A micropillar compression investigation into the plastic flow properties of additively manufactured alloys

The unnotched fatigue behavior of the 17-4 PH martensitic (α’) stainless steel, additively manufactured using the binder jet printing technique (BJP), with varying porosity levels and in two different aging conditions are investigated and are compared to that of the conventionally manufactured (CM) alloy. As expected, fatigue strength is enhanced by the reduction in porosity, with hot isostatic pressing of the BJP alloy resulting in a fatigue strength that is similar to the CM alloy. Over-aging of the alloy improves its fatigue resistance further, which is caused by an enhancement in the threshold stress intensity factor range for fatigue crack initiation. These variations are rationalized by recourse to the analysis of the microstructure-crack interactions. It was found that the combination of plasticity induced crack closure mechanisms and transformation induced plasticity are dominant at the fatigue crack tip of the over-aged alloy. Fracture mechanics-based Kitagawa and Takahashi diagrams were utilized to illustrate the significance of pore size on the unnotched fatigue resistance of BJP 17-4 PH alloys. These results are discussed in terms of designing alloy fabrication using BJP specifically for cyclic loading conditions. 

Fatigue resistance of the binder jet printed 17-4 precipitation hardened martensitic stainless steel

A detailed understanding of the connections between processing – porosity – microstructure – mechanical properties of additively manufactured (AM) alloys is essential before they can be utilized for structural applications. Towards this end, the microstructure and tensile properties of 17-4PH martensitic (α′) stainless steel fabricated using binder jet printing (BJP) were investigated and compared with those of the conventionally manufactured (CM) alloy. Results show that optimizing the printing parameters to increase the relative density of the final part also affects the grain size as well as the morphology and fraction of the δ phase. Hot isostatic pressing (HIP), employed to reduce porosity, also refined the microstructure by dynamic recrystallization. Tempering of the martensitic microstructure through a post-fabrication H1150 over-aging heat treatment improves the strain hardening capability of the alloy and hence enhances its ductility substantially due to the formation of reversed γ phase. The tensile strength and ductility rise asymptotically with the decrease in porosity, until a critical fraction of ∼1.7% is reached. The variation in porosity and δ phase fractions does not influence the strain hardening behavior of the H900 peak aged alloy. In the over-aged condition, the deformation behavior is affected by a combination of porosity, transformation induced plasticity of the γ phase, and Cu partitioning across the α′- δ interface. 

Microstructure and tensile properties of binder jet printed 17–4 precipitation hardened martensitic stainless steel

Role of the solidification cells on the yield strength of the Al-Si-Mg alloy manufactured using laser powder bed fusion: A micropillar compression study

Qodirova Dilnoza Xoliq qizi

Papers

Unnotched fatigue of Inconel 718 produced by laser beam-powder bed fusion at 25 and 600°C