť techniky

The invention relates to powder metallurgy, production, processing and treatment of powdered materials, recycling of raw compact waste, production and treatment of magnetic powdered materials oriented to the production of soft magnetic composites by compacting, use of river-compacted magnetic powders in electrical engineering, electronics and medical applications.

BACKGROUND OF THE INVENTION

The metal powders produced by the spraying process are annealed in order to achieve increased compressibility. The aim of the annealing is to relax the mechanical stresses that arise from the rapid cooling, as well as to remove the oxides resulting from the spraying process on the surface of the metal powder particles. The annealing temperature of the iron-based powders ranges from 700 to 1200 ° C. Annealing to improve the compressibility is carried out in an inert gas reducing atmosphere, typically argon containing 5-25% hydrogen. The hold time at the annealed temperature is usually in the range of 1 to 2 hours. After annealing, the powder is obtained in the form of a sinter, which must be transformed again into the powder form. The sinter is mechanically ground in an attritor or disc mill. Mechanical grinding again brings internal stresses to the powder.

There are annealing technologies that prevent the formation of cakes and eliminate the need for mechanical grinding after annealing. For example, [US3668024] using a temperature of 780-1150 ^C ° C, wherein the temperature zone of the furnace in which the annealing takes place, is supplied and exhausted at the same time a reducing gas with a controlled dew point. In this case, no sintering occurs after a standard annealing time of 1-2 hours. in contrast to the countercurrent system of supplying the reducing atmosphere to the entire furnace including the heating and cooling zones. The disadvantage of this method is the necessity of precise monitoring and control of the process gas dew point and higher consumption of process gases. Another method of preventing caking [US3668024] is to form a mixture of the calcined powder with an easily removable inert powder material, e.g. sodium chloride. The inert powder separates the metal powder particles during annealing. After annealing, the inert material is removed by washing the powder mixture with solvent. The disadvantage of this is the wet removal of the inert component.

The most efficient, economical and standard technique used in technical practice is annealing followed by finely grinding the sinter. This process is effective to improve the compressibility by removing hard oxidic compounds. In the case of the use of powders in applications requiring soft magnetic materials, the disadvantage of this process is the grinding of the sinter, which causes a re-increase in coherence due to mechanical stresses.

Microwave heating of materials is used for speculation, curing and heat treatment of ceramic materials and composites with metal and ceramic matrix. The advantages of microwave heating are fast heating, selectivity of heating and shortening of process times. Microwave annealing with susceptorabolo was designed for the production of silicon-based semiconductors [US .20i.201996453Ai]. The acceleration of heat treatment was designed for Li-ion batteries [US 20130266741A J], Microwave annealing was designed to repair internal semiconductor defects for integrated circuits [US20150294881AIj. Technology has been proposed for producing CMOS semiconductors by microwave annealing two different materials to produce an interface of desired properties [US006051283A j.

SUMMARY OF THE INVENTION

The magnetically soft powder material produced by rapid solidification, mechanical grinding, or a combination of both is characterized in that its internal structure contains a high proportion of defects and internal stresses that increase the mechanical and magnetic hardness. Increasing the mechanical hardness deteriorates the compressibility of the powders. The increase in magnetic hardness, expressed as coercivity Hc [A / m], narrows the application possibilities of the powder in an uncompacted form in the field of magnetically soft applications.

The subject of the invention is the microwave annealing of such magnetic powders in order to reduce or eliminate internal stresses and disturbances of the internal structure of the powder particles. Powdered material is understood to be the pure metals Fe, Ni, Co, their alloys or their alloys with Cr, Mn, Mo, Nb, Ai, Si, B, P. Powdered material is poured into a crucible made of ceramic material characterized by low coefficient absorption of microwave radiation in the applied frequency domain. The alumina crucible is placed in the working chamber of the microwave heating apparatus. The microwave chamber is gas-tight. Microwave heating is carried out in a single- or multi-mode manner in the frequency domain defined for technological applications in the range from 915 MHz to 8 GHz, preferably from 2 GHz to 6 GHz, typically

