Development of a Laser Powder Bed Fusion Process Tailored for the Additive Manufacturing of High-Quality Components Made of the Commercial Magnesium Alloy WE43.

Additive manufacturing (AM) has become increasingly important over the last decade and the quality of the products generated with AM technology has strongly improved. The most common metals that are processed by AM techniques are steel, titanium (Ti) or aluminum (Al) alloys. However, the proportion of magnesium (Mg) in AM is still negligible, possibly due to the poor processability of Mg in comparison to other metals. Mg parts are usually produced by various casting processes and the experiences in additive manufacturing of Mg are still limited. To address this issue, a parameter screening was conducted in the present study with experiments designed to find the most influential process parameters. In a second step, these parameters were optimized in order to fabricate parts with the highest relative density. This experiment led to processing parameters with which specimens with relative densities above 99.9% could be created. These high-density specimens were then utilized in the fabrication of test pieces with several different geometries, in order to compare the material properties resulting from both the casting process and the powder bed fusion (PBF-LB) process. In this comparison, the compositions of the occurring phases and the alloys' microstructures as well as the mechanical properties were investigated. Typically, the microstructure of metal parts, produced by PBF-LB, consisted of much finer grains compared to as-cast parts. Consequently, the strength of Mg parts generated by PBF-LB could be further increased.

Corrosion and Corrosion Fatigue Properties of Additively Manufactured Magnesium Alloy WE43 in Comparison to Titanium Alloy Ti-6Al-4V in Physiological Environment.

Laser powder bed fusion (L-PBF) of metals enables the manufacturing of highly complex geometries which opens new application fields in the medical sector, especially with regard to personalized implants. In comparison to conventional manufacturing techniques, L-PBF causes different microstructures, and thus, new challenges arise. The main objective of this work is to investigate the influence of different manufacturing parameters of the L-PBF process on the microstructure, process-induced porosity, as well as corrosion fatigue properties of the magnesium alloy WE43 and as a reference on the titanium alloy Ti-6Al-4V. In particular, the investigated magnesium alloy WE43 showed a strong process parameter dependence in terms of porosity (size and distribution), microstructure, corrosion rates, and corrosion fatigue properties. Cyclic tests with increased test duration caused an especially high decrease in fatigue strength for magnesium alloy WE43. It can be demonstrated that, due to high process-induced surface roughness, which supports locally intensified corrosion, multiple crack initiation sites are present, which is one of the main reasons for the drastic decrease in fatigue strength.

Severe respiratory failure due to diffuse alveolar hemorrhage: clinical characteristics and outcome of intensive care.

BACKGROUND: The aim of this study was to characterize patients and report outcome of diffuse alveolar hemorrhage (DAH) requiring intensive care unit support. PATIENTS AND METHODS: Thirty-seven patients were identified. Clinical characteristics and outcome were determined by chart review. RESULTS: Eighty-nine percent of patients presented with shortness of breath, 23% with cough, and 3% with hemoptysis. In 9% of patients, a diagnosis of DAH was suspected on admission. Diagnosis was confirmed by finding a progressively hemorrhagic bronchoalveolar lavage fluid in 89% and by a positive iron stain in 11% of patients. Vasculitis was causative in 19%, drug toxicity in 11%, thrombocytopenia in 27%, stem-cell transplantation in 5%, sepsis-associated lung injury in 22%, and unknown mechanisms in 16%. Thirty-two patients were mechanically ventilated, 4 received noninvasive ventilation, and 1 received supplemental oxygen therapy. Overall, 18 (49%) of 37 patients survived the intensive care unit stay. Survival was markedly different between patients with an immunologic/unknown etiology (82%) and patients with thrombocytopenia and/or sepsis (22%). DISCUSSION: Diffuse alveolar hemorrhage should be considered in all patients with persistent pulmonary infiltrates. Both bronchoalveolar lavage fluid and iron stain are mandatory diagnostic means. Patients with an immunologic/idiopathic pathogenetic mechanism have a relatively good prognosis, whereas the outcome in individuals with DAH secondary to cancer therapy or sepsis is poor.