Molybdeno-Aluminizing of Powder Metallurgy and Wrought Ti and Ti-6Al-4Valloys by Pack Cementation process Articles uri icon

publication date

  • August 2016

start page

  • 494

end page

  • 504

volume

  • 118

International Standard Serial Number (ISSN)

  • 1044-5803

Electronic International Standard Serial Number (EISSN)

  • 1873-4189

abstract

  • Wear and high temperature oxidation resistance of some titanium-based alloys needs to be enhanced, and this can beeffectively accomplished by surface treatment. Molybdenizing is a surface treatment where molybdenum is introducedinto the surface of titanium alloys causing the formation of wear-resistant surface layers containing molybdenum, whilealuminizing of titanium-based alloys has been reported to improve their high temperature oxidation properties. Whereaspack cementation and other surface modification methods have been used for molybdenizing or aluminizing of wroughtand/or cast pure titanium and titanium alloys, such surface treatments have not been reported on titanium alloys producedby powder metallurgy (PM). Also a critical understanding of the process parameters for simultaneous one stepmolybdeno-aluminizing of titanium alloys by pack cementation and the predominant mechanism for this process havenot been reported. The current research work describes the surface modification of titanium and Ti-6Al-4V prepared byPM by molybdeno-aluminizing and analyzes thermodynamic aspects of the deposition process. Similar coatings are alsodeposited to wrought Ti-6Al-4V and compared. Characterization of the coatings was carried out using scanning electronmicroscopy and x-ray diffraction. For both titanium and Ti-6Al-4V, the use of a powder pack containing ammoniumchloride as activator leads to the deposition of molybdenum and aluminium into the surface but also introduces nitrogencausing the formation of a thin titanium nitride layer. In addition, various titanium aluminides and mixed titanium aluminiumnitrides are formed. The appropriate conditions for molybdeno-aluminizing as well as the phases expected to beformed were successfully determined by thermodynamic equilibrium calculations.

keywords

  • ti-6al-4v; molybdenizing; powder metallurgy; thermodynamic calculations; pack cementation; nickel-base superalloys; cyclic oxidation behavior; titanium-alloys; corrosion-resistance; mechanical-behavior; wear-resistance; coatings; al; surface