Abstract
Titanium alloys and composites are of great interest for a wide variety of industrial applications; however, most of them suffer from poor tribological performance, especially at elevated temperatures. In this study, spark plasma sintering was utilized to produce a fully dense and thermodynamically stable TiB–Ti composite with a high content of ceramic phase (88 wt.%) from self-propagating high temperature synthesized (SHS) powders of commercially available Ti and B. Microstructural examination, thermodynamic assessments, and XRD analysis revealed the in situ formation of titanium borides with a relatively broad grain size distribution and elongated shapes of different aspect ratio. The composite exhibits a considerable hardness of 1550 HV30 combined with a good indentation fracture toughness of 8.2 MPa·m1/2. Dry sliding wear tests were performed at room and elevated temperature (800 °C) under 5 and 20 N sliding loads with the sliding speed of 0.1 m·s−1 and the sliding distance of 1000 m. A considerable decline in the coefficient of friction and wear rate was demonstrated at elevated temperature sliding. Apart from the protective nature of generated tribo-oxide layer, the development of lubricious boric acid on the surface of the composite was wholly responsible for this phenomenon. A high load bearing capacity of tribo-layer was demonstrated at 800 °C test.
Highlights
A concurrent decrease in combustion temperature and an in crease in pressure creates the kinetic conditions which favored the formation of spherically shaped Ti droplets/particles
A concurrent decrease in combustion temperature and an increase in pressure creates the kinetic conditions which favored the formation of spherically shaped Ti droplets/particles
Ceramic phase content of ~88 wt.% is densified by spark plasma sintering at a temperature of 1200 ◦ C with the application of 50 MPa pressure during 3 min in vacuum
Summary
Growing demand for titanium (Ti) and titanium alloys for a wide variety of industrial applications including, but not limited to, aerospace, marine, automotive, and biomedical industries have made Ti-based materials highly important. Insufficient tribological performance of many alloys has hindered even wider applications of titanium, its alloys, and Ti-based composites [1,2], especially at elevated temperatures. To fill the gap and overcome the associated limitations, several methods including surface modifications [3], hard and soft coatings deposition [4], incorporating self-lubricating mediums [5], and reinforcements inclusion [6] are continuously reported. Titanium monoboride (TiB) is one of the most used additives for Ti matrix to yield improvement in mechanical as well as tribological properties due to Ti and TiB thermodynamic and chemical stability, similar density (4.5 g/cm for Ti and 4.56 g/cm for TiB), close values of coefficient of thermal expansion
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