PSI - Issue 14

Anigani Sudarshan Reddy et al. / Procedia Structural Integrity 14 (2019) 449–466 Author name / Structural Integrity Procedia 00 (2018) 000–000

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heat treatment. Maraging steel and IN718 show an increase in hardness by 57% and 32% due to precipitation hardening. 3.2. Microstructural characterization of monolithic DMLS Alloys Figure 8 (a-b) shows the representative optical micrographs of hybrid of DMLS (DMLS SS316L on X20Cr13 substrate) in the as printed and heat treated condition. It can be seen that the weld pools of DMLS SS316L penetrated and fused with X20Cr13 substrate. The weld pool width and depth was  80 µm in the as printed condition similar to Figure 5(d). After heat treatment columnar grains were seen in the DMLS SS316L, again very similar to Figure 6(d). There was distinct interface that emerged between the substrate and the DMLS build.

Fig. 8. Representative optical micrographs of the hybrid of DMLS (SS316L on X20Cr13 substrate) in the (a) As printed (b) Heat treated condition

Figure 9 represents the variation in the microhardness before and after heat treatment across the hybrid parts. In the X20Cr13 substrate, the hardness remains invariant at 265 HV while in the DMLS SS316L there is a gradual decrease in the hardness from 210 HV in the as printed condition to 185 HV after heat treatment due to relaxation of residual stress. At the interface hardness was seen in between the two at around 240 HV in both the as printed and heat treated condition.

Substrate‐Interface‐Deposit

150 170 190 210 230 250 270 290

HT 650C

Hardness (HV)

‐4000 ‐2000

0

2000 4000

Distance from interface (microns)

Fig. 9. Microhardness taken across the hybrid DMLS SS316L on X20Cr13 substrate, in the as printed condition and after heat treatment.