Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Review: liquid phase sintering

The Wettability of Solids by Liquid Metals

Cemented carbides are, from a technical point of view, one of the most successful composite materials. The physical and chemical aspects of the components (transition-metal carbides and iron-group metals) and of their interaction in hardmetals are reviewed with emphasis on the materials science point of view focusing on those compositions which have gained technical interest. Crystal structures and phase relationships are discussed in detail. The interaction of components (wetting, residual stresses) and some microstructural aspects (size, contiguity, and shape) are treated also. These fundamentals are the basis of understanding the production processes and the properties of cemented carbides.

Physical and chemical nature of cemented carbides

Binder Jet printing is an additive manufacturing technique that dispenses liquid binding agent on powder to form a two-dimensional pattern on a layer. The layers are stacked to build a physical article. Binder Jetting (BJ) can be adapted to almost any powder with high production rates and the BJ process utilizes a broad range of technologies including printing tehniques, powder deposition, dynamic binder/powder interaction, and post-processing methods. A wide variety of materials including polymers, metals, and ceramics have been processed successfully with Binder Jet. However, developing printing and post-processing methods that maximize part performance is a remaining challenge. This article presents a broad review of technologies and approaches that have been applied in Binder Jet printing and points towards opportunities for future advancement.

Binder jetting: A review of process, materials, and methods

The effects of alloying additions on the wetting of two types of carbon, HX30 graphite and vitreous carbon, have been investigated, with a view to developing a system for metal impregnation of carbon fibre assemblies. Pure copper is inert and non-wetting but two additions caused the copper to wet: Cr on both substrates and V on the vitreous carbon only. Many of the additions formed a carbide reaction layer at the interface, and in the two wetting systems this was a thin, continuous, coherent layer. The data have been analysed in terms of the chemical and physical properties of the system and it was found that the wetting behaviour of copper alloys on HX30 graphite and vitreous carbon could be explained in terms of the behaviour of the reaction product carbides of the alloying addition when these existed.

The wetting of carbon by copper and copper alloys

The microstructure of tungsten carbide and titanium carbide base cermets has been evaluated on the basis of wettability of the carbide phase. Incomplete wetting was found to result in a coalescence of the carbide phase leading to an apparent increase in the carbide particle size. Improvement in the wettability of the nickel-titanium carbide systems by the addition of molybdenum was found to promote the dispersion of the carbide phase and to lead to improved hardness and impact resistance.

Michael Humenik

Papers

Cermets: I, Fundamental Concepts Related to Micro‐structure and Physical Properties of Cermet Systems