Direct ageing versus solution annealing plus ageing of LPBF CuCrZr: a defect-tolerant fatigue assessment of two industrial processing routes

Laser powder bed fusion (LPBF) of CuCrZr is attractive for actively cooled, high-heat-flux components; however, the conventional post-heat treatment, solution annealing and ageing, is difficult to transfer to large and geometrically complex additively manufactured parts because quenching may promote distortions and cracking. A quench-free direct ageing would be industrially attractive if it preserves fatigue performance. In the present work, two industrially established LPBF CuCrZr conditions were compared: a directly aged material produced with an 80 μm layer thickness (DAH-80) and a solution-annealed and aged material with a 60 μm layer thickness (SA+AH-60). The routes differ not only in post-processing, but also in layer thickness and LPBF system; they are therefore assessed as production packages rather than isolated heat-treatment variants. Density, hardness, tensile properties, smooth and notched high-cycle fatigue (HCF), notch sensitivity (Theory of Critical Distances and the Averaged Strain Energy Density approaches), defect tolerance (ElHaddad–corrected Kitagawa–Takahashi diagram) and low-cycle fatigue (LCF) were investigated. Despite a large gap in ultimate tensile strength (UTS, 478 vs. 359 MPa), the two routes show the same smooth HCF strength within 4% (133 vs. 138 MPa 107 cycles), probably because this is controlled by lack-of-fusion defects of similar size. On the other hand, DAH-80 showed superior notched HCF strength (88 vs. 72 MPa at 107 cycles). In LCF the routes cross near 2Nf ≈5000 reversals. The results indicate that direct ageing is a mechanically competitive and industrially scalable alternative for large, complex LPBF CuCrZr components.