Plasticity mechanisms in HfN at elevated and room temperature

Area of Science:

• Materials Science
• Solid-State Physics
• Physical Chemistry

Background:

• Hafnium nitride (HfN) is a refractory ceramic with a B1 (NaCl) crystal structure.
• Understanding the deformation mechanisms of HfN is crucial for its application in high-temperature environments.
• Previous studies suggest brittle behavior at lower temperatures, but plasticity at extreme temperatures remains less understood.

Purpose of the Study:

• To investigate the temperature-dependent plasticity of HfN.
• To identify the primary slip systems governing deformation in HfN.
• To elucidate the role of dislocation mobility and stacking faults in the brittle-to-ductile transition.

Main Methods:

• Four-point bend tests were conducted on HfN specimens at room temperature and 2300°C.
• Transmission electron microscopy (TEM) with dynamic diffraction was used to analyze microstructural changes and slip systems.
• First-principles generalized stacking fault energy calculations were performed.

Main Results:

• HfN demonstrated significantly increased plasticity at 2300°C compared to room temperature.
• The primary slip system identified was ⟨110⟩{111}, with ⟨110⟩{110} activating at elevated temperatures.
• Dislocation lines transitioned from linear to curved morphologies with increasing temperature, indicating enhanced mobility.
• First-principles calculations revealed an intrinsic stacking fault (ISF) along ⟨112⟩{111}, facilitating {111} plane slip.

Conclusions:

• The brittle-to-ductile transition in HfN is attributed to increased dislocation mobility at high temperatures.
• The identified slip systems and the ISF mechanism are critical for understanding HfN's plastic deformation behavior.
• This research provides fundamental insights into the mechanical properties of HfN at extreme conditions.