318 Prakt. Met. Sonderband 41 (2009) 
3 Interface Structure and Chemical Stability Results 
3.1 With hBN Interlayer 
Before hot pressing, there is an amorphous layer in the as-coated fiber about 30-40 nm thick be- 
tween the hBN coating and the NiAl matrix (Fig.1). With the help of EFTEM and STEM/EDX 
analysis, the amorphous layer was shown to be made up of 60 at.% O and 40 at.% Al and Ni. The 
formation of this layer can be explained as an incorporation of Ni, Al, and remaining moisture in 
the initial stage of PVD process [4]. 
Fig. 1 Interface structure of an as-coated fiber with hBN 
interlayer after CVD and PVD processing. (a) Bright- 
field EFTEM image shows the interface structure; (b) 
HRTEM image reveals an amorphous structure in the 
interface laver and a graphite structure in hBN interlayer. 
e _ i _ _ a 
XEDS-Analysis (at.%): Rina Measured d value (nm Identified phase and its d-value (nm) 
70.3497 "diouoz on = 0.3328 
Ni Al J B N 0.2908 d100) mar = 0.2890 
3 A 608 365 101 1.7 = 0.2136 d1000) en = 0.2170 
B 07 538 135 33 28.7 : S20 EN ber 
C 05 488 177 73 258 0.1522 da am = 0.1558 
D 333 17.6 133 136 223 0.1454 diaooy wins = 0.1444 
E 142 69 104 314 374 0.1306 doy an = 0.1291 
: 33.2 10.1 9.2 21.7 25.3 0.1219 d11.10)8n = 0.1253 
© 1n1 449 122 407 338 1 0.093 diag) nar = 0.091 
1 n.086 dairy wear = 0.087 _ 
Fig. 2 (a) STEM/HAADF micrograph of the interface structure of an as-diffusion-bonded composite with hBN inter- 
layer; (b) microanalysis of marked area in (a) (results of STEM/EDX analysis at locations A to G are listed in (e)); (c) 
SAD pattern of the hBN interlayer in the marked region; (d) measured plane spacing in (c) for phase identification. 
Evaluated results are listed in (f). 
After hot pressing, the previous amorphous layer observed in the as-coated fiber was replaced by a 
new sublayer about 100nm thick (arrows in Fig.2a) which is assumed to be a reaction product dur- 
ing diffusion bonding. Many nanometer size particles with bright contrast had precipitated in the 
hBN interlayer. The microanalysis with STEM/EDX (Fig. 2e) indicated that this reaction sublayer 
was AIN, one possible reaction product between hBN, amorphous layer, and NiAl at high tempera- 
turs [5]. An SAD pattern (Fig. 2c), consisting of diffuse rings and individual spots, was taken from 
the hBN interlaver to identify the bright precipitates. According to the evaluation in Fig. 2f, the pre-