495 results about "Cermet" patented technology

A composite, comprising a binder, the binder comprising one or more of polymeric, metallic, or ceramic, or pyrolytic carbon binder and a nanostructured carbon having a cellular structure. The cellular structure comprises one or more cell walls having a structure formed by a template and one or more cavities. Each cavity is substantially enclosed by the one or more cell walls and substantially unimpregnated by a liquid or solid.

The invention belongs to the technical field of thermal power heating surface treatment, and provides a gradient functional composite coating applied to a boiler heating surface and a preparation method of the gradient functional composite coating in order to solve the technical problems that an existing protective coating of the boiler heating surface is prone to abrasion and oxidation and high in cost. Collaborative design is formed, and gradient matching of mechanical properties and environmental failure resistance is achieved. The low-melting-point glass powder is combined with the rare earth catalytic effect, low-temperature ceramization is achieved, and thermal damage to a matrix is avoided. After the metal ceramic transition layer is sprayed, high-frequency induction remelting treatment is carried out, meanwhile, laser cladding is carried out on the surface of the ceramic surface layer, a nanocrystalline-amorphous composite structure is formed, and the bonding strength of the coating is improved.

The invention provides a high-speed laser cladding metal ceramic coating, a cast iron brake disc and a preparation method and application of the cast iron brake disc. The high-speed laser cladding metal ceramic coating comprises the following preparation raw materials in percentage by mass: 40%-60% of stainless steel, 10%-20% of SiC, 10%-30% of ZrO2, 5%-10% of Ti and 1%-2% of CeO2. According to the coating, the hardness, the wear resistance, the friction coefficient and the toughness of a cast iron matrix can be remarkably improved, and the braking requirement of a motor vehicle under the extreme working condition can be well met. The invention further provides the cast iron brake disc and a preparation method and application thereof.

The invention provides a high-temperature-resistant and corrosion-resistant ammonia water nozzle coating and a preparation method thereof, and belongs to the field of coatings. The ammonia water nozzle coating is composed of a self-repairing metal ceramic bonding layer, an organic-inorganic hybrid corrosion-resistant layer and a functional surface layer which are sequentially arranged in a stacked mode. A coating of the self-repairing metal ceramic bonding layer is composed of the following components of 90-99 parts of NiCrAlY alloy and 1-8 parts of self-repairing microcapsules. A coating of the organic-inorganic hybrid corrosion-resistant layer is prepared from the following components: 40 to 60 parts of fluorinated polyurethane prepolymer, 20 to 40 parts of silicon-aluminum sol, 1 to 8 parts of disulfide bond modified epoxy resin and 10 to 20 parts of magnesium-aluminum hydrotalcite; the coating of the functionalized surface layer is prepared from the following components: 20 to 30 parts of stearic acid modified TiO2 particles, 60 to 80 parts of waterborne polyurethane and 2 to 7 parts of ionic liquid modified SiO2 nanoparticles. The corrosion resistance, the high temperature resistance and the self-repairing capacity of the ammonia water nozzle are improved at the same time.

A metal-ceramic substrate and an electronic component comprising a metal-ceramic substrate. The metal-ceramic substrate comprises: a) a ceramic body which has a main extension plane, b) a metal layer which is connected to the ceramic body, in a planar manner, the metal layer having a structuring region which comprises: (i) solid material in some areas and (ii) non-solid material in some areas, and c) a contact region comprising silver arranged on the metal layer, wherein, in a cross section through the metal-ceramic substrate perpendicular to the main extension plane, the structuring region has a geometry in which the following requirement is met:A⁡(BCDsolid) / A⁡(BCDtotal)>70⁢%,wherein A (BCDtotal) represents the total area of the triangle described by the points B, C and D, and A (BCDsolid) represents the area of the triangle described by the points B, C and D which is occupied by solid material.

The utility model provides an anti-chip-sticking metal ceramic milling cutter. The anti-chip-sticking metal ceramic milling cutter comprises a connecting column, the knife handle is arranged in the connecting column; the tool bit is arranged at one end of the tool handle, a chip removal groove is formed in a chip cutting part of the tool bit, and the tool handle and the tool bit are made of metal ceramic materials. The threaded rod is rotated to drive the conical block to move upwards, so that the threaded rod is separated from the screw hole, at the moment, the trapezoidal block is reset through the spring, the fixing rod is separated from the inserting hole, and then the extending length of the tool bit can be adjusted; and meanwhile, the conical block moves downwards to extrude the trapezoidal block and the fixing rod to move and compress the spring, so that the fixing rod extends into the insertion hole, and the cutter handle is fixed through the threaded rod and the fixing rod, so that the effect of adjusting the overall length of the milling cutter according to use requirements is achieved, and the use flexibility, applicability and efficiency of the milling cutter are effectively improved.

