What is fiber reinforced metal matrix composites

6.1 Types and basic properties of metal matrix composites

6.1.1 Types of metal matrix composites

1. According to the basic classification

(1) Aluminum matrix composites: good plasticity and toughness, ease of machinability, engineering reliability, and inexpensive, etc.

(2) Nickel matrix composites: Excellent high-temperature performance, is expected to become a combustion turbine blade

(3) titanium matrix composites: high specific strength, medium-temperature strength is better than aluminum-based, supersonic fighter with titanium alloys to do the skin, the main boron fibers with the combination of enhancement

(4) magnesium-based composites: lighter than the aluminum-based, set of ultra-light, high strength, high stiffness, is the preferred material for aerospace materials (dmg =1.74, dAl=2.7)

There are also zinc-based, copper-based, heat-resistant metal-based, intermetallic compound-based composites

2. Classification according to the reinforcing material

(1) Particle-reinforced composites: the reinforcing phase of the more than 20% of the type of dispersion reinforcement, and the strength of its dependence on the diameter of the particles, the pitch and the volume of the ratio

(2) Laminated Composites: Compared to fiber-reinforced composites, it is reinforced in all aspects of the plane (two-dimensional reinforcement, not one-dimensional reinforcement)

(3) Fiber-reinforced composites: There are three types of fibers: long, short and whisker fibers, and the long fibers can also be present in the form of one-dimensional fibers, two-dimensional cloths, and three-dimensional webs. Long fibers must be oriented in the basic regular presence, while short fibers and whiskers are random arbitrary non-directional presence.

6.1.2 Properties of Reinforcements in Metal Matrix Composites

Reinforcements in metal matrix composites are mainly inorganic and metal. Inorganic fibers are C fiber, B fiber, SiC, Al2O3, Si3N4 fiber and so on. Metal fibers are mainly beryllium, steel, stainless steel and tungsten fibers. Reinforcement particles are mainly inorganic non-metallic particles, including graphite, SiC, Al2O3, Si3N4, TiC, B3C3 and so on. Mainly about fiber reinforcement.

Basic requirements of fiber reinforcement:

A high strength,

B high modulus,

C easy to manufacture and inexpensive,

D good chemical stability,

E size and shape of fibers: large-diameter round fibers are good,

F reproducibility and consistency of the performance,

G damage or abrasion resistance,

G resistance to Damage or wear resistance

6.1.3 Strength of metal matrix composites

The longitudinal and transverse strengths of fiber reinforced metal matrix composites are different.

1. Longitudinal Strength (Figure 6-1, P127)

Critical Fiber Volume Ratio VF*

When a weak fiber breaks, three important changes are induced.1) The strength in the cross-section is reduced at that location due to the loss of strength in the broken fibers.2) The concentration of static stresses around the cracks in the broken fibers reduces the effective strength of the material.3) Loss of load in the broken fibers The dynamic stress wave generated when the broken fiber loses load can shock the composite material, which reduces the instantaneous load carrying capacity on the cross-section there.

2. Transverse Strength

The transverse modulus of a composite material increases with the amount of reinforcement, but the change in strength is complex. Because the material always breaks locally, this is not a measure of the average strength, but overall it is basically severely bound by the fibers, and its fracture strength is supposed to be greater than that of the pure matrix material.

6.1.4 Compatibility of composite components

Including physical compatibility and chemical compatibility, physical compatibility and pressure changes, thermal changes in the material's expansion and contraction properties are related to the compatibility of the requirements is the external load can be transmitted to the reinforcement through the basic uniformity of the matrix stress will not be reinforced localized over-concentration of the body of chemical compatibility and the interfacial bonding, interfacial chemical reaction and the chemical reaction of the environment.

6.2 metal matrix composites manufacturing process

Although the composite material process is a lot, roughly: powder metallurgy, hot pressing, hot isostatic pressing, extrusion casting, *** spray deposition method, liquid metal infiltration, liquid metal stirring method, reaction autogenous method and so on, most of these methods are still under continuous development, but the basic manufacturing method can be summarized as follows Several categories: solid state method, liquid method and self-generated method and other preparation methods.

6.2.1 Solid State Method

Substrate and reinforcement are solid. Powder metallurgy method, hot pressing method and hot isostatic pressing method are included in this category.

6.2.2 Liquid metal method

Method of composite with reinforcement when matrix is in liquid state

6.2.3 Self-generated and other methods

Method of generating reinforcement by reaction within the matrix

Other methods: e.g., composite coating (plating) method, the reinforcement of fine particles suspended in the plating solution to form a composite layer by electroplating or chemical plating. Layer.

