Prakt. Met. Sonderband 41 (2009) 319
cipitates were NiAl with a composition deviating from stoichiometry. Besides, an important micro-
structural process during hot pressing is the texture development in the hBN interlayer. As shown in
Fig. 3d, the diffraction intensity in the rings of (002)BN and (004)BN became inhomogeneous
compared to the ones for the as-coated fiber condition in Fig. 3b. Under the radial pressure during
diffusion bonding, the basal planes of hBN would preferably orient themselves parallel to the inter-
nm thick be- face {6].
, STEM/EDX
1 and Ni. The
g moisture in
ber with hBN
0. (a) Bright-
structure; (b)
ucture in the
IN interlaver. Fig. 3 (a, b) Microstructure (HRTEM image) and SAD pattern of the hBN interlayer in as-coated fiber; (c, d) micro-
structure (HRTEM image) and SAD pattern of the hBN interlayer after diffusion bonding.
3.2 With Cr,AlC Interlayer
Before diffusion bonding, a uniform Cr,AlC interlayer with a thickness of about 1~2 um can be
observed between Al,Oj; fiber and NiAl matrix (Fig. 4a-b). The higher C-concentration displayed in
XEDS analysis was caused by carbon sputter on the specimen surface, which is necessary for SEM
observations on non-conducting Al,Ox fibers.
-value (om)
iT MAI
? Em
* b e
‘ XEDS-Analysis (at.%): XEDS-Analysis (at.%):
_ _ _ Ni Al 0 Cr Cc
Ni Al oO C Cr A — 44.4 55.6 —_ —
5 aim _ = B — 5.1 7.8 — 87.1
ith hBN inter- 8 _ 29 0 403 19.9 C 28 75 249 12 637
. X : : : D — 0.3 16.6 64.0 19.0
sted in (e)); (c) c — 196 36 39.8 37.0 E it 437 546 — hl
2 © 2
entification. ne 2 598 372 29 -
Fig. 4 Interface structure and chemistry of as-coated fiber with Cr,AlC interlayer: (a) SEM/SE image shows the inter-
replaced by a face structure, (b) XEDS analysis results in the interfacial area; Interface structure and chemistry of as-diffusion bonded
n product dur- composite: (c) Z-contrast image of STEM/HAAD shows the interface structure, (d) EFTEM analysis reveals the ele-
ipitated in the ment mapping in the area defined by white frame in Fig. 4c. (e) XEDS analysis results in the interfacial area.
action sublayer
high tempera- The composite interface structure after hot pressing at 1300 °C for 1 hour is shown in Fig. 4c as a
vas taken from HAADF/STEM-micrograph with Z-contrast. The former uniform Cr,AlC interlayer has decom-
ig. 2f, the pre- posed during hot pressing, forming subsequently two sublayers with a thickness of about 200~300
