Better understanding of the effect of multimode‐microwave sintering of zirconia‐toughened alumina (ZTA) was investigated. A comparative dilatometric analysis was conducted between conventional and microwave heating processes, to clarify the influence of zirconia on the densification of ZTA under electromagnetic field. The thermal gradient on sample measurements indicates the change to the microwave volumetric heating is improved by zirconia which adsorbs microwave energy better, thus acting as a susceptor. The most beneficial effect on microstructure, toughness, and hardness were observed at the optimal zirconia content of 10 vol%. The results with both microwave and conventional sintering illustrate the strengthening effect on the composite by zirconia. Of special interest, multimode microwave sintering creates a finer homogeneous microstructure, with resulting hardness and toughening comparable to those obtained for conventional sintering, as well as improved densification, and at lower cost.
The objective of this investigation is to deepen the understanding of the mechanism(s) involved in densification and grain growth underlying microwave sintering of ␣-alumina. The densification behavior and microstructure evolution of ␣-alumina powders with different MgO doping levels as well as specific surface areas have been systematically and quantitatively studied during conventional and 2.45 GHz microwave multimode sintering. It is shown that the microwave-induced favorable effects on densification could be more important due to the existence of MgO dopant or a decrease of particle size. Combined with the thermodynamics and kinetics considerations, one assumed that grain-boundary diffusion could be significantly enhanced by microwave non-thermal effect. In addition, the grain growth retardation effect has been attributed to the fine porosity retention induced by microwave electromagnetic field, but not to the local over-heating at grain boundaries.
Conductive polymers represent the next generation of soft, flexible electronics. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is among the most widely used of these, despite having a relatively low conductivity when deposited in the...
International audienceSelective laser melting (SLM) is an additive manufacturing technology widely applied for direct fabrication of functional parts from metal powders. In this paper, the feasibility of the fabrication of three-dimensional cermet objects by SLM using 5-35 mu m boron carbide particles surrounded by similar to 2 mu m cobalt-based layers was explored. Microstructure, composition, porosity, compressive strength and microhardness of the fabricated object were investigated. A highly porous (37%) homogeneous structure containing grains of boron carbides with 2900-3200 HV hardness embedded in the cobalt-based matrix was obtained. It was also found that new phases were formed during SLM as a result of the interaction of B4C with the cobalt-based matrix
Nitrogen is a well-known gamma-stabiliser in austenitic steels, also responsible for significant solid solution hardening of these materials. Yet, only few papers have studied its impact on austenitic high-entropy alloy (HEA) matrixes. This study focuses on a cobalt-free, non equimolar CrFeMnNi HEA doped with nitrogen. A series of alloys was cast under a nitriding atmosphere to promote nitrogen absorption into the liquid alloy. Study of as-cast alloys has shown nitrogen presence in solid solution up to 0.3 wt. % (1.2 at. %). Over the whole range of compositions, a linear increase of hardness (134 HV/wt. % of N) was measured as well as an expansion of the lattice parameter of a/a= 1.01 / wt. % N due to nitrogen addition in the interstitial sites of the lattice. Tests on forged and annealed samples showed that the increase of hardness with nitrogen addition is higher than in as-cast state (210 HV / wt. % of N) surely due to presence of other strengthening mechanisms. Tensile tests confirmed that the presence of dissolved nitrogen increases yield strength and ultimate strength and enhances strain-hardening, without any modification of ductility.
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