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Hydrogen incorporation in Ti‐based metal–matrix composites fabricated by vacuum plasma spraying and vacuum hot pressing
Author(s) -
LI J. H.,
GRANT P. S.,
JENKINS M. L.,
CANTOR B.
Publication year - 1997
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.1997.1550713.x
Subject(s) - materials science , hydride , hydrogen , equiaxed crystals , transmission electron microscopy , microstructure , metal , composite material , metallurgy , chemistry , nanotechnology , organic chemistry
In this paper we investigate the incorporation of hydrogen as a temporary alloying element during vacuum plasma spraying (VPS) of Ti‐based metal–matrix composites and show that it has probable beneficial effects for secondary processing by vacuum hot pressing (VHP). The composites investigated included both commercial purity Ti and Ti–6Al–4V matrices, which were sprayed onto DRA Sigma SiC fibres. The as‐sprayed matrix microstructures were investigated by transmission electron microscopy and X‐ray diffractometry, and were found to consist in both cases of a fine mixture of (1) hexagonal α′‐Ti martensite plates, with an increased lattice parameter relative to the usual value, presumably due to dissolved hydrogen; and (2) an increased proportion of equiaxed b.c.c. β grains, probably stabilized by dissolved hydrogen. Both phases, but particularlyβ, contained needle‐shaped b.c.t. hydride precipitates. It has been found that monotapes produced by VHP can be consolidated more easily by secondary VHP than those produced by electric arc spraying, leading to reduced adverse interfacial reactions between fibre and matrix. This improved processability is believed to be due to the combination of a greater proportion of the more ductile β phase and the very small grain sizes inherent in VPS. However, the dissolved hydrogen and the potentially embrittling hydride precipitates are removed during VHP. The presence of hydrogen after primary VPS may therefore have an overall beneficial effect.