Evaluation of microhardness and fracture toughness of (TiNb)C strengthening layer on Ti-Nb alloy surface by indentation method

The effect of lamellar structure on the microhardness of (TiNb)C strengthening layer on the surface of Ti-Nb alloy was studied by indentation method. The size of a large number of indentations and the length of cracks were measured under effective test load. The fracture toughness was calculated by empirical formulas. The results show that with the increase of the test load, the substrate effect caused by the ‘hard shell-soft bottom’ structure was gradually significant in the vertical surface direction. The effective test load was 2 N, and the average hardness of the L-II layer was 2 594. 13 HV. In the vertical cross section direction, the edge effect caused by the thickness of the strengthening layer was gradually significant. The effective test load was 1 N, and the average hardness of the L-III layer was 2 334. 88 HV. L-II layer had larger particle size, and its hardness and fracture toughness were better than L-III layer.