Phase transition in diamond-structure crystals during hardness measurements

Abstract

The mechanism of microhardness print forming in diamond‐structure crystals is considered to be the result of a local phase transition under the indenter with the formation of a metallic phase due to the high hydrostatic pressure generated in this case. It is shown that at the temperature T < 0.3 to 0.4 Tml, where the microhardness Hv is weakly temperature‐dependent, one has Hv ≈ Pc(Pc transition pressure). In GaAs crystals, where Hv ≪ Pc, the athermal part in the hardness‐temperature curve was not observed. It is shown as well that at the moment when the indenter entering the crystal is stopped there is a thin layer around it which still contains the metallic phase with high electrical conduction. The estimated thickness of the layer is ≈ 0.05 μm. The plastic deformation is supposed not to proceed at this moment because of the friction forces which oppose the squeezing‐out of the metallic layer.

A review on ductile mode cutting of brittle materials

“…(a) DMC by removing a ductile metallized layer resulted from the large contact pressure in cutting region; (b) BMC by material fracture leaving subsurface damages, of which the subsurface damage is as deep as 5-10 µm due to crack propagations in machining of silicon indentation process of brittle materials. The measurement results revealed a substantial increase in the conductivity of the material below the indenter that can be plastically deformed, which supports the theory of transition to a metallic state [25,26].…”

Hardness, Yield Strength, and Dislocation Velocity in Elemental and Compound Semiconductors

“…It is known that the indention of Si (and probably Ge) is associated with a form of phase transformation that leaves an amorphous-like structure after unloading. [17][18][19] In such cases (T 500 C for Si), H V is determined by the pressure for the phase transformation and exhibits a weak temperature dependence, as indicated in Fig. 2.…”

The martensitic transformation in silicon—I experimental observations

“…the material simply tears apart to accommodate the indenter. An alternative accommodation mode is the decrease in the atomic volume 8 of the material underneath the indenter through high pressure phase transformations [25] and/or crystalline-to-amorphous transitions [ 14].…”