A cutting tool includes a substrate at least partially coated with a coating. The substrate is a cemented carbide, cermet or ceramic. The coating includes a layer of Ti(C,N), a layer of Al2O3 and there between a bonding layer. The Ti(C,N) layer is composed of columnar grains, wherein an average grain size D422 of the Ti(C,N) layer is 25-50 nm, and wherein the Ti(C,N) layer includes a portion B1 that is adjacent to the bonding layer. An average grain size of the Ti(C,N) grains in portion B1 is larger than the average grain size D422 in the whole Ti(C,N) layer. In the portion B1 of Ti(C,N) layer the Ti(C,N) grains has an average grain size of 140-300 nm.

The invention relates to an ultrasonic bonding process and a bonding process reliability evaluation method, and belongs to the technical field of semiconductor device packaging. The invention relates to an ultrasonic bonding process, which comprises the following steps of: 1, before bonding, carrying out plasma cleaning on a metal ceramic shell to remove surface contamination and an oxide layer; step 2, enabling the aluminum wire to penetrate into a chopper of a bonding machine, enabling the aluminum wire to be in contact with the surface of the gold-plated layer at the bonding pressure of 250cN-280cN by adopting the chopper, and enabling the aluminum wire to be in contact with the surface gold-plated layer of the bonding area in a low-pressure mode; and step 3, the bonding machine applies ultrasonic power of 10.5-12.3 W for 400-500 ms, the aluminum wire begins to rub and destroy the gold-plated layer on the surface of the bonding area under the action of the ultrasonic power, and after the gold-plated layer is destroyed, the aluminum wire penetrates through the gold-plated layer and forms an atomic-scale mutual diffusion interface with the nickel-plated layer. Reliable combination of gold, aluminum and nickel is achieved, meanwhile, a reliability evaluation method is provided, and therefore it is guaranteed that devices, circuits and the like adopting the ultrasonic bonding technology work reliably in the life cycle.

The invention discloses metal ceramic MAX-phase composite powder for spraying and a preparation method of the metal ceramic MAX-phase composite powder, and belongs to the field of metal ceramic composite materials. The method comprises the following steps: mixing Ni powder, Cr powder and Cr2AlC nano powder with deionized water, a binder and a dispersant according to a specific ratio, and carrying out wet ball milling to prepare uniform slurry; carrying out spray granulation to obtain primary spherical powder; and finally, carrying out spheroidizing treatment on the primary powder by adopting radio frequency plasma under the protection of inert gas to obtain a final product. The core of the preparation method is that through an optimized two-step process, many limitations in the application aspect of an existing MAX phase material are solved, and the composite powder which is high in sphericity degree, good in flowability, compact in interior and stable in MAX phase component is successfully prepared. The powder can be directly used for thermal spraying, and an ideal raw material is provided for preparing a high-performance MAX-phase metal ceramic coating.

The invention relates to the technical field of electronic component manufacturing, solves the technical problem that interface contact resistance bounces and rises due to thermal stress mismatch, and particularly relates to an electronic component preparation parameter optimization method and system. Generating a gradient layer of which the thermal expansion coefficient continuously changes; and calculating a target thermal expansion coefficient for eliminating the interface thermal stress and an actual thermal expansion coefficient of the in-situ monitoring gradient layer based on the metal and ceramic concentration distribution function. According to the method, component continuous transition is achieved through metal / ceramic precursor dynamic flow control, continuous gradual change from metal to ceramic components is achieved, the coefficient of thermal expansion is in smooth transition in the thickness direction, and internal stress accumulation caused by material expansion difference is blocked from the source; and dynamic deposition regulation is combined to ensure that the thermal expansion gradient at any position is lower than a critical threshold value, and stripping or cracking caused by stress concentration in thermal circulation is avoided.

Provided is a multicolour cermet and / or ceramic article, and in particular a bezel of a timepiece, made by a method for injecting at least two materials of distinct colours, said article comprising a relief decoration of a colour different from the rest of the article, said decoration being made by laser ablation after injection of the two materials.

