Micro-CT Evaluation of Defects in Ti-6Al-4V Parts Fabricated by Metal Additive Manufacturing

Microstructure and Mechanical Properties of Hypereutectic Al-High Si Alloys up to 70 wt.% Si-Content Produced from Pre-Alloyed and Blended Powder via Laser Powder Bed Fusion

Hypereutectic Al-high Si alloys are of immense interest for applications in the automotive, space or electronic industries, due their low weight, low thermal expansion, and excellent mechanical and tribological properties. Additionally, their production by laser powder bed fusion (LPBF) technology provides high flexibility in geometrical design and alloy composition. Since, most of the alloy properties could be improved by increasing the Si content, there is much interest in discovering the maximum that could be realized in LBPF Al-high Si alloys, without the appearance of any material failure. For this reason, in this work the production of Al-high Si alloys with extremely high silicon content of up to 70 wt.% was fundamentally investigated with respect to microstructure and mechanical properties. Highly dense (99.3%) and crack-free AlSi50 samples (5 × 5 × 5 mm³), with excellent hardness (225 HV5) and compressive strength (742 MPa), were successfully produced. Further, for the first time, AlSi70 LBPF samples of high density (98.8%) without cracks were demonstrated, using moderate scanning velocities. Simultaneously, the hardness and the compressive strength in the AlSi70 alloys were significantly improved to 350 HV5 and 935 MPa, as a result of the formation of a continuous Si network in the microstructure of the alloy. With respect to the powder source, it was found that the application of powder blends resulted in similar alloy properties as if pre-alloyed powders were used, enabling higher flexibility in prospective application-oriented alloy development.

On Defect Minimization Caused by Oxide Phase Formation in Laser Powder Bed Fusion

The article is devoted to the compressive review of the defects observed in the products of the machinery usage made mainly of anti-corrosion steels of the martensite-austenite group, difficult to process materials such as pure titanium, nickel, and their alloys, super and high entropy alloys and triple fusions produced by laser additive manufacturing, particularly the laser powder bed fusion. Studies were conducted on the structural defects observed in such products to improve their quality in the context of residual stress elimination, porosity reduction, and surface roughness improvement. Electrophysical and electrochemical treatment methods of removing oxide phase formation during melting and remelting of deposed tracks in layers are considered (such as ultrasound, plasma, laser, spark treatment, induction cleaning, redox annealing, gas–flame, plasma–beam, plasma–spark treatment). Types of pollution (physical and chemical) and cleaning methods, particularly plasma-based methods for oxide phase removing, are classified. A compressive comparison of low- and high-pressure plasma sources is provided. Special attention is focused on the atmospheric plasma sources based on a dielectric barrier and other discharges as a part of a production setup that presents the critical value of the conducted review in the context of the novelty for transition to the sixth technology paradigm associated with the Kondratieff’s waves.

Computed Tomography as a Characterization Tool for Engineered Scaffolds with Biomedical Applications

The ever-growing field of materials with applications in the biomedical field holds great promise regarding the design and fabrication of devices with specific characteristics, especially scaffolds with personalized geometry and architecture. The continuous technological development pushes the limits of innovation in obtaining adequate scaffolds and establishing their characteristics and performance. To this end, computed tomography (CT) proved to be a reliable, nondestructive, high-performance machine, enabling visualization and structure analysis at submicronic resolutions. CT allows both qualitative and quantitative data of the 3D model, offering an overall image of its specific architectural features and reliable numerical data for rigorous analyses. The precise engineering of scaffolds consists in the fabrication of objects with well-defined morphometric parameters (e.g., shape, porosity, wall thickness) and in their performance validation through thorough control over their behavior (in situ visualization, degradation, new tissue formation, wear, etc.). This review is focused on the use of CT in biomaterial science with the aim of qualitatively and quantitatively assessing the scaffolds’ features and monitoring their behavior following in vivo or in vitro experiments. Furthermore, the paper presents the benefits and limitations regarding the employment of this technique when engineering materials with applications in the biomedical field.