An R-T-B based permanent magnet includes R-T-B based compounds as main-phase crystal grains. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. A two-grain boundary is contained between the two adjacent main-phase crystal grains. An average grain size of the main-phase crystal grains is 0.9 μm or more and 2.8 μm or less. A thickness of the two-grain boundary is 5 nm or more and 200 nm or less.

An R-T-B based permanent magnet includes R-T-B based compounds as main-phase crystal grains. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. A two-grain boundary is contained between the two adjacent main-phase crystal grains. An average grain size of the main-phase crystal grains is 0.9 μm or more and 2.8 μm or less. A thickness of the two-grain boundary is 5 nm or more and 200 nm or less.

A metal matrix composite tool includes a body having hard composite portion that includes reinforcing particles dispersed in a binder material. At least some of the reinforcing particles comprise a monolithic particle structure including a core having irregular outer surface features integral with the core.

There is provided a sintered bearing having high rotational accuracy and low rotational fluctuation. This bearing includes a bearing surface (4a), and is made of a sintered compact (4″) produced by molding and sintering a raw material powder (10) containing a partially diffusion-alloyed powder (11) in which a copper powder (13) is partially diffused on a surface of an iron powder (12), a tin powder (14) as a low-melting-point metal powder, and a graphite powder as a solid lubricant powder. The sintered bearing has a radial crushing strength greater than or equal to 300 MPa.

There is provided a sintered bearing having high rotational accuracy and low rotational fluctuation. This bearing includes a bearing surface (4a), and is made of a sintered compact (4″) produced by molding and sintering a raw material powder (10) containing a partially diffusion-alloyed powder (11) in which a copper powder (13) is partially diffused on a surface of an iron powder (12), a tin powder (14) as a low-melting-point metal powder, and a graphite powder as a solid lubricant powder. The sintered bearing has a radial crushing strength greater than or equal to 300 MPa.

A metal magnetic particle provided with an oxide layer on a surface of an alloy particle containing Fe and Si. The oxide layer has a first oxide layer, a second oxide layer, and a third oxide layer from a side of the alloy particle. All of the first oxide layer, the second oxide layer, and the third oxide layer contain Si. Also, in line analysis of element content by using a scanning transmission electron microscope-energy dispersive X-ray spectroscopy, the first oxide layer is a layer having Fe content smaller than Si content in the alloy particle, the second oxide layer is a layer having Fe content larger than the Si content in the alloy particle, and the third oxide layer is a layer having Fe content smaller than the Si content in the alloy particle.

A metal magnetic particle provided with an oxide layer on a surface of an alloy particle containing Fe and Si. The oxide layer has a first oxide layer, a second oxide layer, and a third oxide layer from a side of the alloy particle. All of the first oxide layer, the second oxide layer, and the third oxide layer contain Si. Also, in line analysis of element content by using a scanning transmission electron microscope-energy dispersive X-ray spectroscopy, the first oxide layer is a layer having Fe content smaller than Si content in the alloy particle, the second oxide layer is a layer having Fe content larger than the Si content in the alloy particle, and the third oxide layer is a layer having Fe content smaller than the Si content in the alloy particle.

The disclosure relates to a method for preparing Ti(C,N)-based superhard metal composite materials, with Ti(C,N) powder and (W,Mo,Ta)(C,N) powder as main raw materials and Co powder as binding phase for preparation, thereby obtaining a material in which a microstructure is a double-core rim structure that has both a black core rim and a white core rim. The material has a complete and evenly distributed double-core rim structure. In the condition that the ensured hardness of the material is not reduced and even slightly increased, the toughness of the material is significantly improved, wherein the fracture toughness of the material is in the range of 11.3 to 12.5 MPa.Math.m.sup.1/2.

A powder magnetic core containing a magnetic particle of an Fe-based Cr-containing amorphous alloy and an organic binding substance is provided as a powder magnetic core with a small loss and high initial permeability. The depth profile of the composition determined from the surface of the magnetic particle in the powder magnetic core has the following characteristics. (1) An oxygen-containing region with an O/Fe ratio of 0.1 or more can be defined from the surface of the magnetic particle, and the oxygen-containing region has a depth of 35 nm or less from the surface. (2) A carbon-containing region with a C/O ratio of 1 or more can be defined from the surface of the magnetic particle, and the carbon-containing region has a depth of 5 nm or less from the surface. (3) The oxygen-containing region has a Cr-concentrated portion with a bulk Cr ratio of more than 1.

A powder magnetic core containing a magnetic particle of an Fe-based Cr-containing amorphous alloy and an organic binding substance is provided as a powder magnetic core with a small loss and high initial permeability. The depth profile of the composition determined from the surface of the magnetic particle in the powder magnetic core has the following characteristics. (1) An oxygen-containing region with an O/Fe ratio of 0.1 or more can be defined from the surface of the magnetic particle, and the oxygen-containing region has a depth of 35 nm or less from the surface. (2) A carbon-containing region with a C/O ratio of 1 or more can be defined from the surface of the magnetic particle, and the carbon-containing region has a depth of 5 nm or less from the surface. (3) The oxygen-containing region has a Cr-concentrated portion with a bulk Cr ratio of more than 1.