# Additive Manufacturing of PH 13-8 Mo Family: A Review
## 2 PBF-LB of PH 13-8 Mo Family
### Material Properties
#### 2.3.1 Tensile Properties and Hardness
These heat treatments were solution treatment, aging, and solution treatment + aging (900 \({}^{\circ}\)C for 1 h + 530 \({}^{\circ}\)C for 3 h). The as-built sample only showed 0.3% austenite. After solution treatment, the austenite was not detected in the sample, which suggested that solution heat treatment was successful in eliminating austenite. Aging and solution-aging heat treatment increased the hardness and UTS, while only solution heat treatment decreased the hardness and UTS of PBF-LB/CX due to the coarser martensitic microstructure. The solution-aging heat treatment was the best combination, because it resulted in the highest hardness (520 HV0.2) and UTS (1610 MPa) values. Similarly, [PERSON] et al. [49] concluded that solubilizing at 900 \({}^{\circ}\)C for 1 h and aging at 530 \({}^{\circ}\)C for 3 h was the most suitable procedure in terms of the UTS (1683 MPa) and hardness (50.4 HRC). On the contrary, the same solution-aging heat treatment used by [PERSON] et al. [48] did not increase the hardness of the PBF-LB/CX. Solution-aging heat treatment was not found suitable to increase the hardness. Solution heat treatment caused the martensite laths to grow, and this resulted in the impediment of precipitation hardening during aging treatment. However, direct aging treatment resulted in the highest hardness (502 \(\pm\) 15 HV0.3). [PERSON] et al. [61] tried different solutions (850-950 \({}^{\circ}\)C for 1 h and 900 \({}^{\circ}\)C for 0.5-1.5 h) and aging (430-630 \({}^{\circ}\)C for 3 h) heat treatments to find the optimum heat treatment for the PBF-LB/CX. Solution treatment at 900 \({}^{\circ}\)C for 1 h followed by aging at 530 \({}^{\circ}\)C for 3 h was chosen as the optimum due to the achievement of the highest UTS (1598 MPa), YS (1486 MPa), and hardness (526.3 HV0.2). By using DSC, but also the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, for the PBF-LB/CX, [PERSON] et al. [62] tried to establish a suitable heat treatment to strengthen the material. Direct aging heat treatment at 550 \({}^{\circ}\)C for 115 min was chosen as the optimal heat treatment, because the highest hardness was achieved after this treatment. After heat treatment, the tensile strength increased (1032 MPa to 1738 MPa), and the elongation declined slightly (15.3% to 14.7%). The heat treatment was successful in increasing the strength and retaining the dislocation network at the same time, which resulted in maintaining the ductility. The tensile strength of heat-treated PBF-LB/Corrax was found to be comparable to conventional Corrax by [PERSON] et al. [50]. Corrax was built in two different PBF-LB machines (TruPrint1000 and EOS M290) with different process parameters. It was concluded that the defect density and elongation were different between the specimens processed with two different machines, although the strength values were similar. The elongation of Corrax produced by (TruPrint1000) was lower for the heat-treated samples due to the higher amounts of defects. [PERSON] et al. [59] compared the mechanical properties of wrought Corrax and PBF-LB/CX. The materials were solution-treated at 850 \({}^{\circ}\)C for 30 min and then subjected to different aging times (525 \({}^{\circ}\)C for 1, 2, 3, 4, and 6 h). Afterwards, the hardness values were compared. Samples that aged at 525 \({}^{\circ}\)C for 2 h achieved the highest hardness (XY: 50.7 \(\pm\) 0.8 HRC, XZ: 50.4 \(\pm\) 1.0 HRC); therefore, these samples were tensile tested. The UTS, YS, and elongation values of the PBF-LB/CX were higher than in wrought conditions. In addition, anisotropic mechanical properties for the PBF-LB/CX samples were observed, especially in terms of elongation. Horizontal specimens had better elongation compared to vertical ones, because the pores were generally located vertically to the built direction and between the layers. [PERSON] et al. [63] also used heat treatment (850 \({}^{\circ}\)C for 30 min + 525 \({}^{\circ}\)C for 2 h), which is the recommendation from the powder manufacturer for PBF-LB/CX.