Hot isostalic pressing ("HIP") involves the application ot high pressures and temperatures Ihrough Ihe medium ol a pressurizing gas such as argon or nilrogen. HIP consolidales powders ol melals, ceramics, or carbides info fully dense, complex parls wilh nel or nearnet shapes. or info very high quality forging billers HIP .'heals" defects in castings by creep mechanisms and/or compressive plastic delormalion. The clean void surfaces are bonded togelher by diffusion. HIP is also used for diffusion bonding dissimilar materials, and for applying wear. or corrosion resistant coalings to parts exposed to stringent operating conditions.

By consistently improving materials' mechanical properties and by narrowing the scalter band of properties. HIP enables designers lo utilize a very high proportion of the physical strength of materials. This translates into higher reliability and longer service lile, or into smaller, lighter-weight parts, or both.

By reducing rejection rates and scrap losses, minimizing or eliminating machining costs, and consuming less energy, HIP can reduce the total production costs ol a product. following are some of the specific advantages imparted by HIP to several specific categories ol materials or processes.

Conlainerized niches based alloy powder is Hip'ed. cut into segments, centerlessground, and forged into high pressure turbine disks wiln belier properties than wrought disks.

	CASTINGS HIP reduces tolal casilng costs by reducing rejections and scrap losses. Eliminates closed voids, micro. porosily, and shrinkage tears. Improves duclility and fatigue properties, often to Ihe equivalent of forged or wroughl parls. Improves reliability and Service life. Permils smaller, lighter-weighl castings to be used. Up,qrades the properties ol difficult-to-cast materials Such as lilanium and cerlain superalloys to acceptable levels. Rejuvenates mechanical properlies of service. faligued parls lo new or nearly new levels.
718 parts for the F.404 engine case. HIP removes microshrinkage and improves mechanical properties.
	P/M HIP'ing complex parts to net or near-net shape sharply reduces input weight, thereby reducing and in some cases eliminaling- machining costs. Produces line grained, homogeneous microstructures wilh superior mechanical properties which increases reliabilily and service lile. Reduces scrap losses. Enables alloy combinations 1O be produced which are impossible lo allain by other means. HIP conserves costly siralegic maleriats and reduces lotal energy usage.
Titanium castings
	CARBIDES Eliminates voids and microporosity which are stress risers. This improves transverse rupture strength and wear resistance. Permits the use of fine grained, low cobalt mixes which have particularly good wear resistance but which are difficult to manufacture without voids and microporosity. Extends the service life of expensive canning tools, drawing dies, and rolling mills. Reduces rejection rates and scrap losses, and enables scrap to be recycled. Helps prevent very costly premature failures of tricone oilwell rock bits.
Load of tungsten carbide tricone rock bits containing 6-10% cobalt.
	ADVANCED CERAMICS Advanced engineered ceramics are brittle and have poor tolerance to thermal shock. Once cracks develop at flaws or microporosily, ceramics fail rapidly. By eliminating flaws and porosity, HIP provides striking improvements in ceramics' performance and useful lifetime. HIP'ing ceramics to net or near-net shape is also a major advantage because these materials are too hard to machine cost effectively
By removing porosity and producing fully dense material, HIP maximizes the strength of medical prostheses and prevents premature failure.

		As sintered Ti 6AI 4V, 545 X magnification, unetched Density is 93.5% of theoretical. Note presence of large rounded pores and small, non-metallic inclusions.
A 4140 valve body HlP clad wilh IN 625 tor corrosive service. These valves are now in production, they cost tar less than ~olid IN 625 valves.	Cast Nickel-base impeller	As sintered Ti 6AI 4V after HIPing, 545 X magnification, unetched Density is 100% of theoretical Note absence of large ronded pores and spheroidization of small non-metallic inclusions. Photomicrographs courtesy of Gorham International Inc.

Typical Improvements Resulting From HIP

• Fatigue life of aluminum castings improved 300 percent
• Ultimate tensile strength of high chrominum iron castings increased from 91,000 psi to 151,000 psi
• Rejection rate of 17-4 PH impellers reduced from almost 90 percent to nearly zero
• Scrap rate of military turbine engine blades reduced by 75 percent
• Fatigue life of superalloy medical prosthetic devices increased by a factor of 10
• Service life of silicon nitride cutting tools increased by 400 percent
• Buy-to-fly ratio of complex titanium parts improved from 7.5:1 to 3 5:1