The invention relates to a metal-ceramic substrate, to an electronic component comprising a metal-ceramic substrate, and to a method for producing a metal-ceramic substrate. The metal-ceramic substrate comprises: a) a ceramic body which has a main extension plane, b) a metal layer which is connected to the ceramic body in a planar manner, the metal layer having a structuring region which comprises (i) partially solid material and (ii) partially non-solid material, and c) a contact area which is arranged on the metal layer and comprises silver, the structuring region having a geometry in a cross-section through the metal-ceramic substrate perpendicular to the main extension plane, the following requirement being met: S(BCsolid) / S(BCtotal)>60%, wherein: S(BCtotal) represents the total length of the line between points B and C, and S(BCsolid) represents the length of the line between points B and C that intersects the solid material.

A solid oxide fuel cell is disclosed. The solid oxide fuel cell includes: an anode support electrode; a solid oxide electrolyte disposed on the anode support electrode; and a cathode electrode disposed on the solid oxide electrolyte. The anode support electrode includes: a first support layer having a porous structure and including a cermet of nickel and first yttria-stabilized zirconia containing yttria in a proportion of 1 mol% to 5 mol%; a second support layer which has a porous structure, is provided on the first support layer, and is formed from metal ceramic of nickel, second yttria-stabilized zirconia having a higher yttria content than the first yttria-stabilized zirconia, and alumina; and an anode functional layer which is provided on the second support layer so as to be in contact with the solid oxide electrolyte, and which is formed from a cermet of yttria-stabilized zirconia and nickel.

The invention relates to a preparation process of a metal ceramic bionic multilayer film, and belongs to the technical field of metal ceramic films, and the metal ceramic bionic multilayer film comprises a porous metal matrix, a gradient transition layer, a bionic lamination layer and a nanopore separation layer. According to the method, the failure problem of a traditional metal ceramic film under the extreme working condition is systematically solved through the multi-level innovative design, firstly, in the aspects of thermal stress elimination and interface strengthening, a five-layer gradient transition layer structure with the ceramic content changing is adopted, and the plasma spraying-laser remelting synchronous machining technology is combined; the thermal expansion coefficient of the metal matrix and the ceramic layer is continuously and gradually changed, so that the interface thermal stress is effectively reduced, the bonding strength is improved, the problems of cracking and layering under the high-temperature working condition are effectively solved, the service life is effectively prolonged, the structure is strengthened and toughened, and the bionic lamination design simulates the'brick-mud 'structure of a shell pearl layer; the nano-scale metal layer absorbs crack energy, and the ceramic layer provides rigid support, so that the fracture toughness is effectively improved.

The invention relates to the technical field of fuel cells, and provides a solid oxide fuel cell and a preparation method thereof, and the preparation method comprises the following steps: providing a half-cell precursor comprising an electrolyte layer and a NiO-based ceramic layer; placing the half-cell precursor in an acid solution for reaction treatment, selectively etching to remove at least part of NiO phase in the NiO-based ceramic layer, and cleaning to form a porous ceramic layer; injecting nickel slurry into pores of the porous ceramic layer, and performing drying and first calcination treatment to form a porous Ni-based metal ceramic composite anode layer; and preparing a porous cathode layer on the surface of the other side of the electrolyte layer to form the solid oxide fuel cell. According to the method, the NiO phase of the NiO-based ceramic layer is removed by using the pickling solution, and the nickel slurry is injected to construct the porous Ni-based metal ceramic composite anode, so that the problems that the pore structure is random and difficult to control when the porous anode is prepared by pore-forming of a traditional pore-forming agent and reduction of NiO by introducing hydrogen, and the active area of the anode is reduced due to migration, agglomeration and coarsening of Ni particles are solved.

This invention provides a powder material that improves flowability and particle breakage strength compared to existing technologies. The powder material of this invention has a dendritic structure (1). The dendritic structure (1) has a superhard alloy composition or a cermet composition.

