Processing of Interpenetrating Mg-Tini Composites by Spark Plasma Sintering

Abstract

Mg/Ti(49)ANi(50.6) interpenetrating composites have been produced via spark plasma sintering technique. Interpenetrating matrix and the reinforcement networks were formed simply by adjustment of the particle sizes of the starting pure Mg and TiNi alloy powders. Microstructural characterization revealed a good interfacial bonding, i.e. free from porosity, oxide and intermetallic compounds, between Mg matrix and the reinforcement. It has been found that, the microstructure of TiNi shape memory alloy reinforcement material is highly sensitive to processing conditions especially to sintering time. Different sintering times resulted in different phase formations and accordingly different phase transformation temperatures due to the overlap of sintering temperature with aging temperature. Room temperature yield and compressive strength of the composite samples were in the range of 53-113 MPa and 226-315 MPa respectively, depending on the reinforcement content (10-30 vol%) and the texture formation during processing. Ductility of the composites on the other hand was in the range of 9.6-20%. 30% TiNi addition resulted in minimum ductility, whereas composite samples with 20% TiNi reinforcement exhibited the maximum ductility values. Mg/TiNi composites displayed extraordinary mechanical properties at high temperatures. Yield strength and elastic modulus of the composites increased with increasing temperature up to 150 degrees C due to the increase of transformation stress and the elastic modulus of TiNi shape memory reinforcements with increasing temperature. Beyond 150 degrees C both properties decreased with further temperature increase. TiNi alloys seem to be promising candidates for reinforcement of pure Mg and Mg alloys to be used in automotive powertrain applications. Composites produced with 20% and 30% TiNi content meet the high strength and elastic modulus requirements at the service conditions of 150-200 degrees C and the stress levels of 50-70 MPa. (C) 2014 Elsevier B.V. All rights reserved.