Investigating the Effects of Build Height on Mechanical Behavior of Large‐Scale Laser Wire Directed Energy Deposited Nickel Titanium Alloy

This article presents the first comprehensive investigation coupling phase transformation, mechanical properties, and tribological behavior across build height in large scale laser wire directed energy deposition (LW‐DED) fabricated NiTi alloy. A 140 × 135 × 10 mm wall is deposited to conduct location specific characterization and tribo‐mechanical testing that can reveal the phase and property heterogeneity along the build height. X‐ray diffraction quantified B2 austenite decreasing from 23 wt% at the upper region to 0 wt% at the lower region while R‐phase peaked at 45 wt% in the middle region of printed NiTi wall. Differential scanning calorimetry showed martensite start temperatures ranging from 30.20 to 34.21 °C along the build height. Tensile testing demonstrated ultimate strength variations from 412 MPa in the lower region to 578 MPa in the upper region, representing ≈40% strength increase. Reciprocating wear tests on sectioned NiTi samples against AISI 52100 counter ball revealed build height dependent wear resistance, with the upper region exhibiting higher wear volume despite similar friction coefficients. The middle region presented a balance between strength and tensile ductility with the highest R‐phase content, suggesting the crucial effects of thermal gyration during LW‐DED on tribo‐mechanical behavior in large scale NiTi components.