Additive manufacturing of in-situ gas-alloyed functionally-graded titanium

Titanium and its alloys are known to have inadequate tribological properties excluding these alloys from applications involving interacting surfaces. Introducing a method to improve titanium's surface hardness will extend the opportunity to use titanium for applications involving wear surfaces. Additive manufacturing of grade 5 titanium with functionally-graded hardness is demonstrated via in-situ gas alloying. To achieve this, argon:nitrogen mixtures are selectively introduced during a laser directed energy deposition process. Control of the concentration and means of nitrogen introduction is found to effect nitrogen uptake, microstructure, resulting hardness, and propensity for cracking. A functionally-graded titanium structure with surface hardness exceeding 600 HV0.3 and without any instances of cracking was produced. Process-structure-property relationships of in-situ, gas-alloyed titanium are analyzed to investigate the limitations of the technology and identify applications.