Fabrication and Mechanical Characterization of Functionally Graded NiTi/HA Alloys.

In the realm of biomaterials engineering, Functionally Graded Materials (FGMs) have emerged as a novel class of composites, characterized by spatial variations in composition that yield a gradient in properties tailor-made for specific applications. This investigation delineates the development of a multi-layered FGM composed of titanium, nickel, and hydroxyapatite (NiTi/HA), designed to address the challenges associated with bone implant integration. Porous NiTi, renowned for its mechanical compatibility with bone tissue, is coupled with hydroxyapatite, a material celebrated for its osteoconductive properties, to enhance bioactivity and promote bone ingrowth. The fabrication of this NiTi/HA FGM was realized through a powder metallurgy approach, culminating in the production of specimens with either three or five stratified layers that progressively transition from NiTi-rich at one extremity to HA-rich at the other. The compaction of these powders was executed under a pressure of 450 MPa, followed by a sintering process at 1000°C sustained for a duration of three hours--parameters meticulously chosen to optimize material integrity without compromising the functional gradient. Mechanical characterization was systematically conducted, revealing that the microhardness of the FGMs ranged from 269.6 to 458.11 kg/mm² and 365.5 to 436.5 kg/mm² for the three-layered and five-layered specimens, respectively. The density and porosity of these materials were also quantified, with the three-layered FGM (FGM1) exhibiting an apparent density of 2.665 g/cm³ and a porosity of 33.5%, while the five-layered FGM (FGM2) displayed an increased density of 3.754 g/cm³ and a reduced porosity of 24.6%. X-ray diffraction analysis verified the phase composition of the graded specimens, confirming the presence of the anticipated monoclinic NiTi, cubic NiTi, and hexagonal Ni3Ti phases, integral to the material's function. The synergistic combination of the robust mechanical properties of the NiTi alloy with the superior bioactivity of hydroxyapatite underscores the potential of this FGM NiTi/HA for hard tissue implant applications, offering a promising avenue for the advancement of orthopedic treatments. [ABSTRACT FROM AUTHOR]