Lamellar twinned microstructures

Figure 2-12 Microstructure of enstatite- 3-spodumene glass-ceramics showing lamellar twinning in enstatite.

Martensitic Structures. If the cooling rates from the P field are siiffLdently rapid, an acicular or lath-like martensite is formed. In alloys with low concentrations of beta-stabilizing elements, the martensite has a distorted hexagonal crystal lattice, similar to that of a, and is referred to as a. Because of the fine lath width, oc is stronger than lamellar a, but not necessarily brittle. The other principal type of martensite (orthorhombic a") occurs upon the quenching of a P phase that contains intermediate concentrations of beta-stabilizing alloy elements (e.g., between 10 and 15 wt% vanadium). The a" martensite has an orthorhombic structure with a very fine, internally twinned microstructure. The orthorhombic a" martensite is mechanically soft. 

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