Enhanced comprehensive properties of directed energy deposited Inconel 718 by a novel integrated deposition strategy

Nickel-based superalloys fabricated by wire-arc directed energy deposition,also known as wire arc ad-ditive manufacturing(WAAM),usually exhibit inherent columnar grain structure,micro-segregation,and rough surface.A novel deposition strategy,integrating an oscillating arc and forced interlayer cooling,was developed in WAAM of Inconel(IN)718 components.The influences of deposition modes on geometrical characteristics,defects,microstructure,and mechanical properties were systematically evaluated.The re-sults showed that the oscillation mode,compared to the standard parallel mode,can effectively promote the molten pool’s spread and wettability,as well as prevent overflow,finally resulting in high geometric accuracy.In addition,the voids-like defects were reduced by 77.78%,while most common crack defects were not observed.Meanwhile,the forced interlayer cooling process further increased the cooling rate,leading to the reduction of the element segregation as well as the proportion of long-chain-like Laves phases.After a short-process modified heat treatment,the anisotropic mechanical behaviors of the as-deposited samples were almost eliminated.Compared with the parallel mode samples,the yield strength and ultimate tensile strength of the oscillation path samples increased by 5.75%and 9.25%,respectively,while the elongation increased significantly by 51.20%.This signifies that their strength and ductility were simultaneously improved.The strengthening mechanisms were further analyzed based on the distribution of the strengthening phases,as well as the residual Laves phases and porosity.

Adhesion at cerium doped metal-ceramic α-Fe/WC interface:A first-principles calculation

Electronic structure, stability and bonding strength of a-Fe/WC interfaces between Ce-doped and undoped WC cermet coating were investigated by first-principles methodology based on densityfunctional theory(DFT). Based on the minimum mismatched lattices, the relatively stable interface that forms between WC(100) and bcc a-Fe(100) was employed to predict the atomic structure, bonding,and ideal work of adhesion. There are three possible positions which were defined as OT, MT, HCP, taking into account both C-and W-terminations. The sequence of structural stability tested in this paper was:MT > OT > HCP. After full relaxation, the results show that only the first and second layers of the interface have significant influence on the electronic structure between Fe and WC. The interaction of Ce elements at the interface is achieved by comparing the interface structure and electronic structure of the doped and undoped interfaces. Ce doped interface possesses a shorter interface distance(d0 = 0.09776 nm)and a larger interface energy(Wad = 8.98 J/m2) than undoped interface(Wad = 8.76 J/m2,d0= 0.10134 nm).Charge density distribution and difference, and density of states were utilized to characterize the electronic properties and determine the interfacial bonding.The results demonstrate that strong covalent bonding existed in the undoped interface, while a mixed covalent/ionic bonding was formed at the Ce-doped interface.

Elevated temperature wear behaviour of CeO_2 modified WC-12Co coating

With the service environment becoming more and more severe, WC-Co coatings are required to apply in high temperature wear condition. In the present study, the sliding wear tests of CeO_2 modified WC-12 Co coatings were conducted at temperature of 450, 550 and 650 ℃. The wear loss and friction coefficient were recorded. The morphologies of wear tracks were observed every 1 h to investigate the dynamic wear mechanisms. The results show that the volume wear loss decreases with temperature increasing.The lowest volume wear loss is obtained at the temperature of 650 ℃ due to oxide films generated in the process of wearing. The wear mechanism is different at the temperature of 450, 550 and 650 0 C. Micro cutting wear, abrasive wear and oxidation wear dominate the wear mechanism at 450, 550 and 650 ℃,respectively. Abrasive wear and oxidation wear are the wear mechanisms at various temperatures.