Use of hydrogen as a temporary alloying element in titanium alloys is an at
tractive approach for enhancing processability including working, machining
, sintering, compaction, etc., and also for controlling the microstructure
and thereby improving final mechanical properties. In this article, the sta
tus of the methods and applications of thermohydrogen processing (THP) to t
itanium alloys is reviewed. Effects of hydrogen alloying on the phases pres
ent, their composition, and the kinetics of phase reactions are considered.
The effect of hydrogen on the hot workability, composite- and powder-metal
lurgy-product processing, and microstructure modification of wrought and ca
st conventional alloys and intermetallics, including production of nanocrys
talline structures is discussed. Two recently discovered effects, i.e. hydr
ogen-induced softening of alpha titanium and hydrogen-induced hardening of
beta titanium are also discussed. Thermohydrogen processing has clear advan
tages in the development of improved microstructures and mechanical propert
ies. In the case of near net shapes it is the only method for significant m
icrostructural modification. It allows energy savings in processing to fina
l products by improving the workability. (C) 1999 International Association
for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserve
d.