Microstructure and mechanical properties of cp-titanium produced by spark plasma sintering

Titanium alloys are of great interest for several applications, but their processing and application is often difficult and expensive. Metal powder processing permits the reduction of material costs because of limited wasting, even if, sintering of titanium powders has to be carried out under controlled atmospheres, with high processing costs. Spark plasma sintering (SPS) is a new technology which permits processing of hard to sinter materials at lower temperatures and in shorter time compared to conventional technologies; furthermore, SPS can be seen as a potential near net shaping production route for non-complex components. In the present work, the use of SPS on commercial purity titanium grade 1 and grade 3 was investigated. Sintering experiments were conducted in the temperature range 700–1150°C for 5 min, under a uniaxial pressure of 60 MPa, in vacuum. Samples obtained at different temperatures were characterised in term of density, microstructure (grain size), interstitial content (C,O,N), hardness, tensile properties; SEM analysis on fracture surfaces of tensile specimen was also carried out. Results were critically discussed and correlated to sintering temperature, in respect to the typical α→β transformation temperature for each grade. Experimental data confirm that very good microstructural, chemical and mechanical properties can be attained after spark plasma sintering at temperature as low as 900°C.