HIP-ing

Pressure sintering. Sometimes, hardmetals exhibit residual porosity (A and B type), which can occur for several reasons. Since the 1970s pressure sintering (HIP-ing) has been applied to remove this porosity. For that purpose, the sintered specimens are loaded in a HIP-ing device and heated again under Ar or He pressure of 50-150 MPa (temperatures and commonly 25-50 °C below the vacuum sintering temperature). Hence any residual porosity can be removed. Exceptions are gas porosities, which either can occur due to incomplete outgassing of the carbon monoxide, or due to the presence of impurities. 

The use of silicon nitride - 4% yttria composition which is consolidated by glass encapsulated HIP ing. 

The final value of the oxygen on the presintered bar as well as on the MOR bars after HIP ing and machining have also been determined using LECO analysis. For these determinations, the bar is crushed to small pieces, while taking precautions that no contamination or oxidation occurs in the bar while crushing. These pieces (50-60 mg) are used for the LECO analysis. 

During this period two principal tasks were carried out. Evaluation of water-milled silicon nitride compositions required several qualification runs where test tiles from water-milled powders were CIP ed and densified by a Norton proprietary HIP ing process. Concurrently, an experimental evaluation of fixturing approaches to eliminate part warpage during HIP ing was conducted with both CIP ed and injection molded tensile rods. Both densified tiles and tensile rods were submitted for testing. 

In comparing the HIP ing behavior of alcohol-milled silicon nitride-yttria compositions with water-milled compositions, the results to date indicate that water-milled materials, when milled to the same powder specification as alcohol-mi 1 led... 

As indicated by the results provided in Table 5, rigid fixturing designs are fairly successful at eliminating warpage of tensile rods during HIP ing. 

No significant microstructural differences between joined and control MOR bars appeared in SEM pictures, in both NCX-4500 Sic and NCX-5100 SijN. In SiC the join could be seen in most samples, whereas in SijN was invisible, except when the join was obviously of poor quality, due to insufficient closure of the gap between adherent billets during HiP ing,... 

Lundberg R., Nyberg, B., Williander, K., Persson, M., Carlsson R., Glass Encapsulated HIP-ing of SiC Whisker Reinforced Ceramic Composites, Proc. First Int. HIP Conf., LuleA, Sweden, June 15-16,... 

It must be emphasized that differential hardness has been verified in hip simulator studies only for combinations in which a ceramic head articulates against a CoCr Uner. Conversely, it is not recommended that metal heads be used in combination with a ceramic finer. Two case studies of metal-on-ceramic combination bearings have been associated with severe wear and, for one revision case in which a metallic head was used to replace a fractured ceramic component, the head wear that ensued resulted in cobalt pwison-ing and blindness [144,145]. 

O Kelly J, UnswOTfli A, Dowson D, Jobbins B and Wright V (1977) Pendulum and simulator Am-studies of frictim in hip joints, in Evaluatioi of Artificial Joints, Ed. D Dowson and V Wright, The Biological Engineo-ing Society, 19-20. 

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