tailieunhanh - Handbook Properties and Selection Nonferrous Alloys and Spl Purpose Mtls (1992) WW Part 12

Tham khảo tài liệu 'handbook properties and selection nonferrous alloys and spl purpose mtls (1992) ww part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Molybdenum Boride Cermets. The molybdenum borides MoB and Mo2B have less thermal stability than the previously discussed metal borides but their electrical properties hardness and wear resistance are very good. When cemented with nickel these cermets have excellent corrosion resistance for example to dilute sulfuric acid Ref 79 . Nickel-bonded molybdenum boride exhibits interesting behavior in two areas First if the composition corresponds to the compound molybdenum-nickel boride Mo2NiB2 if the cermet contains Mo2B in addition to Mo2NiB2 or if a low-melting intermetallic binder containing chromium boride and nickel is used cutting tool materials can be produced from the composition that are comparable to commercial WC tool tips for machining brass aluminum and cast iron Ref 90 91 . Second the Mo2NiB2-type composition has thermal expansion characteristics that closely match those of the refractory metals and a favorable melting temperature these properties make it ideal for use as a high-temperature braze for molybdenum and tungsten without risk of excessive grain growth or embrittlement of the primary metal structure Ref 79 92 . When used in rod form with shielded arc welding equipment this cermet is suitable for brazing electronic components in applications such as vacuum tubes and magnetrons. Recently a molybdenum boride cemented with an iron-base binder phase alloyed with nickel and chromium has shown promise as a cutting tool material Ref 93 . This cermet exhibits good mechanical properties coupled with excellent wear and corrosion resistance. In specific tool applications such as extrusion dies for hot copper and tools for can making this boride cermet has performed better than cemented carbides. The role of nickel in the Mo2FeB2 cermet and the effect of varying its content up to 10 wt in the composition have also been investigated mainly as part of a study of the corrosion resistance potential of the material Ref 94 . The nickel enters only into

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