Hardness and Damage Tolerance

The MAX phases, unlike the MX carbides, are relatively soft and ecceedingly damage-tolerant. The Vickers hardness values of polycrystaDine MAX phases fall in the range of 2-8 G Pa thus, they are softer than most structural ceramics, but harder than most metals. The low hardness persists - at least in Ti3 iC2 - even at temperatures as low as 77 K [149]. 

When working with chemical vapor deposition (CVD) single crystals, Nickl et al. [150] were the first to note that the hardness of Ti3SiC2 was anisotropic, and higher when loaded along the c-direction. This was later confirmed by Goto and Hirai [ 151], who were the first to show that the hardness was a function of indentation load. Both observations are characteristic of the MAX phases [1,152). With decreasing 

Typically, Vickers indentations in brittle solids result in sharp cracks that extend from comers of the indents and result in sharp reductions in strength. As first 

The importance of such high damage tolerance cannot be overemphasized, as it implies that the MAX phases are much more tolerant to processing and service flaws that typically are quite detrimental to the mechanical properties of brittle solids. This, in turn, should also greatly increase manufacturing yields, as the need for full density is relaxed. 

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