Characterization and thermal analysis of laser metal deposited γ-TiAl thin walls

Abstract

The present work focuses on investigating the effect of process variables (power, travel speed, powder flow rate) on microstructure and mechanical properties of Laser Metal Deposited (LMD) γ-TiAl thin walls. To this end, LMD technique was used to deposit γ-TiAl thin walls at different processing conditions. Microstructures of as-deposited samples were investigated using both optical and scanning electron microscopy. X-ray diffraction (XRD) technique was used to determine the phases present. Microhardness measurements were carried out along both longitudinal and build directions. Microstructural analysis of as-deposited samples revealed a fine lamellar structure comprising of γ and α2 phases. Colony size of 30–60 μm and lamellar spacing between 0.1 and 0.7 μm were observed. XRD analysis confirmed the presence of γ and α2 phases. Comparison of elemental analysis results on both powder and as-deposited samples revealed a negligible loss of Al and no oxygen pick up in the deposited thin walls. Hardness values were found to decrease with an increase in wall height, and hardness values increased marginally (5%) with an increase in travel speed. Further, 3D transient thermal analysis was also carried out to complement the LMD of thin walls in terms of melt pool dimensions and cooling rates. It was found that the melt pool depth (MPDc = 0.266 mm) is smaller at the centre than the edge (MPDe = 0.513 mm) of the wall. Cooling rates decrease with increase in the number of layers deposited.

Keywords

• γ-TiAl alloy
• Laser metal deposition
• Thin wall
• Microstructure
• Hardness
• Cooling rates