Nucleation and Growth of the Ni5Al3 Phase in Ni-Al Austenite and Martensite
نویسندگان
چکیده
The nucleation and growth mechanisms of Ni5A13 precipitates and microtwinned plates in B2 austenite and 2M (3R) martensite phases are described on the basis of conventional and high resolution electron microscopy. In the Ni62.5A137.5 B2 austenite matrix short annealings at 550°C introduce three-pointed star shaped precipitates consisting of twin related parts of different variants of the Ni5A13 structure. Longer annealings result in plates growing separately from these wings and developing microtwinning in order to accommodate stress built-up at the interfaces with the surrounding matrix. Annealing of Nk5AI35 2M martensite plates induces simple reordering into the Ni5A13 phase, increasing the fct c/a ratio by about 1%. As a result stracking faults are introduced in the smallest twin variants.
منابع مشابه
Thermally activated growth of lath martensite in Fe–Cr–Ni–Al stainless steel
The austenite-to-martensite transformation in a partially hardened stainless steel containing 17wt %Cr, 7wt %Ni and 1wt % Al was investigated with Vibrating Sample Magnetometry and Electron Back-Scatter Diffraction. Magnetometry demonstrated that measurable martensite formation can be suppressed on fast cooling to 77K as well as on subsequent fast heating to 373 K. Surprisingly, martensite form...
متن کاملThermally activated growth of lath martensite in Fe- Cr-Ni-Al precipitation hardenable stainless steel
The austenite-to-martensite transformation in a partially hardened stainless steel containing 17wt %Cr, 7wt %Ni and 1wt % Al was investigated with Vibrating Sample Magnetometry and Electron Back-Scatter Diffraction. Magnetometry demonstrated that measurable martensite formation can be suppressed on fast cooling to 77K as well as on subsequent fast heating to 373 K. Surprisingly, martensite form...
متن کاملNucleation of Austenite in Mechanically Stabilized Martensite by Localized Heating
The nucleation of bcc austenite in a single crystal of a mechanically stabilized 2H-martensite of Cu-Al-Ni shape-memory alloy is studied. The nucleation process is induced by localized heating and observed by optical microscopy. It is observed that nucleation occurs after a time delay and that the nucleation points are always located at one of the corners of the sample (a rectangular bar in the...
متن کاملDynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni-Fe-Al alloy
Besides permitting an accurate determination of the ferromagnetic-to-paramagnetic phase transition temperature and the characteristic temperatures for the beginning and end of the growth of martensite (austenite) phase at the expense of austenite (martensite) phase while cooling (heating), the results of an extensive ac susceptibility, sound velocity and internal friction investigation of the t...
متن کاملQuasiconvexity at the boundary and the nucleation of austenite
Motivated by experimental observations of H. Seiner et al., we study the nucleation of austenite in a single crystal of a CuAlNi shape-memory alloy stabilized as a single variant of martensite. In the experiments the nucleation process was induced by localized heating and it was observed that, regardless of where the localized heating was applied, the nucleation points were always located at on...
متن کامل