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The microstructure in the Z-Y surface of Inconel 718 alloys fabricated by selective laser melting (SLM) shows the relatively homogeneous and irregular fine grain structure after the heat treatment process of 1050ºC solid solution + double ageing. A large number of bulk precipitates were observed on the grain boundary, and the typical dendritic crystallization and Laves phases disappeared. It is possible that a large number of δ phases (NbNi 3) were precipitated on the grain boundary since the enrichment effect of element Nb. The hardness in the Z-Y surface increased from 350HV to 500HV, and the residual stress was transformed from the tensile stress to compressive stress.

In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera, and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welding arc, which would increase the depth of penetration as the incensement of the arc force. Several principal parameters including the distance of twin wires intersecting point to base metal, the included angle, and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased, the arc turned brighter while unobvious change of penetration occurred as the arc voltage increased, and the deepest penetration was obtained when the welding speed was 10.5 mm/s.

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The ZrC-ZrB 2 /Ni metal matrix composite coatings were in-situ synthesized from a mixture of Ni, Zr and B 4 C by plasma transferred arc (PTA) cladding process. Microstructures and phase constituents of the coatings were characterized by electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD). Microhardness and wear resistance of the coatings were systematically investigated by means of vickers hardness tester and wear tester. The results showed that the main phases of the composite coatings were ZrB 2 and ZrC. The coatings had a sound metallurgical bonding to the SA-283C steel substrate. Microhardness and wear resistance of the substrate were greatly improved by the composite coatings, and both of them showed a tendency to increase first and then decrease with the increase of the Ni content. As the content of Ni was 30 wt.%, the hardness of the coating reached the maximum value, 1522 HV, and the wear resistance was about 15 times that of the substrate.