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DOE OSTI2020

Materials Data on Ti2S by Materials Project

Ti2S crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. there are six inequivalent Ti sites. In the first Ti site, Ti is bonded in a 4-coordinate geometry to five S atoms. There are a spread of Ti–S bond distances ranging from 2.48–2.85 Å. In the second Ti site, Ti is bonded in a 4-coordinate geometry to four S atoms. There are a spread of Ti–S bond distances ranging from 2.44–2.72 Å. In the third Ti site, Ti is bonded to five S atoms to form distorted edge-sharing TiS5 trigonal bipyramids. There are a spread of Ti–S bond distances ranging from 2.45–2.48 Å. In the fourth Ti site, Ti is bonded in a distorted T-shaped geometry to three S atoms. There are a spread of Ti–S bond distances ranging from 2.51–2.61 Å. In the fifth Ti site, Ti is bonded in a 3-coordinate geometry to three S atoms. There are two shorter (2.44 Å) and one longer (2.52 Å) Ti–S bond lengths. In the sixth Ti site, Ti is bonded in a 4-coordinate geometry to four S atoms. There are two shorter (2.48 Å) and two longer (2.53 Å) Ti–S bond lengths. There are three inequivalent S sites. In the first S site, S is bonded in a 8-coordinate geometry to eight Ti atoms. In the second S site, S is bonded in a 9-coordinate geometry to nine Ti atoms. In the third S site, S is bonded to seven Ti atoms to form distorted edge-sharing STi7 pentagonal bipyramids.

36 MATERIALS SCIENCE↗

NASA NTRS1977

The effect of microstructure and strength on the fracture toughness of an 18 Ni, 300 grade maraging steel

Fractography and metallographic sectioning were used to investigate the influence of microstructure and strength on the fracture toughness (KIc) and fracture mechanism of an 18 Ni, 300 grade maraging steel. Increased yield strength from 1442 to 2070 MN/m squared through precipitation hardening results in a KIc loss from 143 to 55 MN/m superscript 3/2. Ti (C,N) Ti2S, and TiC inclusions in sizes from 1 to 8, 1 to 15, and 0.1 to 2 microns respectively serve as sites for void nucleation and lead to fracture by the dimpled rupture process in all strength levels considered. TiC nucleated dimples occupy more than half the fracture in all conditions. Void nucleation rate and resultant number of dimples per unit area of fracture increase with increasing yield strength. Average dimple size decreases with increasing strength and/or overaging which follows from the decreasing amount of stable void growth measured by sectioning tensile specimens. Void growth is assisted by crack branching along a path of TiC inclusions. Coalescence occurs in the highest strength materials by a combination of TiC void nucleation and premature separation at strengthening precipitates.

Psioda, J. A.↗