Microstructural characterisation of a nickel alloy processed via blown powder direct laser deposition (DLD)

Abstract

A three dimensional structure of varying wall thickness has been manufactured from an alloy similar to 718 and subjected to metallographic characterisation. The technique is evaluated as a process capable of generating complex geometries. This can be used to add features or as a free form fabrication method. However, in order to allow for comparison to structures developed through more traditional techniques, detailed microstructural characterisation has been undertaken to attempt to understand the potential effect of variation on resultant mechanical properties.Samples were extracted from six locations with different wall thicknesses, intricate features and intersecting ligament geometry. A ʺ linearly arrayed structure within a  matrix was consistent throughout the component. Micro-porosity was restricted to isolated, spherical pores less than 1 m in diameter. Electron back-scatter diffraction and X-ray computed microtomography quantitative microstructural analysis techniques have been utilized to assess the influence of layering upon microporosity, patternation and grain structure.A detailed comparison is also made between blown powder Direct Layer Deposition (DLD) and a similar deposition technique, shaped metal deposition (SMD). Blown powder DLD produces a smaller weld pool and results in a more consistent microstructure than SMD, with less evidence of unfavourable phases brought about by prolonged exposure to high temperatures. The improved microstructure, however,

The Hardness of Additively Manufactured Alloys

“…Vickers microhardness as a function of secondary arms spacing for nickel alloys fabricated by AM from [137,151,152,153,154,155]. Error bars represent the standard deviation in measurements.…”

Effect of laser power on porosity and mechanical properties of GH4169 fabricated by laser melting deposition

“…The pore sizes mainly range from 3 to 30 µm in diameter, and the maximum diameter of pores is 76.6 µm. The volume of the pores is ~ 0.28% of the total volume of the as-fabricated specimens at P = 600 W, which is much higher than that of the specimen fabricated by blown powder direct layer deposition (0.095%) [18]. The porosity of P = 600 W specimens determined by 3D-XRT is much higher than that determined by OM, which might be related to the fact that 3D-XRT can detect much smaller pores close to ~ 3 μm, but hardly discriminated by OM.…”

Mechanical property heterogeneity in additively manufactured nickel superalloy

“…Extensive investigation over the last 10 years has shown that laser-based AM of nickel superalloys exhibit non-optimal microstructures and hence mechanical properties. High crystallographic texture [1][2][3], columnar grain structure [4][5][6] and intergranular defects [7] are common due to epitaxial growth. The alloy's use is also limited by high residual stresses [8,9] suboptimal aging [10] and anisotropic mechanical properties [11][12][13][14][15].…”