What are the powder metallurgy mold materials

Powder metallurgy die materials can be roughly divided into two kinds of materials: strengthening materials and typical materials. The following are material characteristics and material applications.

First: strengthening materials

1, metal or alloy matrix phase and highly dispersed, basically insoluble matrix metal or non-metallic phase composed of powder metallurgy.

2, modern powder metallurgy technology gold materials. Its main characteristics are high temperature strength and good creep resistance. The strengthening mechanism is similar to precipitation strengthening. However, when the precipitation hardening alloy is heated higher than the formation temperature of the precipitation phase, the precipitation phase will coarsene and redissolve, so the use temperature is limited. In the case of dispersion-strengthened alloy, the dispersive phase can be stabilized to the solid phase line temperature of the matrix. The existence of dispersion particle changes the yield strength, work hardening, creep and fracture behavior of the alloy.

3. The high temperature strength, especially the creep rate, is affected by the geometrical parameters of the dispersion phase (i.e. the spacing between particles in the matrix, particle diameter, shape (aspect ratio)). The mechanism is affected by both dislocation bypassing the second phase and grain boundary slip, and there is no universally accepted creep model. The general principles of dispersion phase selection are: high free energy of formation, high melting point, inmiscible with matrix, low interphase energy (i.e. good interfacial bonding), etc. The dispersion phase is usually an oxide, but can also be a stable intermetallic compound, or even a pure metal.

Second: typical materials

Manufactured by surface oxidation. SAP has very high temperature strength and creep resistance, the use of temperature up to 500℃, far better than the general aluminum alloy. It is mainly used for nuclear fuel envelope in reactor, aircraft wing and fuselage, compressor impeller, high temperature piston and so on.

1. Copper

Dispersion particle is generally Al2O3, commonly used in internal oxidation process. After dispersion strengthening, the strength and hardness of copper are greatly improved, and the conductivity is not much reduced. It is commonly used as electrodes for resistance welding, incandescent filament leads, vacuum tube parts and other materials in the electronics industry.

The main manufacturing method of dispersion reinforced materials is powder metallurgy, and its representative methods are classified.

2. High temperature alloy

The earliest dispersion strengthened nickel base alloy is ThO2 (2%) strengthened nickel (TD-Ni). It is generally obtained by coprecipitation. It's made by wet process.

The structural parts of powder metallurgy are Ni-Mo, Ni-Co, Ni-Cr-Al and other alloys strengthened by Th02. After the advent of mechanical alloying, a series of nickel -, iron - and cobalt-based alloys were developed. More than 10 kinds have been used. The dispersion phases are generally ThO2 and Y203. Several typical alloys are listed in the table. MA754 has superior properties to ThO2-Ni-Cr and has been used successfully as a jet engine blade. MA956E is a Fe-Cr-Al based material with superior oxidation resistance and corrosion resistance. For MA6000E alloy, the 1000h fracture stress at 800OC is much better than that at TD-Ni and IN792.1100℃. The 1000h fracture stress of TD-Ni and IN792 is only 20~30MPa, while the MA6000E has 160MPa. Therefore, MA6000E is a good leaf material.

3. Others

For example, dispersion strengthened lead (DS-Pb), the only example similar to SAP, has a dispersion phase of PbO, which is used for sound attenuation, chemical appliances, radiation shielding, and batteries; Magnesium alloys containing aluminum and zirconium (aluminum and zirconium are dissolved in magnesium, but A1Zr4 dispersion phase precipitates after dissolution); Al-Fe alloys strengthened by intermetallic compounds FeAl3 and FeNiAl9.

Third: material application

Brake pads, clutch friction sheets, loose hole filters, porous sweat materials, oil bearing, magnet core, electrical contacts, high specific gravity alloy, hard alloy and super hard wear-resistant parts because of a large number of non-metallic components or contain connected pores, can not be made with ordinary casting, forging process, can only be made with powder as raw materials by cold pressing, sintering and other powder metallurgy process. The powder metallurgy materials used in the aerospace industry are more important brake pad materials, porous materials and high strength powder alloy three categories.

1. Brake pads

Brake pad is the core of aircraft wheel brake device. Modern aircraft landing speed up to 200 km/h above, brake load is very large, brake pad surface instantaneous temperature up to 800~1000°C, and is not allowed to bond, so as not to brake failure cause tire burst. Powder metallurgy brake pads (see figure) made of iron powder or copper powder as the main component and non-metallic powder to prevent friction and bonding can meet this requirement. Most military and civilian aircraft use powder metallurgy brake pads. Because every brake will wear, 100~500 times after the need to replace the brake pad, so it is the largest amount of powder metallurgy materials on the aircraft.

2. Loose hole

Namely porous permeable powder metallurgy materials. Bronze or stainless steel filters used in turbine engine lubrication systems and aircraft hydraulic control systems are important components to prevent particle blockage and sticking. The metal fiber porous material has good strength and plasticity, and can be used in high temperature parts, such as the superalloy felt belt for the tip sealing ring of turbojet engine and the sweat cooling porous material for the panel of rocket engine injector, the inner wall of combustion chamber and the throat.

3. Alloy

Fully dense superalloys, aluminum alloys and titanium alloys formed by powder heat. Forged powder superalloy turbodisks and compressor disks have been used in some modern aircraft engines. In order to save raw materials and eliminate forging process of structural parts of powder metallurgy, hot isostatic pressing precision forming can be done directly. The strength of dispersion-strengthened superalloys and rapidly solidified powder superalloys manufactured by mechanical alloying can exceed that of directionally solidified alloys above 1000~1050°C, which is a good material for manufacturing guide blades and turbine blades.

Powder aluminum alloy is mainly used as aircraft and engine structure materials. Mechanical alloyed aluminum alloys and rapidly setting powder aluminum alloys have strengths up to 700 mpa (about 70 kg force/mm). The specific strength can reach the level of titanium alloy and ultra-high strength steel, and the service temperature can reach 250~300°C, expanding the application range of existing aluminum alloys. Compared with the deformed aluminum alloy, the fast solidification aluminum-lithium alloy is 30% higher than the stiffness and twice as high as the strength. If the replacement of aluminum alloy, the weight of the aircraft can be reduced by more than 30%.

There are several types of powder metallurgy materials, according to the application of the industry to choose its material, as well as the shape of the design, size, process requirements, mold material selection and processing method is very important.