Crystallographic, microstructure and mechanical characteristics of dynamically processed IN718 superalloy A.D. Sharma a,⇑ , A.K. Sharma b , N. Thakur a a Department of Physics, Himachal Pradesh University, Shimla 171005, India b Terminal Ballistics Research Laboratory, Chandigarh 160030, India article info Article history: Received 2 April 2013 Received in revised form 15 January 2014 Accepted 3 February 2014 Available online 12 February 2014 Keywords: Metals and alloys Rapid-solidification Crystal structure Mechanical properties Scanning electron microscopy abstract Dynamic consolidation of IN718 superalloy powder without grain-growth and negligible density gradient is accomplished through explosively generated shock wave loading. The compaction of powder and mea- surement of detonation velocity are achieved successfully in a single-shot experiment by employing instrumented detonics. A plastic explosive having a detonation velocity of the order of 7.1 km/s in a direct proximity with superalloy powder is used for the consolidation process. The compacted specimens are examined for structural, microstructure and mechanical characteristics. X-ray diffraction (XRD) study suggests intact crystalline structure of the compacts. A small micro-strain (0.26%) is observed by using Williamson–Hall method. Wavelength dispersive spectroscopy indicates no segregation within the shock processed superalloy compacted specimens. The monoliths investigated for fractography by using field emission scanning electron microscopy (FE-SEM) show original dendritic structure accompanied by re- solidified molten regions across the interparticle boundaries. Depth-sensing indentations (at 1.96 N) on compacted specimens show excellent micro-hardness of the order of (470 ± 3)H v . Tensile and compres- sive strengths of the superalloy monolith are observed to be 806 and 822 MPa, respectively. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction IN718 is a Ni-based superalloy, whose structural components are widely used in aerospace industry, cryogenic storage, gas- turbines, jet-engines, nuclear reactors etc.; due to its very high temperature/corrosion resistant properties and good structural stability [1–3]. Superalloys are readily available in powder state and therefore need to be consolidated for their use. Densification of such powders inexorably causes many difficulties when consol- idated by using conventional metallurgical processes such as hydraulic or hot/cold isostatic pressing techniques. Typical chal- lenges encountered are long processing time, lack of ability to break down the surface oxide layers, distortion of microstructures and grain-growth that could degrade the unique materials proper- ties [4–7]. Shock wave consolidation is an excellent alternative approach to achieve consolidation of such superalloy powders due to its sin- gle-stage processing, easily implementation and the scale-up advantage. This technique is gaining particular interest of material scientists and engineers because under favorable circumstances the particulate material gets compacted by a thin layer of meted re-solidified regions across the particle boundaries, without seri- ous degradation in material properties. It produces quasi-adiabatic heating on the surface of particles without exposing redundant heat into the particles, consequently maintains relatively cool tem- perature at the particle cores [8–14]. Dynamic shock-loading being transient (micro-seconds) phenomenon offers no time for the grain-growth. Moreover, this technique requires no additional bin- der for the compaction. The unique feature of explosive shock wave loading in direct proximity with powder is its controlled detonation pressure, which traverse through the powder and causes interparticle friction, void collapse and deformations resulting into mechanical interlocking between the particles. Extensive efforts were made by various research workers in explosive consolidation of rapidly-solidified powders, particularly, on compaction phenomena, critical explosive parameters and microstructure of resulting monoliths [15–25]. Nevertheless, the information on crystallographic/dendritic structure, particle size/ grain-variation, hardness and mechanical strengths of the com- pacted superalloy monoliths, remains a major concern for the materials scientists working in this field. In the present work, imperative information is reported on crystallographic parameters such as phase/structure and lattice constants, micro-strain, grain- size, chemical segregation, tensile/compressive strengths, micro- hardness and micro-structural/morphological characteristics of http://dx.doi.org/10.1016/j.jallcom.2014.02.011 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 9 418 114422; fax: +91 1 772 830775. E-mail address: ads.hpu@gmail.com (A.D. Sharma). Journal of Alloys and Compounds 597 (2014) 175–180 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom