Phase Transformations in Compositionally Graded Titanium Alloys

摘要

An upcoming technology for laser deposition of full-density near-net shape components from a powder feedstock is the Laser Engineered Net Shape (LENS~(TM)) process. One of the benefits of the LENS~(TM) process is its ability to re-create a designed compositional gradient within a single component, and thus fabricate compositionally and functionally graded materials. Compositionally graded binary Ti-xV and Ti-xMo, and ternary Ti-xAl-xV alloys have been deposited using LENS~(TM). Though the phases across the graded alloys correspond to those typically observed in α/β Ti alloys, the scale and morphology of the microstructural features varies substantially with composition. In addition, the local mechanical properties in a few regions of the graded alloy have been probed using microhardness indentation. Several phase transformations, namely, β→Widmanstatten α, β→ω, and martensitic β→hexagonal α', are encountered in the graded alloy samples during LENS~(TM) deposition and post-deposition heat treatments. The ability to achieve such substantial changes in composition across rather limited lengths make such graded alloys highly attractive candidates for investigating the influence of systematic compositional changes on phase transformations and concurrent microstructural evolution in these alloys and will be discussed in detail in this paper.