Titanium Powder - Powder Consolidation

Powder Consolidation

Several metal consolidation techniques are used to produce the final product. Metal injection moulding (MIM) otherwise known as powder injection moulding is a well-established and cost-effective method of fabricating small-to-moderate size metal components in large quantities. It is derived from the method plastic injection moulding, whereby mixing of a metal powder with a polymer binder forms the feedstock, which is then injected into a mould, after which the binder is removed via heat treatment under vacuum before final sintering. With titanium however, the binders used in MIM results in the introduction of carbon into the matrix due to insufficient binder removal prior to sintering and/or deleterious reactions between the decomposing binder, the debinding atmosphere, and the metal phase. This results in titanium parts with mechanical properties unsuited for critical aerospace applications, but suitable for parts where tensile and impact properties are less important. Recently, work has been carried out to reduce the binder to < 8% volume fraction, resulting in the complete removal of the binder from the moulded component during heat treatment.

In the direct powder rolling (DPR) process BE powder is used to produce sheet and plate and composite multilayered sheet and plates. Sheets between 1.27 and 2.54 mm and 50 to 99+% dense of single layer CP titanium, Ti Grade 5, TiAl (Ti-48Al-2Cr-2Nb) and composite Ti/Grade 5/Ti and Grade 5/TiAl/Grade 5 have been produced by DPR and sintering.

Laser engineered net shaping (LENS) is an additive manufacturing technique for rapidly fabricating, enhancing and repairing metal components directly from CAD data. The processes use a high power solid state laser focused onto a metal substrate to create a ~1 mm diameter melt pool. Metal powder is then injected into the melt pool to increase the material volume and build up the component layer by layer. Experimental gas thrusters (build time 8 hours) and automotive brackets have been manufactured in Ti-Grade 5. Selective Laser Sintering (SLS) is similar, except that the laser selectively fuses powdered material by scanning on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.

In hot isostatic pressing high temperature and pressure are used to consolidate powders to close to their maximum theoretical densities.

Electric current assisted sintering, also known as spark plasma sintering (SPS) relies on fast application of resistive heating and pressure to consolidate powders close to their maximum theoretical densities, without the undesired grain growth effect, thereby retaining close to original grain size and achieving improved mechanical properties in the final product.