Maraging steels are generally characterized by excellent mechanical properties, which make them ideal for various industrial applications. The application field can be further extended by using selective laser melting (SLM) for additive manufacturing of shape complicated products. However, the final mechanical properties are strongly related to the microstructure conditions. The present work studies the effect of heat treatment on the microstructure and mechanical properties of 3D printed samples prepared from powder of high-strength X3NiCoMoTi 18-9-5 maraging steel. It was found that the as-printed material had quite low mechanical properties. After sufficient heat treatment, the hardness of the material increased from 350 to 620 HV0.1 and the tensile yield strength increased from 1000 MPa up to 2000 MPa. In addition, 3% ductility was maintained. This behavior was primarily affected by strong precipitation during processing.

Maraging steels are interesting for research after heat treatment, from which name is derived "maraging" – martensite-aging. After solution annealing and precipitation hardening the X3NiMoCoTi 18-9-5 alloy has excellent mechanical properties (tensile strength reaches up to 2000 MPa and hardness is 50-55 HRC), it is ductile and well weldable. The advantage of these materials is the possibility to be manufactured not only by conventional methods but also by modern additive manufacturing (AM) methods. One of which is selective laser melting (SLM). In this paper, the influence of heat treatment on the final microstructure and mechanical properties of the 3D-printed X3NiMoCoTi 18-9-5 maraging steel is investigated.

The present work describes the influence of Al content on the CoCrFeNiAl high-entropy alloys prepared by the powder metallurgy technique. The preparation procedure consisted of mechanical alloying and subsequent spark plasma sintering. The content of Al varied from 10 -30 at.% which affected the microstructure and mechanical properties. Using scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) was found the microstructure becomes more grain refined with increasing content of Al accompanied by the annihilation of the ductile FCC solid solution (Cr0.25Fe0.25Co0.25Ni0.25) phase and growth of the brittle and hard BCC solid solution phase (α-Fe) and formation of Al(Co0.5Ni0.5) phases, improving the mechanical properties. The best combination of the porosity, hardness HV 30, and ultimate compressive strength (UCS) was achieved for the studied high-entropy alloy when it contained 20 at. % Al.

The main aim of this study was to determine the susceptibility of the additively manufactured high strength X3NiCoMoTi 18-9-5 maraging steel to hydrogen embrittlement. For this purpose, samples produced by selective laser melting technology, before and after heat treatment, were used. The examined samples were electrochemically charged with hydrogen in NaCl + NH4SCN solution at a current density of 50 mA/cm2 for 24 h. The H content increased from about 1 to 15 ppm. Heat treatment did not affect the amount of H trapped in the maraging steel. Tensile testing revealed that the tensile strength of the H-charged samples was much lower than that of the uncharged samples. Moreover, the material became brittle after charging compared to the ductile as-printed and heat-treated samples with elongation values of 7% and 2%, respectively. The loss of plasticity was confirmed by fractography, which revealed transformation of the fracture surface morphology from dimple-like in the as-produced state to a brittle one with smooth facets in the H-charged state.

In this work, a new approach for compaction of the gas-atomized 18Ni300 maraging steel at two different temperatures of 1050 °C and 1150 °C using a progressive SPS technology is studied. Moreover, the influence of two heat treatments combining solution annealing and aging (SAT) and simply aging treatment (AT) on the microstructure and mechanical properties is investigated. It is found that samples compacted at 1050 °C had higher porosity compared to the almost non-porous material produced at 1150 °C. In addition, the difference of 100 °C for the compaction temperature successfully reduces the porosity from 0.86% down to 0.08%. Additionally, we discovered that the higher the compaction temperature, the higher the amount of retained γ-Fe which positively affects the ductility of the samples. The subsequential heat treatment results in precipitation strengthening via the Ni3Mo precipitates. Microhardness of the SPS1050 and SPS1150 samples increase from 303 ± 13 HV0.1 and 360 ± 5 HV0.1 to 563 ± 31 HV0.1 and 606 ± 17 HV0.1, respectively. The sample compacted at 1150 °C shows the highest ultimate tensile strengths reaching up to 1940 ± 6 MPa, while also showing 4% ductility.