Chin. Phys. B, 2022, Vol. 31(5): 056105    DOI: 10.1088/1674-1056/ac3986
 CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES Prev   Next

# Alloying and magnetic disordering effects on phase stability of Co2YGa (Y=Cr, V, and Ni) alloys: A first-principles study

Chun-Mei Li(李春梅), Shun-Jie Yang(杨顺杰), and Jin-Ping Zhou(周金萍)
College of Physics Science and Technology, Shenyang Normal University, Shenyang 110034, China
Abstract  The alloying and magnetic disordering effects on site occupation, elastic property, and phase stability of Co$_{2}Y$Ga ($Y={\rm Cr}$, V, and Ni) shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method. It is shown that with the increasing magnetic disordering degree $y$, their tetragonal shear elastic constant $C'$ (i.e., $(C_{11}-C_{12})/2$) of the $L2_{1}$ phase decreases whereas the elastic anisotropy $A$ increases, and upon tetragonal distortions the cubic phase gets more and more unstable. Co$_{2}$CrGa and Co$_{2}$VGa alloys with $y\geq0.2$ thus can show the martensitic transformation (MT) from $L2_{1}$ to $D0_{22}$ as well as Co$_{2}$NiGa. In off-stoichiometric alloys, the site preference is controlled by both the alloying and magnetic effects. At the ferromagnetism state, the excessive Ga atoms always tend to take the $Y$ sublattices, whereas the excessive Co atom favor the $Y$ sites when $Y={\rm Cr}$, and the excessive $Y$ atoms prefer the Co sites when $Y={\rm Ni}$. The Ga-deficient $Y={\rm V}$ alloys can also occur the MT at the ferromagnetism state by means of Co or V doping, and the MT temperature $T_{\rm M}$ should increase with their addition. In the corresponding ferromagnetism $Y={\rm Cr}$ alloys, nevertheless, with Co or Cr substituting for Ga, the reentrant MT (RMT) from $D0_{22}$ to $L2_{1}$ is promoted and then $T_{\rm M}$ for the RMT should decrease. The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state. At the ferromagnetism state, it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as $Y$ and Ga.
Keywords:  first-principles      martensitic transformation      elastic modulus      magnetic ordering      shape memory alloys
Received:  24 June 2021      Revised:  14 October 2021      Accepted manuscript online:
 PACS: 61.66.Dk (Alloys ) 62.20.de (Elastic moduli) 63.20.dk (First-principles theory) 64.70.K-
Fund: This work was supported by the National Natural Science Foundation of China (Grant Nos.12174269,11674233 and 51301176),the China Postdoctoral Science Foundation (Grant Nos.2013M530133 and 2014T70264),and the Natural Science Foundation of Liaoning Province,China (Grant Nos.2019-MS-287 and L201602672).
Corresponding Authors:  Chun-Mei Li,E-mail:cmli@synu.edu.cn     E-mail:  cmli@synu.edu.cn