Fracture and Fatigue of the Inertia Welded Titanium Alloy Ti-6Al-2Sn-4Zr-6Mo

Miles, Christopher James (2011). Fracture and Fatigue of the Inertia Welded Titanium Alloy Ti-6Al-2Sn-4Zr-6Mo. University of Birmingham. M.Res.

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Abstract

In this thesis the microstructure, microhardness, and mechanical properties of the α/β alloy Ti-6Al-2Sn-4Zr-6Mo inertia welded to itself using a variety of parameters were assessed. The resultant welds were compared to the parent in both the as-welded and post weld heat treated condition (640°C / 2 hours). The mechanical properties of later welds were evaluated at three different temperatures and R ratios. Welding at process parameters within a defined window has produced welds with satisfactory mechanical properties. These welds are harder than the parent in both the as welded and Post Weld Heat Treated (PWHT) conditions. Post Weld Heat Treating of these welds at 640°C for two hours results in the re-precipitation of secondary α throughout the Central Weld Zone and Heat Affected Zone, leading to a local microhardness increase. The weld is deduced to be more resistant to fatigue crack initiation than the parent material, with all low cycle fatigue samples failing in the parent. The fatigue crack growth resistance of welded and parent samples was comparable at all temperatures tested, with no effects of dwell observed. However, a static (intergranular) mode of failure at room temperature caused rapid acceleration of crack growth at higher ∆K values as the peak value of K approaches the fracture toughness. Hence, the onset of final failure in fatigue crack growth tests is strongly dependent on the R ratio, but at lower ∆K values, crack growth rates are independent of R ratio.

Type of Work:

Thesis (Masters by Research > M.Res.)

Award Type:

Masters by Research > M.Res.

Supervisor(s):