ATI Powder Metals' process utilized to produce HIP-consolidated PM material consists of the following 6 basic process steps, as detailed below.
The process begins with the production of powder, utilizing vacuum inducting melting (VIM) coupled with inert gas atomization (IGA). Identical to conventional ingot metallurgy, the desired composition is achieved in the melt furnace, and after refining, rather than pouring the molten metal into molds or ingots, the material is diverted through a nozzle and the resulting stream is impinged by high velocity inert gas. This event results in rapid solidication of the metal, eliminating segregation during cooling, and the powder particles are collected at the bottom of the cooling tower in a cryogenic liquid quenchant for subsequent processing. Each individual powder particle shares a common chemistry, and can be thought of as a "micro-ingot".
Following atomization, which yields a wide size range of powder particles, powder is classified to a desired particle size distribution based on the particular application. Screening is done in a clean room environment under a positive pressure of filtered air.
Following screening, the yield of multiple heats are blended together under vacuum to improve homogeneity of composition and the particle size distribution. The latter is of paramount concern in the production of near-net-shape products due to the influence on packing density of the powder and therefore the extent of distortion realized during consolidation.
Mild steel containers, custom-engineered based on desired finish dimensions and TIG-welded for optimum integrity, are filled with powder under vacuum or in other controlled environments. The containers are vibrated during loading to maximize packing density.
Loaded containers are connected to vacuum pumps and heat is applied. This computer-controlled process removes residual gases and moisture from the compacts, preventing the formation of deleterious oxides etc. during consolidation. Upon completion of this process, the containers are sealed and transferred for HIP.
Hot Isostatic Pressing (HIP)
The outgassed and hermetically sealed containers are loaded into the autoclave with other available parts that share common processing parameters, then high temperature and pressure are simultaneously applied for a predetermined period of time to ensure full consolidation. HIP consolidation yields material exhibiting full theoretical density.