The present application relates to the field of tool processing, and particularly relates to a processing technology for metal ceramic vertical installation forming groove tool. The processing technology comprises the following steps: step 1: processing a blank into a tool finish with a positioning bevel; step 2: processing a reference plane on the end face of the tool finish at the chip rolling groove, the included angle between the reference plane and the end face is the angle of the tool clearance angle; step 3: processing a tool tooth with a clearance angle and a side clearance angle at the reference plane of the tool finish, and detecting the tooth profile data of the tool tooth, the tooth profile data includes tooth width, tooth depth and angle, the detection of the tooth profile data adopts a projection comparison detection method, a standard tooth profile is fixed on a projection surface, and the tool tooth to be detected is enlarged through projection, if the tool tooth data is correct, the tool tooth data is coincident with the standard tooth profile; and step 4: processing the tool chip rolling groove, and performing passivation and coating treatment on the blade edge. Through the implementation of the present application, the processing and detection efficiency of the forming groove tool is improved.

The invention discloses a gradient composite reinforced anti-corrosion treatment method for a metal alloy guardrail, and belongs to the technical field of metal material surface treatment. The method comprises the following steps: carrying out ultrasonic cavitation micro-etching and electrochemical gradient activation pretreatment on the surface of a substrate; a metal ceramic composite layer containing a non-oxide ceramic reinforced phase is generated on the surface in situ through a micro-arc oxidation-chemical vapor deposition coupling process, and a component transition layer is formed with the assistance of vacuum gradient diffusion alloying treatment; and finally, coating an intelligent resin coating containing a corrosion inhibitor capsule and a corrosion indicator, and constructing a super-hydrophobic surface. By constructing a multi-layer composite protection system of the gradient diffusion layer / the metal ceramic layer / the intelligent coating / the super-hydrophobic layer, the anti-corrosion performance is remarkably improved, and the obtained guardrail has excellent bonding strength, wear resistance and long-acting anti-corrosion service life, has the intelligent functions of damage self-repairing and corrosion state visualization and is suitable for popularization and application. The method is especially suitable for harsh service environments.

The invention provides a connecting process of a metal ceramic membrane component, which comprises the following steps: uniformly coating the outer surface of a porous ceramic tube with a coating liquid prepared from ceramic powder and metal powder to obtain a porous ceramic tube with a metal ceramic coating; putting the porous ceramic tube into a mold, forming a plugging clamping groove in one end of the mold, forming a cavity among the outer wall of the porous ceramic tube, the plugging clamping groove and the mold, filling metal powder into the cavity, and arranging a plugging fixing piece at the other end of the mold, and finally, the obtained metal ceramic assembly blank is subjected to high-temperature sintering, and the metal ceramic membrane assembly can be prepared. According to the invention, effective combination of the metal film layer and the ceramic film layer is realized through a co-firing technology by utilizing a mold forming and surface modification process. The prepared metal ceramic membrane assembly can be directly connected with a device in a welded mode in the using process, the membrane layer precision is high, the thermal shock resistance is good, and the metal ceramic membrane assembly is suitable for high-temperature, high-pressure, high-viscosity and other severe systems in the petrochemical industry field.

A turbine blade and related method are disclosed. The blade includes an airfoil body having a radial outermost surface relative to a turbine rotor, a bond coat over the radial outermost surface, and an outermost abrasive layer over the bond coat. The outermost abrasive layer may include a graded oxide ceramic layer or a graded metal ceramic layer. In any event, the outermost abrasive layer is vacuum heat treated to harden the layer, resulting in increased rub and improved clearance between the blade tip, creating a smaller tip gap and lower leakage compared to conventional systems. The heat-treated abrasive layer is also resistant to oxidation at higher temperatures, e.g., greater than 1090° C. (˜2000°F.), caused by the increased use of higher temperature fuels, such as hydrogen. The vacuum heat treatment also results in thermal cycle testing improvements.

The invention discloses a universal array clamp for automatic bonding of a metal ceramic packaging integrated circuit and a bonding method. The universal array clamp comprises a clamp main board, a clamp universal part and a clamp special part, the clamp universal part comprises a linear sliding rail fixed to the clamp main plate, a sliding blocking piece arranged on the linear sliding rail in a sliding mode, and an elastic system providing elastic reset for the sliding blocking piece. The clamp special part is a loading tray which is detachably mounted on the clamp main board, and the loading tray is provided with a placing groove for accommodating a metal ceramic packaging integrated circuit of a specific series and a specific model; the linear sliding rail provides mechanical transmission support for the sliding blocking piece, so that the sliding blocking piece moves along a linear track to press or release the metal ceramic packaging integrated circuit placed on the loading tray. The clamp has the advantages of being compatible with multi-series and multi-model metal ceramic packaging integrated circuits, reducing the abrasion of the clamp and prolonging the service life.

