The TMS symposium on ‘Novel Synthesis and Consolidation of Powder Materials' was held from 16 to 19 March 2015 in Orlando, Florida, USA as part of the TMS 144th Annual Meeting & Exhibition. The symposium attracted 57 oral presentations covering a variety of topics in powder synthesis and consolidation. The eight papers selected in this collection highlight eight different topics discussed at the symposium. All contributions were subjected to thorough peer reviews.
In the first article, Kumar and co-workers discuss a ‘Geometric model of sintering of unequal sized particles’. Most geometric models of sintering assume equal-sized particles. Such an assumption neglects coarsening by inter-particle mass transport and grain boundary migration. In this contribution, the authors formulated a geometric model to quantitatively describe the sintering process of powders with unequal sized particles. It is shown that the model is informative to predict the sintering process of unequal sized particles.
The second article, ‘Ni-base superalloy powder processed porous layer for gas cooling in extreme environments’, deals with the use of Ni-base superalloy materials as porous coatings for advanced airfoil cooling applications at temperatures which are at or exceeding current material limits (e.g. up to 1800°C). Two Ni-base superalloy composition powders were produced for this purpose using high pressure gas atomization. A partial sintering method was developed to form a thin Ni-base superalloy porous layer with controlled porosity in order to allow full-surface, transpirational cooling of the surfaces of airfoils. The characteristics of the porous layers were studied in detail.
In the third article, the authors present a systematic study of ‘Powder metallurgy hollow fly ash cenospheres particles reinforced magnesium composites’. Fly ash cenospheres are available in a wide range of size from nanometre to several millimetres and its incorporation into Mg matrix facilitates interfacial reactions to result in a complex microstructure. This study shows that hollow fly-ash cenosphere particles reinforced magnesium composites have the potential to be used as a new class of lightweight materials.
The fourth article is concerned with the ‘Microstructure and electrical properties of SiC dispersed molybdenum silicide composite’. Bulk molybdenum silicide composite samples with uniformly dispersed β-SiC particles were produced by pressureless sintering of core-shell (SiC-Mo) composite powder compacts at 1400 °C for 10 h. The as-sintered composite samples achieved a relative density of 96.1% and displayed much improved electrical resistivity. The SiC-Mo core-shell composite powder consists of a β-SiC core enveloped by a layer of fine Mo particles (smaller than 200 nm) as the shell.
The fifth article by Wang et al. discusses the ‘Effect of sintering conditions on mechanical strength and gas permeability of long porous Inconel 625 tubes for hot gas filtration’. The authors studied the sintering responses of Inconel 625 powder (80-180 μm) in two different atmospheres. On this basis, long porous Inconel 625 tubes (F54 mm ×1000 mm) shaped by cold isostatic pressing were successfully sintered in hydrogen. The as-sintered porous Inconel 625 tubes demonstrated an outstanding performance over six months of continuous industrial operations in the filtration of SiHCl3-HCl gas mixtures at temperatures up to 400 ºC.
In the sixth article, Nguyen and co-workers investigated the properties of powder metallurgy (PM) magnesium composites reinforced with metastable Al90Y10 powder particles. The authors showed that amorphous Al90Y10, which has a glass transition temperature of about 475°C, can be an attractive reinforcement for magnesium matrix.
The seventh article, ‘Strengthening behaviour and mechanisms of extruded powder metallurgy Ti materials reinforced with ubiquitous light elements’, reports an innovative development in the fabrication of low-cost high-performance PM Ti materials. The authors showed that as-extruded powder metallurgy Ti-0.97O-0.11H (wt.%) alloy exhibited an ultimate tensile strength of 1158 MPa, a yield strength (0.2%) of 990 MPa, and a tensile elongation percentage of 23.9%. These properties are clearly better than those of the mill-annealed Ti-6Al-4V.
The eighth and final article in this collection discusses the ‘Effect of initial state on dispersion evolution of carbon nanotubes in aluminium matrix composites during high energy ball milling process’. The authors recently fabricated strong and ductile carbon nanotubes (CNTs) reinforced aluminium matrix composites by powder metallurgy routes. In this study, they showed how the dispersion of CNTs evolved in different fabrication processes. The results provide new insights into future design of high-strength CNTs reinforced powder metallurgy Al composites.