Download files
Abstract
In this work, different amounts of titanium hydride were blended with commercial
pure (CP) titanium to fabricate titanium parts using conventional powder metallurgy
and container-less Hot Isostatic Pressing (HIP). Titanium composites reinforced with
SiC particulates have also been prepared. In order to restrict the detrimental reactions
between SiC and Ti during the fabrication, electroless nickel plating has been applied
on the surface of SiC.
Four different routes have been employed to produce the Ti specimens from Ti/TiH2
mixture through Sintering-HIP techniques. Route 1: Ti/TiH2 mixture was
vacuum-sintered at 1200°C for 120 min and then HIP was employed at 1000°C for
120 min under 150 MPa. Route 2: Vacuum-sintering was performed at 1200°C for 90
min, followed by HIP at 1000°C for 90min, under 150 MPa. Route 3:
Vacuum-sintering was accomplished at 1100°C for 90 min and followed by HIP at
1000°C for 90 min under 150 MPa. Route 4 included vacuum-sintering at 1100°C for
90 min, followed by HIP at 1000°C for 90 min under 100 MPa.
It was found that the densification and hardness of the blended Ti parts increased with
increasing amounts of TiH2 added. The grain refinement of the product was also
achieved as a result of the TiH2 addition. Containerless HIP of pure Ti (500 mesh)
cannot be carried out at a temperature lower than 1100°C because of the presence of
surface connecting porosity. When pure Ti with a size of 250 mesh was used, a
temperature of more than 1200°C was required for containerless HIP. This illustrated
the advantageous effect of TiH2 blending. In addition, the compacts of large size
particles required a higher sintering temperature to reach the same density as that of
compacts using finer powders.
Route 4 has been identified as the optimized processing route for fabrication of Ti
products via Sinter-HIP. Moreover, the hardness of the final products was increased as TiH2 was added, owing to the grain size refinement and improved densification.Unfortunately, electroless Ni plating of SiC reinforcement was found to be of little use. When nickel layer was deposited on SiC, reactions still exists between SiC and Ti. But the reaction zone was smaller compared to those without Ni coating on SiC. This may be attributed to the dissolution of Ni into Ti matrix at high temperature; hence the effect of protection was lost.