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Titanium parts by powder injection moulding of TiH2-based feedstocks
Technical Paper: PIM International, Vol.4 No.3 September 2010, pages 60-63, 1466 words
[1] Design & Materials Unit, University of Applied Sciences Western Switzerland, CH-1950 Sion
[2] Nabertherm GmbH, 28865 Lilienthal, Germany
Abstract
Titanium parts have been processed from feedstocks composed of titanium hydride powders, low density polyethylene, paraffin wax and stearic acid. A two-step debinding process has been used, which consists of solvent debinding in heptane at 50°C followed by thermal debinding at 500°C. Sintering was performed at 1200°C. Both thermal debinding and sintering were performed under a protective atmosphere in a MIM furnace equipped with molybdenum heating elements and a debinding retort. Special care in powder handling, feedstock preparation, debinding and sintering atmospheres, allowed to limit the residual oxygen, nitrogen and carbon contents, which were determined by quantitative analysis. The mechanical properties of net shape sintered parts were measured by tensile tests. A tensile strength of 580 MPa and an elongation of 1.8% were obtained. Experimental watch bracelet segments were injection moulded, showing good shape preservation and reproducibility.
Introduction
The excellent properties of titanium and titanium alloys have been extensively reported, as well as the complex processing steps, which are currently necessary for the production of engineering parts with these materials [1]. As a consequence, the interest of producers and end-part users on net-shape technologies is growing. Recently, considerable progress in powder injection moulding of titanium and its alloys has been accomplished [2-6]. This is due to the advances in production of good quality base-powders, binders and sintering facilities. However, cost of raw materials, especially for gas atomised powders, is still a limiting factor for a number of applications. In this work, net-shape manufacturing of titanium parts has been performed by powder injection moulding from titanium hydride powders, which have the attractiveness of being less reactive than fine titanium powders, easier to handle, and cheaper.......
Further sections of this paper include:
Experimental
- Raw materials and feedstock processing
- Injection moulding
- Debinding and sintering
- Material characterisation
Results and discussion
Concluding remarks
Figures and Tables:
Fig. 1 Scanning electron microscopy of starting TiH2 powders: fine TIH 25AA (top) and coarse TIH-020A (bottom)
Fig. 2 Mould half for tensile test specimen and dimensions of the mould cavity in mm
Fig. 3 Tool set (mould frame, inserts, slide) and drawing of watch bracelet segment
Fig. 4 Details of the debinding and sintering furnace: (a) heating elements and debinding retort closed, (b) sintered watch bracelet segments on zirconia coated alumina support, placed on molybdenum plates inside the retort
Fig. 5 Thermal cycle for processing Ti parts from solvent debinded TiH2 based feedstocks
Fig. 6 Green and sintered PIM-Ti parts
Fig. 8 Optical metallography showing the microstructure of sintered PIM-Ti (fine powder)
Fig. 9 Titanium watch bracelet segments processed from TiH2 based feedstock
Fig. 10 Watch bracelet segments after successive surface treatments: barrel finishing (dark grey), etching and electropolishing (light grey), and anodic oxidation (blue, yellow)
Table 1 Particle size parameters and specific surface area of fine and coarse TiH2 powders
Table 2 Interstitial content and mechanical properties of base powders, titanium standard grade 4, and PIM-Ti processed from fine (a) and coarse (b) TiH2 powders
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