HIP treatment

Normal reheat treatment can partially restore blade properties however, it does not appear to be capable of full property recovery, although the miscrostructures are comparable to new blades. This shortcoming implies that cavitation may be present and was not removed by conventional reheat treatment. Hot isostatic press (HIP) processing is an alternative that ensures void removal. It has demonstrated its ability to remove even gross internal shrinkage porosity in investment castings. The results of HIP treatment... 

The HIP treatment is eondueted in a five-zone furnaee loeated in a steel pressure vessel that ean be pressurized to 20,000 psi with argon and eapable of temperatures of 2250 F. The blades plaeed inside the furnaee must not be subjeeted to any undue loads and thus are staeked in... 

High-pressure treatments were carried out in two units a hot isostatic press (HIP) and a multiple anvil-type high-pressure generator. The powder sample for HIP treatment were pelletized and sealed in Ag tubes in vacuo, and was then sintered at 0.15 GPa and 823 K for 2 h in N2. High pressures up to 5 GPa were applied to the powder sample in the cubic/ octahedral anvil apparatus according to a technique described elsewhere.34 Briefly, the raw powder sample was packed into a BN capsule and placed at a center of the inner octahedral anvils with pyrophyllite pieces as... 

Although HIP treatment at 0.15 GPa induced almost no sintering, higher pressure and temperature conditions on the octahedral anvil apparatus improved compaction. Sintered samples (columnar, 3.4 mm OD X 5.0 mm long) prepared at 3 GPa and 823 K have good mechanical strength and hardness as determined by a conventional scratch test. 

The samples prepared without the HIP treatment showed substantially the same transformation behavior as the HIP-treated material, with one notable exception The monoclinic and tetragonal forms were seen to coexist over at least a 100 K temperature range in all vanadium-substituted samples that did... 

It has been demonstrated that freeze-diying could play an important role in the synthesis of high quahty Nd YAG nanosized powders [169]. Submicronic neodymium-doped YAG (Y3AI5O12) powder was synthesized from freeze-dried precursors. The powder calcined at 1200 °C, with small crystallite size and the lowest amount of organic residues, showed the highest sinterability. With these powder, although color centers were detected by transmission, transparent ceramics were obtained after a vacuum sintering at 1700 °C for 3 h and completed with a HIP treatment at 1700 °C, 160 MPa of Ar for 90 min. 

Figure 7.14 shows porosity values of the samples after namral sintering in vacuum versus the treatment temperamre and time [75]. With a constant treatment time, the porosity always increases as the sintering temperature is decreased. It was found in this work that if the porosity was higher than 8 %, the HIP treatment was not workable. The samples sintered at 1200 and 1220 °C time duration of 2 h was sufiicient. However, the samples sintered at 1170 and 1185 °C should be kept for 17 h to decrease the porosity to be <4 %. 

Fig. 7.16 Relative density (z) after HIP treatment versus the natural sintering temperature. The HIP parameters are indieated for each data. Reproduced with permission from [75]. Copyright 2011, Elsevier...

Fig. 5.61 SEM micrographs of sintered alumina (a) before and (b) after HIP treatment at 1300 °C for 12 h [25]. With kind permission of Elsevier...

Frictional characteristic of the UHMWPE-on-TZP sliding pair of current joint prostheses was also examined in this test for comparison. The TZP used in this test was the same material used in current ceramic joint prostheses and received hot isostatic pressing (HIP) treatment to reduce internal defects and improve the mechanical strength. The surface roughness of the HTOZ and TZP disk specimens measured by the stylus profilometer was 0.01pm (Ra). 

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