Abstract
The laser powder bed fusion (LPBF) production process often results in large residual stress (RS) in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro-RS (i.e., stress at the component level) by means of diffraction-based techniques is still a great challenge, because the link between diffraction-based strain and macro-RS is not trivial. In this study, we experimentally determine (by means of in-situ synchrotron radiation diffraction) this link for LPBF Ti-6Al-4V. We compare our results with commonly used models to determine the so-called diffraction elastic constants (DECs). We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account (as is the case of additively manufactured materials), a radically new approach is desirable.
Highlights
ONE of the most important issues in laser powder bed fusion (LPBF) additive manufacturing (AM) is the influence of residual stress (RS) on parts during production and service.[1]
The link between the diffractionstrain response to an externally applied macrostress was rationalized in terms of a stress-microstrain conversion tensor (SlECT), as used in micromechanics. We show that such a tensor generalizes the concept of diffraction elastic constants (DECs) and allows a critical discussion on the validity of the approximations made in the current models
The microstructure of the AB sample presents a + a¢ laths (Figure 2(a)); this is typical for Ti-6Al-4V LPBF in the as-manufactured condition
Summary
ONE of the most important issues in laser powder bed fusion (LPBF) additive manufacturing (AM) is the influence of residual stress (RS) on parts during production and service.[1]. Quantification of RS and validation of thermomechanical models by experimental results are among the greatest challenges for qualification of AM parts
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