In situ nitrided titanium alloys: Microstructural evolution during solidification and wear. (15th January 2015)

• Record Type: Journal Article
• Authors: Mohseni, H.; Nandwana, P.; Tsoi, A.; Banerjee, R.; Scharf, T.W.
• Is Part Of: Acta materialia. Volume 83(2015)
• Page Start: 61
• Page End: 74
• Publication Date: 2015-01-15
• Subjects: Titanium alloys -- Nitriding -- Wear -- Transmission electron microscopy (TEM) -- Precession electron diffraction (PED); Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2014.09.026
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Surface and subsurface structural evolution during sliding wear of two in situ nitrided titanium alloys, β Ti–35Nb–7Zr–5Ta (TNZT) and α/β Ti–6Al–4V (Ti64), was studied by cross-sectional transmission electron microscopy coupled with precession electron diffraction. In situ nitriding during the laser engineered net shaping (LENS™) process resulted in the formation of hard and wear-resistant Ti2 N + TiN phases and nitrogen-enriched α phase in TNZT and Ti64, respectively. Subsurface structural analyses of the worn nitrided TNZT revealed the tendency of α grains, and to greater extent β grains, to undergo severe plastic deformation, forming a heavily grain-refined nanocrystalline α and β tribolayer. Corresponding precession–orientation imaging phase maps were used to determine the orientation and percentage of α and β-Ti in the worn nitrided TNZT. The maps revealed that the nanocrystalline grains of soft/compliant β are much smaller (10–100 nm) than hard/stiff α grains (>100 nm). Wear reduction is due to the combination of the above phases and the increase in the alignment of {0 0 0 2}-textured coarser α grains along the sliding direction in absence of texture in the highly refined β grains. Conversely, nitrided Ti64 exhibited slightly increasing wear, despite higher hardness, due to the change in sliding-induced deformation mechanism where shear bands formed and networked leading to brittle fracture and third body abrasive wear particle generation.