Formation of Alpha-Case Layer during Oxidation of Ti6Al4V Surface by Annealing at 1050 °C and Change of Microstructure after Different Cooling Rates

Abstract:

The two-phase titanium alloy Ti6Al4V (often referred to as GRADE 5 or Ti64) is currently probably the most widely used type of Ti alloy. It is characterized by an excellent combination of strength - toughness - chemical stability. However, at temperatures above 500 - 800 °C it is prone to the diffusion of oxygen into surface layers, where the increased oxygen content creates the so-called “alpha-case” layer. The formation of this layer is associated with a reduction mainly in the deformation characteristics of the alloy. The paper focuses on the metallographic analysis of the "alpha-case" layer after annealing at 1050 °C with a holding time of 3 hours and cooling at different cooling rates (500 °C/s, 1 °C/s and 0.08 °C/s). Microstructure changes were observed by light microscopy using polarized light – PL, dark field – DF and phases were identified by SEM methods. The influence of changes in the microstructure on the mechanical properties was determined by measuring the microhardness HV0.2 /10 (STN EN ISO 6507) with Zwick / Roell ZHµ and measuring the resistance to impact stress KU (Charpy system STN EN 10045-1). Based on the microhardness measurement, an increase in the microhardness of the surface layers was observed at all cooling rates and at the same time, a decrease in the impact resistance was observed compared to the initial state.

• Periodical: Materials Science Forum (Volume 1081)
• Pages: 161-166
• DOI: https://doi.org/10.4028/p-r71e1w
• Online since: March 2023
• Authors: Juraj Belan*, Milan Uhríčik, Lenka Kuchariková, Eva Tillová, Lucia Pastierovičová
• Keywords: Alpha-Case Layer, Annealing, Microstructure Changes, Oxidation, Ti6Al4V Alloy

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