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Abstract:The present study deals with the properties of five different metals/alloys (Al-12Si, Cu-10Sn and 316L-face centered cubic structure, CoCrMo and commercially pure Ti (CP-Ti)-hexagonal closed packed structure) fabricated by selective laser melting. The room temperature tensile properties of Al-12Si samples show good consistency in results within the experimental errors. Similar reproducible results were observed for sliding wear and corrosion experiments. The other metal/alloy systems also show repeatable tensile properties, with the tensile curves overlapping until the yield point. The curves may then follow the same path or show a marginal deviation (~10 MPa) until they reach the ultimate tensile strength and a negligible difference in ductility levels (of~0.3%) is observed between the samples. The results show that selective laser melting is a reliable fabrication method to produce metallic materials with consistent and reproducible properties.

We report an experimental investigation of the electronic structure and magnetic properties of bulk and nanosized MnCo 2 O 4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is (Co 2þ 1ÀyA Zn 2þ yA ) A [Mn 3þ Co 3þ ] B O 4+δ , whereas B-site dilution results in (Co 2þ ) A [Mn 3þ 1ÀxB Zn 2þ xB Co 3þ ] B O 4Àδ . The strength of exchange interaction J ij between the magnetic ions in a bulk spinel lattice decreases by 15% for A-site dilution relative to the undiluted compound; however, B-site dilution results in an enhancement in J ij by 17%. The frequency and temperature dependence of dynamic-susceptibility [χ ac (f , T)] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature T F 125:7 K (for x B ¼ 0:2) and 154.3 K (y A ¼ 0:1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent zν ¼ 6:17 and microscopic spin relaxation time τ o ¼ 4:4 Â 10 À15 s for x B ¼ 0:2 (for y A ¼ 0:1, zν ¼ 5:2 and τ o ¼ 5:4 Â 10 À13 s). The amplitude and peak position in χ ac (T) decreases with an increase in the DC bias field, which indicates that the spin-glass phase can survive in the presence of low fields forming a critical line with an exponent 2/3. This behavior is similar to the de Almeida-Thouless (AT-line) analysis in the T-H phase diagram which supports the existence of spin-glass like behavior below T F in these Zn diluted spinels.

The synthesis of novel materials by additive manufacturing requires the optimization of the processing parameters in order to obtain fully-dense defect-free specimens. This step is particularly important for processing of composite materials, where the addition of a second phase may significantly alter the melting and solidification steps. In this work, a composite consisting of a 316L steel matrix and 5 vol.% CeO 2 particles was fabricated by selective laser melting (SLM). The SLM parameters leading to a defect-free 316L matrix are not suitable for the production of 316L/CeO 2 composite specimens. However, highly-dense composite samples can be synthesized by carefully adjusting the laser scanning speed, while keeping the other parameters constant. The addition of the CeO 2 reinforcement does not alter phase formation, but it affects the microstructure of the composite, which is significantly refined compared with the unreinforced 316L material.Technologies 2018, 6, 25 2 of 10 can further enhance mechanical and wear properties at moderate and high temperatures, and expand the range of potential applications of these composites to aerospace and biomedical industries [18,19].Two main features play a decisive role for determining the final microstructure and the mechanical properties of composites synthesized by SLM: the first is related to the processing parameters, such as laser power, laser scan speed, hatch distance, hatch layer thickness, and laser spot size [20] and the second is associated with the characteristics of the reinforcing particles, including particle size and morphology, and their dispersion within the matrix [21]. A uniform distribution of the reinforcing particles in a matrix-reinforcement powder mixture is a prerequisite for its homogeneous distribution in the final bulk composite. Ball milling can be successfully used for the preparation of homogeneous particle mixtures. The uniform distribution of the reinforcement achieved by ball milling, however, it is usually accompanied by a change of the powder morphology resulting from the high energy impacts between particles and milling media [22,23], which in turn may influence the solidification characteristics and the properties of the composite material after SLM [23].Due to the addition of the second phase and the change of the powder morphology, the SLM processing parameters leading to defect-free specimens of the unreinforced matrix might not be suitable for the synthesis of fully-dense composites and the optimization of the parameters might be necessary [24][25][26]. Accordingly, the objective of this work is the optimization of the SLM processing parameters to produce defect-free 316L matrix composites reinforced with 5 vol.% CeO 2 particles. To achieve this aim, different scanning speeds have been employed and the resulting phases, microstructures and densification of the SLM parts have been investigated. The present steel-matrix composite belongs to the family of oxide dispersion strengthened (ODS) alloys, where oxide particles, such as Y ...