Additive manufacturing (AM) has become one of the most important research topics with its ability to manufacture a wide range of alloys like steel, nickel-based super alloys, titanium alloys, aluminum alloys, etc. Al 7075 is not a friendly alloy for laser metal deposition (LMD). This paper reports the successful development of LMD process for deposition of defect-free Al 7075 alloy. By preheating the substrate to 260°C the residual stress decreased and eliminated the hot/solidification cracks in the deposit. LMD is a rapid cooling process due to which the gas bubbles of Mg and Zn are trapped in the deposit. These are identified as gas porosity because of the partial evaporation of low boiling point elements like magnesium and zinc present in this alloy. The least porosity observed was 0.08% at 29 J/mm 2 of energy input. The SEM and EDS investigation of as-deposited Al 7075 revealed the segregation of Cu, Mg, and Zn rich phases along the interdendritic regions and grain boundaries. Cu, Mg, and Zn rich phases at the interdendritic regions dissolved into the α-Almatrix after heat treatment. The XRD scan of laser deposited Al 7075 revealed the presence of Al 2 CuMg and MgZn 2 precipitation hardening phases.

This paper reports the progress of the mechanochemical synthesis of nanocrystalline hydroxyapatite (HA) starting from six different powder mixtures containing Ca(H2PO4)2.H2O, CaO, Ca(OH)2, and P2O5. The reaction kinetics of HA phase formation during high-energy ball milling was systematically investigated. The mechanochemical reaction rate of the Ca(H2PO4)2.H2O–Ca(OH)2 powder mixture found to be very fast as the HA phase started to form at around 2 min and finished after 30 min of ball milling. All six powder mixtures were transformed entirely into HA, with the crystallite size between 18.5 and 20.2 nm after 1 h and between 22.5 and 23.9 nm after 2 h of milling. Moreover, the lattice strain was found to be 0.8 ± 0.05% in the 1 h milled powder and 0.6 ± 0.05% in all six powders milled for 2 h. This observation, i.e., coarsening of the HA crystal and gradual decrease of the lattice strain with the increase of milling time, is opposite to the results reported by other researchers. The gradual increase in crystallite size and decrease in lattice strain result from dynamic recovery and recrystallization because of an increase in the local temperature of the powder particles trapped between the balls and ball and reactor wall during the high-energy collision.

Laser Metal Deposition is an Additive Manufacturing process with an extreme potential in large-scale metal production. Among the printable metals, the Inconel 625 has found a wide variety of cutting-edge applications in the aerospace, defense and space sectors. Thus, knowledge of mechanical properties under static and dynamic conditions is fundamental. In this work, the quasi-static and dynamic compression behaviour of Inconel 625 obtained by Laser Metal Deposition is presented. The curves of printed Inconel 625 showed a change in slope in the work hardening phase, which is due to the mechanics of the dislocation motion. Therefore, a modified Two-Stage Hollomon power-law is proposed to model this specific mechanical behaviour, which identifies a threshold strain that delimit two different hardening behaviours. Furthermore, Johnson-Cook and Cowper-Symonds models were used to represent the effect of strain rate and temperature on the material properties. A variable strain rate sensitivity along the compression strain was found. Hence, double sensitivity terms were introduced into the Two-Stage Hollomon power-law, allowing to reproduce the dynamic behaviour of Inconel 625.

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