6.3 Aluminum Matrix Composites

6.3.1 Particles (whiskers) reinforced aluminum matrix composites

Reinforcement whiskers: SiC, Al2O3, SiO2, BC4, TiC

Performance: excellent performance, low price of reinforcing particles, the application of a wide range of prospects, such as SiC reinforcers: good mechanical properties and wear resistance, tensile strength and elastic modulus. The tensile strength and modulus of elasticity are higher than the matrix, and the smaller the particle size, the larger the particle content, the higher the strength. The same is true for abrasion resistance.

6.3.2 Fiber reinforced aluminum matrix composites

Reinforcing fibers are mainly B,C, SiC, Al2O3

1) BF/Al: boron fiber reinforced material is the earliest research and application of the high temperature performance is particularly outstanding, the tensile strength of the 500 at 500 MPa, which is unimaginable in aluminum alloy materials. Boron fiber specific gravity: 2.5-2.65. Boron in the tungsten wire on the chemical vapor deposition to get the fiber, the surface should also be added ceramic coating to increase its antioxidant properties.

Manufacturing process: fiber arrangement, composite assembly pressing and parts lamination. The volatile binder is used to stick the dimensions together and hot press them together with aluminum foil.

2) C/Al composites: carbon fiber has excellent mechanical properties at a lower price. Carbon fiber surface treatment is critical,

3) SiCF/Al composites: special high-temperature oxidation resistance, can be composite with aluminum at higher temperatures. Product properties. There are high tensile strength flexural strength and excellent wear resistance

4) Short fiber reinforced aluminum matrix composites

Features: wide source of reinforcement, low price, good formability, isotropic material properties, can be used in traditional processes molding and processing. Aluminum matrix alloy reinforced with alumina and aluminum silicate its high-temperature strength is significantly higher than the matrix, the modulus of elasticity at room temperature and high temperature have a greater increase in the coefficient of thermal expansion is small, and wear resistance is improved.

6.3.3 Aluminum matrix composites applications

Good performance, but expensive, so mainly used as the space shuttle, artificial satellites, space stations and other structural materials, followed by missile components, bicycle frames, golf clubs and other sporting goods. Its civil prospects with the reduction of the cost will be very extensive.

6.4 Nickel matrix composites (TMCS)

The composites are expected to be used in the blades of gas turbine engines to withstand high temperatures and loads.

Simple nickel or nickel-chromium alloys reinforced with single-crystal alumina (sapphire) whiskers and rods are the main types of research.

Sapphire and nickel react chemically at high temperatures, so a surface treatment, usually tungsten coating, is applied to the surface.

The manufacturing method is mainly hot pressing of fibers sandwiched between metal plates. For example, Al2O3-NiCr composites have been successfully fabricated by hot pressing. The process is first coated with Y2O3 on the rod, and then coated with a layer of tungsten, and then the rod sandwiched between the metal plate vacuum at 1200 ℃ and pressurized 41.4MPa.

6.5 Titanium Matrix Composites (TMCS)

1) Titanium metal is resistant to high temperatures, corrosion, and low specific gravity (4.5g/cm3), it is the first choice of high-performance structural materials

There are two main types of particles Reinforced and continuous fiber reinforced two categories.

Silicon carbide particles, such as the enhancement of its hardness and stiffness, room temperature strength than the matrix is sometimes reduced, but the high-temperature strength is better than the matrix.

Continuous fiber composite titanium alloy is very difficult, can only use solid phase composite, because titanium is easy to react with the fiber at high temperature. Boron titanium composites are the main object of research. reduction effects.

2) Application: mainly used in aerospace with ultra-high-speed engines for the purpose, but now also used in civilian use, used as automotive materials and sports equipment.

6.6 Carbon fiber reinforced metal matrix composites

1) carbon fiber and many metals lack of compatibility, the current compatibility is better with aluminum, magnesium, nickel and cobalt, etc., and titanium and other metal composite will be formed carbide, so the need for surface treatment.

2) carbon fiber and some materials will have special properties, such as copper, aluminum and lead composite with high strength, electrical conductivity, low friction, low expansion (dimensional stability), etc.

3) and carbon composite metal in addition to aluminum is the main, there are also copper, magnesium, lead, zinc, tin, beryllium and so on.

4)Cf/Al:It is critical to reinforce the fibers with the wettability of aluminum. So that it can be well combined in hot pressing. Coating metallic or non-metallic layers is the desired modification.

5) Cf/Ni:Electrodeposition hot pressing is the main method. However, higher strength is obtained at low pressure due to high pressure damages the fibers.