The present invention is in the field of materials engineering and nanotechnology. More specifically, the present invention discloses: a functional premix comprising nanoparticles and a carrier or compatibilizer; a method of obtaining the premix; a method of altering the properties of a material; and a modified material formed with improved properties. Unexpectedly, the premix of the present invention can be used to alter the properties of different kinds of materials, such as polymers, metals, ceramic materials, and / or composites of different materials. The premix of the present invention has numerous advantages in terms of transportation, use, and incorporation of nanoparticles into different materials. In one embodiment, the present invention provides significant modification of the properties of polymers and, in fact, breaks the existing concepts in this technical field. In another embodiment, the present invention provides advantages in altering the properties of metals and / or ceramic materials.

The invention discloses an AMB ceramic substrate and a manufacturing method thereof, and belongs to the technical field of ceramic substrates. The AMB ceramic substrate provided by the invention comprises a ceramic substrate, a solder layer and a second metal layer, wherein the solder layer and the second metal layer are sequentially stacked on the ceramic substrate; the material of the solder layer comprises matrix metal, active metal, ceramic micro powder and an active metal compound; the thermal expansion coefficient of the solder layer is increased in the direction away from the ceramic substrate, the thermal expansion coefficient of the solder layer is larger than the thermal expansion coefficient of the ceramic substrate, and the thermal expansion coefficient of the solder layer is smaller than the thermal expansion coefficient of the second metal layer. The AMB ceramic substrate provided by the invention has excellent welding reliability, and the peel strength of the copper layer of the obtained ceramic substrate is high.

The invention belongs to the field of powder metallurgy technologies and metal ceramic materials, and discloses a preparation method of a high-entropy binding phase Ti (C, N)-based metal ceramic material and a product of the high-entropy binding phase Ti (C, N)-based metal ceramic material. The preparation method comprises the steps that Fe, Mn, Co and Cr elementary substance metal powder serves as raw materials and is mixed and then subjected to ball milling, obtained high-entropy alloy powder, Ti (C, N) powder and secondary carbide powder form mixed powder, a forming agent and absolute ethyl alcohol are sequentially added for wet milling, mixed slurry is obtained, drying, grinding, screening, pressing, degreasing and sintering are conducted, and the high-entropy alloy composite material is obtained. According to the obtained high-entropy alloy Ti (C, N)-based metal ceramic material, the core-ring structure is evenly distributed, the ring phase transition layer with the moderate thickness effectively inhibits growth of Ti (C, N) grains, fine grain strengthening and solid solution strengthening are achieved, and the high-entropy alloy Ti (C, N)-based metal ceramic material has good bending strength, fracture toughness, high hardness and high density and can be used for high-speed cutting, finish machining, semi-finish machining and the like under complex conditions.

The invention relates to a high-temperature alloy-Ti (C, N) composite metal ceramic material and a preparation method thereof, and belongs to the technical field of metallurgy. The preparation method comprises the following steps that S1, high-temperature alloy powder and Ti (C, N) ceramic powder are subjected to dry grinding, ultrasonic dispersion, wet grinding and drying, and metal ceramic powder is obtained; and S2, the metal ceramic powder is subjected to two-way pressing, vacuum sintering and cooling, and the high-temperature alloy-Ti (C, N) composite metal ceramic material is obtained. The high-temperature alloy-Ti (C, N) composite metal ceramic material prepared by the method has excellent high hardness, obdurability and high-temperature resistance, has outstanding room-temperature and high-temperature mechanical properties, and can meet the strict requirements of extreme working conditions and high-speed cutting on the comprehensive properties of the material.

