Layered stacking characteristics of ternary zirconium aluminum carbides
- PDF / 1,165,286 Bytes
- 9 Pages / 585 x 783 pts Page_size
- 41 Downloads / 171 Views
M.S. Li, J.Y. Wang, and Y.C. Zhoua) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 16 April 2007; accepted 29 May 2007)
Layered stacking characteristics of ternary Zr–Al–C carbides were investigated using scanning transmission electron microscopy (STEM). Three previously unknown compounds, i.e., Zr4Al3C6, Zr5Al6C9, and Zr7Al6C11 were identified. The present study extends the structural information of ternary Zr–Al–C ceramics. The influence of the thickness of the NaCl-type Zr-C slab on the elastic properties of ternary Zr–Al–C ceramics is discussed based on first-principles calculations. In addition, direct atomic-resolution observations illustrate the process for forming the unique layered crystal structures of ternary Zr–Al–C ceramics. These results also provide insights into the formation mechanism of layered ternary Zr–Al–C carbides.
I. INTRODUCTION
Binary transition metal carbides such as TiC, HfC, and ZrC, have a unique combination of properties, e.g., high hardness, high melting point, good wear resistance and electrical conductivity, and chemical inertness, which make them suitable for many technological applications.1 However, the poor oxidation resistance and intrinsic brittleness hinder their extensive applications in hightemperature environments. A possible way to overcome these difficulties is by incorporating Al to form ternary aluminum carbide.2–10 It is known that the toughness and high temperature oxidation resistance of TiC were greatly improved by forming ternary aluminum carbides, such as Ti3AlC2 and Ti2AlC.4–8 Successes in the Ti– Al–C system highlighted a possible way to overcome the difficulties in the applications of ZrC. The crystal structures of Mn+1AXn phases [where M is an early transition metal, A is an A-group (mostly IIIA or IVA) element, X is either C or N] can be described as NaCl-type M-X slabs being intercalated and mirrored by close-packed A atomic planes.2 The nanolayered crystal structures endow MAX phases with attractive properties, such as easy machinability, damage tolerance, and good electrical and thermal conductivities.2–10 The crystal
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0409 3058 J. Mater. Res., Vol. 22, No. 11, Nov 2007 http://journals.cambridge.org Downloaded: 24 Mar 2015
structures for Zr2Al3C4 and Zr3Al3C5 are shown in Figs. 1(a) and 1(b),11–14 which consist of alternatively stacking of NaCl-type Zr-C slab and Al4C3-type Al-C unit. Al-C unit, instead of A atomic plane, links NaCl-type Zr-C slabs; this is the main difference between the crystal structures of Zr–Al–C and those of MAX phases. Compared with those well-studied ceramics in the Ti–Al–C system, ternary Zr–Al–C compounds were less investigated. The reasons can be attributed to the fact that ternary Zr–Al–C compounds are newly developed materials; and knowledge on the microstructural characteristics, mechanical and chemical properties is sparse. Recently
Data Loading...
