By a combination of the nanoindentation and electron probe microanalysis (EPMA) techniques,the traditional diffusion couple technique is extended to map the mechanical property of β-type Ti alloys over a wide composition range,which can be utilized to develop very versatile novel bio-Ti alloys for hard tissue replacements in artificial bones,joints,and dental implants.To create complete single-phase composition ranges of Ti-based bcc solid solution,12 types of bcc Ti-Nb-Zr-Mo/Ti-Nb-Zr-Ta quaternary diffusion couples were fabricated and annealed at 1273 K for 25 h.In this way,the composition-mechanical property relationships in the vast composition space of Ti-based alloys were established using EPMA and nanoindentation probes.Notably,the measured composition-dependent Young's moduli,hardness,and elastic recovery as well as the derived ratio of hardness to Young's modulus,and the ratio of the cube of hardness to the square of Young's modulus,in the developed compositional mechanical property database,were visualized in a five-dimensional scatter plot.This enables an effective tool to screen the Ti-Nb-Zr-based alloys for orthopedic and dental applications according to different clinical requirements,and to rationalize the fundamental mechanical relationships in the rapid development of β-Ti alloys.