Crack Healing Of Ti₂SnC In Vacuum Environment

Crack healing ceramics will lead to improving device reliability, prolonging service life, and decreasing replacement and maintenance costs. The main mechanism of the crack healing in ceramics is the filling of cracks by the formation of oxides in higher temperature and oxidizing environments, achieving partial and/or complete recovery of the performance of materials. However, it is a challenge to heal ceramic materials in vacuum environments where the amount of oxygen is little. So far no report on such challenging work has been found.The aim of the present study is to investigate the crack healing behavior of Ti2SnC in vacuum. Surface cracks were introduced in Ti2SnC by water quenching method. Attempt to heal cracks in vacuum has been made. Micro structures of quenched samples before and after healing were characterized. Electrical conductivities and flexural strengths of materials before and after healing were measured. The results showed that:1) Cracks were effectively introduced in Ti2SnC by water quenching test. The influence of the quenching temperature on the electrical conductivity and flexural strength was investigated. It was firstly demonstrated that Ti2SnC exhibits an abnormal recovery in electrical conductivity after quenching from △T=600℃. The main reason for the abnormal recovery of electrical conductivity is the fill of micro cracks by precipitated Sn from Ti2SnC.2) Ti2SnC exhibits crack healing ability in vacuum environment. The residual electrical conductivity of the quenched samples is completely restored to the initial electrical conductivity after heat treatment at 800℃ for 2h in vacuum. The conductivity recovery is even higher than the initial value after heat treatment at 1000℃ for 2 h. The main crack healing mechanism of Ti2SnC in vacuum is that a large amount of Sn precipitated from Ti2SnC fills most microcracks in the material.3) The residual strength of Ti2SnC gradually increases with increasing temperatures, whereas it is still lower than the initial value of strength. This should be ascribed to the fact that the bonding between Sn and crack faces is weak, detrimental to the recovery strength.