On-line version ISSN 2411-9717
Print version ISSN 0038-223X
J. S. Afr. Inst. Min. Metall. vol.111 n.3 Johannesburg 2011
The use of titanium hydride in blending and mechanical alloying of Ti-Al alloys
I.A. MwambaI, II; L.H. ChownI, II
IAdvanced Materials Division, Mintek
IIDST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand
Titanium sponge, which is almost pure titanium, is extremely ductile and not easily processed into titanium powder. One method of producing powder is the hydride-dehydride (HDH) process, where titanium sponge is hydrided to form brittle titanium hydride (TiH2). Titanium hydride is easily milled to produce powder and is then dehydrided to form Ti powder.
In this work, titanium hydride powder obtained from titanium sponge was used as a starting material for blending and mechanical alloying with elemental powders. Firstly, titanium hydride powder was blended with aluminium elemental powder to produce a homogenized powder, which was then compacted and sintered to produce powder metallurgy compacts. Secondly, titanium hydride powder was mechanically alloyed with aluminium elemental powder and then compacted. The mechanically alloyed powder was characterized in terms of particle size distribution, morphology and microstructure. In both blending and mechanical alloying, the green compacts were characterized by assessing the green density, while the sintered compacts were characterized by their sintered density, microstructure, and hardness. The two processes have resulted in the formation of TiAl3 intermetallic compound.
It was established that by simple mixing and homogenizing, titanium hydride can be used as a starting material to produce powder metallurgy components in which porosity is a benefit rather than a problem, much akin to metallic foams.
From the products obtained in the TiH2-Al system, it appears that titanium hydride can be used as a precursor in mechanical alloying. However, the possible formation of complex hydrides may introduce detrimental properties, and needs to be further investigated. For the production of non-porous components, it would be advisable to dehydrogenate the TiH2 powder before milling i.e. producing titanium powder by the hydride-dehydride (HDH) method.
Keywords: Mechanical alloying, titanium hydride, titanium aluminide and blending
“Full text available only in PDF format”
1. ELIZABETH, J. Dictionary of inorganic compounds, Chapman & Hall, 2-6, Boundary Row, London, SEI 8HN, UK, pp. 3376. [ Links ]
2. REILLY, J.J. Chemistry of intermetallic hydrides, Symposium for Hydrogen Storage Materials, Batteries and Chemistry, Conf. Proc. 180th Meeting of the Electrochemical Society, Phoenix, Arizona, 1991, cited in www.osti.gov/bridge/servlets/purl/6084207-YhGxqp/, 25 May 2010. [ Links ]
3. ELLERN, H. Military and civilian pyrotechnics, Chemical publishing Company Inc., New York, 1968, pp. 17-82. [ Links ]
4. ELIEZER, D., TAL-GUTELMACHER, E., and BOELLINGHAUS, TH. Hydrogen Embrittlement in Hydride- and Non-Hydride Forming Systems - Microstructural/Phase Changes and Cracking Mechanisms, Conf. Proc. 11th Int. Conference on Fracture (ICF11), Turin, Italy, March 20th-25th, 2005, pp. 123-130. [ Links ]
5. TAL-GUTELMACHER, E. and ELIEZER, D. The hydrogen embrittlement of titanium-based alloys, JOM, 2005, pp. 46-49. [ Links ]
6. ELIEZER, D., ELIAZ, N., SENKOV, O.N., and FROES, F.H. Positive effects of hydrogen in metals, Materials Science & Engineering, A280, 2000, pp. 220-224. [ Links ]
7. FROES, F.H., SENKOV, O.N., and QAZI, J.I. Hydrogen as a temporary alloying element in titanium alloys: thermohydrogen processing, International Materials Reviews, vol. 49, no. 3-4, 2004, pp. 227-245. [ Links ]
8. SELVA VENNILA, R., DURYGIN, A., MERLINI, M., WANG, Z., and SAXENA, S.K. Phase stability of TiH2 under high pressure and temperatures, International Journal of Hydrogen energy, vol. 33, 2008, pp. 6667-6671. [ Links ]
10. LIDE, D.R. Handbook of chemistry and physics, CRC Press, Taylor & Francis Group, 2007-2008, pp. 4-96. [ Links ]
11. CROWE, P. Titanium hydride dramatically lowers manufacturing cost of titanium parts, http://thekneeslider.com/archives/2009/08/19titanium,hydride-dramatically-lowers-manufacturing-cost-of-titanium-parts, cited 2010/06/03. [ Links ]
12. CARREŇO-MORELLI, E., KRSTEV, W., ROMEIRA, B., RODRIQUEZ-ARBAIZAR,M., BIDAUX, J.-E., and ZACHMANN, S. Powder injection moulding of titanium TiH2 powders, Nabertherm, website: www.nabertherm.com, accessed 2010/06/04 [ Links ]
13. IVASISHIN, O.M., DEMIDIK, A.N., and SAVVAKIN, D.G. Use of titanium hydride for the synthesis of titanium aluminides from powder materials, Powder Metallurgy and Ceramics, vol. 38, 9-10, 1999, pp. 482-487. [ Links ]
14. DU, Z., ZHANG, X., WANG, Q., and LUO, S. Deformation behaviour of aluminium alloy during semi-solid compression, Solid state phenomena, vol. 141-143, 2008, pp. 647-652. [ Links ]