Effect of milling time on structural, mechanical and tribological behavior of a newly developed Ti-Ni alloy for biomedical applications

Abstract

Ti-Ni alloy is the most attractive material in the medical field for orthopedic implants like total hip replacement due to its special properties. The purpose of this study was to examine the impact of grinding/milling times on the characteristics of the nanostructured Ti50-Ni50 alloys produced via the mechanical alloying process (MA), utilizing a planetary high-energy ball mill at different grinding times (2, 6, 12, and 18 h). The grinding time causes grain refinement and a decrease in the porosity of materials, which allows for the improvement of a material’s mechanical properties and wears resistance. The structural, physical and tribological behavior of Ti50-Ni50 alloy was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation test, and ball-on-disk tribometer operated under varying applied loads of 2, 10, and 20 N. The findings demonstrated that the crystallite size was reduced and the microstrain increased reaching values of 29 nm, and 0.99%, respectively, at higher grinding times. The percentage of porosity in the Ti50-Ni50 alloy was 11%, while the density attained was 89% after 18 h of grinding. Moreover, as the grinding duration increased up to 18 h, the hardness increased (341 HV) owing to the refinement of the grains. It was also noted that the Ti50-Ni50 alloy that was milled at 2 h exhibited the lowest elastic modulus (89 GPa). In addition, it was found that wear rates and the coefficient of friction were decreased reaching the values of 29.67 µm3/N.μm, and 0.31, respectively, for the samples milled at 18 h and examined under 2 N. Enhanced structural and mechanical qualities are responsible for this improvement in tribological properties. These properties make Ti50-Ni50 alloys clinically relevant for human biomedical implantation.