Alloying molybdenum

Nair, F. B. and Briggs, J. Z., Corrosion Resistance of Molybdenum and Molybdenum Base Alloys, Molybdenum Metal... 

Type 316 in this alloy, molybdenum is added to improve the corrosion resistance in reducing conditions, such as in dilute sulphuric acid, and, in particular, to solutions containing chlorides. 

This process, originally designated as RSR (rapid solidification rate), was developed by Pratt and Whitney Aircraft Group and first operated in the late 1975 for the production of rapidly solidified nickel-base superalloy powders.[185][186] The major objective of the process is to achieve extremely high cooling rates in the atomized droplets via convective cooling in helium gas jets (dynamic helium quenching effects). Over the past decade, this technique has also been applied to the production of specialty aluminum alloy, steel, copper alloy, beryllium alloy, molybdenum, titanium alloy and sili-cide powders. The reactive metals (molybdenum and titanium) and... 

Alloying molybdenum with titanium (similarly, chromium with vanadium) results in an increased electron density in the metal. At e/a values < 5.1, empty electron states are still available near the Fermi level however, at higher e/a, the solute hydrogen atoms evidently no longer can pull empty states below the Fermi level, and hydrogen solubility is sharply inhibited. 

Practices for preparation of and electroplating on Chromium (Electrodeposits) on Chromium Copper and Copper-Base Alloys Iron Castings Eead and Eead Alloys Magnesium and Magnesium Alloys Molybdenum and Molybdenum Alloys Nickel Alloys... 

Figure 6.14 Polarization curves of Fe-13Cr-x Mo stainless steels in IM HCl, showing the effect of alloyed molybdenum on the passivation current density. T=30 °C, x = 0, 1,2, 3.5, 5% [9],...

Deviations from linearity in high-alloyed molybdenum steels are due to the favourable effect of nitrogen. For these steels, the nitrogen content can be taken into account in the pitting resistance equivalent. For austenitic stainless steels alloyed with at least 3% molybdenum ... 

Molybdenum sho vs a strong tendency to precipitate. High-alloyed molybdenum steels therefore require particular care in production and processing to preserve the full effect of this alloying element. 

Among the alloying elements used to improve the corrosion resistance of passivated alloys, molybdenum plays a central role in stainless steels. Indeed, stainless steels (iron-chromium or iron-chromium-nickel alloys) that contain molybdenum offer much better corrosion resistance (especially against pitting) than those without molybdenum. Despite the enormous amount of research work carried out on the process involved, using surface analytical methods combined with electrochemical measurements, the exact mechanism of the effect of molybdenum is not fully understood, and is still a matter of debate. However, all the data indicate that the improved corrosion resistance brought about by alloyed molybdenum is due to different phenomena, which may be rationalized in the following way ... 

Unlike steels or copper alloys, molybdenum alloys cannot be hardened by heat treatment due to the lack of lattice transformation. For example, SHN-hardening (Figure 5.31), which is specially developed for molybdenum alloys by an Austrian manufacturer, however, allows the setting of a very high surface hardness, which further lowers the wear rate. Although the SHN process takes place at temperatures above 1,000 °C, the ductile base material remains and leads to the formation of a uniform, about 10 pm thick, adherent diffusion layer (Figure 5.32) with a microhardness of up to 2,000 HV 0.001. Ready-to-go components can be hardened without changing the dimensional tolerances. 

Numerous electrochemical and surface analytical studies have been performed to understand the effect of alloyed molybdenum on the corrosion resistance of stainless steels (see, e.g., the section on the role of Mo in Mo-containing austenitic stainless steels in Chapter 7). 

Keywords Intermetallics, Fe-based alloys. Molybdenum, Metallothermic process... 

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