Influence of the Processing Method on the Properties of Ti-23 at.% Mo Alloy

Abstract

In this paper, binary β type Ti-23 at.% Mo alloys were obtained by arc melting as well as by mechanical alloying and powder metallurgical process with cold powder compaction and sintering or, interchangeably, hot pressing. The influence of the synthesis method on the microstructure and properties of bulk alloys were studied. The produced materials were characterized by an X-ray diffraction technique, scanning electron microscopy and chemical composition determination. Young’s modulus was evaluated with nanoindentation testing method based on the Oliver and Pharr approach. The mechanically alloyed Ti-23 at.% Mo powders, after inductively hot-pressed at 800 °C for 5 min, allowed the formation of single Ti(β) phase alloy. In this case, Young’s modulus and Vickers hardness were 127 GPa and 454 HV0.3, respectively. Among the examined materials, the porous (55%) single-phase scaffold showed the lowest indentation modulus (69.5 GPa). Analytical approach performed in this work focuses also on the surface properties. The estimation includes the corrosion resistance analyzed in the potentiodynamic test, and also some wettability properties as a contact angle, and surface free energy values measured in glycerol and diiodomethane testing fluids. Additionally, surface modification of processed material by micro-arc oxidation and electrophoretic deposition on the chosen samples was investigated. Proposed procedures led to the formation of apatite and fluorapatite layers, which influence both the corrosion resistance and surface wetting properties in comparison to unmodified samples. The realized research shows that a single-phase ultrafine-grained Ti-23 at.% Mo alloy for medical implant applications can be synthesized at a temperature lower than the transition point by the application of hot pressing of mechanically alloyed powders. The material processing, that includes starting powder preparation, bulk alloy transformation, and additional surface treatment functionalization, affect final properties by the obtained phase composition and internal structure.

Keywords

• material processing
• mechanical alloying
• titanium β alloys
• phase transformation
• powder metallurgy
• X-ray diffraction
• fluoroapatite coating
• corrosion resistance
• contact angle measurements