Effect of post processing on the creep performance of laser powder bed fused Inconel 718

In this study, the creep performance of laser powder bed fusion manufactured Inconel 718 specimens is studied in detail and compared with conventional hot-rolled specimens alongside as-built then heat-treated and as-built then hot-isostatic pressed specimens. Hot-rolled specimens showed the best creep resistance, while the hot-isostatic pressed specimens yielded the worst performance, inferior to the as-built condition. Creep testing of all samples showed increased secondary creep rate was consistently correlated with a reduced life. Fractography revealed intergranular fracture was the primary failure mode for all as-built samples. Preferential intergranular precipitation in the case of the hot-isostatic pressed specimens during hot-isostatic pressing extensive intergranular cracking as the primary failure mechanism. Heat-treated specimens possessed only sparse intergranular precipitates, thereby explaining an improved creep lifetime. The hot-rolled specimens, having smallest grain size, showed the least extensive cracking, particularly in locations of finest grains, explaining avoidance of intergranular fracture as a key creep mechanism, thereby explaining the ductile creep fracture surfaces in the case of the hot-rolled samples

Electrolyte jet machining for surface texturing of Inconel 718

Electrolyte jet machining is an emerging non-conventional machining process which is capable of selectively applying multi-scale surface textures. Surfaces processed in this way do not suffer from thermal damage and hence this technique is highly suited to finishing procedures in high value manufacturing across the aerospace and biomedical sectors. Furthermore, input variables can be modified dynamically to create functional graduation across component surfaces. In this study, the development and design of a custom-built EJM system is described, and the capability of the EJM platform to machine and create surface textures in Inconel 718, a widely used nickel based super alloy, is investigated. Through control of machine path programming and parameter variation, multi-scale surface textures are created which have the potential to enhance bonding with subsequent coating layers and also provide fluid dynamic advantage

Spheroidisation of metal powder by pulsed electron beam irradiation

A new powder spheroidisation process has been demonstrated using a large-area, pulsed electron beam technique. This was used to dramatically improve the surface morphology of Stellite 6 metal powder. Powder surface asperities up to 20 μm size can be eliminated by melting and incorporation into the near-surface of the particle. Surface finish is significantly improved. Agitation and rotation of particles due to a beam-induced stress wave enables the irradiation of multiples sides of particles, resulting in uniformly smoothed particles after sufficient pulses. Elemental analysis revealed no measurable contamination as a result of the process. Transmission electron microscopy showed a dense layer is produced within a zone up to 3 μm beneath the surface, with a substantially reduced grain size from ca. 2 μm diameter in the bulk to ca. 40 nm. Elemental homogenisation also was accompanied by grain refinement. The irradiated Stellite 6 showed a reduced basic flowability energy (583 mJ compared to 627 mJ for the untreated), explained by reduced particle-particle cohesion and interlocking, and an increased conditioned bulk density of 4.57 g/ml compared to 4.33 g/ml due to satellite/asperity reduction

Erosion resistance of laser clad Ti-6Al-4V/WC composite for waterjet tooling

AbstractIn waterjet operations, milled surfaces are left with some undesirable dimensional artefacts, thus the use of abrasion resistant mask has been proposed to improve the surface quality of machined components. In this study, the erosion performance of laser clad Ti-6Al-4V/WC composite coating subjected to plain water jet (PWJ) and abrasive water jet (AWJ) impacts to evaluate its potentials for use as waterjet impact resistant mask material and coating on components was investigated. Results showed that composite with 76wt.% WC composition subjected to PWJ and AWJ impacts offered resistance to erosion up to 13 and 8 times that of wrought Ti-6Al-4V respectively. Scanning electron microscopy (SEM) examination of the eroded composite surfaces showed that the erosion mechanism under PWJ impacts is based on the formation of erosion pits, tunnels and deep cavities especially in the interface between the WC particles and the composite matrix owing to lateral outflow jetting and hydraulic penetration. Composite suffered ploughing of the composite matrix, lateral cracking and chipping of embedded WC particles and WC pull-out under AWJ impacts. The composite performance is attributed to the embedded WC particles and the uniformly distributed nano-sized reaction products (TiC and W) reinforcing the ductile β-Ti composite matrix, with its mean hardness enhanced to 6.1GPa. The capability of the Ti-6Al-4V/WC composite coating was demonstrated by effective replication of a pattern on a composite mask to an aluminium plate subjected to selective milling by PWJ with an overall depth of 344μm. Thus, composite cladding for tooling purpose would make it possible to enhance the lifetime of jigs and fixtures and promote rapid machining using the water jet technique

Formation mechanism of electrical discharge TiC-Fe composite coatings

Comparison of electric discharge (ED) processed single deposit and continuum TiC-Fe cermet coatings, formed from a sacrificial powder metallurgy TiC tool electrode at negative polarity, on 304 stainless steel, provided insight into the ED coating (EDC) formation mechanism. A deposit from a single spark event was dominated by TiC, phase separated from a ∼2 wt% Fe matrix, with strongly aligned grains and banded microstructure, indicative of solidification from the coating/substrate interface. Conversely, a continuum coating, subjected to ∼200 spark events per location, exhibited a more complex, banded microstructure, with a mixture of equiaxed and columnar TiC grains within a ∼30 wt% Fe-based matrix, along with some concentrations of carbon from the oil dielectric. It is considered that each sparking event remelts previously solidified coating material, with or without further TiC particle incorporation, leading to gradual TiC dilution and the development of a TiC-Fe composite coating with increasing levels of substrate material forming the matrix

Soluble abrasives for waterjet machining

© 2014 Taylor & Francis Group, LLC. The addition of hard abrasives to the jet in waterjet machining can improve machining rate, however, embedding of particles in machined surfaces is a limitation, which results in reduced fatigue life, and limits the application of well adhered subsequent coatings to the surface. In this study, softer soluble abrasives were investigated as a potential solution. Soluble abrasives yielded a higher material removal rate compared to plain waterjet, although were not as effective as traditional hard abrasives. Soluble abrasives reduced grit embedment on all four workpiece materials. A post-machining surface cleaning operation demonstrated that any remaining soluble abrasive could be removed

Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation

In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr. vol. 98), the main features of the motion of the pair Enceladus-Dione were analyzed in the frozen regime, i.e., without considering the tidal evolution. Here, the results of a great deal of numerical simulations of a pair of satellites similar to Enceladus and Dione crossing the 2:1 mean-motion resonance are shown. The resonance crossing is modeled with a linear tidal theory, considering a two-degrees-of-freedom model written in the framework of the general three-body planar problem. The main regimes of motion of the system during the passage through resonance are studied in detail. We discuss our results comparing them with classical scenarios of tidal evolution of the system. We show new scenarios of evolution of the Enceladus-Dione system through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical Astronom

Reconstruction methods — P‾ANDA focussing-light guide disc DIRC

The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the P‾ANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the P‾ANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development