Variation in the Properties of Ti-6al Alloys Fabricated by Electron Beam Melting Due To Build Plate Location

Abstract

The build plate location and post-processing effects on the properties of Ti-6Al-4V alloys fabricated via electron beam melting (EBM) are investigated in the context of spatial variability. Tensile test specimens are fabricated in four corner and center locations of the EBM machine build plate with three different dimensions. One specimen has standard dimensions of 6 mm gauge length diameter; the second one has 25% higher diameters, called the offset specimens, and the third is a cylinder with a diameter of 15 mm, called the block specimens. The standard specimen dimensions are obtained by applying machining to the block and offset specimens to evaluate the influence of the larger dimension and post-processing on the mechanical properties, including spatial variability. The yield strength, tensile strength, and ductility are obtained by performing tensile tests. The density and surface roughness of the specimens are measured before and after machining. Correlation plots and semivariograms are used to examine the effect of spatial variability on the properties of the fabricated specimens at different build plate locations. The densities of the block, offset, and standard specimens are 99.4%, 98.6%, and 98.8%, respectively. The surface roughness (Ra) values reduced from 29.5 to 0.7 mu m after machining the block specimens, while the roughness is as high as 47.2 mu m for the standard specimens. Following the machining process, the yield strength increases from 970 MPa for the standard specimens to 1039 MPa for the block specimens. The tensile strengths are approximately 1115 MPa and 1074 MPa for the block and offset specimens, respectively, whereas for the standard specimens, it is as low as 996 MPa. Similarly, the ductility increases to 13.8% when the block specimens are machined compared to the standard specimen result of 5.4%. For the standard specimens, approximately 5% change in the parameters could be observed at different build plate locations. The location dependency is lesser for the block and offset specimens after machining. There is higher correlation in material properties without any post-processing, whereas all the properties exhibit spatial variability according to the correlation plots and semivariogram analysis.