Tungsten heavy metal alloys

The term tungsten heavy metal or heavy metal is used for a group of two-phase composites, based on W-Ni-Fe and W-Ni-Cu. They are characterized by a high density and a novel (unique) combination of strength and ductility. 

Fabrication [6.26,6.27]. Heavy metals are produced by conventional P/M techniques. A flow chart of the fabrication process is shown in Fig. 6.14. Elemental powders (W, 

FIGURE 6.13. Optical micrograph of a 95 wt% tungsten heavy metal alloy with 3.2 wt% Ni and 1.8 wt% Cu. By courtesy of Plansee AG, Reutte, Austria. 

Cu) are blended in mixers or ball mills to the desired ratio, compacted to form a green body, and subsequently liquid-phase sintered. Assuming proper manufacturing conditions, they exhibit full or near-theoretical density in the as-sintered condition. 

Sintering is commonly carried out in molybdenum-wire resistance-heated furnaces under hydrogen or nitrogen mixtures (dissociated ammonia) but can also be performed in vacuum units. The use of wet hydrogen has become industrial practice to suppress hydrogen embrittlement (water vapor porosity) [6.29]. The temperature/time program of the sintering cycle must be adjusted to the composition and size of the sintered parts. A 

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In 1935, the first tungsten heavy metal alloys were produced as a material group of growing importance that would continue for the next four decades. 

Heavy-media separation plants, 25 442 feed solids content in, 25 443-445 Heavy melting steel, 22 409 Heavy-metal additives, in PVC, 25 682 Heavy-metal alloy process, of tungsten recycling, 25 357... 

The element-rich solid solubility alloys are of importance in the so-called heavy metal alloys. The tungsten phase formed during liquid-phase sintering is saturated with iron (and nickel) and, vice versa, the nickel-iron binder phase with tungsten. 

Standard penetrator material [6.29]. Nevertheless, recent environmental considerations have put a strong emphasis on substituting depleted uranium by heavy metals because of its radioactivity. Efforts to improve the ballistic performance through proper processing and compositional modifications have failed [6.29,6.39]. Recent research has therefore focused on alternative matrix alloys, such as tungsten-hafhium, tungsten-uranium composites [6.29], or heavy metal alloys with a spiculating core of WC [6.41]. 

Initially refractory metals were applied mainly in the pure state. Extensive developments mainly driven by US aerospace programs led to a wide variety of alloys now commercially available. The compositions of solid-solution, precipitation- and dispersion-strengthened alloys are given in Table 3.1-108. Tungsten heavy metals and refractory-metal-based composite materials are not included here. 

Research in tungsten heavy alloys was previously boosted by the ballistic application as anti-amor kinetic energy penetrator. Numerous papers have appeared in the last years and reviews have recently been published [6.29,6.39,6.40]. Although the basic requirements are the same for civil as for defense applications (i.e., high density, sn ngth, and elongation), there are two more important factors which must be considered for this specific application the behavior of the material imder high strain rate conditions and their ballistic performance (i.e., their penetration ability). In particular, the latter aspect is of critical importance and, to a certain extent, still a weak point of heavy metals. Their ballistic performance is inferior compared to depleted uranium, which is still used as a... 

In order to facilitate use of this survey, the application of tungsten and of its alloys is divided into 13 different fields. The material used for the application(s) is given in parentheses. (Note HM is used for Heavy Metal). 

Miller, A.C., Mog, S., McKinney, L., et al, 2001. Neoplastic transformation of human osteoblast cells to the tumorigenic phenotype by heavy metal-tungsten alloy particles induction of genotoxic effects. Carcinogenesis 22,115-125. 

It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Stellite alloys, containing cobalt, chromium, and tungsten, are used for high-speed, heavy-duty, high temperature cutting tools, and for dies. 

Fused Salt Electrolysis. Only light RE metals (La to Nd) can be produced by molten salt electrolysis because these have a relatively low melting point compared to those of medium and heavy RE metals. Deposition of an alloy with another metal, Zn for example, is an alternative. The feed is a mixture of anhydrous RE chlorides and fluorides. The materials from which the electrolysis cell is constmcted are of great importance because of the high reactivity of the rare-earth metals. Molybdenum, tungsten, tantalum, or alternatively iron with ceramic or graphite linings are used as cmcible materials. Carbon is frequently used as an anode material. 

Alloying the nickel of the anode to improve tolerance for fuel contaminants has been explored. Gold and copper alloying decreases the catalytic activity for carbon deposition, while dispersing the anode with a heavy transition metal catalyst like tungsten improves sulfur resistance. Furthermore, ceria cermets seem to have a higher sulfur tolerance than Ni-YSZ cermets [75],... 

Armor-piercing (AP) ammunition has a projectile or projectile core constructed entirely from a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium. The most effective AP bullets are usually confined to rifle bullets, as velocity and range are important factors in AP requirements. Some revolver and pistol ammunition is described as metal piercing but, although it would be effective against vehicle bodywork and some body armor, it would be ineffective against heavy armor plate. AP bullets are, with very few exceptions, jacketed. 

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