HIP Silicon Nitride VS GPS Silicon Nitride

What is GPS?
 Gas pressure sintering (GPS) process is one of the most promising sintering techniques for the fabrication of high performance silicon nitride ceramics. Almost pore-free densified compacts with low amounts of sintering additives can be obtained by this process. They present high strength with high reliability and good heat resistance. These properties make them one of the best candidate materials for heat engine component as well as other industrial fields application. The gas pressure sintered silicon nitride (GPSSN) ceramics densified to high density have already been applied in turbocharger rotors for automotive application, cutting tools and bearing balls for industrial applications, etc., and have been highly evaluated for high strength and reliability.
 The special feature of the GPS process is a sequence of dewaxing at low pressure, sintering at normal pressure and -after a status is reached with only closed pores being present in the material - sintering at a high pressure, which results in a further densification and faster elimination of the remaining pores. Therefore materials produced in the GPS technology show in general mechanical properties (hardness, strength, Weibull-modulus, fracture toughness) which are superior to those of pore-free materials produced by the conventional sintering method.
 The devices are particularly suitable for sintering such types of ceramics or metals, which tend to decomposition at elevated temperatures or which do not sinter to high densities in standard sintering operations. This process has not the limitations with respect to the shape of the manufactured parts as in hot pressing and it is also an advantageous alternative to the more costly HIP-process.
What is HIP?
 Hot isostatic pressing (HIP) is a manufacturing process, used to reduce the porosity of metals and increase the density of many ceramic materials. This improves the material's mechanical properties and workability.
 The HIP process subjects a component to both elevated temperature and isostatic gas pressure in a high pressure containment vessel. The pressurizing gas most widely used is argon. An inert gas is used, so that the material does not chemically react. The chamber is heated, causing the pressure inside the vessel to increase. Many systems use associated gas pumping to achieve the necessary pressure level. Pressure is applied to the material from all directions (hence the term "isostatic").
 For processing castings, metal powders can also be turned to compact solids by this method, the inert gas is applied between 7,350 psi (50.7 MPa) and 45,000 psi (310 MPa), with 15,000 psi (100 MPa) being most common. Process soak temperatures range from 900 °F (482 °C) for aluminium castings to 2,400 °F (1,320 °C) for nickel-based superalloys. When castings are treated with HIP, the simultaneous application of heat and pressure eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion bonding; this process improves fatigue resistance of the component. Primary applications are the reduction of microshrinkage, the consolidation of powder metals, ceramic composites and metal cladding. Hot isostatic pressing is also used as part of a sintering (powder metallurgy) process and for fabrication of metal matrix composites.