Effect of Co addition on densification of titanium powder compact.

2010

The development of novel extractive metallurgy techniques for titanium offers the prospect of lower cost Ti powder and therefore wider application of Ti. This review is largely confined to coverage of the low cost press and sinter methods of powder metallurgy, consisting of cold pressing of mixed elemental powders followed by sintering without the application of external pressure. Cold die compaction, sintering behaviour and densification are reviewed in detail. Some information on powders and cold isostatic pressing is included. Microstructure, mechanical properties and applications are considered in less detail. The review deals mostly with the sintering of alloys, but there is some reference to synthesis of intermetallic compounds, such as the shape memory alloy NiTi and titanium aluminides for high temperature applications. Densification is discussed in terms of the four fundamental processing variables: compaction pressure, particle size, sintering temperature and sintering time. Other factors such as alloy composition, the form of alloying addition, type and impurity content of powders and heating rate are also considered.

Section: Particle Size Of Alloying Additionmentioning

confidence: 99%

Section: Commercially Pure Titaniummentioning

confidence: 99%

Section: Effect Of Green Density On Sintered Densitymentioning

confidence: 99%

Section: Other Alloysmentioning

confidence: 99%

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Review of densification of titanium based powder systems in press and sinter processing

2010

“…Swelling of the compact and growth of very large pores often occurs when liquid phase is present. [19][20][21][22][23] This is thought to be due to expansion of gas in closed pores, which may also occur in solid state sintering. 17 Gases identified as contributing to reduced densification or swelling include stearic acid process control agent, 24,25 chlorides, 9,23,[26][27][28] Na 2 O, 29 and inert gases.…”

Section: Introductionmentioning

confidence: 99%

Swelling during sintering of titanium alloys based on titanium hydride powder

2010

Compacts were prepared by pressing titanium and titanium hydride powders mixed with nickel powder and sintering under vacuum. Severe swelling was observed only for compacts based on TiH 2 powder. Pressure changes in the vacuum furnace, dilatometry results and mass loss data all indicate that dehydrogenation of TiH 2 powder compacts occurs at lower temperature than any significant sintering. Swelling appears to have been caused by a contaminant in the TiH 2 powder rather than hydrogen. The onset of severe swelling during heating was associated with the formation of liquid phase as the solidus was crossed. However, some swelling appears to take place under solid state sintering conditions. Various results indicate that the mechanism of swelling is high gas pressure within closed pores. Large pores appear to form by breakage of ligaments between small pores followed by opening of the pore. It appears that the use of (uncontaminated) TiH 2 powder in place of Ti powder would allow the benefit of lower green porosity to be retained during sintering to achieve low sintered porosity.

Suitability of nickel as alloying element in titanium sintered in solid state

2009

The suitability of nickel as an alloying element in titanium alloys produced using the blended elemental powder metallurgy approach has been explored. Nickel initially accelerates sintering, providing greater densification at lower temperature than observed for unalloyed titanium. However, it provides only a minor improvement in the density achieved after long sintering times or at high solid state sintering temperatures. Swelling is observed under liquid phase sintering conditions. The highest density was achieved by sintering at just below the solidus temperature. Nickel also accelerates the Ostwald ripening of the pore structure and the conversion of open porosity into closed porosity.