Untitled

The compaction and sintering conditions required for avoidance of swelling and development of very coarse pores during liquid phase sintering of mixed elemental titanium powder metallurgy alloys are described with reference to the titanium-nickel binary system. Swelling is minimised by using low compaction pressure or short sintering time. Swelling appears to require the presence of persistent liquid and closed pores. Gas pressure within closed pores is the probable mechanism of swelling.

Section: Methodsmentioning

confidence: 99%

Swelling during liquid phase sintering of Ti–Ni alloys

Robertson

Schaffer

2009

“…These elements are also fast diffusers in titanium, 119 but alloying with a small amount of a fine (3 mm) powder of even a slowly diffusing species, molybdenum, increased the rate of shrinkage. 120 However, others have reported a lowering of sintered density from addition of small amounts of fine Mo. 56,121 As noted in the section on 'Titanium particle size: other alloys', Ti particle size is important in the densification of IMC, particularly with respect to swelling and the formation of transient liquid phases.…”

Section: Particle Size Of Alloying Additionmentioning

confidence: 99%

“…56 It was suggested that the gas might be used to atomise the Al powder. Other alloys for which the effect of sintering temperature was reported include Ti with 0-100%Mo, 120 Ti b-eutectoid binaries, 118 Ti with 5% and 10%Al, 92 Ti-1?5Si, 106 Ti-5Al-2?5Fe 90 and equiatomic TiNi with different amounts of TiH 2 substituted for Ti. 129 Heating rate and sintering time Sintering time has a relatively small effect compared with particle size and sintering temperature.…”

Section: Other Alloysmentioning

confidence: 99%

“…Dilatometry curves often reveal small amounts of swelling early in the sintering heat treatment caused by melting of Al or Sn, formation of other liquids, unbalanced solid state diffusion or formation of IMC. 25,56,79,81,82,87,[101][102][103]111,118,120,122,123,[130][131][132][133][134][135][136] Extensive swelling can also occur late in the sintering heat treatment due to high gas pressure within closed pores (i.e. above y90% density).…”

Section: Other Alloysmentioning

confidence: 99%

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

Robertson

Schaffer

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.

“…Examples include Al, [5][6][7][8][9][10] Co and Ni, [11][12][13] Fe, 7,8,12,[14][15][16] Cr, Cu and Mn, 12,17 Si 12,18 and Mo. 8,[19][20][21] Later work showed that when the particle size of the alloying elements is the same as that of the titanium powder, the densification of binary alloys is roughly correlated with the diffusivity of the element in titanium. 22 High density (y99%) has been reached for additions of up to 10% of the fast diffusing elements Fe, Co and Ni.…”

Section: Introductionmentioning

confidence: 99%

Design of titanium alloy for efficient sintering to low porosity

Robertson¹,

Schaffer²

2009

Few Ti alloys have been designed for ease of sintering. This paper considers the design of alloys for processing using the mixed elemental technique, in which powders are mixed, cold pressed in a die to near net shape and sintered under vacuum at high temperature. The authors describe steps in the process of developing a Ti-Ni-Sn alloy, able to be sintered to near full density at a sintering temperature as low as 1100uC without requiring unusually fine powder or high compaction pressure. Higher sintering temperature allows the Ni content of the alloy to be reduced, but swelling of the alloy probably imposes an upper limit on practical sintering temperature. The increase in green density, and hence sintered density, conferred by Sn in Ti-Sn alloys, and the increase in sintered density due to the high diffusivity of Ni in Ti-Ni alloys, are combined in Ti-Ni-Sn alloys.