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

Cemented carbides cover a wide range of applications in many relevant industries, i.e. as cutting tools (turning, milling, drilling) for machining of metal components in the automotive and/or aerospace industry, as components of drill bits or road headers in the rock tools and mining area or as wear parts in wire drawing dies or punch tools. In this review selected cemented carbide and cermet microstructures are presented. The focus is on microstructures, both those that are already established in the cemented carbide industry and those which have drawn scientific attention due to new potential applications. Cemented carbides are here divided in four groups based on microstructure and chemistry: WC morphology and chemistry, cubic carbide containing cemented carbide and cermets, functionally graded cemented carbides, and binder design of cemented carbides. Furthermore, this review covers some historical background that motivated the microstructure design as well as the status of each class of materials nowadays. The paper aims at categorising cemented carbides in a structured way and to serve as an introduction to cemented carbide microstructures for engineers, researchers and scientists.

Cemented carbide microstructures: a review

The intention of this paper is to give an overview of selected RD high resolution microscopy and electron backscatter diffraction. Amongst emerging trends, coupling between experiments and modelling at different scales is growing, as well as three dimensional modelling of microstructure evolution. Trends are discussed and an outlook for future development in the respective fields is given.

Trends in the P/M hard metal industry

Using pulsed current activated sintering method, the densification of binderless WC and WC–xwt.%Co (x = 8, 10, 12) hard materials were accomplished using ultra fine powder of WC and WC–Co. Nearly fully dense WC and WC–Co with a relative density of up to 99.2% could be obtained with simultaneous application of 60 MPa pressure and electric current within 2 min without significant change in grain size. The average grain sizes of WC produced by PCAS were about 380 nm. The hardness and fracture toughness of the dense WC and WC–Co composites produced by PCAS were investigated.

Consolidation of ultra fine WC and WC–Co hard materials by pulsed current activated sintering and its mechanical properties

Sintering behavior and mechanical properties of WC-10Co, WC-10Ni and WC-10Fe hard materials produced by high-frequency induction heated sintering

A study has been made of the shape development of WC crystals in cemented carbides during liquid phase sintering. The relative influence of shape relaxation and carbide crystal growth processes on the shape is discussed. An effect of titanium additions on the shape of WC crystals in WC–Ni cemented carbides was observed. A shape parameter referred to as shape equiaxiality has been defined and calculated theoretically for various triangular prisms. The observed change of shape equiaxiality with titanium concentration in the binder phase of WC–Ni cemented carbides is discussed in terms of titanium segregation at the interphase boundary.

I.V. Shatova

Papers

The shape of WC crystals in cemented carbides