Sintering of nanocrystalline materials: Sintering parameters

Abstract

Nanostructured materials (NsM) are typical materials with structural length scales of one, two, or three dimensions in the range of 1-100 nm. In the development of NsM, the microstructure of a material, which is an integral factor in determining the intrinsic performance of a material, is susceptible to changes that may hinder the desired nano-state properties under different processing routes and associated varying processing parameters. NsM exhibits distinct superior properties when compared to conventional coarse-structured materials. They exhibit distinct and rapid development during production due to their unique surface area, which requires concise control measures over coarse materials. These promising excellent properties of nanocrystalline materials have caught the attention of material scientists and engineers towards their developments. In order to exploit the abundance of excellent properties of NsM, investigations on the processing-structure-property correlations have been employed in recent years to understand their complications and subsequent development of novel materials. This review aims to understand the sintering of nanomaterials, with a clear focus on the spark plasma sintering technique and its associated sintering parameters, bordering on intricate issues on densification, coarsening of particles, and grain growth.

Keywords: Grain growth; Microstructure; Nanostructured materials; Spark plasma sintering (SPS).

Fig. 1

Dimensional classifications of Nanostructured Materials.

Fig. 2

Schematic representation of Hot Isostatic Pressing.

Fig. 3

Schematic diagram representing the effect of sintering on metallic particles (i) neck formation, (ii) pore reduction in between particles as a result of continuous necking and grain boundaries, (iii) elimination of pores.

Fig. 4

Schematic diagram of spark plasma sintering system.

Fig. 5

Schematic diagram of spark plasma sintering mechanism.

Fig. 6

A schematic diagram showing a comparison between (a) spark plasma sintering (SPS) system and (b) Hybrid heating (SPS + resistance/induction heating).

Fig. 7

Effect of different calcination temperature and isothermal dwell time on the grain size distribution of YSZ nanocrystals at (a) 400 °C and (b) 1000 °C [54].

Fig. 8

SPS response of MgO nanopowders (a) Plot of relative density and grain size versus sintering temperature at 30 MPa, and (b) effect of sintering temperature on microhardness of sintered material at 30 MPa [25].