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HIPing stands for Hot Isostatic Press-ing. Hot isostatic pressing is a process in which components are subjected to the simultaneous application of heat and high pressure in an inert gas medium. Because the pressure is applied by a gas, it is uniform in all directions, or isostatic . HIP is on one hand a forming technique, on the other hand a densifying technique .
- porosity elimination (and simultaneous heat treatment),
- rejuvenation of fatigue or creep-induced damage in components,
- compaction of metal powder,
- post-densification of sintered ceramics or metal parts,
- joining of materials and infiltration combined with densification.
Clearly HIP can also be applied to metal components built using additive manufacturing technologies such as selective manufacturing. HIP post-processing eliminates virtually all trace of gas porosity, cracks, decreases hot tearing susceptibility and improves fatigue behaviour.
How does HIPing work?
The simultaneous application of heat and pressure combine to collapse voids and porosity by creep mechanisms, plastic deformation, and diffusion bonding the void surfaces together with minimum distortion. Components of complex geometry can be treated without complex or expensive tooling. The many investigations conducted on several classes of materials show that HIP treatment provides startling improvements in mechanical properties, such as higher strength, enhanced toughness, improved fatigue resistance, and longer creep life [1-4].
HIP cycles 
HIP parameters and their optimisation 
The general rule  says that the HIP temperature should be 0.8xTM, TM is the melting temperature. When HIP is used as a densifying post-treatment, the lowest temperature ever possible in regard to HIP-mechanisms should be choosen for avoiding defects in the material.
For good densification, the pressure of the more plastic material of the composite should lie something around the stress of the Young's modulus at HIP-temperature.
The third parameter, the time, allows to control diffusion effects and grain growth. Even controlled phase transformations are time dependent. In general the time for HIP densification is not longer than two/three hours.
To sum up
 Barre C., Hot Isostatic Pressing, Advanced Materials & Processes. 155.3 (Mar. 1999): p47. Copyright 1999 ASM International
 Richter D., Haour G. & Richon D., Hot Isostatic Pressing, Materials & Design, Vol. 6, Dec. 1985, p303-306
 H.-D. Steffens, J. Lebkuchner-Neugebauer and B. Wielage, Hot Isostatic Pressing, Mat.-wiss. u. Werkstofftech. 21, 28-31 (1990)
 E. Arzt, M. F. Ashby, K. E. Easterling, 1983, Met. Trans. A,Vol. 14A, p. 211.