PSI - Issue 24

Jacopo De Nisi et al. / Procedia Structural Integrity 24 (2019) 541–558 Paolo Folgarait et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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all the groups (except for 0 group) 2σ is much lower than 1 .0 HRC, a typical measurement uncertainty in HRC hardness tests. In any case, hardness measurements satisfied minimum value requested by the reference Standard (ASTM A564/A564M Standard). The heat treatment conditions recommended by EOS for PH1 (B1 group) allowed reaching the highest HRC values for the metal alloy. As referred in Table 6 , the reference value assumed for the 0 group ( as-built conditions, no heat treatment applied) is that for solution treated specimen (and the two conditions appear to be quite close each other). From the other side, HRC values assumed by the C group (highest ageing temperature and holding time) showed a drop in strength and hardness behavior, due to the formation of precipitates having semi-coherency or incoherent with matrix or crystal’s lattice and coarser in size, conditions allowing mobile dislocations to bypass obstacles easier

Fig. 3 . HRC indentation tests performed on specimen group 0 to C, position 1 to 9 (namely position A to I, as per Fig. 2).

HV1 hardness HV1 hardness indentation tests have been performed on the same transverse sections of 3D printed (heat treated and as-built) used for HRC tests, according to ASTM E92-17 Standard. Each hardness specimen preventively submitted to finishing to obtain perfectly parallel surfaces and smoothing till the aimed surface to be tested. HV indentation tests performed on a calibrated universal hardness equipment AFFRI model WYKY200JS3 with load cells. Each test point has been resulted in the average among 6 (six) independent measurements, assessed on metallographic samples (equally selected among horizontally and vertically fabricated). Experimental data are summarized in Table 7 . Results showed ( Fig. 4 ) that for each group the (measured) hardness is independent on the specific location on the building platform. In fact, all trends show to be linear and flat (= very low slope = nearly constant behavior within the building positions), especially for A2 e B2 groups (for which conditions a preliminary solution annealing is applied) and B1 group (higher ageing temperature than A1). For those cases for which the linear correlation relationship shows a slight (positive or negative) slope (for example B1 and C group), the maximum hardness value excursion is included within the error bar. For all groups the full error bar is equivalent to 2σ ( - σ; + σ; symmetric), σ being the standard