The reciprocating wear behaviour of TiC–304L stainless steel composites prepared by melt infiltration

The direct synthesis of TiC and (Ti, W)C in liquid nickel or iron in an electric arc furnace has been studied. The synthesis of carbides in solvent metals proceeds differently from self-propagating high temperature rate synthesis. The solvent metal constitutes the matrix in which the carbides are embedded after the solidification of the melt. Molten metal promotes the dissolution of carbon, titanium and also tungsten and leads to their complete reaction to form carbides with a high level of combined carbon. The combined carbon within carbides as well as the chemistry of the metal matrix, evaluated by X-ray diffraction analysis and microhardness measurements, depends upon the carbon-to-titanium atomic ratio of reagents. Even though the synthesis of composites containing 40–80 vol.% has been successfully achieved, the 60 vol.% carbide composite seems to be more adapted for further development because of its microstructure. It is composed of fine, rounded and well-dispersed crystals in a nickel or iron matrix. Crystalline carbon as graphite is preferred to carbon black because it leads to dense composites. To adapt the direct synthesis of carbides in solvent metals so as to obtain composite plasma-sprayed coatings, it is, however, necessary to compensate for carbon loss.

Synthesis of TiC and (Ti, W)C in solvent metals

TiC-(Ti,M)C core-rim structures in solid-state manufactured steel-based MMCs

The original abstract from thesis is below. Ceramic metal composites, or cermets, currently have widespread applications in the chemical, automotive and oil and gas sectors, due to their combination of high wear resistance, and aqueous corrosion resistance. In the present study, a family of novel titanium carbide (TiC)-stainless steel cermets has been produced as potential materials for use as erosion and corrosion resistant materials. The development of the TiC-stainless steel cermets is based on a simple melt infiltration technique, with the stainless steel “binder” contents varied from 5 to 30 vol.%, using the austenitic grades 304L and 316L, and the martensitic grade 410L. These materials have subsequently been evaluated for their wear and corrosion response, as well as characterisation of their basic mechanical properties and microstructure.
Reciprocating wear tests involved a ball-on-flat geometry (using a WC-Co counter face sphere), with loads varied from 20 to 80 N, for up to 120 minutes. The wear tracks were assessed using a high-resolution optical profilometer, in order to determine the wear volume. The specific wear rate of the cermets was found to increase with both the applied load and the steel binder content. To investigate the morphology of worn surfaces, scanning electron microscopy (SEM), and associated energy dispersive x-ray spectroscopy (EDS) were used, in order to fully understand the operative wear mechanisms. A transition from two- to three-body abrasive wear was observed, together with the formation of a oxygen-rich tribolayer, indicating that adhesive wear was also occurring on the cermets.
In order to assess the electrochemical behaviour of the cermets in a simulated seawater environment, the samples were evaluated using potentiodynamic, cyclic and potentiostatic polarisation tests, with basic corrosion parameters and rates subsequently determined through Tafel extrapolation and weight loss measurement. Each stage of electrochemical assessment was then evaluated by characterising the corroded surfaces and solution using SEM, EDS and inductively coupled plasma optical emission spectrometry. Microstructural observations using SEM images revealed significant degradation of the samples, with steel binder preferentially dissolved while TiC remained relatively unaffected. The corrosion rate of the cermets increases with steel binder content, which is attributed to the preferential dissolution of the binder.

Assessment of the wear and corrosion behaviour of titanium carbide-stainless steel composites

SUMMARY

A new technique for preparing electron-transparent specimens of hard particle powders is described. It consists of mechanically embedding the powder into a thin foil of soft metal followed by ion-beam etching. This has numerous advantages over other methods of examining powders, such as their direct examination when supported by a carbon film, or by using epoxy resin as an embedding medium. The metal foil can be chosen to minimize overlap of the spectrographic peaks of the metal and the hard particles.

Preparation of hard particle powders for examination in the transmission electron microscope

The development of microstructure during processing of WC, (W, Ti)C, and TiC carbides alloyed with 0–15 wt-% Co has been examined. Changes that occur in carbide and carbide-cobalt powder characteri...

B. Roebuck

Papers

Characterization of Powders and Dislocation Structures in Processing of WC–Co, (W, Ti)C–Co, and TiC–Co Hardmetals