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e use and application of b titanium alloys as biomedical alloys have increased over the past few years owing to their excellent biocompatibility, corrosion resistance, high mechanical and fatigue resistance, low density, adequate wear resistance, and low elastic modulus.[1,2] Ti-13Nb-13Zr (TNZ) is one such alloy that exhibits all the aforementioned properties.[3,4] Tribological behavior is a major factor in the acceptance of a material for bio-implants. Studies performed by Rack on TNZT, B-21SRX, and Ti-64 ELI (extralow interstitial) showed that post-wear testing and extensive plastic deformation, along with micro-plowing and micro-cracking, were observed perpendicular to the sliding direction.[5] Niinomi studied efforts to increase wear resistance via heat treatments, which had little effect on wear properties.[6] Adding hard secondary phases, such as boride reinforcements, in the Ti matrix has raised considerable interest. Boron, unlike other interstitial elements such as oxygen and hydrogen, is

S.A. MANTRI, T. TORGERSON, T.W. SCHARF, and R. BANERJEE are with the Department of Materials Science and Engineering, University of North Texas, Denton, TX 76207. Contact e-mail: [email protected] E. IVANOV is with the Tosoh SMD Inc, Grove City, OH 43123. Manuscript submitted September 5, 2017.

METALLURGICAL AND MATERIALS TRANSACTIONS A

almost insoluble in titanium in the solid state and, thus, does not embrittle the lattice.[7] Studies have demonstrated that micro-B additions to the conventional a + b Ti alloys (Ti64 and Ti6242S) produced dramatic (by a factor of 10) grain refinement in the as-cast condition.[8,9] The small additions have also been shown to improve the mechanical behavior of these alloys[10] and consequently enhancing their wear resistance.[11] The recent developments in various additive manufacturing techniques have led to an increased interest in the manufacturing of these biomedical alloys via 3D printing.[12,13] While most of the work in the reported literature is focused on cast alloys for the biomedical applications, there are rather limited investigations on the mechanical hardness and sliding wear properties and their mechanisms of additively manufactured biomedical alloys.[14] The addition of small amounts of boron to control the texture and grain growth has been studied previously,[15,16] but the studies did not provide any information regarding the effect of boron on the mechanical behavior and wear properties. The rapid heating and cooling rates associated with AM processes has a pronounced effect on the microstructure of the materials and the resulting mechanical and wear behavior. As such, in the present study, TNZ and TNZ-0.5B alloys with less b-stabilizers than previously studied TNZT alloy were additively manufactured to study the influence of boron addition to mechanical properties and wear resistance. Ti-13Nb-13Zr and Ti-13Nb-13Zr-0.5B (in wt pct) were deposited using the laser-engineered net shaping (LENS) process from a feedstock consisting of pre-alloyed TNZ powders provided by TOSOH