Investigation of Single-Crystal and Polycrystalline Titanium Diboride: Microstructural Features and Microhardness

摘要

A Widmanstatten precipitate was observed in the basal (c) plane of the crystal. This line or platelet pattern occurs in the expected crystal habit with triangular or rhomboid configurations at 60 or 120 degree angles. In the prism (a) planes which are perpendicular to the basal plane, the platelets or lines of the Widmanstatten precipitate are viewed as parallel lines. A variation of this pattern occurs with harsher etching procedures to produce an acicular structure. Evidence of slip lines, dislocations, and subboundaries is found. The effects of annealing on the microstructure have been investigated. Below 2100 C the effects are slight, above 2300 C the Widmanstatten precipitate is dispersed throughout the matrix. Variations in Knoop microhardness have been correlated with orientation and structural imperfections in the crystals. The effect of various etchants on the microhardness has been investigated. Optimum results have been achieved with a 100-gram load. Indentations were classified into the classic six cracking classes. The highest values obtained were 3250=150 kg/sq mm for unannealed specimens and 3710=250 kg/sq mm for annealed specimens. (Author)