Effect of Fe content on microstructure and hardness of Ti-4.5Mo–5Al-1.8Zr-2.5Cr-1.1Sn titanium alloy based on high-throughput diffusion couple

Taking advantage of the fact that conventional solid-to-solid diffusion couples have the limited diffusion ability of elements and the diffusion ability of metal iron in liquid state is stronger than that in solid state, a novel Ti-4.5Mo–5Al-1.8Zr-2.5Cr-1.1Sn-xFe (T20C-xFe) high-throughput diffusion couple with Fe content gradient was prepared. Microstructure observations and composition analysis indicate that when Fe content is in the range of 0-5 wt%, microstructures are made up of β matrix and α laths. Besides, with the decrease of Fe content to 0 wt%, the volume fraction and the width of α laths both increase gradually, and the aspect ratio fluctuates obviously. The variation trends of these factors are explained by the proposed nucleation and growth models of α laths. Furthermore, a dimensionless parameter δ comprehensively considering the influence of the volume fraction, the length and the aspect ratio of α laths was introduced and found to determine the hardness. When Fe content decreases gradually, δ value changes in a trend like that of hardness. The peak hardness can be attributed to the highest quantity of thin short α laths in the region with Fe content of 2.78 wt%, which leads to strong effect of dislocation strengthening during deformation, thus causing the increase of hardness.