320 Prakt. Met. Sonderband 41 (2009) 
nm at the location of the former interlayer, which can be distinguished by the different contrast 
(bright or dark). Moreover, many particles with different size have precipitated in the NiAl matrix 
and in the ALO; fiber next to the interfaces with these sublayers. EFTEM/element mapping (Fig. 4d) 
and STEM/XEDS results (Fig. 4¢) revealed that the sublayer with dark contrast close to the Al,Os 
fiber was a carbon-rich sublayer, whereas the one with bright contrast adjacent to NiAl was a Cr- 
rich sublayer. The precipitates in NiAl near the boundary to the Cr-rich sublayer were identified as 
Al-oxide particles, while the particles observed in the Al Os fiber close to the interface to the C-rich 
sublaver were determined to be carbon particles. 
3.3 With V,AIC Interlayer 
0 
Fig. 5 Interface structure and chem- 
XEDS-Analysis (at.%): istry of as-coated fiber with V,AIC 
- WwW Ao ¢ Vv interlayer. (a) SEM/SE image shows 
7 B07 273 20 the interface structure. (b) Results of 
B 07 56 — 426 83 XEDS analysis in the interfacial 
5 395 249 14 342 7.7 area 
XEDS-Analysis (at.%): 
N AO Cc Vv 
A 04 04 104 429 46.2 
B 06 295 284 198 21.8 
C 102 439 280 17.9 — 
D — 357 499 144 — 
E 558 409 31 — 02 
= . 328 503 159 — 
Fig. 6 Interface structure and chemistry of as-diffusion bonded composite with a V,AIC interlayer. (a) Z-contrast image 
of STEM/HAAD shows the interface structure. (b) EFTEM analysis reveals the element mapping in the area defined by 
the white frame in Fig. 6a. (c¢) XEDS analysis in the interfacial area. 
The results of the SEM study on interface structure and chemistry of the as-coated sapphire fiber 
with a V,AIC interlayer are shown in Fig. Sa-b, respectively. A uniform V,AIC interlayer with a 
thickness of about 1 pm can be observed between alumina fiber and NiAl matrix. The thin continu- 
ous ridge (about 200 nm thick) between V,AIC and NiAl was identified by TEM to be comprised of 
fine equiaxed NiAl grains, which formed during the initial stage of PVD coating and was then sur- 
rounded by large columnar grains. The thick sublayer between fiber and V,AIC interlayer was as- 
certained to be the grounding and polishing substance, which was embedded in the crack on the 
fiber surface due to interface debonding during metallographic preparation. The interface structure 
of the as-diffusion bonded composite with a V,AIC interlayer is shown in Fig. 6a as a 
HAADF/STEM-micrograph with Z-contrast. The interfacial area of the former uniform MAX- 
phase interlayer had decomposed and contained many particles with different contrast. Since Fig. 6a