Prakt. Met. Sonderband 41 (2009) 317
transforms the EFTEM, STEM and EDX analysis of the modified interface in NiAl-Al,O; com-
<inetics of the posites
d by the novel
metallographic
J. Song’, W. Hu, T. Weirich?, Y. Zhong’ and G. Gottstein’,
1. Institute of Physical Metallurgy and Metal Physics, RWTH Aachen University
2. Central Facility for Electron Microscopy, RWTH Aachen University
3. Mubea Fahrwerksfedern GmbH, WeiBensee
28.
an, Physica C
1 Introduction
2005, 26, 337-
Recently NiAl composites reinforced by single-crystalline Al,O3 continuous fibers were considered
1g Technology for structural application at the high temperatures. In such ceramic continuous fiber-reinforced in-
termetallic matrix composites (IMCs), the. interfacial shear strength (controlled by the interface
structure and chemistry developed during composite fabrication) plays an important role for the
letals, Edward load transfer from the matrix to the fiber and thus, determining the strength and ductility of the
composites. Additionally, the remaining fiber quality after fabrication can influence the mechanical
‘ 1988. performance of NiAl composites as well. Fiber damage and fiber strength degradation are pro-
+ Alloys. Boca nounced in sapphire fiber reinforced NiAl composites owing to the axial thermal residual stress
during cooling after hot pressing [1-2]. To overcome this deficiency, an interlayer was introduced to
Is, M. Dekker, modify the interface and to decrease fiber damage.
The hexagonal structure of boron nitride and of MAX-phases (with the common formula MAX,
where M is an early transition metal, A is a group IIIA or IVA element, and X is either C and/or N,
VE 1969, 245, Cr,AlC and V,AIC in this study) were selected as the candidates based on their attractive properties,
like good thermal conductivity, reasonable thermal stability and most importantly damage tolerance,
6, 447-452. which could help to relieve the interfacial residual stress and to improve interface ductility. EFTEM,
STEM and EDX were used to analyse the structural and chemical stability in the interface region.
During High-
2 Experimental
The fiber used in the present investigation was a single crystalline o-Al,Os fiber (sapphire) with a
diameter of about 125 um, in which the c-axis of a-Al,0; was parallel to the long direction of the
fiber. The fiber was firstly coated with hBN (5um) or MAX-phase (Cr,AlC or V,AIC respectively,
about 1~2 um thick) by a CVD process and then further coated with NiAl by a PVD process. The
thickness of the NiAl-coating was about 30 pm corresponding to a fiber volume fraction of about
50%. The coated fibers were placed into a channel-die and hot pressed for 1 hour at 1300 °C with a
pressure of 40 MPa in vacuum (5x107 Pa). Under these conditions complete consolidation was
achieved. Both the as-coated fibers and as-diffusion bonded composites were prepared for micro-
characterization and microanalysis (SEM/TEM, XEDS, EELS and SAD). Details of the methods for
specimen preparation can be found elsewhere [3].
