Influence of Processing Routes on the Micro-mechanical behavior of alpha’-martensite in Ti-6Al-4V alloy

In this work, the micro-mechanical behavior of alpha’ martensite obtained from different manufacturing conditions is studied. One sample obtained from Direct Metal Deposition (DMD) process is compared to two other heat treated (HT) samples. The DMD sample manufactured with a low incident energy exhibits a martensitic matrix within wavy columnar grains (Fig. 1). The two HT samples exhibit fully martensite structure within equiaxed grains obtained after 30’ of solution treated annealing at 1000°C and 1050°C respectively, followed by water
quenching.
The micro-mechanical behavior is obtained while carrying out hardness tests at different scales. Each scale level (macro, meso, micro or nano) highlights related local contributions (prior grain size, martensite lath, lath joint, dislocations or crystal orientation).
The complete characterization of HT samples serves as a basis for comparison with equivalent results obtained on the DMD sample. The indentation size effect is established.
Difference between HT and DMD samples are discussed thus highlighting the effects of both process and metallurgical features on the hardness. This work is useful not only to better understand the micro-mechanical behavior of martensite, but it can also serve as a reference for setting thermo-kinetics models describing microstructure evolution under Additive manufacturing processing.