Localized pore evolution assisted densification during spark plasma sintering of nanocrystalline W-5wt.%Mo alloy

Abstract

The present work reports the role of different atomic mobility induced localized pore evolution on densification during spark plasma sintering of nanocrystalline W-Mo alloy powder. The shrinkage (or expansion) behavior of cold compacted milled powders was studied using dilatometry during non-isothermal sintering up to 1600 °C. Subsequently, the milled powders were densified to ~95% relative density using spark plasma sintering up to 1600 °C. The enhanced localized Joule heating due to dynamically evolved porous structure could be attributed for the densification during spark plasma sintering.Spark plasma sintering (SPS) has shown a great promise over the last few decades due to several advantages than the conventional sintering processes, such as densifying variety of materials to fully dense structure at a lower temperature in a short duration of time with a possibility of retaining the fine grain structure [1][2][3]. These benefits are primarily attributed to localized heating mechanism [4,5]. However, localized heating mechanisms are highly dependent on the nature of contact between the particles in due course of sintering process of conductive materials. It has been established that the localized heating and electrosintering mechanisms will be highest and largely contributing at the initial stages of sintering (with more point contacts and higher current) and gradually decreases with time [6,7]. The nature

Microstructure evolution and densification during spark plasma sintering of nanocrystalline W-5wt.%Ta alloy

“…Almost similar grain sizes, irrespective of the densification process, suggests the same origin of microstructural stability during the sintering process. It is worth noting here that the pure W processed under similar conditions results in grain sizes almost 6.5 times bigger than in the present case [23].…”

“…The pronounced expansion can be well understood in view of a Kirkendall effect arising from the different atomic mobilities of W and Ta as reported by Lenz and Riley [19]. The Kirkendall porosity might play a major role in the early expansion of W-Ta, followed by a sudden drop as shrinkage caused by enhanced interdiffusion at higher temperatures and aided by alloying where the Kirkendall effect plays its role in a positive way [20,23]. Almost similar grain sizes, irrespective of the densification process, suggests the same origin of microstructural stability during the sintering process.…”

“…X-ray diffraction profile of mechanically milled W-5wt.%Ta alloy powder was collected using an X'Pert Pro (PANalytical, The Netherlands) X-ray diffractometer with Cu-Kα radiation in the 2θ range 10-140° using 0.02° step size with a 30 s time per step. A lineprofile analysis [23][24][25][26] was used for profile fitting using the pseudo-Voigt function in High Score Plus software (version 3.0e). Furthermore, the full width at half-maximum (FWHM) and the shape parameter (η) from the fitted profile were used as input parameters for the double-Voigt analysis [27,28] using the BREADTH programme (version 4) [29] for the quantification of crystallite size and root-mean-square strain (RMSS) in the milled powder sample.…”

“…The process can facilitate a high degree of densification at the lowest temperatures and for shorter periods with better grain refinement [21,22]. Moreover, Srivastav et al [23] has shown that localised diffusion-couple-induced pore evolution could be advantageous for densifying such materials by adopting the SPS process on account of the inherent localised heating mechanisms.…”

Microstructure and mechanical properties of W-10 wt-%Ta alloys prepared by spark plasma sintering

“…Many studies have focused on the densification mechanism of binary sintering of tungsten materials. W-5 wt-%Mo alloy was prepared by high-energy ball milling and SPS [35]. In this method, the heating rate was 100°C min −1 , the sintering temperature was 1600°C, and the temperature was directly cooled to room temperature.…”