Carbide mechanical properties

Properties of Dense Silicon Carbide. Properties of the SiC stmctural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for appHcations at temperatures over 1400°C and the Hquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

The physical and mechanical properties of steel depend on its microstmcture, that is, the nature, distribution, and amounts of its metaHographic constituents as distinct from its chemical composition. The amount and distribution of iron and iron carbide determine most of the properties, although most plain carbon steels also contain manganese, siUcon, phosphoms, sulfur, oxygen, and traces of nitrogen, hydrogen, and other chemical elements such as aluminum and copper. These elements may modify, to a certain extent, the main effects of iron and iron carbide, but the influence of iron carbide always predominates. This is tme even of medium alloy steels, which may contain considerable amounts of nickel, chromium, and molybdenum. 

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

Sintered sihcon carbide retains its strength at elevated temperatures and shows excellent time-dependent properties such as creep and slow crack growth resistance. Reaction-bonded SiC, because of the presence of free sihcon in its microstmcture, exhibits slightly inferior elevated temperature properties as compared to sintered sihcon carbide. Table 2 (11,43) and Table 3 (44) show selected mechanical properties of sihcon carbide at room and elevated temperatures. 

To imrove mechanical properties, increased axial molecular orientation was required. Union Carbide workers under government contract worked on... 

Mechanical properties depend on the alloying elements. Addition of carbon to the cobalt base metal is the most effective. The carbon forms various carbide phases with the cobalt and the other alloying elements (see Carbides). The presence of carbide particles is controlled in part by such alloying elements such as chromium, nickel, titanium, manganese, tungsten, and molybdenum that are added during melting. The distribution of the carbide particles is controlled by heat treatment of the solidified alloy. 

Stacking faults thereby providing barriers to sHp. If carbides are allowed to precipitate to the point of becoming continuous along the grain boundaries, they often initiate fracture (see Fracture mechanics). A thorough discussion of the mechanical properties of cobalt alloys is given in References 29 and 30 (see also Refractories). 

The above measurements all rely on force and displacement data to evaluate adhesion and mechanical properties. As mentioned in the introduction, a very useful piece of information to have about a nanoscale contact would be its area (or radius). Since the scale of the contacts is below the optical limit, the techniques available are somewhat limited. Electrical resistance has been used in early contact studies on clean metal surfaces [62], but is limited to conducting interfaces. Recently, Enachescu et al. [63] used conductance measurements to examine adhesion in an ideally hard contact (diamond vs. tungsten carbide). In the limit of contact size below the electronic mean free path, but above that of quantized conductance, the contact area scales linearly with contact conductance. They used these measurements to demonstrate that friction was proportional to contact area, and the area vs. load data were best-fit to a DMT model. 

Note The principal reinforcement, with respect to quantity, is glass fibers, but many other types are used (cotton, rayon, polyester/TP, nylon, aluminum, etc.). Of very limited use because of their cost and processing difficulty are whishers (single crystals of alumina, silicon carbide, copper, or others), which have superior mechanical properties. 

Ti02 particles, the benzene-thermal reaction of TiCLi. and NaN3, chemical vapor reactions, plasma syntheses, or arc-melting [15-20], The optical properties of low-concentrated TiN nanoparticle systems were studied by Quinten [21], Highly dispersed TiN was used as an additive to improve the mechanical properties of titanium carbide-based cermets [22],... 

Catalysts may be metals, oxides, zeolites, sulfides, carbides, organometallic complexes, enzymes, etc. The principal properties of a catalyst are its activity, selectivity, and stability. Chemical promoters may be added to optimize the quality of a catalyst, while structural promoters improve the mechanical properties and stabilize the particles against sintering. As a result, catalysts may be quite complex. Moreover, the state of the catalytic surface often depends on the conditions under which it is used. Spectroscopy, microscopy, diffraction and reaction techniques offer tools to investigate what the active catalyst looks like. 

Suitable mechanical carbon as recommended by vendor for the service conditions Carbon with an appropriate filler material (usually metal) to enhance its mechanical properties ASTM D1418 FKM elastomer, such as DuPont Viton Union Carbide Grafoil (or the equivalent)... 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

As noted earlier, CVl is nsed primarily to form ceramic-fiber-reinforced ceramic matrix composites. The most common of these combinations is SiC fiber/SiC matrix composites. One commercially available product has a two-dimensional 0/90 layup of plain weave fabric and fiber volume fraction of about 40%. This same composite can be fabricated with unidirectional fibers and with 45° architectures. The most commonly used SiC fiber for the preforms is Nicalon , the mechanical properties for which were provided earlier in Section 5.4.2.7. A number of other carbide and nitride fibers are also available, including Si3N4, BN, and TiC. Preform geometries can be tailored to the application in order to maximize strength and toughness in the direction of maximnm stresses. The reactions used to form the matrix are similar to those used in CVD processes (cf. Section 7.2.4) and those described previously in Eq. (3.105). 

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