Refractory Hard Metals With a closer look at Tungsten What are Refractory Hard Metals ? Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group differs. The most common definition includes five elements: niobium, molybdenum, tantalum, tungsten, and rhenium). They all share some properties, including a melting point above 2000 °C and high hardness at room temperature. They are chemically inert and have a relatively high density. Their high melting points make powder metallurgy the method of choice for fabricating components from these metals. Some of their applications include tools to work metals at high temperatures, wire filaments, casting molds, and chemical reaction vessels in corrosive environments. Partly due to the high melting point, refractory metals are stable against creep deformation to very high temperatures. The wider definition, including all elements with a melting point above 3,362 F(1,850 °C), includes a varying number of nine additional elements: titanium, vanadium, chromium, zirconium, hafnium, ruthenium, rhodium, osmium and iridium. Carbides A carbide is a compound composed of carbon and a less electronegative element. . Examples include calcium carbide (CaC2), silicon carbide (SiC), tungsten carbide (WC) (often called simply carbide when referring to machine tooling Nitrides a nitride is a compound of nitrogen where nitrogen has a formal oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications.[ Like carbides, nitrides are often refractory materials owing to their high lattice energy which reflects the strong attraction of "N3−" for the metal cation. Thus, titanium nitride and silicon nitride are used as cutting materials and hard coatings. Borides A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. The borides can be classified loosely as boron rich or metal rich. The transition metals tend to form metal rich borides. Metal-rich borides, as a group, are inert and have high melting temperature. Silicides A silicide is a compound that has silicon with (usually) more electropositive elements. Silicides are structurally closer to borides than to carbides. Carbides Nitrides Borides Silicides Metal Carbides Nitrides Borides Silicides Ti TiC TiN Ti2B Ti2B5 Ti5Si3 TiB TiSi TiB2 TiSi2 Zr ZrC ZrN ZrB Zr4Si Zr6Si5 ZrB2 Zr2Si ZrSi ZrB12 Zr3Si2 ZrSi3 Zr4Si3 Carbides Nitrides Borides Silicides Hf HfC HfN HfB HfB2 V VC V2N VB VN VB2 Nb NbC Nb2N Nb3B Nb3B4 Nb2Si NbN Nb2B NbB2 NbSi2 NbB Ta Ta2C Ta2N Ta3B Ta3B4 Ta5Si Ta5Si3 TaC Ta2B TaB2 Ta5Si2 TaSi2 TaB Carbides Nitrides Borides Silicides Cr Cr23C6 Cr2N Cr2B Cr3B4 Cr3Si CrSi2 Cr3C2 CrN Cr3B2 CrB2 Cr2Si Cr7C3 CrB CrSi Mo Mo2C Mo2N Mo2B MoB2 Mo3Si MoC MoN Mo3B2 Mo2B5 Mo3Si2 MoB MoSi2 W W2C W2N W2B W2B5 Mo3Si2 WC WB WSi2 History History 1897 French chemist Moissan published first studies of refractory carbides. Made able by the electric arc furnace he developed. Refractory metals were of little practical interest until the advent of electricity. First interest was to replace diamond dies for drawing tungsten filaments Development of Tool Material Before 1894 Carbon steel Before 1900 Self-hardening steel 1900 First high-speed steel 1906-1913 New high-speed steels 1909 First Stellites 1914 Cast Tungsten Carbide (Cr,Mo,Ta,Co,Fe,C,W) 1917-1923 Tizit Alloys (Cr,Fe,Ti,C,W) 1922 Sintered WC-Co alloys Wida first commercial 1926 1929 Sintered Mo2C-TiC-Ni alloys 1930 Sintered TaC-Ni-Co alloys 1931 Sintered WC-TaC-Co alloys 1931 Sintered WC-TiC-Co alloys 1932 Sintered WC-TaC-TiC-Co alloys Physical Properties Metal Specific Gravity Melting Point Boiling Point Tungsten (W) 19.3 6170 10,700 Rhenium (Rh) 21.02 5767 10,170 Osmium (Os) 22.59 5491 9054 Tantalum (Ta) 16.69 5463 9856 Molybdenum (Mo) 10.28 4753 8382 Niobium (Nb) 8.57 4491 8571 Iridium (Ir) 22.56 4435 7466 Ruthenium (Ru) 12.45 4233 7502 Hafnium (Ha) 13.31 4051 8317 Rhodium (Ro) 12.41 3567 6683 Vanadium (V) 6 3470 6165 Chromium (Cr) 7.19 3465 4840 Zirconium (Zr) 6.52 3371 7911 Titanium (Ti) 4.506 3034 5949 Niobium (Nb) Niobium, formerly columbium, is a chemical element with symbol Nb(formerly Cb) and atomic number 41. It is a soft, grey, ductile metal, often found in the minerals pyrochlore and columbite. Its name comes from Greek mythology, specifically Niobe, who was the daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, making them difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801 and named it columbium. Niobium was officially adopted as the name of the element in 1949, but the name columbium remains in current use in metallurgy in the United States. It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron which has a niobium content of 60-70%. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although these alloys contain a maximum of 0.1%, the small percentage of niobium enhances the strength of the steel. The temperature stability of niobium-containing super alloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials. These superconducting alloys, also containing titanium and tin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include welding, nuclear industries, electronics, optics, numismatics, and jewelry. In the last two applications, the low toxicity and iridescence produced by anodization are highly desired properties. Molybdenum Mo Molybdenum minerals have been known throughout history, but the element was discovered (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm. Molybdenum does not occur naturally as a free metal on Earth; it is found only in various oxidation states in minerals. The free element, a silvery metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of world production of the element (about 80%) is used in steel alloys, including high- strength alloys and super alloys. Most molybdenum compounds have low solubility in water, but when molybdenum- bearing minerals contact oxygen and water, the resulting molybdate ion MoO2−4 is quite soluble. Industrially, molybdenum compounds(about 14% of world production of the element) are used in high-pressure and high-temperature applications as pigments and catalysts. Molybdenum-bearing enzymes are by far the most common bacterial catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation. Iridium Ir Iridium Ir a very hard, brittle, silvery-white metal of the platinum group. Iridium is the second densest element. It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. ,finely divided iridium dust is much more reactive and can be flammable. Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium for the Greek goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Iridium is one of the rarest elements in Earth's crust, with annual production and consumption of only three tons. The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in industrial catalysis, and in research. Iridium metal is employed when high corrosion resistance at high temperatures is needed, as in high- performance spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkaline process. Iridium radioisotopes are used in some radioisotope thermoelectric generators. Iridium is found in meteorites in much higher abundance than in the Earth's crust It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum-group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten. Osmium Os Osmium Os is a hard, brittle, bluish-white metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element, with a density of 22.59 g/cm3. Its alloys with platinum, iridium, and other platinum-group metals are employed in fountain pen nib tipping, electrical contacts, and other applications where extreme durability and hardness are needed. Rhodium Rh Rhodium Rh It is a rare, silvery-white, hard, corrosion resistant and chemically inert metal. It is a noble metal and a member of the platinum group. Naturally occurring rhodium is usually found as the free metal, alloyed with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals. Rhodium is found in platinum or nickel ores together with the other members of the platinum group metals.