3.5. Strength model
Values for the bulk material position at 5 mm were obtained from previous characterization of the material provided by Senkovet al. [20]. Results from the characterization are summarized in Table 3. Because this research was investigating evolution of γ′ within LSHR, precipitate size and volume measurements and chemical compositions were conducted only on the LSHR side of the weld.
3.5.1. Strength model chemical compositions
The strength model uses PandatTM to estimate the chemical composition based upon calibrated LSHR heat treatment experiments conducted by NASA [6]. The antiphase boundary energy values and other model parameters were also obtained using previously calibrated results for LSHR [6]. The estimated equilibrium phase chemistries shown in Fig. 10 compared favorably to the measured values using APT, with the slight exception of Cr and Co. The PandatTM software slightly under-estimated the amount of Co and Cr in the matrix, possibly due to the non-equilibrium condition (the sample may have experienced slower diffusion due to the rapid cooling rate).
3.5.2. Predicted hardness values
The strength model employed the predicted chemistries and parameters from Table 3 to provide the projected hardness values for each of the positions (Fig. 11). Hardness values were converted from the predicted yield strength assuming the strength is approximately 2.6 times the HVN. The value of 2.6 providedcalculated hardness values within the range of experimental values. Although for steel alloys the strength is approximately 3 times the HVN, the data applies to ferrous alloys and depends on many microstructural factors [31]. However, because we are interested in the relative impact of each strengthening mechanism and its contribution to the total strength, the exact value of the multiplication value is not critical. The exact simulation values compared favorably with the measured results, with a slightly lower strength value at the 1 mm position.