S K 288686 B6

2.45 GHz. An inert gas or dry air is introduced into the working chamber depending on the nature of the material to be treated, the temperature and the annealing time. Temperature during microwave heating is monitored by optical pyrometer or thermocamera. The measured temperature is used to control the parameters of the microwave heating. The annealing temperature is selected depending on the chemical composition, phase composition and internal structure of the material to be treated. The annealing temperature range is in the range 100-1,500 ° C, preferably in the range 150-1,200 ° C, typically in the range 400-800 ° C. The holding time at the annealing temperature is selected depending on the characteristics of the powdered material to be treated, such as particle size, particle shape, diffusion coefficients, kinetic and translimitation coefficients. The annealing time ranges from 10 seconds to 120 minutes, preferably from 1 to 45 ruins, typically from 5 to 30 minutes. The annealing temperature cooling is carried out in the process chamber without the effect of microwave radiation at a rate dependent on the amount of powdered material to be processed. The cooling rate is less than 15 ° C7min. The annealing can be carried out by a batch process as described or by a continuous process. Continuous microwave annealing is carried out in a microwave device with a processing chamber allowing the feeding of powdered material on an endless sliding belt. In this case, the annealing time is controlled by the feed belt feed rate, as is the case with conventional conventional furnaces. The output of the microwave annealing process is a powder without significant signs of agglomeration or sintering. Microwave annealed powder material does not need to be mechanically treated, e.g. crushing, grinding, forging, etc. The microwave annealing process results in reduced coercivity and mechanical hardness of the treated powder material. As described, the annealed 'powdered' material has no increased surface activity or increased affinity for oxygen. Thus, the microwave annealed powder material is characterized by an increase in compressibility due to a decrease in mechanical hardness. The coercivity of the microwave-annealed powdered material is minimal with respect to the theoretically achievable value taking into account all material parameters resulting in a change in the coercivity of the magnetically soft materials.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Technically pure iron in the form of water sprayed powder ASC 100.29 had a coefficient of Hc = 210 A / m in the delivered state. The treated powder material weighing 300 g was poured into a 100 mm diameter crucible. A crucible made of alumina with powder was placed in a stainless steel working chamber which was cooled with water. The working space was evacuated to a technical vacuum and subsequently filled with 99.95% argon purity. The applied microwave radiation had a frequency of 2.45 GHz. The total power of the microwave source was continuously adjustable in the range of 300 - 2800 W. The current power of the microwave source was regulated based on the current temperature. The temperature of the treated powder was measured by a non-contact optical infrared pyrometer. The batch was heated by microwave irradiation at 500 ° C at a rate of 30 ° C / minute. After endurance 15 min. at .500 ° C, the batch was cooled at a rate of 8 ^. € 7π · ίη. at 40 ° C. The calcined powder was poured from the crucible into the prepared duster. The coercivity of the microwave annealed powder was Hc - 185 A / m.

Example 2

Technically pure iron ASC 100.29 from Example 1 was pressed at 800 MPa to form prisms of 4 x 5 x 20 mm. Crude moldings whose shape or dimensional deviations exceeded the error tolerance interval were discarded for recycling. The discarded moldings were mechanically ground to obtain a powdered material for reuse. The coercivity of the powder recycled by grinding was Hc = 350 A / m. The recycled powder was treated with the annealing procedure of Example 1. The microwave annealed recycled powder ASC 100.29 had a coercivity of Hc = 180 A / m.

Example 3

The Ni-20Fe-4,4Mo-0,3Mn-0,3Si supermalloy powder alloy produced by mechanical grinding of pure metals had a coercivity Hc = 350 A / m. Mechanochemically produced supermalloy was characterized by reduced compressibility. The compressibility was limited to the interval of 425 - 475 MPa, higher than 475 MPa caused the blanks to expand by springing. Pressures below -425 MPa led to insufficient handling strengths of the blanks. Supermalloy powder was microwave annealed at 430 ° C for 20 min. in a protective atmosphere of argon. The other annealing parameters were the same as in Example 1. Microwave annealing reduced the supercmail powder coercivity to Hc = 100 A / m. The compressibility increased to 800 MPa with a corresponding decrease in the porosity and increased strength of the blank.

Claims (1)

P A T E N T O N O R O K ¥ Method of microwave annealing of soft magnetic powders, characterized in that the powdered material wherein the material is Fe, Co, Ni and their alloys or alloys of these metals with Cr, Mn, Mo, Nb, Ai, Si, B, P is placed in a microwave crucible with low microwave absorption in an inert gas or dry air atmosphere and subjected to microwave radiation in the range of 915MHz. 8 to the CH and the metal powder is allowed to warm to a temperature of 100-1500 ° CPOC 10 seconds to 120 minutes and the material was slowly cooled to 15 ^C at a rate of C / min.