The invention relates to the technical field of chute lining plates, and discloses a high-wear-resistance chute lining plate and a preparation method thereof.The high-wear-resistance chute lining plate comprises a chute lining plate body, and the chute lining plate body comprises a ceramic layer and a buffer layer; in the ceramic layer, a matrix is prepared from 35wt% of alpha-Al2O3, and a toughening phase is prepared from 7wt% of zirconium oxide whiskers and 4wt% of TiCN nanoparticles; the buffer layer is hydrogenated butadiene-acrylonitrile rubber, and the acrylonitrile content is 34%. According to the preparation method disclosed by the invention, through a three-stage technical route of component gradient design, gel precision forming and interface reaction regulation and control, strengthening and toughening, high-temperature performance optimization and multi-scale enhancement of the alumina-based ceramic are realized: macro-scale (zirconia whisker) + mesoscale (TiCN nanoparticles) + micro-scale (NiCr metal phase) cross-scale synergy is realized; and in-situ reaction: vacuum sintering at 1850 DEG C is utilized to trigger TiCN / NiCr interface reaction, a TiC-NiCr metal ceramic transition layer is generated, and the mechanism compressive strength is improved through a metal ceramic composite material, so that the chute lining plate has better impact resistance and wear resistance effects.

This invention provides a multi-metal co-doped WC-Co coating and its preparation method, belonging to the field of metal-ceramic coating technology. The preparation method includes: weighing tungsten, yttrium, cerium, chromium, and vanadium sources, mixing and dissolving them in deionized water, adjusting the pH to 3-4, and obtaining a precursor through co-precipitation, washing, and drying; subjecting the precursor to sequential aerobic calcination, hydrogen reduction, and carbonization treatments to generate a WC phase, resulting in a rare-earth-transition multi-metal co-doped WC-based composite material; using the WC-based composite material, cobalt powder, and additives as raw materials, spraying the raw materials onto the substrate surface via thermal spraying to form a multi-metal co-doped WC-Co coating. The WC-Co coating prepared by this invention incorporates four elements—yttrium, cerium, chromium, and vanadium—forming a multiple synergistic mechanism of grain refinement, interface strengthening, and decarburization inhibition, effectively improving the hardness, wear resistance, corrosion resistance, and toughness of the WC-Co coating.

This invention relates to the field of heat exchange materials technology, and discloses a high-temperature, high-pressure nano-conductivity heat exchange material. The heat exchange material comprises a metal matrix, a linearly distributed metal-ceramic gradient transition layer, and a nano-composite ceramic surface layer. The surface layer consists of 90-95 parts of nano-alumina and zirconium oxide composite powder and 5-10 parts of cubic phase nano-titanium nitride powder. The former is fused and stacked to form a continuous ceramic matrix, while the latter is monodispersed and anchored within it, with adjacent particles in contact. The heat exchange material is prepared by gradient layer spraying with a linearly decreasing plasma current as the ceramic composition increases, followed by back-side cooling of the matrix. The surface layer is sprayed using a coaxial air knife in a reducing atmosphere combined with a low-enthalpy jet to inhibit oxidation and vacuum diffusion annealing. This invention synergistically regulates the above-mentioned structure and interface state to achieve a balance between high thermal conductivity, excellent corrosion resistance, and high bonding strength, which helps extend the service life of heat exchange components under high-temperature and high-pressure environments.

This invention belongs to the field of fuel cell technology, specifically relating to a metal-ceramic material for bipolar plates in proton exchange membrane fuel cells and its preparation method. The metal-ceramic material is a Ta-doped modified niobium-aluminum-carbon material, and the chemical formula of the modified niobium-aluminum-carbon is (Nb... 1‑ x Ta x 2AlC. The modified niobium aluminum carbon material prepared by this invention possesses the excellent properties of both metals and ceramics. This ceramic material exhibits excellent electrical and thermal conductivity at room temperature, a high elastic modulus, and a certain degree of ductility at room temperature, allowing it to be machined like metals and graphite. Simultaneously, it possesses the characteristics of ceramic materials, exhibiting high yield strength, high melting point, high thermal stability, and excellent corrosion resistance. Furthermore, the solid solution doping of Ta at the Nb position of the niobium aluminum carbon material significantly improves the corrosion resistance of the niobium aluminum carbon bulk, enabling it to operate stably in the PFMFC working environment.

A cermet sintered body according to the present disclosure comprises: a first hard phase mainly composed of TiCN; a second hard phase that is a composite carbonitride solid solution of Ti and at least one of the metals of Groups 4, 5, and 6 of the periodic table; and a binder phase containing W and at least one of Co and Ni. The average particle size of the second hard phase in an internal region and the average particle size of the second hard phase in a surface region are each 0.35-0.6 μm. The strength σ1 in the surface region and the strength σ2 in the internal region are each 2300 MPa or more, and the strength ratio of σ1 to σ2 is 0.8 or more.