Abstract
The powder bed fusion method using a heat source for 3D printing can be applied to fabricate the geometrical shapes of some parts, and enables rapid melting and cooling. 3D EBM additive manufacturing can supply a near-net-shape or net-shape and precise parts better than micro scale casting and precision casting. Casting parts have residual stress in the matrix and their microstructure, which can affect the dynamic properties, but if they are heat-treated under the optimal conditions, the residual stress can be reduced to enhance the dynamic-mechanical properties of 3D printed parts. In this study, Ti-6Al-4V bulk bars were fabricated by EBM additive manufacturing, and the microstructures, residual stress, and various interior defects of the specimens were analyzed. The residual stress and surface tension were measured and calculated in different specimens heat-treated at 850~950 ℃ . The relationship between the residual stress and surface tension was explained using the related equations and the influence on the high cycle fatigue properties was evaluated.
Highlights
The relationships between the residual stress, and surface tension according to various heat treatment conditions were analyzed and the changes in their values were measured in regions with and without pores inside the electron beam melting (EBM) Ti-6Al-4V specimens
Ψ was fixed to 0.5, which is based on examples of license patents [8]: Where Ac is the actual contact area measured by a nano indenter and hct is the actual contact depth
These values were lower than those of the as-fabricated sample, which means a decrease in residual stress by post heat treatment
Summary
The relationships between the residual stress, and surface tension according to various heat treatment conditions were analyzed and the changes in their values were measured in regions with and without pores inside the EBM Ti-6Al-4V specimens. The high cycle fatigue properties as a function of the heat treatment conditions were evaluated and the correlation between their values and the residual stress were investigated. The residual stress of EBM Ti-6Al-4V alloy specimens was measured using a Nanoindenter (CSM Instruments, NHT2) This method evaluates the nano hardness, which gives a loading force to the surface by the nano indenter tip and calculates the hardness. The actual contact area (Ac) of each heat-treated specimen was calculated using the nano hardness and the factor ‘Λ’ was fixed to 0.2. The fatigue cycle was aimed at 107 cycles with a load of more than 400MPa
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