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Quench-Hardening and Mechanical Properties of Ni-Rich TiNi Compounds

1970; Japan Institute of Metals and Materials; Volume: 34; Issue: 3 Linguagem: Inglês

10.2320/jinstmet1952.34.3_337

1880-6880

Toshiyuki Suzuki,

Corrosion Behavior and Inhibition

The relation between the Ni content and the hardening capability of Ni-rich TiNi compounds, and the effect of heat treatment on the mechanical properties of a TiNi compound containing 54.7 at%Ni have been investigated. TiNi compounds containing more than 52 at%Ni show a considerable increase in hardness by quenching, and the maximum hardness is attained at about 54.5 at%Ni. According to the phase diagrams which are considered to be most reliable, the composition from which the hardening effect appears corresponds to the composition of the boundary between the TiNi phase and the TiNi+TiNi3 phase at lower temperatures and the composition at which the maximum value of hardness is obtained coincides with the composition of the same boundary at quenching temperature. This fact seems to suggest that the hardening capability in the Ni-rich TiNi compound is related to the existence of excess point defects which are introduced by deviation from the stoichiometric TiNi composition at the quenching temperature. The TiNi compound containing 54.7 at%Ni is hardened by quenching from temperatures above 600°C, and the hardness increases with increasing temperature. When the TiNi is quenched from 1100°C into water, the Vickers hardness of about 700 is obtained. The hardness of the quench-hardened TiNi decreases with annealing time. However, no hardening effect due to the precipitation of TiNi3 is observed. The tensile strength of the TiNi is 80 kg/mm2 in the annealed state and 100 kg/mm2 when annealed at a relatively high temperature after quenching. Although the Young’s modulus of the TiNi in the annealing state is anomalously low as compared with the values of the constituent metals, quenching from 1000°C gives a nearly 25% increase of the value.