Abstract
Wire Arc-Based Additive manufacturing is a high deposition rate process suitable for building large-scale aerospace components. However, the larger heat source can cause greater microstructural heterogeneity and, in particular, a coarse columnar ß grain structure. The effect of the subsequent related transformation microstructure heterogeneity on the mechanical behaviour is investigated, in both standard WAAM materials and samples subjected to inter-pass rolling, which leads to substantial ß grain refinement and texture randomisation. Full-field strain maps were produced by digital image correlation, using tensile samples loaded in different orientations. When loaded normal to the columnar grain structure, it is shown that the coarse ß grains lead to a highly heterogeneous deformation distribution, which is linked the presence of dominant hard and soft α variants in texture colonies within each parent ß grain. ß grain refinement through the application of inter-pass rolling was found to be very effective at homogenising the strain localisation for all test orientations.
Highlights
Additive Manufacturing (AM) is increasingly enabling the production of near-net shape components, with shorter lead times and greater design flexibility [1,2,3]
Single pass wide walls (250 mm long, 55 mm high and 1.1 mm thick) was produced by plasma wire deposition (PWD) at Cranfield University Welding Engineering Research Centre UK using the parameters in Table 1 [24]
The strain concentration in the unrolled sample tested normal to its columnar ß grain structure is clearly related to the limited ß parent grain orientations within the gauge length, but does not appear to be as localised at the GB boundaries as previously suggested [17]
Summary
Additive Manufacturing (AM) is increasingly enabling the production of near-net shape components, with shorter lead times and greater design flexibility [1,2,3]. In contrast to conventional deposits, where the columnar ß grains can be several centimetres in length, inter-pass rolling can produce an equiaxed ß grain size of less than 100 μm with weak texture [24], which leads to an improvement in mechanical properties [24](Fig. 1) including an increase in strength and a significant reduction in both the scatter and anisotropy in tensile performance. While this improvement has been linked qualitatively to the influence of heterogeneity in the local texture inherited from the parent ß-grains [17], and the concentration of failure in the grain boundary α regions, the strain distribution in such materials has not been previously quantitatively correlated to their microtexture
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