Interface dynamic behavior between individual carbon nanotubes (CNTs) and tungsten (W) electrodes is observed directly at a nearly atomic resolution. The W tip-end absorbs the source CNT atoms, which then penetrate deep into its body, form a carbide, and finally precipitate as freshly formed graphitic tubular shells encapsulating the electrode. CNT wall-thickness shaping via stepwise absorption of the nanotube core shells into a W electrode is demonstrated for the first time. This work provides novel one-dimensional CNT-carbide-metal heterojunctions, as well as new and detailed understanding of the CNT catalytic growth.